Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OFNAVAL ENGINEERINGPrepared byBUREAU OF NAVAL PERSONNELNAVPERS 10788-B

PREFACEThis text provides an introduction to the theory and design of engineeringmachinery and equipment aboard ship. Primary emphasis is placedon helping the student acquire an overall view of shipboard engineeringplants and an understanding of basic theoretical considerations thatunderlie the design of machinery and equipment. Details of operation,maintenance, and repair are not included in this text.The text is divided into five major parts. Part I deals with the developmentof naval ships, ship design and construction, stability and buoyancyof ships, and preventive and corrective damage control. Certain theoreticalconsiderations that apply to virtually all engineering equipment arediscussed in part II. Part III takes up the major units of machinery in themain propulsion cycle of the widely used steam turbine propulsion plant.Auxiliary machinery and equipment are discussed in part IV. Other typesof propulsion machinery, together with a brief survey of new developmentsin naval engineering, are considered in part V. In addition to these fivemajor parts, the text includes an appendix which surveys and brieflydescribes a number of references that should be of value to engineeringofficers.This text was prepared by the Training Publications Division, NavalPersonnel Program Support Activity, Washington, D. C, for the Bureauof Naval Personnel. Review of the manuscript and technical assistancewere provided by Officer Candidate School at Newport, Rhode Island;Naval Development and Training Center, San Diego, California; ServiceSchool Command, Great Lakes, Illinois; and Naval Ship Systems Command.First edition 1958Revised 1966, 1970Stock Ordering No.0502-LP-053-9400

For sale by the Superintendent of Documents, U.S. Government Printing OfficeWashington, D.C. 20402Stock No. 008-047-00127-4/ Catalog No. D208.112/:EN3/2/970.ii

PART ITHE NAVAL SHIPCONTENTSPage1Chapter 1 The Development of Naval Ships 3Chapter 2 Ship Design and Construction 15Chapter 3 Stability and Buoyancy 34Chapter 4 Preventive and Corrective Damage Control61PART IIBASIC ENGINEERING THEORY 83Chapter 5 Fundamentals of Ship Propulsionand Steering 85Chapter 6 Theory of Lubrication 112Chapter 7 Principles of Measurement 119Chapter 8 Introduction to Thermodynamics 157PART niTHE CONVENTIONAL STEAM TURBINEPROPULSION PLANT 191Chapter 9 Machinery Arrangement andPlant LayoutI93Chapter 10 Propulsion Boilers 230Chapter 11 Boiler Fittings and Controls 276Chapter 12 Propulsion Steam Turbines 3 19Chapter 13 Condensers and Other Heat Exchangers .343PART IV AUXILIARY MACHINERY AND EQUIPMENT 361Chapter 14 Piping, Fittings, and Valves 363Chapter 15 Pumps and Forced Draft Blowers 391Chapter 16 Auxiliary Steam Turbines 422Chapter 17 Compressed Air Plants 437Chapter 18 Distilling Plants 450Chapter 19 Refrigeration and Air ConditioningPlants 471Chapter 20 Shipboard Electrical Systems 492Chapter 21 Other Auxiliary Equipment 520PART V OTHER TYPES OF PROPULSION PLANTS 541Chapter 22 Diesel and Gasoline Engines 543Chapter 23 Gas Turbines 595Chapter 24 Nuclear Power PlantsChapter 25 New Developments in Naval614Engineering 628INDEX 654111

CREDITSThe illustrations indicated below are included in this edition of Principlesof Naval Engineering through the courtesy of the designatedpublishers, companies, and associations. Permission to reproduce theseillustrations must be obtained from the original sources.SourceFiguresAmerican Engineering Co.

PRINCIPLES OF NAVAL ENGINEERINGSourceFiguresNaval Auxiliary Machinery (Cont'd) 14-20, 14-27, 14-2915-20, 17-5, 21-5,21-6Naval Boilers 11-15, 11-17Naval Turbines 12-6, 12-7, 12-9,12-10,12-11,12-12,12-13, 12-14, 12-15,12-18,12-20,12-21,16-1, 16-2, 16-3,16-4, 16-5, 16-6Velan Engineering Companies 14-8Westinghouse Electric Corp. 15-32, 15-33, 15-34,15-36, 24-7, 24-8,24-9, 24-10,24-11

PART l-THE NAVAL SHIPChapter 1Chapter 2Chapter 3Chapter 4The Development of Naval ShipsShip Design and ConstructionStability and BuoyancyPreventive and Corrective Damage ControlThe four chapters included in this part of the text deal primarily withthe ship as a whole, rather than with specific items of engineering equipment.Most of the information given in this part applies to naval ships ingeneral, without regard to the type of ship or the type of propulsion plantemployed.Chapter 1 provides a brief historical survey of the development ofnaval ships. Chapter 2 takes up basic design considerations, ship flotation,ship structure, compartmentation, and the geometry of the ship.Chapter 3 deals with the basic principles of stability and buoyancy; althoughthis information is largely theoretical, it is essential for a trueunderstanding of the naval ship and for an understanding of many aspectsof damage control. Chapter 4 is concerned with preparations to resistdamage, the damage control organization, material conditions of readiness,the investigation of damage, the control of damage, and certainaspects of nuclear, biological, and chemical defense.

CHAPTER 1THE DEVELOPMENT OF NAVAL SHIPSThe story of the development of naval shipsis the story of prime movers: oars, wind-filledsails, reciprocating steam engines, steam turbines,internal combustion engines, gas turbineengines. It is also the story of the conversionand utilization of energy: mechanical energy,thermal energy, chemical energy, electricalenergy, nuclear energy. Seen in broader context,the development of naval ships is merelyone fascinating aspect of man's long struggleto control and utilize energy and thereby releasehimself from the limiting slavery ofphysical labor.We have come a great distance in thesearch for the better utilization of energy,from the muscle power required to propel anancient Mediterranean galley to the vast reservesof power available in a shipboard nuclearreactor. No part of this search has been easy;progress has been slow, difficult, and oftenbeset with frustrations. And the search is farfrom over. Even within the next few years, newdevelopments may drastically change our presentconcepts of energy utilization.This chapter touches briefly on some of thehighlights in the development of naval ships.In any historical survey, it is inevitable that afew names will stand out and a few discoveriesor inventions will appear to be of crucial significance.We may note, however, that ourpresent complex and efficient fighting shipsare the result not only of brilliant work by arelatively small number of well known men butalso of the steady, continuing work of thousandsof lesser known or anonymous contributors whohave devised small but important improvementsin existing machinery and equipment. The primitiveman who invented the wheel is often citedas an unknown genius; we might do well toremember also the unknown genius who discoveredthat wheels work better when they turnin bearings. Similarly, the basic conceptsinvolved in the design of steam turbines, internalcombustion engines, and gas turbine engines maybe attributed to a few men; but the innumerablesmall improvements that have resulted in ourpresent efficient machines are very largelyanonymous.THE DEVELOPMENT OF STEAMMACHINERYOne of the earliest steam machines of recordis the aeolipile developed about 2000 years agoby the Greek mathematician Hero. This machine,which was actually considered more of atoy or novelty than a machine, consisted of ahollow sphere which carried four bent nozzles.The sphere was free to rotate on the tubes thatcarried steam from the boiler, below, to thesphere. As the steam flowed out through thenozzles, the sphere rotated rapidly in a directionopposite to the direction of steam flow. ThusHero's aeolipile may be considered as theworld's first reaction turbine.^Giovanni Battista della Porta's treatise onpneumatics (1601) describes and illustrates adevice which utilizes steam pressure to forcewater up from a separate vessel. In the sametreatise, the author suggests that the condensationof steam could be used to create a vacuum,and that the vacuum could be utilized to drawwater upward from a lower level— a remarkablysophisticated concept, for the time.Throughout the 17th century, many other deviceswere suggested (and some of them built)which attempted to utilize the motive power ofsteam. In many instances the scientific principleswere sound but the technology of the daydid not permit full development of the devices.Hero's aeolipile is illustrated in chapter 12 of thistext.

2PRINCIPLES OF NAVAL ENGINEERINGIn 1698, Thomas Savery patented a condensingsteam engine which was designed to raisewater. This machine consisted of two displacementchambers (or one, in some models), amain boiler, a supplementary boiler, and appropriatepiping and valves. The operatingprinciples are simple, though most ingenious forthe time. When steam is admitted to one of thedisplacement vessels, it displaces the waterand forces it upward through a check valve.When the displacement vessel has been emptiedof water by this method, the supply of steam iscut off. The steam already in the displacementvessel is condensed as cold water is sprayedon the outside surface of the vessel. The condensationof the steam creates a vacuum in thedisplacement vessel, and the vacuum causesmore water to be drawn up through suctionpiping and a check valve. When the displacementvessel is again full of water, steam is againadmitted to the vessel and the cycle is repeated.In a model with two displacement chambers, thecycles are alternated so that one vessel is dischargingwater upward while the other is beingfilled with water drawn up through the suctionpipe.Although technological difficulties preventedSavery's engine from being used as widely asits inventor would have liked, it was successfullyused for pumping water into buildings, forfilling fountains, and for other applications whichrequired a relatively low steam pressure. Themachine was originally designed as a device forremoving water from mines, and Savery wasconvinced that it would be suitable for thispurpose. It was never widely used in mines,however, because very high steam pressureswould have been required to lift the water therequired distance. The metalworking skills ofthe time were simply not up to producing suitablepressure vessels for containing steam at highpressures.Although Savery's machine was used throughoutthe 18th century and well into the 19th century,two new steam engines had meanwhilemade their appearance. The first of these,Newcomen's "atmospheric engine," representsa real breakthrough in steam machinery. Like^It is reported that Savery attempted to use steampressures as high as 8 or 10 atmospheres. When oneconsiders the weakness of his pressure vessels andthe total lack of safety values, it appears somewhatremarkable that he survived.Savery's device, the Newcomen engine wasoriginally designed for removing water frommines, and in this it was highly successful.However, the significance of the Newcomenengine goes far beyond mere pumping. The secondwas the Watt engine, which brought thereciprocating steam engine to the point where itcould be used as a prime mover on land and atsea.The Newcomen engine was the first workablesteam engine to utilize the piston and cylinder.As early as 1690, Denis Papin^ had suggesteda piston and cylinder arrangement for a steamengine. The piston was to be raised by steampressure from steam generated in the bottom ofthe cylinder. After the piston was raised, theheat would be removed and condensation ofsteam in the bottom of the cylinder would createA vacuum. The downward stroke of the pistonwould thus be caused by atmospheric pressureacting on top of the piston. Papin's theory wasgood but his engine turned out to be unworkable,chiefly because he attempted to generate thesteam in the bottom of the cylinder. WhenPapinheard of Savery's engine, he stopped working onhis own piston and cylinder device and devotedhimself to improving the Savery engine.The Newcomen engine, shown in figure 1-1,was built by Thomas Newcomen and his assistant,John Cawley, in the early part of the 18thcentury.^ The Newcomen engine differs fromthe engine suggested by Papin in several importantrespects. Most important, perhaps, is thefact that Newcomen separated the boiler fromthe cylinder of the engine.As may beseen in figure 1-1, the boiler islocated directly under the cylinder. Steam isadmitted through a valve to the bottom of thecylinder, forcing the piston up. The piston isconnected by a chain to the arch on one side ofa large, pivoted, working beam. The arch on theother side of the beam is connected by a chainto the rod of a vertical lift pump.3papin is also credited with the invention of the safetyvalve.4The year 1712 is frequently given as the date of theNewcomen engine, and it is probably the year in whichthe engine was first demonstrated to a large public.It is likely, however, that previous versions of theengine were. built at a considerably earlier date, andsome authorities give the year 1705 as the date of theNewcomen engine.

Chapter 1-THE DEVELOPMENT OF NAVAL SHIPSWORKING BEAMCHAINCHAINWATER INJECTION VALVEPUMP RODSTEAM ADMISSION VALVEAUTOMATIC VALVEGEARDRAIN LINE-^t^T'jipw*^-:INJECTIONWATER PUMP"VERTICALLIFTPUMPFigure 1-1.— The Newcomen engine.147.1After the steam has forced the piston to itstop position, the steam valve is shut and a jet ofcold water enters the cylinder, condensing thesteam and creating a partial vacuum. Atmosphericpressure then causes the down stroke(work stroke) of the piston.As the piston comes down, the working beamis pulled down on the cylinder side. As the beamrises on the pump side, the pump rod also risesand water is lifted upward. As soon as the pressurein the cylinder equals atmospheric pressure,an escape valve in the bottom of the cylinderopens and the condensate is dischargedthrough a drain line into a sump.The use of automatic valve gear to controlthe admission of steam and the admission ofcold water made the Newcomen engine the firstself-acting mechanism since the invention of theclock. In the earliest versions of the Newcomenengine, it is most likely that the admission ofsteam and cold water was controlled by themanual operation of taps rather than by automaticgear. The origin of the automatic gearis a matter of some dispute. One story has itthat a young boy named Humphrey Potter, whowas hired to turn the taps, invented the valvegear so that he could go fishing while the enginetended itself. This story, although persistent,is considered "absurd" by some serious historiansof the steam engine,^James Watt, although often given credit forinventing the steam engine, did not even beginworking on steam engines until some 50 years^See, for example, Eugene S. Ferguson, "The Originsof the Steam Engine," Scientific American . January1964, pp. 98-107.

PRINCIPLES OF NAVAL ENGINEERINGor so after the Newcomen engine was operational.However, Watt's brilliant and originalcontributions were ultimately responsible forthe utilization of steam engines in a wide varietyof applications beyond the simple pumping ofwater.In 1799 Watt was granted a patent for certainimprovements to "fire-engines" (Newcomenengines). Since some of these improvementsrepresent major contributions to steam engineering,it may be of interest to see how Watthimself described the improvements in a specification:"My method of lessening the consumption ofsteam, and consequently fuel, in fire-engines,consists of the following principles:—" First , That vessel in which the powers ofsteam are to be employed to work the engine,which is called the cylinder in common fireengines,and which I call the steam vessel,must, during the whole time the engine is atwork, be kept as hot as the steam that entersit; first by inclosing it in a case of wood, orany other materials that transmit heat slowly;secondly, by surrounding it with steam or otherheated bodies; and thirdly, by suffering neitherwater nor any other substance colder than thesteam to enter or touch it during that time." Secondly , In engines that are to be workedwholly or partially by condensation of steam,the steam is to be condensed in vessels distinctfrom the steam-vessels or cylinders, althoughoccasionally communicating with them; thesevessels I call condensers; and, whilst the enginesare working, these condensers ought atleast to be kept as cold as the air in the neighbourhoodof the engines, by application of wateror other cold bodies." Thirdly ,Whatever air or other elasticvapour is not condensed by the cold of the condenser,and may impede the working of theengine, is to be drawn out of the steam-vesselsor condensers by means of pumps, wrought bythe engines themselves or otherwise." Fourthly , I intend in many cases to employthe expansive force of steam to press on thepistons, or whatever may be used instead ofthem, in the same manner in which the pressureof the atmosphere is now employed in commonfire-engines. In cases where cold water cannotbe had in plenty, the engines may be wrought bythis force of steam only, by discharging thesteam into the air after it has done its office."As a result of these and other improvements,the Watt engine achieved an efficiency (in termsof fuel consumption) which was twice that of theNewcomen engine at its best. Among the othermajor contributions made by Watt, the followingwere particularly significant in the developmentof the steam engine:1. The development of devices for translatingreciprocating motion into rotary motion.Although Watt was not the first to devise sucharrangements, he was the first to apply themto the task of making a steam engine drive arevolving shaft. This Ofie improvement aloneopened the way for the application of steamengines to many uses other than the pumping ofwater; in particular, it paved the way for theuse of steam engines as propulsive devices.2. The use of a double-acting piston— thatis, one which is moved first in one directionand then in the opposite direction, as steam isadmitted first to one end of the cylinder and thento the other.3. The development of parallel-motion linkagesto keep a piston rod vertical as the beammoved in an arc.4. The use of a centrifugal "flyball" governorto control the speed of the steam engine.Although the centrifugal governor had been usedbefore. Watt brought to it the completely new—and very significant— concept of feedback. Inprevious use, the centrifugal governor had beencapable of making a machine automatic; by addingthe feedback principle. Watt made his machinesself-regulating.6Neither Newcomen nor Watt were able toutilize the advantages of high pressure steam,largely because a copper pot was about the bestthat could be done in the way of a boiler. Thefirst high pressure steam engines were built byThe distinction between automatic machines andself-regulating machines is of considerable significance.An automatic pump, for example, can operatewithout a human attendant but it cannot change its modeof operation to fit changing requirements. A selfregulatingpump, on the other hand, operates automaticallyand can change its speed (or some othercharacteristic) to meet increased or decreased demandsfor the fluid being pumped. To be self-regulating,a machine must have some type of feedbackinformation from the output side of the machine tothe operating mechanism.

Chapter 1-THE DEVELOPMENT OF NAVAL SHIPSOliver Evans, in the United States, and RichardTrevethick, in England. The Evans engine,which was built in 1804, had a vertical cylinderand a double-acting piston. A boiler, made ofcopper but reinforced with iron bands, providedsteam at pressures of several atmospheres.The boiler was one of the first "fire-tube"boilers; the "tubes" were actually flues whichwere installed in such a way as to carry thecombustion gases several times through thevessel in which the water was being heated.This type of boiler, with many refinements andvariations, became the basic boiler design of the19th century. Trevethick, using a similar type ofboiler, built a successful steam carriage in1801; in 1804, he built what was probably thefirst modern type of steam locomotive.Continuing efforts by many people led tosteady improvements in the steam engine and toits eventual application as a prime mover forships. For many years, the major effort was toimprove the reciprocating steam engine. However,the latter half of the 19th century saw theintroduction of the first practicable steam turbines.Sir Charles Parsons, in 1884, and Dr.Gustaf de Laval, in 1889, made major contributionsto the development of the steam turbine.The earliest application of a steam turbine forship propulsion was made in 1897, when a 100-ton vessel was fitted with a steam turbine whichwas directly coupled to the propeller shaft. Afterthe installation of the steam turbine, the vesselbroke all existing speed records for ships of anysize. In 1910, Parsons introduced the reductiongear, which allowed both the steam turbine andthe screw propeller to operate at their mostefficient speeds— the turbineat very high speeds,the propeller at much lower speeds. With thisimprovement, the steam turbine became the mostsignificant development in steam engineeringsince the development of the Watt engine. Withfurther refinements and improvements, thesteam turbine is today the primary device forutilizing the motive power of steam.THE DEVELOPMENT OFMODERN NAVAL SURFACE SHIPSFulton. The ship, which is shown in figure 1-2,was built in the United States in 1815. The shiphad a displacement of 2475 tons. A paddle wheel16 feet in diameter, was mounted in a trough ortunnel inside the ship, for protection from gunfire.The paddle wheel was driven by a onecylindersteam engine with a 48-inch cylinderand a 60- inch stroke.The next large steam-driven warship to bebuilt in the United States was the Fulton 2nd .This ship was built in 1837 at the BrooklynNavy Yard. The Fulton 2nd , like the Fulton (orDemologos) before it, was fitted with sails aswell as with a steam engine. The plant efficiencyof the Fulton 2nd has been calculated'^ to be about3 percent. Its maximum speed was about 15knots, with a shaft horsepower of approximately625.The Fulton 2nd was rebuilt in 1852 and namedthe Fulton 3rd . The Fulton 3rd had a somewhatdifferent kind of steam engine, and its operatingsteam pressure was 30 psi, rather than the 11psi of the Fulton 2nd . Several other significantchanges were incorporated in the Fulton 3rd—butthe ship still had sails as well as a steam engine.The Navy was still a long ways away fromabandoning sails in favor of steam.The Mississippi and the Missouri , built in1842, are sometimes regarded as marking thebeginning of the steam Navy— even though they,too, still had sails. The two ships were verymuch alike except for their engines. The Mis -souri had two inclined engines. The Mississippihad two side-lever engines of the type shown infigure 1-3. Three copper boilers were used oneach ship. Operating steam pressures wereapproximately 15 psi.The Michigan ,which joined the steam Navyabout 1843, had iron boilers rather than copperones. These boilers lasted for 50 years. TheMichigan operated with a steam pressure of 29psi.The Princeton , which joined the steam Navyin 1844, was remarkable for a number of reasons.It was the first warship in the world to usescrew propellers, although they had been triedThe 19th century saw the application ofsteam power to naval ships. The first steamdrivenwarship in the world was the Demologos(voice of the people) which was later renamedthe Fulton in honor of its builder, Robert7See Morris Welling, Gerald M. Boatwright, andMaurice R. Hauschildt, "Naval Propulsion Machinery,"Naval Engineers Journal , May 1963, pp. 339-348.

'PRINCIPLES OF NAVAL ENGINEERINGBOILER P ADDLES ENGINEFigure 1-2.— The Demologos :the first steam-driven warship.147.2out more than forty years before. ° The Princetonhad an unusual oscillating, rectangular -pistontype of engine (fig. 1-4). The piston rod was connecteddirectly to the crankshaft, and the cylinderoscillated in trunnions. This ship was also noteworthyfor being the first warship to have allmachinery located below the waterline, the firstto burn hard coal, and the first to supply extraair for combustion by having blowers dischargeto the fireroom. But even the Princeton stillhad sails.Almost twenty steam-driven warships joinedthe steam Navy between 1854 and 1860. One of^In 1802, Colonel John Stevens applied Archimedesscrew as a means of ship propulsion. The first shipthat Stevens tried the screw on was a single-screwship, which unfortunately ran in circles. The secondapplication— a twin-screw shipwiththe screws revolvingin opposite directions—was more successful. JohnEricsson, who designed the Princeton , developed theforerunner of the modern screw propeller in 1837. Itis interesting to note that the original problem withscrew propellers was that they were inefficient at theslow speeds provided by the large, slow engines of thetime. This is just the opposite of the present-dayproblem. Both then and now, the solution is gears:step-up gears, in the old days, and reduction gears,at the present time.these was the Merrimac . Another was thePensacola , which was somewhat ahead of itstime in several ways. The Pensacola had thefirst surface condenser (as opposed to a jetcondenser) to be used on a ship of the U.S.Navy, It also had the first pressurized firerooms.It was not until 1867 that the U.S. Navyobtained a completely steam-driven ship. In theNavy's newly created Bureau of Steam Engineering,a brilliant designer, Benjamin Isherwood,conceived the idea for a fast cruiser. Oneof Isherwood's ships, the Wampanog, attainedthe remarkable speed of 17.75 knots during hertrial runs, and maintained an average of 16.6knots for a period of 38 hours in rough seas.The Wampanog had a displacement of 4215tons, a length of 335 feet, and abeam of 45 feet.The engines consisted of two 100-inch singleexpansioncylinders turning one shaft. The engineshaft was geared to the propeller shaft, drivingthe propeller at slightly more than twice thespeed of the engines. Steam was generated byfour boilers at a pressure of 35 psi and wassuperheated by four more boilers. TheWampanog propulsion plant, shown in figure1-5, was a remarkable power plant for its time.

Chapter 1-THE DEVELOPMENT OF NAVAL SHIPSSad to relate, the Wampanog came to anignominious end. A board of admirals concludedthat the ship was unfit for the Navy, that thefour-bladed propeller was an interference togood sailing, and that the four superheaterboilers were merely an unnecessary refinement.As a result of this expert opinion, two of thefour propeller blades and all four of the superheaterboilers were removed. The Wampanogwas thus reduced from a superior steam-drivenship to an inferior sailing vessel, with steamused merely as an auxiliary source of power.The modern U.S. Navy may be thought of asdating from 1883, the year in which Congressappropriated funds for the construction of thefirst steel warships. The major type of enginewas still the reciprocating steam engine;however, the latter part of the 19th century sawincreasing interest in the development of internalcombustion engines and steam turbines.- PADDLE-WHEELSHAFTFigure 1-3.— Side-lever engine,USS Mississippi (1842).Figure 1-4.— Oscillating engine,USS Princeton (1844).147.3147.4Ship designers approached the close of the19th century with an intense regard for speed.Shipbuilders were awarded contracts with bonusand penalty clauses based on speed performance.In the construction of the cruisers Columbia andMinneapolis, a speed of 21 knots was specified.The contract stipulated a bonus of $50,000 pereach quarter-knot above 21 knots and a penaltyof $25,000 for each quarter-knot below 21 knots.The Columbia maintained a trial speed of 22.8knots for 4 hours, and thereby earned for herbuilders a bonus of $350,000. Her sister ship,the Minneapolis, made 23.07 knots on her trials,earning $414,600 for that performance. Othershipbuilders profited in similar fashion from thespeed race. And some, of course, were penalizedfor failure. The builders of the Monterey , forexample, lost $33,000 when the ship failed tomeet the specified speed.By the early part of the 20th century, steamwas here to stay; the ships of all navies of theworld were now propelled by reciprocating steamengines or by steam turbines. Coal was still thestandard fuel, although it had certain disadvantagesthat were becoming increasingly apparent.One of the problems was the disposal of ashes.The only practicable way to get rid of them wasto dump them overboard, but this left a telltalefloating line on the surface of the sea, easilyseen and followed by the enemy. Furthermore,the smoke from the smokestacks was enough toreveal the presence of a steam-driven ship evenwhen it was far beyond the horizon. The militarydisadvantages of coal were further emphasizedby the fact that it took at least one day to coalthe ship, another day to clean up— a minimum oftwo days lost, and the coal would only last foranother two weeks or so of steaming.Then came oil. The means for burning oilwere not developed until the early part of the20th century. C^ce the techniques and equipmentwere perfected, the change from coal tooil took place quite rapidly. Our first oil-burningbattleships were the Oklahoma and theNevada , which were laid down in 1911. All coalburningships were later altered to burn oil.While the coal-to-oil conversion was in progress,a tug-of-war was going on in another area.The reciprocating steam engine and the steamturbine each had its proponents. To settle thematter, the Bureau of Engineering made thedecision to install reciprocating engines in theOklahoma and steam turbines in the Nevada .Although there were still many problems to besolved, the steam turbine was well on its way

PRINCIPLES OF NAVAL ENGINEERINGto becoming the major prime mover for navalships.With the advent of the steam turbine, theproblem of reconciling the speed of the primemover and the speed of the propeller becamecritical. The turbine operates most efficientlyat high speed, and the propeller operates mostefficiently at low speed. The obvious solutionwas to use reduction gears between the shaftof the prime mover and the shaft of the propeller;and, basically, this is the solution thatwas adopted and that is still in use on navalships today. However, other solutions are possible;and one—the use of turboelectric drivewastried out on a fairly large scale.During World War I, the collier Jupiter (laterconverted to the aircraft carrier Langley ) wasfitted with turboelectric drive. The high speedturbines drove generators which were electricallyconnected to low speed motors. The "bigfive" battleships— the Maryland, the Colorado ,the West Virginia , the California , and theTennessee— were all built with turboelectricdrive. Ultimately, however, starting with themodernization of the Navy in 1934, the turboelectricdrive gave way to the geared-turbinedrive; and today there are relatively few shipsof the Navy that have turboelectric drive.The period just before, during, and afterWorld War II saw increasing improvement andrefinement of the geared-turbine propulsionplant. One of the most notable developmentsof this period was the increase in operatingsteam pressures—from 400 psi to 600 psi andfinally, on some ships, to 1200 psi. Other improvementsincluded reduction in the size andweight of machinery and the use of a varietyof new alloys for high pressure and high temperatureservice.Although the development of naval surfaceships, unlike the development of submarines,has been largely dependent upon the developmentof steam machinery, we should not overlookthe importance of an alternate line ofwork—namely, the development of internal combustionengines. In the application of dieselengines to ship propulsion, Europe was considerablymore advanced than the United States;as late as 1932, in fact, the United States wasin the embarrassing position of having to buyGerman plans for diesel submarine engines. Aconcerted effort was made during the 1930's

Chapter 1-THE DEVELOPMENT OF NAVAL SHIPS9 (top); USSFigure 1-6. -The nuclear surface fleet, 1965: USS Long Beach ,CGNEnterprise, CVAN 65 (middle); and USS Bainbridge, DLGN 25 (bottom).147.6to develop an American diesel industry, and theU.S. Naval Engineering Experiment Station (nowthe Marine Engineering Laboratory) at Annapolisundertook the testing and evaluation of prototypediesel engines developed by American manufacturers.The success of this effort may be seenin the fact that by the end of World War II thediesel horsepower installed in naval vesselsexceeded the total horsepower of naval steamplants.Since World War II, the gas turbine enginehas come into increasing prominence as a possibleprime mover for naval ships. It is consideredlikely that the next few years will seeenormously increased application of the gasturbine engine for ship propulsion, either singlyor in combination with steam turbines or dieselengines.One of the most dramatic events in theentire history of naval ships is the applicationof nuclear power, first to submarines and thento surface ships. The first three ships of ournuclear surface fleet are shown in figure 1-6.The middle ship is the aircraft carrier USSEnterprise ,CVAN 65; on the flight deck, crewmembers are shown forming Einstein's famousequation which is the basis of controlled nuclearpower. The other two ships are (top) the guidedmissile cruiser USS Long Beach,CGN 9, and(bottom) the guided missile frigate USS Bain -bridge, DLGN 25. The fourth nuclear surfaceship to join the fleet was the USS Truxton,DLGN 35. A fifth nuclear surface ship soonto join the fleet is the USS Nimitz , CVAN 68,Although the full implications of nuclear propulsivepower may not yet be fully realized,11

PRINCIPLES OF NAVAL ENGINEERINGone thing is already clear: the nuclear-poweredship is virtually free of the limitations on steamingradius that apply to ships using other formsof fuel. Because of this one fact alone, the futureof nuclear propulsive power seems assured.THE DEVELOPMENT OF SUBMARINESAlthough ancient history records numerousattempts of varying degrees of success to buildunderwater craft and devices, the first successfulsubmersible craft— and certainly the first tobe used as an offensive weapon in naval warfare—wasthe Turtle , a one-man submersibleinvented by David Bushnell during the AmericanRevolutionary War. The Turtle , which was propelledby a hand-operated screw propeller, attemptedto sink a British man-of-war in NewYork Harbor. The plan was to attach a chargeof gunpowder to the ship's bottom with screwsand to explode it with a time fuse. After repeatedfailures to force the screws through thecopper sheathing of the hull of the British ship,the submarine gave up, released the charge, andwithdrew. The powder exploded without anyresult except to cause the British man-of-warto shift to a berth farther out to sea.closed automatically when the water reacheda certain level.In 1798, Robert Fulton built a small submersiblewhich he called the Nautilus. Thisvessel, which is shown in figure 1-8, had anoverall length of 20 feet and a beam of 5 feet.The craft was designed to carry three peopleand to stay submerged for about an hour. Thefirst Nautilus carried sails for surface propulsionand a hand-driven screw propeller forsubmerged propulsion. The periscope had notyet been invented, but Fulton's craft had a modifiedform of conning tower which had a portholefor underwater observation. In 1801, Fulton triedto interest France, Britain, and America in hisidea, but no nation was willing to sponsor thedevelopment of the craft, even though this wasthe best submarine that had yet been designed.Interest in the development of the submarinewas great during the period of the Civil War,but progress was limited by the lack of a suitablemeans of propulsion. Steam propulsion wasattempted, but it had many drawbacks, and handpropulsion was obviously of limited value. Thefirst successful steam-driven submarine wasbuilt in 1880 in England. The submarine had acoal-fired boUer and a retractable smokestack.TOPPEOO SCREW-VENTILATO«S-VERTICALPROPELLERDEPTH-GAUGEOUODER PUMPVBALLAST TANK-'BALLAST-DETACMABLE BALLAST-^AND ANCHOR/./ TLOOOING',- VALVEBALLAST TANKFigure110.1041-7.— The Turtle—the first submersibleused in naval warfare.The Turtle , shown in figure 1-7, looked somewhatlike a lemon standing on end. The vesselhad a water ballast system with hand-operatedpumps, as well as the hand-operated propeller.It also had a crude arrangement for drawing infresh air from the surface. The vent pipes even

Chapter 1-THE DEVELOPMENT OF NAVAL SHIPScraft suffered from one major defect: its batterieshad to be recharged and overhauled atsuch short intervals that its effective rangenever exceeded 80 miles.In 1875, in New Jersey, John P. Holland builthis first submarine. Twenty-five years and nineboats later, Holland finally built the U.S. Navy'sfirst submarine, the USS Holland (fig. 1-9). AlthoughHolland's early models had features whichwere later discontinued, many of his initialideas, perfected in practice, are still in usetoday. The Holland had a length of 54 feet and adisplacement of 75 tons. A 50-horsepower gasolineengine provided power for surface propulsionand for battery charging; electric motorsrun from the storage batteries provided powerfor underwater running.Just before Holland delivered his first submarineto the Navy, his company was reorganizedinto the Electric Boat Company, which continuedto be the chief supplier of U.S. Navy submarinesuntil 1917. After the acceptance of the Holland ,new contracts for submarines came rapidly. TheA-boats, of which there were seven, were completedin 1903. These were improved versionsof the Holland ; they were 67 feet long and wereequipped with gasoline engines and electricmotors. This propulsion combination persistedthrough a series of B-boats, C-boats, and D-boats turned out by the Electric Boat Company.The E-boat type of submarine was the firstto use diesel engines. Diesel engines eliminatedmuch of the physical discomfort that had beencaused by fumes and exhaust gases of the oldgasoline engines. The K-boats, L-boats, andO-boats of World War I were all driven bydiesel engines.There was little that was spectacular aboutsubmarine development in the United Statesbetween 1918 and 1941. The submarines builtjust before and during World War II rangedfrom 300 to 320 feet in length and displacedapproximately 1500 tons on the surface. Theseincluded such famous classes as Balao , Gato,Tambor , Sargo , Salmon , Perch, and Pike .In the latter part of World War II, theGermans adopted a radical change in submarinedesign known as the "schnorkel." The spellingwas reduced to "snorkel" by the Americans andto "snort" by the British. The snorkel is abreathing tube which is raised while the submarineis at periscope depth. With the snorkelin the raised position, air for the diesel enginescan be obtained from the surface.The snorkel was developed and improved bythe U.S. Navy at the end of World War II and wasinstalled on a number of submarines. Anotherpost-war development was the Guppy submarine.The Guppy (Greater Underwater PropulsionPower) was a conversion of the fleet-type submarineof World War II. The main change wasin the superstructure of the hull; this was changedby reducing the surface area, streamlining everyprotruding object, and enclosing the periscopeshears in a streamlined metal fairing.With the advent of nuclear power, a newera of submarine development has begun. Thefirst nuclear submarine was the USS Nautilus ,SSN 571, which was commissioned on 30 September1954. At 1100 on 17 January 1955, theNautilus sent its historic message: "Underwayon nuclear power."The Nautilus broke all existing records forspeed and submerged endurance, but even theseFigure 1-9. — The USS Holland ; first U.S. Navy submarine. 71.113

PRINCIPLES OF NAVAL ENGINEERINGrecords were soon broken by subsequent generationsof nuclear-powered submarines. Themodern nuclear-powered submarine is sometimesconsidered "the first true submarine"because it is capable of staying submerged almostindefinitely.With the development of the modern missilefiring submarine— a nuclear-powered submarinewhich is capable of submerged firing of thePolaris/Poseidon missile— the submarine hasbecome one of the most vital links in ournational defense. The modern nuclear-poweredmissile firing submarine is a far cry fromDavid Bushnell's hand-propelled Turtle , butan identical need led to the development of bothtypes of vessels: the need for better and moreeffective fighting ships.14

CHAPTER 2SHIPDESIGN AND CONSTRUCTIONAs ships have increased in size and complexity,plans for building them have becomemore detailed and more numerous. Today onlymeticulously detailed plans and well conceivedorganization, from the designers to the menworking in the shops and on the ways, can producethe ships required for the Navy.After intensive research, many technical advanceshave been adopted in the design and constructionof warships. These changes werebrought about by the development of weldingtechniques, by the rapid development in aircraft,submarines, and weapons, and by developmentsin electronics and in propulsion plants.This chapter presents information concerningbasic ship design considerations, ship flotation,basic ship structure, ship compartmentation,and the geometry of the ship.BASIC DESIGN CONSIDERATIONSCombat efficiency is the prime requisite ofwarships. Some important factors contributingto combat efficiency are sea-keeping capabilities,maneuverability, and ability to remain inaction after sustaining combat damage.Basic considerations involved in the designof naval ships include the following:1. Cost .— The initial cost is important inwarship design, but it is not the only costconsideration. The cost of maintenance andoperation, as well as the cost and availabilityof the required manning, are equally importantconsiderations.2. Life Expectancy .— The life expectancy ofa ship is limited by ordinary deterioration inservice and also by the possibility of obsolescencedue to the design of more efficient ships.3. Service .— The service to be performedsubstantially affects the design of any ship.4. Port Facilities . — The port facilitiesavailable in the normal operating zone of theship affect the design to some extent. Dockyardfacilities available for drydocking and maintenancework must be taken into consideration.5. Prime Mover .— The type of propellingmachinery to be used must be considered fromthe point of view of the required speed of theship, the location in the ship, space and weightrequirements, and the effect of the machineryon the center of gravity of the ship.6. Special Considerations.— Special considerationssuch as the fuel required, the crew tobe carried, and special weapons are factorswhich restrict the designer of a naval ship.Naval ships are designed for maximum simplicitythat is compatible with the requirementsof service. Naval ships are designed as simplyas possible in order to lower building and operatingcosts and in order to ensure greater availabilityof construction facilities.The following operating considerations affectthe size of a naval ship:1. Width and Length of Canal Locks andDock Facilities . These considerations obviouslyhave an effect on the size of ships that mustuse the canals or dock facilities,2. Effect of Speed . — For large ships, speedmay be maintained with a smaller fraction ofdisplacement devoted to propulsion machinerythan is the case for smaller ships. Also, largeships lose proportionately less speed throughadverse sea conditions.3. Effect of Radius of Action . — An increasingcruising radius may be obtained by increasingdisplacement without increasing thefraction of displacement allotted to fuel andstores. If the fraction of displacement setaside for fuel and stores is increased, someother weight must be decreased. Since the hull15

PRINCIPLES OF NAVAL ENGINEERINGweight is a constant percentage of tiie displacement,an increase in the fraction of the displacementassigned to one military characteristicinvolves the reduction of other fractionsof displacement. By increasing the displacementof the ship as a whole, it is possible to increasethe speed and the radius of action withoutadversely affecting the other requiredcharacteristics.4. Effect of Seagoing Capabilities.— Largerships are more seaworthy than smaller ships.However, smaller ships are more maneuverablebecause they have smaller turning circleradii than larger ships, where all other factorsare proportional. The maneuverability of largeships may be increased somewhat by the useof improved steering gear and large rudders.In general, larger ships have the advantageof greater protection because of their greaterdisplacement. From the point of view of underwaterattack, larger ships also have an advantage.K compartments are of the same size,the number of compartments increases linearlywith the displacement. It is apparent, then, thatprotection against both surface and subsurfaceattacks may be more effective on larger shipswithout impairing other military characteristics.Many compromises must be made in designingany ship, since action which improvesone feature may degrade another. For example,in the design of a conventionally powered shipthere is the problem of choosing the hull linefor optimum performance at a cruising speedof 20 knots and at a trial speed of 30 knots ormore. One may select a hull type which wouldminimize resistance at top speed, and thuskeep the weight of propulsion machinery toa minimum. When this is done, however, resistanceat cruising speed may be high and thefuel load for a given endurance may be relativelygreat, thus nullifying some of the gainfrom a light machinery plant. On the other hand,one may choose a hull type favoring cruisingpower. In this case, fuel load will be lighterbut the shaft horsepower required to maketrial speed may be greater than before. Nowthe machinery plant is heavier, cancelling someof the weight gain realized from the lighterfuel load. A compromise based on the interrelationshipof these considerations must usuallybe adopted. The need for compromise is alwayspresent, and the manner in which it is madehas an important bearing on the final design ofany naval ship.SHIP FLOTATIONWhen a body floats in still water, the forcewhich supports the body must be equal to theweight. Assume that an object of given volumeis placed under water. If the weight of thisobject is greater than the weight of an equalvolume of water, the object will sink. It sinksbecause the force which buoys it up is lessthan its own weight. However, if the weight ofthe submerged object is less than the weightof an equal volume of water, the object willrise. It rises because the force which buoys itup is greater than its own weight. The objectwill continue to rise until part of it is abovethe surface of the water. Here it floats at sucha depth that the submerged part of the objectdisplaces a volume of water, the weight ofwhich is equal to the weight of the object.The principle implied in this discussion isknown as Archimedes' law: the weight of afloating body is equal to the w^ght of the fluiddisplaced .The cube of steel shown in part A of figure2-1 is a solid cube of the dimensions shown.If this cube is dropped into salt water, it willsink because it weighs approximately 490 poundsand the weight of the salt water it displacesis approximately 64 pounds. If the cube ishammered out into a watertight flat plateof the dimensions shown in part B of figure2-1, with the edges bent up one foot all around,the box thus formed will float. This box couldbe made from the same volume of steel asthat of the cube. The box will not only float;in calm water, it will carry an additional 1800pounds of weight before sinking. As a box, themetal displaces a greater volume than the sameamount of metal does as a 1-foot cube.8.44Figure 2-1.— Steel cube and box madefrom same volume of steel.16

Chapter 2-SHIP DESIGN AND CONSTRUCTIONBASIC SHIP STRUCTUREIn considering the structure of a ship, itis common practice to liken the ship to a boxgirder. Like a box girder, a ship may be subjectedto tremendous stresses. The magnitudeof stress is usually expressed in pounds persquare inch (psi).When a pull is exerted on each end of a bar,as in part A of figure 2-2, the bar is under thetype of stress called tension . When a pressureis exerted on each end of a bar, as in partB of figure 2-2, the bar is under the type ofstress called compression. If an equal butopposite pull is exerted on the upper and lowerbars, as shown in part C of figure 2-2, thepins connecting these bars are subjected to astress at right angles to their length. Thisstress is called shear. When a shaft, bar, orother material is subjected to a twisting motion,the resulting stress is known as torsionalstress . Torsional stress is not illustrated infigure 2-2.When a material is compressed, it is shortened.When it is subjected to tension, it islengthened. This change in shape is called strain .The change of shape (strain) may be regardedas an effect of stress.If a simple beam is supported at its twoends and various vertical loads are appliedover the center of the span, the beam willbend (fig. 2-3). As the beam bends, the uppersection of the beam compresses and the lowerpart stretches. Somewhere between the top andbottom of the beam, there is a section whichis neither in compression nor in tension; thisis known as the neutral axis . The greateststresses in tension and compression occurnear the middle of the length of the beam,where the loads are applied.LONGITUDINAL BENDING AND STRESSESIn an I-beam, the greater mass of structuralmaterial is placed in the upper and lowerflanges to resist compression and tension. Relativelylittle material is placed in the webwhich holds the two flanges so that they canwork together; the web, being near the neutralaxis, is less subject to tension and compressionstresses than are the flanges. The webdoes take care of shearing stresses, whichare sizeable near the supports.A ship in a seaway can be considered similarto this I-beam (or, more correctly, it can belikened to a box girder) with supports and distributedloads. The supports are the buoyantforces of the waves; the loads are the weightof the ship's structure and the weight of everythingcontained within the ship.The ship shown in figure 2-4 is supportedby waves, with the bow and stern each ridinga crest and the midship region in the trough.This ship will bend with compression at thetop and tension at the bottom. A ship in thiscondition is said to be sagging . In a saggingship, the weather deck tends to buckle undercompressive stress and the bottom plating tendsto stretch under tensile stress. A sagging shipis undergoing longitudinal bending—that is, itis bending in a fore-and-aft direction.When the ship advances half a wave length,so that the crest is amidships and the bow andstern are over troughs, as shown in figure 2-5,OAO LOAD LOAD NEUTRAL ^^^^^If ^ f ''r^^ I-BEAM I147.8Figure 2-2.— Stresses in metal: (A) tension;(B) compression; (C) shear.Figure 2-3.— I-beam with load placedover center.147.917

PRINCIPLES OF NAVAL ENGINEERING1;;=Tttf + +COMPRESSIONTENSIONFigure 2-4.— Sagging.H147.10the stresses are reversed. The weather deckis now In tension and the bottom plating is incompression. A ship in this condition is saidto be hogging. Hogging, like sagging, is a formof longitudinal bending. The effects of longitudinalbending must be considered in the designof the ship, with particular reference to theoverall strength that the ship must have.In structural design, the terms hull girderand ship girder are used to designate the structuralparts of the hull. The structural partsof the hull are those parts which contribute toits strength as a girder and provide what isknown as longitudinal strength . Structural partsinclude the framing (transverse and longitudinal),the shellplating, the decks, and the longitudinalbulkheads. These major strength membersenable the ship girder to resist the variousstresses to which it is subjected.The ship girder is subjected to rapid reversalof stresses when the ship is in a seawayand is changing from a hogging condition to asagging condition (and vice versa), since thesechanges occur in the short time required forthe wave to advance half a wave length. Otherdynamic stresses are caused by pressure loadsforward due to the ship's motion ahead, bypantingl of forward plating due to variationsof pressure, by the thrust of the propeller, andby the rolling of the ship.HULL MEMBERSThe principalstrength members of the shipgirder are at the top and bottom, where thegreatest stresses occur. The top flange includesthe main deck plating, the deck stringers,and the sheer strakes of the side plating. Thebottom flange includes the keel, the outer bottomplating, the inner bottom plating, and any continuouslongitudinals in way of the bottom. Theside webs of the ship girder are composed ofthe side plating, aided to some extent by anylong, continuous fore-and-aft bulkheads. Someof the strength members of a destroyer hullgirder are indicated in figure 2-6.KeelThe keel is a very important structuralmember of the ship. The keel, shown in figure2-7, is built up of plates and angles into anI-beam shape. The lower flange of this I-beamstructure is the flat keel plate, which formsthe center strake of the bottom plating-2The web of the I-beam is a solid plate whichis called the vertical keel . The upper flangeis called the rider plate ;this forms the centerstrake of the inner bottom plating. An innervertical keel of two or more sections, consistingof I-beams arranged one on top of theother, is found on many large combatant ships.FramingFrames used in ship construction may be ofvarious shapes. Figure 2-8 illustrates framesof the angle, I-beam, tee, bulb angle, and channelshapes. Figure 2-9 shows two types of'3E m. -j3Transverse stress results from the pressureof the water on the ship's sides whichsubjects the transverse framing, deck beams,and shellplating below water to a hydrostaticload. Local stresses occur in the vicinity ofmasts, windlasses, winches, and heavy weights.These areas are strengthened by thicker deckplating or by deeper or reinforced deck beams.S\TENSIONCOMPRESSION\\\Figure 2-5.— Hogging.147.11Panting isat the bow.a small In-and-out working of the platingOn large ships, an additional member is attached tothis flange to serve as the center strake.18

PRINCIPLES OF NAVAL ENGINEERINGMAIN DECKSTRINGERLONGITUDINALSVCL11.30(147)AFigure 2-8.— Angle, I-beam, tee, bulbangle, and channel frames.WELO' (SHELL ORBULKHEAD)REVERSE BARFRAME BAR11,30(147)BFigure 2-9.— Built-up frames.SOLID WEB147.14Figure 2-10.—Web frame used in wingtank construction.Both intercostal and continuous frames areshown in figure 2-12.A cellular form of framing results from acombination of longitudinal and transverseframing systems utilizing closely spaced deepframing. Cellular framing is used on mostnaval ships.BILGEKEELLONGITUDINALSKEEL147.15Figure 2-11.— Basic frame section(longitudinal framing).In the bottom framing, which is probablythe strongest part of a ship's structure, thefloors and keelsons are integrated into a rigidcellular construction (fig. 2-13). Heavy loadssuch as the ship's propulsion machinery arebolted to foundations which are built directlyon top of the bottom framing (fig. 2-14).Double BottomIn many naval ships, the inner bottom platingis a watertight covering laid on top of thebottom framing. The shellplating, framing,and inner bottom plating form the space knownas the double bottom . This space may be usedfor stowage of fresh water or fuel oil or itmay be used for ballasting.The inner bottom plating is a second skininside the bottom of the ship. It preventsflooding in the event of damage to the outerbottom, and it also acts as a strength member.Stem and Bow StructureThe stem assembly, which is the forwardmember of the ship's structure, varies in form20

PRINCIPLES OF NAVAL ENGINEERINGMACHINERYFOUNDATION^n~rn3147.18Figure 2-14.— Deep floor assembly formachinery foundations.Stern StructureThe aftermost section of the ship's structureis the stern post^ which is rigidly secured to thekeel, shellplating, and decks. On single-screwships, the stern post is constructed to accommodatethe propeller shaft and rudder stockbosses. Because of its intricate form, the sternpost is usually either a steel casting or a combinationof castings and forgings. Inmodern warshipshaving transom sterns, multiple screws,and twin rudders, the stern post as such is difficultto define, since it has been replaced by anequivalent structure of deep framing. This structure(fig. 2-17) consists of both longitudinal andtransverse framing that extends throughout thewidth of the bottom in the vicinity of the stern.In order to withstand the static and dynamic loadsimposed by the rudders, the stern structure isstrengthened in the vicinity of the rudder post bya structure known as the rudder post weldment.Figure 2-15.— Bulbous-bow configuration.147.1922

Chapter 2-SHIP DESIGN AND CONSTRUCTIONPlating147.20Figure 2-16.—Relationship of stem assembly tokeel.The outer bottom and side plating forms astrong, watertight shell. Shellplating consists ofapproximately rectangular steel plates arrangedlongitudinally in rows or courses called strakes .The strakes are lettered, beginning with the Astrake (also called the garboard strake ) whichis just outboard of the keel and working up tothe uppermost side strake (called the sheerstrake ).The end joint formed by adjoining plates in astrake is called a butt . The joint between theedges of adjoining strakes is called a seam.Butts and seams in side plating are illustratedin figure 2-18.Since the hull structure is composed of agreat many individual pieces, the strength andtightness of the ship as a whole depend verymuch upon the strength and tightness of theconnections between the individual pieces. Inmodern naval ships, welded joints are used to aDECK PLATINGFigure 2-17.— Stern structure.147.2123

PRINCIPLES OF NAVAL ENGINEERINGINNER BOTTOM PLATINGTRANSVERSEBUTTSEAMLONGITUDINALSTANCHIONA" STRAKEFigure 2-18.— Section of ship, showing plating and framing.3.92very great extent. However, riveted joints arestill used for some applications.Bilge KeelsBilge keels, which may be seen in figures2-11, 2-13, and 2-14, are fitted in practicallyall ships at the turn of the bilge. The bilge keelsextend fifty to seventy-five percent of the lengthof the hull. A bilge keel usually consists of aplate about 12 inches deep, standing at rightangles to the shellplating and secured to theshellplating by double angles. On more recentships, bilge keels consist of two plates forminga Vee shape welded to the hull and on largeships may extend out from the hull nearly threefeet. Bilge keels serve to reduce the extent ofthe ship's rolling.DecksDecks provide both longitudinal and transversestrength to the ship. Deck plates, whichare similar to the plates used in side and bottomshellplating, are supported by deck beams anddeck longitudinals.The term strength deck is generally appliedto the deck which acts as the top flange of thehull girder. It is the highest continuous deckusuallythe main or weather deck. However, theterm strength deck may be applied to any continuousdeck which carries some of the longitudinalload. On destroyers and similar shipsin which the main deck is the only continuoushigh deck, the main deck is the strength deck.The flight deck is the strength deck on recentlarge aircraft carriers (CVAs) and helicoptersupport ships (LPH), but the main or hangardeck is the strength deck on older types of carriers.The main deck is supported by deck beamsand deck longitudinals. Deck beams are thetransverse members of the framing structure.The beams are attached to and supported by theframes at the sides, as shown in figure 2-19.24

Chapter 2-SHIP DESIGN AND CONSTRUCTIONIn most naval construction, light deck beams areinterspaced at regular intervals with deep deckbeams. Deck longitudinals are used to providelongitudinal strength. When possible, the heaviestlongitudinals are located at the center andnear the outboard edges.The outboard strake of deck plating whichconnects with the shellplating is called the deckstringer (fig, 2-11). The deck stringer, whichis heavier than the other deck strakes, servesas a continuous longitudinal stringer, providinglongitudinal strength to the ship's structure.Upper Decks and SuperstructureThe decks above the main deck are notstrength decks on most ships other than CVAs.The upper decks are usually interrupted at intervalsby expansion joints. The ejcpansion jointskeep the upper decks from acting as strengthdecks (which they are not designed to be) andthus prevent cracking and buckling of deckhouses and superstructure.StanchionsIn order to reinforce the deck beams andto keep the deck beam brackets and side framesfrom carrying the total load, vertical stanchionsor columns are fitted between decks. Stanchionsare constructed in various ways of various materials.Some are made of pipe or rods; othersare built up of various plates and shapes, weldedor riveted together. The stanchion shown infigure 2-20 is in fairly common use; this pipestanchion consists of a steel tube which is fittedwith special pieces for securing it at the upperend (head) and at the lower end (heel).147.22Figure 2-19.— Deck beam and frame.BRACKETDECK BEAMSTANCHIONBulkheadsBulkheads are the vertical partitions which,extending athwartships and fore and aft, providecompartmentation to the interior of the ship.Bulkheads may be either structural or nonstructural.Structural bulkheads, which tie the shellplating,framing, and decks together, are capableof withstanding fluid pressure; these bulkheadsusually provide watertight compartmentation.Nonstructural bulkheads are lighter; they areused chiefly for separating activities aboardship.WELDFigure 2-20.— Pipe stanchion.147.2325

PRINCIPLES OF NAVAL ENGINEERINGBulkheads consist of plating and reinforcingbeams. The reinforcing beams are known asbulkhead stiffeners . Two types of bulkhead stiffenersare shown in figure 2-21, Bulkheadstiffeners are usually placed in the verticalplane and aligned with deck longitudinals; thestiffeners are secured at top and bottom to anyintermediate deck by brackets attached to deckplating. The size of the stiffeners dependsupon their spacing, the height of the bulkhead,and the hydrostatic pressure which the bulkheadis designed to withstand.Bulkheads and bulkhead stiffeners must bestrong enough to resist excessive bending orbulging in case of flooding in the compartmentswhich they bound. If too much deflection takesplace, some of the seams might fail.In order to form watertight boundaries,structural bulkheads must be joined to alldecks, shellplating, bulkheads, and other structuralmembers with which they come in contact.Main transverse bulkheads extend continuouslythrough the watertight volume of the ship, fromthe keel to the main deck, and serve as floodingboundaries in the event of damage below thewaterline.In general, naval ships are divided into asmany watertight compartments, both above andbelow the waterline, as are compatible with themissions and functions of the ships. The compartmentationprovided by transverse and longitudinalbulkheads is illustrated in the bow sectionshown in figure 2-22.T-BAR'ANGLE'11.30(147)CFigure 2-21.— Bulkhead stiffeners.SHIP COMPARTMENTATIONEvery space in a naval ship (except forminor spaces such as peacoat lockers, linenlockers, cleaning gear lockers, etc.) is consideredas a compartment and is assigned an identifyingletter-number symbol. This symbol ismarked on a label plate secured to the door,hatch, or bulkhead of the compartment.There are two systems of numbering compartments,one for ships built prior to March1949 and the other for ships built after March1949. In both of these systems, compartmentson the port side end in an even number and thoseon the starboard side end in an odd number. Inboth systems, a zero precedes the deck numberfor all levels above the main deck.Figure 2-23 illustrates both systems ofnumbering decks. The older system identifiesdecks by the numbers 100, 200, 300, etc., withthe number 900 always being used for the double147.24Figure 2-22.— Compartmentation provided bytransverse and longitudinal bulkheads.bottoms. In the newer system, decks are identifiedas 1, 2, 3, 4, etc., and the double bottomsare given whatever number falls to them.26

Chapter 2-SHIP DESIGN AND CONSTRUCTION

LetterPRINCIPLES OF NAVAL ENGINEERING

Chapter 2-SHIP DESIGN AND CONSTRUCTIONAn example of a compartment symbol on aship built prior to March 1949 is given in figure2-25.SHIPS BUILT AFTER MARCH 1949For ships constructed after March 1949, thecompartment numbers consist of a deck number,frame number, relation to centerline ofship, and letter showing use of the compartment.These are separated by dashes. The A, B, Cdivisional system is not used.The main deck is always numbered 1. Thefirst deck or horizontal division below the maindeck is numbered 2; the second below is numbered3; etc., consecutively for subsequentlower division boundaries. Where a compartmentextends down to the bottom of the ship,the number assigned the bottom compartmentsis used. The first horizontal division above themain deck is numbered 01, the second above isnumbered 02, etc., consecutively, for subsequentupper divisions. The deck number becomes thefirst part of the compartment number and indicatesthe vertical position within the ship.The frame number at the foremost bulkheadof the enclosing boundaryof a compartment is itsframe location number. Where these forwardboundaries are between frames, the frame numberforward is used. Fractional numbers are notused. The frame number becomes the secondpart of the compartment number.Compartments located so that the centerlineof the ship passes through them carry the number0. Compartments located completely tostarboard of the centerline are given odd numbersand those completely to port of the centerlineare given even numbers. Where two ormore compartments have the same deck andframe number and are entirely to port or entirelyto starboard of the centerline, they haveconsecutively higher odd or even numbers, asthe case may be, numbering from the centerlineoutboard. In this case, the first compartmentoutboard of the centerline to starboard is 1; thesecond is 3, etc. Similarly, the first compartmentoutboard of the centerline to port is 2;the second 4, etc. When the centerline of theship passes through more than one compartment,the compartment having that portion ofthe forward bulkhead through which the centerlineof the ship passes carries the number 0,and the. others carry the numbers 01, 02, 03,etc., in any sequence found desirable. Thesenumbers indicate the relation to the centerline.and are the third part of the compartmentnumber.The fourth and last part of the compartmentnumber is the capital letter which identifiesthe assigned primary usage of the compartment.A single capital letter is used, except thaton dry and liquid cargo ships a double letterdesignation is used to identify compartmentsassigned to cargo carrying. The compartmentletters for ships built after March 1949 areshown in figure 2-26. An example of a compartmentsymbol on a ship built after March1949 is given in figure 2-27,3-.75..4-ML Ammunition compartmentFigureSecond compartment outboard ofthe centerline to port.Forward boundary is on or immediatelyaft of frame 75.Third deck147.272-27.— Example of compartment symbolon ship built after March 1949.GEOMETRY OF THE SHIPSince a ship's hull is a three-dimensionalobject having length, breadth, and depth, andsince the hull has curved surfaces in each23.191Figure 2-28.— Transverse, horizontal, and verticalplanes.29

PRINCIPLES OF NAVAL ENGINEERINGdimension, no single drawing of a ship cangive an accurate and complete representationof the lines of the hull. In naval architecture,a hull shape is shown by means of a linesdrawing (sometimes referred to merely as thelines of the ship). The lines drawing consistsof three views or projections— a body plan, ahalf-breadth plan, and a sheer plan-which areobtained by cutting the hull by transverse,horizontal, and vertical planes (fig. 2-28). Theuse of these three planes to produce the threeprojections is illustrated in figure 2-29.Figure 2-30.— Diagonal plane.23.195147.28Figure 2-29.— Half-breadth plan, body plan, andsheer plan.In addition to using transverse, horizontal,and vertical planes, ship designers frequentlyuse a set of planes known as diagonals . Adiagonal plane is illustrated in figure 2-30.As a rule, three diagonals are used; these areidentified as diagonal A, diagonal B, and diagonalC. Diagonals are frequently shown asprojections on the body plan and on the halfbreadthplan.23.192Figure 2-31. — Transverse planes and body plan.30

Chapter 2-SHIP DESIGN AND CONSTRUCTIONFigure 2-32.— Body plan of a YTB.147.29BODY PLANTo visualize the projection known as the bodyplan, we must imagine the ship's hull cuttransversely in several places, as shown inpart A of figure 2-31. The shape of a transverseplane intersection of the hull is obtained at eachcut; when the resulting curves are projectedonto the body plan (part B of fig. 2-31) they showthe changing shape of transverse sections of thehull.Since the hull is symmetrical about thecenterline of the ship, only one-half of eachcurve obtained by a transverse cut is shown onthe body plan. Each half curve is called a halfstation . The right-hand side of the body planshows the forward half stations— that is, thehalf stations resulting from transverse cutsbetween the bow and the middle of the ship.The left-hand side of the body plan shows theaft half stations— that is, the half stationsresulting from transverse cuts between thestern and the middle of the ship.As may be inferred, a station is a completecurve such as would be obtained if each transversecut were projected completely, ratherthan as half a curve, onto the body plan. Thestations are numbered from forward to aft,dividing the hull into equally spaced transversesections. The station where the forward endof the designer's waterline^ and the stemcontour intersect is known as the forwardperpendicular, or station O. The station at theintersection of the stern contour and the designer'swaterline is known as the after perpendicular.The station midway between theThe waterline at which the ship is designed to floatis known as the designer's waterline.31

PRINCIPLES OF NAVAL ENGINEERINGWATERLINES\V B ^-~ _.BDIAGONALSFigure 2-33.— Horizontal planes and half-breadth plan.23.194forward and after perpendiculars is known as 6-foot waterline, an 8-foot waterline, a 10-footthe middle perpendicular.waterline, and so forth.An actual body plan for a YTB is shown infigure 2-32. Note the projection of the diagonalson this body plan.HALF-BREADTH PLANTo visualize the half-breadth plan, we mustimagine the ship's hull cut horizontally inseveral places, as shown in part A of figure2-33. The cuts are designated as waterlines .although the ship could not possibly float atmany of these lines. The base plane whichserves as the point of origin for waterlinesis usually the horizontal plane that coincideswith the top of the flat keel. Waterlines aredesignated according to their distance abovethe base plane; for example, we may have aThe waterlines are projected onto the halfbreadthplan, as shown in part B of figure 2-33.Since the hull is symmetrical, only half of thewaterlines are shown in the half-breadth plan.Diagonals are frequently shown on the other halfof the half-breadth plan.SHEER PLANTo visualize the sheer plan, we must imaginethe ship's hull cut vertically in several places,as shown in part A of figure 2-34. The resultantcurves, known as buttocks or as bow and buttocklines , are projected onto the sheer plan,as shown in part B of figure 2-34. The centerlineplane is designated as zero buttock . Theother buttocks are designated according to their32

Chapter 2-SHIP DESIGN AND CONSTRUCTIONFigure 2-34.— Vertical planes and sheer plan.23.193distance from zero buttock. The spacing ofthe vertical cuts is chosen to show the contoursof the forward and after quarters of theship.33

CHAPTERSSTABILITY AND BUOYANCYThis chapter deals with the principles ofstability, stability curves, the inclining experiment,effects of weight shifts and weight changes,effects of loose water, longitudinal stability andeffects of trim, and causes of impaired stability.The damage control aspects of stability arediscussed in chapter 4 of this text.PRINCIPLES OF STABILITYA floating body is acted upon by forces ofgravity and forces of buoyancy. The algebraicsum of these forces must equal zero if equilibriumis to exist.Any object exists in one of three states ofstability: stable, neutral, or unstable. We mayillustrate these three states by placing threecones on a table top, as shown in figure 3-1.When cone A is tipped so that its base is offthe horizontal plane, it tends, up to a certainangle of inclination, to assume its originalposition again. Cone A is thus an example of astable body— that is, one which tries to attainits original position through a specified rangeof angles of inclination.Cone B is an example of neutral stability.When rotated, this cone may come to rest atany point, reaching equilibrium at some angle ofinclination.Cone C, balanced upon its apex, is an exampleof an unstable body. Following any slight inclinationby an external force, the body willcome to rest in a new position where it willbe more stable.From Archimedes' law, we know that anobject floating on or submerged in a fluid isbuoyed up by a force equal to the weight of thefluid it displaces. The weight (displacement)of a ship depends upon the weight of all parts,equipment, stores, and personnel. This totalweight represents the effect of gravitationalforce. When a ship is floated, she sinks intothe water until the weight of the fluid displacedby her underwater volume is equal to the weightof the ship. At this point, the ship is in equilibrium—thatis, the forces of gravity (G) andthe forces of buoyancy (B) are equal, and thealgebraic sum of all forces acting upon the shipis equal to zero. This condition is shown inpart A of figure 3-2. If the underwater volumeof the ship is not sufficient to displace anamount of fluid equal to the weight of the ship,the ship will sink (part B of fig. 3-2) becausethe forces of gravity are greater than theforces of buoyancy.The depth to which a ship will sink whenfloated in water depends upon the density ofthe water, since the density affects the weightper unit volume of a fluid. Thus we may expecta ship to have a deeper draft in fresh waterthan in salt water, since fresh water is lessdense (and therefore less buoyant) than saltwater.Although gravitational forces act everywhereupon the ship, it is not necessary to attempt toconsider these forces separately. Instead, wemay regard the total force of gravity as a singleresultant or composite force which acts verticallydownward through the ship's center ofgravity (G). Similarly, the force of buoyancymay be regarded as a single resultant forcewhich acts vertically upward through the centerof buoyancy (B) located at the geometric centerof the ship's underwater body. When a ship isat rest in calm water, the center of gravityand the center of buoyancy lie on the samevertical line.DISPLACEMENTSince weight (W) is equal to the displacement,it is possible to measure the volume of the underwaterbody (V) in cubic feet and multiply thisvolume by the weight of a cubic foot of sea34

Chapter 3-STABILITY AND BUOYANCYFigure 3-1.— Three states of stability.147.30WATERLINEThe volume of an underwater body for a givendraft line can be measured in the drafting roomby using graphic or mathematical means. Thisis done for a series of drafts throughout theprobable range of displacements in which a shipis likely to operate. The values obtained areplotted on a grid on which feet of draft are measuredvertically and tons of displacement horizontally.A smooth line is faired through thepoints plotted, providing a curve of displacementversus draft, or a displacement curve as it isgenerally called. The result is shown in figure3-4 for a cruiser.To use the curve shown in figure 3-4 forfinding the displacement when the draft is given,locate the value of the mean draft on the draftscale at left and proceed horizontally acrossthe diagram to the curve. Then drop verticallydownward and read the displacement from thescale. For example, if the mean draft is ?4 feet,the displacement found from the curve is approximately14,700 tons.B = G 147.31KB VERSUS DRAFTFigure 3-2. — Interaction of force of gravityand force of buoyancy.water, in order to find what the ship weighs.This relationship may be written as:where(1) W= V X(2) V = 35W135V = volume of displaced sea water, incubic feetAs the draft increases, the center of buoyancy(B) rises with respect to the keel (K). Figure3-5 shows how different drafts result in differentvalues of KB, the height of the center ofbuoyancy from the keel (K). A series of valuesfor KB is obtained and these values are plottedon a curve to show KB versus draft. Figure 3-6illustrates a typical KB curve.To read KB when the draft is known, startat the proper value of draft on the scale at theleft and proceed horizontally to the curve.Then drop vertically downward to the baseline(KB).Thus, if a ship were floating at a mean draftof 19 feet, the KB found from the chart wouldbe approximately 10.5 feet.W =weight, in tons35 = cubic feet of sea water per ton(When dealing with ships, it is customaryto use the long ton of 2240pounds.)WATERLINE 128 FEET 1It is also obvious, then, that displacementwill vary with draft. As the draft increases,the displacement increases. This is indicated infigure 3-3 by a series of displacements shownfor successive draft lines on the midship sectionof a cruiser.

PRINCIPLES OF NAVAL ENGINEERING

Chapter 3-STABILITY AND BUOYANCYRM =W X GZwhere24 FOOT WflTERLINE20 FOOT WATERLINE16 FOOT WATERLINEBASE LINE8.5Figure 3-5. — Successive centers of buoyancy(B) for different drafts.

PRINCIPLES OF NAVAL ENGINEERINGm DIRECTION OFRIGHTING MOMENT8.52Figure 3-8. — Development of righting momentwhen a stable ship inclines.is exaggerated in the drawing), establishing ametacenter at M. The ship's righting arm GZis one side of the triangle GZM. In this triangleGZM, the angle of heel is at M. The side GMis perpendicular to the waterline at even keel,and ZM is perpendicular to the waterline whenthe ship is inclined.It is evident that for any angle of heel notgreater than 7°, there will be a definite relationshipbetween GM and GZ because GZ = GMsin . Thus, GM acts as a measure of GZ, therighting arm.GM is also an indication of whether the shipis stable or unstable at small angles of inclination.If M is above G, the metacentric heightis positive, the moments which develop whenthe ship is inclined are righting moments, andthe ship is stable (part A of fig. 3-11). But ifM is below G, the metacentric height is negative,the moments which develop are upsetting moments,and the ship is unstable (part B of fig.3-11).INFLUENCE OF METACENTRIC HEIGHTFORCE OF BUOYANCYDIRECTION OFUPSETTINGMOMENTWhen the metacentric height of a ship islarge, the righting arms that develop at smallangles of heel are also large. Such a ship resistsroll and is said to be stiff. When the8.53Figure 3-9.— Development of upsetting momentwhen unstable ship inclines.initial position is referred to as M. The distancefrom the center of buoyancy (B) to the metacenter(M) when the ship is on even keel is themetacentric radius.METACENTRIC HEIGHT (GM)The distance from the center of gravity (G)to the metacenter is known as the ship's metacentricheight (GM). Figure 3-11 shows aship heeled through a small angle (the angleFigure 3-10.— The metacenter.8.5438

^Chapter S-STABILITY AND BUOYANCYANGLE OFHEELdamage. However, a smaller GM is sometimesdesirable for the slow, easy roll which makes formore accurate gunfire. Thus the GM value fora naval ship is the result of compromise.STABILITY CURVESWhen a series of values for GZ at successiveangles of heel are plotted on a graph, the resultis a stability curve . The stability curve shown infigure 3-12 is called a curve of static stability .The word static indicates that it is not necessaryfor the ship to be in motion for the curve toapply; if the ship were momentarily stopped atany angle during its roll, the value of GZ givenby the curve would still apply.To understand the stability curve, it is necessaryto consider the following facts:1. The ship's center of gravity does notchange position as the angle of heel is changed.2. The ship's center of buoyancy is alwaysat the center of the ship's underwater hull.3. The shape of the ship's underwater hullchanges as the angle of heel changes.Putting these facts together, we see that theposition of G remains constant as the ship heelsthrough various angles, but the position of Bchanges according to the angle of inclination.Initial stability increases with increasing angleof heel at an almost constant rate; but at largeangles the increase in GZ begins to level off andgradually diminishes, becoming zero at verylarge angles of heel.EFFECT OF DRAFT ON RIGHTING ARM8.55Figure 3-11. — (A) Stable condition, G is belowM. (B) Unstable condition, G is above M.metacentric height is small, the righting armsare also small. Such a ship rolls slowly and issaid to be tender . Some GM values for variousnaval ships are: CLs, 3 to 5 feet; CAs, 4 to 6feet; DDs, 3 to 4 feet; DEs, 3 to 5 feet; and AKs,1 to 6 feet.Large GM and large righting arms are desirablefor resistance to the flooding effects ofA change in displacement will result in achange of draft and freeboard; and B will shiftto the geometric center of the new underwaterbody. At any angle of inclination, a change indraft causes B to shift both horizontally andvertically with respect to the waterline. Thehorizontal shift in B changes the distance betweenB and G, and thereby changes the lengthof the righting arm. GZ. Thus, when draft isincreased, the righting arms are reducedthroughout the entire range of stability. Figure3-13 shows how the righting arm is reducedDesign engineers usually use GM values as a measureof stability up to about 7 heel. For angles beyond 7°,a stability curve is used.39

PRINCIPLES OF NAVAL ENGINEERINGa:

Chapter 3-STABILITY AND BUOYANCYwhen the draft is increased from 18 feet to 26feet, when the ship is inclined at an angle of 20°.At smaller angles up to 30°, certain hull typesshow flat or slightly increasing righting armvalues with an increase in displacement.A reduction in the size of the righting armusually means a decrease in stability. When thereduction in GZ is caused by increased displacement,however, the total effect on stabilityis more difficult to evaluate. Since the rightingmoment is equal to W times GZ, the rightingmoment will be increased by the gain in W atthe same time that it is decreased by the reductionin GZ. The gain in the righting moment,caused by the gain in W, does not necessarilycompensate for the reduction in GZ.In brief, there are several ways in which anincrease in displacement affects the stability ofa ship. Although these effects occur at the sametime, it is best to consider them separately.The effects of increased displacement are:1. Righting arms (GZ) are decreased as aresult of increased draft.2. Righting moments (foot-tons) are decreasedas a result of decreased GZ (for a givendisplacement).3. Righting moments may be increased as aresult of the increased displacement (W), if(GZ X W) is increased.CROSS CURVES OF STABILITYTo facilitate stability calculations, the designactivity inclines a lines drawing of the ship at agiven angle, and then lays off on it a series ofwaterlines. These waterlines are chosen atevenly spaced drafts throughout the probablerange of displacements. For each waterline thevalue of the righting arm is calculated, using anassumed center of gravity rather than the truecenter of gravity. A series of such calculationsis made for various angles of heel—usually 10 ,20°, 30°, 40°, 50°, 60°, 7C°, 80°, and 90°- and theresults are plotted on a grid to forma series ofcurves known as the cross curves of stability(fig. 3-14). Note that, as draft and displacementincrease, the curves all slope downward, indicatingincreasingly smaller righting arms.The cross curves are used in the preparationof stability curves. To take a stability curvefrom the cross curves, a vertical line (such asline MN in fig. 3-14) is drawn on the cross curvesheet at the displacement which corresponds tothe mean draft of the ship. At the intersection ofthis vertical line with each cross curve, thecorresponding value of the righting arm on thevertical scale at the left can be read. Then thisvalue of the righting arm at the correspondingangle of heel is plotted on the grid for the stabilitycurve. When a series of such values of therighting arms from 10 "through 90° of heel havebeen plotted, a smooth line is drawn throughthem and the uncorrected stability curve for theship at that particular displacement is obtained.The curve is not corrected for the actual heightof the ship's center of gravity, since the crosscurves are based on an assumed height of G.However, the stability curve does embody theeffect on the righting arm of the freeboard fora given position of the center of gravity.Figure 3-15 shows an uncorrected stabilitycurve (A) for the ship operating at 11,500 tonsdisplacement, taken from the cross curvesshown in figure 3-14. This stability curve cannotbe used in its present form, since the crosscurves are made up on the basis of an assumedcenter of gravity. In actual operation, the ship'scondition of loading will affect its displacementand, therefore, the location of G. To use a curvetaken from the cross curves, therefore, it isnecessary to correct the curve for the actualheight of G above the keel (K)— that is, it isnecessary to use the distance KG. As far as thenew center of gravity is concerned, when aweight is added to a system of weights, thecenter of gravity can be found by taking momentsof the old system plus that of the new weight anddividing this total moment by the total finalweight. Detailed information concerning changesin the center of gravity of a ship can be obtainedfrom chapter 9880 of the Naval Ships TechnicalManual .Assume that the cross curves are made upon the basis of an assumed KG of 20 feet, and theactual KG, which includes the added effects ofFree Surface , for the particular condition ofloading, is 24 feet. This means that the true Gis 4 feet higher than the assumed G, and that therighting arm (GZ) at each angle of inclinationwill be smaller than the righting arm shown infigure 3-15 (curve A) for the same angle. Tofind the new value of GZ for each angle ofinclination, the increase in KG (4 feet) is multipliedby the sine of the angle of inclination, andthe product is subtracted from the value of GZshown on the cross curves or on the uncorrectedstability curve. In order to facilitate the correctionof the stability curves, a table showing thenecessary sines of the angles of inclination is41

PRINCIPLES OF NAVAL ENGINEERINGINCLINING EXPERIMENT, U. S. S. MIDDLETomL. IShMt ...,lS...tI....

(rChapter 3-STABILITY AND BUOYANCY

PRINCIPLES OF NAVAL ENGINEERINGTAN e = TANGENT OF ANGLE OF LIST = -5-.a diagonal movement can be divided into componentsin each of the three directions, and onecomponent can be studied at a time without referenceto the others. For example, if a weightis moved from the main deck, starboard side,aft, to a storeroom on the 4th deck, port side,forward, this movement may be regarded astaking place in three steps, as follows:1. from main deck to 4th deck (down)2. from starboard side to port side (across)3. from stern to bow (forward)VERTICAL WEIGHT SHIFT147.32Figure 3-16.— Measuring the angle of list producedin performing the inclining experiment.EFFECTS OF WEIGHT SHIFTSIf one weight inasystemof weights is moved,the center of gravity of the whole system movesalong a path parallel to the path of the componentweight. The distance that the center of gravityof the system moves may be calculated fromthe formula.pp _ ws^^°1- wIf a weight is moved straight up a verticaldistance on a ship, the ship's center of gravitywill move straight up on the centerline (fig.3-17). The vertical rise in G (explained laterin the chapter) can be computed from the formulamentioned previously.Example : A ship is operating with a displacementof 11,500 tons. Her ammunition,totaling 670 tons, is to be moved from themagazines to the main deck, a distance of 36feet. Find the rise in G.„„ 670 x 36^n 11,500w RELOCATEDTO HERE^I2.1 feetwherew = component weight, in tonss = distance component weight is moved, infeetW = weight of entire system, in tonsGG^ = shift in center of gravity of system, infeetWeight movements in a ship can take placein three possible directions— athwartships, foreand aft, and vertically (perpendicular to thedecks). The most general type of movement isinclinedwith respect to all three of these. SuchFigure 3-17. -Shift147.33in G due to vertical weightshift.44

Chapter 3-STABILITY AND BUOYANCYSince moving a weight which is already aboardwill cause no change in displacement, there canbe no change in M, the metacenter. If M remainsfixed, then the upward movement of thecenter of gravity results in a loss of metacentricheight:whereGjM GM - GG 1G,M = new metacentric height (after weightmovement), in feetGM = old metacentric height (before weightmovement), in feetGGj^ = rise in center of gravity,in feetIf the ammunition on the main deck is moveddown to the 6th deck, the positions of G and Gjwill be reversed. The shift in G can be foundfrom thesame formula as before, the only differencebeing that GGj^ now becomes a gain inmetacentric height instead of a loss (fig. 3-18).If a weight is moved vertically downward, theship's center of gravity, G, will move straightdown on the centerline and the correction is additive.In this case the sine curve is plotted belowthe abscissa. The final stability curve is thatportion of the curve above the sine correctioncurve.A vertical shift in theship'scenter of gravitychanges every righting arm throughout the entirerange of stability. If the ship is at any angle ofheel, such as 6 in figure 3-18, the righting armis GZ with the center of gravity at G. But if thecenter of gravity shifts to G^ as the result of avertical weight shift upward, the righting armbecomes Gj^Zj^, which is smaller than GZ by theamount of GR. In the right triangle GRGj, theangle of heel is at Gj; hence the loss of therighting arm may be found fromGR = GG^ X sin $This equation may be stated in words as: Theloss of righting arm equals the rise in the centerof gravity times the sine of the angle of heel . Thesine of the angle of heel is a ratio which can befound by consulting a table of sines.If the loss of GZ is found for 10°, 20°, 30°,and so forth by multiplying GG^ by the sine ofthe proper angle, a curve of loss of rightingarms can be obtained by plotting values ofGG^ X sin e vertically against angles of heelhorizontally, which results in a sine curve. Whenplotted, the curve is as illustrated in figure 3- 19.The sine curve may be superimposed on theoriginal stability curve to show the effect onstability characteristics of moving the weight upin a ship. Inasmuch as displacement is unchanged,the righting arms of the old curve needbe corrected for the change of G only, and noother variation occurs. Consequently, if GGj^ xsin e is deducted from each GZ on old stabilitycurve, the result will be a correct righting armcurve for the ship after the weight movement.In figure 3-20 a sine curve has been superimposedon an original stability curve. The dottedarea is that portion of the curve which was lostdue to moving the weight up, whereas the linedarea is the remaining or residual portion of thecurve. The residual maximum righting arm isAB and occurs at an angle of about 37°. The newrange of stability is from 0°to 53°.The reduced stability of the new curve becomesmore evident if the intercepted distancesbetween the old GZ curve and the sine curve aretransferred down to the base, thus forming anew curve of static stability (fig, 3-21). Wherethe old righting arm at 30° was AB, the new onehas a value of CB, which is plotted up from thebase to locate point D (CB = AD) and thus a pointis established at 30° on the new curve. A seriesof points thus obtained by transferring intercepteddistances down to the base line delineatesthe new curve, which maybe analyzed as follows:GM is now the quantity represented by EF.Maximum righting arm is now the quantityrepresented by HI.Angle at which maximum righting arm occursis 37 °.Range of stability is from 0° to 53°.Total dynamic stability is represented by theshaded area.HORIZONTAL WEIGHT SHIFTWhen the ship is upright, G lies in the foreand aft centerline, and all weights on board arebalanced. Moving any weight horizontally willresult in a shift in G in an athwartship direction,parallel to the weight movement. B and Gare no longer in the same vertical line and anupsetting moment exists at 0° inclination, whichwill cause the ship to heel until B moves underthe new position of G. In calm water the ship will45

PRINCIPLES OF NAVAL ENGINEERINGFigure 3-18. — Loss of righting arm due to rise in center of gravity.147.34GGi=2.11020 30 40 50 60ANGLES OF HEEL IN DEGREES70 80Figure 3-19.— Sine curve showing the loss of righting arm at various angles of heel.147.3546

Chapter 3-STABILITY AND BUOYANCYCURVE OF GGiXsineozHXOCAGGi=2.110 20 30 40 50 60 7080 90ANGLE OF HEEL IN DEGREESFigure 3-20.— Sine curve superimposed on original stability curve.147.36abZHs

PRINCIPLES OF NAVAL ENGINEERINGFigure 3-22. — Loss of righting arm when center of gravity ismoved off the center line.147.38loss of righting arm involved in an athwartshipmovement of G is equal at any angle of heel toG1G2 X cos 6 . This variable distance (G1G2 xcos 6 ) is called the ship's inclining arm; whenthis value is multiplied by the displacement,W, the product is the ship's inclining moment.The expression G^T = G1G2 x cos(9may bestated as: The inclining arm is equal to theathwartship shift in the center of gravity timesthe cosine of the angle o f heel. The cosine ofthe angle of heel is a ratio which can be foundby consulting a table of cosines. If the incliningarm is computed for 10 ,20°, 30°, etc. bymultiplying G1G2 by the cosine of the properangle, a curve of inclining arms can be obtainedby plotting values of G1G2 x cos^ verticallyagainst angles of heel horizontally, which resultsin a cosine curve. Note that the cosinecurve (fig. 3-23) is just the opposite of the sinecurve (fig. 3-20) but is otherwise identical inshape.Just as the sine curve was superimposedon the GZ curve, so may the cosine curve besuperimposed on the stability curve to show theeffect on stability of moving a weight athwartship.The cosine curve has been placed on theoriginal stability curve, corrected for the actualheight of the center of gravity. The dotted area(fig. 3-23) is that portion of the curvewhich waslost due to the weight shift, and the lined areais the remaining or residual portion of the curve.The residual maximum righting arm js ABwhich develops at an angle of about 37 . Thenew range of stability is from ?0° to 50°.The new curve of static stability can beplotted on the base by transferring down theintercepted distances between the cosine curveand the old GZ curve. For example, in figure3-24 the old righting arm at 37° was AD, theloss of righting arm (inclining arm) at thisangle is AC, leaving a residual GZ of CD. Thisvalue has been plotted up from the base as ABto provide one point on the final curve. Theresidual stability may be analyzed on the newcurve as follows:48

; onChapter S-STABILITY AND BUOYANCYMaximum righting arm AB.Angle of maximum righting arm at A.Range of stability 20° to 50°.Total dynamic stability is representedby the lined area.The ship will have a permanent list at 20 °ch is the angle where B is under G, inclining1 equals original righting arm, cosine curvesses original GZ curve, and residual rightarmis zero. In a seaway the ship will rollut this angle of list. If it rolls farther to theed side, a righting moment develops whichis to return it toward the angle of list. If•oils back towards the upright, an upsettingnent develops which tends to return it todthe angle of list. The upsetting moment;ween ° and the angle of list) is the differebetween the inclining and righting moments.GONAL WEIGHT SHIFTA weight may beshifted diagonally, so thatnoves up or down and athwartship at thele time, or by moving one weight up or downanother athwartship. A diagonal shift shouldtreated in two steps; first by finding the ef-GM and stability of the vertical shift,second, by finding the effect of the horitalmovement. The corrections are appliedjreviously described.EFFECTS OF WEIGHT CHANGESThe additional removal of any weight in aD may affect list, trim, draft, displacement,and stability. Regardless of where the weightis added (or removed), when determining thevarious effects it should be considered firstto be placed in the center of the ship, thenmoved up (or down) to its final height, nextmoved outboard to its final off-center location,and finally shifted to its fore or aft position.Assume that a weight is added to a ship sothat the list or trim is not changed, and G willnot shift. The first thing to do is find the newdisplacement, which is the old displacementplus the added weight:whereNew displacement = W +w tonsW = old displacement (tons)w = added weight (tons)With the new value of displacement, enter thecurves of form and on the displacement curvefind the corresponding draft, which is the newmean draft. Figure 3-25 shows typical displacementand other curves generally referred toas curves of form.If the change in draft is not over 1 foot, theprocedure can be reversed. Find the tons-perinchimmersion for the old mean draft fromthe curves of form, divide the added weight(in tons) by the tons-per-inch immersion inorder to get the bodily sinkage in inches, andadd this bodily sinkage to the old mean draftto get the new mean draft. Using the new meandraft, enter the curves of form and find thenew displacement.2

PRINCIPLES OF NAVAL ENGINEERINGa:2p tNCLINING ARM CURVE OLD RIGHTING ARM CURVEgHXO5u,2 wANGLE OF HEEL IN DEGREESa -c3147.40Figure 3-24.— New curve of static stability after correction for horizontal weight movement.VERTICAL WEIGHT CHANGESAssume that the weight added above is shiftedvertically on the ship's centerline to its finalheight above the keel. This movement willcause G to shift up or down. To compute thevertical shift of G use the formulawhereGGiwzW(W+ w)GGi =wz(W + wshift of G up or down, in feetadded weight, in tonsvertical distance w is added aboveor below original location of G, infeetold displacement, in tonsnew displacement, in tonsThis vertical shift must be added to or subtractedfrom the original height of the centerof gravity above the keel.To do this, the original height KG must beknown:whereKGiKGKGi = KG + GGiG above keel (in feet)new height ofold height of G above keel ( in feet)wzGGl = shift of G from formula GGl =(W+ w)If the final position of the added weight isbelow the original position of G, then GGj^ isminus; if it is above, then GGi is plus.To find the new metacentric height, enterthe curves of form with the new mean draftand find the height of the transverse metacenterabove the base line. This is KM^. Thenew metacentric height is determined by theformula.whereGiMi= KMi - KGlGiMi= new metacentricKMi = new KMKGl = "^w KGheight (in feet)With the new displacement (W + w), enterthe cross curves and pick out a new, uncorrectedcurve of stability. Correct this curve for thenew height of the ship's center of gravity abovethe base line. This is accomplished by findingAGi (which is KGl minus KA) and subtractingAGi X sin 6 from every vertical on the stabilitycurve, provided Gl is above A. If Gl is belowA, the values of AGi x sin 6 must be added tothe curve, as previously explained. The resultingcurve of righting arms is now correct forthe loss of freeboard due to the added weightand for the final height of the ship's center ofgravity resulting from weight addition.50

Chapter 3-STABILITY AND BUOYANCYblZop111agz2 P5sos5£Z»-u.inoP^5>•o m111ii.S OSuOzz8 zuin5b.8

wPRINCIPLES OF NAVAL ENGINEERINGExample : Add four gun mounts topside to aship with the curves of form shown in figure3-25. Assume an initial KG of 24.5 feet. Assumethat the gun mounts weigh 28 tons each and thattheir center of gravity is located 48 feet abovethe keel. What is the effect on stability?1. New displacement = W+ w= 11,500+ (4 x28) =11,612 tons.2. New mean draft = 19.7 feet (fig. 3-25).wz3. GGi = W+w= 4 X 28= 112 tonsz =48 - 24.5 =23.5 feet112 X 23.5GGi = 11,6120.23 feet4. KG^ = 24,50 +0.23 = 24.73 feet.5. New KMj = 28.4 feet (fig. 3-25).6. New GiMi = KM^ - KGi = 28.43.7 feet.- 24.7=7. The values for the angles (0 °— 70°) aretaken from the cross curves for 11,612tons displacement (fig. 3-14). KA is 20 feet.Corrections are made for AGi x sini? =(24.73 - 20) sin(9=4.73 sinS. The correctionsare applied to the curve (fig. 3-26)as previously explained. Figure 3-26shows the curve of righting arms correctedfor weight addition,HORIZONTAL WEIGHT CHANGESIn the previous example of weight addition,suppose the gun mounts are located with theircenter of gravity 29 feet to starboard of thecenterline and the weight is moved athwartshipto its final off-center location. The shift in Gmay be found by using the proper formula, makingthe required corrections, and applying thecorrections to the curve in figure 3-26. Thisgives a correct curve of righting arms. Toobtain a curve of righting moments, the rightingarms are multiplied by the new displacement(W+w) = 11,612 tons, and plotted in figure 3-27.WEIGHT REMOVALThe results of a weight removal are computedby using the previous procedure, the onlydifference being that most of the operationsand results will be found just the reverse ofthose which relate to adding a weight.EFFECTS OF LOOSE WATERWhen a tank or a compartment in a ship ispartially full of liquid that is free to move asthe ship heels, the surface of the liquid tends toremain level. The surface of the free liquid isreferred to as free surface . The tendency of theliquid to remain level as the ship heels is referredto as free surface effect . The term loosewater is used to describe liquid that has a freesurface; it is not usedtodescribe water or otherliquid that completely fills a tank or compartmentand thus has no free surface.FREE SURFACE EFFECTFree surface in a ship always causes a reductionin GM with a consequent reduction ofstability, superimposed on any additional weightwhich would be caused by flooding. The flow ofthe liquid is an athwartship shift of weight whichvaries with the angle of inclination. Whereverfree surface exists, a free surface correctionmust be applied to any stability calculation. Thiseffect may be considered to cause a reduction ina ship's static stability curve in the amount ofwhere4i-x sin^, due to a virtual rise inGi = the moment of inertia of the surface ofwater in the tank about a longitudinal axisthrough the center of area of that surface(or other liquid in ratio of its specificgravity to that of the liquid in which theship is floating)^V = existing volume of displacement of theship in cubic feet. For a rectangular compartment,i may be found fromwhereb^i12"b= athwartship breadth of the free surface(with the ship upright) in feet1= fore-and-aft length of the free surface infeetIt is usual to assume all liquids are salt water, andthus neglect density, unless very accurate determinationsare required.52

Chapter 3-STABILITY AND BUOYANCYTo understand what is meant by a virtualrise in G, refer to figure 3-28. This figureshows a compartment in a ship partially filledwith water, which has a free surface, fs, withthe ship upright. When the ship heels to anysmall angle, such as e, the free surface shiftsto fisi, remaining parallel to the waterline.The result of the inclination is the movementof a wedge of water from fofi to sqsi. Calling%\ the center of gravity of this wedge whenthe ship was upright, and g2 its center ofgravity with the ship inclined, it is evidentthat a small weight has been moved fromthe compartment contained solids rathergl to g2.Point G is the center of gravity of the shipwhen upright, and G would remain at this positionifthan a liquid. As the ship heels, however,the shift of a wedge of water along the pathg]^g2 causes the center of gravity of the shipto shift from G to G2. This reduces the rightingarm, at this angle, from GZ to G2Z2.To compute GG2 and the loss of GZ foreach angle of heel is a laborious and complicatedtask. However, an equivalent rightingarm, G3Z3 (which equals G2Z2), can be obtainedby extending the line of action of theforce of gravity up to intersect the ship'scenterline at point G3. Raising the ship'scenter of gravity from G to G3 would havethe same effect on stability at this angle asshifting it from G to G2.MINUS (D EQUALS ©(3) MINUS © EQUALS (S)UNCORRECTED GZSFROM CROSS CURVES''///u.H^© SINE CURVEOC z£CORRECTED FORACTUAL KG,10 20 30 40 5060ANGLE OF HEEL IN DEGREESFigure 3-26.— Curve of righting arms corrected for weight addition.147.4253

xPRINCIPLES OF NAVAL ENGINEERINGenZ.hOb30,000Zu20,000O%oH10.000Zo10 20 30ANGLE OF HEEL IN DEGREES'40 50 60 70MAXIMUM RIGHTING MOMENT- DEVELOPS AT 38'Figure 3-27. — Curve of righting moments.147.43The distance G3Z3 is the righting arm theship would have if the center of gravity hadrisen from G to G3 and this virtual rise of Gmay be computed from the formula:GG3= J-VReferring to the formula, loss in GZ=—sin . This formula is accurate for small anglesof heel only, due to the pocketing effect as theangle increases. In case several compartmentsor tanks have free surface, their surface momentsof inertia are calculated individuallyand their sum used in the correction for freesurface. The effect of a given area of looseliquid at a given angle of heel is entirely independentof the depth of the liquid in the compartment,as is apparent in the formula,b"^l12where the only factors are the dimensions ofthe surface and the displacement of the ship.The free surface effect is also independent ofthe free surface location in the ship, whetherit is high or low, forward or aft, on the centerlineor off, as long as the boundaries remainintact.The loss of metacentric height can obviouslycan be reduced by reducing the breadth of thefree surface, as bythe installation of longitudinalbulkheads. However, off-center flooding afterdamage then becomes possible, causing the shipto take on a permanent list and usually bringingabout a greater loss in stability than if thebulkhead were not present.The loss of GZ due to free surface is alwayslessened to some extent by pocketing. This isthe contact of the liquid with the top of the compartmentor the exposure of the bottom surfaceof the compartment, either of which takes placeat some definite angle and reduces the breadthof the free surface area. To understand howpocketing of the free surface reduces the freesurface effect, study figure 3-29. Part A showsa compartment in which the free surface effectis not influenced by the depth of the loose water.The compartment shown in part B, however, containsonly a small amount of water; when theship heels sufficiently to reduce the waterline54

Chapter 3-STABILITY AND BUOYANCYaNGLE OF HEELEXflGGERATEDFOR CLARITYFORCE OF GRAVITYFORCE OF BUOrflNCY147.44Figure 3-28.— Diagram showing virtualrise in G.FigureA PARTIALLY FULLBCSHALLOWALMOST FULL8.613-29. — Pocketing of free surface.in the compartment from wl to Wj^lj, the breadthof the free surface is reduced and the free surfaceeffect is thereby reduced. A similar reductionin free surface effect occurs in the almostfull compartment shown in part C, againbecause of the reduction in the breadth of thefree surface. As figure 3-29 shows, the beneficialeffect of poclceting is greater at largerangles of heel.The effect of pocketing in reducing the overall free surface effect is extremely variableand not easily determined. In practice, therefore,it is usually ignored and tends to providea margin of safety when computing stability.Most compartments of a ship contain somesolid objects, such as machinery and storeswhich would project through and above the surfaceof any loose water. If these objects aresecured so that they do not float or move about,and if they are not permeable, then the freesurface area and the free surface effect is reducedby their presence. The actual value ofthe reduction (surface permeability effect) isdifficult to calculate and, like the value ofpocketing, if ignored when calculating stabilitywill provide a further margin of safety.Swash bulkheads (nontight bulkheads piercedby drain holes) are fitted in deep tanks anddouble bottoms to hinder the flow of liquid inits attempt to remain continuously parallel tothe waterline as the ship rolls. They diminishthe free surface effect if the roll is quick, butthey have no effect when the roll is slow. Aship taking on a permanent list will inclinejust as far as if the swash plate were not there.When a fore- and -aft bulkhead separating twoadjacent compartments is holed (ruptured) sothat any flooding water present in one is freeto flow athwartship from one compartment tothe other, a casualty duplicating the effect ofa swash bulkhead has occurred. In this case,it is incorrect to add the free surface effectsof the two compartments together; an entirelynew figure for the flooding effect must be computed,regarding the two as one large compartment.In summary, the addition of a liquid weightwith a free surface has two effects on the metacentricheight of a ship. First, there is theeffect on GM and GZ of the weight addition(considered as a solid) which influences thevertical position of the ship's center of gravity,and the location of the transverse metacenter,M. Secondly, there is a reduction in GM and GZdue to the free surface effect.55

PRINCIPLES OF NAVAL ENGINEERINGFREE COMMUNICATION EFFECTIf one or more of the boundaries of an offcentercompartment are ruptured so that thesea may flow freely in and out with a minimumof restriction as the ship rolls, a condition ofpartial flooding with free communication withthe sea exists. The added weight of the floodingwater and the virtual rise in G due to the freesurface effect cause what is known as freecommunication effect. With an off-center spaceflooded, a ship will assume a list which willbe further aggravated by the free surface effect.As the ship lists, more water will flow intothe compartment from the sea and will tend tolevel off at the height of the external waterline.The additional weight causes the ship to sinkfurther allowing more water to enter, causingmore list until some final list is reached. Thereduction of GM due to free communicationeffect is approximately equal in magnitude towherefeetay^area of the free surface in squarey = perpendicular distance from the geometriccenter of the free surface area to thefore-and-aft centerline of the intact waterlineplane in feetV = new volume of ship's displacementafter flooding, in cubic feet. Thus reduction inGM is additional to and separate from the freesurface effect.The approximate reduction in GZ may becomputed fromGZ =ay2Vsin eThis may be considered as a virtual rise inG, superimposed upon the virtual rise in G dueto the free surface effect.K two partially filled tanks on opposite sidesof an intact ship are connected by an open pipeat or near their bottoms allowing a free flow ofliquid between them, the effect on GM is thesame as if both tanks were in free communicationwith the sea. Hence, valves in cross connectionsbetween such tanks should never beleft open without anticipating the accompanyingdecrease in stability,as sluicing.Such free flow is knownSUMMARY OF EFFECTS OF LOOSE WATE ,The addition of loose water to a ship altersthe stability characteristics by means of threeeffects that must be considered separately:(1) the effect of added weight; (2) the effect offree surface; and (3) the effect of free communication.Figure 3-30 shows the development of astability curve with corrections for added weight,free surface, and free communication. CurveA is the ship's original stability curve beforeflooding. Curve B represents the situation afterflooding; this curve shows the effect of addedweight (increased stability) but it does notshow the effects of free surface or of freecommunication. Curve C is curve B correctedfor free surface effect only. Curve D is curveB corrected for both free surface effect andfree communication effect. Curve D, therefore,is the final stability curve; it incorporatescorrections for all three effects of loose water.LONGITUDINAL STABILITY ANDEFFECTS OF TRIMThe important phases of longitudinal inclinationare changes in trim and longitudinalstability. A ship pitches longitudinally in contrastto rolling transversely and it trims forand-aft,whereas it lists transversely. Thedifference in forward and after draft is definedas trim.CENTER OF FLOATATIONWhen a ship trims, it inclines about an axisthrough the geometric center of the waterlineplane. This point is known as the center offlotation. The position for the center of flotationaft of the mid- perpendicular for variousdrafts may be found from a curve on the curvesof form (fig. 3-25). When a center of flotationcurve is not available, or when precise calculationsare not required, the mid-perpendicularmay be used in lieu of the center of flotation.CHANGE OF TRIMChange of trim may be defined as the changein the difference between the drafts forwardand aft. If in changing the trim, the draft forward56

Chapter 3-STABILITY AND BUOYANCY4 rCURVE BCURVE ACURVE CCURVE D10 20 30 40 50 60ANGLE OF HEEL.IN DEGREESFigure 3-30.— Stability curve corrected for effects of added weight,free surface, and free communication.8.64becomes greater, then the change is said to beby the bow. Conversely, if the draft aft becomesgreater, the change of trim is by the stern .Changes of trim are produced by shiftingweights forward or aft or by adding or subtractingweights forward of or abaft of the center offlotation.LONGITUDINAL STABILITYLongitudinal stability is the tendency of aship to resist a change intrim. For small anglesof inclination, the longitudinal metacentric heightmultiplied by the displacement is a measure ofinitial longitudinal stability. The longitudinalmetacentric height is designated GM' and isfound fromGM'= KB +BM' - KGr= the moment of inertia of the ship'swaterline plane about an athwartshipaxis through the center of flotationV = the ship's volume of displacementThe value of BM' is very large— sometimesmore than a hundred times that of BM. Thevalues of BM' for various drafts may be foundfrom the curves of form (fig. 3-25).MOMENT TO CHANGE TRIM ONE INCHThe measure of a ship's ability to resist achange of trim is the moment required to producea change of trim of a definite amount, suchas one inch. The value of the moment to changetrim one inch isobtained fromMTI = GM' X W12 LwhereKB and KG are the same as for transversestability BM' (the longitudinal metacentricradius) is equal toBM'=wherewhereGM'= longitudinal metacentric height (feet)W= displacement (tons)L = length between forward and afterperpendiculars (feet)57

PRINCIPLES OF NAVAL ENGINEERINGFor practical work. BM' is usually substitutedfor GM' since they are both large and the differencebetween them is relatively small. Whenthis is done, howver, MTI is called the approximatemoment to change trim one inch. Thisvalue may often be found as a curve in the curvesof form (fig. 3-25). If not, the approximatemoment to change trim one inch may be calculatedfromMTI = BM' X W12 LCALCULATION OF CHANGE OF TRIMThe movement of weight aboard ship in afore-and-aft direction produces a trimmingmoment. This moment is equal to the weightmultiplied by the distance moved. The changeof trim in inches may be calculated by dividingthe trimming moment by the moment to changetrim one inch:change of trimw X t=MTIThe direction of change of trim is the sameas that of weight movement. If we are using midshipsas our axis of rotation, the change in draftforward equals the change in draft aft. Thischange of draft forward or aft is one-half thechange of trim; for example, for a change oftrim by the stern the after draft increases thesame amount the forward draft decreases, thatis, one-half the change of trim. The reverseholds true for a change of trim by the bow.Example: If 50 tons of ammunition are movedfrom approximately 150 feet forward of thecenter of flotation to approximately 150 feet aftof the center of flotation (300 feet), what are thenew drafts?MTIdraft fwd= 19 feet 9 inchesdraft aft= 20 feet 3 inchesmean draft = 20 feettrimming moment = 50 x 300 = 15, 000 foot-tonsmoment tochange trim one inch = 1940 foottons,from the following calculation:BM' X W_ 1150 xll.80012 L 12 X 582(BM' from curve in figure 3-25)1940 foot-tons.fchange of . trim- - 15,000 _o -8. , , ^^inches by the stern1940change of draft — 4 inches fwd, 4 inches aftnew draft fwd= 19 feet 5 inchesnew draft aft = 20 feet 7 inchesLONGITUDINAL WEIGHT ADDITIONThe addition of a weight either directly aboveor below the center of flotation will cause anincrease in mean draft but will not change trim.All drafts will change by the same amount asthe mean draft. The reverse is true when aweight is removed at the center of flotation.To determine the change in drafts forwardand aft due to adding a weight on the ship, thecomputation is in two steps. First, the weight isassumed to be added at the center of flotation.This increases the mean draft and all the draftsby the same amount. The increase is equal tothe weight added, divided by the tons-per-inchimmersion. With the ship at its new drafts, theweight is assumed to be moved to its ultimatelocation. Moving the weight fore and aft producesa trimming moment and therefore a change intrim which is calculated as previously described.FLOODING EFFECT DIAGRAMFrom the flooding effect diagram of theship's Damage Control Book it is possible toobtain the change in draft fore and aft due tosolid flooding of a compartment. The weight ofwater to flood specific compartments is givenand trimming moment produced may be computed,as well as list in degrees which may becaused by the additional weight. Additional informationon the flooding effect diagram can beobtained from Chapter 9880 of the Naval ShipsTechnical Manual.EFFECT OF TRIM ON TRANSVERSESTABILITYThe curvesof form prepared for a ship arebased on the design conditions, i.e., with notrim. For most types of ship, so long as trimdoes not become excessive, the curves are stillapplicable, and may be used without adjustment.When a ship trims by the stern, the transversemetacenter is slightly higher than indicatedby the KM curve, because both KB andBM increase. The center of buoyancy rises becauseof the movement of a wedge of buoyancyupward. The increased BM is the result of anenlarged waterplane as the ship trims by thestern.58

.Chapter 3-STABILITY AND BUOYANCYTrim by bow usually means a decreased KM.The center of buoyancy will rise slightly, butthis is usually counteracted by the decreasedBM caused by the lower moment of inertia ofthe trimmed waterplane.CAUSES OF IMPAIRED STABILITYThe stability of a ship may be impaired byseveral causes, resulting from mistakes or fromA summary of these causes andenemy action.their effects follows:ADDITION OF TOPSIDE WEIGHTThe addition of appreciable amounts of topsideweight may be occasioned by unauthorizedalterations; icing conditions; provisions, ammunition,or stores not struck down; deck cargo;and other conditions of load. Whenever a weightof considerable magnitude is added above theship's existing center of gravity the effects are:1. Reduction of reserve buoyancy.2. Reduction of GM and righting arms due toraising G.3. Reduction of GM and righting arms dueto loss of freeboard (change of waterplane).4. Reduction of righting arms if G is pulledaway from the centerline.5. Increase in righting moment due to increaseddisplacement.The net effect of added high weight is alwaysa reduction in stability. The reserve buoyancyloss is added weight in tons. The new metacentricheight can be obtained from:GjM^ =KM^ - KG^Stability is determined by selecting a newstability curve from the cross curves and correctingit for AG^ sine and G1G2 cos e.LOSS OF RESERVE BUOYANCYReserve buoyancy may be lost due to errors,such as poor maintenance, failure to close fittingsproperly, improper classification of fittings,and overloading the ship; or it may be lostas a result of enemy action such as fragment ormissile holes in boundaries, blast which carriesaway boundaries or blows open or warps fittings,and flooding which overloads the ship. When theabove-water body is holed, some reserve buoy-ancy is lost. The immersion of buoyant volumeis necessary to the development of a rightingarm as the ship rolls; if the hull is riddled itcan no longer do this on the damaged side,toward which it will roll. In effect, the riddlingof the above- water hull is analogous to losing apart of the freeboard, thus reducing stability.When this happens, if the ship takes wateraboard on the roll, the combined effects of highadded weight and free surface operate to cutdown the righting moment. Therefore, the underwaterhull and body should be plugged andpatched, and every effort should be made to restorethe watertightness of external and internalboundaries in the above- water body.FLOODINGFlooding may take place because of underwaterdamage, shell or bomb burst below decks,collision, topside hit near the waterline, firefightingwater, ruptured poping, sprinkling ofmagazines, counterflooding, or leakage. Regardlessof how it takes place it can be classifiedin three general categories, each of which canbe further broken down, as follows:1with respect to boundariesa. solid footingb. partial floodingc. partial flooding in free communicationwith the sea2. with respect to height in the shipa. center of gravity of the flooding wateris above Gb. center of gravity of the flooding wateris below G3. with respect to the ship's centerlinea. symmetrical floodingb. off-center floodingSolid FloodingThe term solid flooding designates the situationin which a compartment is completelyfilled from deck to overhead. In order for thisto occur the compartment must be vented as byan air escape, an open scuttle or vent fitting, orthrough fragment holes in the overhead. Solidflooding water behaves exactly like an added59

PRINCIPLES OF NAVAL ENGINEERINGweight and has the effect of so many tons placedexactly at the center of gravity of the floodingwater. It is more likely to occur below thewaterline, where it has the effect of any addedlow weight. Inasmuch as G is usually a littleabove the waterline in warships, the net effectof solid flooding below the waterline is mostfrequently a gain in stability, unless a sizeablelist or a serious loss of freeboard results in anet reduction of stability. The reserve buoyancyconsumed is the weight of flooding water in tons,and the new GM and stability characteristicsare found as previously explained.Partial Flooding with Boundaries IntactThe term partial flooding refers to a conditionin which the surface of the flooding waterlies somewhere between the deck and the overheadof a compartment. The boundaries of thecompartment remain watertight and the compartmentremains partially but not completelyfilled. Partial flooding can be brought about byleakage from other damaged compartments orthrough defective fittings, seepage, shippingwater on the roll, downward drainage of water,loose water from firefighting, sprinklers, rupturedpiping, and other damage.Partial flooding of a compartment that hasintact flooding boundaries affects the stabilityof the ship because of (1) the effect of addedweight, and (2) the effect of free surface. Theeffect of the added weight will depend uponwhether the weight is high in the ship or low,and whether it is symmetrical about the centerlineor is off-center. The effect of free surfacewill depend primarily upon the athwartshipbreadth of the free surface. Unless the freesurface is relatively narrow and the weight isadded low in the ship, the net effect of partialflooding in a compartment with intact boundariesis likely to be a very definite loss in overallstability.Partial Flooding in Free Communicationwith the SeaFree communication can exist only in partiallyflooded compartments in which it ispossible for the sea to flow in and out as theship rolls. Partial flooding with free communicationis most likely to occur when there is alarge hole that extends above and below thewaterline. It may also occur in a waterlinecompartment when there is a large hole in theshell below the waterline, if the compartmentis vented as the ship rolls. Where free communicationdoes exist, the water level in thecompartment remains at sea level as the shiprolls.When a compartment is partially flooded andin free communication with the sea, the ship'sstability is affected by (1) added weight, (2) freesurface effect, and (3) free communication effect.In general, net effect of partial floodingwith free communication is a decided loss instability.60

CHAPTER 4PREVENTIVE AND CORRECTIVE DAMAGE CONTROLAboard ship, the overall damage and casualtycontrol function is composed of two separate butrelated phases: the engineering casualty controlphase and the damage control phase. The engineeringofficer is responsible for both phases.The engineering casualty control phase isconcerned with the prevention, minimization, andcorrection of the effects of operational and battlecasualties to the machinery, electrical systems,and piping installations, to the end that all engineeringservices may be maintained in a state ofmaximum reliability under all conditions of operation.Engineering casualty control is handledalmost entirely by personnel of the engineeringdepartment.The damage control phase, on the other hand,involves practically every person aboard ship.The damage control phase is concerned with suchthings as the preservation of stability and watertightintegrity, the control of fires, the control offlooding, the repair of structural damage, and thecontrol of nuclear, biological, and chemicalcontamination. Although under the control of theengineer officer, damage control is an all-handsresponsibility.This chapter presents some basic informationon the principles of the damage controlphase of the damage and casualty control function.Information on engineer ing casualty controlis not included here; any such information wouldbe relatively meaningless without a considerablebackground knowledge of the normal operatingcharacteristics of shipboard machinery andequipment.PREPARATIONS TO RESIST DAMAGENaval ships are designed to resist accidentaland battle damage. Damage resistant features includestructural strength, watertight compartmentation,stability, and buoyancy. Maintainingthese damage resistant features and maintaininga high state of material and personnel readinessbefore damage is far more important for survivalthan are any damage control measuresthat can be taken after the ship has been damaged.It has been said that 90 percent of thedamage control needed to save a ship takes placebefore the ship is damaged and only 10 percentcan be done after the damage has occurred. Inspite of all precautions and all preparatorymeasures, however, the survival of a ship sometimesdepends upon prompt and effective damagecontrol measures taken after damage has occurred.It is essential, therefore, that all shipboardpersonnel be trained in damage control procedures.The maintenance of watertight integrity is avital part of any ship's preparations to resistdamage. Each undamaged tank or compartmentaboard ship must be kept watertight if floodingis not to be progressive after damage. Watertightintegrity can be lost in a number of ways.Failure to secure access closures and impropermaintenance of watertight fittings and compartmentboundaries, as well as external damage tothe ship, can cause loss of watertight integrity,a thorough system of tests and inspections isprescribed. The condition of watertight boundaries,compartments, and fittings is determinedby visual observation and by various tests, includingchalk tests and air tests. All defectsdiscovered by any test or inspection must beremedied immediately.For most ships, a mandatory schedule of watertightintegrity tests and inspections is prepared.This schedule informs each ship of thecompartments subject to test and/or inspection,specifying which type of test or inspection shallbe applied. Ships not provided with such a scheduleare nevertheless required to make inspectionsof important watertight boundaries as requiredby chapter 9290 of the of Naval ShipsTeclinical Manual.61

PRINCIPLES OF NAVAL ENGINEERINGDAMAGE CONTROL ORGANIZATIONIn order to ensure damage control trainingand to provide prompt control of casualties, adamage control organization must be set up andkept active on all ships.As previously noted, the engineer officer isresponsible for damage control. The damagecontrol assistant (DCA), who is under the engineerofficer, is responsible for establishing andmaintaining an effective damage control organization.Specifically, the DCA is responsible forthe prevention and control of damage, the trainingof ship's personnel in damage control, andthe operation, care, and maintenance of certainauxiliary, machinery, piping, and drainage systemsnot assigned to other departments or divisions.Although naval ships may be large or small,and although they differ in type, the basic principlesof the damage control organization aremore or less standardized. Some organizationsare larger and more elaborate than others, butthey all function on the same basic principles.A standard damage control organization,suitable for large ships but followed by all shipsas closely as practicable, includes damage controlcentral and repair stations. Damage controlcentral is integrated with propulsion and electricalcontrol in a Central Control Station onnew large ships and is a separate Station onolder and small ships. Repair parties are assignedto specifically located repair stations.Repair stations are further subdivided into unitpatrols to permit dispersal of personnel and awide coverage of the assigned areas.DAMAGE CONTROL CENTRALThe primary purpose of damage control centralis to collect and compare reports from thevarious repair stations in order to determinethe condition of the ship and the corrective actionto be taken. The commanding officer is keptposted on the condition of the ship and on importantcorrective measures taken. The damagecontrol assistant, at his battle station in damagecontrol central, is the nerve center and directingforce of the entire damage control organization.He is assisted in damage control centralby a stability officer, a casualty board operator,and a damage analyst. In addition, representativesof the various divisions of the engineeringdepartment are assigned to damage controlcentral.In damage control central, repair party reportsare carefully checked so that immediateaction can be taken to isolate damage and tomake emergency repairs in the most effectivemanner. Graphic records of the damage aremade on various damage control diagrams andstatus boards, as the reports are received. Forexample, reports concerning flooding are markedup, as they come in, on a status board whichindicates liquid distribution before damage. Withthis information, the stability and buoyance ofthe ship can be estimated and the necessarycorrective measures can be determined.If damage control central is destroyed or isfor other reasons unable to retain control, therepair stations, in designated order, take overthese same functions. Provisions are also madefor passing the control of each repair stationdown through the officers, petty officers, andnonrated men, so that no group will ever bewithout a leader.REPAIR PARTIESA standard damage control organization onlarge ships includes the following repair stations:Repair 1 (deck or topside repair).Repair 2 (forward repair).Repair 3 (after repair).Repair 4 (amidship repair).Repair 5 (propulsion repair).Repair 6 (ordnance repair).On carriers, there are two additional repairstations— Repair 7 (gallery deck and islandstructure repair) and Repair 8 (electronics repairparty). Carriers also have special organizedteams such as Aviation Fuel Repair, Crashand Salvage, and Ornance Disposal. On smallships, there are usually three repair stations-Repair 2, Repair 3, and Repair 5.The organization of repair stations is basicallythe same on all types of ships; however,more men are available for manning repairstations on large ships than on small ships. Thenumber and the ratings of men assigned to arepair station, as specified in the battle bill,are determined by the location of the station,the portion of the ship assigned to that station,and the total number of men available.Each repair party has an officer in charge,who may in some cases be a chief petty officer.The second in charge is usually a chief petty62

Chapter 4- PREVENTIVE AND CORRECTIVE DAMAGE CONTROLofficer who is qualified in damage control andwho is capable of taking over the supervisionof the repair party.Many repair stations have unit patrol stationsat key locations in their assigned areas tosupplement the repair station. Operating instructionsshould be posted at each repair station.In general, instructions should include thepurpose of the repair station; the specific assignmentsof space for which that station isresponsible; instructions for assigning and stationingpersonnel; methods and procedures fordamage control communications; instructionsfor handling machinery and equipment locatedin the area; procedures for nuclear, biological,and chemical (NBC) defense; sequence and procedurefor passing control from one station toanother; a list of current damage control bills;and a list of all damage control equipment andgear provided for the repair station.MATERIAL CONDITIONS OF READINESSMaterial conditions of readiness refers tothe degree of access and system closure tolimit the extent of damage totheship. Maximumclosure is not maintained at all times becauseit would interfere with the normal operation ofthe ship. For damage control purposes, navalships have three material conditions of readiness,each condition representing a differentdegree of tightness and protection. The threematerial conditions of readiness are calledX-RAY, YOKE, and ZEBRA. These titles, whichhave no connection with the phonetic alphabet,are used in all spoken and written communicationsconcerning material conditions.Condition X-RAY, which provides the leastprotection, is set when the ship is in no dangerfrom attack, such as when it is at anchor in awell protected harbor or secured at a home baseduring regular working hours.Condition YOKE, which provides somewhatmore protection than condition X-RAY, is setand maintained at sea. It is also maintained inport during wartime and at other times in portoutside of regular working hours.Condition ZEBRA is set before going to seaor entering port, during wartime. It is also setimmediately, without further orders, whenmanning general quarters stations. ConditionZEBRA is also set to localize and control fireand flooding when not at general quarters stations.The closures involved in setting the materialconditions of readiness are labeled as follows:X-RAY, marked with a black X. These closuresare secured during conditions X-RAY,YOKE, and ZEBRA.YOKE, marked with a black Y. These closuresare secured during conditions YOKE andZEBRA.ZEBRA, marked with a red Z. These closuresare secured during condition ZEBRA,Once the material condition is set, no fittingmarked with a black X, a black Y, or a red Zmay be opened without permission of the commandingofficer (through the damage controlassistant or the officer of the deck.) The repairparty officer controls the opening andclosing of all fittings in his assigned area duringgeneral quarters.Additional fitting markings for specific purposesare modifications of the three basic conditions,as follows:CIRCLE X-RAY fittings, marked with a blackX in a black circle, are secured during conditionsX-RAY, YOKE, and ZEBRA. CIRCLEYOKE fittings, marked with a black Y ina blackcircle, are secured during conditions YOKE andZEBRA. Both CIRCLE X-RAY and CIRCLEYOKE fittings may be opened without specialauthority when going to or securing from generalquarters, when transferring ammunition,or when operating vital systems during generalquarters; but the fittings must be secured whennot in use.CIRCLE ZEBRA fittings, marked with a redZ in a red circle, are secured during conditionZEBRA. CIRCLE ZEBRA fittings may be openedduring prolonged periods of general quarters,when the condition may be modified. Openingthese fittings enables personnel to prepare anddistribute battle rations, open limited sanitaryfacilities, ventilate battle stations, and provideaccess from ready rooms to flight deck. Whenopen, CIRCLE ZEBRA fittings must be guardedfor immediate closure if necessary.DOG ZEBRA fittings, marked with a red Zin a black D, are secured during conditionZEBRA and during darken ship condition. TheDOG ZEBRA classification applies to weatheraccesses not equipped with light switches orlight traps.WILLIAM fittings, marked with a black W,are kept open during all material conditions.This classification applies to vital sea suctionvalves supplying main and auxiliary condensers,fire pumps, and spaces that are manned during63

PRINCIPLES OF NAVAL ENGINEERINGconditions X-RAY, YOKE, and ZEBRA; it alsoapplies to vital valves that, if secured, wouldimpair the mobility and fire protection of theship. These items are secured only as necessaryto control damage or contamination and toeffect repairs to the units served.CIRCLE WILLIAM fittings, marked with ablack W in a black circle, are normally keptopen (as WILLIAM fittings are) but must besecured as defense against nuclear, biological,or chemical attack.INVESTIGATION OF DAMAGEThe DC A must be given all available informationconcerning the nature and extent of damageso that he will be able to analyze the damageand decide upon appropriate measures of control.The repair parties that are investigatingthe damage at the scene are normally in thebest position to give dependable information onthe nature and extent of the damage. All repairparty personnel should be trained to makeprompt, accurate, and complete reports to damagecontrol central. Items that should normallybe reported to damage control central include:1. Description of important things seen,heard, or felt by personnel.2. Location and nature of fires, smoke, andtoxic gases.3. Location and nature of progressive flooding.4. Overall extent and nature of flooding.5. Structural damage to longitudinal strengthmembers.6. Location and nature of damage to vitalpiping and electrical systems.7. Local progress made in controlling fire;halting flooding; isolating damaged systems; andrigging jury piping, casualty power, and emergencycommunications.8. Compartment-by-compartment informationon flooding, including depth of liquid in eachflooded compartment.9. Condition of boundaries (decks, bulkheads,and closures) surrounding each flooded compartment.10. Local progress made in reclaiming compartmentsby plugging, patching, shoring, andremoving loose water.11. Areas in which damage is suspected butcannot be reached or verified.The DCA must ascertain just what informationthe commanding officer desires concerningthe extent of the damage incurred and thecorrective measures taken.The DCA must alsofind out how detailed the information to the COshould be and when it is to be furnished. Withthese guidelines in mind, the DCA must sift allinformation coming into damage control centraland pass along to the bridge only the type ofinformation that the CO wants to have.CORRECTIVE MEASURESMeasures for the control of damage may bedivided into two general categories: (1) overallship survival measures, and (2) immediatelocal measures.OVERALL SHIP SURVIVAL MEASURESOverall ship survival measures are thoseactions initiated by damage control central forthe handling of list, trim, buoyance, stability,and hull strength. Operations in this categoryhave five general objectives: improving GMand overall stability, correcting for off-centerweight, restoring lost freeboard and reservebuoyancy, correcting for trim, and relievingstress in longitudinal strength members.Improving GMand Overall StabilityThe measures used to improve GM and overallstability in a damaged ship include (1)suppressing free surface, (2) jettisoning topsideweights, (3) ballasting, (4) lowering liquidor solid weights, and (5) restoring boundaries.Correcting forOff- Center WeightOff-center weight may occur as the resultof unsymmetrical flooding or as the result ofCorrectingan athwartship movement of weight.for off-center weight may be accomplished by(1) pumping out off-center flooding water, (2)pumping liquids across the ship, (3) counterflooding,(4) jettisoning topside weights fromthe low side of the ship, (5) shifting solidweights athwartships, and (6) pumping liquidsoverboard from intact wing tanks on the lowside.Restoring Lost Freeboardand Reserve BuoyancyRestoring lost freeboard and reserve buoyancyrequires the removal of large quantities64

Chapter 4- PREVENTIVE AND CORRECTIVE DAMAGE CONTROLof weight. In general, the most practicable wayof accomplishing this is to restore watertightboundaries and to reclaim compartments bypumping them out. Any corrective measurewhich removes weight from the ship contributesto the restoration of freeboard.Correcting for TrimThe methods used to correct for trim afterdamage include (1) pumping out flood water, (2)pumping liquids forward or aft, (3) counterfloodingthe high end, (4) jettisoning topsideweights from the low end, (5) shifting solidweights from the low end to the high end, and(6) pumping liquids over the side from intacttanks at the low end. The first of these methods—that is, pumping out flood water— is in mostcases the only truly effective means of correctinga severe trim.The correction of trim is usually secondaryto the correction of list, unless the trim is sogreat that there is danger of submerging theweather deck at the low end.Relieving Stress inLongitudinal Strength MembersWhen a ship is partially flooded, the longitudinalstrength members are subject to greatstress. In cases where damage has carriedaway or buckled the strength members amidships,the additional stress imposed by theweight of the flooding water may be enough tocause the ship to break up. The only effectiveway of relieving stress caused by flooding isto remove the water. Other measures, such asremoving or shifting weight, may be helpfulbut cannot be completely effective. In some instances,damaged longitudinals may be strengthenedby welding.IMMEDIATE LOCAL MEASURESImmediate local measures are those actionstaken by repair parties at the scene of the damage.In general, these measures include allon-scene efforts to investigate the damage, toreport to damage control central, and to accomplishthe following:1. Establish flooding boundaries by selectinga line of intact bulkheads and decks to whichthe flooding may be held and by rapidly plugging,patching, and shoring to make these boundarieswatertight and dependable.2. Control and extinguish fires.3. Establish secondary flooding boundariesby selecting a second line of bulkheads and decksto which the flooding may be held if the firstflooding boundaries fail.4. Advance flooding boundaries by movingin toward the scene of the damage, plugging,patching, shoring, and removing loose water.5. Isolate damage to machinery, piping,and electrical systems.6. Restore piping systems to service bythe use of patches, jumpers, clamps, couplings,etc.lighting.9. Rescue personnel and care for the wounded.7. Rig casualty power.8. Rig emergency communications and10. Remove wreckage and debris.11. Cover or barricade dangerous areas.12. Ventilate compartments which are filledwith smoke or toxic gases.13. Take measures to counteract the effectsof nuclear, biological, and chemical contaminationor weapons.Immediate local measures for the controlof damage are of vital importance. It is notnecessary for damage control central to decideon these measures; rather, they should be carriedout automatically and rapidly by repairparties. However, damage control central shouldbe continuously and accurately advised of theprogress made by each party so that the effortsof all repair parties may be coordinated to thebest advantage.PRACTICAL DAMAGE CONTROLBoth the immediate local measures and theoverall ship survival measures have, of course,the common aim of saving the ship and restoringit to service. The following subsections dealwith the practical methods used to achieve thisaim: controlling fires, controlling flooding, repairingstructural damage, and restoring vitalservices.It should be noted that controlling the effectsof nuclear, biological, and chemical warfareweapons or agents may in some situations takeprecedence over other damage control measures.Because of the complex nature of NBCdefense, this subject is treated separately in alater section of this chapter.65

PRINCIPLES OF NAVAL ENGINEERINGCONTROL OF FIRESFire is a constant potential hazard aboardship. All possible measures must be taken toprevent its occurrence or to bring about itsrapid control and extinguishment. In many cases,fire occurs in conjunction with other damage,as a result of enemy action, weather, or accident.Unless fire is rapidly and effectively extinguished,it may cause more damage than theinitial casualty and it may, in fact, cause theloss of a ship even after other damage has beenrepaired or minimized.Fires are classified according to the natureof the combustible material. Class A fires arethose which involve ordinary combustible materialsuch as wood, paper, mattresses, canvas,etc. Class B fires are those which involve theburning of oils, greases, gasoline, and similarmaterials. Class C fires are those which occurin electrical equipment. Class D fires are thosewhich involve certain metals such as magnesium,potassium, powdered aluminum zinc,sodium, titanium, zirconium and others.Class A fires are extinguished by the useof water. Class B fires are extinguished chieflyby smothering with foam, fog, steam, or purpleK powder dry chemical agent (as appropriatefor the particular fire). Class C fires arepreferably extinguished by the use of carbondioxide. Because of the danger of electric shock,a solid stream of water must never be usedto extinguish a class C fire. Class D fires arepresently extinguished by using large amountsof water. Personnel safety is of prime concernwhen fighting this class fire; toxic gasses,possible hydrogen explosions, splattering ofmolten metal, and intense heat are prime characteristicsof this type of fire. Presently,intensive research is being conducted on bettermethods of attack and more suitable extinguishingagents.The organization of a firefighting party dependson the number of men available. Figure4-1 shows the basic organization of a smallfirefighting party, and figure 4-2 shows thebasic organization of a large firefighting party.At times it is necessary for one person to performmore than one of the indicated duties, andthis fact is taken into consideration in organizingfirefighting parties.One man in the firefighting party must bedesignated as the groupor scene leader (investigator).His first duty is to get to the fire quickly;he investigates the situation, determines the

Chapter 4- PREVENTIVE AND CORRECTIVE DAMAGE CONTROLSCENE LEADER(INVESTIGATOR)TALKERFIREFIGHTINGPARTYMESSENGERATTACKINGNOZZLEMANHOSEMENINVESTIGATORSPLUGMANFOAM LIQUIDACCESS MENSUPPORTINGELECTRICIANAND KITHOSPITALCORPSMANAND KITFOAM EQUIPMENTOPERATORSHOSEMENOXYACETYLENECUTTING OUTFITPUMPING EQUIPMENTSTANDBYNOZZLEMANHOSEMENINVESTIGATORSPLUGMANFOAM LIQUIDCLOSURE DETAILALUMINIZED FIRE PROXIMITY SUIT(OR ASBESTOS SUIT) MENVENTILATION LIGHTINGAND POWER MENDEWATERING EQUIPMENTFigure 4-2. — Organization of large firefighting party.8.81The CO2 dry powder supply men take extinguishersto the fire and operate them as necessary.The OBA men have their gear on and readyfor immediate use throughout the firefightingoperation. OBA tenders are in charge of tendinglines, when used, and keeping spare canistersreadily available. The OBA men assist in makingthe investigation in situations where oxygenbreathing apparatus is necessary for entry.The OBA men also work with hoses and performother duties in spaces containing toxicgases.The closure detail secures all doors, hatches,and openings around the fire area to isolatethe fire area. This group secures all ventilationclosures and fans in the area of smoke andheat, establishes secondary fire boundaries bycooling down nearby areas, and assists infightingthe fire as necessary.Hospital Corpsmen render first aid to theinjured. The JZ talker establishes and maintainscommunications with damage control central,either directly or through the local repairparty.Since no two fires are exactly alike, thedeployment of men and equipment is not alwaysthe same. In most situations, however, the followinggeneral rules are observed:1. The attacking party, which is the firstline of defense, must have a sufficient numberof men. The attacking party makes the initialinvestigation and moves in to contain the fire.2. The supporting party should not have anymore men than are actually required to bringup auxiliary equipment, assist with foam and67

PRINCIPLES OF NAVAL ENGINEERINGCO2 supply, and fight the fire. Men at the firewho are not actually engaged in fighting thefire should be sent to the standby party. Thestandby party makes the closures necessary toisolate the fire area, cools the surroundingareas, supplies foam and CO2, and assists infighting the fire when necessary.3. The firefighting party must be quiet andorderly. There should be only two men talkingat a fire: the leader of the firefighting partyand the messenger or phone talker,4. All orders issued at the scene must beclear, concise, and accurate.5. All reports to damage control centralmust be clear, concise, and accurate.6. All possible safety precautions must beobserved.7. Precautions must be taken to see that thefire does not spread. Fire boundaries must beestablished, and men must be stationed in adjacentcompartments to see that the fire doesnot spread. Even distant compartments mayrequire checking, since fire can spread a greatdistance through ventilation ducts.Figures 4-3 and 4-4 show members of ashipboard firefighting party in action.CONTROL OF FLOODINGFlooding! may occur from a number of differentcauses. Underwater or waterline damage,ruptured water piping, the use of large quantitiesof water for firefighting or counterflooding,and the improper maintenance of boundariesare all possible causes of flooding aboard ship.It should be noted that ballasting fuel oil tankswith sea water after the oil has been removedis not considered a form of flooding; ballastingmerely consists of replacing one liquid withanother in order to maintain the ship in a conditionof maximum resistance to damage.If a ship suffers such extensive damage thatit never stops listing, trimming, and settlingin the water, the chances are that it will godown within a very few minutes. If, on the otherhand, a ship stops listing, trimming, and settlingshortly after the damage occurs, it is not likelyto sink at all unless progressive flooding isallowed to occur. Thus there is an excellentchance of saving any ship that does not sinkimmediately. There is no case on record of a•The effects of various types of flooding on stabilityare discussed in chapter 3 of this text.ship sinking suddenly after it has stopped listing,trimming, and settling, except in caseswhere progressive flooding occurred.The control of flooding requires that theamount of water entering the hull be restrictedor entirely stopped. The removal of floodingwater cannot be accomplished until floodingboundaries have been established. Pump capacityshould never be wasted on compartmentswhich cannot be quickly and effectively madetight. If a compartment fills rapidly, it is asign that pumping capacity will be wasted untilthe openings have been plugged or patched. Thefutility of merely circulating sea water shouldbe obvious.Once flooding boundaries have been established,the removal of the flooding water shouldbe undertaken on a systematic basis. Loosewater— that is, water with free surface— andwater that is located high in the ship should beremoved first. Compartments which are solidlyflooded and which are low in the ship are generallydewatered last, unless the flooding issufficiently off-center to cause a serious list.Compartments must always be dewatered in asequence that will contribute to the overallstability of the ship. For example, a ship couldbe capsized if low, solidly flooded compartmentswere dewatered while water still remainedin high, partially flooded compartments.In order to know which compartments shouldbe dewatered first, it is necessary to know theeffect of flooding on all ship's compartments.This information is given in the flooding effectdiagram in the ship's Damage Control Book.The flooding effect diagram consists of a seriesof plan views of the ship at various levels,showing all watertight, oiltight, airtight, fumetight,and fire- retarding subdivisions. Compartmentson the flooding effect diagram are coloredin the following way:1. If flooding the compartment results in adecrease in stability because of high weight,free surface effect, or both, the compartmentis colored pink.2. If flooding the compartment improvesstability even though free surface exists, thecompartment is colored green.3. If flooding the compartment improvesstability when the compartment is solidly floodedbut impairs stability when a free surface exists,the compartment is colored yellow.4. If flooding the compartment has no verydefinite effect on stability, the compartment isleft uncolored.68

Chapter 4- PREVENTIVE AND CORRECTIVE DAMAGE CONTROLFigure 4-3.— Members of firefighting party cooling hatch.8.120The flooding effect diagram also shows theweight of salt water (in tons) required to fillthe compartment; this is indicated by a numeralin the upper left-hand corner. In addition, thetransverse moment of the weight (in foot-tons)about the centerline of the ship is indicated forall compartments which are not symmetricalabout the centerline.Facilities for dewatering compartments consistof the fixed drainage systems of the shipand portable equipment such as electric submersiblepumps, P-500 pumps, P-250 pumps,and eductors. On a large combat ship, thefixed drainage systems have a total pumpingcapacity of about 12,200 gallons per minuteless,it might be noted, than the amount of69

PRINCIPLES OF NAVAL ENGINEERINGFigure 4-4.— Members of firefighting party coolingentrance to compartment.8.122water admitted by a hole 1 square foot in sizein an area located 15 feet below the waterline.Portable submersible pumps used aboardnaval ships are centrifugal pumps driven by awater-jacketed, constant- speed a-c or d-cmotor. When a submersible pump is being usedto dewater a compartment, the pump is loweredinto the water and a discharge hose is led to thenearest point of discharge. Since the deliveryof the pump increases as the discharge headdecreases, dewatering can be accomplishedfaster if the water is discharged at the lowestpracticable point and if the discharge hose isshort and free from kinks. When it is necessaryto dewater against a high discharge head, twosubmersible pumps can be used in tandem, asshown in figure 4-5. The pump at the lowerlevel lifts water to the suction side of the pumpat the higher level.The P-500 portable pump, originally developedfor firefighting, is also used for dewateringflooded spaces. This pump is of the centrifugal70

Chapter 4- PREVENTIVE AND CORRECTIVE DAMAGE CONTROLknow how much water is coming in while wateris being pumped out.REPAIR OF STRUCTURAL DAMAGEFigure 4-5.— Tandem connections forsubmersible pumps.11.359type; it is driven by a water-cooled gasolineengine of special design. The pump delivers500 gallons per minute at 100 pounds per squareinch pressure, with a suction lift of 16 feet.The capacity may be increased by decreasingthe discharge pressure.The P-250 pump, which is similar to theP-500 pump except for capacity, is scheduledto replace the P-500 pump aboard ship. A P-250pump is shown in figure 4-6.In order to estimate the number of pumpsrequired to handle a flooding situation, it isnecessary to consider the amount and locationof the water to be removed, the capacity andavailability of the installed drainage systems,and the capacity of the available portable pumps.It is also necessary to know whether the leaksare completely plugged, partially plugged, ornot plugged at all— in short, it is necessary toThe kinds of damage that may have to berepaired while a ship is still in the battle areainclude holes above and below the waterline;cracks in steel plating; punctured, weakened,or distorted bulkheads; warped or sprung doorsand hatches; weakened or ruptured beams, supports,and other strength members; ruptured orweakened decks; ruptured or cracked piping;severed electrical cables; broken or distortedfoundations under machinery; broken or piercedmachinery units; and a wide variety of miscellaneouswreckage that may interfere with thefunctioning of the ship.One of the most important things to rememberin connection with the repair of structuraldamage is that a ship can sink just as easilyfrom a series of insignificant- looking smallholes as it can from one larger and moredramatic-looking hole. A natural enough tendency—andone which can lead to the sinkingof a ship— is to attack the large, obvious damagefirst and to overlook the smaller holes throughinterior bulkheads. Men sometimes waste hourstrying to patch large holes in already floodedcompartments, disregarding the smaller holesthrough which progressive flooding is graduallytaking place. In many situations, it would bebetter to concentrate on the smaller interiorholes; as a rule, the really large holes in theunderwater hull cannot be repaired anyway untilthe ship is drydocked.Holes in the hull at or just above the waterlineshould be given immediate attention. Althoughholes in this location may appear to berelatively harmless, they are actually extremelyhazardous. As the ship rolls or loses buoyancy,the holes become submerged and admit waterat a level that is dangerously high above theship's center of gravity.The methods and materials used to repairholes above the waterline are also used, forthe most part, for the repair of underwaterholes. The greatest difficulty encountered inrepairing underwater damage is usually theinaccessibility of the damage. If an inboardcompartment is flooded, opening doors orhatches to get to the damage would result infurther flooding of other compartments. In sucha case, it is usually necessary to send a manwearing a shallow-water diving apparatus down71

PRINCIPLES OF NAVAL ENGINEERING^nTirii'iif-'Hiiiiiu-|i.'IAN UALRIMINGBOWL""^Vji

Chapter 4-PREVENTIVE AND CORRECTIVE DAMAGE CONTROLfollow is this: in case of doubt, it is alwaysbetter to shore than to gamble on the strengthof an important deck, bulkhead, hatch, or othermember.Some examples of shoring are illustrated infigure 4-7.RESTORATION OFVITAL SERVICESThus far we have considered practical damagecontrol operations from the point of view ofcombatting fires, getting rid of flooding water.STRONGBflCKTHIS IS THE SIMPLEST ANDSTRONGEST SHORING STRUGTURE.THE BASIC STRUCTURE ISREPEATED AS OFTEN AS NECESSARY.^THE USUAL METHOD OF IN-STALLING SHORES IS BY ATRIANGULATION SYSTEM.WHEN OBSTRUCTIONS PREVENT USEOF THE TRIANGULATION SYSTEMTHIS METHOD MAY BE USED.THIS IS BADTHIS SHORE IS UNDERCROSS-AXIAL PRESSUREAND MAY SNAP!OBSTRUCTIONADDITIONAL STRENGTH IS AFFORDED BY SHORES BAND C. HORIZONTAL SHORE B IS SUPPORTED BY d"AND A, AND IS BRACED AGAINST A UNIT OF MACHINERY BYMEANS OF E.Figure 4-7. — Examples of shoring.17.1073

PRINCIPLES OF NAVAL ENGINEERINGrepairing structural damage, and in generalrestoring the ship to a stable and seaworthycondition. To function as a fighting unit, however,a ship must be more than stable andseaworthy— it must also be able to move. Therestoration of vital services is therefore anintegral part of damage control, even though itmust often be accomplished after fires andflooding have been controlled.The restoration of vital services includesmaking repairs to machinery and piping systemsand reestablishing a source of electrical power.The casualty power system, developed as aresult of war experience, has proved to be oneof the most important damage control devices.The casualty power system is a simple electricaldistribution system used to maintain asource of electrical supply for the most vitalmachinery. It is used to supply power only inemergencies. The casualty power system isdiscussed in chapter 20 of this text.DEFENSE AGAINST NBC ATTACKThe basic guidelines for defensive and protectiveactions to be taken in the event of nuclear,biological, or chemical (NBC) attack areset forth in the Nuclear, Biological, and ChemicalDefense Bill contained in Shipboard Procedures, NWP 50 (effective edition). Aboard ship,the engineer officer is responsible for maintainingthis bill and ensuring that it is currentand ready for immediate execution.NBC defense measures may be divided intotwo phases: (1) preparatory measures taken inanticipation of attack, and (2) active measurestaken immediately following an attack.Preparatory measures to be taken beforean attack include the following:1. Thorough indoctrination and training ofship's force.2. Removal of material that may constitutecontamination hazards.3. Masking of personnel who maybe exposed(and of other personnel, as ordered).4. Establishment of ship closure, includingclosing of CIRCLE WILLIAM fittings.5. Donning of protective clothing by exposedpersonnel, as ordered.6. Evasive action by the ship.7. Activation of water washdown systems.Active measures to be taken immediatelyfollowing an attack include the following:1. Evasive and self-protective action bypersonnel.2. Evacuation and remanning of exposed stations,as ordered.3. Decontamination of personnel.4. Detection and prediction of contaminatedareas.5. Ventilation of contaminated spaces, assoon as the ship is in a clean atmosphere.It is obvious that NBC defense is an enormouslycomplex and wide-ranging subject, andone in whicii policies and procedures are subjectto constant change. The present discussionis limited to a few aspects of NBC defense thatare of primary practical importance aboardship. More detailed information on all aspectsNBC defense may be obtained from chaptersof9770 and 9900 of the Naval Ships TechnicalManual and from Disaster Control (Ashore andAfloat), NavPers 10899-B.PROTECTIVE CLOTHINGThere are three types of clothing that areuseful in NBC defense: permeable, impregnated,protective clothing, foul weather clothing, andordinary work clothing.Permeable protective clothing is supplied toships in quantities sufficient to outfit 25 percentor more of the ship's compliment. Permeableclothing is olive green in color. A completeoutfit includes impregnated socks, gloves,trousers with attached suspenders, and jumper(parka) with attached hood. Permeable clothingis treated with a chemical agent that neutralizeschemical agents; a chlorinated paraffin is usedas a binder. The presence of these chemicalsgives the permeable clothing a slight odor ofchlorine and a slightly greasy or clammy feel.It is believed that the impregnation treatmentshould remain effective from 5 to 10 years (orpossibly longer) if the clothing is stowed inunopened containers in a dry place with cool orwarm temperatures and if it is protected fromsunlight or daylight.Permeable protective clothing should not beworn longer than necessary, especially in hotweather; prolonged wearing may cause a rashto develop where the skin comes in contact withthe impregnated material.Foul weather clothing of stock issue servesto protect ordinary clothing and the skin againstpenetration by liquid chemical agents and radioactiveparticles. It also reduces the amount ofvapor that penetrates to the skin. Foul weather74

Chapter 4-PREVENTIVE ANfD CORRECTIVE DAMAGE CONTROLclothing, which includes a parka, trousers,rubber boots, and gloves, is easily decontaminated.Ordinary work clothing (including long underwear,field socks, coverall, field boots, andwatcli cap) is partially effective in preventingdroplets of liquid chemical agents and vaporsfrom reaching the skin. However, ordinary workclothing is not as effective as the other typesof clothing in preventing contamination. Undersome conditions, personnel may wear two layersof ordinary work clothing to achieve greaterprotection than can be obtained with one layer.PROTECTIVE MASKSThe protective mask is a very importantitem of protective equipment, since it protectssuch vulnerable areas as the eyes, the face, andthe respiratory tract. The protective mask providesprotection against NBC contamination byfiltering the air before it is inhaled.In general, all protective masks operate onthe same principles. As the wearer inhales, airis drawn into a filtering system. This systemconsists of a mechanical filter which clears theair of solid or liquid particles and a chemicalfilling (usually activated charcoal) which absorbsor neutralizes toxic and irritating vapors. Thepurified air then passes to the region of themask, where it can be inhaled. Exhaled air isexpelled from the mask through an outlet valvewhich is so constructed that it opens only topermit exhaled air to escape.Protective masks do not afford protectionagainst ammonia or carbon monoxide, nor arethey effective in confined spaces where theoxygen content of the atmosphere is too low(less than about 16 percent) to sustain life.When it is necessary to enter spaces wherethere is a deficiency of oxygen, the Navy oxygenbreathing apparatus (OBA) is used.DETECTION OF NBC CONTAMINATIONThe very nature of NBC contamination makesdetection and identification difficult. Nuclearradiation cannot be seen, heard, felt, or otherwiseperceived through the senses. Biologicalagents are small in size and have no characteristiccolor or odor to help in identification.Although- some chemical agents do have a characteristiccolor and odor, recently developednerve agents are usually colorless and odorless.It is obvious, then, that with contaminationwhich cannot be seen, smelled, felt, tasted, orheard, specialized methods of detection arerequired. Mechanical, chemical, and electronicdevices are available or under development forthe detection of NBC contamination.Detection of Nuclear RadiationThe instruments used for detecting radiologicalcontamination are known as radiacs ,the name being an abbreviation of radiation ,detection, indication, and computation . Varioustypes of radiacs are used aboard ship and atshore stations, since no single type of radiaccan make all the radiological measurementsthat may be required.The radiacs used aboard ship include (1)intensity meters for measuring gamma radiation;(2) intensity meters for measuring betaand gamma radiation; (3) survey meters formeasuring alpha radiation; and (4) dosimetersfor measuring accumulated doses of radiationreceived by individuals. These basic types ofradiacs are described briefly here. Specificinformation on operating principles and detailedinstructions for operating the instruments maybe obtained from the manufacturer's technicalmanual furnished with each instrument.GAMMA METERS. — Intensity meters formeasuring gamma radiation include both portableinstruments and fixed systems installedaboard ship. The intensity of gamma radiationis measured in roentgens per hour (r/hr) or inmilliroentgens per hour (mr/hr). The roentgenis a unit of measurement for expressing theamount of gamma radiation or X-ray radiation.A milliroentgen is 1/1000 of a roentgen. Radiacsused for measuring large amounts of gammaradiation are called high- range intensity meters ;these instruments are usually calibrated inroentgens per hour. Radiacs designed for measuringsmaller amounts of gamma radiation arecalled low- range intensity meters ; they areusually calibrated in milliroentgens per hour.Both high-range and low-range instruments arelikely to have several scales; a range selectorswitch allows selection of the appropriate scalefor each monitoring survey.BETA AND GAMMA METERS. -Intensitymeters which measure gamma radiation and alsodetect or measure beta radiation are usually ofthe Geiger-Mueller type. These instruments can75

PRINCIPLES OF NAVAL ENGINEERINGmeasure gamma radiation alone or tiiey canmeasure combined gamma radiation and betaradiation; an indirect measure of beta radiationcan be obtained by subtracting the gamma radiationfrom the gamma-beta radiation.ALPHA SURVEY METERS.-Meters formeasuring alpha radiation are usually calibratedto give a meter reading in counts per minute(c/m, or cpm). However, some alpha surveymeters give a reading in a unit called disintegrationsper minute (d/m). The two units arenot the same numerically.DOSIMETERS. -There are two basic typesof dosimeters. Self- reading dosimeters can beread by the person wearing the instrument.Nonself- reading dosimeters cannot be readdirectly by the wearer but must be read with theaid of special instruments. Some dosimetersare calibrated in roentgens, others in milliroentgens.Both self- reading and nonself- readingdosimeters measure exposure to radiationover a period of time— in other words, theymeasure accumulated radiation exposure.Self- reading dosimeters are provided invarious ranges for use by personnel aboard ship.Some of these self-reading dosimeters indicateaccumulated gamma radiation from to200mr;others indicate doses from to 100 r; othersfrom to 200 r; and still others from to 600 r.The dosimeter selected for any particular usewill depend on the radiological situation existingat the time. Self-reading dosimeters must becharged before they are used. A special chargingunit is furnished for shipboard use.High-range nonself- reading dosimeters ofthe DT-60/PD type are furnished for use aboardship. A dosimeter of this type consists of aspecial phosphor glass between lead filters,encased in a bakelite housing. The dosimeter,which is small, lightweight, and rugged, is wornon a chain around the neck. This dosimeter willmeasure accumulated doses of gamma radiationfrom 25 r to 600 r. A special instrument, theCP-95/PD computer- indicator, is required toread the DT-60/PD dosimeter.Film badge dosimeters are nonself- readingdevices for measuring both gamma radiationand beta radiation in low or moderate ranges.A film badge uses a special photographic filmwhich is surrounded with moisture-proof andlight-proof paper and shielded with lead, cadmium,plastic, or other shielding material. Bythe use of different shielding materials, the badgecan be made to differentiate between gammaradiation and beta radiation. Laboratory techniquesare required for the development andreading of the film.Detection of Biological AgentsBasically, there are two possible approachesto the problem of detecting biological agents.Physical detection is based on the measurementof particles within a specified size range (andpossibly the simultaneous measurement of otherphysical properties of the particles). Researchis currently being done with a view to developingeffective methods of physical detection.Biological detection involves growing the organisms,examining them under a microscope,and subjecting them to a variety of biochemicaland biologicaltests. Although positive identificationcan frequently be made by biologicaldetection methods, the procedure is difficult,exacting, and relatively slow. By the time abiological agent has been detected and identifiedin this fashion, personnel may well be showingsymptoms of illness.Biological detection may be divided into twophases: the sampling phase and the laboratoryphase. The sampling phase may be a joint responsibilityof damage control personnel and ofthe medical department. The laboratory phaseis obviously a medical department responsibility.Detection of Chemical AgentsVarious detection devices have been developedfor the detection and identification ofchemical agents. Most of these devices indicatethe presence of chemical agents by color changeswhich are chemically produced. To date, nosingle detector has been developed which iseffective under all conditions for all chemicalagents. A number of devices, including airsampling kits, papers, crayons, silica gel tubes,and indicator solutions, are in naval use. Someof these devices are also useful in establishingthe completeness of decontamination and in estimatingthe hazards of operating in contaminatedareas.MONITORING AND SURVEYINGThe monitoring and surveying of any areacontaminated with NBC contamination is a vitalpart of NBC defense. In general, monitoring76

Chapter 4- PREVENTIVE AND CORRECTIVE DAMAGE CONTROLand surveying are done for the purposes oflocating the hazards, isolating the contaminatedareas, recording the results of the survey, andreporting the findings through the appropriatechain of command.Specifically, the purpose of a radiologicalmonitoring survey is to determine the location,type, and intensity of radiological contamination.The type of monitoring survey made at anygiven time depends on the radiological situationand on the tactical situation. Gross or rapidsurveys are made as soon as possible after anuclear weapon has been exploded, to get ageneral idea of the extent of contamination.Detailed surveys are made later, to obtain amore complete picture of the radiological situation.Aboard ship, two main types of radiologicalsurveys would be required after a nuclearattack. Ship surveys (first gross, then detailed)include surveys of all weather decks, interiorspaces, machinery, circulating systems, equipment,and so forth. Personnel safety surveys(usually detailed) are concerned with protectingpersonnel from skin contamination and internalcontamination. Personnel safety surveys includethe monitoring of skin, clothing, food, andwater, and the measurement of concentrations ofradioactive material in the air (aerosols). Bothship surveys and personnel safety surveys aremade aboard ship by members of the damagecontrol organization. The medical departmentmakes clinical tests, maintains dosage records,and makes specific recommendations concerningthe monitoring of food, water, air, etc.; butthe actual surveys are made by damage controlpersonnel of the engineering department.Detailed instructions for making monitoringsurveys cannot be specified for all situations.since a great many factors (type ship, distancefrom blast, extent of damage, tactical situation,etc.) must necessarily be considered beforemonitoring procedures can be decided upon.However, certain basic guidelines that apply tomonitoring situations may be stated as follows:1 . Monitors must be thoroughly trained beforethe need for monitoring arises. Learning tooperate radiacs takes time. Simulated practiceas,for example, walking through a drill usinga block of wood to represent a radiac— may teacha man something about the general movementsmade by a monitoring team, but it will notprepare him for actually using the instruments.All personnel who may be required to performmonitoring operations must be given adequateinstruction and training in the use of the availableradiacs.2. Standard measuring techniques must beused. A measurement of radiation is meaninglessunless the distance between the source ofradiation and the point of measurement is known.For example, a radiac held 2 feet away from asource of radiation will indicate only one-fourthas much radiation as the same instrumentwould indicate if it were held 1 foot away fromthe same source, A radiac held 3 feet from thesource will indicate only one-ninth as muchradiation as when it is held 1 foot from thesource. As may be seen, therefore, the distancebetween the source of radiation and the radiacmust be known before the radiac reading canhave any significance.3. All necessary information must be recordedand reported. The information obtainedby monitoring parties is forwarded to damagecontrol central, where the measurements areplotted according to location and time. In orderto develop an accurate overall picture of theradiological condition of the ship, damage controlcentral must have precise and completeinformation from allmonitoring parties. Eachmonitoring party must record and report theobject or area monitored, the location of theobject or area in relation to some fixed point,the intensity and type of radiation, the distancebetween the radiac and the source of radiation,the time and date of the measurements, the nameof the man in charge of the monitoring party(or other identification of the party), and thetype and serial number of the instrument used.CONTAMINATION MARKERSA standard system for marking areas contaminatedby nuclear, biological, or chemicalcontamination has been adopted by nations includedin the North Atlantic Treaty Organization.These standard survey markers are illustratedin figure 4-8.NBC DECONTAMINATIONThe basic purpose of decontamination is tominimize NBC contamination through removalor neutralization so that the mission of the shipor activity can be carried out without endangeringthe life or health of assigned personnel. Thepurpose of radiological decontamination is toremove contamination and shield personnel who77

PRINCIPLES OF NAVAL ENGINEERINGNATO COUNTRIES INCLUDING UNITED STATESFRONTGASCHEMICALBACKDATE ANDTIMEOF DETECTIONNAAAE OF AGENT,IFKNOWNBIOLOGICALDATE AND TIMEOF DETECTIONNAME OF AGENT,IFKNOWNUSE OF TREFOILISOPTIONALRADIOLOGICAL^>DOSE RATEDATE AND TIMEOF READINGDATE AND TIMEIFOF BURST,KNOWNCURRENTLY USED WITHIN UNITED STATESRADIOLOGICALDOSE RATEDATE AND TIMEOF READINGDATE AND TIMEIFOF BURST,KNOWNFigure 4-8.— NBC contamination markers.C3.17878

Chapter 4-PREVENTIVE AND CORRECTIVE DAMAGE CONTROLare required to work in contaminated areas.The purpose of biological decontamination is todestroy the biological agents. The purpose ofchemical decontamination is to remove or neutralizethe chemical agents so that they will nolonger be a hazard to personnel.Decontamination operations may be both difficultand dangerous, and personnel engaged inthese operations must be thoroughly trained inthe proper techniques. Certain operations, suchas the decontamination of food and water, shouldbe done only by experts qualified in such work.However, all members of a ship's companyshould receive adequate training in the elementaryprinciples of decontamination so that theycan perform emergency decontamination operations.After an attack, data from NBC surveys willbe used to determine the extent and degree ofcontamination. Contaminated personnel must bedecontaminated as soon as possible. Beforedecontamination of installations, machinery, andgear is undertaken, appraisals of urgency mustbe made in light of the tactical situation.Radiological DecontaminationRadiological decontamination neither neutralizesnor destroys the contamination; instead,it merely removes the contamination from oneparticular area and transfers it to an area inwhich it presents less of a hazard. At sea,radioactive waste is disposed of directly overthe side. At shore installations, the problem ismore difficult.Several methods of radiological decontaminationhave been developed; they differ ineffectivenessin removing contamination, in applicabilityto given surfaces, and in the speed withwhich they may be applied. Some methods areparticularly suited for rapid gross decontamination;others are better suited for detaileddecontamination.GROSS DECONTAMINATION.-The purposeof gross decontamination is to reduce the radiationintensity as quickly as possible to a safelevel— or at least to a level which will be safefor a limited period of time. In gross decontamination,speed is the major consideration.Flushing with water, preferably water underhigh pressure, is the most practicable way ofaccomplishing gross decontamination. Aboardship, a water washdown system is used to washdown all the ship's surfaces, from high to lowand from bow to stern. The washdown systemconsists of piping and a series of nozzles whichare specially designed to throw a large spraypattern on weather decks and other surfaces.The washdown system is particularly effectiveif it is activated before the ship is exposed tocontamination; a film of water covering theship's surfaces keeps the contaminating materialfrom sticking to the surfaces. Figure 4-9shows a water washdown system in operation.Manual methods may be used to accomplishgross decontamination, but they are slower andless effective than the ship's washdown system.Manual methods that may be used by ship'sforce include (1) firehosing the surfaces withsalt water, and (2) scrubbing the surfaces withdetergent, firehosing the surfaces, and flushingthe contaminating material over the side. Figure4-10 shows men performing gross decontaminationoperations by manual scrubbing.Steam is also a useful agent for gross decontamination,particularly where it is necessaryto remove greasy or oily films. Steamdecontamination is usually followed by hosingwith hot water and detergents.DETAILED DECONTAMINATION.-As timeand facilities permit, detailed decontaminationis carried out. The main purpose of detaileddecontamination is to reduce the contaminationto such an extent that only a minimum ofradiological hazard to personnel would persist.Three basic methods of detailed decontaminationmay be used— surface decontamination,aging and sealing, and disposal. Each of thesemethods has a specific purpose; one method canoften be used to supplement another. Surfacedecontamination reduces the contamination withoutdestroying the utility of the object. In agingand sealing, radioactivity is allowed to decreaseby natural decay and any remaining contaminationis then sealed onto the surface. The disposalmethod merely consists of removing contaminatedobjects and materials to a place wherethey can do little or no harm.Biological DecontaminationThe methods available for biological decontaminationinclude scrubbing, flushing, heating,and the use of disinfectant sprays, disinfectantvapors, and sterilizing gases. The method to beused in any particular case depends upon thenature of the area or equipment to be decontaminatedand upon the nature of the agent (ifthis is known).79

PRINCIPLES OF NAVAL ENGINEERINGFigure 4-9.— Water washdown system in operation.3.193Chemical DecontaminationThe major problem in chemical decontaminationis to decontaminate successfully after anattack by any of the blister or nerve agents.The general methods used in chemical decontaminationinclude natural weathering, chemicalaction, the use of heat, the use of sealing, andphysical removal.Natural weathering relies on the effects ofsun, rain, and wind to dissipate, evaporate, ordecompose chemical agents. Weathering is byfar the simplest and most widely applicablemethod of chemical decontamination; in somecases, it offers the only practicable means ofneutralizing the effects of chemical agents,particularly where large areas are contaminated.Decontamination by chemical action involvesa chemical reaction between the chemical agentand the chemical decontaminant. The reactionusually results in the formation of a harmlessnew compound or a compound which can beremoved more easily than the original agent.Neutralization of chemical agents can resultfrom chemical reactions of oxidation, chlorination,reduction, or hydrolysis.Expendable objects or objects of little valuemay be burned if they become contaminated.This procedure should not be used except as anemergency measure or as a means of disposingof material which has been highly contaminated.If this method is used, a very hot fire must beused. Intense heat is necessary for destructionof chemical agents; moderate or low heat mayserve only to volatilize the agent and spread itby means of secondary aerosols. When a largeamount of highly contaminated material is beingburned, downwind areas may contain a dangerousfSr-^8.100Figure 4-10.— Decontamination by manualscrubbing.80

Chapter 4-PREVENTIVE AND CORRECTIVE DAMAGE CONTROLFigure 4-11.— Decontamination team hosing down a gun mount.103.12381

PRINCIPLES OF NAVAL ENGINEERINGconcentration of toxic vapors; personnel shouldbe kept away from such areas.Hot air may be blown over a contaminatedsurface to decontaminate it. Steam, especiallyhigh pressure steam, is also a useful decontaminatingagent; the steam hydrolyzes andevaporates chemical agents and flushes themfrom the surfaces. Chemical decontaminationmay also be accomplished by sealing off poroussurfaces to prevent the absorption of chemicalagents or to prevent volatilization of agents alreadyon the surface.Decontamination can also be effected byphysically removing the toxic agents from thecontaminated surfaces. This can be done bywashing or flushing the surfaces with water,steam, or various solvents. Figure 4-11 showsa decontamination party hosing down a gun mountin order to physically remove toxic agents.DAMAGE CONTROL PRECAUTIONSThe urgent nature of damage control operationscan lead to a dangerous neglect of necessarysafety precautions. Driven by the need toact rapidly, men sometimes take chances theywould not even consider taking in less hazardoussituations. This is unfortunate, since there arefew areas in which safety precautions are asimportant as they are in damage control. Failureto observe safety precautions can lead— and, infact,has led— to the loss of ships.Because damage control includes so manyoperations and involves the use of so manyitems of equipment, it is not feasible to list allthe detailed precautions that must be observed.Some of the basic precautions that apply topractically all damage control work are notedbriefly in the following paragraphs.No one should be allowed to take any actionto control fires, flooding, or other damage untilthe situation has been investigated and analyzed.Although speed is essential for effective damagecontrol, correct action is even more important.The extent of damage must not be underestimated.It is always necessary to rememberthat hidden damage may be even more severethan visible damage. Very real dangers mayexist from damage which is not giving immediatetrouble. For example, small holes at orjust above the waterline may appear to be relativelyminor; but they have been known to sinka ship.It is extremely dangerous to assume thatdamage has been permanently controUedmerelybecause fires have been put out, leaks plugged,and compartments dewatered. Fires may flareup again, plugs may work out of holes, andcompartments may spring new leaks. Constantchecking is required for quite some time afterthe damage appears to be controlled.Doors, hatches, and other accesses shouldbe kept open only as long as necessary whilerepairs are being made. Wartime records ofnaval ships show many cases of progressiveflooding which were the direct result of failureto close doors or hatches.No person should attempt to be a one-mandamage control organization. All damage mustbe reported to damage control central or to arepair party before any individual action istaken. The damage control organization is thekey to successful damage control. Separate,uncoordinated actions by individual men mayactually do more harm than good.Many actions taken to control damage canhave a definite effect on ship's characteristicssuch as watertight integrity, stability, andweight and moment. The dangers involved inpumping large quantities of water into the shipto combat fires should be obvious. Less obvious,perhaps, is the fact that the repair of structuraldamage may also affect the ship's characteristics.For example, the addition of high or offcenterweight produces the same general effectas high or off-center solid flooding.While most repairs made in action would notamount to much in terms of weight shifts oradditions, it is possible that a number of relativelysmall changes could add up sufficientlyto endanger an already damaged and unstableship. The only way to control this kind of hazardis by making sure that all damage control personnelreport fully and accurately to damagecontrol central. Ship stability problems areworked out in damage control central, but theinformation must come from repair personnel.In all aspects of damage control, it is importantto make full use of all available devicesfor the detection of hazards. Several types ofinstruments are available on most ships fordetecting dangerous concentrations of explosive,flammable, toxic, or asphyxiating gases. Personnelshould be trained to use these devicesbefore entering potentially hazardous compartmentsor spaces.82

PART ll-BASIC ENGINEERING THEORYChapter 5Chapter 6Chapter 7Chapter 8Fundamentals of Ship Propulsion and SteeringTheory of LubricationPrinciples of MeasurementIntroduction to ThermodynamicsWe cannot proceed very far in the study of naval engineering withoutrealizing the need for basic theoretical knowledge in many areas. Tounderstand the functioning of the machinery and equipment discussed inlater parts of this text, we must know something of the principles of mechanics,the laws of motion, the structure of matter, the behavior of moleculesand atoms and subatomic particles, the properties and behavior ofsolids and liquids and gases, and other principles and concepts derivedfrom the physical sciences.Chapter 5 takes up the fundamentals of resistance, the developmentand transmission of propulsive power, and the principles of steering. Theremaining three chapters of part II deal with basic scientific theory andengineering principles that have wide— indeed, almost universal—applicationin the field of naval engineering. Chapter 6 is concerned with lubrication,a subject of vital importance in practically all machinery andequipment. Chapter 7 takes up the principles of measurement and discussesbasic types of measuring devices. Chapter 8 provides an introductionto some of the most fundamental concepts of energy and energytransformations, thus establishing a theoretical basis for much of thesubsequent discussion of shipboard machinery and equipment. Theoreticalconsiderations of a more specialized nature are discussed in other chaptersthroughout the text, as they are required for an understanding of theparticular machinery or equipment under discussion.83

CHAPTERSFUNDAMENTALS OF SHIP PROPULSION AND STEERINGThe ability to move through the water and theability to control the direction of movement areamong the most fundamental of all ship requirements.Ship propulsion is achieved through theconversion, transmission, and utilization ofenergy in a sequence of events that includes thedevelopment of power in a prime mover, thetransmission of power to the propellers, the developmentof thrust on the working surfaces ofthe propeller blades, and the transmission ofthrust to the ship's structure in such a way asto move the ship through the water. Control ofthe direction of movement is achieved partiallyby steering devices which receive their powerfrom steering engines and partially by the arrangement,speed, and direction of rotation ofthe ship's propellers.This chapter is concerned with basic principlesof ship propulsion and steering and withthe propellers, bearings, shafting, reductiongears, rudders, and other devices required tomove the ship and to control its direction ofmovement. The prime movers which are thesource of propulsive power are discussed in detailin other chapters of this text, and are thereforementioned only briefly in this chapter.RESISTANCEThe movement of a ship through the waterrequires the expenditure of sufficient energy toovercome the resistance of the water and, to alesser extent, the resistance of the air. Thecomponents of resistance may be considered as(1) skin or frictional resistance, (2) wave-makingresistance, (3) eddy resistance, and (4) air resistance.Skin or frictional resistance occurs becauseliquid particles in contact with the ship are carriedalong with the ship, while liquid particlesa short distance away are moving at much lowervelocities. Frictional resistance is thereforethe result of fluid shear between adjacent layersof water. Under most conditions, frictional resistanceconstitutes a large part of the total resistance.Wave-making resistance results from thegeneration and propagation of wave trains by theship in motion. Figure 5-1 illustrates bow, stern,and transverse waves generated by a ship in mo-When the crests of the waves make an ob-tion.lique angle with the line of the ship's direction,the waves are known as diverging waves. Thesewaves, once generated, travel clear of the shipand give no further trouble. The transversewaves, which have a crest line at a 90° angle tothe ship's direction, do not have visible, breakingcrests. The transverse waves are actually theinvisible part of the continuous wave train whichincludes the visible divergent waves at the bowand stern. The wave-making resistance of theship is a resistance which must be allowed forin the design of ships, since the generation andpropagation of wave trains requires the expenditureof a definite amount of energy.Eddy resistance occurs when the flow lines donot close in behind a moving hull, thus creatinga low pressure area in the water behind the sternof the ship. Because of this low pressure area,energy is dissipated as the water eddies. Mostships are designed to minimize the separation ofthe flow lines from the ship, thus minimizing eddyresistance. Eddy resistance is relatively minorin naval ships.Air resistance , although small, also requiresthe expenditure of some energy. Air resistancemay be considered as frictional resistance andeddy resistance, with most of it being eddy resistance.THE DEVELOPMENT AND TRANSMISSIONOF PROPULSIVE POWERFigure 5-2 illustrates the general principlesof ship propulsion and shows the functional85

PRINCIPLES OF NAVAL ENGINEERINGTRANSVERSEWAVES(NOT VISIBLE)STERNDIVEPGENTSBOW DIVERGENTWAVES147.45Figure 5-1. — Bow, stern, and transverse waves.relationships of the units required for the developmentand transmission of propulsive power.The geared-turbine installation is chosen for thisexample because it is the propulsion plant mostcommonly used in naval service today. The samebasic principles apply to all types of propulsionplants.The units directly involved in the developmentand transmission of propulsive power are theprime mover, the shaft, the propelling device,and the thrust bearing. The various bearingsused to support the shaft and the reduction gears(in this installation) may be regarded as necessaryaccessories.The prime mover provides the mechanicalenergy required to turn the shaft and drive thepropelling device. The steam turbines shown infigure 5-2 constitute the prime mover of thisinstallation; in other installations the primemover may be a diesel engine, a gas turbineengine, or a turbine-driven generator.The propulsion shaft provides a means oftransmitting mechanical energy from the primemover to the propelling device and transmittingthrust from the propelling device to the thrustbearing.The propelling device imparts velocity to acolumn of water and moves it in the directionopposite to the direction in which it is desiredto move the ship. A reactive force (thrust) isthereby developed against the velocity-impartingdevice; and this thrust, when transmitted to theship's structure, causes the ship to move throughthe water. In essence, then, we may think ofpropelling devices as pumps which are designedto move a column of water in order to build upa reactive force sufficient to move the ship. Thescrew propeller is the propelling device usedon practically all naval ships.The thrust bearing absorbs the axial thrustthat is developed on the propeller and transmittedthrough the shaft. Since the thrust bearingis firmly fixed inrelationtothe ship's structure,any thrust developed on the propeller must betransmitted to the ship in such a way as to movethe ship through the water.WATERCOLUMNPROPELLERSTRUTBEARINGDIRECTION OFREACTIVE FORCE(THRUST)Figure 5-2.— Principles of ship propulsion,47.42A86

Chapter 5-FUNDAMENTALS OF SHIP PROPULSION AND STEERINGThe purpose of the bearings which supportthe shaft is to absorb radial thrust and to maintainthe correct alignment of the shaft and thepropeller.The reduction gears shown in figure 5-2 areused to allow the turbines to operate at high rotationalspeed while the propellers operate atlower speeds, thus providing for most efficientoperation of both turbines and propellers.The propellers, bearings, shafting, and reductiongears which are directly or indirectlyinvolved in the development and transmission ofpropulsive power are considered in more detailfollowing a general discussionof power requirementsfor naval ships.POWER REQUIREMENTSThe power output of a marine engine is expressedin terms of horsepower. One horsepoweris equal to 550 foot-pounds of work persecond or 33,000foot-poundsof work per minute.Different types of engines are rated in differentkinds of horsepower. Steam reciprocating enginesare rated in terms of indicated horsepower(IHP); internal combustion engines are usuallyrated in terms of brake horsepower (BHP); andsteam turbines are rated in terms of shaft horsepower(SHP).Indicated horsepower is the power measuredin the cylinders of the engine.Brake horsepower is the power measured atthe crankshaft coupling by means of a mechanical,hydraulic, or electric brake.Shaft horsepower is the power transmittedthrough the shaft to the propeller. Shaft horsepowercan be measured with a torsionmeter; itcan also be determined by computation. Shafthorsepower may vary from time to time withinthe same plant; for example, a plant that develops10,000 shaft horsepower at 100 rpm onone occasion may develop 12,000 shaft horsepowerat the same rpm on another occasion. Thedifference occurs because of variations in thecondition of the bottom, the draft of the ship, thestate of the sea, and other factors. Shaft horsepowermay be determined by the formulawhereSHP27rNT33,000SHP = shaft horsepowerN = rpmT= torque (in foot-pounds) measuredwith torsionmeterThe amount of power which the propellingmachinery must develop in order to drive a shipat a desired speed may be determined by directcalculation or by calculations based on the measuredresistance of a model having a definite sizerelationship to the ship.When the latter method of calculating powerrequirements is used, ship models are towed atvarious speeds in long tanks or basins. The mostelaborate facility for testing models in this wayis the Navy's David W. Taylor Model Basin atCarderock, Maryland. The main basin is 2775feet long, 51 feet wide, and 22 feet deep. Apowered carriage spanning this tank and ridingon machine rails is equipped to tow an attachedmodel directly below it. The carriage carriesinstruments to measure and record the speed oftravel and the resistance of the model. Fromthe resistance, the effective horsepower (EHP)(among other things) maybe calculated. Effectivehorsepower is the horsepower required to towthe ship. Therefore,whereREHP =R6080VT 6033,000= tow rope resistance, in poundsV - speed, in knotsThe speed in knots is multiplied by 6080 toconvert it to feet per hour, and is divided by 60to convert this to feet per minute. We have then6080 R^V60 6080 R^VEHP =33,000 60.33,000608 R^V 608 R^V' 6.33,000 98 X 103= 3.0707 X 10-3 R^v: 0.0030707 R^VThe relationship between effective horsepowerand shaft horsepower is called the propulsiveefficiency or the propulsive coefficientof the ship. It is equal to the product of the propellerefficiency and the hull efficiency.87

PRINCIPLES OF NAVAL ENGINEERINGVariation of hull resistance at moderatespeeds of any well-designed ship is approximatelyproportional to the square of the speed.The power required to propel a ship is proportionalto the product of the hull resistance andspeed. Therefore, it follows that under steadyrunning conditions, the power required to drivea ship is approximately proportional to the cubeof propeller speed. While this relationship isnot exact enough for actual design, it does serveas a useful guide for operating the propellingplant.Since the power required to drive a ship isapproximately proportional to the cube of thepropeller speed, 50 percent of full power willdrive a ship at about 79.4 percent of the maximumspeed attainable when full power is usedfor propulsion, and only 12.5percent of full poweris needed for about 50 percent of maximum speed.The relation of speed, torque, and horsepowerto ship's resistance and propeller speedunder steady running conditions can be expressedin the following equations:whereS = k.X (rpm)v2T = k_ x (rpm)shp __27rk2_ X (rpm)33,000S = ship's speed, in knotsT = torque required to turn propeller, infoot-poundsshp = shaft horsepowerrpm = propeller revolutions per minutek. , k„ 3 proportionality factorsThe proportionalityconditions such as displacement, trim, conditionof hull and propeller with respect to fouling,depth of water, sea and wind conditions, and theposition of the ship. Conditions that increasethe resistance of the ship to motion cause kj tobe smaller and k2 to be larger.In a smooth sea, the proportionality factorsk^ and k2 can be considered as being reasonablyconstant. In rough seas, however, a ship is subjectedto varying degrees of immersion and wavefactors depend on manyimpact which cause these factors to fluctuateover a considerable range. It is to be expected,therefore, that peak loads in excess of the loadsrequired in smooth seas will be imposed on thepropulsion plant to maintain the ship's ratedspeed. Thus, propulsion plants are designed withsufficient reserve power to handle the fluctuatingloads that must be expected.There is no simple relationship for determiningthe power required to reverse the propellerwhen the ship is moving ahead or the power requiredto turn the propeller ahead when the shipis moving astern. To meet Navy requirements,a ship must be able to reverse from full speedahead to full speed astern within a prescribedperiod of time; the propulsion plant of any shipmust be designed to furnish sufficient power formeeting the reversing specifications.PROPELLERSThe propelling device most commonly usedfor naval ships is the screw propeller, so calledbecause it advances through the water in somewhatthe same way that a screw advances throughwood or a bolt advances when it is screwed intoa nut. With the screw propeller, as with a screw,the axial distance advanced with each completerevolution is known as the pitch. The path of advanceof each propeller blade section is approximatelyhelicoidal.There is, however, a difference between theway a screw propeller advances and the way abolt advances in a nut. Since water is not a solidmedium, the propeller slips or skids; hence theactual distance advanced in one complete revolutionis less than the theoretical advance for onecomplete revolution. The difference between thetheoretical and the actual advance per revolutionis called the slip . Slip is usually expressed asa ratio of the theoretical advance per revolution(or, in other words, the pitch ) and the actual advanceper revolution. Thus,whereSlip ratioE = shaft rpm x pitch = engineminutedistance perA = actual distance advanced per minuteScrew propellers may be broadly classifiedas fixed pitch propellers or controllable pitchpropellers. The pitch of a fixed pitch propeller88

Chapter 5-FUNDAMENTALS OF SHIP PROPULSION AND STEERINGcannot be altered during operation; the pitch ofa controllable pitch propeller can be changedcontinuously, subject to bridge or engineroomcontrol. Most propellers in naval use are of thefixed pitch type, but some controllable pitch propellersare in service.A screw propeller consists of a hub and several(usually three or four) blades spaced atequal angles about the axis. Where the bladesare integral with the hub, the propeller is knownas a solid propeller . Where the blades are separatelycast and secured to the hub by means ofstuds and nuts, the propeller is referred to asa builtup propeller .Solid propellers may be further classified ashaving constant pitch or variable pitch . In a constantpitch propeller, the pitch of each radius isthe same. On a variable pitch propeller, the pitchat each radius may vary. Solid propellers of thevariable pitch type are the most commonly usedfor naval ships.Propellers are classified as being right-handor left-hand propellers, depending upon the directionof rotation. When viewed from astern,with the ship moving ahead, a right-hand propellerrotates in a clockwise direction and a lefthandpropeller rotates in a counterclockwisedirection. The great majority of single-screwships have right-hand propellers. Multiplescrewships have right hand propellers to port.Reversing the direction of rotation of a propellerreverses the direction of thrust and consequentlyreverses the direction of the ship's movement.Some of the terms used in connection withscrew propellers are identified in figure 5-3,The term face (or pressure face ) identifies theafter side of the blade, when the ship is movingahead. The term back (or suction back ) identi-,fies the surface opposite the face. As the propellerrotates, the face of the blade increasesthe pressure on the water near it and gives thewater a positive astern movement. The back ofthe blade creates a low pressure or suction areajust ahead of the blade. The overall thrust is derivedfrom the increased water velocity whichresults from the total pressure differential thuscreated.The tip of the blade is the point most distantfrom the~Tiub. The root of the blade is the areawhere the blade arm joins the hub. The leadingedge is the edge which first cuts the water whenthe ship is going ahead. The trailing edge (alsocalled the following edge ) is opposite the leadingedge. A rake angle exists when there is a rakeeither forward or aft—that is, when the blade isFigure 5-3.— Propeller blade.147.46not precisely perpendicular to the long axis ofthe shaft.Blade AngleThe blade angle (or pitch angle) of a propellermay be defined as the angle included betweenthe blade and a line perpendicular to theshaft centerline. If the blade angle were 0° , nopressure would be developed on the blade face.If the blade angle were 90° , the entire pressurewould be exerted sidewise and none of it aft.Within certain limits, the amount of reactivethrust developed by a blade is a function of theblade angle.Blade VelocityThe sternward velocity imparted to the waterby the rotationof the propeller blades is partiallya function of the speed at which the blades rotate.In general, the higher the speed, the greaterthe reactive thrust.However, every part of a rotating blade doesnot give equal velocity to the water unless theblade is specially designed to do this. For example,consider the flat blade shown in figure5-4. Points A and Z move about the shaft centerwith equal angular velocity (rpm) but with differentinstantaneous linear velocities. Point Zmust move farther than point A to complete onerevolution; hence the linear velocity at point Zmust be greater than at point A, With the samepitch angle, therefore, point Z will exert more89

PRINCIPLES OF NAVAL ENGINEERINGthe propeller. Within certain limits, the thrustthat can be developed increases as the diameterand the total blade area increase. Since it isimpracticable to increase propeller diameterbeyond a certain point, propeller blade area isusually made as great as possible by using asmany blades as are feasible under the circumstances.Three-bladed and four-bladed marinepropellers are commonly used.Thrust DeductionFigure 5-4.— Linear velocityand reactive thrust.147.47Because of the friction between the hull andthe water, water is carried forward with the hulland is given a forward velocity. This movementof adjacent water is called the wake . Since thepropeller revolves in this body of forward movingwater, the sternward velocity given to thepropeller is less than if there were no wake.Since the wake is traveling with the ship, thespeed of advance over the ground is greater thanthe speed through the wake.At the same time, a propeller draws waterfrom under the stern of the ship, thus creating asuction which tends to keep the ship from goingahead. The increase in resistance that occursbecause of this suction is known as thrust deduction.pressure on the water and so develop more reactivethrust than point A. The higher the linearvelocity of any part of a blade, the greater willbe the reactive thrust.Real propeller blades are not flat but are designedwith complex surfaces (approximatelyhelicoidal) to permit every infinitesimal area toproduce equal thrust. Since point Z has a higherlinear velocity than point A, the thrust at pointZ must be decreased by decreasing the pitchangle at point Z. Point M, lying between pointsZ and A, would have (on a flat blade) a linearvelocity less than Z but greater than A. In a realpropeller, then, point M must be set at a pitchangle which is greater than the pitch angle atpoint Z but less than the pitch angle at point A.Since the linear velocity of the parts of a bladevaries from root to tip, and since it is desiredto have every infinitesimal area of the blade produceequal thrust, it is apparent that a real propellermust vary the pitch angle from root to tip.Propeller SizeThe size of a propeller—that is, the size ofthe area swept by the blades— has a definite effecton the total thrust that can be developed onNumber and Locationof PropellersA single propeller is located on the ship'scenterline as far aft as possible to minimize thethrust deduction factor. Vertically, the propellermust be located deep enough so that instill waterthe blades do not draw in air but high enough sothat it can benefit from the wake. The propellermust not be located so high that it will be likelyto break the surface in rough weather, since thiswould lead to racing and perhaps a broken shaft.A twin-screw ship has the propellers locatedone on each side, well aft, with sufficient tipclearance to limit thrust deduction.A quadruple-screw ship has the outboardpropellers located forward of and above the inboardpropellers, to avoid propeller stream interference.Controllable Pitch PropellersAs previously noted, controllable pitch propellersare in use on some naval ships. Controllablepitch propellers give a ship excellentmaneuverability and allow the propellers to developmaximum thrust at any given engine rpm.90

Chapter 5- FUNDAMENTALS OF SHIP PROPULSION AND STEERINGA ship with controllable pitch propellers requiresmuch less distance for stopping than aship with fixed pitch propellers. The controllablepitch propellers are particularly useful for landingships because they make it possible for theships to hover offshore and because they makeit easier for the ships to retract and turn awayfrom the beach.Controllable pitch propellers may be controlledfrom the bridge or from the engineroomas shown in figure 5-5. Hydraulic or mechanicalcontrols are used to apply a blade actuating forceto the blades.A hydraulic system as shown in figure 5-6,is the most widely used means of providing theforce required to change the pitch of a controllablepitch propeller. In this type of system, avalve positioning mechanism actuates an oilcontrol valve. The oil control valve permitshydraulic oil, under pressure, to be introducedto either side of a piston (which is connected tothe propeller blade) and at the same time allowsfor the controlled discharge of hydraulic oil fromthe other side of the piston. This action repositionsthe piston and thus changes the pitch of thepropeller blades.Some controllable pitch propellers have mechanicalmeans for providing the blade actuatingforce necessary to change the pitch of the blades.In these designs, a worm screw and crossheadnut are used instead of the hydraulic devices fortransmitting the actuating force to the connectingrods. The torque required for rotating theworm screw is supplied either by an electricmotor or by the main propulsion plant throughpneumatic brakes. The mechanically operatedactuating mechanism is usually controlled bysimple mechanical or electrical switches.Propeller ProblemsOne of the major problems encountered withpropellers is known as cavitation. Cavitation isthe formation of a vacuum around a propellerwhich is revolving at a speed above a certaincritical value (which varies, depending upon thesize, number, and shape of the propeller blades).The speed at which cavitation begins to occuris different in different types of ships; the turbulenceincreases in proportion to the propellerrpm. Specifically, a propeller rotating at a highspeed will develop a stream velocity that createsa low pressure. This low pressure is less thanthe vaporization point of the water, and fromeach blade tip there appears to develop a spiralof bubbles (fig. 5-7). The water boils at the lowpressure points. As the vapor bubbles of cavitationmove into regions where the pressure ishigher, the bubbles collapse rapidly and producea high-pitched noise.The net result of cavitation is to produce:(1) high level of underwater noise; (2) erosionof propeller blades; (3) vibration with subsequentblade failure from metallic fatigue; and (4)overall loss in propeller efficiency, requiring aproportionate increase in power for a givenspeed.In naval warfare, the movements of surfaceships and submarines can be plotted by sonarbearings on propeller noise. Because of the highpas PILOTHOUSE PITCHCONTROL SWITCHSENG RMS. PITCH CONTROLPROPULSION CONTROLTRANSFER SWITCHPas PILOTHOUSEINDICATORSpas PROPELLERSAND HUBSSERVO MOTORSREDUCTION GEARSTARBOARD PITCHCONTROL UNITFigure 5-5.— General arrangement of pitch propeller control.121.2491

4IPRINCIPLES OF NAVAL ENGINEERINGinC4u(U—f—S3.(Uo u-*->co u1Iin92

Chapter 5-FUNDAMENTALS OF SHIP PROPULSION AND STEERINGFigure 5-7.— Cavitating propeller.71,23(147B)static water pressure at submarine operationaldepths, cavitation sets in when a submarine isoperating at a much higher rpm than when nearthe surface. For obvious reasons, a submarinethat is under attack will immediately dive deepso that it can use high propeller rpm with theleast amount of noise.A certain amount of vibration is alwayspresent aboard ship. Propeller vibration ,however,may also be caused by a fouled blade orby seaweed. If a propeller strikes a submergedobject, the blades may be nicked.Another propeller phenomen is the "singing"propeller. The usual cause of this noise is thatthe trailing edges of the blades have not beenproperly prepared before installation. Theflutter caused by the flow around the edges mayinduce a resonant vibration. A "singing" propellercan be heard for a great distance.BEARINGSFrom the standpoint of mechanics, the termbearing may be applied to anything which supportsa moving element of a machine. However,this section is concerned only with those bearingswhich support or confine the motion of sliding,rotating, and oscillating parts on revolving shaftsor movable surfaces of naval machinery.In view of the fact that naval machinery isconstantly exposed to varying operating conditions,bearing material must meet rigid standards.A number of nonferrous alloys are usedas bearing metals. In general, these alloys aretin-base, lead-base, copper-base, or aluminumbasealloys. The term babbitt metal is oftenused for lead-base and tin-base alloys.Bearings must be made of materials whichwill withstand varying pressures and yet permitthe surfaces to move with minimum wear andfriction. In addition, bearings must be held in93

PRINCIPLES OF NAVAL ENGINEERINGposition with very close tolerances permittingfreedom of movement and quiet operation. Inview of these requirements, good bearing materialsmust possess a combination of the followingcharacteristics for a given application.1. The compressive strength of the bearingalloy at maximum operating temperature mustbe such as to withstand high loads withoutcracking or deforming.2. Bearing alloys must have high fatigueresistance to prevent cracking and flaking undervarying operating conditions.3. Bearing alloys must have high thermalconductivity to prevent localized hot spots withresultant fatigue and seizure.4. The bearing materials must be capable ofretaining an effective oil film.5. The bearing materials must be highly resistantto corrosion.ClassificationSOLID TYPE JOURNALBEARING (BUSHING)SPLIT-TYPE JOURNAL BEARINGGUIDE BEARINGSPLIT-TYPE COMBINATIONJOURNAL AND THRUST BEARINGThe reciprocating and rotating elements ormembers, supported by bearings, may be subjectto external loads which can be resolved intocomponents having normal, radial, or axialdirections, or a combination of the two. Bearingsare generally classified as sliding surface(friction) or rolling contact (antifriction) bearings.Sliding surface bearings may be definedbroadly as those bearings which have slidingcontact between their surfaces. In these bearings,one body slides or moves on the surfaceof another and sliding friction is developed ifthe rubbing surfaces are not lubricated. Examplesof sliding surface bearings are thrustbearings and journal bearings (fig. 5-8), suchas the spring or line shaft bearings installedaboard ship.Journal bearings are extensively used aboardship. Journal bearings may be subdivided intodifferent styles or types, the most common ofwhich are solid bearings, half bearings, twopartor split bearings. A typical solid stylejournal bearing application is the piston bearing(part A of fig. 5-8), more commonly called abushing . An example of a solid bearing is apiston rod wristpin bushing such as found incompressors. Perhaps the most common applicationof the half bearing in marine equipmentis the propeller shaft bearing. Since theload is exerted only in one direction, they obviouslyare less costly than a full bearing ofany type. Split bearings are used more frequently147.50Figure 5-8.— Various types of friction bearings,than any other friction-type bearing. A goodexample is the turbine bearing. Split bearingscan be made adjustable to compensate for wear.Guide bearings (part B of fig. 5-8), as thename implies, are used for guiding the longitudinalmotion of a shaft or other part. Perhapsthe best illustrations of guide bearings are thevalve guides in an internal combustion engine.Thrust bearings are used to limit the motionof, or support a shaft or other rotating partlongitudinally. Thrust bearings sometimes arecombined functionally with journal bearings.Antifriction-type, or rolling contact, bearingsare so-called because their design takesadvantage of the fact that less energy is requiredto overcome rolling friction than is requiredto overcome sliding friction. These bearingsmay be defined broadly as bearings which haverolling contact between their surfaces. Thesebearings may be classified as roller bearingsor ball bearings according to shape of the rolling94

Chapter 5- FUNDAMENTALS OF SHIP PROPULSION AND STEERINGelements. Both roller and ball bearings aremade in different types, some being arrangedto carry both radial and thrust loads. In thesebearings, the balls or rollers generally areassembled between two rings or races, thecontacting faces of which are shaped to fit theballs or rollers.The basic difference between ball and rollerbearings is that a ball at any given instantcarries the load on two tiny spots diametricallyopposite while a roller carries the load on twonarrow lines (fig. 5-9). Theoretically, the areaof the spot or line of contact is infinitesimal.Practically, the area of contact depends on howmuch the bearing material will distort underthe applied load. Obviously, rolling contactbearings must be made of hard materials becauseif the distortion under load is appreciablethe resulting friction will defeat the purpose ofthe bearings. Bearings with small, highly loadedcontact areas must be lubricated carefully ifthey are to have the antifriction properties theyare designed to provide. If improperly lubricated,the highly polished surfaces of the ballsand rollers soon will crack, check, or pit, andfailure of the complete bearing follows.Both sliding surface and rolling contactbearings may be further classified by theirfunction as follows: radial, thrust, and angularcontact(actually a combination of radial andthrust) bearings. Radial bearings, designedprimarily to carry a load in a direction perpendicularto the axis of rotation, are used tolimit motion in a radial direction. Thrust bearingscan carry only axial loads; that is, a forceparallel to the axis of rotation, tending to causeendwise motion of the shaft. Angular-contactbear ings can support both radial and thrust loads.The simplest forms of radial bearings arethe integral and the insert types. The integralSPOT CONTACT LINE CONTACT LINE CONTACT77,66Figure 5-9.— Load-carrying areas of ball androller bearings.type is formed by surfacing a part of the machineframe with the bearing material, while the insertbearing is a plain bushing inserted into and heldin place in the machine frame. The insert bearingmay be either a solid or a split bushing, andmay consist of the bearing material alone or beenclosed in a case or shell. In the integral bearingthere is no means of compensating for wear,and when the maximum allowable clearance isreached the bearing must be resurfaced. Theinsert solid bushing bearing, like the integraltype,has no means for adjustment due to wear,and must be replaced when maximum clearanceisreached.The pivoted shoe is a more complicated typeof radial bearing. This bearing consists of ashell containing a series of pivoted pads orshoes, faced with bearing material.The plain pivot or single disk type thrustbearing consists of the end of a journal extendinginto a cup-shaped housing, the bottom ofwhich holds the single disk of bearing material.The multi-disk type thrust bearing is similarto the plain pivot bearing except that severaldisks are placed between the end of the journaland the housing. Alternate disks of bronze andsteel are generally used. The lower disk isfastened in the bearing housing and the upperone to the journal, while the intermediate disksare free.The multi-collar thrust bearing consists ofa journal with thrust collars integral with orfastened to the shaft; these collars fit into recessesin the bearing housing which are facedwith bearing metal. This type bearing is generallyused on horizontal shafts carrying lightthrust loads.The pivoted shoe thrust bearing is similar tothe pivoted shoe radial bearing except that it hasa thrust collar fixed to the shaft which runsagainst the pivoted shoes. This type bearing isgenerally suitable for both directions of rotation.Angular loading is generally taken by usinga radial bearing to restrain the radial load andsome form of thrust bearing to handle the load.This may be accomplished by using two separatebearings or a combination of a radial and thrust(radial thrust). A typical example is the multicollarbearing which has its recesses entirelysurfaced with bearing material; the faces of thecollars carry the thrust load and the cylindricaledge surfaces handle the radial load.95

PRINCIPLES OF NAVAL ENGINEERINGMain Reduction Gear andPropulsion Turbine BearingsReduction gear bearings of the babbitt-linedsplit type are rigidly mounted and dowelled intothe bearing housings. These bearings are splitin halves, but the split is not always in a horizontalplane. On many pinion and bull gear bearings,the pressure is against the cap and notalways in a vertical direction. The bearingshells are so secured in the housing that thepoint of pressure on both ahead and astern operationis as nearly midway between the joint facesas practicable.Turbine bearings are pressure lubricated bymeans of the same forced-feed system that lubricatesthe reduction gear bearings.Main Thrust BearingsThe main thrust bearing, which is usuallylocated in the reduction gear casing, serves toabsorb the axial thrust transmitted through theshaft from the propeller.Kingsbury or pivoted segmental shoe thrustbearings of the type shown in figure 5-10 arecommonly used for main thrust bearings. Thistype of bearing consists of pivoted segments orshoes (usually six) against which the thrustcollar revolves. Ahead or astern axial motionof the shaft, to which the thrust collar is secured,is thereby restrained by the action of thethrust shoes against the thrust collar. Thesebearings operate on the principle that a wedgeshapedfilm of oil is more readily formed andmaintained than a flat film and that it can thereforecarry heavier loads for any given size.In a segmental pivoted-shoe thrust bearing,upper leveling plates upon which the shoes restand lower leveling plates equalize the thrustload among the shoes (fig. 5-11). The base ring,which supports the lower leveling plates, holdsthe plates in place and transmits the thrust onthe plates to the ship's structure. Shoe supports(hardened steel buttons or pivots) located betweenthe shoes and the upper leveling platesenable the shoe segments to assume the anglerequired to pivot the shoes against the upperleveling plates. Pins and dowels hold the upperand lower leveling plates in position, allowingample play between the base ring and the platesto ensure freedom of movement of the levelingplates. The base ring is kept from turning by itsnotched construction, which secures the ring toits housing.147.51XFigure 5-10.—Kingsbury pivoted-shoe thrustbearing.Main Line Shaft BearingsBearings which support the propulsion lineshafting and which are located inside the hullare called line shaft bearings, spring bearings,or line bearings. These bearings are of thering-oiled, babbitt-faced, spherical-seated,shell type. Figure 5-12 illustrates the arrangementof a line shaft bearing. The bearing isdesigned to align itself to support the weightof the shafting. The spring bearings of allmodern naval ships are provided with both upperand lower self-aligning bearing halves.Stern Tube and Strut BearingsThe stern tube is a steel tube built into theship's structure for the purpose of supportingand enclosing the propulsion shafting where itpierces the hull of the ship. The section of theshafting enclosed and supported by the sterntube is called the stern tube shaft. The propellershaft is supported at the stern by twobearings, one at each end of the stern tube.These bearings are called stern tube bearings .A packing gland known as the stern tube gland96

Chapter 5-FUNDAMENTALS OF SHIP PROPULSION AND STEERINGTHRUSTCOLLARBASERINGOILFILMA STATIONARY VIEWB ROTATING VIEWLEVELING PLATES BASE RING ^JOINT IN BASE RINGC EXTENDED VIEWFigure 5-11.— Diagrammatic arrangement of Kingsbury thrust bearing.38.86Xis located at the inner end of the stern tube.This gland, which is shown in figure 5-13, sealsthe area between the shaft and the stern tube,but still allows the shaft to rotate.The stuffing box of the stern tube gland isflanged and bolted to the stern tube. The castingis divided into two annular compartments. Theforward space is the stuffing box proper; theafter space has a flushing connection for providinga positive flow of water through the sterntube for lubricating, cooling, and flushing. Theflushing connection is supplied by the fire andflushing system. A drain connection may beprovided,A strut bearing is shown in figure 5-14; Thestrut bearing has a composition bushing which issplit longitudinally into two halves. The outersurface of the bushing is machined with steps tobear on matching landings in the bore of thestrut. One end is bolted to the strut.The shells of both stern tube and strut bearingsare of bronze lined with a suitable bearingwearing material. The shells are normallygrooved longitudinally to receive strips ofOIL RINGS CARRYOIL TO THE TOPOF THE SHAFTOIL GROOVES DISTRIBUTETHE OIL WITHIN THE BEARINGEXCESS OIL DRAINSBACK TO THE RESERVOIR,WHERE IT COOLSBEFORE RECIRCULATION47.39XFigure 5-12.— Line shaft bearing.97

PRINCIPLES OF NAVAL ENGINEERINGlaminated resin bonded composition or strips ofcomposition faced witli rubber or synthetic rubbercompounds as wearing materials. The laminatedstrips are cut and installed in the bearingshell so as to present the end grain to the shaft.In naval craft other than major combatant ships,resin bonded composition bearings or full moldedrubber faced bearings are used,PROPULSION SHAFTING47.40Figure 5-13.— Stern tube stuffing box and gland.The propulsion shafting, which ranges indiameter from 18 to 21 inches for small twinscrewdestroyers to approximately 30 inches forlarge four-screw carriers, is divided into fourfunctional sections: the thrust shaft, the lineLENGTH OF BEARING AND NUMBER OFSTEPS TO S,BUSHINGSTRUT,Figure 5-14.— Strut bearing. (A) Longitudinal cutaway view. (B) Cross-sectional view.(C) Arrangement of rubber stripping in the bearing bushing.47.4198

Chapter 5-FUNDAMENTALS OF SHIP PROPULSION AND STEERINGshaft, the stern tube shaft, and the propelleror tail shaft. These portions of the shafting maybe seen in figure 5-15.Segments of the line shaft and the thrustshaft are joined together with integral flangetypecouplings. The stern tube shaft is joined tothe after end of the line shaft with an inboardstern tube coupling which has a removable aftersleeveflange. The tail shaft is joined to thestern tube shaft by a muff-type outboard coupling.On single-screw ships, the portion of the outboardshaft which turns in the stern tube bearingis normally covered with a shrunk-on compositionsleeve. This is done to protect the shaftfrom corrosion and to provide a suitable journalfor the water-lubricated bearings. On multiplescrewships, these sleeves normally cover onlythe bearing areas; on such ships, the exposedshafting between the sleeves is covered withsynthetic sheet rubber to protect the shaftingfrom sea water corrosion.On carriers and cruisers, the wet shafting—that is, the shafting outboard in the sea— iscomposed of three sections: a tail shaft, anintermediate or dropout section, and a sterntube section. Integral flanged ends of these sectionsare usually used for joining the sectionstogether.Circular steel or composition shields knownas fairwaters are secured to the bearing bushingsof the stern tube and strut bearings and toboth the forward and the after ends of the underwateroutboard couplings. These are intendedprimarily to reduce underwater resistance. Thecoupling fairwaters are secured to both the shaftand coupling flanges and are filled with tallowto protect the coupling from corrosion.REDUCTION GEARSReduction gears are used in many propulsionplants to allow both the prime mover and thepropeller to operate at the most efficient speed.Reduction gears are also used in many kinds ofauxiliary machinery, where they serve the samepurpose. Some of the gear forms commonly usedin shipboard machinery are shown in figure5-16.Reduction gears are classified by the numberof steps used to bring about speed reduction andby the general arrangement of the gearing. Asingle reduction gear consists of a small piniongear which is driven by the turbine shaft and alarge main gear (or bull gear) which is drivenby the pinion. In this type of arrangement, theratio of speed reduction is proportional to thediameters of the pinion and the bull gear. In a2 to 1 single reduction gear, for example, thediameter of the driven gear is twice that of thedriving pinion. In a 10 to 1 single reduction gear,the diameter of the driven gear is ten timesthat of the pinion.All main reduction gearing in current combatantships makes use of double helical gears(sometimes referred to as herringbone gears).STRUT BUmNEF«IIIW«TER,Sl[E»ESAFTER STERN TUBEBEARINCBU|i GEAR SHAFT(THRUST SHAH)PORT MAIN REDUCTIONGEARMAIN THRUSTBEARINGAFTER ENGINE ROOMFigure 5-15.— Propulsion shafting, twin-screw ship.47.42B99

PRINCIPLES OF NAVAL ENGINEERINGDOUBLE HELICAL GEARINTERNAL SPUR GEARWORM GEARSINGLE HELICAL GEAREXTERNAL SPUR GEARBEVEL GEAR5.22Figure 5-16.— Gear forms used in shipboardmachinery.Double helical gears have smoother action andless tooth shock than single reduction gears.Since the double helical gears have two sets ofteeth at complementary angles, end thrust (suchas is developed in single helical gears) is prevented.In the double reduction gears used on mostships, a high speed pinion which is connected tothe turbine shaft by a flexible coupling drives anintermediate (first reduction) gear. The firstreduction gear is connected by a shaft to thelow speed pinion which in turn drives the bull(second reduction) gear mounted on the propellershaft. If we suppose a 20 to 1 speed reductionis desired, this could be accomplishedby having a ratio of 2 to 1 between the high speedpinion and the first reduction gear and a ratio of10 to 1 between the low speed pinion on the firstreduction gear shaft and the second reductiongear on the propeller shaft.A typical double reduction gear installationfor a DD 692 class destroyer is shown in figure5-17. In this type of installation, the cruisingturbine is connected to the high pressure turbinethrough a single reduction gear. The cruisingturbine rotor carries with it a pinion whichdrives the cruising gear, coupled to the highpressure turbine shaft. The cruising turbinerotor and pinion are supported by three bearings,one at the forward end of the turbine andone on each side of the pinion in the cruisingreduction gear case.The high pressure turbine and the low pressureturbine are connected to the propeller shaftthrough a locked train double reduction gear ofthe type shown in figure 5-18, First reductionpinions are connected by flexible couplings tothe turbines. Each of the first reduction pinionsdrives two first reduction gears. Attached toeach of the first reduction gears by a quill shaftand flexible couplings (fig. 5-19) is a secondreduction pinion (low speed pinion). These fourpinions drive the second reduction gear (bullgear) which is attached to the propeller shaft.Locked train reduction gears have the advantageof being more compact than other types, forany given power rating. For this reason, all highpowered modern combatant ships have lockedtrain reduction gears. Another type of reductiongearing, known as nested gearing, is illustratedin figure 5-20. Nested gearing is used on mostauxiliary ships but is not used on combatantships. As may be seen, the nested gearing isrelatively simple; it employs no quill shaftsand uses a minimum number of bearings andflexible couplings.FLEXIBLE COUPLINGSPropulsion turbine shafts are connected tothe reduction gears by flexible couplings whichare designed to take care of very slight misalignmentbetween the two units. Most flexiblecouplings are of the gear type shown in figure5-21. The coupling consists of two shaft ringshaving internal gear teeth and an internal100

Chapter 5-FUNDAMENTALS OF SHIP PROPULSION AND STEERINGCRUISING TURBINESINGLE REDUCTION-GEARVLOW PRESSURE-TURBINEHIGH PRESSURE-TURBINEQUILL SHAFT1st.REDUCTIONGEAR1st.REDUCTIONGEAR2nd. REDUCTIONPINION2nd.REDUCTIONGEARJACKINGGEAR ENCASEDMAIN SHAFT COUPLING47.30Figure 5-17.— Turbines and locked train double reduction gearing of DD 692 class destroyer.floating member (or distance piece) which hasexternal teeth around the periphery at each end.The shaft rings are bolted to flanges on the twoshafts to be connected; the floating member isplaced so that its teeth engage with those of theshaft rings.Cruising turbine couplings which transmitlower powers may use external floating memberswith internal teeth. With this design, theshaft rings become spur gears with externalteeth on the ends of the pinion shaft and turbineshaft. Figure 5-22 shows a flexible coupling of101

PRINCIPLES OF NAVAL ENGINEERINGLOW PRESSURE 1STREDUCTION GEARSLOW PRESSURE 2noREDUCTION PINIONSMAIN (bull)GEARLOW PRESSURE 1stREDUCTION PINIONHIGH PRESSURE 1stREDUCTION PINIONHIGH PRESSURE 1stREDUCTION GEARSHIGH PRESSURE 2ndREDUCTION PINIONSFigure 5-18.— Locked train double reduction gearing.47.271ST REDUCTION GEAR2ND REDUCTIDN PINIONFLEXIBLECOUPLINEBEARINGSFigure 5-19. — Quill shaft assembly.FLEXIBLECOUPLING47.32X102

Chapter 5- FUNDAMENTALS OF SHIP PROPULSION AND STEERING2ND REDUCTIONPINION1ST REDUCTION1ST REDUCTIONGEAR2ND REDUCTIONOR MAIN GEAR1ST REDUCTION GEAR| p. pinionmm1ST REDUCTION GEAR L.P. PINIONREDUCTION1ST REDUCTION GEAR1ST REDUCTION GEARFigure 5-20.— Nested reduction gearing.49.29Xthis type which is used on destroyers. Thecoupling is installed between the cruisingturbinereduction gear and the high pressure turbine.In this coupling, the floating member isatransverselysplit sleeve having internal teeth whichmesh completely with the external teeth of thespur gears mounted on the connected shaft ends.CARE OF REDUCTION GEARS,SHAFTING AND BEARINGSThe main reduction gear is one of the largestand most expensive units of machinery found inthe engineering department. Main reductiongears that are installed properly and operated103

PRINCIPLES OF NAVAL ENGINEERINGTUMINEFIANCE47,31XFigure 5-21.— Gear-type flexible coupling.properly will give years of satisfactory service.However, a serious casualty to main reductiongears, will either put the ship out of commissionor force it to operate at reduced speed.Extensive repairs to the main reduction gearcan be very expensive because they usuallyhave to be made at a shipyard.Some things are essential for the properoperation of reduction gears. Proper lubricationincludes supplying the required amount ofoil to the gears and bearings, plus keeping theoil clean and at the proper temperature. Lockingand unlocking the shaft must be done in accordancewith the manufacturer's instructions.Abnormal noises and vibrations must be investigatedand corrective action taken. Gears mustbe inspected in accordance with the currentinstructions issued by NavShips, the type commander,or other proper authority. Preventiveand corrective maintenance must be conductedin accordance with the 3-M System.PROPER LUBRICATION.-Lubrication ofreduction gears and bearings is of the utmostimportance. The correct quantity and quality oflubricating oil must, at all times, be availablein the main sump. The oil must be CLEAN; andit must be supplied to the gears and bearings atthe pressure and temperature specified by themanufacturer.In order to accomplish proper lubrication ofgears and bearings, several conditions must bemet. The lube oil service pump must deliver theproper discharge pressure. All relief valves inthe lube oil system must be set to function attheir designed pressure. On most older ships.each bearing has a needle valve to control theamount of oil delivered to the bearing. On newerships, the quantity of oil to each bearing is controlledby an orifice in the supply line. Theneedle valve setting or the orifice opening mustbe in accordance with the manufacturer's instructionsor the supply of oil will be affected.Too small a quantity of oil will cause the bearingto run hot. If too much oil is delivered tothe bearing, the excessive pressure may causethe oil to leak at the oil seal rings. Too muchoil may also cause a bearing to overheat.Lube oil must reach the bearing at the propertemperature. If the oil is too cold, one of theeffects is insufficient oil flow for cooling purposes.If the oil supply is too hot, some lubricatingcapacity is lost.For most main reduction gears, the normaltemperature of oil leaving the lube oil coolershould be between 120° F and 130° F. For fullpower operation, the temperature of the oilleaving the bearings should be between 140° Fand 160° F. The maximum TEMPERATURE RISEof oil passing through any gear or bearing, underany operating conditions, should not exceed 50° F;and the final temperature of the oil leaving thegear or bearing should not exceed 180 °F. Thistemperature rise and limitation may be determinedby installed thermometers or resistancetemperature elements.Cleanliness of lubricating oil cannot be overstressed.Oil must be free from impurities, suchas water, grit, metal, and dirt. Particular caremust be taken to clean out metal flakes and dirtwhen new gears are wearing in or when gearshave been opened for inspection. Lint or dirt, ifleft in the system may clog the oil spray nozzles.The spray nozzles must be kept open at alltimes. Spray nozzles must never be altered withoutthe authorization of the Naval Ship SystemsCommand.The lube oil strainers perform satisfactorilyunder normal operating conditions, but they cannottrap particles of metal and dirt which arefine enough to pass through the mesh. These fineparticles can become embedded in the bearingmetal and cause wear on the bearings andjournals. These fine abrasive particles passingthrough the gear teeth act like a lapping compoundand remove metal from the teeth.LOCKING AND UNLOCKING THE MAINSHAFT. — In an emergency, or in the event of acasualty to the main propulsion machinery of aturbine-driven ship, it may be necessary to stop104

Chapter 5- FUNDAMENTALS OF SHIP PROPULSION AND STEERINGOIL OUTLET OIL OUTLETHUB GEAR \ BOLT / KEY SLEEVE\ / / / HUB GEAROILINLETH. P. TURBINESHAFTSETSCREWLOCK NUTCRUISINGGEAR SHAFTHOLES FOR JACKING(USE COUPLING BOLT)SECTION A-AFigure 5-22. — Flexible coupling between cruising gear and high pressure turbine.47,33and lock a propeller shaft to prevent damage tothe machinery. Wien the shaft is stopped, engagingthe turning gear and then applying thebrake is the most expeditious means of lockinga propeller shaft while under way.By carrying out actual drills, engineroompersonnel should be trained to safely lock andunlock the main shaft. Each steaming watchshould have sufficient trained personnel availableto stop and lock the main shaft.CAUTION: During drills the shaft should notbe locked more than 5 minutes, if possible. Theahead throttle should NEVER be opened when theturning gear is engaged. The torque produced bythe ahead engines is in the same direction as thetorque of the locked shaft; to open the aheadthrottle would result in damage to the turninggear.The maximum safe operating speed of a shipwith a locked shaft can be found in the manufacturer'stechnical manual. Additional informationon the safe maximum speed that your ship cansteam with a locked shaft can be found in Nav -Ships Technical Manual , chapter 9410. If theshaft has been locked for 5 minutes or more, theturbine rotors may have become bowed, andspecial precautions are recommended. Beforethe shaft is allowed to turn, men should be stationedat the turbines to check for unusualnoises and vibration. When the turning gear isdisengaged, the astern throttle should be slowlyclosed, the torque produced by the propellerpassing through the water will start the shaftrotating. If, when the propeller starts to turn,vibration indicates a bowed rotor, the ship'sspeed should be reduced to the point where littleor no vibration of the turbine is noticeable andthis speed should be maintained until the rotoris straightened. If operation at such a slowspeed is not practicable, the turbines should beslowed by use of the astern throttle, to the pointof least vibration but with the turbines stilloperating in the ahead direction. When the turbinesare slowed to the point of little or novibration, the shaft should be operated at thatspeed and the ahead throttle should be openedslightly to permit some steam flow through theaffected turbine. The heat from the steam willwarm the shaft and aid in straightening it. Loweringthe main condenser vacuum will add additionalheat to the turbines; this will increase theexhaust pressure and temperature.As the vibration decreases, the asternthrottle can be closed gradually, allowing thespeed of the shaft to increase. The shaft speedshould be increased slowly and a check for105

PRINCIPLES OF NAVAL ENGINEERINGvibration should be maintained. The turbine isnot ready for normal operation until vibrationhas disappeared at all possible speeds.NOISES AND VIBRATION. -On steamturbinedriven ships, noises may occur at lowspeeds or when maneuvering, or when passingthrough shallow water. Generally, these noisesdo not result from any defect in the propulsionmachinery and will not occur during normaloperation. A rumbling sound which occurs atlow shaft rpm is generally due to the low pressureturbine gearing floating through its backlash.This condition has also been experiencedwith cruising reduction gears. The rumbling andthumping noises which may occur during maneuveringor during operation in shallow water, arecaused by vibrations initiated by the propeller.These noises referred to are characteristic onlyof some ships and should be regarded as normalsounds for these units. These sounds will disappearwith a change of propeller rpm or whenthe other causes mentioned are no longerpresent. These noises can usually be noticed indestroyers when the ship is backing, especiallyin choppy seas or in ground swells.A properly operating reduction gear has adefinite sound which an experienced watchstandercan easily learn to recognize. At differentspeeds and under various operatingconditions, the operator should be familiar withthe normal operating sound of the reductiongears on his ship.If any abnormal sounds occur, an investigationshould be made immediately. In making aninvestigation, much will depend on how the operatorinterprets the sound or noise.The lube oil temperature and pressure mayor may not help an operator determine thereasons for the abnormal sounds. A badly wipedbearing may be indicated by a rapid rise in oiltemperature for the individual bearing. A certainsound or noise may indicate misalignment orimproper meshing of the gears. K unusualsounds are caused by misalignment of gears orforeign matter passing through the gear teeth,the shaft should be stopped and a thorough investigationshould be made before the gears areoperated again.For a wiped bearing, or any other bearingcasualty that has caused a very high temperature,this procedure should be followed: If thetemperature of the lube oil leaving any bearinghas exceeded the permissible limits, slow orstop the unit and inspect the bearing for wear.The bearing may be wiped only a small amountand the shaft may be operated at a reduced speeduntil the tactical situation allows sufficient timeto inspect the bearing.The most common causes of vibration in amain reduction gear installation are: faultyalignment, bent shafting, damaged propellers,and improper balance.A gradual increase in the vibration in a mainreduction gear that has been operating satisfactorilyfor a long period of time can usually betraced to a cause outside of the reduction gears.The turbine rotors, rather than the gears, aremore likely to be out of balance.When reduction gears are built, the gearsare carefully balanced (both statically and dynamically).A small amount of unbalance in thegears will cause unusual noise, vibration, andabnormal wear of bearings.When the ship has been damaged, vibration ofthe main reduction gear installation may resultfrom misalignment of the turbine, the mainshafting, the main shaft bearings, or the mainreduction gear foundation. When vibration occurswithin the main reduction gears, damage to thepropeller should be one of the first things to beconsidered. The vulnerable position of the propellersmakes them more liable to damage thanother parts of the plant. Bent or broken propellerblades will transmit vibration to the mainreduction gears. Propellers can also becomefouled with line or cable which will cause thegears to vibrate. No reduction gear vibrationis too trivial to overlook. A complete investigationshould be made, preferably by a shipyard.MAINTENANCE AND INSPECTION.-Undernormal conditions, major repairs and majoritems of maintenance on main reduction gearsshould be accomplished by a shipyard. Whena ship is deployed overseas and at other timeswhen shipyard facilities are not available, emergencyrepairs should be accomplished, if possible,by a repair ship or an advanced base.Inspections, checks, and minor repairs shouldbe accomplished by ship's force.Under normal conditions, the main reductiongear bearings and gears will operate for an indefiniteperiod. If abnormal conditions occur,the shipyard will normally perform the repairs.Spares are carried aboard sufficient to replace50 percent of the number of bearings installedin the main reduction gear. Usually each bearingis interchangeable for the starboard or port installation.The manufacturer's technical manual106

Chapter 5-FUNDAMENTALS OF SHIP PROPULSION AND STEERINGmust be checked to determine interchangeabilityof gear bearings.Special tools and equipment needed to liftmain reduction gear covers, to handle the quillshaft when removing bearings from it, and totake required readings and measurements, arenormally carried aboard. The special tools andequipment should always be aboard in caseemergency repairs have to be made by repairships or bases not required to carry these items.The manufacturer's technical manual is thebest source of information concerning repairsand maintenance of any specific reduction gearinstallation. Chapters 9420, 9430, and 9440 ofNavShips Technical Manual gives the inspectionrequirements for reduction gears, shafting,bearings, and propellers.The inspections mentioned here are the minimumrequirements only. Where defects are suspected,or operating conditions so indicate, inspectionsshould be made at more frequentintervals.To open any inspection plates or other fittingsof the main reduction gears, permissionshould first be obtained from the engineer officer.Before replacing an inspection plate,connection, or cover which permits access tothe gear casing, a careful inspection shall bemade by an officer of the engineering departmentto ensure that no foreign matter has entered orremains in the casing or oil lines. If the work isbeing done by a repair activity, an officer fromthe repair activity must also inspect the gearcasing. An entry of the inspections and the nameof the officer or officers must be made in theEngineering Log. The inspections required onthe main engine reduction gears are shown onthe Maintenance Index Page, figure 5-23.The importance of proper gear tooth contactcannot be overemphasized. Any abnormal conditionwhich may be revealed by operationalsounds or by inspections should be correctedas soon as possible. Any abnormal conditionwhich is not corrected will cause excessive wearwhich may result in general disintegration of thetooth surfaces.If proper tooth contact is obtained when thegears are installed, little wear of teeth willoccur. Excessive wear cannot take place withoutmetallic contact. Proper clearances and adequatelubrication will prevent most gear toothtrouble.If proper contact is obtained when the gearsare installed, the initial wearing, which takesplace under conditions of normal load and adequatelubrication, will smooth out rough anduneven places on the gear teeth. This initialwearing-in is referred to as NORMAL WEARor RUNNING IN. As long as operating conditionsremain normal, nofurther wear will occur.Small shallow pits starting near the pitchline, will frequently form during the initial stageof operation; this process is called INITIALPITTING. Often the pits (about the size of apinhead or even smaller) can be seen only undera magnifying glass. These pits are not detrimentaland usually disappear in the course ofnormal wear.Pitting which is progressive and continuesat an increasing rate is known as DESTRUCTIVEPITTING. The pits are fairly large and are relativelydeep. Destructive pitting is not likely tooccur under proper operating conditions, butcould be caused by excessive loading, too softmaterial, or improper lubrication. It is usuallyfound that this type of pitting is due to misalignmentor to improper lubrication.The condition in which groups of scratchesappear on the teeth (from the bottom to the topof the tooth) is termed abrasion, or scratching.It may be caused by inadequate lubrication, orby the presence of foreign matter in the lubricatingoil. When abrasion or scratching is noted,the lubricating system and the gear spray fixturesshould immediately be examined. If it isfound that dirty oil is responsible, the systemmust be thoroughly cleaned andthe whole chargeof oil centrifuged.The term "scoring" denotes a general rougheningof the whole tooth surface. Scoring marksare deeper and more pronounced than scratchingand they cover an area of the tooth, instead ofoccurring haphazardly, as in scratching or abrasion.Small areas of scoring may occur in thesame position on all teeth. Scoring, with properalignment and operation, usually results frominadequate lubrication, and is intensified by theuse of dirty oil. If these conditions are not corrected,continued operation will result in a generaldisintegration of the tooth surfaces.Under normal conditions all alignment inspectionsand checks, plus the necessary repairs,are accomplished by naval shipyards.Incorrect alignment will be indicated by abnormalvibration, unusual noise, and wear of theflexible couplings or main reduction gears. Whenmisalignment is indicated, a detailed inspectionshould be made by shipyard personnel.Two sets of readings are required to get anaccurate check of the propulsion shafting. One107

.PRINCIPLES OF NAVAL ENGINEERINGSjritem, Subsystem, or CemponenIReference PublicaliontReduction GearsBuraou CordControl No.Mainfonanco RoquiromonIMR.No.RotoRoq'd.MortHeurtRolotodMointononcoMBZZZFGE53550251. Inspect the reduction gear includingspray nozzles .Q-1EOMMlMM31.01.0NoneMBJZ2FSC16542901. Measure main shaft thrust clearance.Q-2EOMMlMM20.30.3NoneMBJZZFGEl8450641. Inspect and clean oil sump andreduction gear casing.S-1EOMMlMM32FN5.06.012.0NoneMBZZ1FCW465A1881. Inspect flexible couplings. MeasureclearancesA-1MMCMMl2FN2.08.016.0NoneMBZZZFGE57866691. Sound and tighten foundation bolts.A-2FN1.0NoneFigure 5-23.— Maintenance Index Page.98.171108

Chapter 5- FUNDAMENTALS OF SHIP PROPULSION AND STEERINGset of readings is taken with the ship in drydockand another set of readings is taken with theship waterborne— under normal loading conditions.The main shaft is disconnected, marked,and turned so that a set of readings can be takenin four different positions. Four readings aretaken (top, bottom, and both sides). The alignmentof the shaft can be determined by studyingthe different readings taken. The naval shipyardwill decide whether or not corrections in alignmentare necessary.NOTE: During shipyard overhauls, the followinginspections should be made:a. Inspect condition and clearance of thrustshoes to ensure proper position of gears. Blowout thrusts with dry air after the inspection.Record the readings. Inspect the thrust collar,nut, and locking device.b. If turbine coupling inspection has indicatedundue wear, check alignment between pinions andturbines.c. Clean oil sump.When conditions warrant or if trouble is suspected,a work request may be submitted to anaval shipyard to perform a "seven year" inspectionof the main reduction gears. Thisinspection includes clearances and condition ofbearings and journals; alignment checks andreadings; and any other tests, inspections, ormaintenance work that may be considered necessary.Naval Ship Systems Command authorizationis not necessary for lifting reduction gearcovers. Covers should be lifted when trouble issuspected. An open gear case is a serious hazardto the main plant, therefore, careful considerationof the dangers of uncovering a gear casemust be balanced against the reasons for suspectinginternal trouble, before deciding to liftthe gear case. The seven-year interval may beextended by the type commander if conditionsindicate that a longer period between inspectionsis desirable.The correction of any defects disclosed byregular tests and inspections, and the observanceof the manufacturers' instructions, shouldensure that the gears are ready for full powerat all times.In addition to inspections which may bedirected by proper authority, open the inspectionplates, examine the tooth contact, the conditionof teeth, and the operation of the spraynozzles. It is not advisable to open gear cases,bearings, and thrusts immediately BEFORE fullpower trials.In addition to the inspections which may bedirected by proper authority, open the inspectionplates, and examine the tooth contact and the conditionof the teeth to note changes that may haveoccurred during the full power trials. Runningfor a few hours at high power will show any possiblecondition of improper contact or abnormalwear that would not have shown up in months ofoperation at lower power. Check the clearanceof the main thrust bearing.SAFETY PRECAUTIONSThe following precautions must be observedby personnel operating or working with propulsionequipment.1. If there is churning or emulsification ofoil and water in the gear case, the gear must beslowed down or stopped until the defect is remedied.2. If the supply of oil to the gear fails, thegears should be stopped until the cause can belocated and remedied.3. When bearings have been overheated,gears should not be operated, except in extremeemergencies, until bearings have been examinedand defects remedied.4. If excessive flaking of metal from thegear teeth occurs, the gears should not be adjusted,except in an emergency, until the causehas been determined.5. Unusual noises should be investigated atonce, and the gears should be operated cautiouslyuntil the cause for the noise has been discoveredand remedied.6. No inspection plate, connection, fitting, orcover which permits access to the gear casingshould be removed without specific authorizationby the engineer officer.7. The immediate vicinity of an inspectionplate should be kept free from paint and dirt.8. When gear cases are open, precautionsshould be taken to prevent the entry of foreignmatter. The openings should never be left unattendedunless satisfactory temporary closureshave been installed.9. Lifting devices should be inspected carefullybefore being used and should not be overloaded.10. When ships are anchored in localitieswhere there are strong currents or tides,109

PRINCIPLES OF NAVAL ENGINEERINGprecautions should be taken to lock the mainshaft.11. Where the rotation of the propellers mayresult in injury to a diver over the side, or indamage to the equipment, propeller shafts shouldbe locked.12. When a ship is being towed, the propellersshould be locked, unless it is permissible andadvantageous to allow the shafts to trail with themovement of the ship.13. When a shaft is allowed to turn or trail,the lubrication system must be in operation. Inaddition, a careful watch should be kept on thetemperature within the low pressure turbinecasing to see that windage temperatures cannotbe built up to a dangerous degree. This can becontrolled either by the speed of the ship or bymaintaining vacuum in the main condenser.14. The main propeller shaft must be broughtto a complete stop before the clutch of the turninggear is engaged. (If the shaft is turning,considerable damage to the turning gear willresult.)15. When the turning gear is engaged, thebrake must be set quickly and securely to pre-shaft turning and damaging the turningvent thegear.BALANCEDSEMIBALANCEDRUDDER STOCKPLATFORM DECKSHELL PLATINGUNBALANCEDFigure 5-24.— Rudder assembly.147.523.99 Figure 5-25.— Balanced, semibalanced, andunbalanced rudders.110

Chapter 5-FUNDAMENTALS OF SHIP PROPULSION AND STEERING16. When a main shaft is to be unlocked, precautionsmust be taken to disengage the jackinggear clutch before releasing the brake. If thebrake is released first, the main shaft maybegin to rotate and cause injury to the turninggear and to personnel.17. In an emergency, where the ship is steamingat a highspeed, the main shaft can be stoppedand held stationary by the astern turbine untilthe ship has slowed down to a speed at whichthe main shaft can be safely locked.18. Where there is a limiting maximum safespeed at which a ship can steam with a lockedpropeller shaft, this speed should be known andshould not be exceeded.19. Before the turning gear is engaged andstarted, a check should be made to see thatthe turning gear is properly lubricated. Someships have a valve in the oil supply line leadingto the turning gear. The operator should seethat a lube oil service pump is in operation andthat the proper oil pressure is being supplied tothe turning gear before the motor is started.20. It should be definitely determined thatthe turning gear has been disengaged before themain engines are turned over.21. While working on or inspecting open mainreduction gears, the person or persons performingthe work should not have any articleabout their person which may accidentally fallinto the gear case.22. Tools, lights, mirrors, etc. used forworking on or inspecting gears, bearings, etc.should be lashed and secured to prevent accidentaldropping into the gear case.STEERINGAs noted at the beginning of this chapter, thedirection of movement of a ship is controlledpartly by steering devices which receive theirpower from steering engines and partially bythe arrangement, speed, and direction of rotationof the ship's propellers.The steering device is called a rudder . Therudder is a more or less rectangular metalblade (usually hollow on large ships) which issupported by a rudder stock . The rudder stockenters the ship through a rudder post and awatertight fitting, as shown in figure 5-24. Ayoke or quadrant , secured to the head of therudder stock, transmits the motion imparted bythe steering mechanism.Basically, a ship's rudder is used to attainand maintain a desired heading. The forcenecessary to accomplish this is developed bydynamic pressure against the flat surface of therudder. The magnitude of this force and thedirection and degree to which it is applied producesthe rudder effect which controls sternmovement and thus controls the ship's heading.In order to function most effectively, a ruddershould be located aft of and quite close to thepropeller. Many modern ships have twin rudders,each set directly behind a propeller toreceive the full thrust of water. This arrangementtends to make a ship highly maneuverable.Three types of rudders are in general use—the unbalanced rudder, the semibalanced rudder,and the balanced rudder. These three types areillustrated in figure 5-25. Other types of ruddersare also in naval use. For example, someships have a triple-blade rudder which providesan increased effective rudder area.Ill

CHAPTER 6THEORY OF LUBRICATIONLubrication reduces friction between movingparts by substituting fluid friction for solid friction.Without lubrication, it is difficult to move ahundred-pound weight across a rough surface;with lubrication, and with proper attention to thedesign of bearing surfaces, it is possible to movea million-pound load with a motor that is smallenough to be held in the hand. By reducingfriction, thereby reducing the amount of energythat is dissipated as heat, lubrication reducesthe amount of energy required to perform mechanicalactions and also reduces the amountof energy that is dissipated as heat.Lubrication is a matter of vital importancethroughout the shipboard engineering plant. Movingsurfaces must be steadily supplied with theproper kinds of lubricants, lubricants must bemaintained at specified standards of purity, anddesigned pressures and temperatures must bemaintained in the lubrication systems. Withoutadequate lubrication, a good many units of shipboardmachinery would quite literally grind toa screeching halt.The lubrication requirements of shipboardmachinery are met in various ways, dependingupon the nature of the machinery. This chapterdeals with lubrication in general— with basicprinciples of lubrication, with lubricants usedaboard ship, and with the shipboard devices usedto maintain lubricating oils in the required conditionof purity. The separate lubrication systemsthat are installed for many shipboard unitsare discussed in other chapters of this text.FRICTIONThe friction that exists between a body atrest and the surface uponwhichit rests is calledstatic friction. The friction that exists betweenmoving bodies (or between one moving body anda stationary surface) is called kinetic friction .Static friction, which must be overcome to putany body in motion, is greater than kineticfriction, which must be overcome to keep thebody in motion.There are three types of kinetic friction:sliding friction, rolling friction, and fluid friction.Sliding friction exists when the surface ofone solid body is moved across the surface ofanother solid body. Rolling friction exists whena curved body such as a cylinder or a sphererolls upon aflat or curved surface. Fluid frictionis the resistance to motion exhibited by a fluid.Fluid friction exists because of the cohesionbetween particles of the fluid and the adhesionof fluid particles to the object or medium whichis tending to move the fluid. If a paddle is usedto stir a fluid, for example, the cohesive forcesbetween the molecules of the fluid tend to holdthe molecules together and thus prevent motionof the fluid. At the same time, the adhesive forcesof the molecules of the fluid cause the fluid toadhere to the paddle and thus create friction betweenthe paddle and the fluid. Cohesion is themolecular attraction between particles that tendsto hold a substance or a body together; adhesionis the molecular attraction between particles thattends to cause unlike surfaces to stick together.From the point of view of lubrication, adhesionis the property of a lubricant that causes it tostick (or adhere) to the parts being lubricated;cohesion is the property which holds the lubricanttogether and enables it to resist breakdownunder pressure.Cohesion and adhesion are possessed by differentmaterials in widely varying degrees. Ingeneral, solid bodies are highly cohesive butonly slightly adhesive. Most fluids are quitehighly adhesive but only slightly cohesive; however,the adhesive and cohesive properties offluids vary considerably.FLUID LUBRICATIONFluid lubrication is based on the actual separationof surfaces so that no metal-to- metal112

Chapter 6-THEORY OF LUBRICATIONcontact occurs. As long as the lubricant filmremains unbroken, sliding friction and rollingfriction are replaced by fluid friction.In any process involving friction, some poweris consumed and some heat is produced. Overcomingsliding friction consumes the greatestamount of power and produces the greatestamount of heat. Overcoming rolling friction consumesless power and produces less heat. Overcomingfluid friction consumes the least powerand produces the least amount of heat.LANGMUIR THEORYA presently accepted theory of lubrication isbased on the Langmuir theory of the action offluid films of oil between two surfaces, one orboth of which are in motion. Theoretically, thereare three or more layers or films of oil existingbetween two lubricated bearing surfaces. Two ofthe films are boundary films (indicated as I andV in part Aof fig.6-1), one of which clings to thesurface of the rotating journal and one of whichclings to the stationary lining of the bearing.Between these two boundary films are one ormore fluid films (indicated as II, III, and IV inpart A of fig. 6-1). The number of fluid filmsshown in the illustration is arbitrarily selectedfor purposes of explanation.When the rotating journal is set in motion(part B of fig. 6-1), the relationship of the journalto the bearing lining is such that a wedge of oilis formed. The oil films II, III, and IV begin toslide between the two boundary films, thus continuouslypreventing contact between the twometal surfaces. The principle is again illustratedin part C of figure 6-1, where the position of theoil wedge W is shown with respect to the positionof the journal as it starts and continues in motion.The views shown in part C of figure 6-1 representa journal or shaft rotating in a solidbearing. The clearances are exaggerated in thedrawing in order to illustrate the formation ofthe oil film. The shaded portion represents theclearance filled with oil. The film is in theprocess of being squeezed out while the journalis at rest, as shown in the stationary view. Asthe journal slowly starts to turn and the speedincreases, oil adhering to the surfaces of thejournal is carried into the film, increasing the'film thickness and tending to lift the journal asshown in the starting view. As the speedincreases, the journal takes the position shown inthe running view. Changes in temperature, withconsequent changes in oil viscosity, causechanges in the film thickness and in the positionof the journal.If conditions are correct, the two surfaces areeffectively separated, except for a possible momentarycontact at the time the motion is started.FACTORS AFFECTING LUBRICATIONSTATIONARYVIEWSTARTINGVIEWRUNNINGVIEW47.78Figure 6-1.— Oil film lubrication. (A) Stationaryposition, showing several oil films; (B) surfaceset in motion, showing principle of oil wedge;(C) principle of (A) and (B) shown in a journalbearing.A number of factors determine the efficacyof oil film lubrication, including such things aspressure, temperature, viscosity, speed, alignment,condition of the bearing surfaces, runningclearances between the bearing surfaces, startingtorque, and the nature and purity of the lubricant.Many of these factors are interrelated andinterdependent. For example, the viscosity ofany given oil is affected by temperature and thetemperature is affected by running speed; hencethe viscosity is partially dependent upon the runningspeed.A lubricant must be able tosticktothe bearingsurfaces and support the load at operating113

PRINCIPLES OF NAVAL ENGINEERINGspeeds. More adhesiveness is required to makea lubricant adhere to bearing surfaces at highspeeds than at low speeds. At low speeds, greatercohesiveness is required to keep the lubricantfrom being squeezed out from between the bearingsurfaces.Large clearances between bearing surfacesrequire high viscosity and cohesiveness in thelubricant to ensure maintenance of the lubricatingoil film. The larger the clearance, the greatermust be the resistance of the lubricant to beingpounded out, with consequent destruction of thelubricating oil film.High unit load on a bearing requires high viscosityof the lubricant. A lubricant subjected tohigh loading must be sufficiently cohesive to holdtogether and maintain the oil film.LUBRICANTSAlthough there is a growing use of syntheticlubricants, the principal source of the oils andgreases used in the Navy is still petroleum. Byvarious refining processes, lubricating stocksare extracted from crude petroleum and blendedinto a multiplicity of products to meet all lubricationrequirements. Various compounds or additivesare used in some lubricants (both oilsand greases) to provide specific properties requiredfor specific applications.Types of Lubricating OilsLubricating oils approved for shipboard useare limited to those grades and types deemed essentialto provide proper lubrication under allanticipated operating conditions.For diesel engines, it is necessary to use adetergent-dispersant type of additive oil in orderto keep the engines clean. In addition, these lubricatingoils must be fortified with oxidation inhibitorsand corrosion inhibitors to allow longperiods between oil changes and to prevent corrosionof bearing materials.For steam turbines, it is necessary to havean oil of high initial film strength. This oil isthen fortified with anti-foaming additives andadditives that inhibit oxidation and corrosion. Inaddition, it isnecessary to use extreme pressure(EP) additives to enable the oil to carry the extremelyhigh loading to which it is subjected inthe reduction gears.For the hydraulic systems in which petroleumlubricants are used, and for generallubrication use, the Navy usesa viscosity seriesof oils reinforced with oxidation and corrosioninhibitors and anti-foam additives. The compoundedoils, which are mineral oils to whichsuch products as rape seed, tallow, or lard oilare added, are still used in deck machinery and inthe few remaining steam plants that utilize reciprocatingsteam engines.A great many special lubricating oils areavailable for a wide variety of services. Theseare listed in the Federal Supply Catalog. Amongthe more important specialty oils are those usedfor lubricating refrigerant compressors. Theseoils musthavea very low pour point and be maintainedwith a high degree of freedom from moisture.The principal synthetic lubricants currentlyin naval use are (1) a phosphate ester type offire-resistant hydraulic fluid, used chiefly in thedeck-edge elevators of carriers (CVAs); and (2)a water-base glycol hydraulic fluid used chieflyin the catapult retracting gear.Classification ofLubricating OilsThe Navy identifies lubricating oils by symbols.Each identification number consists of fourdigits (and, in some cases, appended letters) . Thefirst digit indicates the class of oil according totype and use; the last three digits indicate theviscosity of the oil. The viscosity digits are actuallythe number of seconds required for 60 millilitersof the oil to flow through a standardorifice at a specified temperature. The symbol3080, for example, indicates that the oil is in the3000 series and that a 60-ml sample flowsthrough a standard orifice in 80 seconds when theoil is at a specified temperature (210 F, in thisinstance). To take another example, the symbol2135 TH indicates that the oil is in the 2000 seriesand that a 60-ml sample flows througha standard orifice in 135 seconds when the oil isat a specified temperature (130' F, in this case).The letters H, T, TH, or TEP added to a basicsymbol number indicate that the oil contains additivesfor special purposes.Lubricating Oil CharacteristicsLubricating oils used by the Navy are testedfor a number of characteristics, including viscosity,pour point, flash point, fire point, autoignitionpoint, neutralization number, demulsibility,and precipitation number. Standard testmethods are used for making all tests.114

Chapter 6-THEORY OF LUBRICATIONThe viscosity of an oil is its tendency to resistflow. An oil of high viscosity flows veryslowly. Raising the temperature of an oil lowersits viscosity; lowering the temperature increasesthe viscosity. The measurement of viscosityis discussed in chapter 7 of this text.The viscosity index of an oil is a number indicatingthe effect of temperature changes onviscosity. A low viscosity index signifies a relativelylarge change of viscosity with changesof temperature. An oil which becomes thin athigh temperatures and thick at low temperaturesis said to have a low viscosity index; a high viscosityindex signifies that the viscosity changesrelatively little with changes of temperature.The pour point of an oil is the lowest temperatureat which the oil will barely flow froma container. The pour point is closely related tothe viscosity of the oil. In general, an oil of highviscosity will have a higher pour point than anoil of low viscosity.The flash point of an oil is the temperatureat which enough vapor is given off to flash whena flame or spark is applied under standard testconditions.The fire point (higher than the flash point) ofan oil is the temperature at which the oil willcontinue to burn when it is ignited.The auto- ignition point of an oil is the temperatureat which the flammable vapors givenoff from the oil will burn without the applicationof a spark or flame.The neutralization number of an oil is a measureof the acid content; it is defined as the numberof milligrams of potassium hydroxide (KOH)required to neutralize one gram of the oil. Allpetroleum products oxidize in the presence ofair and heat, and the products of oxidation includeorganic acids. The acids, if present insufficient concentration, have harmful effectson alloy bearings at high temperatures. Thepresence of acids also may result in the formationof sludge and emulsions too stable to bebroken down. An increase in acidity is an indicationthat lubricating oil is deteriorating.The demulsibility of an oil is the ability ofthe oil to separate cleanly from any water present.Demulsibility is an important characteristicof lubricating oils used in forced-feed lubricationsystems.The precipitation number of an oil is a measureof the amount of solids classified as asphaltsor carbon residue contained in the oil. The precipitationnumber is reached by diluting a knownquantity of oil with naphtha and separating theprecipitate by centrifuging. The volume of theseparated solids equals the precipitation number.An oil with a high precipitation number isnot suitable for certain applications because itmay leave deposits in an engine or plug up valvesand pumps.Lubricating GreasesSome lubricating greases are simple mixturesof soaps and lubricating oils. Others aremore exotic liquids such as silicones anddi-basic acid esters, thickened with metals orinert materials to provide adequate lubrication.Requirements for oxidation inhibition, corrosionprevention, and extreme pressure performanceare met by incorporating special additives.Lubricating greases are supplied in threegrades: soft, medium, and hard. The soft greasesare used for high speeds and low pressures; themedium greases areusedfor medium speeds andmedium pressures; the hard greases are used forslow speeds and high pressures.CARE OF LUBRICATING OILLubricating oils may be kept in service forlong periods of time, provided the purity of theoils is maintained at the required standard. Thesimple fact is that lubricating oil does not wearout.-^ although it can become unfit for use whenit is robbed of its lubricating properties by thepresence of water, sand, sludge, fine metallicparticles, acid, and other contaminants.Proper care of lubricating oil requires, then,that the oil be kept as free from contaminationas possible and that, once contaminated, the oilmust be purified before it can be used again.PREVENTING CONTAMINATIONStrainersor filters are used in many lubricatingsystems to prevent the passage of grit,scale, dirt, and other foreign matter. Duplexstrainers are used in lubricating systems inwhich an uninterrupted flow of lubricating oilmust be maintained; the flow may be divertedfrom one strainer basket to the other while oneis being cleaned. Filters may be installed directlyin pressure lubricating systems or theymay be installed as bypass filters.The additive content of an oil may be exhausted asthe additive combats the special conditions for whichit was included in the oil; but this is a gradual processand is never catastrophic.115

PRINCIPLES OF NAVAL ENGINEERINGThe use of strainers and filters does notsolve the problem of water contamination of lubricatingoil. Even a very small amount of waterin lubricating oil can be extremely damaging tomachinery, piping, valves, and other equipment.Water in lubricating oil can cause widespreadpitting and corrosion; also, by increasing thefrictional resistance, water can cause the oilfilm to break down prematurely. Every effortmust be made to prevent the entry of water intoany lubricating system.REMOVING CONTAMINATIONIn spite of all efforts, a certain amount ofcontamination of lubricating oil is to be expected.Aboard ship, centrifugal purifiers are used toremove impurities from lubricating oil and settlingtanks are provided to permit used oil tostand while water and other impurities settle out.Centrifugal PurifiersA centrifugal purifier is essentially a bowlor hollow cylindrical container which is rotatedat high speed while contaminated oil is forcedthrough and rotated with the container. The centrifugalforce imposed on the oil by the highrotational speed of the container causes the suspendedforeign matter to separate from the oil.Materials that are soluble in each other cannotbe separated by centrifugal force. For example,salt cannot be removed from sea waterby centrifugal force because the salt and waterCOVER CLAMP HOOKLARGE SPRINGCOVER CLAMP SPRINGLONG COVER CLAMPINLET ARM SEAL RINGSPRING GUIDEBALL CHECK SPRINGINLET ARMREGULATING TUBECOVER TOPCOVER TOP SCREWCOVER CLAMP NUTFRAME COVERBALL CHECK VALVEVALVE STOP SCREW^HOPPERSEAL RINGSHORT COVER CLAMPSEAL RINGBRAKEBOWLSTUDTOP BEARINGFRAMEBOWL SPINDLEBOTTOM SCREWFigure 6-2.— Disk-type centrifugal purifier.75.231116

Chapter 6-THEORY OF LUBRICATIONPURIFIED OtLREGULATING TUBETUBULAR SHAFTDISTRIBUTINGPLUG75.233Figure 6-3.— Path of contaminated oil throughdisk-type purifier bowl (DeLAVAL).are in solution. However, water can be separatedfrom lubricating oil because water and oil do notform a solution when mixed. For separation totake place by centrifugal force, there must be adifference in the specific gravity of oil and thespecific gravity of water.When a mixture of oil, water, and sedimentis allowed to stand undisturbed, gravity tends tocause the formation of an upper layer of oil, anintermediate layer of water, and a lower layerof sediment. The layers form because of differencesin the specific gravities of the various substances.If the oil, water, and sediment mixtureis placed in a rapidly revolving centrifugal purifier,the effect of gravity is negligible in comparisonwith the effect of centrifugal force. Centrifugalforce, acting at right angles to the axisof rotation of the container, forces the sedimentinto an outer layer, the water into an intermediatelayer, and the oil into an innermost layer. Centrifugalpurifiers are so designed that the separatedwater is discharged as waste and the oil isdischarged for use. The solids remain in the rotatingunit and are cleaned out after each purificationoperation.Two types of centrifugal purifiers are usedaboard ship. The main difference between thetwo types is in the design of the rotating units.In the disk-type purifier, the rotating elementis a bowl-like container which encases a stackof disks. In the tubular-type purifier, the rotatingelement is a hollow tubular rotor.A disk-type centrifugal purifier is shown infigure 6-2. The bowl is mounted on the upperend of the vertical bowl spindle, which is drivenby a worm wheel and friction clutch assembly.A radial thrust bearing is provided at the lowerend of the bowl spindle tocarry the weight of thebowl spindle and to absorb any thrust createdby the driving action.Contaminated oil enters thetopof the revolvingbowl through the regulating tube. The oil thenpasses down the inside of the tubular shaft andout at the bottom of the stack of disks. As thedirty oil flows up through the distribution holes inthe disks, the high centrifugal force exerted bythe revolving bowl causes the dirt, sludge, andwater to move outward and the purified oil tomove inward toward the tubular shaft. The disksdivide the space within the bowl into many separatenarrow passages. The liquid confined withineach passage is restricted so that it can only flowalong that passage. This arrangement preventsexcessive agitation of the liquid as it passesthrough the bowl and creates shallow settlingdistances between the disks. The path of contaminatedoil passing through a disk-type purifieris shown in figure 6-3.Most of the dirt and sludge remains in thebowl and collects in a more or less uniform layeron the inside vertical surface of the bowl shell.Any water that may be present, together withsome dirt and sludge, is discharged through thedischarge ring at the top of the bowl. The purifiedoil flows inward and upward through thedisks, discharging from the neck of the top disk.A tubular-type centrifugal purifier is shownin figure 6-4. This type of purifier consists essentiallyof a hollow rotor or bowl which rotatesat high speeds. The rotor has an opening in thebottom through which the dirty lubricating oilenters; two sets of openings at the top allow theoil and water (or the oil alone) to discharge. (Seeinsert, fig. 6-4.) The bowl or hollow rotor of thepurifier is connected by a coupling unit toa spindle which is suspended from a ball bearingassembly. The bowl is belt-driven by an electricmotor mounted on the frame of the purifier.The lower end of the bowl extends into a flexiblymounted guide bushing. The assembly, ofwhich the bushing is a part, restrains movementof the bottom of the bowl but allows enough movementso that the bowl can center itself about itsaxis of rotation when the purifier is in operation.Inside the bowl is a device which consists of threeflat plates equally spaced radially. This deviceis commonly referred to as the three-wing device117

-IPRINCIPLES OF NAVAL ENGINEERINGBELT GUARDMOTOR PULLEY-•SPINDLECOUPLING NUTFUNNEL COVERFUNNEL BODY-[^^*- PURIFIED|j\ OIL OUTLET\ \—CLARIFIERFigure 6-4.— Tubular-type centrifugal purifier. 75.234or as the three-wing . The three-wing rotateswith the bowl and forces the liquid in the bowl torotate at the same speed as the bowl. The liquidto be centr ifuged is fed into the bottom of the bowlthrough the feed nozzle, under pressure, so thatthe liquid jets into the bowl in a stream.The process of separation is basically thesame in the tubular-type purifier as in the disktypepurifier. In both types, the separated oil assumesthe innermost position and the separatedwater moves outward. Both liquids are dischargedseparately from the bowl, and the solidsseparated from the liquid are retained in thebowl.Settling TanksLubrication systems aboard ship include settlingtanks in which used oil is allowed to standwhile water and other impurities settle out. Lubricatingoil piping is generally arranged to permittwo methods of purification: batch purificationand continuous purification.In the batch process, the lubricating oil istransferred from the sump to a settling tank bymeans of a purifier or a transfer pump. In thesettling tank, the oil is heated to approximately160 F and allowed to settle for several hours.Water and other impurities are removed fromthe settling tanks. The oil isthencentrifugedandreturned to the sump from which it was taken.In the continuous purification process, thecentrifugal purifier takes suction from a sumptank and, after purifying the oil, discharges itback to the same sump. The continuous methodof purification is used while a ship is underway.118

CHAPTER7PRINCIPLES OF MEASUREMENTMeasurement is, in a very real sense, thelanguage of engineers. The shipboard engineeringplant contains an enormous number of gagesand instruments that tell operating personnelwhether the plant is running properly or whethersome abnormal condition— excessive speed, highpressure, low pressure, high temperature, lowwater level— requires corrective action. Thegages and instruments also provide essentialinformation for the hourly, daily, and weeklyentries for station operating logs and for otherengineering records and reports.This chapter describes some of the basictypes of gages and instruments used in shipboardengineering plants for the measurement ofimportant variables such as temperature, pressure,fluid flow, liquid level, and rotationalspeed. Because of the wide variety of gages andinstruments used in connection with shipboardengineering equipment, no attempt is made tocover all types that might possibly be encountered;instead, basic principles of measurementand commonly used types of gages are emphasized.Unusual or highly specialized measuringdevices, or ones that have particular applicationto some one type of rnachinery or equipmentaboard ship, are in general discussed in thechapters of this text that deal with the particularequipment; where an unusual type of measuringdevice j^ discussed in this chapter, it isincluded chiefly as a means of bringing outsome interesting or important aspect of measurement.Detailed information on most gagesand instruments used aboard ship can be obtainedfrom manufacturers' technical manuals andother instructional materials furnished withshipboard engineering equipment.THE CONCEPT OF MEASUREMENTOne of the primary ways in which we extendour knowledge and understanding of the universeand of the world around us is by the measurementof various quantities. Because we live ina world in which practically everything seemsto be in some way measured or counted, weoften tend to assume that measurement isbasically simple. In reality, however, it maybequite difficult to develop an appropriate mode ofmeasurement even after we have recognized theneed; and, without an appropriate mode ofmeasurement, we may even fail to recognizethe significance of the phenomena we observe.Thus the development of scientific and engineeringprinciples has been, and undoubtedly willcontinue to be, inextricably tied to the conceptof measurement.Many of our views on the nature of thingsare profoundly influenced by the procedures wedevise for measurement. It is interesting tonote how often in the history of science theapplication of a new instrument or the refinementof a measuring technique has led to newideas about the universe or about the nature ofthe thing being measured.! Until approximatelythe middle of the seventeenth century, it wascommonly believed that water rose in a suctionpump because "nature abhors a vacuum. "2The concept of a "sea of air" surrounding theAs Sir Humphry Davy (1778-1829) stated, "Nothingtends so much to the advancement of knowledge as theapplication of a new instrument." (Quoted in HarvardCase Histories in Experimental Science, James BryantConant, general editor, and Leonard K. Nash, associateeditor, Cambridge, Massachusetts, 1957. Vol. l.page119.)9"'The explanation that "nature abhors a vacuum "persistedfor quite some time in spite of the observedfact that water would not rise more than about 32feet in the suction pumps of the time and in spite ofGalileo's observation that "Evidently nature's horrorof a vacuum does not extend beyond 32 feet."119

PRINCIPLES OF NAVAL ENGINEERINGearth and exerting pressure upon it was veryclosely related to Torricelli's experiments witha column of mercury in a glass tube. The notionthat the air above us exerts a pressure wasnot fully accepted until after Pascal had arrangedan experiment to test the hypothesis. Pascalsuggested using Torricelli's new instrument,the barometer, at the base of a mountain andthen again at the top of the mountain. If the airexerts a pressure, Pascal reasoned, the mercuryshould stand higher in the glass columnat the base of the mountain than it should at thetop. The experiment was performed by Pascal'sbrother-in-law in 1648, and the prediction wasconfirmed. Further experimentation and measurementby Robert Boyle and others led to thedevelopment of many important concepts concerningthe nature of air and other gases, andled eventually to an understanding of the relationshipbetween the volume and the pressure ofa gas (Boyle's law).Perhaps an even more striking example ofthe effects of measurement upon our basic conceptsof the nature of things is to be found inthe study of heat. Quantitative studies of heatwere not possible before the invention of thethermometer. 2 It was not until the middle ofthe nineteenth century that the concept of heatas a form of energy, rather than as an invisible,weightless fluid called "caloric," was firmlyestablished. The persistence of the calorictheory to such a late date was due partly tofaulty interpretations of experimental results;but these faulty interpretations were at least inpart the result of difficulties of measurement.The downfall of the caloric theory was necessarybefore we could conceive of heat as energy,rather than as a nebulous kind of matter, andbefore we could understand the relationshipbetween heat and work.^ In summary, it wouldJoseph Black (1728-1799), commentingon the discoverythat heat tends to flow from hotter to colder bodiesuntil a state of thermal equilibrium is reached, stated:"No previous acquaintance with the peculiar relation ofeach body to heat could have assured us of this, and weowe the discovery entirely to the thermometer."(From Black's Lectures on the Elements of Chemistry ,assembled from notes and published in 1803 by JohnRobinson. Quoted in Harvard Case Histories in ExperimentalScience, op. cit. , vol. 1, page 128.)4 The relationship between heat and work is, of course,basic to the entire field of engineering. Chapter 8 ofthis text deals with this topic in considerable detail.not be unreasonable to say that the thermometerhad to be invented before we could arrive at anunderstanding of the nature of heat, the relationshipbetween heat and mechanics, and the principleof the conservation of energy.SYSTEMS, UNITS, AND STANDARDSOF MEASUREMENTPractically all units of measurement arederived from a few basic quantities or fundamentaldimensions , as they are sometimescalled. In all commonly used systems of measurement,length and time are taken as two ofthe fundamental dimensions. A third is MASS insome systems and force (or weight) in others.In all systems, temperature is the fourth fundamentaldimension^The first three fundamental dimensionslength,time, and either mass or force— aresometimes called mechanical quantities or dimensions.All other important mechanical quantitiescan be defined in terms of these threefundamentals. Temperature, the fourth fundamentaldimension, is in a different categorybecause it is not a mechanical quantity. By usingthe three mechanical fundamental quantities andthe quantity of temperature, practically allquantities of any importance may be derived.It is often said that there are two systems ofmeasurement— a metric system and a Britishsystem. Actually, however, there are severalmetric systems and several British systems.A more meaningful classification of systems ofmeasurement can be made by saying that somesystems are gravitational and others are absolute.In gravitational systems, the units of forceare defined in terms of the effects of the forceof gravity upon a standard sample of matter ata specified location on the surface of the earth.In absolute systems, the units of force are definedin terms that are completely independentof the effects of the force of gravity. Thus ametric system could be either gravitational orabsolute, and a British system could be eithergravitational or absolute, depending upon theterms in which force is defined in the particularsystem.MASS AND WEIGHTTo understand what is meant by gravitationaland absolute systems of measurement, it is necessaryto have a clear understanding of thedifference between mass and weight. Mass, ameasure of the total quantity of matter in an120

Chapter 7-PRINCIPLES OF MEASUREMENTobject or body, is completely independent of theforce of gravity, so the mass of any given objectis always the same, no matter where it islocated on the surface of the earth; indeed, thebody would have the same mass even if it werelocated at the center of the earth, on the moon,in outer space, or anywhere else. Weight,onthe other hand, is a measure of the force ofattraction between the mass of the earth andthe mass of another body or object. Since theforce of attraction between the earth and anotherbody is not identical in all places, the weight ofa body depends upon the location of the bodywith respect to the earth.The relationship between mass and weightcan be understood from the equationwherewmsw = weightm= massg = acceleration due to gravityThe value for acceleration due to gravity(normally represented by the letter g) is almostconstant for bodies at or near the surface of theearth. This value is approximately 32 feet persecond per second in British systems of measurement,9.8 meters per second per second inone metric system, and 980 centimeters persecond per second in another metric system.More precise values of g, including variationsthat occur with changes in latitude and changesin elevation, may be obtained from physics andengineering textbooks and handbooks.BASIC MECHANICAL UNITSTable 7-1 shows the basic mechanical quantitiesof length, mass or force, and time, togetherwith a number of derived units, used inseveral systems of measurement. By examiningsome of the units, we may see how forceis defined and thus see why each system iscalled "absolute" or "gravitational," as thecase may be.In the metric absolute meter-kilogramsecond(MKS) system of measurement, the unitof mass is the kilogram, the unit of length isthe meter, the unit of time is the second, andthe unit of acceleration is meters per secondper second. (This is sometimes written asm/sec2.) The unit of force is called a Newton.By definition, 1 newton is the force required toaccelerate a mass of 1 kilogram at the rate of 1meter per second per second. In other words,the unit of force is defined in such a way thatunit force gives unit acceleration to unit mass.^The same thing holds true in the other metricabsolute system shown in table 7-1. In themetric absolute centimeter-gram-second (CGS)system of measurement, the gram is the unitof mass, the centimeter is the unit of length,the second is the unit of time, and centimetersper second (cm/sec^) is the unit of acceleration.In this system, the unit of force is calleda dyne. By definition, 1 dyne is the force required^to accelerate a mass of 1 gram at therate of 1 centimeter per second per second.Again, force is defined in such a way that unitforce gives unit acceleration to unit mass.The same applies to the British absolutefoot-pound-second (FPS) system of measurement,where the pound is the unit of mass, thefoot is the unit of length, the second is the unitof time, and feet per second per second is theunit of acceleration. In this system, the unit offorce is called a poundal. By definition, 1poundal is the amount of force required to givea mass of 1 pound an acceleration of 1 foot persecond per second. Again, force is defined insuch a way that unit force gives unit accelerationto unit mass.Now let's look at a British gravitationalsystem— the foot-pound-second (FPS) gravitationalsystem that we use in the United Statesfor most everyday measurements. The foot isthe unit of length, the pound is the unit of mass,the second is the unit of time, and feet persecond per second is the unit of acceleration.In this system, the unit of force is called thepound. (Actually, it should be called the poundforce;but this usage is rarely followed.) inthis system, a force of 1 pound acting upon amass of 1 pound produces an acceleration of 32feet per second per second. Note that unitforce does not produce unit acceleration whenacting on unit mass; rather, unit force producesunit acceleration when acting on unit weight.Since force is defined in gravitational terms,rather than in absolute terms, we say that thisis a gravitational system of measurement.The gravitational system that is usuallycalled the British Engineering System also usesthe pound (or, more precisely, the pound-force)as the unit of force. But this system has itsown unit of mass: the slug . By definition, 1slug is the quantity of mass that is accelerated121

PRINCIPLES OF NAVAL ENGINEERINGTable 7-1. — Units of measurement in Several Common Systems.147.183

Chapter 7-PRINC[PLES OF MEASUREMENTor psi) is equally acceptable and is very commonlyused. Similar conversions can be madefor any of the other units, as long as the basicrelationships of the system are accurately maintained.When converting values from a metric systemto a British system (or vice versa) it isnecessary to understand the units used in eachsystem. Most of us know quite a bit about theunits commonly used in British systems, butless about the units used in metric systems.A description of the basic structure of the metricsystems follows.All metric systems of measurement aredecimal systems— that is, the size of the unitsvary by multiples of 10. This makes computationsvery simple. Another handy thing aboutthe metric systems is that the prefixes for thenames of the units tell you the relative size ofthe units. Take the prefix kilo-, for example.Kilo-indicates 1000; so a kilogram is 1000grams, a kilometer is 1000 meters, and so forth.Or take the prefix milli-, for another example;it indicates a thousandth. So 1 millimeter is 1thousandth of a meter, 1 milligram is 1 thousandthof a gram, and so forth. Perhaps thebest way to become familiar with the units inthe metric systems is to associate the morecommonly used prefixes with the positive andnegative powers of 10, as shown in table 7-2.Table 7-2. —Metric System Prefixes and CorrespondingPositive and Negative Powers of 10.METRIC SYSTEM PREFIXES POSITIVE AND NEGATIVE POWERS OF 10DEKA- or DECA101010100HECTO-KILO-10^1000MEGA- 10 1, 000, 000DECI- 10 0. 1 (or 1/10)CENTI- 10 0.01 (or 1/100)MILLI- 10 0.001 (or 1/1000)MICRO- 10 0.000001 (or 1/1,000,000)123

PRINCIPLES OF NAVAL ENGINEERINGTable 7-3 gives some selected values formechanical units in British systems of measurement.Table 7-4 gives some selected valuesfor mechanical units in metric systems ofmeasurement. Table 7-5 gives some Britishmetricand metric-British equivalents. The examplesgiven in these tables are chosen primarilyto help you develop an understanding ofthe relative sizes of the mechanical units. Morecomplete tables are available in many physicsand engineering textbooks and handbooks.STANDARDS OF MEASUREMENTThe importance of having precise and uniformstandards of measurement is recognized by allthe major countries of the world, and internationalconferences on weights and measuresare held from time to time. The InternationalBureau of Weights and Measures is in France,Each major country has its own bureauor officecharged with the responsibility of maintainingthe required measurement standards, includingthe basic standards of length, mass, and time.In the United States, the National Bureau ofStandards (NBS) is responsible for maintainingbasic standards and for prescribing precisemeasuring techniques.LengthUntil quite recently, the international standardof length was a platinum- iridium alloy barkept at the International Bureau of Weights andMeasures in France. By definition, the standardmeter was the distance between two parallellines marked on this bar, measured at 0°C.Copies of this international standard were maintainedby other countries; the United StatesTable 7-3. —Selected Values of Mechanical Unitsin British Systems of Measurement.TYPE OF MECHANICAL UNIT

Chapter 7-PRINCIPLES OF MEASUREMENTTable 7-4. —Selected Values of Mechanical Units inMetric Systems of Measurement.TYPE OF MECHANICAL UNIT

-PRINCIPLES OF NAVAL ENGINEERINGTable 7-5. —Selected British-Metric and Metric -British Conversions,TYPE OFMECHANICALUNITBRITISH-METRIC CONVERSIONSMETRIC -BRITISH CONVERSIONSLENGTH 1 inch = 2. 540 centimeters1 foot = 0. 3048 meter1 yard = 0.9144 meter1 mile = 1.6093 kilometers1 mile = 1609. 3 meters1 centimeter = 0. 3937 inch1 meter = 39. 37 inches1 kilometer = 0.62137 mileAREA 1 in. 6. 452 cm1 ft =2929 cm1yd" 0.8361 m21 mi^ = 2. 59 km100 mm = 0. 15499 in,100 cm^ =^15.499 in,100 m^ = 119,6 yd^1 km 0. 386 miVOLUME1 in,'1 ftlyd^16, 387 cm0,0283 m^0,7646 m^1000 mm^ = 0.06102 ^ in.1000 cm^ = 61.02 ^in.1 m^ = 35.314 ft^231 in.'3, 7853 liters1 liter = 1. 0567 liquid quartsWEIGHT 1 grain = 0.0648 gram1 ounce = 23. 3495 grams1 piound = 453. 592 grams1 pound = 0.4536 kilograms1 gram1 gram1 gram1 kilogram15.4324 grains0.03527 ounce0. 002205 pound2. 2046 poundsUnited States standard kilogram mass is keptat the National Bureau of Standards.The standard of mass is kept in a vault. Notmore than once a year, the standard is removedfrom the vault and used for checking the valuesof smaller standards. The United States standardkilogram mass has been taken to Francetwice in the last seven years for comparisonwith the international standard. Every precautionis taken to keep the kilogram standard massin perfect condition, free of nicks, scratches,and corrosion. The standard is always handledwith forceps; it is never touched by humanhands.When the national standard is compared ona precision balance with high precision copies,the copies are found to be accurate to withinone part in 100 million.TimeBefore 1960, the standard of time was themean solar second—that is, 1/86,400 of a meansolar day, as determined by successive appearancesof the sun overhead, averaged over ayear. In 1960, the standard of time was changedto the tropical year 1900, which is the time ittook the sun to move from a designated point126

Chapter 7-PRINCIPLES OF MEASUREMENTback to the same point in the year 1900.By definition, 1 second was equal to1/31,556,925.9747 of the tropical year 1900.The subdivision of the tropical year 1900 intosmaller time intervals was accomplished bymeans of laboratory-type pendulum clocks,together with observation of natural phenomenasuch as the nightly movement of the stars andthe moon.Although the standard of time was changedto the tropical year 1900 in 1960, the sameGeneral Conference of Weights and Measuresthat approved this change also urged that workgo forward on the development of an atomicclock. In 1967, the General Conference of Weightsand Measures adopted as the basic standardof time the time required for the transitionbetween two energy states of the cesium- 133atom. In accordance with this standard, 1 secondis defined as 9,192,631,770 cycles of this particulartransition in the cesium- 133 atom.The United States standard of time is maintainedby a cesium clock which is kept at theNational Bureau of Standards laboratories inBoulder, Colorado. The time signals that arebroadcast by four radio stations operated bythe National Bureau of Standards are based onthis cesium clock.MEASUREMENT OF TEMPERATURETemperature is measured by bringing ameasuring system (such as a thermometer) intocontact with the system in which we need tomeasure the temperature. We then measuresome property of the measuring system--theexpansion of a liquid, the pressure of a gas,electromotive force, electrical resistance, orsome other mechanical, electrical, or opticalproperty that has a definite and known relationshipwith temperature. Thus we infer the temperatureof the measured system by the measurementof some property of the measuringsystem.But the measurement of a property otherthan temperature will take us only so far inutilizing the measurement of temperature. Forconvenience in comparing temperatures and innoting changes in temperature, we must be ableto assign a numerical value to any given temperature.For this we need temperature scales.Until 1954, temperature scales were constructedaround the boiling point and the freezingpoint of pure water at atmospheric pressure.These two fixed and reproducible points wereused to define a fairly large temperature intervalwhich was then subdivided into the uniformsmaller intervals called degrees. The twomost famiUar temperature scales constructedin this manner are the Celsius scale and theFahrenheit scale.The Celsius scale is often called the centigradescale ii the United States and GreatBritain. By international agreement, however,the name was changed Trom centigrade to Celsiusin honor of the eighteenth-century Swedishastronomer, Anders Celsius. The symbol fora degree on this scale (no matter whether it iscalled Celsius or centigrade) is °C. The Celsiusscale takes 0° C as the freezing point and100" C as the boiling point of pure water atatmospheric pressure. The Fahrenheit scaletakes 32° F as the freezing point and 212° Fas the boiling point of pure water at atmosphericpressure. The interval between freezing pointand boiling point is divided into 100 degreeson the Celsius scale and divided into 180 degreeson the Fahrenheit scale.Since the actual value of the interval betweenfreezing point and boiling point is identical, itis apparent that numerical readings on Celsiusand Fahrenheit thermometers have no absolutesignificance and that the size of the degree isarbitrarily chosen for each scale. The relationshipbetween degrees Celsius and degreesFahrenheit is given by the formulas°F = -^ °C f 325°C = -^ (°F - 32)yMany people have trouble remembering theseformulas, with the result that they either getthem mixed up or have to look them up in abook every time a conversion is necessary. Ifyou concentrate on trying to remember the basicrelationships given by these formulas, you mayfind it easier to make conversions. The essentialpoints to remember are these:1. Celsius degrees are larger than Fahrenheitdegrees. One Celsius degree is equal to 1.8Fahrenheit degrees, and each Fahrenheit degreeis only 5/9 of a Celsius degree.2. The zero point on the Celsius scale representsexactly the same temperature as the32-degree point on the Fahrenheit scale.127

-PRINCIPLES OF NAVAL ENGINEERING3. The temperatures 100° C and 212 Fare identical.In some scientific and engineering work,particularly where heat calculations areinvolved, an absolute temperature scale is used.The zero point on an absolute temperature scaleis the point called absolute zero . Absolute zerois determined theoretically, rather than byactual measurement. Since the pressure of agas at constant volume is directly proportionalto the temperature, it is logical to assume thatthe pressure of a gas is a valid measure ofits temperature. On this assumption, the lowestpossible temperature (absolute zero) is definedas the temperature at which the pressure of agas would be zero.Two absolute temperature scales have beenin use for many years. The rankine absolutescale is an extension of the Fahrenheit scale;it is sometimes called the Fahrenheit absolutescale. Degrees on the Rankine scale are thesame size as degrees on the Fahrenheit scale,but the zero point on the Rankine scale is at-459.67 ° Fahrenheit. In other words, absolutezero is zero on the Rankine scale and -459.67degrees on the Fahrenheit scale.A second absolute scale, the kelvin, is morewidely used than the Rankine. The Kelvin scalewas originally conceived as an extension of theCelsius scale, with degrees of the same sizebut with the zero point shifted to absolute zero.Absolute zero on the Celsius scale is -273.15° C.In 1954, a new international absolute scalewas developed. The new scale was based uponone fixed point, rather than two. The one fixedpoint was the triple point of water— that is,the point at which all three phases of water(solid, liquid, and vapor) can exist together inequilibrium. The triple point of water, whichis 0.01° C above the freezing point of water,was chosen because it can be reproduced withmuch greater accuracy than either the freezingpoint or the boiling point. On this new scale,the triple point was given the value 273.16 K.Note that neither the word 'degrees" nor thesymbol ° is used; instead, the unit is calleda "kelvin" and the symbol is K rather than°K.In 1960, when the triple point of water wasfinally adopted as the fundamental referencefor this temperature scale, the scale was giventhe nameof International Practical TemperatureScale. However, you will often see this scalereferred to as the Kelvin scale.Although the triple point of water is consideredthe basic or fundamental reference forthe International Practical Temperature Scale,five other fixed points are used to help definethe scale. These are the freezing point of gold,the freezing point of silver, the boiling point ofsulfur, the boiling point of water, and the boilingpoint of oxygen.Figure 7-1 is a comparison of the Kelvin(International-Practical), Celsius, Fahrenheit,and Rankine (Fahrenheit-Absolute) temperaturescales. All of the temperature points listedabove absolute zero are considered ^s fixedpoints on the Kelvin scale except for the freezingpoint of water. The other scales, as previouslymentioned, are based on the freezingand boiling points of water.TEMPERATURE MEASURING DEVICESSince temperature is one of the basic engineeringvariables, temperature measurementis essential to the proper operation of a shipboardengineering plant. The temperature ofsteam, water, fuel oil, lubricating oil, and othervital fluids must be measured at frequent intervalsand the results of this measurementmust in many cases be entered in engineeringrecords and logs.Devices used for measuring temperature maybe classified in various ways. In this discussionwe will consider the two major categories of(1) expansion thermometers, and (2) pyrometers.Expansion ThermometersExpansion thermometers operate on theprinciple that the expansion of solids, liquids,and gases has a known relationship to temperaturechanges. The types of expansion thermometersdiscussed here are (1) liquid-in-glassthermometers, (2) bimetallic expansion thermometers,and (3) filled-system expansionthermometers.LIQUID - EST - GLASS THERMOMETERS.Liquid- in- glass thermometers are probably theoldest, the simplest, and the most widely useddevices for measuring temperature. A liquidin-glassthermometer (fig. 7-2) consists of abulb and a very fine bore capillary tube containingmercury, mercury-thallium, alcohol,toluol, or some other liquid which expandsuniformly as the temperature rises and contractsuniformly as the temperature falls. Theselection of liquid is based on the temperature128

•5Chapter 7-PRINCIPLES OF MEASUREMENT(K) °C) TF) TR)FREEZING POINT OF GOLD1336.21063.01945.42405.07FREEZING POINT OK SILVER-12 34.0960.81761.42221.07SOILING POINT OF SULFUR-717.8444.6832,31291.97BOILING POINT OF WATER-373,15100.0212.0671.67TRIPLE POINT OF WATERFREEZING POINT OF WATER-273.16273.150.0132.01832.00491.708491 .69BOILING POINT OF OXYGEN-90.18-182.97-297.35162.32ABSOLUTEZEROCONVERSION FACTORSTEMP F -h 40= 1,8 (TEMP C-(-40) KELVIN CELSIUSTEMP F 1.8 (TEMP C) -(- 32 (INTERNATIONALTEMP C = (TEMP F -32)/ 1.8 PRACTICAL)TEMP K = TEMP C -I- 273.15-273.15-459.67(*)(*)(*)(*)FAHRENHEITRANKINE(FAHRENHEIT-ABSOLUTE)Figure33.11(147B)7-1. — Comparison of Kelvin, Celsius, Fahrenheit, and Rankine temperature.range in which the thermometer is to be used.Mercury (or mercury-thallium) is commonlyused because it is a liquid over a wide rangeof temperatures (—60° to 1200° F) and becauseit has anearly constant coefficient of expansion.Almost all liquid-in-glass thermometers aresealed so that atmospheric pressure will notNot all hquids are suitable for use in thermometers.Water, for e.xample. would be an almost impossiblechoice as a thermom.etric liquid at ordinary temperaturesbecause its coefficient of expansion variesenormously at temperatures near 0° C. In the temperaturerange between 0° C and 4° C, water expandswhen cooled and contracts when heated; thus it actuallyhas a negative coefficient of expansion in this range.affect the reading. The space above the liquidin this type of thermometer may be a vacuumor it may be filled with an inert gas such asnitrogen, argon, or carbon dioxide.The capillary bore may be either round orelliptical. In any case, it is very small so thata relatively small expansion or contraction ofthe liquid will cause a relatively large changein the position of the liquid in the capillary tube.Although the capillary bore itself is very smallin diameter, the walls of the capillary tube arequite thick. Most liquid-in-glass thermometersare made with an expansion chamber at the topof the bore to provide a margin of safety forthe instrument if it should accidentally be overheated.129

PRINCIPLES OF NAVAL ENGINEERINGLiquid-in-glass thermometers may havegraduations etched directly on the glass stemor the graduations may be carried on a separatestrip of material which is placed behind thestem. Many thermometers used in shipboardengineering plants have the graduations markedon a separate strip, since this type is in generaleasier to read than the type which has thegraduations marked directly on the stem.Liquid- in-glass thermometers are made invarious designs. The stem may be straight orit may be angled in various ways, dependingupon the requirements of service. The thermometersmay be armored or they may be partiallyenclosed by a metal case, if such protection isnecessary. Several types of angle-stem liquidin-glassthermometers of the type commonlyused aboard ship are shown in figure 7-3. Thesethermometers are used in 5-inch, 7-inch, and9-inch scale lengths. However, bimetallic thermometersare currently being substituted aboard-EXPANSION CHAMBER-STEM-CAPILLARY BORE> GRADUATIONSship for the 5-inch scale liquid-in-glass thermometers.Most liquid - in - glass thermometers usedaboard ship are provided with wells or separablesockets. The well is installed in the piping systemor equipment where the temperature is tobe measured, and the thermometer glass bulband part of the glass stem are fitted into a thinmetal protection tube, packed with a heattransfermaterial, and fastened in place in thewell. The well is made of metals that willwithstand the temperatures, pressures, andfluid velocities without damage; it protects theglass sensing bulb against damage and alsoeliminates the need for closing down a systemor securing a piece of machinery merely inorder to replace a thermometer.One disadvantage of the well type of installationis that a certain amount of time is requiredfor the thermometer to reach thermalequilibrium with the system in which the temperatureis being measured. To some extent,the time lag can be decreased by filling the spacearound the bulb in the well with a heat transfermedium such as graphite. Where rapid responseto temperature changes is a vital requirement,however, bare bulb thermometers are used insteadof the well type of installation. Bare bulbthermometers have very much faster responseto changes in temperature, but they cannot beremoved for replacement or servicing whilethe machinery is operating or the line is underpressure.-LIQUID COLUMN45 RECLINED AN6LE 45 INCLINEDANCLELEFT SIDE ANGLE RIGHT SIDE ANGLE^==mi^ eoapi=-33.11(147A)Figure 7-2. — Liquid-in-glass thermometer.61.26Figure 7-3.— Angle-stem liquid-in-glassthermometers.130

Chapter 7-PRINCIPLES OF MEASUREMENTWhere special requirements exist, specialtypes of liquid-in-glass thermometers are used.For example, maximum and minimum indicatingthermometers are used in magazines aboardship, for weather observations, and for variousother applications where it is necessary toknow the highest and the lowest temperaturesthat have occurred during a certain intervalof time. One type of maximum indicating thermometeris shown in figure 7-4, and one typeof minimum indicating thermometer is shownin figure 7-5.The maximum indicatingthermometer shownin figure 7-4 is a mercury thermometer witha special constriction in the bore. When thetemperature rises, the pressure of the expandingmercury in the bulb forces mercury pastthe constriction in the bore. When the temperaturefalls, the mercury does not return to thebulb. Why? Even if the thermometer were in anupright position, the constriction in the borewould prevent the normal return flow of mercuryby gravity in addition, the maximum indicatingthermometer is mounted with the bulb a fewdegrees above the horizontal position, so that themercury column slopes downward from the constriction.Thus the thermometer always indicatesthe highest temperature that has beenreached since the instrument was last set. Expansionand contraction of the mercury in thebore above the constriction does occur withtemperature changes, but it is so slight as toCONSTRICTIONSUPPORTLOWER CAREFULLYTO VERTICALPOSITION TO READFigure 7-4.— Maximum indicating thermometer.5.65AINVERT FORSETTINGCURRENT CURRENT & MIN.TEMPERATURENDEXFigure 7-5.—Minimum indicating thermometer.5.65B131

PRINCIPLES OF NAVAL ENGINEERINGbe negligible for most purposes because only avery small amount of mercury is contained inthe very narrow bore.The minimum indicating thermometer shownin figure 7-5 is an alcohol-in-glass thermometerwith an unusually large bore. The upper part ofthe bore is filled with air underpressure to helpprevent evaporation of the alcohol. The thermometeris mounted with the bulb a few degreesbelow the horizontalposition. A dumbbell-shapedpiece of black glass (called an index ) is thedevice that makes possible a reading of the minimumtemperature that has occurred since thethermometer was last set. As the temperatureincreases, the alcohol readily flows upward pastthe index without moving it. As the temperaturedecreases, the retreating alcohol column flowspast the index until the top of the column touchesthe upper end of the index. With a further decreasein temperature, the alcohol retreats stillmore and surface tension causes the index tobecarried along down with the column. If the temperatureincreases again, the index is left undisturbedat its lowest point while the alcoholcolumn rises again. Thus the top of the indexalways indicates the lowest temperature that hasoccurred since the thermometer was last set.BIMETALLIC EXPANSION THERMOM-ETER.— Bimetallic expansion thermometersmake use of the fact that different metals havedifferent coefficients of linear expansion. Theessential element in a bimetallic expansionthermometer is a bimetallic strip consisting oftwo layers of different metals fused together.When such a strip is subjected to temperaturechanges, one layer expands or contracts morethan the other, thus tending to change the curvatureof the strip.The basic principle of a bimetallic expansionthermometer isillustrated in figure 7-6. Whenone end of a straight bimetallic strip is fixed inplace, the other end tends to curve away from theside that has the greater coefficient of linearexpansion when the strip is heated.COLDTHIS METAL HAS GREATERCOEFFICIENT OF LINEAREXPANSIONTHIS METAL HAS-SMALLER COEFFICIENTOF LINEAR EXPANSION147.53Figure 7-6.— Effect of unequal expansion ofbimetallic strip.For use in thermometers, the bimetallicstrip is normally wound into a flat spiral (fig.7-7), a single helix, or a multiple helix. Theend of the strip that is not fixed in position isfastened to the end of a pointer which movesover a circular scale. Bimetallic thermometersare easily adapted for use as recording thermometers;a pen is attached to the pointer andis positioned in such a way that it marks on arevolving chart.Bimetallic thermometers used aboard shipare normally used in thermometer wells. Thewells are interchangeable with those used formercury-in-glass thermometers.FILLED-SYSTEMTHERMOMETERS.-Ingeneral, filled-system thermometers are designedfor use in locations where the indicatingpart of the instrument must be placed somedistance away from the point where the temperatureis to be measured.' For this reasonthey are often called distant- reading thermometers.A filled-system thermometer (fig. 7-8) consistsessentially of a hollow metal sensing bulbThe coefficient of linear expansion is defined as thechange In length per unit length per degree change intemperature. As is apparent from this definition, thenumerical value of the coefficient of linear expansionis independent of the units in which the length is expressedbut is not independent of the temperature scalechosen.This is not true of all filled-system thermometers.In a few designs the capillary tubing is extremely shortand in a few it is nonexistent. In general, however,filled-system thermometers are designed to be distant-readingthermometers, and most of them do infact serve this purpose. Some distant-reading thermometersmay have capillaries as long as 125 feet.132

Chapter 7— PRINCIPLES OF MEASUREMENTat one end of a small-bore capillary tube, connectedat the other end to a Bourdon tube or otherdevice which responds to volume changes or topressure changes. The system is partially orcompletely filled with afluid which expands whenheated and contracts when cooled. The fluid maybe a gas, mercury, an organic liquid, or a combinationof liquid and vapor.The device usually used to indicate temperaturechanges by its response to volume changesor to pressure changes is called a Bourdontube. " A Bourdon tube is a curved or twistedtube which is open at one end and sealed at theother. The open end of the tube is fixed in positionand the sealed end is free to move. Thetube is more or less elliptical in cross section;it does not form a true circle. The cross sectionof a noncircular tube which is sealed at one endtends to become more circular when there is anincrease in the volume or in the internal pressureof the contained fluid, and this tends tostraighten the tube. Opposing this action, thespring action of the tube metal tends to coil thetube.^ Since the open end of the Bourdon tubeis rigidly fastened, the sealed end moves asthe volume or pressure of the contained fluidchanges. When a pointer is attached to the sealedend of the tube through appropriate linkages,and when the assembly is placed over an appropriatelycalibrated dial, the result is a Bourdontubegage that may be used for measuring temperatureor pressure, depending upon the designof the gage and the calibration of the scale.Bourdon tubes are made in several shapesfor various applications. The C- shaped Bourdontube shown in figure 7-9 is perhaps the mostcommonly used type; spiral and helical Bourdontubes are used where design requirements includethe need for a longer length of Bourdontube.There are two basic types of filled-systemthermometers: those in which the Bourdon tuberesponds primarily to changes in the volume of147.54Figure 7-7.— Bimetallic thermometer(flat spiral element).the filling fluid and those in which the Bourdontube responds primarily to changes in the pressureof the filling fluid. Obviously, there isalways some pressure effect in volumetricthermometers and some volumetric effect in8Bourdon tubes are sometimes called Bourdon springs,Bourdon elements , or simply Bourdons . Other devicessuch as bellows or diaphragms are used in somefilled-system thermometers, but they are by no meansas common as the Bourdon tube for this application.9 The precise nature of Bourdon-tube movement withpressure and volume changes is extremely complexand not completely describable in purely analyticalterms. Bourdon-tube instruments are designed forspecific applications on the basis of a series of empiricalobservations and tests.61.28XFigure 7-8.— Distant- reading Bourdon-tubethermometer.133

PRINCIPLES OF NAVAL ENGINEERINGBOURDONTUBE- SEALED END(FREE TO MOVE)TIPTRAVELjunction) and the reference junctions (cold junctions),the indicating instrument can be markedoff to indicate degrees of temperature eventhough it is actually measuring emf's. The indicatinginstrument is a millivoltmeter or someother electrical device capable of measuringand indicating small direct-current emf's. Thestrips or wires of dissimilar metals are welded,twisted, fused, or otherwise firmly joined together.The extension leads are usually of thesame metals as the thermocouple itself.PRESSURECONNECTIONSTATIONARYSOCKET38.211(147B)Figure 7-9.— C-shaped Bourdon tube.pressure thermometers; the distinction dealswith the major response of the Bourdon tube.PyrometersThe term pyrometer is used to include anumber of temperature measuring deviceswhich, in general, are suitable for use at relativelyhigh temperatures; some pyrometers,however, are also suitable for use at low temperatures.The types of pyrometers we areconcerned with here include thermocouplepyrometers, resistance thermometers, radiationpyrometers, and optical pyrometers.THERMOCOUPLE PYROMETERS.-The operationof a thermocouple pyrometer (sometimescalled a thermoelectric pyrometer ) is based onthe observed fact that an electromotive force(emf)lO is generated when the two junctions oftwo dissimilar metals are at different temperatures.A simple thermocouple is illustrated infigure 7-10. Since the electromotive force generatedis proportional to the temperature differencebetween the measuring junction (hotBasic information on electricity is given in chapter20 of this text.METAL AMETAL 8REFERENCE JUNCTIONS(COLD JUNCTIONS)EXTENSIONLEADSINDICATINGINSTRUMENT(MILLIVOLTMETER,POTENTIOMETER,ETC.)147.55Figure 7-10.— Simple thermocouple.RESISTANCETHERMOMETERS. -Resistancethermometers are based on the principlethat the electrical resistance of a metal changeswith changes in temperature. A resistance thermometeris thus actually an instrument whichmeasures electrical resistance but which iscalibrated in degrees of temperature rather thanin units of electrical resistance.The sensitive element in a resistance thermometeris a winding of small diameter nickel,platinum, or other metallic wire. The resistancewinding is located in the lower end of a bulb(sometimes called a stem ); it is electrically butnot thermally insulated from the stem. The resistancewinding is connected by two, three, orfour leads to the circuit of the indicating instrument.The circuit is a Wheatstone bridge or someother simple circuit which contains known resistanceswith which the resistance of the thermometerwinding is compared.RADIATION AND OPTICAL PYROMETERS.-Radiation and optical pyrometers are used tomeasure very high temperatures. Both types ofpyrometers measure temperature by measuringthe amount of energy radiated by the hot object.The main difference between the two types is intheir range of sensitivity; radiation pyrometersare (theoretically, at least) sensitive to the134

Chapter 7-PRINCIPLES OF MEASUREMENTentire spectrum of radiant energy, while opticalpyrometers are sensitive to only one wavelengthor to a very narrow band of wavelengths.Figure 7-11 illustrates schematically thegeneral operating principle of a simple radiationpyrometer. Radiant energy from the hotobject is concentrated on the detecting deviceby means of a lens or, in some cases, a conicalmirror or a combination of mirror and lens.The detecting device may be a thermocouple, athermopile (that is, a group of thermocouplesin series), a photocell, or some other elementin which some electrical quantity (emf, resistance,etc.) varies as the temperature of thehot object varies. The meter or indicated partof the instrument may be a millivoltmeter orsome similar device.An optical pyrometer measures temperatureby comparing visible light emitted by the hotobject with light from a standard source. Acommon type of optical pyrometer is shown infigure 7-12. This instrument consists of aneyepiece, a telescope which contains a filamentsimilar to the filament of an electric light bulband a potentiometer.The person operating the optical pyrometerlooks through the eyepiece and focuses thetelescope on the hot object, meanwhile alsoobserving the tin glowing filament across thefield of the telescope. While watching the hotobject and the filament, the operator adjuststhe filament current (and consequently thebrightness of the filament) by turning a knob onthe potentiometer until the filament seems todisappear and to merge with the hot object.When the filament current has been adjustedso that the filament just matches the hot objectin brightness, the operator turns another knobslightly to balance the potentiometer. The potentiometermeasures filament current but the dialis calibrated in degrees of temperature. As maybe noted from this description, this type of opticalpyrometer requires a certain amount of skilland judgment on the part of the operator. Insome other types of optical pyrometers, automaticoperation is achieved by use of photoelectriccells arranged in a bridge network.MEASUREMENT OF PRESSUREPressure, like temperature, is one of thebasic engineering variables and one that mustfrequently be measured aboard ship. Before takingup the devices used to measure pressure, letus consider certain definitions that are importantin any discussion of pressure measurement,PRESSURE DEFINITIONSPressure is defined as force per unit area.The simplest pressure units are ones thatindicate how much force is applied to an areaof a certain size. These units include poundsper square inch, pounds per square feet, ouncesper square inch, newtons per square millimeter,and dynes per square centimeter, depending uponthe system being used.You will also find another kind of pressureunit, and this type appears to involve length.These units include inches of water, inches ofmercury (Hg), and inches of some other liquidof known density. Actually, these units do notinvolve length as a fundamental dimension.Rather, length is taken as a measure of forceor weight. For example, a reading of 1 inch ofwater (1 in. H2O) means that the exerted pressureis able to support a column of water 1 inchDETECTING ELEMENT(THERMOPILE, PHOTOCELL, ETC.)PEEPHOLEINDICATING INSTRUMENT(MILLIVOLTMETER, POTENTIOMETER,ETC.)Figure 7-11.— Simple radiation pyrometer.147.56135

PRINCIPLES OF NAVAL ENGINEERINGFigure 7-12. — Optical pyrometer.102. 20Xhigh, or that a column of water in a U-tubewould be displaced 1 inch by the pressure beingmeasured. Similarly, a reading of 12 inches ofmercury (12 in. Hg) means that the measuredpressure is sufficient to support a column ofmercury 12 inches high. What is really beingexpressed (even though it is not mentioned in thepressure unit) is the fact that a certain quantityof material (water, mercury, etc.) of knowndensity will exert a certain definite force upona specified area. Pressure is still force perunit area, even if the pressure unit refers toinches of some liquid.It is often necessary to convert from onetype of pressure unit to another. Complete conversiontables may be found in many texts andhandbooks. Conversion factors for pounds persquare inch, inches of mercury, and inches ofwater are:1 in. Hg= 0.49 psi1 psi = 2.036 in. Hgin. H2O:1 psi0.036 psi27.68 in. HoO1 in. H2O1 in. Hg0.074 in. Hg13.6 in. HgOIn interpreting pressure measurements, agreat deal of confusion arises because the zeropoint on most pressure gages represents atmosphericpressure rather than zero absolutepressure. Thus it is often necessary to specifythe kind of pressure being measured under anygiven conditions. To clarify the numerous meaningsof the word pressure, the relationshipsamong gage pressure, atmospheric pressure,vacuum, and absolute pressure, is illustratedin figure 7-13.Gage Pressure is the pressure actually shownon the dial of a gage that registers pressure ator above atmospheric pressure. An ordinarypressure gage reading of zero does not meanthat there is no pressure in the absolute sense;rather, it means that there is no pressure inexcess of atmospheric pressure.Atmospheric pressure is the pressure exertedby the weight of theatmosphere. At sea level,the average pressure of the atmosphere is136

HChapter 7-PRINCIPLES OF MEASUREMENTabsolutepressure"(PSIA)30PSIA4.7 PSIAPSIAPRESSURE RELATIONSHIPATMOSPHERIC PRESSURE(AVERAGE AT SEA LEVEL)15.3 PSIG GAGE^PRESSURE(PSIG)OPSIGOIn.Hg,29.92 In.g>. VACUUM(In.Hg.)147.181Figure 7-13.— Relationships among gage pressure,atmospheric pressure, vacuum, andabsolute pressure.sufficient to hold a column of mercury at theheight of 76.0 millimeters or 29.92 inches ofmercury. Since a column of mercury 1 inch highexerts a pressure of 0.49 pound per square inch,a column of mercury 29.92 inches high exerts apressure that is equal to 29.92 x 0.49, or approximately14.7 psi. Since we are dealing now inabsolute pressure, we say that the averageatmospheric pressure at sea level is 14.7 poundsper square inch absolute . It is zero on theordinary pressure gage.Notice, however, that the figure of 14.7pounds per square inch absolute (psia) representsthe average atmospheric pressure at sealevel, and does not always represent the actualpressure being exerted by the atmosphere at themoment that a gage is being read.Barometric pressure is the term used todescribe the actual atmospheric pressure thatexists at any given moment. Barometric pressuremay be measured by a simple mercurycolumn or by a specially designed instrumentcalled an aneroid barometer.A space in which the pressure is less thanatmospheric pressure is said to be undervacuum. The amount of vacuum is expressed interms of the difference between the absolutepressure in the space and the pressure of theatmosphere. Most commonly, vacuum is expressedin inches of mercury, with the vacuumgage scale marked from to 30 inches of mercury.When a vacuum gage reads zero, the pressurein the space is the same as atmosphericpressure— or, in other words, there is novacuum. A vacuum gage reading of 29.92 inchesof mercury would indicate a perfect (or nearlyperfect) vacuum. In actual practice, it is impossibleto obtain a perfect vacuum even underlaboratory conditions.Absolute pressure is atmospheric pressureplus gage pressure or minus vacuum. For example,a gage pressure of 300 psig equals anabsolute pressure of 314.7 psia (300 +14.7). Or,for example, consider a space in which themeasured vacuum is 10 inches of mercuryvacuum; the absolute pressure in this spacemust then be 19.92 or approximately 20 inchesof mercury absolute. It is important to note thatthe amount of pressure in a space under vacuumcan only be expressed in terms of absolutepressure.You may have noticed that sometimes we saypsig to indicate gage pressure and other timeswe merely say psi. By common convention, gagepressure is always assumed when pressure isgiven in pounds per square inch, pounds persquare foot, or similar units. The "g" (forgage) is added only when there is some possibilityof confusion. Absolute pressure, on theother hand, is always expressed as pounds persquare inch absolute (psia), pounds per squarefoot absolute (psfa), and so forth. It is alwaysnecessary to establish clearly just what kind ofpressure we are talking about, unless this isvery clear from the nature of the discussion.To this point, we have considered only themost basic and most common units of measurement.It is important to remember that hundredsof other units can be derived from these units,and that specialized fields require specializedunits of measurement. Additional units of measurementare introduced in appropriate placesthroughout the remainder of this training manual.When you encounter more complicated unitsof measurement, you may find it helpful to reviewthe basic information given here previously.PRESSURE MEASURING DEVICESMost pressure measuring devices usedaboard ship utilize mechanical pressure137

.PRINCIPLES OF NAVAL ENGINEERINGelements. 1^ There are two major classes ofmechanical pressure elements: (1) liquid-columnelements, and (2) elastic elements.Liquid-Column ElementsVACUUMrr^Liquid-column pressure measuring elementsinclude the devices commonly referred to asbarometers and manometers. Liquid-columnelements are simple, reliable, and accurate.They are used particularly (although not exclusively)for the measurement of relatively lowpressures or small pressure differentials.Liquids commonly used in this type of pressuregage include mercury, water, and alcohol.One of the simplest kinds of liquid-columnelements is the fixed-cistern barometer (fig. 7-14) which is used to measure atmospheric pressure.Mercury is always used as the liquid inthis type of instrument. Atmospheric pressureacts upon the open surface of the mercury inthe cistern. Since the tube is open at the cisternend, and since there is a vacuum above themercury in the tube, the height of the mercuryin the tube is at all times an indication of theexisting atmospheric (barometric) pressure.A simple U-tube liquid-column element formeasuring absolute pressure is shown in figure7-15. The liquid used in this device is mercury.There is a vacuum above the mercury at theclosed end of the tube; the open end of the tubeis exposed to the pressure to be measured. Theabsolute pressure is indicated by the differencein the height of the two mercury columns.Manometers are available in many differentsizes and designs. Some are installed in sucha way that the U-tube is readily recognizable,as in part A of figure 7-16; but in some designsthe U-tube is inverted or inclined at an angle.The so-called single-tube or straight-tubemanometer (part B of fig. 7-16) is actually aU-tube in which only one leg is made of glass.MERCURY-ATMOSPHERICPRESSUREATMOSPHERICPRESSURE ININCHES OFMERCURY3025

Chapter 7-PRINCIPLES OF MEASUREMENTPRESSURE.BEING-MEASUREDHEIGHTOFMERCURYCOLUMNfl--VACUUMMERCURY7-17, 7-18, and 7-19 has only one Bourdon tubeand measures only one pressure. (The pointermarked RED HAND in figure 7-17 is a manuallypositioned hand that is set to the normal workingpressure of the machinery or equipment onwhich the gage is installed; the hand markedPOINTER is the only hand that moves in responseto pressure changes.)When two Bourdon tubes are mounted in asingle case, with each mechanism acting independentlybut with the two pointers mounted ona common dial, the assembly is called a duplexgage. The dial of a duplex gage is shown infigure 7-20. The two Bourdon tubes and theoperating mechanism are shown in figure 7-21,and the gear mechanism is shown in figure 7-22. Note that each Bourdon tube has its ownpressure connection and its own pointer. Duplexgages are used to give simultaneous indicationof the pressure at two different locations.Bourdon-tube vacuum gages are marked offin inches of mercury, as shown in figure 7-23.147.57Figure 7-15.— U-tube liquid-column element formeasuring absolute pressure.RED HANDPOINTER_ien,61. 4XFigure 7-16. — Two types of manometers.(A) Standard U-tube. (B) Single-tube.B38.211BXFigure 7-17.— Dial of a simplex Bourdon-tubepressure gage.139

PRINCIPLES OF NAVAL ENGINEERINGBOURDON TUBEHAIRSPRINGSECTOR GEARCASESEALED ENDCONNECTINGLINKM V E M E NT^''''^^^^^HKSUPPORT-^ ^^^^IHFIXED end/ /STATIONARY OPEN END

Chapter 7-PRINCIPLES OF MEASUREMENT38.211CAFigure 7-22.— Gear mechanism of duplexBourdon-tube pressure gage.1510 20r25-

PRINCIPLES OF NAVAL ENGINEERINGSCALEHAIRSPRINGSECTORELLOWSCASEPRESSURECONNECTION61.3(147B)AFigure 7-26.— Simple bellows gage.38.211KXFigure 7-25. — Bourdon-tube differentialpressure gage.Although some bellows-type instruments canbe designed for measuring pressures up to 800psig, their primary application aboard ship isin the measurement of quite low pressures orsmall pressure differentials. For example,bellows elements are widely used in boilercontrol systems^2 because the air pressures ofthe control systems are generally very low.Many differential pressure gages are of thebellows type. In some designs, one pressure isapplied to the inside of the bellows and the otherpressure is applied to the outside. In otherdesigns, a differential pressure reading is obtainedby opposing two bellows in a single case.Bellows elements are used in various applicationswhere the pressure-sensitive devicemust be powerful enough to operate not only theindicating pointer but also some type of recordingdevice.DIAPHRAGM ELASTIC ELEMENTS.-Diaphragmelastic elements are used for themeasurement of relatively low pressures or^^Boiler control systems are discussed in chapter 11of this text.142

Chapter 7-PRINCIPLES OF MEASUREMENTsmall pressure differences. Both metallic andnonmetallic diaphragms are in common use.Metallic diaphragms are made from stainlesssteel, phosphor bronze, brass, or othermetal. A metallic diaphragm element may consistof one or more capsules. Each capsuleconsists of two diaphragm shells (flat or corrugatedcircular disks) which are welded, brazed,or otherwise firmly fastened together to formthe capsule. The capsules are all rigidly connectedso that the applicationof pressure causesall capsules to deflect. The amount of deflectionof a diaphragm gage depends upon thenumber of capsules, the design and the numberof the corrugations, and other factors.Nonmetallic diaphragms, also called slackor limp diaphragms, are made of leather,treated cloth, neoprene, or some other softmaterial. Nonmetallic diaphragms are springloaded.One common type of nonmetallic diaphragmpressure gage is shown in figure 7-27.When pressure is applied to the underside ofthe slack diaphragm, the diaphragm moves upward,although it is opposed by the action of thecalibrating spring. As the spring moves, thelinkage system causes the pointer to move to ahigher reading. Thus the reading on the scaleis proportional to the amount of pressure exertedon the diaphragm, even though the movementof the diaphragm is opposed by the calibratingspring.HAIRSPRINGSCALEPRESSURECONNECTIONCONNECTINGLINKPRESSURE GAGE INSTALLATIONBourdon tube pressure gages used for steamservice are always installed in such a way thatthe steam cannot actually enter the gage. Thistype of installation is necessary to protect theBourdon type from very high temperatures. Anexposed uninsulated coil is provided in the lineleading to the gage, and the steam condensesinto water in this exposed coil. Thus thereis always a condensate seal between the gageand the steam line.Pressure gage connections are normallymade to the top of the pressure line or to thehighest point on the machinery in which thepressure is to be measured. Pressure gagesare usually mounted on flat-surfaced gageboards in such a way as to minimize virbration;this is a matter of considerable importance,since some ships experience very great structuralvibration from screws and machinery.Efforts are currently beingmade to design gagescapable of withstanding any vibration that may38.212(147B)Figure 7-27.— Nonmetallic diaphragmpressure gage,be expected from machinery. Pressure gagesdesigned to withstand shock and vibration frequentlyuse small size capillary tubing betweenthe connections and the elastic elements toprotect the gage mechanism and the pointer;small size tubing is used between the test connectionor gage valve and the gage so that pipingdeflections will not cause errors in the gagereadings,MEASUREMENT OF FLUID FLOWA great many devices, many of them quiteingenious, have been developedfor the measurementof fluid flow. The discussion here is concernedprimarily with the types of fluid flowmeasuring devices that find relatively wideapplication in shipboard engineering. These143

PRINCIPLES OF NAVAL ENGINEERINGdevices may be classified as (1) positive-displacementmeters, (2) head meters, and (3) areameters.POSITIVE-DISPLACEMENT METERSPositive-displacement meters are used formeasuring liquid flow. In a meter of this type,each cycle or complete revolution of a measuringelement displaces a definite, fixed volumeof liquid. Measuring elements used in positivedisplacementmeters include disks, pistons,lobes, vanes, and impellers. The motion of thesedevices may be classified as reciprocating,rotating, oscillating, or nutating, depending uponthe type of measuring element used and thegeneral design of the meter read-out or register.A positive-displacement meter of the nutating-pistontype is shown in figure 7-28. Theflow of oil through the meter causes the piston(also ca disk) to move with a nutatingmotion. Understanding the nature of this motionis the key to understanding the operation of themeter. A nutating motion (fig. 7-29) might bedescribed as a "rocking around" motion; it issimilar to the motion of a spun coin just beforethe coin settles flat on its side. The piston inthe meter cannot settle flat on its side like aspun coin, since the piston is nutating (or rockingaround) on a lower spherical bearing surface.38.64XFigure 7-28.— Nutating-piston meter formeasuring liquid flow.38.66XFigure 7-29.— Diagram showing nutating motionof piston and rotary motion of pin in nutatingpistonmeter.The piston cannot rotate because it is heldin place by a fixed vane or guide that runsvertically through a slot in the piston. However,the nutating motion of the piston imparts arotary motion to the pin that projects from theupper spherical surface. The rotary movementof the pin rotates the gears, and the movementof the gears actuates a counting device or registerat the top of the meter.Although the action of the nutating pistonis smooth and continuous, there is neverthelessa definite cycle involved in the measurementof liquid flow through this meter. Thenutating action of the piston seals the measuringchamber off into separate compartments, andthese compartments are alternately filled andemptied. The meter is properly classed as apositive-displacement meter, since each compartmentholds a definite volume of the liquid.Totalizing meters have a read-out in gallonsor pounds of liquid; however, they may also144

Chapter 7-PRINCIPLES OF MEASUREMENTindicate rate of flow in gallons per minute (gpm)or in other flow units.HEAD METERSHead meters measure fluid flow by measuringthe pressure differential across a speciallydesigned restriction in the flow line. The restrictionmay be an orifice plate, a flow nozzle,a venturi tube, an elbow, a pitot tube, or somesimilar device. As the fluid flows toward therestriction, the velocity decreases and the pressure(or "head") increases; as the fluid flowsthrough the restriction, the velocity increasesand the pressure decreases. Figure 7-30 illustratesthe pressure changes that occur as a fluidflows through a line that contains an orificeplate or similar restriction. Note that there isa slight increase in pressure just ahead of therestriction and then a sudden drop in pressureat the restriction. The point of minimum pressureand maximum velocity is slightly downstreamfrom the restriction; this point is calledthe vena contracta . Beyond the vena contracta,the velocity decreases and the pressure increasesuntil eventually normal flow is reestablished.The flow nozzle, orifice plate, or otherrestriction in the line is called the primaryelement of the head meter. A high pressure tapupstream from the restriction and a low pressuretap downstream from it are connected toa differential bellows, a diaphragm, or someother device for measuring differential pressure.The pressure drop occurring in a fluid flowingthrough a restriction varies as the square ofthe fluid velocity; or, to put it another way, thesquare root of the pressure differential is proportionalto the rate of fluid flow. Because of thesquare-root relationship between the pressuredifferential and the rate of fluid flow, a squarerootextracting device is usually included so thatthe scale can be graduated in even steps or increments.Without a device for extracting thesquare root of the pressure differential, thescale would have to be unevenly divided, withwider divisions at the top of the scale than atthe bottom.AREA METERSAn area meter indicates the rate of fluidflow by means of an orifice that is varied inarea by variations in the fluid flow. The variationsin the area of the orifice are producedby some type of movable device which is positionedby the pressure of the flowing fluid. Sincethe fluid itself positions the movable device andthus varies the area of the orifice, there is nosignificant pressure drop between the upstreamside and the downstream side of the variableorifice. Since there is an essentially linearrelationship between the area of the orifice andthe rate of flow, there is no need for a squarerootextracting device in an area meter.ORIFICE PLATEDIRECTION OF FLOW^FLANGESFigure 7-30.— Pressure changes in fluid flowing through restriction in line.147.59145

PRINCIPLES OF NAVAL ENGINEERINGMost area meters are classified as (1) rotameters,or (2) piston-type meters, dependingupon the type of device used to vary the area ofthe orifice.Figure 7-31 shows a simple rotameter of atype used in some shipboard distilling plants.A tapered glass tube is installed vertically,with the smaller end at the bottom. Water flowsin at the bottom, upward through the tube, andout at the top. A rod, supported by the end fittingsof the tube, is centered in the tube. Amovable rotor rides freely on the rod and ispositioned by the fluid. Variations in the pressureof the fluid lead to variations in the positionof the rotor; and, since the glass tube istapered, the size of the annular orifice betweenthe rotor and the tube is different at each positionof the rotor. An increase in flow is thusFLOWSCHEMATIC75.290Figure 7-31.— Area meter (rotameter type) formeasuring fluid flow.indicated by the rotor rising on the rod. Theglass tube is so calibrated that the flow may beread directly, with the reading being taken atthe top of the rotor.In a piston-type area meter, a piston islifted by fluid pressure. As the piston is lifted,it uncovers a port through which the fluid flows.The port area uncovered by the lifting of thepiston is directly proportional to the rate offluid flow. Therefore, the position of the pistonprovides a direct indication of the rate of flow.The means by which the position of the piston istransmitted to an indicating dial varies accordingto the design of the particular meter andthe service for which it is intended.MEASUREMENT OF LIQUID LEVELIn the engineering plant aboard ship, it isfrequently necessary for operating personnel toknow the level of various liquids in variouslocations. The level of the water in the ship'sboilers is a prime example of a liquid level thatmust be known at all times, but there are otherliquid levels that are also important—the levelof fuel oilin service and stowage tanks, the levelof water in deaerating feed tanks, the level oflubricating oil in the oil sumps of main andauxiliary machinery, and drains in various draintanks, to name but a few.A wide variety of devices, some of themsimple and some complex, are available formeasuring liquid level. Some measure liquidlevel quite directly by measuring the height of acolumn of liquid. Others measure pressure,volume, or some other property of the liquidfrom which we may then infer liquid level.The gage glass is one of the simplest kindsof liquid level measuring devices and one that isvery commonly used. Gage glasses are used onboilers, on deaerating feed tanks, on inspectiontanks, and on other shipboard machinery. Basically,a gage glass is just one leg of a U-tube,with the other leg being the tank, drum, or othervessel in which the liquid level is to be measured.The liquid level in the gage glass is thusthe same as the liquid level in the tank or drum,and the reading can be made by direct visualobservation. Gage glasses vary in details ofconstruction, depending upon the pressure, temperature,and other service conditions they mustwithstand.The measurement of liquid level in tanksaboard ship may be accomplished by simpledevices such as direct-reading sounding rules146

Chapter 7-PRINCIPLES OF MEASUREMENTand gaging tapes or by some form of permanentlyinstalled, remote reading gaging system. (Althoughremote reading gaging systems are oftenreferred to as "tank level indicators," it shouldbe noted that the scale may be calibrated toshow level, volume, or weight; frequently thereare two scales— one to show volume and one toshow level.)A static head gaging system of a type commonlyused for measuring liquid level in fueloil tanks aboard ship is shown in figure 7-32.This system balances a head of liquid in thetank against a column of liquid in a manometeror against a bellows or diaphragm differentialpressure unit; the system illustrated uses amercury manometer. The balance chamber islocated so that its orifice is near the bottomof the tank; a line connects the top of the balancechamber to the mercury-filled bulb of theindicator gage, and another line connects thespace above the mercury column to the top ofthe tank. Since the height of the liquid in thetank bears a definite relationship to the pressureexerted by the liquid, the scale can becalibrated to show height (or liquid level). Whenthe size of the tank is known, the measurement ofheight can readily be converted to measurementof volume; and, when the volume of the tank andthe specific weight of the liquid are known, thescale can be calibrated to indicate weight. Thereading on this type of tank gaging system isalways taken after compressed air has beenadmitted to the balance chamber through thecontrol valve; to ensure proper readings, asufficient amount of compressed air must beadmitted to force the liquid down to the level ofthe bottom of the standpipe.MEASUREMENT OF ROTATIONALSPEEDThe rotational speed of propeller shafts,turbines, generators, blowers, pumps, and otherkinds of shipboard machinery is measured bymeans of tachometers. For most shipboardmachinery, rotational speed is expressed inrevolutions per minute (rpm). The tachometersmost commonly used aboard ship are of thecentrifugal type, the chronometric type, and theresonance type. Stroboscopic tachometers arealso used occasionally.Some types of machinery are equipped withpermanently mounted tachometers, but portabletachometers are used for checking the rpm ofmany units. A portable tachometer of the centrifugaltype or of the chronometric type isapplied manually to a depression or a projectionat the center of a moving shaft. Each portabletachometer is supplied with several hardrubber tips; to use the instrument, the operatorselects a tip of the proper shape, fits it over theend of the tachometer drive shaft, and holds theSometip against the center of the moving shaft.tachometers are also supplied with a smallwheel which can be fitted to the end of the driveshaft and used to measure the linear velocity(in feet per second) of a wheel or a journal; withthis type of instrument, the wheel is held againstthe outer surface of the moving object. Portabletachometers are used only for intermittent reading,not for continuous operation.CENTRIFUGAL TACHOMETERSCOMPRESSED AIR SUPPLYBALANCE CHAMBER-ORIFICE'w/>/m/?Mwy7;ĀM61. 5XFigure 7-32.— Tank gaging system.As the name implies, a centrifugal tachometerutilizes centrifugal force for its operation.The main parts of a centrifugal tachometer areshown in figure 7-33 and the dial of the instrumentis shown in figure 7-34. Centrifugal forceacts upon weights or flyballs which are connectedby linkage to an upper and a lower collar. Theupper collar is fixed to the drive shaft, but the147

PRINCIPLES OF NAVAL ENGINEERING:,5r«2i^;^S4^ra;-,-- -FIXED-MOVABLECOLLARDRIVESHAFT2.66XFigure 7-33.— Main parts of centrifugaltachometer.lower collar is free to move up and down theshaft. A spring which fits over the drive shaftconnects the upper collar and the lower collar.As the drive shaft begins to rotate, the flyballsspin around with it. Centrifugal force tends topull the flyballs away from the center, thusraising the lower collar and compressing thespring. The lower collar is connected to thepointer, and the upward movement of the collarcauses the pointer to move to a higher rpm readingon the dial. The centrifugal tachometer registersrpm of a rotating shaft as long as it is incontact with the shaft. For this reason it is calleda constant-reading tachometer.CHRONOMETRIC TACHOMETERSA chronomotric tachometer (fig. 7-35) is acombination of a watch and a revolution counterwhich measures the average number of revolutionsper minute of a rotating shaft. The deviceis not a constant-reading instrument; the outerdrive shaft runs free when the instrument isapplied to a rotating shaft until a starting buttonis depressed to start the timing element. Afterthe drive shaft has been disengaged from therotating shaft, the pointer remains in position onthe dial until it is returned to the zero positionby the operation of a reset button (which may bethe same as the starting button.)RESONANCE TACHOMETERSA resonance tachometer (fig. 7-36) consistsof a number of steel reeds, each one of which2.66XFigure 7-34.— Dial of centrifugal tachometer.2.66XFigure 7-35.— Chronometric tachometer.148

Chapter 7-PRINCIPLES OF MEASUREMENTThe instruments give continuous readings andmake very rapid— almost instantaneous— adjustmentsto changes in rotational speed.STROBOSCOPIC TACHOMETERS61.16XFigure 7-36.— Resonance tachometer mountedon rotating machine.vibrates at a different frequency. The reeds arefastened in a row, in order of frequency; the rowis mounted with the reeds at right angles to theback of the instrument. The unattached ends ofthe reeds extend through a horizontal slit in theface of the instrument; the scale is stampedalong the slit. When the instrument is solidlyattached to the foundation or casing of a rotatingmachine, the reeds which are nearest in frequencyto the rpm of the machine begin tovibrate. In figure 7-36, notice that five reedsare out of line with the rest of the reeds; thesefive are vibrating noticeably more than theothers, and the one in the middle is vibratingmore than the other four. To read the rpm ofthe machine, then, it is only necessary to readthe scale marking underneath the reed that isvibrating the most— that is, the one which ismost out of line with the others in the horizontalslit.Resonance tachometers are particularly usefulfor measuring high rotational speeds such asthose that occur in turbines, generators, andforced draft blowers. They are also particularlyuseful in applications where it is difficult orimpossible to get at the moving ends of shafts.A stroboscopic tachometer is a device whichallows rotating, reciprocating, or vibrating machineryto be viewed intermittently, under flashinglight, in such a way that the movement ofthe machinery appears to be slowed, stopped,or reversed. Because the illumination is intermittent,rather than steady, the eye receives aseries of views rather than one continuous view.When the speed of the flashing light coincideswith the speed of the moving machinery,the machinery appears to be motionless. Thiseffect occurs because the moving object is seeneach time at the same point in its cycle of movement.K the flashing rate is decreased slightly,the machinery appears to be moving slowly inthe true direction of movement; if the flashingrate is increased slightly, the machinery appearsto be moving slowly in the reverse direction.To measure the speed of a machine,therefore, it is only necessary to find the rateof intermittent illumination at which the machineryappears to be motionless. To observethe operating machinery in slow motion, it isnecessary to adjust the stroboscope until themachinery appears to be moving at the desiredspeed.The stroboscopic tachometer furnished forshipboard use is a small, portable instrument.It is calibrated so that the speed can be readdirectly from the control dial. The flashing rateis determined by a self-contained electronicpulse generator which can be adjusted, by meansof the direct-reading dial, to any value between600 and 14,400 rpm. The relationship betweenrotational speed and flashing rate may be illustratedby an example. If an electric fan is operatingat a rate of 1800 rpm, it will appear to bemotionless when it is viewed through a stroboscopictachometer which is flashing at therate of 1800 times per minute.Because the stroboscopic tachometer isnever used in direct contact with moving machinery,it is particularly useful for measuringthe speed or observing the operation of machinerywhich is run by a relatively small powerinput. It is also very useful for measuring thespeed of machinery which is installed in relativelyinaccessible places.149

PRINCIPLES OF NAVAL ENGINEERINGMEASUREMENT OF SPECIFIC GRAVITYThe specific gravity of a substance is definedas the ratio of the density of the substance tothe density of a standard substance. The standardof density for liquids and solids is purewater; for gases, the standard is air. Eachstandard (water or air) is considered to have aspecific gravity of 1.00 under standard conditionsof pressure and temperature. -"^^ For asolid or a liquid substance, then, we may saythatSp. gr. of solid or liquid=density of substancedensity of waterDensity is sometimes defined as the massper unit volume of a substance and sometimesas weight per unit volume. In engineering,fortunately, this difference in defintions rarelycauses confusion because we are usually interestedin relative densities— or, in other words,in specific gravity. Since specific gravity is theratio of two densities, it really does not matterwhether we use mass densities or weight densities;the units cancel out and give us a purenumber which is independent of the system ofunits used.Aboard ship, it is sometimes necessary tomeasure the specific gravity of various liquids.This is usually done by using a device called ahydrometer . A hydrometer measures specificgravity by comparing the buoyancy (or loss ofweight) of an object in water with the buoyancyof the same object in the liquid being measured.Since the buoyancy of an object is directly relatedto the density of the liquid, then"built in" by the calibration of the hydrometer.For fuel oil and other petroleum products,it is customary to measure degrees API, ratherthan specific gravity, in accordance with a scaledeveloped by the American Petroleum Institute.The relationship between specific gravity andAPI gravity is given by the formulaSp.gr.=141.5131.5 -t- degrees APIA hydrometer of the type normally usedaboard ship to measure the degrees API of fueloil is shown in figure 7-37. The major differencebetween this hydrometer and others usedaboard ship is that this one is calibrated to readdegrees API rather than specific gravity.MEASUREMENT OF VISCOSITYThe viscosity of a liquid is a measure of itsresistance to flow. A liquid is said to have highviscosity if it flows sluggishly, like cold molasses.It is said to have low viscosity if itflows freely, like water. The viscosity of mostliquids is greatly affected by temperature; ingeneral, liquids are less viscous at higher temperatures.Sp. gr. of liquid:buoyant force of liquidbuoyant force of waterA hydrometer is merely a calibrated rodwhich is weighted at one end so that it floats ina vertical position in the liquid being measured.Hydrometers are calibrated in such a way thatthe specific gravity of the liquid may be readdirectly from the scale; in other words, thecomparison between the density of the liquidbeing measured and the density of water is13 For most engineering purposes, the standard pressureand temperature conditions for water as a4.135standard of specific gravity are atmospheric pressureand 60° F. Figure 7-37.— Hydrometer.150

Chapter 7-PRINCIPLES OF MEASUREMENTAboard ship, it is necessary to measure theviscosity of fuel oil and of lubricating oil. Theviscosity of an oil is usually expressed as thenumber of seconds required for a given amountof oil to flow through an orifice of a specifiedsize when the oil is at a specified temperature.Devices used to measure the rate of flow (andhence the viscosity) are called viscosimetersor viscometers .The viscosimeter furnished for shipboarduse is a Saybolt viscosimeter with two orifices.The larger orifice is called the Saybolt Furolorifice; the smaller one is called the SayboltUniversal orifice. The Furol orifice is used formeasuring the viscosity of relatively heavyoils; the Universal orifice is used for measuringthe viscosity of relatively light oils.A Saybolt viscosimeter consists of an oiltube, a constant-temperature oil bath whichmaintains the correct temperature of the samplein the tube, a 60-cc (cubic centimeter) graduatedreceiving flask, thermometers for measuringthe temperature of the oil sample and of theoil bath, and a timing device. A Saybolt viscosimeteris shown in figure 7-38; figure 7-39shows details of the viscosimeter oil tube.The oil to be tested is strained and pouredinto the oil tube. The tube is surrounded by theconstant-temperature oil bath. When the oilsample is at the correct temperature, the corkpulled from the lower end of the tube and theissample flows through the orifice and into thegraduated receiving flask. The time (in seconds)required for the oil to fill the receiving flaskto the 60-cc mark is noted.The viscosity of the oil is expressed byindicating three things: first, the number ofseconds required for .60 cubic centimeters ofoil to flow into the receiving flask; second, thetype of orifice used; and third, the temperatureof the oil sample at the time the viscositydetermination is made. For example, supposethat a sample of Navy Special fuel oil is heatedto 122° F and that 132 seconds are required for60 cc of the sample to flow through a SayboltUniversal orifice and into the receiving flask.The viscosity of this oil is said to be 132 secondsSaybolt Universal at 122° F. This is usuallyexpressed in shorter form as 132 SSU at 122° F.Saybolt Furol viscosities are obtained at122° F. The same temperature (122° F) is usedfor obtaining Saybolt Universal viscosities offuel oil, but various other temperatures areused for obtaining Saybolt Universal viscositiesof oils other than fuel oil. Thus it is importantthat the temperature be included in the statementof viscosity.OTHER TYPES OF MEASUREMENTThus far in this chapter, we have beenlargely concerned with basic principles ofmeasurement and with widely used kinds ofmeasuring devices. We have taken up many ofthe devices used to measure the fundamentalvariables of temperature, pressure, fluid flow,liquid level, and rotational speed, and we haveconsidered the measurement of the propertiesof specific gravity and viscosity. For the mostpart, we have dealt with measuring devices thatmight be considered as basically mechanical innature.Before concluding this chapter, it might bewell to point out that many other kinds of measurementare required in the shipboard engineeringplant. While it is true that many of the principlesof measurement discussed in this chapterapply to measuring devices other than thosedescribed here, it is also true that a specificapplication may require a measuring device thatis not precisely the same as any device we haveconsidered. Where appropriate, other types ofmeasuring devices are discussed in other chaptersof this text, as they relate to some particularkind of machinery or equipment. In some instances,the student may find it helpful to comeback to the present chapter to renew his understandingof the basic principles of measurementwe have considered here.NAVY CALIBRATION PROGRAMThe calibration of all measuring devicesbegins with and is dependent upon the basicinternational and national standards of measurementjust discussed. Obviously, however, wecan't rush off to the National Bureau of Standardsevery time we need to measure a length, a mass,a weight, or an interval of time. Therefore, theNational Bureau of Standards prepares and calibratesa great many practical standards thatcan be used by government and industry. Governmentand industry, in turn, prepare andcalibrate their own practical standards. Thusthere is a continuous linkage of measurementstandards that begins with the internationalstandards, comes down through the nationalstandards, and works all the way on down tothe rulers, weights, clocks, gages, and otherdevices that we use for everyday measurement.151

PRINCIPLES OF NAVAL ENGINEERINGFigure 7-38.— Saybolt viscosimeter.38.213As may be seen (fig. 7-40) in the structureof this program (Navy Calibration Program),the National Bureau of Standards is the highestlevel standards agency in the United States andthat it has custody of this Nation's basic physicalstandards. The National Bureau of Standardsprovides the common reference for all measurementsand certifies the Navy Standards that aremaintained by the Navy Type I Standards Laboratories.The Navy Type I Standards Laboratoriesmaintain the highest standards within the NavyCalibration Program. The Type I StandardsLaboratories obtain calibration services fromthe National Bureau of Standards and providecalibration of standards and associated152

Chapter 7-PRINCIPLES OF MEASUREMENTHEATING OilVESSELCORK38.214Figure 7-39.— Details of viscosimeter tube.measuring equipment received from Type IIStandards Laboratories. There are only twoType I Standards Laboratories: the Eastern SL,in Washington D.C., and the Western SL, in SanDiego, California.Navy Standards Laboratories designated asType II furnish the second highest level of calibrationservices to assigned geographical areaswithin the Naval Establishment. The Tj^De IIStandards Laboratories obtain standards calibrationservices from the cognizant Type IStandard Laboratory and calibrate standardsand associated measuring equipment receivedfrom lower level laboratories. There are halfa dozen Type II Navy Standards Laboratories,located in various shore activities throughoutthe United States.Navy Calibration Laboratories furnish thethird highest level of calibration services in theNavy Calibration Program. The Navy CalibrationLaboratories obtain calibration servicesfrom the Type n Standards Laboratories andthey calibrate test equipment received fromships and from shore activities. There are twobasic types of Navy Calibration Laboratories.Fleet Calibration Laboratories, which are locatedon repair ships and tenders (MIRCS) receiveand calibrate fleet equipment only. ShoreCalibration Laboratories, which are located invarious shore activities of the Navy, receive andcalibrate shore equipment and also handle theoverflow from Fleet Calibration Laboratories.As indicated in figure 7-40 equipment to becalibrated may go directly to a Navy CalibrationLaboratory or it may go to a shop or repairfacility for "qualification." Qualification is notthe same as calibration, and the two termsshould be clearly distinguished.Calibration is the process by which CalibrationLaboratories and Standards Laboratoriescompare a standard or a measuring instrumentwith a standard of higher accuracy in order toensure that the item being compared is accuratewithin specified limits throughout its entirerange. The calibration process involves the useof approved instrument calibration procedures;it may also include any adjustments or incidentalrepairs necessary to bring the standard or instrumentbeing calibrated within specifiedlimits. Calibration of standards is consideredmandatory.Qualification is the process by which anactivity other than officially designated StandardsLaboratories or Calibration Laboratoriescompares a test or measuring instrument withone of higher accuracy in order to determinethe need for calibration. Qualification may beperformed by ships or stations that have beenfurnished with approved measurement standardsand procedures. However, the instruments usedto qualify the test or measuring equipmentshould be calibrated periodically by a NavyStandards Laboratory or a Navy CalibrationLaboratory in order for the qualification to bevalid.Several additional terms used in connectionwith the Navy Calibration Program are definedin the following paragraphs. It is important tounderstand the precise meaning of these termsand to use them correctly.Calibration Procedure is the term used fora document that outlines the steps and operationsto be followed by standards and calibrationlaboratory personnel in the performance ofinstrument calibration.Calibration cycle is the length of time betweencalibration services during which eachtest equipment is expected to maintain reliablemeasurement capability. The Metrology153

PRINCIPLES OF NAVAL ENGINEERINGNATIONAL BUREAU OF STANDARDSNAVY STANDARDS LABORATORIES—TYPE IEASTERN SL, WASHINGTON, D.C.WESTERN SL, SAN DIEGO, CALIF.NAVY STANDARDS LABOR ATORIES— TYPE 3L(SHORE BASED)

Chapter 7-PRINCIPLES OF MEASUREMENTAn acceptance for limited use indicates thatan instrument which has failed certain tests orwhich has not been tested against all acceptancecriteria is nevertheless suitable for certainspecified (limited) usage. In such a situation,a limited use label (rather than a CALIBRATEDor QUALIFIED label) is placed on the instrumentto draw attention to the conditional acceptance.In addition to the label, a limited usetag is attached to the instrument. This tag isfilled in by the servicing activity; it includesa full description of the reservations or precautionswhich should be observed in using theinstrument. The label and the tag indicating thatthe instrument is suitable only for limited usemust remain on the instrument until the nextcalibration or qualification.The term rejected is used when an instrumentfails to meet the acceptance criteria duringcalibration or qualification and when it cannotbe made to meet these criteria by incidentalrepair. Under these conditions, a REJECTEDlabel is placed on the instrument and all otherservicing labels are removed. In addition to thelabel, a REJECTED tag is attached to the instrument.The tag, which is filled in by theservicing activity, gives the reason for rejectionand such other information as may be required.Repair is defined as the repair and/orreplacement of malfunctioning parts of a measuringinstrument or standard to the degreerequired to restore the instrument or standardto an operating condition.Traceability iswhen the accuracy of a measurementmade by the fleet can be directly traceablethrough the echelons of calibration toReference Standards maintained by the NationalBureau of Standards (unbroken chain of properlyconducted calibrations.)INSTRUMENT ACCURACYAs we have seen, all measurement is subjectto a certain amount of error. The internationaland national standards have some error, eventhough it is almost unbelievably small. Theerror in secondary standards, while still extremelysmall, is somewhat greater than theerror in the primary standards. When we getdown to the actual measuring devices used evenfor precision measurement, the error is largerstill.Although it may sound backwards, the accuracyof an instrument is expressed by giving theamount of error of the instrument. For example.an instrument with an accuracy of 1 percent issaid to have an error of ± 1 percent.The error of an instrument is the differencebetween the reading shown on the instrument andthe true value of the variable being measured.Error may be expressed in scale units, in percentof scale span, in percent of range, or inpercent of indicated value (iv). By agreementamong instrument manufacturers, error in instrumentswith uniform scales is most commonlyexpressed as a percentage of the fullscale length, regardless of where the measurementis made on the scale. The exception tothis general rule is that the measurement is notmade at the extreme top or the extreme bottomof the scale, since an instrument is almost sureto be less accurate in these areas than in theworking range of the scale.Using the full scale length as a basis fordetermining instrument error can lead to someconfusion. For example, consider several pressuregages, each one of which has a guaranteedaccuracy of 1 percent. K the scale reads to 30psi, the allowable error is± 0.3 psi. If the scalereads to 100 psi, the allowable error is + 1 psi.If the scale reads to 500 psi, the allowableerror is + 5 psi. If the scale reads to 1000,the allowable error is ±10 psi.As far as accuracy ratios are concerned,there are recommended low and high accuracyratios that should exist between the test andmeasuring equipment, and the measuring systemor Standard, also between echelons of Standards.The lower limit ratio should be at least 4 to1; a ratio below this limit is impracticable fortechnical reasons. The upper limit ratio shouldnot be more than 10 to 1; if the ratio is higher,equipment costs will become excessive.Calibration error is taken care of by linearityand range errors . Linearity error is whenthe lowest and the highest indications are correct,and there is an error in between theseindications. Range error occurs when the lowestindication is on and the highest indication is off,above or below the true value.If an instrument does not give the same readingwhen it comes from the top of the scale downto the point of measurement as it does when itgoes from the bottom of the scale up to the pointof measurement, the error is called hysteresis.Hysteresis occurs from a variety of factors thatcause loss of energy within the instrument; itmight occur because of friction or binding ofparts, fatigue of a spring, excessive play ingears, or other mechanical difficulties.155

PRINCIPLES OF NAVAL ENGINEERINGBecause there will always be some error ofmeasurement, and because the error may actuallybe considerably greater than that indicatedby the percentage of guaranteed accuracy, thecalibration of any measuring device requiresthe highest possible precision.Instrument sensitivity is sometimes confusedwith instrument accuracy. This is a big mistake.The sensitivity of an instrument refers to theability of the instrument to respond to changesin the value of the measured variable. K aninstrument can respond to very small changesin the measured variable, it is a very sensitiveinstrument; if larger changes in the measuredvariable are required to produce effective motionof the measuring element, the instrument is lesssensitive.Sensitivity is quite directly related to frictionwithin an instrument. An instrument thathas relatively small energy losses because offriction will, all other things being equal, bemore sensitive than an instrument with relativelylarge friction losses.156

CHAPTER 8INTRODUCTION TO THERMODYNAMICSThe shipboard engineering plant may bethought of as a series of devices and arrangementsfor the exchange and transformation ofenergy. The energy transformation of greatestimportance in the shipboard plant is the productionof mechanical work from thermal energy,since we depend largely upon this transformationto make the ship move through the water. Onsteam-driven ships, steam serves the vital purposeof carrying energy to the engines. Thesource of this energy may be the combustion ofa conventional fuel oil or the fission of a radioactivematerial. In either case, the steam that isgenerated is the medium by which thermal energyis carried to the ship's engines, where it isconverted into mechanical energy which propelsthe ship. In addition, energy transformationsrelated directly or indirectly to the basic propulsionplant energy conversion provide powerfor many vital services such as steering, lighting,ventilation, heating, refrigeration and airconditioning, the operation of various electricaland electronic devices, and the loading, aiming,and firing of the ship's weapons.In order to acquire a basic understanding ofthe design of shipboard engineering plants, it isnecessary to have some understanding of certainconcepts in the field of thermodynamics. In thebroadest sense of the term, thermodynamics isthe physical science that deals with energy andenergy transformations. The branch of thermodynamicswhich is of primary interest to engineersis usually referred to as applied thermodynamicsor engineering thermodynamics ;itdeals with fundamental design and operationalconsiderations of boilers, turbines, internalcombustion engines, air compressors, refrigerationand air conditioning equipment, and othermachinery in which energy is exchanged ortransferred in order to produce some desiredeffect.This chapter deals with certain thermodynamicconcepts that are particularly necessaryas a basis for understanding the shipboardengineering plant. The information given hereis introductory in nature; obviously, it is not inany sense a complete or thorough explorationof the subject. Insofar as possible, we willdepend upon verbal description rather thanmathematical analysis to develop our understandingof the laws and principles of energyexchanges and transformations.It should perhaps be noted that many of theterms used in this chapter— including such basicterms as energy and heat—have more specializedand more precise meanings in the study of thermodynamicsthan they do in everyday life oreven in the study of general physics. This isonly to be expected; thermodynamics is a highlyspecialized branch of physics and, like any otherspecialty, it requires a certain refinement ofterminology. If any difficulty arises from thefact that familiar terms are used in a somewhatunfamiliar sense, the difficulty can be largelyminimized by paying particular attention to theexact meaning of each term, as defined here,rather than depending upon a general knowledgefor an understanding of the terms.ENERGYAlthough energy has a general meaning toalmost everyone, it is not easy to define theword in a completely satisfactory way. Energyis intangible and is largely known through itseffects. Because energy is so often manifestedby the production of work, energy is commonlydefined as "the capacity for doing work." However,this is not entirely adequate as a definition,since work is not the only effect that isThe student who has the mathematical backgroundrequired for further study of thermodynamics will findit profitable to consult thermodynamics texts to amplifythe information given in this chapter.157

PRINCIPLES OF NAVAL ENGINEERINGproduced by energy. For example, heat can flowfrom one body to another without doing any workat all, but the heat must still be considered asenergy and the process of heat transfer must berecognized as a process that has produced aneffect. A broader definition, then, and one whichsatisfies more of the conditions under which weknow energy to exist, is "the capacity for producingan effect."Energy exists in many forms. For convenience,we usually classify energy according tothe size and nature of the bodies or particleswith which the energy is associated. Thus wesay that mechanical energy is the energy associatedwith large bodies or objects— usually,things that are big enough to see. Thermalenergy is energy associated with molecules.Chemical energy is energy that arises from theforces that bind the atoms together in a molecule.Chemical energy is demonstrated whenevercombustion or any other chemical reaction takesplace. Electrical energy, light, X-rays, andradio waves are examples of energy associatedwith particles that are even smaller than atoms.Each of these types of energy must be furtherclassified as (1) stored energy, or (2) energy intransition. Stored energy can be thought of asenergy that is actually "contained in" or "storedin" a substance or system. There are two kindsof stored energy: (1) potential energy, and (2)kinetic energy. When energy is stored in a systembecause of the relative positions of two ormore objects or particles, we call it potentialenergy . When energy is stored in a system becauseof the relative velocities of two or moreobjects or particles, we call it kinetic energy .It should be emphasized that all stored energyis either potential energy or kinetic energy.Energy in transition is, as the name implies,energy that is intheprocess of being transferredfrom one object or system to another. All energyin transition begins and ends as stored energy.In order to understand any form of energy,then, we need to know the relative size of thebodies or particles in the energy system and weneed to know whether the energy is stored or intransition. Bearing in mind these two modes ofclassification, let us now examine mechanicalenergy and thermal energy— the two forms ofenergy which are of particular interest in practicallyall aspects of shipboard engineering.MECHANICAL ENERGYEnergy associated with a system composedof relatively large bodies is called mechanicalenergy. The two forms of stored mechanicalenergy are (1) mechanical potential energy,and (2) mechanical kinetic energy. 2 Mechanicalenergy in transition is manifested by work.Mechanical potential energy is stored in asystem by virtue of the relative positions ofthe bodies that make up the system. The mechanicalpotential energy associated with thegravitational attraction between the earth andanother body provides us with many everydayexamples. A rock resting on the edge of a cliffin such a position that it will fall freely ifpushed has mechanical potential energy. Waterat the top of a dam has mechanical potentialenergy. A sled that is being held at the top of anicy hill has mechanical potential energy. Notethat in each of these examples the energy residesneither in the earth alone nor in the other objectalone but rather in an energy system of whichthe earth is merely one component.Mechanical kinetic energy is stored in asystem by virtue of the relative velocities ofthe component parts of the system. Push thatrock over the edge of the cliff, open the gate ofthe dam, or let go of the sled— and somethingwill move. The rock will fall, the water willflow, the sled will slide down the hill. In eachcase the mechanical potential energy will bechanged to mechanical kinetic energy. Since itis customary toascribezero velocity to an objectwhich is at rest with respect to the earth, it isalso customary to think of kinetic energy asthough it pertained only to the object which isin motion with respect to the earth. It should beremembered, however, that kinetic energy, likepotential energy, is properly assigned to thesystem rather than to any one component of thesystem.In these examples of mechanical potentialenergy and mechanical kinetic energy, we haveused an external source of energy to get thingsstarted. Energy from some outside source isrequired to push the rock, open the gate of thedam, or let go of the sled. All real machinesand processes require this kind of a boost froman energy source outside of the system; similarly,the energy from any one system is bound2 Although all forms of energy may be stored as potentialenergy or as kinetic energy, these terms refer, incommon usage, to mechanical potential energy andmechanical kinetic energy, unless some other form ofenergy (thermal, chemical, etc.) is specified.158

Chapter 8 -INTRODUCTION TO THERMODYNAMICSto affect other energy systems, since no onesystem can be completely isolated as far asenergy is concerned. However, it is easier tounderstand the basic energy concepts if we disregardall the other energy systems that miglitbe involved in or affected by each energy process.Hence we will generally consider one system ata time, disregarding energy boosts that may bereceived from an outside source and disregardingthe energy transfers that may take placebetween the system we are considering and anyother system.It should be emphasized that mechanicalpotential energy and mechanical kinetic energyare both stored forms of energy. Some confusionarises because mechanical kinetic energy isoften referred to as the "energy of motion,"thus leading to the false conclusion that "energyin transition" is somehow involved. This is notthe case, however. Work— mechanical work— isthe only form of mechanical energy which canproperly be considered as energy in transition.Mechanical potential energy and mechanicalkinetic energy are mutually convertible. To takethe example of the rock resting on the edge ofthe cliff, let us suppose that some external forcepushes the rock over the edge so that it falls.As the rock falls, the system loses potentialenergy but gains kinetic energy. By the time therock reaches the ground at the base of the cliff,all the potential energy of the system has beenconverted into kinetic energy. The sum of thepotential energy and the kinetic energy is identicalat each point along the line of fall, but theproportions of potential energy and kineticenergy are constantly changing as the rock falls.To take another example, consider a baseballthat is thrown straight up into the air. The ballhas kinetic energy while it is in upward motion,but the amount of kinetic energy is decreasingand the amount of potential energy is increasingas the ball travels upward. When the ball hasjust reached its uppermost position, before itstarts to fall back toward the earth, it has onlypotential energy. Then, as the ball falls backtoward the earth, the potential energy is convertedinto kinetic energy again.The magnitude of the mechanical potentialenergy stored in a system by virtue of the relativepositions of the bodies that make up thesystem is proportional to (1) the force of attractionbetween the bodies, and (2) the distanceIn the case of the rock whichbetween the bodies.is ready to fall from the edge of the cliff, we areconcerned with (1) the force of attractionbetween the earth and the rock— tliat is, the forceof gravity acting upon the rock, or the weight ofthe rock, and (2) the linear separation betweenthe two objects. If we measure the weight inpounds and the distance in feet, the amount ofmechanical potential energy stored in the systemby virtue of the elevation of the rock is measuredin the unit called the foot-pound. Specifically,whereE =PWx DE = mechanical potential energy, in foot-^ poundsW =D -weight of body, in poundsdistance between earth and body, in feetThe magnitude of mechanical kinetic energyis proportional to the mass and to the square ofthe velocity of an object which has velocity withrespect to another object, orwhereE = mechanicalpoundsM =MVmass of body, in poundskinetic energy, in foot-V = velocity of body relative to the earth,in feet per secondWhere it is more convenient to use the weightof the body, rather than the mass, the equationbecomeskwhere W^ is the weight of the body, in pounds,and_g^is the acceleration due to gravity, generallytaken as 32.2 feet per second per second.Work, as we have seen, is mechanical energyin transition— that is, it is a transitory form ofmechanical energy which occurs only betweentwo or more other forms of energy. Work isdone when a tangible body or substance is movedthrough a tangible distance by the action of atangible force. Thus we may define work as the2g159

PRINCIPLES OF NAVAL ENGINEERINGenergy which is transferred by the action of aforce through a distance, orwhereE .FD^wk =F X D= work, in foot pounds= force, in pounds= distance (or displacement), in feetIn the case of work done against gravity, theforce is numerically the same as the weight ofthe object or body that is being displaced.It is important to note that no work is doneunless something is displaced from its previousposition. When we lift a 5-pound weight fromthe floor to a table that is 3 feet high, we havedone 15 foot-pounds of work. If we merely standand hold the 5-pound weight, we do not performany work in the technical sense of the term, eventhough we may feel like we are working. In thiscase, actually, all we are doing is exerting forcein order to support the weight against the actionof the force of gravity. The forces are balanced;there is no motion or displacement of the weight,so no work is done.If the force and the displacement are neitheracting in the same direction nor acting in totalopposition, work is done only by that componentof the force which is acting in the direction ofthe displacement of the body or object. A manpushing a lawnmower, for example, is exertingsome force that acts in the direction in whichthe lawnmower is moving; but he is also exertingsome force which acts downward, at rightangles to the direction of displacement. In thiscase, only the forward component of the exertedforce results in work— that is, in the forwardmotion of the lawnmower.Suppose that we move an object in such a waythat it returns to its original position. Have wedone work or haven't we? Let us consider againthe example of lifting a 5-pound weight to thetop of a 3-foot table. By this act ion we have performed15 foot-pounds of work. Now supposethat we let the weight fall back to the floor, sothat it ends up in the same position it had originally.Displacement is zero, so work must bezero. But what has happened to the 15 foot-poundsof work we put into the system when we liftedthe weight to the top of the table? By doing thiswork, we gave the system 15 foot-pounds ofmechanical potential energy. When the weightfell back to the floor, the mechanical potentialenergy was converted into mechanical kineticenergy. In one sense, therefore, we say thatour work was "undone" and that no net workhas been done.On the other hand, we may choose to regardthe two actions separately. In such a case, wesay that we have done 15 foot-pounds of work bylifting the weight and that the force of gravityacting upon the weight has done 15 foot-poundsof work to return the weight to its original positionon the floor. However, we must regard onework as positive and the other as negative. Thetwo cancel each other out, so there is again nonet work. But in this case we have recognizedthat 15 foot-pounds of work were performedtwice, in two separate operations, by two differentagencies.This example has been elaborated at somelength because we may draw several importantinferences from it. First, it may help to clarifythe concept of work as a form of energy thatmust be accounted for. Also, it may help toconvey the real meaning of the statement thatwork is mechanical energy in transition. Workis energy in transition because it occurs onlytemporarily, between other forms of energy, andbecause it must always begin and end as storedenergy. And finally, the example suggests theneed for arbitrary reference planes in connectionwith the measurement of potential energy,kinetic energy, and work. The quantitativeconsideration of any form of energy requires aframe of reference which defines the startingpoint and the stopping point of any particularoperation; the reference planes are practicallyalways relative rather than absolute.Note that mechanical potential energy, mechanicalkinetic energy, and work are allmeasured in the same unit, the foot-pound. Onefoot-pound of work is done when a force of 1pound acts through a distance of 1 foot. Onefoot-pound of mechanical kinetic energy or 1foot-pound of mechanical potential energy isthe amount of energy that would be required toaccomplish 1 foot-pound of work.The amount of work done has nothing to dowith the length of time required to do it. If aweight of 1 pound is lifted through a distanceof 1 foot, 1 foot-pound of work has been done,regardless of whether it was done in half asecond or half an hour. The rate at which workis done is called power. In the field of mechanicalengineering, the horsepower (hp) is thecommon unit of measurement for power. By160

Chapter 8-INTRODUCTION TO THERMODYNAMICSdefinition, 1 horsepower is equal to 33,000 footpoundsof work per minute or 550 foot-pounds ofwork per second. Thus a machine that is capableof doing 550 foot-pounds of work per second issaid to be a 1-horsepower machine.THERMAL ENERGYEnergy associated primarily with systemsof molecules is called thermal energy. Likeother kinds of energy, thermal energy may existin stored form (in which case it is called internalenergy) or as energy in transition (inwhich case it is called heat) .In common usage, the term heat is often usedto include all forms of thermal energy. However,this lack of distinction between heat and thestored forms of thermal energy can lead toserious confusion. In this text, therefore, theterm internal energy is used to describe thestored forms of thermal energy , and the termheat is used only to describe thermal energyin transition.Internal EnergyInternal energy, like all stored forms ofenergy, exists either as potential energy or askinetic energy.Internal potential energy is the energy associatedwith the forces of attraction that existbetween molecules. The magnitude of internalpotential energy is dependent upon the mass ofthe molecules and the average distance by whichthey are separated, in much the same way thatmechanical potential energy depends upon themass of the bodies in the system and the distanceby which they are separated. The force ofattraction between molecules is greatest insolids, less in liquids and yielding substances,and least of all in gases and vapors. Wheneversomething happens to change the average distancebetween the molecules of a substance,there is a corresponding change in the internalpotential energy of the substance.Internal kinetic energy is the energy associatedprimarily with the activity of molecules,just as mechanical kinetic energy is the energyassociated with the velocities of relatively largebodies. It is important to note that the temperatureof a substance arises from and is proportionalto the molecular activity with which internalkinetic energy is associated.For most purposes, we will not need todistinguish between the two stored forms ofinternal energy. Instead of referring to internalpotential energy and internal kinetic energy,therefore, we may often simply use the terminternal energy . When used in this way, withoutqualification, the term internal energy shouldbe understood to mean the sum total of allinternal energy stored in the substance or systemby virtue of the motion of molecules or byvirtue of the forces of attraction betweenmolecules.HeatAlthough the term heat is more familiar thanthe term internal energy ,it may be more difficultto arrive at an accurate definition of heat.Heat is thermal energy in transition. Like work,heat is a transitory energy form existing betweentwo or more other forms of energy.Since the flow of thermal energy can occuronly when there is a temperature differencebetween two objects or regions, it is apparentthat heat is not a property or attribute of anyone object or substance. If a person accidentallytouches a hot stove, he may understandably feelthat heat is a property of the stove. More accurately,however, he might reflect that his handand the stove constitute an energy system andthat thermal energy flows from the stove to hishand because the stove has a higher temperaturethan his hand.As another example of the difference betweenheat and internal energy, consider two equallengths of piping, made of identical materialsand containing steam at the same pressure andtemperature. One pipe is well insulated, one isnot. From everyday experience, we expect moreheat to flow from the uninsulated section of pipethan from the insulated section. When the twopipes are first filled with steam, the steam inone pipe contains exactly as much internal enetgyas the steam in the other pipe. We know this istrue because the two pipes contain equal volumesof steam at equal pressures and temperatures.After a few minutes, the steam in the uninsulatedpipe will contain much less internal energythan the steam in the insulated pipe, as we cantell by reading the pressure and temperaturegages on each pipe. What has happened? Storedthermal energy— internal energy— has movedfrom one place to another, first from thesteam to the pipe, then from the uninsulatedpipe to the air. It ic this movement, orthis flow, of energy that should properly becalled heat. Temperature is a reflection of the161

PRINCIPLES OF NAVAL ENGINEERINGamount of internal kinetic energy possessed byan object or a substance, and it is therefore anattribute or property of the substance. The movementor flow of thermal energy— or, in otherwords, heat— is an attribute of the energy systemrather than of any one component of it."^Units of MeasurementIn engineering, heat is commonly measuredin the unit called the British thermal unit (Btu).Originally, 1 Btu was defined as the quantity ofheat required to raise the temperature of 1 poundof water through 1 degree on the Fahrenheitscale. A similar unit called the calorie (cal) wasoriginally defined asthequantity of heat requiredto raise the temperature of 1 gram of waterthrough 1 degree on the Celsius scale. Theseunits are still in use, but the original definitionshave been abandoned by international agreement.The Btu and the calorie are now defined in termsof the unit of energy called the joule. ^ TheThe correct definition of heat is emphasized here inorder to avoid subsequent misunderstanding in thestudy of thermodynamic processes. It is obvious that"heat" and related words are sometimes used in ageneral way to indicate temperature. For example,we have no simple way of referring to an object witha large amount of internal kinetic energy except to saythat it is "hot." Similarly, a reference to "the heat ofthe sun" may meaneither the temperatureof the sun orthe amount of heat being radiated by the sun. Even"heat flow" or "heat transfer"—the terms quite properlyused to describe the flow of thermal energy— aresometimes used in such a way as to imply that heat isa property of one object or substance rather than anattribute of an energy system. To a certain extent,such inaccurate use of "heat" and related words isreally unavoidable; we must continue to "add heat"and "remove heat" and perform other impossibleoperations, verbally, unless we wish to adopt a verystuffy and long-winded form of speech. It is essential,however, that we maintain a clear understanding ofthe true nature of heat and of the distinction betweenheat and the stored forms of thermal energy.Several reasons contributed to the abandonment of theoriginal definitions of the Btu and the calorie. For onething, precise measurements indicated that the quantityof heat required to raise a specified amount of waterthrough 1 degree on the appropriate scale was not constantat all temperatures. Second— and perhaps evenmore important—the recognition of heat as a form ofenergy makes the Btu and the calorie unnecessary. Indeed,it has been suggested that the calorie and the Btucould be given up entirely and that heat could be expresseddirectly in joules, ergs, foot-pounds, or otherestablished energy units. Some progress has been madein this direction, but not much; the Btu and the calorieare still theunitsof heat most widely used in engineeringand in the physical sciences generally.following relationships have thus been establishedby definition or derived from the establisheddefinitions:1 calorie = -^^ watt-hour= 4.18605 joules= 3.0883 foot-pounds1 Btu = 251.996 calories= 778.26 foot-pounds= 1054.886 joulesThe values given here are, of course, considerablymore precise than those normally requiredin engineering calculations.When large amounts of thermal energy areinvolved, it is often more convenient to use multiplesof the Btu or the calorie. For example, wemay wish to refer to thousands or millions ofBtu, in which case we would use the unit kB(1 kB = 1000 Btu) or the unit mB (1 mB =1,000,000 Btu). Similarly, the kilocalorie maybe used when we wish to express calories inthousands (1 kilocalorie = 1000 calories). Thekilocalorie. also called the "large calorie," isthe unit normally used for indicating the thermalenergies of various foods. Thus a portion offood which contains "100 calories" actually contains100 kilocalories or 100,000 ordinary calories.Heat TransferHeat flow, or the transfer of thermal energyfrom one body, substance, or region to another,takes place always from a region of higher temperatureto a region of lower temperature.^ Inthermodynamics, the high temperature regionmay be called the source or the emitting region;the low temperature region may be called thesink, the receiver , or the receiving region.This statement, although entirely true for all practicalengineering applications, should perhaps be qualified.Energy exchanges between molecules may bethought of as being random, in the statistical sense;therefore, some exchanges of thermal energy may indeed"go in the wrong direction"—that is, from acolder region to a warmer region. On the average,however, the flow of heat is always from the higher tothe lower temperature.162

Chapter 8-INTRODUCTION TO THERMODYNAMICSAlthough three modes of heat transferconduction,radiation, and convection— are commonlyrecognized, we will find it easier tounderstand heat transfer if we make a distinctionbetween conduction and radiation, on the onehand, and convection, on the other. Conductionand radiation may be regarded as the primarymodes of heat flow. Convection may best bethought of as a related but basically differentand special kind of process which involves themovement of a mass of fluid from one place toanother.CONDUCTION.— Conduction is the mode bywhich heat flows from a hotter to a colder regionwhen there is physical contact between thetwo regions. For example, consider a metal barwhich is held so that one end of it is in boilingwater. In a very short time the end of the barwhich is not in the boiling water will have becometoo hot to hold. We say that heat has beenconducted from molecule to molecule along theentire length of the bar. The molecules in thelayer nearest the source of heat become increasinglyactive as they receive thermalenergy. Since each layer of molecules is boundto the adjacent layers by cohesive forces, themotion is passed on to the next layer which, inturn, sets up increased activity in the next layer.The process of conduction continues as long asthere is a temperature difference between thetwo ends of the bar.The total quantity of heat conducted dependsupon a number of factors. Let us consider a barof homogeneous material which is uniform incross-sectional area throughout its length. Oneend of the bar is kept at a uniformly high temperature,the other end. is kept at a uniformlylow temperature. After a steady and uniformflow of heat has been established, the total quantityof heat that will be conducted through thisbar depends upon the following relationships:1. The total quantity of heat passing throughthe conductor in a given length of time is directlyproportional to the cross-sectional areaof the conductor. The cross-sectional area ismeasured normal to (that is, at right angles to)the direction of heat flow.2. The total quantity of heat passing throughthe conductor in a given length of time is proportionalto the thermal gradient— that is, to thedifference in temperature between the two endsof the bar, divided by the length of the bar.3. The quantity of heat is directly proportionalto the time of heat flow.4. The quantity of heat depends upon thethermal conductivity of the material of whichthe bar is made. Thermal conductivity (k) isdifferent for each material.These relationships may be expressed bythe equationwhereQ =kTA ^1-^2Q = quantity of heat, in Btu or caloriesk =coefficient of thermal conductivity(characteristic of each material)T = time during which heat flowsA =cross-sectional area, normal to the pathof heatt. = temperature at the hot end of the bart„ = temperature at the cold end of the barL =distance between the two ends of the barThis equation, which is sometimes called thegeneral conduction equation , applies whether weare using a metric system or a British system.Consistency in the use of units is, of course,vital.t. - t„The quantity ^5^ =- is called the thermalgradient or the temperature gradient. In themetric CGS system, the temperature gradient isexpressed in degrees Celsius per centimeter oflength; the cross-sectional area is expressed insquare centimeters; and the time is expressedin seconds. In British units, the temperaturegradient is expressed in Btu per inch (or sometimesper foot) of length; the cross-sectionalarea is expressed in square feet; and the time isexpressed in seconds or in hours. (As may benoted, some caution is required in using theBritish units; we must know whether the temperaturegradient indicates Btu per inch or Btuper foot, and we must know whether the time isexpressed in seconds or in hours.)From the general conduction equation, wemay infer that the coefficient of thermal163

1PRINCIPLES OF NAVAL ENGINEERINGconductivity (k) represents the quantity of heat•which will flow through unit cross section andunit length of a material in unit time when thereis unit temperature difference between the hotterand the colder faces of the material .Thermal conductivity is determined experimentallyfor various materials. We may perhapsvisualize the process of conduction more clearlyand understand its quantitative aspects morefully by examining an apparatus for the determinationof thermal conductivity and by settingup a problem.Figure 8-1 shows a device that could be usedfor determining thermal conductivity. Assumethat we have a bar of uniform diameter, madeof an unknown metal. (If we knew the kind ofmetal, we could look up the thermal conductivityin a table; since we do not know the metal,we shall find k experimentally.) One end of thebar is inserted into a steam chest in which aconstant temperature is maintained; the otherend of the bar is inserted into a water chest.The quantity of water flowing through the waterchest and the entrance and exit temperature ofthe water are measured. Also, the temperatureof the bar itself is measured at two points bymeans of thermometers inserted into holes inthe bar; we may choose any two points along thebar, provided they are reasonably far apart andprovided they are some distance away from thesteam chest and the water chest.We will assume that the entire apparatus isperfectly insulated so that the temperature differencebetween t. and t„ is an accurate reflectionof the heat conducted along the bar and sothat the amount of heat absorbed by the circulatingwater in the water chest is a true indicationof the heat conducted from the hotter end of thebar to the colder end. We will assume that thefollowing data are known at the outset or learnedby measurement or determined in the course ofthe experiment:Specific heat of water =1.00Temperature of water entering water chest20° CTemperature of water leaving water chest =30" CMass of water passing through water chest =1300 gramst- (temperature at hotter end of bar) = SO^Ct„ (temperature at cooler end of bar) 60° CA (cross-sectional area of bar) • 20 squarecentimetersL (distance between points of temperaturemeasurement on bar) = 10 centimetersT (time of heat flow) = 6 minutes = 360 secondsTo determine the thermal conductivity, k, ofour unknown metal, we will use two equations.tit2WATER INSTEAM INSTEAMCHESTBARr< ^IWATERCHEST a 1 1 11 1 1 1 1 ftSTEAMOUTWATEROUTFigure 8-1.— Device for measuring thermal conductivity.147.60164

VChapter 8-INTRODUCTION TO THERMODYNAMICSOne is the general conduction equationQ = kTA 4-^2where, as we have seen, Q may be expressedin calories or in Btu. In this example, we areusing the metric CGS system and must thereforeexpress ^in calories. The second equation wewill use gives us a second way of calculatingQ— that is, by determining the amount of heatabsorbed by the circulating water. Thus,Q =mass of water x temperature changeof water x specific heat of waterSubstituting some of our known values inthis second equation, we find thatQ = (1300) (10) (1) = 13,000 caloriesUsing this value of Q and substituting otherknown values in the general conduction equation,we find that13,000 = k (360) (20) (80 - 60 )100.9 = k= k (360) (20) (2)= 14,400 kIt should be noted that the general conductionequation applies only when there is a steadystatethermal gradient— that is, after a uniformflow of heat has been established. It should benoted also that k_ varies slightly as a function oftemperature, although for many purposes therise in }^that goes with a rise in temperatureis so slight that it can safely be disregarded.In considering the experimental determinationof thermal conductivity, why do we include"specific heat of water = 1.00" as one of theknown data? What is specific heat, and what isits utility? Specific heat (also called heat capacityor specific heat capacity) is, like thermalconductivity, a thermal property of matter thatmust be determined experimentally for eachsubstance. In general, we may say that specificheat is the property of matter that explains whythe addition of equal quantities of heat to twodifferent substances will not necessarily producethe same temperature rise in the two substances.We may define the specific heatof any substanceas the quantity of heat required to raise thetemperature of unit mass of that substance 1degree. ^ In the metric CGS system, specificheat is expressed in calories per gram perdegree Celsius; in the metric MKS system, itis expressed in kilocalories per kilogram perdegree Celsius; and in British systems, it isexpressed in Btu per pound per degree Fahrenheit.The specific heat of water is 1.00 in anysystem, and the numerical value of specificheat for any given substance is the same in allsystems (although the units are, of course, different).Specific heat is determined experimentallyby laboratory procedures which are extremelycomplex and difficult in practice, althoughbasically simple in theory. One of the commonestmethods of determining specific heat isknown as the method of mixtures. In this procedure,a known mass of finely divided metal isheated and then mixed with a known mass ofwater. The temperatures of the metal beforemixing, of the water before mixing, and of themixture just as it reaches thermal equilibriumare measured. Then, on the simple premise thatthe heat lost by one substance must be gainedby the other substance, the specific heat of themetal can be found by using the equationm^c^ (tl -*3^ ='"2^2^*3-wherem- = mass of metalm„ = mass of waterc^- specific heat of metalc„ = specific heat of water (known to be 1.00)t- . temperature of metal before mixingt„ = temperature of water before mixingt„ = temperature at which water and metalreach thermal equilibriumSpecific heat as defined here should not be confusedwith the relatively useless concept of specific heatratio , by which the heat capacity of each substance iscompared to the heat capacity of water (taken as 1.00).The specific heat ratio is, obviously, a pure numberwithout units.165

PRINCIPLES OF NAVAL ENGINEERINGIn words, then, we may say that the masstimes the specific heat times the temperaturechange of the first substance must equal themass times the specific heat times the temperaturechange of the second substance. In thisequation and in this verbal statement, we areignoring the thermal energy absorbed by theapparatus, by the stirring rods, and by thethermometers. In actually determining specificheats, it is often necessary to account for allthermal energy, even that relatively minutequantity which is absorbed by the equipment.In such a case, the heat absorbed by the equipmentis merely added to the right-hand side ofthe equation.Specific heat is primarily useful in thatit allows us to determine the quantity of heatadded to a substance merely by observing thetemperature rise, when we know the mass andthe specific heat of the substance. And this, infact, is precisely what we did in the thermalconductivity problem, where we calculated theamount of heat that had been absorbed by thewater in the water chest by using the equationQ =mass x temperature change x specific heatSpecific heat varies, in greater or lesserdegree, according to pressure, volume, andtemperature. Specific heat values quoted forsolids and liquids are obtained through experimentalprocedures in which the substance iskept at constant pressure. The specific heat ofany gas may vary tremendously, having in factan almost infinite variety of values because ofthe almost infinite variety of processes andstates during which energy is transferred to orby a gas. For convenience, specific heats ofgases are given as specific heat at constantvolume (Cy) and specific heat at constant pressure(Cp).RADIATION.— Thermal radiation is a modeof heat transfer that does not involve any physicalcontact between the emitting region and thereceiving region. A person sitting near a hotstove is warmed by thermal radiation from thestove, even though the air in between remainsrelatively cold. Thermal radiation from thesun warms the earth without warming the spacethrough which it passes. Thermal radiationpasses through any transparent substance— air,glass, ice—without warming it to any extentbecause transparent materials are very poorabsorbers of radiant energy.All substances— solids, liquids, and gasesemitradiant energy at all times. We tend tothink of radiant energy as something that isemitted only by extremely hot objects such asthe sun, a stove, or a furnace, but this is a verylimited view of the nature of radiant energy.The earth absorbs radiant energy emitted by thesun, but the earth in turn radiates energy to thestars. A stove radiates energy to everythingsurrounding it, but at the same time all the surroundingobjects are radiating energy to thestove. A child standing near a snowman maywell believe that the snowman is "radiatingcold" rather than emitting radiant energy; actually,however, both the child and the snowmanare emitting radiant energy. The child, of course,is radiating far more energy than the snowman,so the net effect of this energy exchange is thatthe snowman grows warmer and the child gi-owscolder. We are literally surrounded by— and apart of— such energy exchanges at all times. Aswe consider these energy exchanges, we may arriveat a new view of thermal equilibrium:when objects are radiating precisely as muchthermal energy as they are receiving, in anygiven period of time, they are in thermal equilibrium.Thermal radiation is an electromagneticwave phenomenon, differing from light, radiowaves, and other electromagnetic phenomenonmerely in the wavelengths involved. When thewavelengths are in the infrared part of the electromagneticspectrum— that is, when they arejust below the range of visible light waves—werefer to the radiated energy as thermal radiation. It should be noted, however, that all electromagneticwaves transport energy which canbe absorbed by matter and which can in manycases result in observable thermal effects. Forexample, one energy unit of light absorbed bya substance produces the same temperature risein that substance as is produced by the absorptionof an equal amount of thermal (infrared)energy.When radiant energy falls upon a body thatcan absorb it, some of the energy is absorbedand some is reflected. The amount absorbed andthe amount reflected depend in large part uponthe surface of the receiving body. Dark, opaquebodies absorb more thermal radiation than shiny,bright, white, or polished bodies. Shiny, bright,white, or polished bodies reflect more thermalradiation than dark, opaque bodies. Good radiatorsare also good absorbers and poor radiators166

Chapter 8 -INTRODUCTION TO THERMODYNAMICSare poor absorbers. In general, good reflectorsare poor radiators and poor absorbers.In considering thermal radiation, the conceptof black body radiation is frequently a usefulconstruct. A black body is conceived of as anideal or theoretical body which, being perfectlyblack, is a perfect radiator, a perfect absorber,and a perfect nonreflector of radiant energy.The thermal radiation emitted by such a perfectblack body is proportional to T^— that is, to theabsolute temperature raised to the fourth power.Because of the fourth power relationship, doublingthe absolute temperature increases theradiation 16 times, tripling the absolute temperatureincreases the radiation 81 times, andso forth. The thermal radiation emitted by realbodies is also proportional to the fourth power ofthe absolute temperature, although the totalradiation emitted by a real body depends alsoupon the surface of the body. Consideration ofthe relationship between the thermal radiationof a body and the fourth power of the absolutetemperature of that body explains why the problemof thermal insulation against radiationlosses increases so enormously as the temperatureincreases.CONVECTION.— Although convection is oftenloosely classified as a mode of heat transfer, itis more accurately regarded as the mechanicaltransportation of a mass of fluid (liquid or gas)from one place to another. In the process of thistransportation, all the thermal energy storedwithin the fluid remains in stored form unless itis transferred by radiation or by conduction.Since convection does not involve thermal energyin transition, we cannot in the most fundamentalsense regard it as a modeof heat transfer.Convection is the transportation or the move -ment of some portions within amass of fluid. Asthis movement occurs, the moving portions ofthe fluid transport their contained thermalenergy to other parts of the fluid. The effect ofconvection is thus to mix the various portions ofthe fluid. The part that was at the bottom ofthe container may move to the top or the partthat was at one side may move to the other side.As this mixing takes place, heat transfer occursby conduction and radiation from one part of thefluid to another and between the fluid and itssurroundings. In other words, convection transportsportions of the fluid from one place to another,mixes the fluid, and thus provides anopportunity for heat transfer to occur. Butconvection does not, in and of itself, "transfer"thermal energy.Convection serves a vital purpose in bringingthe different parts of a fluid into closecontact with each other so that heat transfer canoccur. Without convection, there would be littleheat transfer from, to, or within fluids, sincemost fluids are very poor at transferring heatexcept when they are in motion.Two kinds of convection may be distinguished.Natural convection occurs when there are differencesin the density of different parts of thefluid. The differences in density are usuallycaused by unequal temperatures within the massof fluid. As the air over a hot radiator is heated,for example, it becomes less dense and thereforebegins to rise. Cooler, heavier air is drawnin to replace the heated air that has moved upward,and convection currents are thus set up.Another example of natural convection, and onethat may be quite readily observed, may befound in a pan of water that is being heated ona stove. As the water near the bottom of the panis heated first, it becomes less dense and movesupward. This displaces the cooler, heavier waterand forces it downward; as the cooler water isheated in turn, it rises and displaces the waternear the top. By the time the water has almostreached the boiling point, a considerable amountof motion can be observed in the water.Forced convection occurs when some mechanicaldevice such as a pump or a fan producesmovement of a fluid. Many examples of forcedconvection may be observed in the shipboardengineering plant: feed pumps transporting waterto the boilers, fuel oil pumps moving fuel oilthrough heaters and meters, lubricating oilpumps forcing lubricating oil through coolers,and forced draft blowers pushing air throughboiler double casings, to name but a few.The mathematical treatment of convectionis extremely complex, largely because theamount of heat gained or lost through the convectionprocess depends upon so many differentfactors. Empirically determined convection coefficientswhich take account of these manyfactors are available for most kinds of engineeringequipment.Sensible Heat and Latent HeatThe terms sensible heat and latent heat areoften used to indicate the effect that the transferof heat has upon a substance. The flow of167

PRINCIPLES OF NAVAL ENGINEERINGheat) from one substance to another is normallyreflected in a temperature change in eachsubstance— that is, the hotter substance becomescooler and the cooler substance becomeshotter. However, the flow of heat is not reflectedin a temperature change in a substancewhich is in process of changing from one physicalstate ' to another. When the flow of heat isreflected in a temperature change, we say thatsensible heat has been added to or removedfrom a substance. When the flow of heat is notreflected in a temperature change but is reflectedin the changing physical state of a substance,we say that latent heat has been addedor removed.Since heat is defined as thermal energy intransition, we must not infer that sensible heatand latent heat are really two different kinds ofheat. Instead, the terms serve to distinguishbetween two different kinds of effects producedby the transfer of heat; and, at a more fundamentallevel, they indicate something about themanner in which the thermal energy was or willbe stored. Sensible heat involves internal kineticenergy and latent heat involves internal potentialenergy.The three fundamental physical states of allmatter are solid, liquid, and gas (or vapor). Thephysical state of a substance is closely relatedto the distance between molecules. Themolecules are closest together in solids, fartherapart in liquids, and farthest apart in gases. Whenthe flow of heat to a substance is not reflected ina temperature change, we know that the energyis being used to increase the distance betweenthe molecules of the substance and thus changeit from a solid to a liquid or from a liquid to agas. In other words, the addition of heat to asubstance that is in process of changing fromsolid to liquid or from liquid to gas results inan increase in the amount of internal potentialIn thermodynamics, the physical state of a substance(solid, liquid, or gas) is usually described by the termphase, while the term state is used to describe thesubstance with respect to all of its properties—phase,pressure, temperature, specific volume, and so forth.Thus the phase of a substance may be considered asmerely one of the several properties that fix the stateof the substance. While the precision of this usagehas some obvious advantages, it is not in standard useamong engineers. In this text, therefore, the termphysical state (or sometimes state) is used to denotethe molecular condition of a substance that determineswhether the substance is a solid, a liquid, or a gas.energy stored in the substance, but it does notresult in an increase in the amount of internalkinetic energy. Only after the change of statehas been fully accomplished does the addition ofheat result in a change in the amount of internalkinetic energy stored in the substance; hence,there is no temperature change until after thechange of state is complete.In a sense, we may think of latent heat asthe energy price that must be paid for a changeof state from solid to liquid or from liquid togas. But the energy is not lost; rather, it isstored in the substance as internal potentialenergy. The energy price is "repaid," so tospeak, when the substance changes back fromgas to liquid or from liquid to solid; duringthese changes of state, the substance gives offheat without any change in temperature.The amount of latent heat required to causea change of state— or, on the other hand, theamount of latent heat given off during a changeof state—varies according to the pressure underwhich the process takes place. For example, ittakes about 970 Btu to change 1 pound of waterto steam at atmospheric pressure (14.7 psia)but it takes only 62 Btu to change 1 pound ofwater to steam at 3200 psia.Figure 8-2 shows the relationship betweensensible heat and latent heat for one substance,water, at atmospheric pressure." If we startwith 1 pound of ice at 0°F,we must add 16 Btuto raise the temperature of the ice to 32° F. Wecall this adding sensible heat. To change thepound of ice at 32°F to a pound of water at 32°F,we must add 144 Btu (the latent heat of fusion ).There will be no change in temperature whilethe ice is melting. After all the ice has melted,however, the temperature of the water will beraised as additional heat is supplied. Again, weare adding sensible heat. If we add 180 Btu—that is, 1 Btu for each degree of temperaturebetween 32° F and 212°F-the temperature of thewater will be raised to the boiling point. Tochange the pound of water at 212°F to a poundof steam at 212°F, we must add 970 Btu (thelatent heat of vaporization ). After all the waterhas been converted to steam, the addition ofmore heat will cause an increase in the temperatureof the steam. If we add 42 Btu to theThe same kind of chart could be drawn up for othersubstances, but different amounts of thermal energywould of course be required for each change of temperatureor of physical state.168

Chapter 8- INTRODUCTION TO THERMODYNAMICSpound of steam which is at 212°F,wecan superheat^it to 300° F.The same relationships apply when heat isbeing removed. The removal of 42 Btu from thepound of steam which is at 300° F will causethe temperature to drop to212°F. As the poundof steam at 212°F changes to a pound of waterat 212°F, 970 Btu are given off. When a gas orvapor is changing to a liquid, we usually use theterm latent heat of condensation; numerically,of course, the latent heat of condensation isexactly the same as the latent heat of vaporization.The removal of another 180 Btu will lowerthe temperature of thepoundof water from 2 12°Fto 32° F. As the pound of water at 32° F changesto a pound of ice at 32° F, 144 Btu are given offwithout any accompanying change in temperature.Further removal of heat causes the temperatureof the ice to decrease.Heat Transfer ApparatusAny device or apparatus designed to allowthe flow of thermal energy from one fluid toanother is called a heat exchanger. The shipboardengineering plant contains an enormousnumber and variety of heat exchangers, rangingfrom large items such as boilers and main condensersto relatively small items such as fueloil heaters and lubricating oil coolers.As a basis for understanding something aboutheat transfer in real heat exchangers, it is necessaryto visualize the general configuration ofthe most commonly used type of heat exchanger.With few exceptions, 1^ heat exchangers usedaboard ship are of the indirect or surface type—that is, heat flows from one fluid to anotherthrough some kind of tube, plate, or other "surface"that separates the two fluids and keepsthem from mixing. Most surface heat exchangersA vapor or gas is said to be superheated when itstemperature has been raised above the temperatureof the liquid from which the vapor or gas is beinggenerated. As may be inferred from the discussion,it is impossible to superheat a vapor or gas as longas it is in contact with the liquid from which it is beinggenerated.A notable exception is the deaerating feed tank,discussed in chapter 13 of this text. Deaerating feedtanks are basically described as direct-contact heatexchangers,' rather than surface heat exchangers, becauseheat transfer is accomplished by the actualmixing of the hotter and the colder fluids.are of the shell-and-tube types, consisting of abundle of metal tubes that fit inside a shell.One fluid flows through the inside of the tubesand the other flows through the shell, aroundthe outside of the tubes.The exchanges of thermal energy that takeplace in even a simple heat exchanger are reallyquite complex. The processes of conduction,radiation, and convection are involved in practicallyall heat exchangers. Processes involvinglatent heat— that is, the processes of evaporation,condensation, melting, and solidificationmaycontribute to the heat transfer problem. Inall cases, heat transfer is affected by physicalproperties of the fluids which are exchangingthermal energy and by physical properties of themetal through which the change is being effected.The temperature differences involved,the extent and nature of the fluid films, thethickness and nature of the metals through whichheat transfer takes place, the length and areaof the path of heat flow, the types of surfacesinvolved, the velocity of flow, and other factorsalso determine the amount of heat transferredin any heat exchanger.Because heat transfer is such a complexphenomenon, heat transfer calculations are necessarilycomplex. For some purposes, heattransfer problems are simplified by the use ofan overall coefficient of heat transfer (U) whichmay be determined experimentally for anyspecific set of conditions. Tabulated values ofy are available for various kinds of heat exchangermetal tubes, for building materials, andfor other materials; in most cases the values ofU. are approximate, since various conditionssuch as temperature, velocity of flow, conditionof the heat transfer surfaces, and the physicalproperties of the fluids have a profound effectupon the amount of heat transferred.The transfer of heat in a heat exchangerinvolves the flow of heat from the hot fluid tothe tube metal and from the tube metal to thecold fluid. In addition, heat must also be transferredthrough two layers of fluid (one on theinside and one on the outside of the tube) whichare not flowing with the remainder of the fluidbut are almost motionless. These relativelystagnant layers, known as boundary layers orfluid films , are extremely small in size buthave an extremely important effect on heattransfer.As previously noted, most fluids are verypoor transferrers of heat. As a fluid is flowing,however, convection and mechanical mixing of169

PRINCIPLES OF NAVAL ENGINEERINGLATENT HEATOF VAPORIZATION(OR LATENT HEATOF CONDENSATION)BTU PER POUND OF WATERFigure38.18-2.—Relationship between sensible heat and latent heat for water at atmospheric pressure.the fluid bring the molecules into such intimatecontact that heat transfer can and does occur.Other things being equal, increasingthe velocityof fluid flow increases heat transfer. ^^Since the fluid film is almost motionless,heat transfer through the film is very poor. Theeffect of fluid films on heat transfer is shown infigure 8-3. The temperature line indicates thechanges in temperature that occur as heat istransferred from the hot fluid to the fluid film,It is important here to maintain the distinction,previously established, between heat and temperature.Increasing the velocity of flow increases the amountof heat that is transferred, but decreasing the velocityincreases the temperature of the fluid. This fact is ofconsiderable practical importance in the design andoperation of heat exchangers. In a heat exchangerdesigned for high velocity flow, stagnation of the flowis likely to cause severe overheating of the heat exchangermetal.from thistube metal to the other fluid film,fluid film to the tube metal, from theand from thisfluid film to the cold fluid. As may be seen, themajor part of the temperature drop occurs in thefluid films rather than in the tube metal. Note,also, that the thicker fluid film is more resistantto heat transfer than the thinner fluid film.The velocity of flow and the amount of turbulencein the flow affect heat transfer by alteringthe thickness of the fluidfilm. Increasingthevelocity of flow diminishes the thickness of thefluid film and thus increases heat transfer.Turbulent flow breaks up the fluid film and thusincreases heat transfer. Although there are someobvious disadvantages to excessive turbulence,many heat exchangers are designed to operatewith a certain amount of turbulence so that thefluid films will be kept to a minimum.In real heat exchangers, the accumulation ofdeposits of scale, soot, or dirt on the inside orthe outside of the tubes has a profound and170

Chapter 8-INTRODUCTION TO THERMODYNAMICStr

PRINCIPLES OF NAVAL ENGINEERINGuniverse is always the same . Regardless of themode of expression, the principle of the conservationof energy applies to all kinds of energy. ^Energy equations for many thermodynamicprocesses are based directly upon the principleof the conservation of energy. When the principleof the conservation of energy is written inequation form, it is known as the general energyequation and is expressed as:energy in = energy outor, in more detail, it may be stated that theenergy entering a system equals the energyleaving the system plus any accumulation andminus any dimunition in the amount of energystored within the system.The first law of thermodynamics, a specialstatement of the principle of the conservationof energy, deals with the transformation ofmechanical energy to thermal energy and ofthermal energy to mechanical energy. The firstlaw is commonly stated as follows: Thermalenergy and mechanical energy are mutuallyconvertible, in the ratio of 778 foot-pounds to 1Btu.The ratio of conversion between mechanicalenergy and thermal energy is known as themechanical equivalent of heat , or Joule's equivalent.It is symbolized by the letter J and, in12 The principle of the conservation of energy and theprinciple of the conservation of mass have been basicto the development of modern science. Until the establishmentof the theory of relativity, with its implicationof the mutual convertibility of energy and mass,the two principles were considered quite separate.According to the theory of relativity, however, theymust be considered merely as two phases of a singleprinciple which states that mass and energy areinterchangeable and the total amount of matter andenergy in the universe is constant . Nuclear fission,a process in which atomic nuclei split into fragmentswith the release of enormous quantities of energy,is a dramatic example of the actual conversion ofmatter into energy. Even in the familiar process ofcombustion, modern techniques of measurement haveled to the discovery that a very minute quantity ofmatter is converted into energy; for example, about0.00007 ounce of matter is converted into energy when6 tons of carbon are burned with 16 tons of oxygen.In spite of the mutual convertibility of energy andmass, the principle of the conservation of energy maystill be regarded separately as the cornerstone of thescience of thermodynamics. Machinery designed underthis principle alone still functions in an orderly andpredictable fashion.SECONDFIRSTFLUIDFIRST FLUID -FIRSTFIRSTFLUID-FLUID-FLUID-98,32Figure 8-6.— Cross flow in heat exchanger.accordance with the first law of thermodynamics,it is expressed asorJ =J =778 ft-lb per Btu778 ft-lb1 BtuThe mechanical equivalent of heat providesus, directly or by extension, with a number ofuseful numerical values relating to heat, work,and power. Some of the most widely used valuesare given here; others may be obtained fromengineering handbooks and similar publications.1 Btu = 778 ft-lb1 hp = 33,000 ft-lb per min =550 ft-lb per sec1 kw = 1.341 hp1 hp = 2545 Btu per hr =42.42 Btu per min1 kw = 3413 Btu per hr1 kw - 44,256 ft-lb per min1 hp-hr = 2545 Btu1 kw-hr = 3413 BtuThe first law of thermodynamics is oftenwritten in equation form asU2 - Ui = Q wwhereU. = internal energy of a system at the beginningof a processU„ = internal energy of the system at the endof the processQ = net heat flowing into the system duringthe processW = net work done by the system during theprocess172

Chapter 8 -INTRODUCTION TO THERMODYNAMICSAnother common statement of the first lawof thermodynamics is that a perpetual motionmachine of the first class is impossible. Tounderstand the significance of this statement, itis necessary to understand the classification ofperpetual motion machines. Although no perpetualmotion machine exists— or, indeed, hasever been constructed— it is possible to conceiveof three different categories. Aperpetual motionmachine of the first class is one which would putout more energy in the form of work than it absorbedin the form of heat. Since such a machinewould actually create energy, it would violatethe first law of thermodynamics and the principleof the conservation of energy. Aperpetual motionmachine of the second class would permit thereversal of irreversible processes and wouldthus violate the second law of thermodynamics,as discussed presently. A machine of the thirdclass would be one in which absolutely no frictionexisted. Interestingly enough, there are notheoretical grounds for declaring that a machineof the third class is completely impossible; however,such a machine would be entirely contraryto our experience and would violate some of ourprofoundest convictions about the nature ofenergy and matter.THERMODYNAMIC SYSTEMSA thermodynamic system may be defined asa bounded region which contains matter. Theboundaries may be fixed or they may vary inshape, form, and location. The matter within asystem may be matter in any form— solid,liquid, or gas— or in some combination of forms.For some purposes, devices such as engines,pumps, boilers, and so forth may be regardedas being matter included within a thermodynamicsystem; for other purposes, each such devicemay be considered as a system in itself. Athermodynamic system may be entirely real,entirely imaginary, or a mixture of real andimaginary, A thermodynamic system may becapable of exchanging energy, in the form ofheat and/or work, with its environs; or it maybe an isolated system, in which case no heat canflow to or from the system and no work can bedone on or by the system.If a thermodynamic system appears to be aflexible thing, consider the further statement that"... a system may be said to be whatever oneis talking about, and itsenvirons are everythi..gelse."^*^ Such flexibility of definition is entirelyreasonable for most purposes. When we mustaccount for energy, however, we will find itnecessary to rigidly define and limit the systemor systems under consideration. It is interms of energy accounting, then, that the conceptof a thermodynamic system is most useful.A thermodynamic system requires a workingsubstance to receive, store, transport, anddeliver energy. In most systems, the workingsubstance is a fluid— liquid, vapor, or gas.l^The state of a thermodynamic system is specifiedby giving the values of two or more properties.These properties, which are called statevariables or thermodynamic coordinates m-elude such common properties as pressure,temperature, volume, and mass, as well asmore complex properties such as enthalpy andentropy (discussed later). Although some systemsare adequately described by giving the valueof only two variables, many systems require thespecification of three or more variables.THERMODYNAMIC PROCESSESA thermodynamic process may be defined asany physical occurrence during which an effectis produced by the transformation or redistributionof energy. The occurrence of a thermodynamicprocess is evidenced by changes in someor all of the state variables of the system. Theprocesses of most interest in engineering arethose involving heat and work.In connection with any process, it is usuallynecessary to consider the physical character ofthe process; the manner in which energy istransformed or redistributed as the processtakes place; the kind and amount of energy thatis stored in the system before and after theprocess, and the location of such energy; and thechanges which are brought about in the system13Kiefer, Kinney, and Stuart, Principles of EngineeringThermodynamics , 2nd ed., John Wiley & Sons, NewYork, 1954 (p. 32),14 Some writers use the term gas to indicate a gaseoussubstance that can be liquefied only by very largechanges in pressure or temperature, reserving theterm vapor for a gaseous substance that can be liquifiedmore easily, by slight changes of pressure ortemperature. Other writers define a vapor as a gaswhich is in equilibrium with its liquid. For a greatmany purposes, the properties of a vapor are essentiallythe same as the properties of real gases; hencethe distinction is not always important.173

PRINCIPLES OF NAVAL ENGINEERINGas the result of the process. It is also necessaryto consider the energy exchanges that occurbetween the system and its surroundings duringthe process, since such energy exchanges willhave an effect on the final state of the system.The lifting of an object— as, for example, thelifting of a rock from the base of a cliff to thetop of the cliff— is a simple example of a processinvolving work against gravity. Before the processbegins, the energy which will be required tolift the rock is stored in some form in some otherenergy system. While the process is occurring,energy in the form of work flows from the externalsystem to the earth-rock system. At theend of the process, the energy is stored in theearth-rock system in the form of mechanicalpotential energy. The change which has beenbrought about by this process is manifested bythe separation of the rock and the earth.Now suppose we push the rock off the top ofthe cliff and allow it to fall freely toward thebase of the cliff. Disregarding the push (whichis actually an inputof energy from some externalsystem), the process which now takes place is anexample of work done by gravity. The work doneby gravity converts the mechanical potentialenergy of the system into mechanical kineticenergy. Thus it is clear that energy in transition—work,in this case—begins and ends asstored energy.When the rock hits the earth, other processesoccur. Some work will be expended in compressingthe earth upon which the rock falls, and someenergy will then be stored as internal kineticenergy in the rock and in the earth. The increasein internal kinetic energy will be manifested bya rise in the temperature of the rock and of theearth, and still another process will then takeplace as heat flows from the rock and from theearth. Some energy may also be stored as internalpotential energy because of moleculardisplacements in the rock and the earth.The compression of a spring provides anexample of a process involving elastic deformation.As force is applied to compress thespring, work is done. The major effect of theenergy thus supplied as work is to decrease thedistance between molecules in the spring, thusincreasing the amount of internal potentialenergy stored in the spring. If we suddenlyrelease the spring, the stored internal potentialenergy is suddenly released and the spring shootsaway.The turning of a shaft— as, for example, apropeller shaft of a ship— is another example ofa process involving elastic deformation. Supposethat a strong twisting force is applied to a shaftat rest. The first part of this process will causean elastic deformation of the shaft. The distancebetween molecules in the shaft is changed, andthere is a storage of internal potential energybefore the shaft begins to turn. When the appliedforce becomes great enough to turn the shaft,there will also be a storage of mechanical kineticenergy. As long as the applied force remainsconstant and the shaft continues to turn, thesestored forms of energy will remain stored inunchanging amount. Meanwhile, a great deal ofmechanical energy in transition (work) willcontinuously flow through the shaft to someother system.When a solid body is dragged across a roughhorizontal surface, the process is one of workagainst friction. The work done in moving theobject will be equal to the force required toovercome the friction multiplied by the distancethrough which the object is moved. In this process,the energy supplied as work is transformedvery largely into internal kinetic energy, as evidencedby an increase in temperature. Some ofthe energy may be transformed into internalpotential energy because of molecular displacementsin the object and in the surface over whichit is being moved.A propeller rotating in water is an exampleof a process in which work causes fluid turbulence.The first effect of the movement of thepropeller is to impart various motions to thewater, thus causing turbulence. For a shorttime this movement of the water representsmechanical kinetic energy, but the energy israpidly transformed into internal kinetic energy,as evidenced by a rise in the temperature of thewater.The addition of thermal energy to a piece ofmetal is a simple example of a process involvingheat. As the metal is heated, the temperaturerises, indicating a storage within the metal ofinternal kinetic energy. Also, the metal expands;thus we know that some part of the energy deliveredas heat is transformed into work as themetal expands against the resistance of its surroundings.If we continue heating the metal to itsmelting point, we will note a process in whichthe flow of heat results in a change in the physicalstate of the substance but does not, at thispoint, result in a further rise in temperatm-e.Because of the enormous number and varietyof processes that may occur, some basic classificationof processes involving heat and work is174

Chapter 8- INTRODUCTION TO THERMODYNAMICSdesirable. We will consider first a classificationof processes according to the type of flow andthen consider a classification according to thetype of state change. Discussion of processes as"reversible" or "irreversible" isreservedfora later section.Type of FlowWhen classified according to type of flow ofthe working fluid, thermodynamic processes maybe considered under the general headings of (1)non-flow processes, and (2) steady-flow processes.A non-flow process is one in which the workingfluid does not flow into or out of its containerin the course of the process. The same moleculesof the working fluid that were present at the beginningof the process are therefore present atthe end of the process. Non-flow processes occurin reciprocating steam engines, air compressors,internal combustion engines, and otherkinds of machinery. Since apiston-and-cylinderarrangement is typical of most non-flow processes,let us examine a non-flow process suchas might occur in the cylinder shown in figure8-7.Suppose that we move the cylinder fromposition 1 to position 2, thereby compressingthe fluid contained in the cylinder above thepiston. Suppose, further, that we imagine thisto be a completely ideal process, and one whichis thus entirely without friction. The aspectsof this process that we might want to know aboutare (1) the heat added or removed in the courseof the process; (2) the work done on the workingfluid or by the working fluid; and (3) the netchange in the internal energy of the workingsubstance.From the general energy equation, we knowthat energy in must equal energy out. For thenon-flow process, the general energy equationmay be written aswhereQl2 = (^2 - Uj) +Wk12BtuQl2 " total heat transferred, in Btu (positive ifheat is added during process, negative ifheat is removed during process)Ui = total internal energy, in Btu, at state 1U2 = total internal energy, in Btu, at state 2Ug — U. = net change in internal energy fromstate 1 to state 2W.C 12 = work done between state 1 and state 2,in ft-lb (positive if work is done by theworking substance, negative if work isdone on the working substance)'•..• .•: ;--^WORKINGSUBSTANCE&,}^&(BEFORE •^2S'^'- COMPRESSION) '3-\'m^i'ri.^>i^'j WORKING ^*>i>f4« SUBSTANCE liffi|M (AFTER ^J,.!!*-.COMPRESSION) RSJ = the mechanical equivalent of heat, 778 ft-lbper BtuWk12= total work done by or on the working"^substance, in Btu (positive if work isdone by the substance, negative ifwork is done on the substance)©©147.16.0Figure 8-7.— Piston-and-cylinder arrangementfor non-flow process.This equation deals with total heat, totalwork, and total internal energy. K it is moreconvenient to make calculations in terms of 1pound of the working substance, we would writethe equation as42wk12(U2 - Uj )Btu per lbwhere the value of J remains the same andwhere q, u, and wk have the general meanings175

—PRINCIPLES OF NAVAL ENGINEERINGnoted above but refer to the values for 1 pound Again, the negative answer indicates thatof the working substance rather than to the work is done on_the working substance rathervalues for the total quantity of the working substance.In both equations, it should be noted A steady-flow process is one in which athan b^the working substance.that the subscripts 1 and 2 refer to a separation working substance flows steadily and uniformlyin time rather than to a separation in space. through some device. Boilers, turbines, condensers,centrifugal pumps, blowers, and manyEXAMPLE: Four pounds of working substanceare compressed in the cylinder shown flow processes. In an ideal steady-flow process,other actual machines are designed for steady-in figure 8-7, The process is accomplished the following conditions exist:without the addition or removal of any heat but1. The properties—pressui-e, temperature,with a net increase in total internal energy of specific volume, etc.— of the working fluid remainconstant at any particular cross section120 Btu. Find the work done on or by the workingsubstance, in Btu per pound and in footpoundsper pound.viously must change as the fluid proceeds fromin the flow system, although the properties ob-section to section.SOLUTION: First arrange the equation to fit2. The average velocity of the working fluidthe problem, as follows:remains constant at any selected cross sectionin the flow system, although it may change aswkthe fluid proceeds from section to section.12(ug -3.Uj) + The system is always completely filledq 12with the working fluid, and the total weight ofthe fluid in the system remains constant. Thus,for each pound of working fluid that enters theSince no heat is added or removed, q2^2 = '^• system during a given period of time, there isSince U2 - Uj, or the net increase in total internalenergy, is equal to 120 Btu, and since we period of time.a discharge of 1 pound of fluid during the sameare dealing with 4 pounds of the working sub-4. The net rate of heat transfer and the work120performed on or by the working fluid remainstance, uo — Ui = = 30 Btu per pound.constant.In actual machinery designed for steady-flowThe work done on or by the working substance,in Btu per pound, is given by the ex-entirely satisfied at certain times. For example,processes, some of these conditions are notwk^2pression — —a steady-flow machine such as a boiler or ai. Thus,turbine is not actually going through a steadyflowprocess until the warming-up period isover and the machine has settled down to steadywk operation. For most practical purposes, minor12(- 30) + Btu per lbfluctuations of properties and velocities causedby load variations do not invalidate the use of- 30 Btu per lbsteady-flow concepts. In fact, even suchpistonand-cylinderdevices as air compressors andreciprocating steam engines may be consideredas steady-flow machines if there are enoughThe answer is negative, indicating that the cylinders or if some other arrangement is usedwork is done on the working substance rather to smooth out the flow so that it is essentiallythan by the working substance.uniform at the inlet and the outlet.To find the work done on the working substancein foot-pounds per pound, we merely based on the general energy equation— that is,The equations for steady-flow processes arewkj2 energy in must equal energy out. Steady-flowsolve the equation for wk^, rather than for — = equations are written in various ways, dependingupon the forms of energy that are involvedand substitute. Thus,in the process under consideration. The formsof energy which, to greater or lesser degree,wkj2 = (-30) (778) = -23, 340 ft-lb per lb enter into any general equation for steady-flow176

Chapter 8- INTRODUCTION TO THERMODYNAMICSprocesses are (1) internal energy, (2) heat, (3)mechanical potential energy, (4) mechanicalkinetic energy, (5) work, and (6) flow work.The first five of these energy terms arefamiliar, but the last one may be new. Flowwork,sometimes called displacement energy,isthe mechanical energy necessary to maintainthe steady flow of a stream of fluid. The numericalvalue of flow work may be calculated byfinding the product of the absolute pressure {inpounds per square feet) and the volume of thefluid (in cubic feet). Thus.flow work = pV ft-lbor, more conveniently, using specific volumerather than total volume,flow work = pv ft-lb per lbThe product py will, of course, have a numericalvalue even when there is no flow offluid. However, this value represents flow workonly when there is a steady, continuous flow offluid. Flow work may also be expressed interms of Btu per pound, asflow work =^YBtu per lbAs mentioned before, the steady-flow equationstake various forms, depending upon thenature of the process under consideration. However,the terms for internal energy and flowwork almost invariably appear in any steadyflowprocess. For convenience, this combinationof internal energy and flow work has beengiven a name, a symbol, and units of measurement.The name is enthalpy (accent on secondsyllable). The symbol is' H for total enthalpyor h for specific enthalpy— that is, enthalpy perpound. Total enthalpy, H, may be measured inBtu or in foot-pounds. Specific enthalpy (enthalpyper pound), h, may be measured in Btuper pound or in foot-pounds per pound. Theenthalpy equation may be written aswhereH =pv + BtuH = total enthalpy, in BtuU = total internal energy, in Btup = absolute pressure, in pounds per squarefootV = total volume, in cubic feetJ = the mechanical equivalent of heat, 778ft-lb per BtuSince it is frequently more convenient inthermodynamics to make calculations in termsof 1 pound of the working substance, we shouldnote also the equation for specific enthalpy:h =pvu + -^ Btu per lbhere h^ u^ and v are specific enthalpy, specificinternal energy, and specific volume, respectively.When it is desired to calculate enthalpyin foot-pounds, rather than in Btu, it is onlynecessary to drop the jJ from the equations.The terms heat content and total heat aresometimes used to describe this property whichwe have designated as enthalpy. However, theterms heat content and total heat tend to be misleadingbecause the change in enthalpy of a workingfluid does not always measure the amount ofenergy transferred as heat, nor is it necessarilycaused by the transfer of energy in the form ofheat. Also, the transferred energy that causesa change in enthalpy is not entirely "contained"in the working fluid, as the terms heat contentand total heat tend to imply; although the internalenergy, u^, is stored in the working fluid, the pvcannot in any way be considered as "contained"in the fluid.Type of State ChangeThus far we have considered processes classifiedas non-flow or steady-flow. The nature ofthe state changes undergone by a working fluidprovides us with another useful way of classifyingprocesses. The terms used to identify certaincommon types of state changes are definedbriefly in the following paragraphs.STATE CHANGES.-An isobaricISOBARICstate change is one in which the pressure of andon the working fluid is constant throughout thechange. In other words, an isobaric change is aconstant-pressure change. Isobaric changes occurin some piston-and-cylinder devices in whichthe piston operates in such a fashion as to maintaina constant pressure. Isobaric state changesare not typical of most steady-flow processes,but they are approximated in some steady-flowprocesses in which friction and shaft work are ofinsignificant magnitude.177

PRINCIPLES OF NAVAL ENGINEERINGAn isobaric state change involves changes ofenthalpy. One equation which has frequent applicationto isobaric state changes is written aswhere^"iu^p'-h-h(q, 9) = heat transferred between state 1 and^ state 2, with subscript p indicatingconstant pressureh- = enthalpy of working fluid at state 1h„ . enthalpy of working fluid at state 2ISOMETRIC STATE CHANGES. - A statechange is said to be isometric when the volume(and the specific volume) of the working fluid ismaintained constant. In other words, an isometricchange is a constant-volume change. Isometricchanges involve changes in internal energy,in accordance with the equationwhere^ ="2-"la = heat transferred, with subscript vindicating constant volumeu^ ; specific internal energy of workingsubstance at state 1u„ - specific internal energy of workingsubstance at state 2ISOTHERMAL STATE CHANGES.-An isothermalchange is one in which the temperatureof the working fluid remains constant throughoutthe change.ISENTHALPIC STATE CHANGES. -When theenthalpy of the working fluid does not changeduring the process, the change is said to be isenthalpic.Throttling processes are basically isenthalpic—that is, h^ = h„.ISENTROPICSTATE CHANGES.-An isentropicstate change is one in which there is nochange in the property known as entropy . Thesignificance of entropy and of isentropic statechanges is discussed in a later section of thischapter.ADIABATIC STATE CHANGES.-An adiabaticstate change is one which occurs in such a waythat there is no transfer of heat to or from thesystem while the process is occurring. In manyreal processes, adiabatic changes are producedby performing the process rapidly. Since heattransfer is relatively slow, any rapidly performedprocess can approach being adiabatic.Compression and expansionof working fluids arefrequently achieved adiabatically. For an adiabaticprocess, the energy equation may be writtenaswhereU2-Ui =U^ z internal energy of working fluid atstate 1U„ = internal energy of working fluid atstate 2W =Wwork performed on or by the workingfluidIn words, we may say that the net change ofinternal energy is equal to the work performedin an adiabatic process. The work term may beeither positive or negative, depending uponwhether work is done on the working substance,as in compression, or by the working substance,as in expansion.THERMODYNAMIC CYCLESA thermodynamic cycle is a recurring seriesof thermodynamic processes through which aneffect is produced by the transformation or redistributionof energy. In other words, a cycleis a series of processes repeated over and overagain in the same order.All thermodynamic cycles may be classifiedas being open cycles or closed cycles. An opencycle is one in which the working fluid is takenin, used, and then discarded. A closed cycle isone in which the working fluid never leaves thecycle, except through accidental leakage; instead,the working fluid undergoes a series ofprocesses which are of such a nature that thefluid is returned periodically to its initial stateand is then used again.The open cycle is exemplified by the internalcombustion engine, in which atmospheric airsupplies the oxygen for combustion and in which178

Chapter 8- INTRODUCTION TO THERMODYNAMICSthe exhaust products are returned to the atmosphere.In fact, another way to describe an opencycle is to say that it is one which includes theatmosphere at some point.The closed cycle is exemplified by the condensingsteam power plant used for ship propulsionon many naval ships. In such a cycle, theworking substance (water) is changed to steam inthe boilers. The steam performs work as it expandsthrough the turbines, and is then condensedto water again in the condenser. The water isreturned to the boilers as boiler feed, and isthus used over and over again.Thermodynamic cycles are also classifiedas heated-engine cycles or as unheated-enginecycles, depending upon the point in the cycle atwhich heat is added to the working substance. 1^In a heated-engine cycle, heat is added to theworking substance in the engine itself. An internalcombustion engine has a heated-enginecycle. In an unheated-engine cycle, the workingsubstance receives heat in some device whichis separate from the engine. The condensingsteam power plant has an unheated-engine cycle,since the working substance is heated separatelyin the boilers and then piped to the engines (steamturbines).There are five basic elements in any thermodynamiccycle: (1) the working substance, (2) theengine, (3) a heat source, or high-temperatureregion, (4) a heat receiver, or low-temperatureregion, and (5) a pump.The working substance is the medium bywhich energy is carried through the cycle. Theengine is the device which converts the thermalenergy of the working substance into useful mechanicalenergy in the form of work. The heatsource supplies heat to the working substance.The heat receiver absorbs heat from the workingsubstance. The pump moves the working substancefrom the low pressure side of the cycleto the high pressure side.The essential elements of a closed, unheatedenginecycle are shown in figure 8-8. This isthe basic plan of the typical condensing steampower plant.15 The terms heated ensine and unheated engine shouldnot be confused with the term heat engine. Any machinewhich is designed to convert thermal energy tomechanical energy in the form of work is known as aheat engine. Thus, both internal combustion enginesand steam turbines are heat engines; but the first hasa heated-engine cycle and the second has an unheatedenginecycle.PUMP• WORKING SUBSTANCEfmmmmmMHEATSOURCEI-UNHEATEDENGINEIHEATRECEIVER147.62Figure 8-8. — Essential elements of closed,unheated-engine cycle.In an open, heated-engine cycle such as thatof an internal combustion engine, the essentialelements are all present but are arranged in aIn this type of cycle,somewhat different order.atmospheric air and fuel are both drawn into thecylinder of the engine. Combustion takes placein the cylinder, either by compression or byspark, and the resulting internal energy of theworking substance is transformed into work bywhich the piston is moved. Since the space abovethe piston is a high pressure area when the pistonis near the top of its stroke and a low pressurearea when the piston is near the bottom, thepiston may be thought of as a pump in the sensethat it "pumps" the working fluid from the lowpressure to the highpressure side of the system.Thus, in terms of function, the piston-andcylinderarrangement may be thought of as includingthe heat source, the engine, and the pump.An open, heated-engine cycle might therefore berepresented as shown in figure 8-9.THE CONCEPT OF REVERSIBILITYWhen we put a pan of water on the stove andturn on the heat, we expect the water to boilrather than to freeze. After we have mixed hotand cold water, we do not expect the resultingmixture to resolve itself into two separatebatches of water at two different temperatures.When we open the valve on a cylinder of compressedair, we expect compressed air to rushout; we would be quite surprised if atmosphericair rushed into the cylinder and compressed179

PRINCIPLES OF NAVAL ENGINEERINGWORKINGSUBSTANCE(MIXTURE OFATMOSPHERICAIR AND FUEL)(LOW PRESSURE ORHIGH PRESSURE SIDEOF THE CYCLE,DEPENDING UPON "POSITION OF PISTONIN THE CYLINDER)HEAT SOURCE(COMPRESSION OR SPARK)HEAT RECEIVER(ATMOSPHERE)HEATED ENGINE(PISTON ANDCYLINDER)147.63Figure 8-9.— Essential elements of open,heated-engine cycle.itself. When a shaft is rotating, we expect a temperaturerise in the bearings; when the shaft hasbeen stopped, we would be truly amazed to observeinternal energy from the bearings flowingto the shaft and causing it to start rotating again.When we drag a block of wood across a roughsurface, we expect some of the mechanical energyexpended in this act to be converted into thermalenergy— that is, we expect a storage of internalenergy in the wooden block and the rough surface,as evidenced by temperature rises in these materials.But if this stored internal energy shouldsuddenly turn to and move the wooden block backto its original position, our incredulity wouldknow no bounds.All of which merely goes to show that we havecertain expectations, based on experience, as tothe direction in which processes will move. Thereasonableness of our expectations is attested bythe fact that in all recorded history there is noreport of water freezing instead of boiling whenheat is applied; there is no report of a lukewarmfluid unmixing itself and separating into hot andcold fluids; there is no report of a gas compressingitself without the agency of some externalforce; there is no report of the heat of frictionbeing spontaneously utilizedtoperform mechanicalwork.Are these actions really impossible? Thefirst law of thermodynamics says that mechanicalenergy and thermal energy are mutually convertible,but it says nothing about the directionof such conversions. If we consider only the firstlaw, all the improbable actions just mentionedare perfectly possible and all processes could bethought of as being reversible. In an absolutesense, perhaps, we cannot guarantee that waterwill never freeze instead of boil when it is placedon a hot stove; but we are certainly safe in sayingthat this or any other completely reversiblethermodynamic process is at the outer limits ofprobability. For all practical purposes, then,we will say that there is no such thing as a completelyreversible process.Nevertheless, the concept of reversibility isextremely useful in evaluating real thermodynamicprocesses. At this point, therefore, let usdefine a reversible thermodynamic process asone which would have the following characteristics:(1) the process could be made to occur inprecisely reverse order, so that the energy systemand all associated systems would be returnedfrom their final condition to the conditionsthat existed before the process started; and (2)all energy that was transformed or redistributedduring the process would be returned from itsfinal to its original form, amount, and location.THE SECOND LAW OF THERMODYNAMICSSince the first law of thermodynamics doesnot deal with the direction of thermodynamicprocesses, and since experience indicates thatactual processes are not reversible, it is apparentthat the first law must be supplemented bysome statement of principle that will limit thedirection of thermodynamic processes. Thesecond law of thermodynamics is such a statement.Although the second law is perhaps moreempirical than the first law, and perhaps somethingless of a ''law" in an absolute sense, it isof enormous practical value in the study ofthermodynamics. 16The second law of thermodynamics may bestated in various ways. One statement, known asthe Clausius statement, is that no process ispossible where the sole result is the removal ofheat from a low temperature reservoir and theabsorption of an equal amount of heat by a hightemperature reservoir. Amongother things, thisThe interested stu(dent will find an excellent (iiscusslonof the second law of thermodynamics in MaxPlanck, Treatise on Thermodynamics . Dover Publications,New York, 1945. (A. Ogg. trans.)180

Chapter 8-INTRODUCTION TO THERMODYNAMICSstatement indicates that water will not freezewhen heat is applied. Note that the Clausiusstatement includes and goes somewhat beyondthe common observation that heat flows onlyfrom a hotter to a colder substance.The statement that no process is possiblewhere the sole result is the removal of heatfrom a single reservoir and the performanceof an equivalent amount of work is known as theKelvin-Planck statement of the second law.Among other things, this statement says thatwe cannot expect the heat of friction to reverseitself and perform mechanical work. Morebroadly, this statement indicates a certain onesidednessthat is inherent in thermodynamicprocesses. Energy in the form of work can beconverted entirely to energy in the form of heat;but energy in the form of heat can never beentirely converted to energy in the form ofwork.A very important inference to be drawnfrom the second law is that no engine, actualor ideal, can convert all the heat supplied to itinto work, since some heat must always be rejectedto a receiver which is at a lower temperaturethan the source. In other words, therecan be no heat flow without a temperature differenceand there can be no conversion to workwithout a flow of heat. A further inference fromthis inference is sometimes given as a statementof the second law: No thermodynamic cycle canhave a thermal efficiency of 100 percent.We must say, then, that the first law ofthermodynamics deals with the conservation ofenergy and with the mutual convertibility ofheat and work, while the second law limits thedirection of thermodynamic processes and theextent of heat-to-work energy conversions.THE CONCEPT OF ENTROPYThe concept of reversibility and the secondlaw of thermodynamics are closely related tothe concept of entropy . In fact, the second lawmay be stated as: No process can occur in whichthe total entropy of an isolated system decreases;the total entropy of an isolated systemcan theoretically remain constant in some reversible(ideal) processes, but in all irreversible(real) processes the total entropy of an isolatedsystem must increase.From other statements of the second law, weknow that the transformation of heat to work isalways dependent upon a flow of heat from a hightemperature region to a low temperature region.The concept of the unavailability of a certainportion of the energy supplied as heat to anythermodynamic system is clearly implied in thesecond law, since it is apparent that some heatmust always be rejected to a receiver which isat a lower temperature than the source, if thereis to be any conversion of heat to work. Theheat which must be so rejected is thereforeunavailable for conversion into mechanical work.Entropy is an index of the unavailability ofenergy. Since heat can never be completely convertedinto work, we may think of entropy as ameasure or an indication of how much heatmust be rejected to a low temperature receiverif we are to utilize the rest of the heat for theproduction of useful work. We may also think ofentropy as an index or measure of the reversibilityof a process. All real processes areirreversible to some degree, and all real processesinvolve a "growth" or increase of entropy.Irreversibility and entropy are closelyrelated; any process in which entropy has increasedisan irreversible process.The entropy of an isolated system is at itsmaximum value when the system is in a stateof equilibrium. The concept of an absoluteminimum— that is, an absolute zero—value ofentropy is sometimes referred to as the thirdlaw of thermodynamics (or Nernst's law). Thisprinciple states that the absolute zero of entropywould occur at the absolute zero of temperaturefor any pure material in the crystallinestate. By extension, therefore, it should bepossible to assign absolute values to the entropyof pure materials, if such absolute values wereneeded. For most purposes, however, we areinterested in knowing the values of the changesin entropy rather than the absolute values ofentropy. Hence an arbitrary zero point forentropy has been established at 32° F.Entropy changes depend upon the amount ofheat transferred to or from the working fluid,upon the absolute temperature of the heat source,and upon the absolute temperature of the heatreceiver. Although actual entropy calculationsare complex beyond the scope of this text, oneequation is given here to indicate the units inwhich entropy is measured and to give therelationship between entropy and heat and temperature.Note that this equation applies only toa reversible isothermal process in which Tj =T2.S S Q^2 ~ ''l = T181

PRINCIPLES OF NAVAL ENGINEERINGwhereSj = total entropy of working fluid at state1, in Btu per° RSg = total entropy of working fluid at state2, in Btu per°RQ = heat supplied, in BtuT = absolute temperature at which processtakes place, in° RThe fact that the total entropy of an isolatedsystem must always increase does not mean thatthe entropy of all parts of the system must alwaysincrease. In many real processes, we findincreases in entropy in some parts of a systemand, at the same time, decreases in entropy inother parts of the system. But the importantthing to note is that the increases in entropy arealways greater than the decreases; therefore,the total entropy of an isolated system must alwaysincrease.Each increase in entropy is permanent. In auniversal sense, entropy can be created but itcan never be destroyed or gotten rid of, althoughit may be transferred from one system to another.Every natural process that occurs in theuniverse increases the total entropy of the universe,and this increase in entropy is irreversible.The concept of the universe eventually"running down" might be expressed in terms ofentropy by saying that the entropy of the universeis constantly "building up." The so-called"heat death of the universe" is envisioned asthe ultimate result of all possible natural processeshaving taken place and the universe beingin total equilibrium, with entropy at the absolutemaximum. Such a statement need not imply atotal lack of energy remaining in the universe;but any energy that might remain would becompletely unavailable and therefore completelyuseless.THE CARNOT PRINCIPLEAccording to the second law of thermodynamics,no thermodynamic cycle can have athermal efficiency of 100 percent— that is, no heatengine can convert into work all of the energythat is supplied as heat. The question now arisesas to how much heat must be rejected to a receiverwhich is at a lower temperature than thesource? Or, looking at it another way, what isthe maximum thermal efficiency that couldtheoretically be achieved by a heat engine operatingwithout friction and withoutanyother of theirreversible processes that must occur in allreal machines?To answer this question, Carnot, a Frenchengineer, developed an imaginary and completelyreversible cycle. In the Carnot cycle, all heatis supplied at a single high temperature and allheat that must be rejected is rejected at a singlelow temperature. The cycle is fully reversible.When proceeding in one direction, the Carnotcycle takes in a certain amount of heat, rejectsa certain amount of heat, and puts out a certainamount of work. When the cycle is reversed, thequantity of work that was originally the outputof the cycle is now put into the cycle; the amountof heat that was originally taken in is now theamount rejected; and the amount of heat that wasoriginally rejected is now the amount taken in.When thus reversed, the cycle is called a Carnotrefrigeration cycle.Obviously, no real machine is capable ofsuch complete reversibility, but the concept ofthe Carnot cycle is nonetheless an extremelyuseful one. By analysis of the Carnot cycle, itcan be proved that no engine, actual or ideal,can be more efficient than an ideal, reversibleengine operating on the ideal, reversible Carnotcycle. The thermal efficiency of the Carnot cycleis given by the equationthermal efficiency:T —work output , sheat input ~ Twhere Tg equals the absolute temperature atwhich heat flows from the source to the workingfluid and Tj. equals the absolute temperature atwhich heat is rejected to the receiver.The implications of this statement are ofprofound importance, since it establishes thefact that thermal efficiency depends only uponthe temperature difference between the heatsource and the heat receiver. Thermal efficiencydoes not depend upon the propertiesof the workingfluid, the type of engine used in the cycle,or the nature of the process— combustion, nuclearfission, etc.— that produces the heat at theheat source. The basic principle thus establishedby analysis of the Carnot cycle is called theCarnot principle, and may be stated as follows:The motive power of heat is independent of theagents employed to realize it, its quantity beingfixed solely by the temperatures of the bodiesbetween which the transfer of heat occurs.182

Chapter 8-INTRODUCTION TO THERMODYNAMICSWORKING SUBSTANCESAs previously noted, a thermodynamic systemrequires a working substance to receive,store, transport, and deliver energy. The workingsubstance is almost always a fluid and istherefore frequently referred to as the workingfluid . Water (together with its vapor, steam) isone of the most commonly used working fluids,although air, ammonia, carbon dioxide, and awide variety of other fluids are used in certainkinds of systems. A working substance maychange its physical state during the course of athermodynamic cycle or it may remain in onestate, depending upon the nature of the cycleand the processes involved.To understand the behavior of working fluids,we should have some understanding of the lawsof perfect gases, of the relationships betweenliquids and their vapors, and of the ways inwhich the properties of working fluids may berepresented and tabulated. These topics arediscussed in the following sections.Laws of Perfect GasesThe relationships of the volume, the absolutepressure, and the absolute temperature in thehypothetical substances known as "perfectgases" were stated by the physicists Boyle andCharles in the form of various gas laws. Thelaws thus established may be combined andsummarized in the general statement: For agiven weight of any gas, the product of theabsolute pressure and the volume, divided bythe absolute temperature, is a constant. Or, inequation form.wherep =pv"tp V p V11_I = _2_2.Ti T2absolute pressureV = total volumeT = absolute temperatureR = the gas constantAlthough the laws of perfect gases weredeveloped on the basis of experiments madewith air and other real gases, later experimentsshowed that these relationships do not hold preciselyfor real gases over the entire range ofpressures and temperatures. However, air andother gases used as working fluids may beRtreated as perfect gases over quite a wide rangeof pressures and temperatures without any appreciableerror being introduced. Values of thegas constant for some common gases are:Air 53,3Oxygen 48.3Nitrogen 55.0Hydrogen 766.0Helium 386.0Liquids and Their VaporsWhen heat is transferred to a liquid, theaverage velocity of the molecules is increasedand the amount of internal kinetic energy storedin the liquid is increased. As the average velocityof the molecules increases, some moleculeswhich are at or near the surface of the liquidmomentarily achieve unusually high velocities;and some of these escape from the liquid andenter the space above, where they exist in thevapor state. As more and more of the moleculesescape and come into the vapor state, the probabilityincreases that some of the vapor moleculeswill momentarily have unusually lowvelocities; these molecules will be captured bythe liquid. As a result of this exchange ofmolecules between the liquid and the vapor, acondition of equilibrium is reached and anequilibrium pressure is established. The equilibriumpressure depends upon the molecularstructure of the fluid and upon its temperature.For any given fluid, therefore, there is a definiterelationship between the temperature and thepressure at which a liquid and its vapor mayexist in equilibrium contact with each other.As long as the vapor is in contact with theliquid from which it is being generated, theliquid and the vapor will remain at the sametemperature. If the liquid and the vapor are ina closed container (such as a boiler with allsteam stop valves closed) both the temperatureand the pressure of the liquid and its vapor willincrease as heat is added. If the vapor is permittedto leave the steam space at a rate equalto the evaporation rate, an equilibrium will beestablished at the equilibrium pressure for theparticular temperature.The pressure and the temperature which arerelated in the manner just described are knownas the saturation pressure and the saturationtemperature. Thus, for any specified pressurethere is a corresponding temperature of vaporizationknown as the saturation temperature;183

PRINCIPLES OF NAVAL ENGINEERINGand for any specified temperature there is acorresponding saturation pressure.A liquid \which is under any specified pressureand at the saturation temperature for thatparticular pressure is called a saturated liquid.A liquid which is at any temperature below itssaturation temperature is said to be subcooledliquid . For example, the saturation temperaturewhich corresponds to atmospheric pressure(14.7 psia) is 212°F for water. Therefore, waterat 212°F and under atmospheric pressure is saidto be a saturated liquid. Water flowing in a riveror standing in a pond is also under atmosphericpressure, but it is at a much lower temperature;hence, this water is said to be subcooled.A vapor which is under any specified pressureand at the saturation temperature correspondingto that pressure is said to be a saturatedvapor . Thus, water at 14.7 psia and 212°F producesa vapor known as saturated steam . Aspreviously noted, it is impossible to raise thetemperature of a vapor above the temperatureof its liquid as long as the two are in contact.If the vapor is drawn off into a separate container,however, and additional heat is suppliedto the vapor, the temperature of the vapor israised. A vapor which has been raised to a temperaturethat is above its saturation temperatureis called a superheated vapor , and thevessel or container in which the saturated steamis superheated is Called a superheater . The elementaryboiler and superheater illustrated infigure 8-10 show the general principle of generatingand superheating steam. Practically allnaval propulsion boilers have superheaters forsuperheating the saturated steam generated inthe generating sections of the boiler; the steamis then called superheated steam. The amountby which the temperature of a superheated vaporexceeds the temperature of a saturated vaporat the same pressure is known as the degree ofsuperheat . For example, if saturated steam at apressure of 600 psia and a corresponding saturationtemperature of 486° F is superheated to786° F, the degree of superheat is 300° F.For any substance there is a critical pointat which the properties of the saturated liquidare exactly the same as the properties of thesaturated vapor. For water, the critical pointis reached at 3206.2 psia (critical pressure)and 704.40°F (critical temperature). At thecritical point, the vapor and the liquid areindistinguishable. No change of physical stateoccurs when the pressure is increased or whenadditional heat is supplied; the vapor cannot bemade to liquefy and the liquid cannot be madeto vaporize as long as the substance is at orabove its critical pressure and critical temperature.At this point, we could no longer referto "water" and "steam", since we cannot tellthe water and the steam apart; instead, thesubstance is now merely called a "fluid" ora "working fluid." Boilers designed to operateabove the critical point are called supercriticalboilers. Supercritical boilers are not used atpresent in the propulsion plants of naval ships;however, some boilers of this type are used instationary steam power plants.Representation of PropertiesThe condition of a working fluid at any pointwithin a thermodynamic cycle or system isestablished by the properties of the substanceat that point. The properties that are of specialinterest in engineering thermodynamics includepressure, temperature, volume, enthalpy, entropy,and internal energy. These properties^SATUF SATURATED STEAMSUPERHEATED STEAMFEED WATERGENERATINGFURNACEFigure 8-10.— Elementary boiler and superheater.38.3184

Chapter 8 -INTRODUCTION TO THERMODYNAMICSPROPERTIESOF SATURATED STEAMABS.

PRINCIPLES OF NAVAL ENGINEERINGColumn 5 gives the enthalpy per pound of thesaturated liquid at the pressure and temperatureshown. The enthalpy of saturated water at 32 °Fand the corresponding saturation pressure of0.08854 psis is taken as zero; hence, all enthalpyfigures indicate enthalpy with respect to thisarbitrarily assigned zero point. For example,the enthalpy of 1 pound of saturated water at 190psia and 377. 51°F is 350.79 Btu more than theenthalpy of 1 pound of saturated water at 0.08854psia and 32° F.Column 6 gives the enthalpy of evaporation,per pound of working fluid— that is, the change inenthalpy that occurs during evaporation. Thiscolumn is of particular significance since it indicatesthe Btu per pound that must be suppliedto change the saturated liquid (water) to thesaturated vapor (steam) at the pressure andtemperature shown. In other words, the enthalpyof evaporation is what we formerly describedas the latent heat of vaporization.Column 7 gives the enthalpy per pound of thesaturated vapor at the pressure and temperatureshown. Note that this is the sum of the enthalpy ofthe saturated liquid and the enthalpy of evaporation.Column 8 gives the entropy per pound of thesaturated liquid at the pressure and temperatureshown. The zero point for entropy, like the zeropoint for enthalpy, is arbitrarily established at32° F and the corresponding saturation pressureof 0.08854 psia.Column 9 gives the entropy of evaporationper pound of working fluid at the indicated pressureand temperature. In other words, thiscolumn shows the change of entropy that occursduring evaporation.Column 10 gives the entropy per pound of thesaturated vapor at the pressure and temperatureshown. Note that this is the sum of the entropy ofthe saturated liquid and the entropy of evaporation.Columns 11 and J^ give the internal energyof the saturated liquid and the internal energyof the saturated vapor, respectively.In addition to giving properties of the saturatedliquid and the saturated vapor, theKeenanand Keyes steam tables include data on the superheatedvapor and other pertinent information.GRAPHICAL REPRESENTATION OF PROP-ERTIES.— It is frequently useful to show therelationship between two or more properties ofa working fluid by means of thermodynamicgraphs or diagrams.The relationships among pressure, volume,and temperature of a perfect gas are sometimesrepresented by a three-dimensional diagram ofthe type shown in figure 8-12. The p-v-T surfaceof a real substance may also be representedin this way, but the diagrams become much morecomplex because the relationships among theproperties are more complex. A simplifiedp-v-T surface for water is shown in figure 8-13.147.65Figure 8-12.— Three-dimensional representationof p-v-T surface for perfect gas.VOLUME147.66Figure 8-13.— Three-dimensional representationof p-v-T surface for water.186

Chapter S-INTRODUCTION TO THERMODYNAMICSThe significance of some of the lines on thisdiagram will become clearer as we considersome of the related two-dimensional diagrams.Three-dimensional diagrams are extremelyuseful in giving an overall picture of the p-v-Trelationships, but they are difficult to constructand are somewhat difficult to use for detailedanalysis. Two-dimensional graphs are frequentlyprojected from the three-dimensionalp-v-T surfaces. Even on a two-dimensional diagram,a great many relationships of propertiescan be indicated by means of contour lines orsuperimposed curves.The p-v diagram is made by plotting knownvalues of pressure (p) along the ordinate andvalues of specific volume (v) along the abscissa.^®To illustrate the construction of ap-v diagram, let us consider the isothermalcompression of 1 pound of air from an initialpressure of 1000 pounds per square foot absoluteto a final pressure of 6000 psfa. Let us assumethat the air is at a temperature of 90° F, or 550°R. Since we may treat air asaperfect gas underthese conditions of pressure and temperature, wemay use the laws of perfect gases and the equationpv =RTwherep = absolute pressure, psfaV = specific volume, cu ft per lbR = gas constant (53.3 for air)T = absolute temperature, °RBy plotting these values on graph paper, weobtain the p-v diagram shown in figure 8-14.The curve applies only to the indicated temperature—that is, it is an isothermal curve. Thevalues of p and _v may be calculated for the sameprocess at other temperatures, and plotted asbefore; in this case we obtain a series of isothermalcurves (or isotherms) such as thoseshown in figure 8-15.A p-v diagram for water and steam is shownin figure 8-16. This diagram— and, in fact, mostdiagrams for real substances in the region of astate change— is not drawn to scale because of thevery great difference in the specific volume ofthe liquid and the specific volume of the vapor.Even though it is not drawn to scale, the p-vdiagram serves a useful purpose in indicatingthe general configuration of the saturated liquidline and the saturated vapor line. These lines,which are called process lines , blend smoothlyat the critical point. The shape formed by theprocess lines is characteristic of water and willbe observed on all p-v diagrams of this substance.A two-dimensional pressure-temperature(p-T) diagram of the type shown in figure 8-17is useful because it indicates the way in whichthe phase of a substance depends upon pressureand temperature. The solid-liquid curve, forexample, indicates the effects of pressure onSince the compression is isothermal, T isconstant and the expression RT is equal to53.3 X 550, or 29,315. It is apparent from theequation that p and v must vary inversely—thatis, as p goes up, v goes down. Hence, for anygiven value of p we may find a value of v merelyby dividing 29,315 by p. Choosing six values ofp and computing the values of y, we obtain thefollowing values:STATE ASTATE BSTATE CSTATE DSTATE ESTATE Fp = 1000, V = 29.3p = 2000, V = 14.7p = 3000, V = 9.8p = 4000, V = 7.3p = 5000, V = 5.9p = 6000, V = 4.9

PRINCIPLES OF NAVAL ENGINEERINGsooo7000iOOO5000400030002000lOOO30 35 40 45VOLUME (CUBIC FT PER LB)147,68Figure 8-15.— Group of isothermal curves onp-v diagram.the melting (or freezing) point; the liquid-vaporcurve indicates the effects of pressure on theboiling point; and the solid-vapor indicates theeffects of pressure on the sublimation point.

Chapter 8-INTRODUCTION TO THERMODYNAMICSWORK OUT; THERMALENERGY OF STEAMCONVERTED TO MECHANICALENERGY IN TURBINESCONDENSATEPUMPTHERMAL ENERGY OFAUXILIARY STEAMCONVERTED TOMECHANICAL ENERGYTHERMAL ENERGY OFAUXILIARY EXHAUST STEAMUSED HERE TO HEAT ANDDEAERATE FEED WATER:FEEDmT6ipipspiiipp?S^i^Figure 8-18.— Energy relationships in the basic propulsion cycle of conventional steam-driven ship.38.2propulsion cycle of a conventional steam-drivenship with geared turbine drive and shows someof the major energy transformations that takeplace.The first energy transformation occurs whenfuel oil is burned in the boiler furnace. By theprocess of combustion, the chemical energystored in the fuel oil is transformed into thermalenergy. Thermal energy flows from the hot combustiongases to the water in the boiler. Whilethe boiler stop valves are still closed, steambegins to form in the boiler; the volume of thesteam remains constant but the pressure andtemper atuire increase, indicating a storage ofinternal energy. When operating pressure isreached and the steam stop valves are opened,the high pressure of the steam causes it to flowto the turbines. The pressure of the steam thusprovides the potential for doing work; the actualconversion of heat to work takes place in theturbines. The changes in internal energy betweenthe boiler and the condenser (as evidencedby changes in pressure and temperature) indicatetliat heat has been converted to work in the turbines.The work output of the turbines turns theshaft and so drives the ship.Two main energy transformations are involvedin converting thermal energy to work inthe turbines. First, the thermal energy of thesteam is transformed into mechanical kineticenergy as the steam flows through one or morenozzles. And second, the mechanical kinetic189

PRINCIPLES OF NAVAL ENGINEERINGenergy of the steam is transformed into workas the steam impinges upon the projecting bladesof the turbine and thus causes the turbine toturn. The turning of the turbine rotor causesthe propeller shaft to turn also, although at aslower speed, since the turbine is connected tothe propeller shaft through reduction gears. Thesteam exhausts from the turbine to the condenser,where it gives up its latent heat of condensationto the circulating sea water.For the remainder of this cycle, energy isrequired to get the water (condensate and feedwater) back to the boiler where it will again beheated and changed into steam. The energy usedfor this purpose is generally the thermal energyof the auxiliary steam. In the case of turbinedrivenfeed pumps, the conversion of thermalenergy to mechanical energy occurs in the sameway as it does in the case of the propulsion turbines.In the case of motor-driven pumps, theenergy conversion is from thermal energy toelectrical energy (in a turbogenerator) and thenfrom electrical energy to mechanical energy(work) in the pumps.ENERGY BALANCESFrom previous discussion, it should beapparent that putting 1 Btu in at the boilerfurnace does not mean that 778 foot-pounds ofwork will be available for propelling the shipthrough the water. Some of the energy put in atthe boiler furnace is used by auxiliary machinerysuch as pumps and forced draft blowers tosupply the boiler with feed water, fuel oil, andcombustion air. Distilling plants, turbogenerators,steering gears, steam catapults, heatingsystems, galley and laundry equipment, andmany other units throughout the ship use energyderived directly or indirectly from the energyput in at the boiler furnace.In addition, there are many "energy losses"throughout the engineering plant. As we haveseen, energy cannot actually be lost. But whenit is transformed into a form of energy whichwe cannot use, we say there has been an energyloss. Since no insulation is perfect, some thermalenergy is always lost as steam travels throughpiping. Friction losses occur in all machineryand piping. Some heat must be wasted as thecombustion gases go up the stack. Some heatmust be lost at the condenser as the steam exhaustedfrom the turbines gives up heat to thecirculating sea water. We cannot expect allof the heat supplied to be converted into work;even in the most efficient possible cycle, weknow that some heat must always be rejectedto a receiver which is at a lower temperaturethan the source. Thus, each Btu that is theoreticallyput in at the boiler furnace must bedivided up a good many ways before the energycan be completely accounted for. But the energyaccount will always balance. Energy in mustalwaysequal energy out.Designers of engineering equipment useenergy balances to analyze energy exchangesand to compute the energy requirements forproposed equipment or plants. Operating engineersuse energy balances to evaluate plantperformance. The engineer officer of a navalship may find it necessary to make energybalances in order to find out whether the plantis operating at designed efficiency or whetherdefects are causing unnecessary waste of steam,fuel, and energy.An energy balance for an entire engineeringplant is usually made up in the form of a flowdiagram similar to (but more detailed than) theone shown in figure 8-18. Anumber of numericalvalues are entered on the flow diagram, the mostimportant of which are the quantities of theworking fluid flowing per hour at various pointsand the thermodynamic states of the workingfluid at various points. The quantity of fluidflowing per hour may be obtained by directmeasurement of flow through flow meters ornozzles or by calculation; in some instances,it is necessary to estimate steam consumptionof pumps and other units on the basis of availabletest data. Data on the state of the workingfluid is obtained from pressure and temperaturereadings. Enthalpy calculations are made andnoted at various points on the diagram. Thecomplete energy balance includes tabular dataas well as the data shown on the flow diagram.190

PART lll-THECONVENTIONAL STEAM TURBINEPROPULSION PLANTChapter 9Chapter 10Chapter 11Chapter 12Chapter 13Machinery Arrangement and Plant LayoutPropulsion BoilersBoiler Fittings and ControlsPropulsion Steam TurbinesCondensers and Other Heat ExchangersThis part of the text deals with the major units of machinery in theconventional steam turbine propulsion plant-a type of plant which is atpresent widely used in naval ships. For the most part, the discussion isconcerned with geared-turbine drive; but some of the information is alsoapplicable to those few ships with turboelectric drive. The term "conventional"is used here to indicate that the plants under discussionutilize conventional boilers, rather than nuclear reactors, as the sourceof heat for the generation of steam.Chapter 9 introduces the conventional steam turbine propulsion plantby taking up the arrangement of propulsion machinery and the majorengineering piping systems found aboard conventional steam-driven ships.Chapters 10 and 11 deal with propulsion boilers and their fittings andcontrols. Chapter 12 describes propulsion steam turbines. Chapter 13discusses the condensers and other heat transfer apparatus used in thecondensate and feed system of the conventional steam turbine propulsionplant.As may be noted, the sequence of presentation follows the sequenceof the thermodynamic cycle. The boiler is the heat source ,or hightemperatureregion; the turbine is the engine in which the thermalenergy of the steam is converted into mechanical energy which drivesthe ship; and the condenser is the heat receiver to which some heatmust always be rejected in order to allow the conversion of heat to work.191

CHAPTER 9MACHINERY ARRANGEMENT AND PLANT LAYOUTTo understand a shipboard propulsion plant,it is necessary to visualize the general configurationof the plant as a whole and tounderstand the physical relationships among thevarious units. This chapter provides generalinformation on the distribution and arrangementof propulsion machinery in conventional steamturbine propulsion plants and on the arrangementof the major engineering piping systemsthat connect and serve the various units ofmachinery.It is important to note that the informationgiven in this chapter is general rather thanspecific. No two ships— not even sister shipsareexactly alike in their arrangement of machineryand piping. The examples given in thischapter are based on the arrangements usedin various kinds of ships, large and small, oldand new. The examples give some idea of thevariety of arrangements that may be found onsteam-driven surface ships, and they indicatethe basic functions of the machinery and piping;but the examples cannot provide an exactpicture of the machinery and piping on any oneship. For detailed information concerning thearrangements on any particular ship, it isnecessary to consult the ship's blueprints,various ship's manuals, and the manufacturers'technical manuals that cover the engineeringequipment and piping systems installed in theship.ARRANGEMENT OF PROPULSIONMACHINERYThe propulsion machinery on conventionalsteam-driven surface ships includes (1) thepropulsion boilers, (2) the propulsion turbines,(3) the condensers, (4) the reduction gears, and(5) the pumps, forced draft blowers, deaeratingfeed tanks, and other auxiliary machinery unitswhich directly serve the major propulsion units.On most steam-driven surface ships otherthan oilers, tankers, and certain auxiliaries,the propulsion machinery is located amidships.Turbogenerators and their auxiliary condensersare usually located in the propulsion machineryspaces; other engineering equipment that is notdirectly associated with the operation of themajor propulsion units may be located in ornear the propulsion machinery spaces or inother parts of the ship, as space permits.A word about terminology may be helpfulat this point. The boilers in a propulsion plantmay be identified as propulsion boilers (oroccasionally as main boilers) when it is necessaryto distinguish between propulsion boilersand the auxiliary boilers that are installed onsome ships. The turbines are identified aspropulsion turbines when it is necessary todistinguish between them and the many auxiliaryturbines that are used on all steam-driven shipsto drive pumps, forced draft blowers, and otherauxiliary units. The propulsion turbines arealso sometimes referred to as the main engines,although this usage is not considered particularlydesirable. The term propulsion unitis correctly used to identify the combinationof propulsion turbines, main reduction gears,and main condenser in any one propulsion plant;however, the term propulsion unit may alsobe used in a more general sense to indicateany major unit in the propulsion plant.Each propulsion shaft has an identifyingnumber which is based on the location of theshaft, working from starboard to port. Theshaft nearest the starboard side is the No. 1shaft, the one next inboard is the No. 2 shaft,and so forth. On recent ships, the propulsionmachinery that serves each shaft is given thesame number as that shaft. For example, theNo. 2 shaft is served by the No. 2 propulsionunit and the No. 2 boiler. Where two similarunits serve one shaft, the identifying number193

PRINCIPLES OF NAVAL ENGINEERINGis followed by a letter. If two boilers serve theNo. 3 propulsion unit and the No. 3 shaft, forexample, the boilers would be identified as No.3A and No. 3B. Where letters are used, theyare used in sequence going from starboard toport and then from forward to aft.On older ships, the practice of identifyingpropulsion units by the number of the shaftthey serve is slightly different. In general, eachpropulsion unit is numbered to correspondwith the number of the shaft it serves; butthe numbering of the boilers is generally notthe same as the numbering of the propulsionunits and the shafts. On an older ship, for example,the No. 1 boiler and the No. 2 boilermight serve the No. 1 propulsion unit and theNo. 1 shaft, while the No. 3 boiler and the No. 4boiler would serve the No. 2 propulsion unit andthe No. 2 shaft.The functional relationships of the majorpropulsion units and of many auxiliaries areshown in figure 9-1. This illustration does notindicate the actual location of the machineryunits; indeed, the physical location is oftensurprisingly different from the location thatmight be assumed from a diagram of this type.In considering the physical arrangement ofmachinery, however, we must keep the functionalrelationships clearly in mind. The three majorpiping systems shown in figure 9-1 are themain steam system, the auxiliary steam system,and the auxiliary exhaust system; again, afunctional rather than a physical relationshipis indicated. The three systems are discussedin more detail later in this chapter; at this pointit is only necessary to note the relationshipsof these vital systems to the propulsion unitsand auxiliaries.The propulsion machinery spaces may bephysically arranged in several ways. Some shipshave firerooms, containing boilers and the stationsfor operating them, and enginerooms,containing propulsion turbines and the stationsfor operating them. On some ships, one fireroomserves one engineroom; on others, twofirerooms serve one engineroom. Instead offirerooms and enginerooms, many large shipsof recent design have spaces which are calledmachinery rooms. Each machinery room containsboth the boilers and the propulsion turbinesthat serve a particular shaft. On some recentships that have certain automatic controls, thepropulsion machinery is very largely operatedfrom separate enclosed operating stations locatedwithin the machinery room.No matter what arrangement of machineryspaces is used, the propulsion machinery isusually on two levels. The condensers and themain reduction gears are on the lower level.The propulsion turbines and the high speedpinion gears to which they are connected areon the upper level with the low pressure turbineexhaust directly over the condenser. Theboilers occupy both the lower level and the upperlevel; the stations for firing the boilers(sometimes referred to as "the firing aisle")are on the lower level, while the stations foroperating the valves that admit feed water tothe boilers are on the upper level. The boilersare usually located on the centerline of theship or else they are distributed symmetricallyabout the centerline. The long axis of theboiler drums runs fore and aft rather than athwartship.Other machinery, including the propulsionauxiliaries, is arranged in various waysas space and weight considerations permit.Figure 9-2 shows the general arrangementof propulsion machinery on destroyers of theDD 445 and DD 692 classes. The machinery isarranged so that the forward fireroom and theforward engineroom can be operated together asone completely independent plant, while theafter fireroom and the after engineroom canbe operated together as another completelyindependent plant. All propulsion machinery,including auxiliaries, is duplicated in eachplant. The arrangement shown in figure 9-2 istypical of most destroyers, even the newerones; however, the newer destroyers containa non-machinery separation space between theforward and after machinery plants.Figures 9-3, 9-4, 9-5, and 9-6 show thearrangement of machinery in the No. 1 fireroomand the No. 1 engineroom of the frigatesDLG 14 and DLG 15. The arrangement shownin these illustrations is also typical of that inthe frigates DLG 6-13. The forward (No. 1)fireroom and engineroom may be operated togetheras a separate plant, as may the after(No. 2) fireroom and engineroom.Figure 9-7 shows the general arrangementof propulsion machinery on the CA 68 class ofheavy cruisers. This arrangement is typicalof cruisers commissioned during World WarII. The two forward firerooms and the forwardengineroom constitute one plant; the two afterfirerooms and the after engineroom constitutethe other plant. Cross-connections make itpossible for other operational arrangementsto be used.194

O HAUXILIARY TURBINECENTRIFUGAL PUMPSCREW-TYPE NOTARY PUMP'.UU> IUL..I-..A .Hi"^ MAIN STEAM (SUPERHEATED)^B TURBOGENERATOR STEAM (SUPE[)HEATED)CONDENSATEFEED WATERAUXILIARY STEAM (SATURATED)TURUOGENEliATOR STIAM (SATURATED)AUXILIARY EXHAUST STEAMFORCED DRAFT BLOWER FAN147.71Figure 9-1. — Functional relationships of propulsion units, auxiliaries, mainsteam system, auxiliary steam system, and auxiliary exhaust system(Facing page 194).

is foi:No. 3exam I3A arare u;port aOnpropulthey spropu]with tthe mthe s£:unitsamplemightNo. 1boilerthe NoThpropulshownindicaiunits;surprimightIn coimachiirelaticpipingmain sand tlfunctioisindiin morit is cof thesand au:Thephysic;have f:tionscontairfor opiroomfirerocfirerocof recfmachintains bthat seships tpropuL'from scated V

Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUT" 2 MAIN ENGINE^>

PRINCIPLES OF NAVAL ENGINEERINGFigure 9-3.— Arrangement of machinery on upper level of No. 1DLG 14 and DLG 15.196fireroom,147.72

Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUTFigure 9-4.-Arrangement of machinery on lower level of No. 1 fireroom, DLG 14 and DLG 15147.73197

—PRINCIPLES OF NAVAL ENGINEERINGt^i^^"^ '^ ^Figure 9-5.—Arrangement of machinery on upper level of No. 1DLG Hand DLG 15.engineroom,147.74198

Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUT3,3. TURBO-QEN. COND.CONDENSATE PUMP,NO. IBMC SETV?""^^DEGAUSSINGA" COILFigure 9-6.—Arrangement of machinery on lower level of No. t engineroom,DLG 14 and DLG 15.147.75199

IPRINCIPLES OF NAVAL ENGINEERING00CO00CO=10}00

Chapter Q-MACHINERY ARRANGEMENT AND PLANT LAYOUT00CO

IPRINCIPLES OF NAVAL ENGINEERINGPIPE FITTINGS, TYPES OFCONNECTIONSSCREWED ENDSFLANGED ENDSBELL-ANDSPICOT ENDSWELDED AND BRAZED ENDSSOLDERED ENDSELBOW, 90 DEGREESELBOW, 45 DEGREESELBOWSELBOW, OTHER THAN 90 OR 45DEGREES, SPECIFY ANGLEELBOW, LONG RADIUSr^30"CAPCOUPLINGPLUGREDUCER, CONCENTRICUNION, FLANGEDUNION, SCREWEDEXPANSION JOINT.BELLOWSEXPANSION JOINT,SLIDINGT-w«--CCOhVALVES, TYPES OF CONNECTIONSSCREWED ENDSFLANGED ENDSBELLAND-SPICOT ENDSWELDED AND BRAZED ENDSSOLDERED ENDSSTODP COCK, PLUG OR CYLINDER ~©~VA LVE, 3 WAY. 3 PORT|>STOP COCK, PLUG OR CYLINDERVALVE, 4 WAY, 4 PORTRELIEF, REGULATING, AND SAFETYVALVESGENERAL SYMBOLANGLE, RELIEFBACK PRESSUREGLOBE, RELIEFYELBOW,REDUCINGELBOW, SIDE OUTLET,OUTLET DOWNELBOW, SIDE OUTLET,OUTLET UPELBOW, TURNED DOWNELBOW, TURNED UPr r(M—GENERAL SYMBOLSTOP VALVESrGLOBE, RELIEF ADJUSTABLE,OR SPRING LOADED REDUCINGPRESSURE REDUCING ORPRESSURE REGULATING.INCREASED ACTUATINGPRESSURE CLOSES VALVEPRESSURE REDUCING ORPRESSURE REGULATING,INCREASED ACTUATINGPRESSURE OPENS VALVEX—C5*0—-cfe-ELBOW,UNIONTEESGATE, ANGLEGLOBEYPRESSURE REGULATING,WEIGHT. LOADEDSAFETY, BOILER-0X3-YTEECHECK VALVESTEE, DOUBLE SWEEPGLOBE, AIR OPERATED,SPRING CLOSING-cJfcO-VALVETEE, OUTLET DOWNTEE, OUTLET UPTEE, SINGLE SWEEP, ORPLAIN T YOTHER PIPE FITTINGS-^e^--KEM-TI/ \CLOBE, DECK OPERATED _t:Q3_GLOBE, HYDRAULICALLYOPERATEDSTOP COCK, PLUG OR CYLINDERVALVE, 2 WAY_/T\_~VL/"GENERAL SYMBOLCHECK, LIFTCHECK, SWINGFITTINGBUSHINGSTOP COCK, PLUG OR CYLINDERVALVE, 3 WAY, 2 PORT —0~GLOBE, STOP CHECKFigure 9-10.— Engineering symbols.11.330.1(11A)202

Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUTOTHER VALVESBUCKET TRAPVACUUM-PRESSURE(7)vPFLOAT TRAPTHERMOMETERAUTOMATIC, OPERATED BYGOVERNORrftb-C>1

PRINCIPLES OF NAVAL ENGINEERINGjunction of interconnecting systems. Short runsof piping which serve an immediately obviouspurpose, such as short vents or drains, need notbe marked. As a rule, piping on the weather decksdoes not require marking; if it does requiremarking, label plates (rather than stenciledpaint or prepainted vinyl labels) are used.Each valve is marked on the rim of the handwheel,on a circular label plate secured by thehandwheel nut, or on a label plate attached to theship's structure or to adjacent piping. The valvelabel gives the name and purpose of the valve, ifthis information is not immediately apparentfrom the piping system marking, and it gives thelocation of the valve. The location is indicated bythree numbers which give, in order, the verticallevel, the longitudinal position, and the transverseposition. Consider, for example, a drainbulkhead stop valve that is labelled:2-85-1The location of this valve is indicated by thesenumbers. The first number indicates the verticalposition— in this case, the second deck. The secondnumber indicates the longitudinal position bygiving the frame number— in this case, frame 85.The third number indicates the transverse position—starboardside if the number is odd, portside if the number is even. The numbers indicatingtransverse position begin atthecenterlineofthe ship and progress out toward the sides. Forexample, a second drain bulkhead stop installedon the same level and at the same frame, but fartherto starboard, would be indentified as2-85-3In either case, of course, the valve would alsobe identified as to system (DRAIN BULKHEADSTOP, in these examples) if the piping systemidentification did not make the system obvious.A slightly different system of marking is usedfor identifying main line valves, cross-connectionor split-plant valves, and remote-operatedvalves in vital engineering piping systems. Insteadof being identified bylocation, these valvesare assigned casualty control identification numbers,by system, asMain steam MSI, MS2, MS3, etc.Auxiliary steam ASl, AS2, ASS, AS4, etc.Auxiliary condensate. . . ACNl, ACN2, etc.Auxiliary exhaust AEl, AE2, AE3, etc.Fuel oil service FOSl, FOS2, etc.On newer ships, the system for markingvalves in the vital engineering systems is slightlydifferent, consisting of a three-part designationin the following sequence: (1) a number designatingthe shaft or plant number; (2) lettersdesignating the system; and (3) a number, or acombination of a number and a letter, indicatingthe individual valve. Individual valve numbersare assigned in sequence, beginning at the originof a system and going in order to the end of thesystem, excluding branch lines. In other words,the first valve in the mainline is No. 1, the secondis No. 2, and so forth. Since parallel flowpaths frequently exist, it is often necessary toassign a shaft number and a system designationto the parallel flow paths as well as to the basicmain line of the system. The valves in the parallelflow paths are then numbered in sequence;identical numbers areusedfor valves which performlike functions in each of the parallel flowpaths, but a letter suffix is added to distinguishbetween the similar valves. This system of identificationis illustrated for part of a 'main steamsystem in figure 9-11.It is of utmost importance that all engineeringpersonnel (officer and enlisted) become familiarwith the valve markings used in the vitalengineering systems. Use of the identificationnumbers tends to prevent confusion and errorwhen the plant is being split or cross-connectedand when damaged sections are being isolated,since it provides a means of ordering any particularvalve to be opened or closed without takingtime to describe the actual physical location ofthe valve. However, the identification markingscannot serve their intended purpose unless allengineering personnel are throroughly familiarwith the physical location and the identificationnumber of each valve they may be requiredeither to operate themselves or to order openedor closed.Most shipboard piping is painted to match andblend in with its surrounding bulkheads, overheads,or other structures. In a very few systems,color is used in a specified manner to aidin the rapid identification of the systems. Forexample, JP-5 piping in interior spaces ispainted purple. Gasoline valves in interiorspaces are painted yellow, except for movingparts of the valves; in exterior locations, partof the valve handwheel or the operating lever Ispainted yellow. Green is similarly used to identifyoxygen, and red is used for fireplugs andfoam discharge valves.204

Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUTNO. 2 SHAFTRED.GEARSNO. 2MAINENGINE2MS32MS2B2MS2A^2MS1B)2MS4B2MS5BTURBO-GEN.2BNO. 2ENGINEROOM

PRINCIPLES OF NAVAL ENGINEERINGsoot blowers. On some recent ships (both 600-psi and 1200-psi) the main steam system suppliessuperheated steam to several other unitsas well. For example, some carriers use superheatedsteam to supply steam catapult systems;also, some carriers and other ships usesuperheated steam to operate forced draftblowers, main feed pumps, main circulatingpumps, and other auxiliaries. The soot blowersare not supplied from the main steam systemon some ships that have 1200-psi main steamsystems; instead, steam for the soot blowers istaken from the 1200-psi auxiliary steam system,as discussed later in this chapter.Figure 9-12 illustrates the main steam systemfor the forward plant (No. 1 fireroom andNo. 1 engineroom) of a steam-driven destroyerescort. The after plant (No. 2 fireroom and No.2 engineroom) main steam system is very similar.There is one boiler in each fireroom. Eachboiler is provided with a boiler stop valve whichcan be operated either locally from the fireroomor remotely from the main deck. A secondline stop valve in each fireroom providestwo-valve protection for the boiler when it isnot in use, and permits effective isolation incase of damage. This type of two-valve protectionis standard for all boilers installed in U.S.Navy ships.For ahead operation, the superheated steampasses through a main steam strainer, a guardingvalve, and a throttle valve before enteringthe high pressure turbine. From the high pressureturbine, the steam passes through a crossoverpipe to the low pressure turbine; then itexhausts to the condenser. For astern operation,the superheated steam passes through thesteam strainer and through a stop valve; thenit goes to the steam chest of the astern element,which is located at one end of the low pressureturbine.The forward and after main steam systemsare connected by cross-connection piping betweenthe forward engineroom and the afterfireroom. By means of this piping, either boilercan be used with either or both propulsion unitsand turbogenerators. Thus the two propulsionplants can be operated either independently(split-plant) or together (cross-connected).Soot blowers are devices for removing soot from theboiler firesides while the boiler is steaming. Sootblowers are discussed in chapter 11 of this text.Note that superheated steam for the sootblowers goes from the superheater outlet pipinginto a soot blower steam header. 4 Branchesgo from the header to the individual soot blowers.A 600-psi main steam system is shown infigure 9-13. This is the main steam system forthe two forward plants (No. 1 and No. 4) on aheavy cruiser of the CA 139 class. Although thisdrawing is more complicated, the system itselfis still basically simple.A 600-psi main steam system for destroyersof the DD 445 and DD 692 classes is shown infigure 9-14. A later modification was made onthese ships to provide a separate superheatedsteam supply to the turbogenerators. With thismodification, this main steam system is typicalof most destroyers, even those that are considerablymore recent than the DD 445 and DD 692classes.For comparison, figure 9-15 shows a 1200-psi main steam system for the forward plant ofthe frigates DLG 14 and DLG 15. Note that the1200-psi main steam system does not supplysteam to the soot blowers but that it does supplysteam to the main feed pumps. In both of theserespects, the 1200-psi system differs from theDD 445 and DD 692 main steam system describedabove.AUXILIARY STEAM SYSTEMSAuxiliary steam systems supply steam at thepressures and temperatures required for the operationof many systems and units of machinery,both inside and outside the engineering spaces.Although auxiliary steam is often called "saturated"steam, it has some degree of superheatin some auxiliary steam systems. Constant andintermittent service steam systems, steamsmothering systems, whistles and sirens, fueloil heaters, fuel oil tank heating coils, air ejectors,forced draft blowers, and a wide variety ofpumps are typical of the systems and machineryThe term header is commonly used in engineeringtodescribe any tube, chamber, drum, or similar piece towhich a series of tubes or pipes are connected in sucha way as to permit a flow of fluid from one tube (orgroup of tubes) to another. In essence, a header is akind of manifold. In common usage, a distinction ismade between drums and headers on the basis of size:a large piece of this kind is likely to be called a drum,a smaller one a header.206

Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUTTURBOGENERATORSUPERHEATEDTURBOGENERATORSTEAM-CROSS-CONNECTION

; N0.4,——-.PRESfCIPLES OF NAVAL ENGINEERINGMACHINERY ROOM NO. 4C.H-P TURBINE NO. 4y'RCDUCTIONGEAR N04VP^ L-P I. ASTERNI TURBINE NO. 4MSI4MS 12Mr TEST'CONNAHEAD GUARDIAN BYPASS1 AHEAD GUARDIAN^AHEAD NOZZLE VALVESMAIN CACEBOARPASTERN THROTTLE'—'—«r'5- -7"ASTERN THROTTLEBYPASSrI%CT9"1 »M9I0 PROPULSION TURBINECROSS-CONNECTIONqb;p.Oo c>UlzX o

Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUTMACHINERYROOM NO. Izooca.zZio.ASTERN THROTTLE BYPASSASTERNTHROTTLEMAINGACEBOARDAHEAD NOZZLEVALVESH-P TURBINE NO IAHEADGUARDIANAHEAD GUARDIANBYPASS©- PRESSURE GAGE

PRINCIPLES OF NAVAL ENGINEERINGMost ships that have 600-psi main steamsystems have a 600-psi auxiliary steam systemand a 150-psi auxiliary steam system, plussome lower pressure service systems. The600-psi auxiliary steam system serves somemachinery directly and also supplies the 150-psisystem through reducing valves or reducingstations. The 150-psi auxiliary steam systemserves some units directly and also providesauxiliary steam for units or systems that requireauxiliary steam at even lower pressures.Figure 9-16 shows part of a 600-psi auxiliarysteam system for the two forward plants (No. 1and No. 4) on a heavy cruiser of the CA 139class. Note that the system is arranged inloop form, with cross connections at requiredintervals and with branch lines serving thevarious units and systems. Note, also, thatthe auxiliary steam system is, like the mainsteam system, basically rather simple.Ships that havea 1200-psi main steam systemhave a 1200-psi auxiliary steam system, a600-psi auxiliary steam system, a 150-psiauxiliary steam system, and several constantand intermittent steam service systems. Theauxiliary steam systems of the DLG 14 andDLG 15 are described here in some detail asexamples of auxiliary steam systems on shipshaving 1200-psi main steam systems.The 1200-psi and the 600-psi auxiliary steamsystems for the forward plant of the DLG 14and DLG 15 are shown in figure 9- 17. A similararrangement exists in the after plant. The1200-psi auxiliary steam system for each plantis entirely separate and independent; the 600-psi systems can be cross-connected but arenot normally operated that way. Each plant hastwo boilers, both of which supply steam to the1200-psi auxiliary steam system of that plant.The steam comes from the desuperheater outletof each boiler; it is desuperheated fromapproximately 950° F (the operating temperatureat the superheater outlet) to approximately700° F. Note that the steam in this auxiliarysteam system still has something more than200° F of superheat, so it is not strictly"saturated" steam. The 1200-psi auxiliarysteam lines from each boiler are interconnectedso that either boiler can provide steam foreverjrthing served by this system.The 1200-psi auxiliary steam system suppliessteam directly to the soot blowers, theforced draft blowers, and the reducing stationsthat reduce the pressure from 1200 to 600 psig;it also supplies augmenting steam at 12 psigto the auxiliary exhaust system, when necessary.The 600-psi auxiliary steam system suppliessteam at 600 psig and approximately 650° F toboth fireroom and engineroom equipment. Inthe fireroom, the 600-psi system suppliessteam to the fuel oil service pumps, the mainfeed booster pump, the fire pump, and thereducing stations that reduce the pressure from600 to 150 psig. In the engineroom, the 600-psi system supplies steam to the standby lubeoil service pump, the main condensate pump,the main circulating pump, and a reducingstation that reduces the pressure from 600 to150 psig.The 150-psi and the 50-psi auxiliary steamsystems for the after plant of the DLG 14 andDLG 15 are shown in figure 9-18. The forwardplant has similar systems.The 150-psi auxiliary steam system in eachplant provides all machinery, equipment, andconnections which require 150-psi steam. Thissystem also supplies steam to other reducedpressure systems, via reducing stations, andmay deliver steam to other ships or receivesteam from outside sources through specialpiping and deck connections. Another functionof the 150-psi system is to augment the auxiliaryexhaust system; in fact, this function isnormally performed by the 150-psi system,although it may be performed directly by the1200-psi auxiliary steam system when necessary.Steam for the 150-psi system in the fireroomis supplied from the reducing stations thatreduce the pressure from 600 to 150 psig. Thereare two such stations ineachfireroom. A spraytypedesuperheater reduces the temperatureof the fireroom 150-psi system to 400° F. Servicesand auxiliaries operated from the 150-psi system in the fireroom include superheaterprotection steam, 5 service steam systems,oil heating systems, boiler casing steamsmothering systems, fireroom bilge steamsmothering system, bilge and fuel oil tankstripping pumps (in No. 1 fireroom and No. 2engineroom only), steam for burner cleaningservice, and hose connections for boiling outboilers. In emergencies, the fireroom 150-psiauxiliary steam system can also supply steamfor some units that are normally supplied bythe engineroom 150-psi system.Superheater protection steam is discussed in chapter10 of this text.210

Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUTThe reducing station that reduces steam from600 to 150 psig in the engineroom suppliessteam at 150 psig and 610° F to the main andauxiliary air ejectors, the distilling plant airejectors, and the turbine gland seal systems.Line desuperheaters are not installed in the150-psi system in the engineroom.In the No. 2 engineroom, a reducing stationreduces steam pressure from 150 psig to 100psig and supplies steam at 100 psig and 385° Fto the ship's laundry and tailor shop equipment.This 100-psi auxiliary steam system is calledthe 100-psi constant service system.The 150-psi system also supplies two50-psisystems— one a constant service system, one anintermittent service system. Both of these systemsare shown in figure 9-18.AUXILIARY EXHAUST SYSTEMSThe auxiliary exhaust system receives exhauststeam from pumps, forced draft blowers,and other auxiliaries which do not exhaust directlyto a condenser. Auxiliary exhaust steamis used in various units, including deaeratingfeed tanks, distilling plants, and (on many ships)turbine gland seal systems.The pressure in the auxiliary exhaust systemis maintained at about 15 psig. If the pressurebecomes too high, automatic unloading valves(dumping valves) allow the excess steam to goto the main or auxiliary condensers; in theevent of failure of these unloading valves, reliefvalves allow the steam to escape to atmosphere.If the pressure in the auxiliary exhaust systemdrops too low, makeup steam is supplied froman auxiliary steam system (usually the 150-psisystem) through augmenting valves.The auxiliary exhaust system must be clearlydistinguished from the various auxiliary steamsystems. Even though the auxiliary exhaustsystem is a steam system, it is not consideredan auxiliary steam system. A reexamination offigure 9-1 may be helpful at this point to clarify#2 ENGINEROOM #2 FIREROOM #1 ENGINEROOM #1 FIREROOMFigure 9-14.— Main steam system, DD 445 and DD 692 classes.ODECK OPERATED VALVE147.76211

PRINCIPLES OF NAVAL ENGINEERINGo

Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUTthe relationships between the auxiliary exhaustsystem and the main and auxiliary steamsystems.STEAM ESCAPE PIPINGSteam escape piping is installed to providean unobstructed passage for the escape of steamfrom boiler safety valves and from the reliefvalves installed on steam-driven auxiliaries. Aline is also provided from the auxiliary exhaustsystem to the escape piping to allow the auxiliaryexhaust to unload to atmosphere if thepressure becomes excessively high. Steam escapepiping is usually shown on the same plansor drawings as the ones that show the auxiliaryexhaust piping.GLAND SEAL AND GLANDEXHAUST SYSTEMSGland sealing steam is supplied to the shaftglands^ of propulsion turbines and turbogeneratorturbines to seal the shaft glands againsttwo kinds of leakage: (1) air leakage into theturbine casings, and (2) steam leakage out ofthe turbine casings. These two kinds of leakagemay seem contradictory; however, each kindof leakage could occur under some operatingconditions if the shaft glands were not sealed.Pressures in the gland seal system are low,ranging from about 3/4 psig to 2psig, dependingupon the conditions of operation. Gland exhaustpiping carries the steam and air from the turbineshaft glands to the gland exhaust condenser,where the steam is condensed and returned tothe condensate system.On most ships, gland sealing steam is suppliedfrom the auxiliary exhaust system, althoughon some ships it is supplied from the 150-psiauxiliary steam system. In either case, thesteam is supplied through reducing valves orreducing stations. Figure 9-19 illustrates atypical gland seal and gland exhaust system forpropulsion turbines on an older type of destroyer.CONDENSATE AND FEED SYSTEMSCondensate and feed systems include all thepiping that carries water from the condensers6shaft glands are devices for holding various kindsof packing at the point where the shaft extends throughthe turbine casing. Shaft glands and shaft gland packingare discussed in chapter 12 of this text.to the boilers and from the feed tanks to theboilers. The condensate system includes themain and auxiliary condensers, the condensatepumps, and the piping. The boiler feed systemincludes the feed booster pump, the main feedpump, and the piping required to carry waterfrom the deaerating feed tank to the boilers.Together, the condensate and feed systemsbegin at the condenser and end at the economizerof the boiler.It is a little hard to say whether the deaeratingfeed tank is part of the condensate systemor part of the boiler feed system, since thetank is generally taken as the dividing line betweenthe two systems. The water is calledcondensate between the condenser and thedeaerating feed tank. It is called feed water orboiler feed between the deaerating feed tankand the economizer of the boiler. Since thecondensate and feed systems actually formone continuous system, the terms feed systemand feed water system are quite commonlyused to include both the condensate systemand the boiler feed system.Four main types of feed systems have beenused on naval ships: (1) the open feed system,(2) the semiclosed feed system, (3) the vacuumclosedsystem, and (4) the pressure-closed system.The development of these systems, in thesequence listed, has gone along with the developmentof boilers. As boilers have been designedfor higher operating pressures andtemperatures, the removal of dissolved oxygenfrom the feed water has become increasinglyinportant, since the higher pressures and temperaturesaccelerate the corrosive effects ofdissolved oxygen. Each new type of feed systemrepresents an improvement over the one beforein reducing the amount of oxygen dissolved orsuspended in the feed water.Since practically all modern naval shipshave pressure- closed feed systems, this isthe only type discussed here. Pressure- closedsystems are used on all naval ships havingboilers operating at 600-psi and above; theyare also used on some ships that have lowerboiler operating pressures.In a pressure- closed system, all condensateand feed lines throughout the system (exceptfor the very short line between the condenserand the suction side of the condensate pump)are under positive pressure. The system isclosed to prevent the entrance of air. A pressure-closedsystem is shown in figure 9-20.213

PRINCIPLES OF NAVAL ENGINEERINGKMCHINERY ROOM NO. 4MAIN CONDSTEPUMPy-285 PSl403 IiM' (C*l]4 • 141)r i (C*I19)f < »* Assa2Oa.>a.iijzI2Xy-zM PSl_^jj^ y A ASIS7 ll ASI79EliCRC PECOPUMPBILGE k FO TANKDRAIN PUMPIXJ GLOBE STOP VALVEGLOBE STOP VALVE, LOCKED SHUT^ ANGLE STOP VALVEt»] GATE VALVENEEDLE VALVEtik]Figure 9-16.— Part of 600-psi auxiliary steam system, CA 139 class.38.10.1214

Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUTMACHINERYROOM NO. I[^ GOVERNOR VALVEK> REDUCING VALVE^ RELIEF VALVEj-Dh STEAM STRAINER®- PRESSURE GAGEFigure 9-16.— Part of 600-psi auxiliary steam system, CA 139 class- -Continued.38.10.2215

PRINCIPLES OF NAVAL ENGINEERINGCOoQaaQ73oato>.MsCOo,o oCOI1>Kh^Xh-Oxh[f^^^'-tXjCaCOa.oCMIo 2Soa:O z0.Z ino z< os uu3bO216

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1PRINCIPLES OF NAVAL ENGINEERING--T--^--—CROSSOVERPIPEPACKINGTO GLANDIEXHAUST< J ^—CONDENSERmhbhGland sealSTEAM!•GLAND LEAK-OFFSTEAMWEIGHT-LOADEDREGULATINGVALVEFROMAUXILIARYEXHAUSTSYSTEM38.12Figure 9-19.— Gland seal and gland exhaust system for propulsion turbines (destroyer).Following this illustration, let us trace the condensateand feed system."^The main condenser is the beginning of thecondensate system. The main condenser is aheat exchanger in which exhaust steam from thepropulsion turbines is condensed as it comes incontact with tubes through which cool sea wateris flowing. The condenser is maintained undervacuum. Condensate is pumped from the condenserto the deaerating feed tank by the condensatepump. In the deaerating feed tank, theThe main condenser, the air ejectors, the deaeratingfeed tank, and other major units in the condensate andfeed system are discussed in detail in chapter 13 ofthis text. The description given in the present chapteris intended merely to provide an overall view of thecondensate and feed system.water is heated by direct contact with auxiliaryexhaust steam and is deaerated; the water (nowcalled feed water) is pumped to the boiler by themain feed pump, with the feed booster pump providinga positive suction for the main feed pump.Meanwhile, the air ejectors are being used toremove air and other noncondensable gases fromthe condenser. Condensate, on its way from themain condenser to the deaerating feed tank, isused in the air ejector condensers and in twoother exchangers (the gland exhaust condenserand the vent condenser) to cool and condense thesteam from steam— air mixtures and return theresulting water to the feed system. Note that theair ejectors remove air only from the condenser,not from this condensate which passes throughthe air ejector condensers, the gland exhaustcondenser, and the vent condenser.Makeup feed water from reserve feed tanksor from a makeup feed tank is brought into the218

Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUTSTEAM TOAIR EJECTORSTOATMOSPHEREVAPOR FROM-TURBINE GLANDSH P DRAINSi »ECONOMIZERMAIN FEEDPUMP®>-^

PRINCIPLES OF NAVAL ENGINEERINGBut steam is used throughout the ship in agood deal of machinery, equipment, and pipingwhich does not exhaust either to a condenser orto the auxiliary exhaust system. Therefore,steam and fresh water drain systems are providedso that water can be recovered and putback into the feed system after it has been used(as steam) in fuel oil heaters, distilling plants,steam catapult systems, water heaters, whistles,and many other units and systems throughout theship. The systems of piping which carry the waterto the feed systems, and also the water carriedin the systems, are known as drains.On ships built to Navy specifications, thereare four steam and fresh water drain systemswhich recover feed water from machinery andpiping: (1) the high pressure steam drainage system,(2) the service steam drainage system, (3)the oil heating drainage system, and (4) the freshwater drain collecting system. In addition, afifth system is provided for collecting contaminateddrains which cannot be returned to the feedsystem. These five systems are described in thefollowing paragraphs.The high pressure steam drainage systemgenerally includes drains from superheaterheaders, throttle valves, main and auxiliarysteam lines, steam catapults (on carriers), andother steam equipment or systems which operateat pressures of 150 psi or above. On many ships,the high pressure drains are led directly intothe deaerating feed tank. On some newer ships,the high pressure drains go intothe auxiliary exhaustline just before the auxiliary exhaust steamenters the deaerating feed tank. In either case,of course, the high pressure drains end up in thesame place— that is, in the deaerating feedtank.The service steam drainage system collectsuncontaminated drains from low pressure (below150 psi) steam piping systems and steam equipmentoutside of the machinery spaces. Spaceheaters and equipment used in the laundry, thetailor shop, and the galley are typical sources ofdrains for the service steam drainage system.On some ships, these drains are discharged intothe most convenient fresh water drain collectingtank. On other ships, particularly on large combatantships such as carriers, the service steamdrains discharge to special service steam draincollecting tanks located in the machinery spaces.The contents of the service steam drain collectingtanks are discharged to the condensate system;in addition, each tank has gravity drain connectionsto the fresh water drain collecting tankand to the bilge sump tank located in the samespace.Note that the service steam drainage systemcollects only clean drains which are suitable foruse as boiler feed. Contaminated service steamdrains (such as those from laundry presses, forexample) are discharged overboard.The oil heating drainage system collectsdrains from the steam side of fuel oil heaters,fuel oil tank heating coils, lubricating oil heaters,and other steam equipmentusedtoheat oil. Sinceleakage in the heating equipment could cause oilcontamination of the drains, and so eventuallycause oil contamination of the boilers, thesedrains are collected separately and are inspectedbefore being discharged to the feed system.The oil heating drains are collected in oilheating drain mains and are then discharged toinspection tanks. In ships that have separate engineroomsand firerooms, there is one inspectiontank in the fireroom and one in the engineroom.On ships that have machinery rooms,rather than firerooms and enginerooms, eachmachinery room has one or more inspectiontanks for the oil heating drains. The inspectiontanks have small gage glasses or glass stripsalong the side to permit inspection of the drains.The inspection tanks normally discharge to thedeaerating feed tank, but they have connectionswhich allow the drains to be discharged to thefresh water drain collecting tank.The fresh water drain collecting system,often called low pressure drain system, collectsdrains from various piping systems, machinery,and equipment which operate at steam pressuresof less than 150 psi. As previously noted, both theservice steam drainage system and the oilheating drainage system can discharge to thefresh water drain collecting tank, although theynormally discharge more directly to the feedsystem. In general, the fresh water drain collectingsystem collects gravity drains (open-funnelor sight-flow drains), turbine gland seal drains,auxiliary exhaust drains, air ejector after condenserdrains, and a variety of other low pressuredrains that result from the condensation ofsteam during the warming up or operating ofsteam machinery and piping.Fresh water drains are collected in freshwater drain collecting tanks located in the machineryspaces. The contents of these tanks mayenter the feed system in two ways: they may bedrawn into the condenser by vacuum drag, or insome installations they may be pumped to the220

Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUTcondensate system just ahead of the deaeratingfeed tank.A contaminated drainage system is installedin each main and auxiliary machinery spacewhere dry bilges must be maintained. The contaminateddrainage system collects oil and waterfrom machinery and piping which normally hassome leakage, and also collects drainage fromany other services which may at times be contaminated.The contaminated drains are collectedin a bilge sump tank located in the machineryspace from which the drains are being collected.The contents of the bilge sump tank are removedby the bilge drainage system; they do not go tothe feed system.FUEL OIL SYSTEMSBoiler fuel oil systems aboard ship includefuel oil tanks, fuel oil piping, fuel oil pumps, andthe equipment used for heating, straining, measuring,and burning fuel oil.Three main kinds of tanks are used for holdingboiler fuel oil: (1) storage tanks, (2) servicetanks, and (3) contaminated oil settling tanks.The main fuel oil storage tanks are an integralpart of the ship's structure. They may belocated forward and aft ofthe machinery spaces,abreast of these spaces, and in double-bottomcompartments. However, fuel oil storage tanksare never located in double-bottom compartmentsdirectly under boilers. Some fuel oil storagetanks, called fuel oil storage or ballast tanks,have connections that allow them to be filled eitherwith fuel oil or with sea water from the ballastingsystem. Other fuel oil storage tanks aredesignated as fuel oil overflow tanks; these tanksreceive the overflow from fuel oil storage tankswhich are not fitted with independent overboardoverflows. Overflow tanks which can also befilled with sea water from the ballasting systemare called fuel oil overflow or ballast tanks.Fuel oil is taken aboard by means of fuelingtrunks or special connections and is piped intothe storage tanks. From the storage tanks, oil ispumped to the fuel oil service tanks. All fuel oilfor immediate use is then drawn from the servicetanks. The fuel oil service tanks are consideredpart of the fuel oil service system.Contaminated oil settling tanks are used tohold oil which is contaminatedwithwater or otherimpurities. After the oil has settled, the unburnablematerial such as water and sludge ispumped out through low suction connections. Theburnable oil remaining in the tanks is then transferredto a storage tank or a service tank.The contaminated oil settling tanks alsoserve to receive and store oil or oily water untilit can be discharged overboard without violationof the Oil Pollution Acts. 8 These Acts prohibitthe overboard discharge of oil and ofwater containing oil in port and in prohibitedzones in oceans and seas throughout the world.It is standard practice, therefore, to empty thecontaminated oil settling tanks before coming intoport or into a prohibited zone so that thetanks will be available for storing oil and oilywater until such time as it can be dischargedoverboard or to barges.Fuel oil tanks are vented to atmosphere bypipes leading from the top of the tank to a locationabove decks. The vent pipes allow the escapeof vapor when the tank is being filled andallow the entrance of air when the tank is beingemptied. Most fuel oil tanks are equipped withmanholes, overflow lines, sounding tubes, liquidlevel indicators, heating coils, and lines forfilling, emptying, and cross-connecting.The fuel oil piping system includes (1) thefuel oil filling and transfer system, (2) the fueloil tank stripping system, and (3) the fuel oilservice system. The fuel oil systems are arrangedin such a way that different fuel oil pumpstake suction from the tanks at different levels.Stripping system pumps have low level suctionconnections. Fuel oil service pumps have highsuction connections from the fuel oil servicetanks. Fuel oil booster and transfer pumps takesuction above the stripping system pumps.The fuel oil filling and transfer system isused for receiving fuel oil and filling the fuel oilstorage tanks; filling the fuel oil service tanks;changing the list of the ship by transferring oilbetween port tanks and starboard tanks; changingthe trim of the ship by transferring oil betweenforward tanks and after tanks; discharging oilfor fueling other ships; and, in emergencies,transferring fuel oil directly to the suction sideof the fuel oil service pumps.The filling system on small ships such asdestroyers consists of a trunk filling and tanksluicing arrangement. Larger steam-drivenships have pressure filling systems which areThe Oil Pollution Act of 1924 (as amended) and theOil Pollution Act of 1961 are both in effect. The 1961Act broadens and extends the 1924 Act.221

PRINCIPLES OF NAVAL ENGINEERINGconnected to the transfer mains so that thefilling lines and deck connections can be usedboth for receiving and for discharging fuel oil.Pressure filling systems operate with a minimumpressure of approximately 40 psi at thedeck connections.In general, the filling and transfer systemconsists of large mains running fore and aft;transfer mains; cross-connections; risers fortaking on or discharging fuel oil; fuel oil boosterand transfer pumps; and lines and manifoldsarranged so that the fuel oil booster and transferpumps can transfer oil from one tank toanother and, when necessary, can deliver fueloil to the suction side of the fuel oil servicepumps.The fuel oil tank stripping system serves toclear fuel oil storage tanks and fuel oil servicetanks of sludge and water before oil is pumpedfrom these tanks by fuel oil booster and transferpumps or by fuel oil service pumps. The strippingsystem is connected through manifolds tothe bilge pump or, in some installations, tospecial stripping system pumps. The strippingsystem discharges the contaminated oil, sludge,and water overboard or to the contaminated oilsettling tanks.The fuel oil service system includes the fueloil service tanks, a service main, manifolds,piping, fuel oil service pumps, meters, heaters,strainers, burner lines, and other items neededto deliver fuel oil to the boiler fronts at the requiredpressures and temperatures. The fuel oilservice system used on any ship depends partlyon the type of fuel oil burners^ installed on theboilers. Figure 9-21 illustrates schematicallya fuel oil service system typically found on shipshaving double-furnace boilers and straightthrough-flowatomizers in the fuel oil burners.Figure 9-22 shows the fuel oil service systemfor the forward plant of the frigates DLG 14 andDLG 15, which use return-flow atomizers in thefuel oil burners. As may be seen in figure 9-22,a system of this type requires fuel oil returnlines as well as fuel oil supply lines. Also, theuse of return-flow atomizers in these burnersrequires a fuel oil cooler to cool the oil returnedfrom the burners. The cooler (which is not partof the fuel oil service system on ships that donot have return-flow atomizers) serves to keepthe temperature of the returned fuel oil belowthe flash point.In any type of fuel oil service system, thesuction arrangements for oil service pumpsallow rapid changes of pump suction from oneservice tank (or one tank group manifold) toanother. The pump suction piping is arranged tominimize contamination that might result fromone service pump taking suction from a servicetank that is contaminated with water.Three classes of fuel oil service pumps arecommonly used: main fuel oil service pumps,port and cruising fuel oil service pumps, andhand or emergency fuel oil service pumps.Main fuel oil service pumps are usuallyscrew-type rotary pumpslO that are driven bysteam turbines. However, other types of pumpsare used for this purpose on some ships.Port and cruising fuel oil service pumps onrecent ships are very similar to the main fueloil service pumps except that they are drivenby two-speed electric motors. The capacity ofthese pumps can be adjusted by selecting therequired speed of the motor and also by using abypass arrangement to recirculate unused oilfrom the pump discharge to the pump suction.On older ships, the port and cruising fuel oilservice pumps may be rotary pumps or they maybe axial-piston variable-stroke pumps; in eithercase, they are normally driven by electric motorsrather than by steam turbines.Hand or emergency fuel oil service pumpsare used on some ships when boilers must belighted off and neither steam nor electric poweris available. Most hand or emergency fuel oilservice pumps are herringbone gear pumps. Onrecent ships, other means of lighting off withoutsteam or power are used, and the hand or emergencyfuel oil service pump is not required.The fuel oil service system contains a numberof valves, all of which are important to thesafe and efficient operation of the boiler. Themajor valves in the fuel oil service systemshown in figure 9-20 are listed here both to givesome idea of the complexity of the fuel oil servicesystem and to indicate the degree of precisionrequired of operating personnel in liningup, operating, securing, and controlling casualtiesin the fuel oil service system.Fuel oiltext.burners are discussed in chapter 10 of thisBasic types of pumps are discussed in chapter 15 ofthis text.222

-I—Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUTMAIN FUEL OILVALVES (ONE TOEACKBOILER )TOOTHERBOILERSUPERHEATERSIDE BUHNERMANIFOLDRECIRCULATINGVALVETO OVERBOARD OROIL SETTLING TANK^^-^^ ^SATURATEO-SIDRECIRCULATING/^^ BURNER MANIFOVALVEi^RECIRCULATINGLINEDUPLEXSTRAINER^-03FHEATERS^ -I'-CKH,*-CXHHEATER BYPASS VALVEREMOTE -OPERATEDQUICK -CLOSING VALVEFSERVICE-CHECK PUMP,?< VALVETO FILLING AND DISCHARGEDECK CONNECTIONV9»—ixiFUEL OIL SERVICETANKFigure 9-21.— Fuel oil service system on ship with double furnace boilershaving straight-through-flow atomizers.38.63Suction and discharge valves allow the pumpsto be lined up for the delivery of fuel oil. Theremote-operated quick- closing valve in the supplymain on the discharge side of the fuel oilservice pump provides a means for rapidlyshutting off the fuel oil from a remote location.The remote operating gear for this valve isarranged so that the valve may be operatedfrom two places; (1) from the fuel oil pumpitself, and (2) from the fireroom escape trunkor from the deck above and near the accessto the space. Fuel oil meter and meter bypassvalves allow the fuel oil meter to be used orto be bypassed, as the situation requires; thefuel oil meter is bypassed when oil is beingrecirculated. A fuel oil heater bypass valve223

PRINCIPLES OF NAVAL ENGINEERINGPRESSURESWITCHSTOPS PUMPAT 800 PSIGFigure 9-22.— Fuel oil service system for forward plant, DLG 14 and DLG 15.147.80is installed to permit bypassing the fuel oilheaters in unusual operating situations. Fueloil heater valves control the flow of oil intothe heaters and permit shifting from one heaterto another.The main fuel oil valve controls the flowof fuel oil in the line leading to each boiler.The emergency quick- closing valve can beoperated from both the upper level and thelower level at the boiler front. In some installations,a latched-open solenoid valve, arrangedfor local tripping, is installed adjacent to eachburner supply manifold; where a solenoid valveof this type is installed, it takes the place ofthe emergency quick- closing valve.A micrometer valve is installed at the topof each burner manifold. The micrometer valveis used for the manual control of fuel oil pressure;thus it is the valve that controls the amountof oil being burned in the boiler furnace. Fromthe burner manifold, a small flexible line goesto each burner. A small valve called a burnerroot valve is installed in each burner line topermit shutting off the supply of oil to any burnerthat is not in use. And finally, an atomizervalve is installed on each burner at the atomizerconnection. This valve allows oil to go throughthe atomizer and be sprayed out into the boilerfurnace in such a way that combustion takesplace.At the lower end of each burner manifold,a recirculating valve is installed. By means ofthese valves and the recirculating line, fuel oilcan be returned from the burner manifold tothe suction side of the fuel oil service pump.The recirculating line is used to circulate oilthrough the fuel oil heaters and thus bring theoil up to the proper temperature for lighting224

Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUToff. A clearing line branches off from the recirculatingline. Valves in the recirculatingline and in the clearing line permit fuel oil tobe discharged to the suction side of the fuel oilservice pump or to the contaminated oil settlingtank (or overboard). A check valve in the recirculatingline prevents the back flow of oilfrom the fuel oil suction main; another checkvalve at the connection of the clearing line andthe contaminated oil settling tank prevents backflow from the contaminated oil settling tankthrough the clearing line and into the recirculatingline.The valves just listed are typically found infuel oil service systems on ships which usestraight-through-flow atomizers. Where returnflowatomizers are used, additional valves arerequired in the fuel oil service system to controlthe return flow of oil and (in some installations)to control the flow of oil through a cooler.Where automatic boiler controls are installed,still more valves are required in the fuel oilservice system; these include fuel oil supplyand return valves which are operated by theboiler control system.BALLASTING SYSTEMSThe ballasting system allows the controlledflooding of certain designated tanks, when suchflooding is required for stability control. Alltanks that are designated as fuel oil and ballasttanks (and also certain voids) may be floodedby the ballasting system. Sea water is used forballasting; it may be taken from the firemainor it may be taken directly from sea chests.Combined ballasting and drainage systemsare arranged so that all designated compartmentsand tanks can be ballasted either separatelyor together and drained either separately ortogether. Drainage pumps or eductors are usedto remove the ballast water.DIESEL OIL AND JP-5 SYSTEMSDiesel oil systems are found even on steamdrivenships. Ships that carry large suppliesof diesel oil have fairly complex diesel oilsystems which are quite similar to the boilerfuel oil systems already described. Althoughthe diesel oil systems are separate from theboiler fuel oil systems, they are arranged sothat the diesel oil can be discharged to the fueloil service system and burned in the boiler furnacein case of emergency.On aircraft carriers, JP-5 aviation fuel canalso be used as boiler fuel in case of emergency.The JP-5 system is separate from the boilerfuel oil system but can be connected so as todischarge JP-5 to the fuel oil service system.DISTILLATE FUEL SYSTEMThe Department of Defense has authorizedthe Navy to convert to an all-distillate marinetype diesel fuel (Navy Special Distillate Fuel)(NSDF) to replace the Navy Special Fuel Oil(NSFO) now in use on steam-driven ships.Testing is now being conducted on gas turbinesand diesel engines for the feasibility ofconverting the Navy to a "one fuel" Navy forlogistic simplicity and reduction of overalloperating costs.Piping system conversion and changes willrequire the upgrading and validation of theexisting systems on all ships using NSFO.Therefore, all instructions issued by NavShipsand NavSec shall be followed in upgrading andvalidation of the existing NSFO systems beforeNSDF can be introduced into the system.Stability and buoyancy will also be affecteddue to the variation in specific gravity of NSFO(7.9 lbs/gal average) verses NSDF (7.2 lbs/galaverage), therefore, solid ballast will be requiredin those ships which are now near thenaval architectural limits for stability. Theexisting liquid loading instructions which specifysea water ballasting of empty fuel tanks willstillremain in effect.MAIN LUBRICATING OIL SYSTEMSMain lubricating oil systems on steamdrivenships provide lubrication for the turbinebearings and the reduction gears. The mainlube oil system usually includes a filling andtransfer system, a purifying system, andseparate service systems for each propulsionplant. On most ships, each lube oil servicesystem includes three positive-displacementlube oil service pumps: (1) a shaft-driven pump,(2) a turbine-driven pump, and (3) a motordrivenpump. The shaft-driven pump, attachedto and driven by either the propulsion shaft orthe quill shaft of the reduction gear, is usedas the regular lube oil service pump when theshaft is turning fast enough so that the pumpcan supply the required lube oil pressure. Theturbine-driven pump is used while the ship isgetting underway and is then used as standby225

1PRINCIPLES OF NAVAL ENGINEERINGat normal speeds. The motor-driven pumpserves as standby for the other two lube oilservice pumps.Figure 9-23 illustrates the lube oil supplyand lube oil drain piping of the service systemon the frigates DLG 14 and DLG 15.COMPRESSED AIR SYSTEMSCompletely independent compressed air systemswith individual compressors include thehigh pressure air system, the ship's serviceair system, the aircraft starting and coolingair system, the combustion control air system,the air deballasting system, and the oxygennitrogenproducer air system. For other services,air is taken from the high pressuresystem or from the ship's service air system,as required. Air is provided by high pressure,medium pressure, or low pressure air compressors,as appropriate.The high pressure air system is designedto provide air above 600 psi and up to 5000 psifor charging air banks and, at required pressures,for services such as missiles, dieselengine starting and control, torpedo charging,and torpedo workshops. When air is requiredfor these services at less than the system pressure,the outlet from the high pressure airsystem is equipped with a reducing valve.Air for diesel engine starting and controlis provided on some ships by a medium rangecompressure at a pressure of 600 psi or fromthe high pressure system, through appropriatereducing valves.The ship's service compressedair system isa low pressure system that is installed onpractically all surface ships. This system providescompressed air at the required pressurefor the operation of pneumatic tools, the operationof oil-burning forges and furnaces, thecharging of pump air chambers, the cleaningof equipment, and a variety of other uses. Theship's service air system is normally designedfor a working pressure of 100 psi; on shipssuch as tenders and repair ships, however,where there is a greater demand for air, thesystem is designed for a higher working pressure(usually about 125 psi). The ship's serviceair system is normally supplied from a lowpressure air compressor; on some ships, however,the system may be supplied from a higherpressure system, through reducing valves.An aircraft starting and cooling air systemis installed on aircraft carriers. This systemis designed to provide air at various temperatures(50° to 500° F) and pressures (48 psia to62 psia) by gas turbine. The system suppliescompressed air to meet the conditions of startingand cooling aircraft being served.Combustion control air systems (more properlycalled boiler control air systems) areinstalled on some ships to provide supply airfor the pneumatic units in automatic boilercontrol systems. A boiler control air systemusually consists of an air compressor, an airreceiver, and the piping required to supplyair to all units of the boiler control systemOn some older ships, compressed air for theoperation of the boiler controls is taken fromthe ship's service air system, through reducingvalves.An air deballasting system is provided onsome ships for deballasting by air. This systemis designed to provide large quantities of air(7500 cubic feet per minute) at low pressure(200 psi). All compressors discharge to a commonair loop distribution which feeds all ballasttanks.Oxygen-nitrogen producer air systems areinstalled on aircraft carriers and submarinetenders. The air is supplied by high pressureair compressors, via oil filters and moistureseparators, directly to the oxygen- nitrogenproducer.FIREMAIN SYSTEMSThe firemain system receives water pumpedfrom the sea and distributes it to fireplugs,sprinkling systems, flushing systems, auxiliarymachinery cooling water systems, washdownsystems, and other systems as required.There are three basic types of firemainsystems used on naval ships: the single mainsystem, the horizontal loop system, and thevertical loop system. The type of firemainsystem installed in any particular ship dependsupon the characteristics and functions of theship. Small ships generally have single mainfiremain systems; large ships usually haveone of the loop systems or a composite systemwhich is some combination or variation of thethree basic types.The single main firemain system consistsof one main which extends fore and aft. Themain is generally installed near the centerlineof the ship, extending as far forward and as faraft as necessary. The horizontal loop firemainsystem consists of two single fore-and-aft226

''Chapter 9-MACHrNERY ARRANGEMENT AND PLANT LAYOUTLUBE OIL SERVICE.PUMP (MOTOR)SUCTION FROMSTORAGE ANDSETTLING TANKSDUPLEX MAGNETICSTRAINERLUBE OILr COOLER• 600 PSIG STEAMLUBE OIL SERVICEPUMP (TURBINE)LUBE OIL SERVICEPUMP(ATTACHED)TO PURIFIERSUCTIONREDUCTION GEARS —LUBE OIL SUPPLY PIPINGDRAIN TO BUCKETH.P. TURBINEDRAIN TO SUMPFROM JOURNAL'AND THRUSTLUBE OIL SERVICEPUMP (ATTACHED)LUBE OILSUMP TANKTURBINEH.P. TURBINEMAIN REDUCTIONGEARFROM JOURNAL""AND THRUSTLEAKAGEALONG SHAFTSFROM SPRAYAND JOURNALLUBE OIL DRAIN PIPINGFigure 9-23.— Lubricating oil service system, DLG 14 and DLG 15.147.81227

PRINCIPLES OF NAVAL ENGINEERINGcross-connected mains. The two mains areinstalled in the same horizontal plane but areseparated athwartships as far as practicable.In general, the two mains are installed on thedamage control deck. The vertical loop firemainsystem consists of two single fore-and-aftcross-connected mains. The two mains areseparated both athwartship and vertically. Asa rule, the lower main is located below thelowest complete watertight deck and the uppermain is located below the highest completewatertight deck.FLUSHING SYSTEMSThe shipboard flushing system is suppliedwith sea water by a branch from the firemain.On very small ships, a separate sanitary andflushing pump is provided which takes suctionfrom the sea. When the flushing system issupplied from the firemain, the branch is takenas near the top of the main as possible so thatsediment from the firemain will not enter theflushing system. Since the firemain pressure istoo high for a flushing system, the water isled through a strainer to a reducing valve whichreduces the pressure to 35 psi. Air chambersare installed in the flushing system where itruns to urinals and water closets; the airchambers absorb water hammer caused by thequick closing of the flush valves and springclosingfaucets.DRAINAGE SYSTEMSThe drainage system aboard ship is dividedinto two parts: (1) the main and secondary systems,and (2) the plumbing and deck drains.Between them, these systems collect and disposeoverboard all the shipboard waste fluids.The main drainage system consists of pipinginstalled low in the ship, with suction branchesto spaces to be drained and direct connectionsto eductors or drainage pumps. This systemgenerally serves the main machinery spacesand a few other spaces.The secondary drainage system supplementsthe main drainage system wherever the maindrainage system cannot be extended because ofinterference of spaces through which the passageof piping is prohibited or because the length ofpiping would be too great for efficient drainage.Each secondary drainage system is independentof the main drainage system and has its ownpumps or eductors and its own sea connections.Plumbing and deck drains are divided intotwo groups— soil drains and waste drains. Soildrains convey fluids from urinals and waterclosets. Waste drains convey fluids from allother plumbing fixtures and deck drains.SPRINKLING SYSTEMSSprinkling systems are installed aboard shipin magazines, turret handling rooms, hangardecks, missile spaces, and other spaces whereflammable materials are stowed. Water forthese systems is supplied from the firemainthrough branch lines.Most sprinkling systems aboard ship areof the dry type— that is, they are not chargedwith water beyond the sprinkling control valvesexcept when they are in use. Sprinkling systemsin magazines which contain missiles are of thewet type. The sprinkling control valves inmagazine sprinkling systems are operated automaticallyby heat-actuated devices. Othersprinkling control valves are operated manuallyor hydraulically, either locally or from remotestations. In those areas of the ship in whichmajor flammable liquid fires could occur,such as in aircraft hangars, foam sprinklingsystems are provided.WASHDOWN SYSTEMSWashdown systems are installed aboard shipfor the purpose of removing radioactive contaminationfrom the topside surfaces of a ship.Essentially, a washdown system is a dry-pipesprinkler system, with nozzles especially designedto throw a large spray pattern on allweather decks. For ships under constructionor conversion, a permanent washdown systemis installed; for ships already in service,interim washdown system kits are providedfor installation by ship's force. In either case,water for the washdown system is suppliedfrom the firemain.POTABLE WATER SYSTEMSPotable water systems are designed to providea constant supply of potable water for allship's service requirements. Potable water isstored in various tanks throughout the ship.The system is pressurized either by a pumpand pressure tank or by a continuously operatingcirculating pump. The potable water systemsupplies scuttlebutts, sinks, showers, scullery,228

Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUTand galley, as well as providing makeup waterfor various fresh water cooling systems.HYDRAULIC SYSTEMSHydraulic systems are used aboard ship tooperate steering gear, anchor windlasses, hydraulicpresses, remote control valves, andother units. 11 Hydraulic systems operate on theprinciple that, since liquids are noncompressible,force exerted at any point on an enclosedliquid is transmitted equally in all directions.Hence a hydraulic system permits the accomplishmentof a great amount of work with relativelylittle effort on the part of shipboardpersonnel.The medium used to transmit and distributeforces in hydraulic systems may be a petroleumbaseproduct (hydraulic oil) or a pure phosphateester fluid. Phosphate ester fluid is more resistantto fire and explosion than the petroleumbaseoil that was used in all hydraulic systemsuntil fairly recently. Phosphate ester fluid isnow used in aircraft carrier elevators, surfaceship missile systems, jet blast deflectors],seaplane servicing booms, high pressure sub(-marine systems, and all hydraulic systemsoperating at pressures of more than 500 psiin new construction and conversion surfaceships.METHODS OF PROPULSIONPLANT OPERATIONThe major engineering systems on mostnaval ships are provided with cross-connectionswhich allow the engineering plants to be operal^Manyhydraulically operated units are discussed inchapter 21 of this text.ted either independently (split-plant) or together(cross-connected). In cross- connected operation,boilers may supply steam to propulsionturbines which they do not serve when the plantis split. In split-plant operation, the boilers,turbines, pumps, blowers, and other machineryare so divided that there are two or moreseparate and complete engineering plants.Cross- connected operation was formerlystandard for peacetime steaming, and splitplantoperation was used only when maximumreliability was required— as, for example, whena ship was operating in enemy waters in timeof war, operating in heavy seas, maneuveringin restricted waters, or engaged in underwayfueling. However, the greater reliability ofsplit-plant operation has led to its increasinguse. At the present time, split-plant operationis the standard method of underway operationfor most naval ships; cross- connected operationis used for in- port steaming but is rarelyused for underway steaming.On some ships the engineering plants can beoperated by a method known as group operation.For example, the USS Forrestal. CVA 59, hasfour separate propulsion plants. The two forwardplants (No. 1 and No. 4) constitute theforward group and the two after plants (No. 2and No. 3) constitute the after group. Althougheach of these four plants is normally used forthe independent (split-plant) operation of oneshaft, the boilers in any one plant can be crossconnectedto supply steam to the turbines in theother plant in the same group. While underway,therefore, the boilers in the No. 1 plant can becross- connected to supply steam to the No. 4plant, although they cannot be cross- connectedto supply steam to the two plants in the othergroup. For in-port operation, any boiler can becross- connected to supply steam to any turbogeneratorand to all other steam-driven auxiliaries.229

CHAPTER 10PROPULSION BOILERSIn the conventional steam turbine propulsionplant, the boiler is the source or high temperatureregion of the thermodynamic cycle. Thesteam that is generated in the boiler is led tothe propulsion turbines, where its thermalenergy is converted into mechanical energywhich drives the ship and provides power forvital services.In essence, a boiler is merely a containerin which water can be boiled and steam generated.A teakettle on a stove is basically aboiler, although a rather inefficient one. Indesigning a boiler to produce a large amountof steam, it is obviously necessary to find somemeans of providing a larger heat transfer surfacethan is provided by a vessel shaped like ateakettle. In most modern boilers, the steamgenerating surface consists of between one andtwo thousand tubes which provide a maximumamount of heat transfer surface in a relativelysmall space. As a rule, the tubes communicatewith a steam drum at the top of the boiler andwith water drums and headers at the bottom ofthe boiler. The tubes and part of the drums areenclosed in an insulated casing which has spaceinside it for a furnace. As we will see presently,a boiler appears to be a fairly complicated pieceof equipment when it is considered with all itsfittings, piping, and accessories. It may be helpful,therefore, to remember that the basic componentsof a saturated-steam boiler are merelythe tubes in which steam is generated, the drumsand headers in which water is contained andsteam is collected, and the furnace in whichcombustion takes place.Practically all boilers used in the propulsionplants of naval ships are designed to produceboth saturated steam and superheated steam.To our basic boiler, therefore, we must now addanother component: the superheater. The superheateron most boilers consists of headers,usually located at the back or at the bottom ofthe boiler, and a number of superheater tubeswhich communicate with the headers. Saturatedsteam from the steam drum is led through thesuperheater; since the steam is now no longerin contact with the water from which it was generated,the steam becomes superheated withoutany appreciable increase in pressure as additionalheat is supplied. In some boilers, there isa separate superheater furnace; in others, thesuperheater tubes project into the same furnacethat is used for the generation of saturatedsteam.Some question may arise concerning the needfor both saturated steam and superheated steam.Many steam-driven auxiliaries—particularly ifthey have reciprocating engines—require saturatedsteam for the lubrication of the movingparts of the driving machine. The propulsionturbines, on the other hand, and many auxiliariesas well, perform much more efficiently whensuperheated steam is used. There is more availableenergy in superheated steam than in saturatedsteam at the same pressure, and the use ofhigher temperatures vastly increases the thermodynamicefficiency of the propulsion cyclesince the efficiency of a heat engine depends uponthe absolute temperature at the source (boiler)and at the receiver (condenser). In some instances,the gain in efficiency resulting from theuse of superheated steam may be as much as 15percent for 200 degrees of superheat. This increasein efficiency is particularly important fornaval ships because it allows substantial savingsin fuel consumption and in space and weight requirements.A further advantage in using superheatedsteam for propulsion turbines is that itcauses relatively little erosion or corrosionsince it is free of moisture.BOILER DEFINITIONSIn order to ensure accuracy and uniformityin the use of boiler terms, the Naval Ship Systems230

Chapter 10- PROPULSION BOILERSCommand has established a number of standarddefinitions relating to boilers. Since these termsare quite widely used, the student will find ithelpful to understand the following terms andto use them correctly.BOILER FULL-POWER CAPACITY. -Thetotal quantity of steam required to develop contractshaft horsepower of the ship, divided bythe number of boilers installed in the ship, givesboiler full-power capacity. Boiler full-powercapacity is expressed as the number of poundsof steam generated per hour at a specified pressureand temperature. Boiler full-power capacityis listed in the design data section of themanufacturer's technical manual for the boilerson each ship; it may be listed as capacity at fullpower or as designed rate of actual evaporationper boiler at full power.BOILER OVERLOAD CAPACITY.-Boileroverload capacity is usually 120 percent ofboiler full-power capacity. Boiler overloadcapacity is listed in the design data section ofthe manufacturer's technical manual for theboilers; it may be listed as boiler overloadcapacity or as full power plus 20 percent.SUPERHEATER OUTLET PRESSURE. -Superheateroutlet pressure is the actual steampressure carried at the superheater outlet.STEAM DRUM PRESSURE.-Steam drumpressure is the pressure actually carried in theboiler steam drum.OPERATING PRESSURE. -Operating pressureis the constant pressure at which the boileris operated in service. Depending upon variousfactors, chiefly design features of the boiler, theconstant pressure may be carried at the steamdrum or at the superheater outlet. Operatingpressure is specified in the design of the boilerand is given in the manufacturer's technicalmanual. Operating pressure is the same assuperheater outlet pressure or steam drumpressure (depending upon which is used as thecontrolling pressure) only when the boiler isoperating at full-power capacity, for combatantships, or some other specified rate, for otherships. When the boiler is operating at less thanfull-power capacity (or other specified rate),the actual pressure at the steam drum or at thesuperheater outlet will vary from the designatedoperating pressure.DESIGN PRESSURE. -Design pressure is thepressure specified by the boiler manufactureras a criterion for boiler design. It is oftenapproximately 103 percent of steam drum pressure.Operating personnel seldom have occasionto be concerned with design pressure; the termis noted here because there is a good deal ofconfusion between design pressure and operatingpressure. The two terms do not mean the samething.DESIGN TEMPERATURE. -Design temperatureis the intended maximum operating temperatureat the superheater outlet, at somespecified rate of operation. The specified rateof operation is normally full-power capacity forcombatant ships.OPERATING TEMPERATURE. -Operatingtemperature is the actual temperature at thesuperheater outlet. As a rule, operating temperatureis the same as design temperatureonly when the boiler is operating at the ratespecified in the definition of design temperature.BOILER EFFICIENCY. -The efficiency of aboiler is the ratio of the Btu per pound of fuelabsorbed by the water and steam to the Btu perpound of fuel fired. In other words, boiler efficiencyis output divided by input, or heat utilizeddivided by heat available. Boiler efficiencyis expressed as a percentage.FIREROOM EFFICIENCY.-Boiler Efficiencycorrected for blower and pump steam consumptionis called fireroom efficiency. Note:Fireroom efficiency is NOT boiler plant efficiencyor propulsion plant efficiency.STEAMING HOURS.-The term steaminghours is used to include all time during whichthe boiler has fires lighted for raising steamand all time during which steam is being generated.Time during which fires are not lightedis not included in steaming hours.HEATING SURFACES.-The total heatingsurface of a boiler includes all parts of theboiler which are exposed on one side to the gasesof combustion and on the other side to the waterand steam being heated. Thus the total heatingsurface equals the sum of the generating surface,the superheater surface, and the economizersurface. All heating surfaces are measured onthe combustion gas side.231

2PRINCIPLES OF NAVAL ENGINEERINGThe generating surface is that part of thetotal heating surface in which water is beingheated and steam is being generated. The generatingsurface includes the generating tubes,the water wall tubes, the water screen tubes,and any water floor tubes that are not coveredby refractory material.The superheater surface is that part of thetotal heating surface in which the steam issuperheated after leaving the boiler steam drum.The economizer surface is that portion of thetotal heating surface in which the feed water isheated before it enters the generatingpartof theboiler.DESUPERHEATERS.— On boilerswith noncontrolledsuperheaters, all steam is superheatedbut a small amount is redirected througha desuperheater line. The desuperheater can belocated in either the water drum or the steamdrum; most generally, the desuperheater will befound in the steam drum below the normal waterlevel. The purpose of the desuperheater is tolower the superheated steam temperature backto or close to saturated steam temperature forthe proper steam lubrication of the auxiliarymachinery. The desuperheater is most generallyan "S" shaped tube bundle that is flanged to thesuperheater outlet on the inlet side and theauxiliary steam stop on the outlet side.BOILER CLASSIFICATIONAlthough boilers vary considerably in detailsof design, most boilers may be classified anddescribed in terms of a few basic features orcharacteristics. Some knowledge of these methodsof classification provides a useful basis forunderstanding the design and construction of thevarious types of modern naval boilers.Location of Fire and Water SpacesOne basic classification of boilers is madeaccording to the relative location of the fire andwater spaces. By this method of classification,all boilers may be divided into two classes: firetubeboilers and water-tube boilers. In fire-tubeboilers, the gases of combustion flow through thetubes and thereby heat the water which surroundsthe tubes. In water-tube boilers, thewater flows through the tubes and is heated bythe gases of combustion that fill the furnace andheat the outside metal surfaces of the tubes.All boilers used in the propulsion plants ofmodern naval ships are of the water-tube type.Fire-tube boilers^ were once used extensivelyin marine installations and are still used in thepropulsion plants of some older merchant ships.However, fire-tube boilers are not suitable foruse as propulsion boilers in modern naval shipsbecause of their excessive weight and size, theexcessive length of time required to raise steam,and their inability to meet demands for rapidchanges in load. The only fire-tube boilers currentlyin naval use are some small auxiliaryboilers.Type of CirculationWater-tube boilers are further classifiedaccording to the cause of water circulation. Bythis mode of classification, we have naturalcirculation boilers and controlled circulationboilers.In natural circulation boilers, the circulationof water depends on the difference between thedensity of an ascending mixture of hot water andsteam and a descending body of relatively cooland steam-free water. The difference in densityoccurs because the water expands as it is heatedand thus becomes less dense. Another way todescribe natural circulation is to say that it iscaused by convection currents which result fromthe uneven heating of the water contained in theboiler.Natural circulation may be either free oraccelerated. Figure 10-1 illustrates free naturalcirculation. Note that the generating tubes areinstalled at a slight angle of inclination whichallows the lighter hot water and steam to riseand the cooler and heavier water to descend.When the generating tubes are installed at agreater angle of inclination, the rate of watercirculation is definitely increased. Therefore,boilers in which the tubes slope quite steeplyfrom steam drum to water drum are said tohave accelerated natural circulation. This typeof circulation is illustrated in figure 10-2.Most modern naval boilers are designed foraccelerated natural circulation. In such boilers,large tubes (3 or more inches in diameter) areAs, for example, the old "Scotch marine boiler."2 Auxiliary boilers (some water-tube, some fire-tube)are installed in diesel -driven ships and in many steamdrivencombatant ships. They are used to supply steamor hot water for galley, and other "hotel" servicesand for other auxiliary requirements in port.232

Chapter 10- PROPULSION BOILERSArrangement of Steam andWater SpacesFLAME AND GASES147.83Figure 10-1.— Natural circulation (free type).installed between the steam drum and the waterdrums. These large tubes, called downcomers ,are located outside the furnace and away fromthe heat of combustion, thereby serving as pathwaysfor the downward flow of relatively coolwater. When a sufficient number of downcomersare installed, all small tubes can be generatingtubes, carrying steam and water upward, and alldownward flow can be carried by the downcomers.The size and number of downcomersinstalled varies from one type of boiler to another,but some are installed on all modern navalboilers.Controlled circulation boilers are, as theirname implies, quite different in design from theboilers that utilize natural circulation. Controlledcirculation boilers depend upon pumps,rather than upon natural differences in density,for the circulation of water within the boiler.Because controlled circulation boilers are notlimited by the requirement that hot water andsteam must be allowed to flow upward whilecooler water flows downward, a great variety ofarrangements may be found in controlled circulationboilers.Controlled circulation boilers have been usedin a few naval ships during the past few years.In general, however, they are still consideredmore or less experimental for naval use.Natural circulation boilers are classified asdrum-type boilers or as header-type boilers,depending upon the arrangement of the steamand water spaces. Drum-type boilers have oneor more water drums (and usually one or morewater headers as well). Header-type boilershave no water drum; instead, the tubes enter agreat many water headers.What is a header, and what is the differencebetween aheader andadrum? The term HEADERis commonly used in engineerlngto describe anytube, chamber, drum, and similar piece to whicha series of tubes or pipes are connected in such away as to permit the flow of fluid from one tube(or group of tubes) to another. Essentially, aheader is a type of manifold. As far as boilersare concerned, the only distinction between adrum and a header is the distinction of size.Drums are larger than headers, but both servebasically the same purpose.Drum-type boilers are further classifiedaccording to the overall configuration of theboiler, with particular regard to the shapeformed by the steam and water spaces. Forexample, double-furnace boilers are often called"M-type boilers" because the arrangement oftubes is roughly M-shaped. Single-furnaceboilers are often called "D-type boilers" becausethe tubes form (rouglily) the letter D.3Number of FurnacesAll boilers that are now commonly used inthe propulsion plants of naval ships may beclassified as being either single-furnace boilersor double-furnace boilers. The D-type boiler isa single-furnace boiler; the M-type boiler is adouble-furnace (or divided-furnace) boiler.Furnace PressureRecent developments in naval boilers make itconvenient to classify boilers on the basis of theAn interesting variation in this terminology occurredwhen the single-furnace or D-type boiler becamestandard for steam-driven destroyer escorts and thussubsequently became known as a "DE-type boiler."The term "DE-type boiler" is still used rather freely;its use should be discouraged, however, as this generaltype of boiler is now installed on many shipsother than destroyer escorts.233

PRINCIPLES OF NAVAL ENGINEERINGCOOL WATERFLOWS DOWNHOTGASESMIXTURE OFHOT WATERAND STEAMFLOWS UPFigure 10-2.— Natural circulation(accelerated type).139.17air pressure used in the furnace. Most boilersnow in use in naval propulsion plants operatewith a slight air pressure (seldom over lOpsig)in the boiler furnace. This slight pressure, whichresults from the use of forced draft blowers tosupply combustion air to the boilers, is not sufficientto warrant calling these boilers "pressurized-furnaceboilers." However, a new typeof boiler has recently appeared on the scene andis being installed in some ships. This new boileris truly a pressurized-furnace boiler, since thefurnace is maintained under a positive air pressureof approximately 65 psia (about 50 psig)when the boiler is operating at full power. Theair pressure in the furnace is maintained by aspecial air compressor. Hence we must nowmake a distinction between this new pressurizedfurnaceboiler, on the one hand, and all othernaval propulsion boilers, on the other hand, withrespect to the pressure maintained in the furnace.Type of SuperheaterOn almost all boilers currently used in thepropulsion plants of naval ships, the superheatertubes are protected from radiant heat by waterscreen tubes. The water screen tubes absorbthe intense radiant heat of the furnace, and thesuperheater tubes are heated by convectioncurrents rather than by radiation. Hence, thesuperheaters are referred to as convection-typesuperheaters.On a few older ships, the superheater tubesare not screened by water screen tubes but areexposed directly to the radiant heat of the furnace.Superheaters of this kind are calledradiant-type superheaters. Although radianttypesuperheaters are rarely used at present, itis possible that they may come into use again infuture boiler designs.Control of SuperheatA boiler which provides some means of controllingthe degree of superheat independently ofthe rate of steam generation is said to havecontrolled superheat . A boiler in which suchseparate control is not possible is said to haveuncontrolled superheat .Until recently, the term superheat controlboiler was used to identify a double-furnaceboiler and the term uncontrolled superheatboiler (or no control superheat boiler ) was usedto identify a single-furnace boiler. Most doublefurnaceboilers now in use do, in fact, havecontrolled superheat, and most single-furnaceboilers do not have controlled superheat. However,recent developments in boiler design makesuperheat control independent of the number offurnaces in the boiler. Single-furnace boilersWITH controlled superheat and double-furnaceboilers WITHOUT controlled superheat are bothpossible. The time has come, therefore, to stoprelating the number of furnaces in a boiler tothe control (or lack of control) of superheat.Operating PressureFor some purposes it is convenient to classifyboilers according to operating pressure.Most classifications of this type are approximaterather than exact. Header-type boilers and someolder drum-type boilers are often called "400-psi boilers" even though the operating pressuresmay range from 300 psi (or even lower) to about450 psi. The term "600-psi boiler" is oftenapplied to various double-furnace and singlefurnaceboilers with operating pressures rangingfrom about 435 psi to about 700 psi.The term "high pressure boiler" is at presentused rather loosely to identify any boilerthat operates at substantially higher pressurethan the so-called "600-psi boilers." In general,we will consider any boiler that operatesat 751 psi or above as a high pressure boiler.A good many boilers recently installed on navalships operate at approximately 1200 psi; forsome purposes, it is convenient to group theseboilers together and refer to them as "1200-psiboilers."234

Chapter 10- PROPULSION BOILERSAs may be seen, classifying boilers by operatingpressure is not very precise, since actualoperating pressures may vary widely within onegroup. Also, any classification based on operatingpressure may easily become obsolete. Whatis called a high pressure boiler today might wellbe called a low pressure boiler tomorrow.BOILER COMPONENTSMost propulsion boilers now used by theNavy have essentially the same components:steam and water drums, generating and circulatingtubes, superheaters, economizers, fueloil burners, furnaces, casings, supports, and anumber of accessories and fittings required forboiler operation and control. The basic componentsof boilers are described here. In latersections of this chapter we will see how thecomponents are arranged to form various commontypes of naval propulsion boilers.Drums and HeadersDrum-type boilers are installed in the shipin such a way that the long axis of the boilerdrums will run fore and aft rather than athwartships,so that the water will not surge from oneend of the drum to the other as the ship rolls.The steam drum is located at the top of theboiler. It is cylindrical in shape, except that onsome boilers, it may be slightly flattened alongits lower curved surface. The steam drum receivesfeed water and serves as a place for theaccumulation of the saturated steam that is generatedin the tubes. The tubes enter the steamdrum below the normal water level of the drum.The steam and water mixture from the tubesgoes through separators which separate thewater from the steam.Figure 10-3 shows the way in which a steamdrum is constructed. Two sheets of steel arerolled or bent to the required semicircularshape and then welded together. The upper sheetis called the wrapper sheet; the lower sheet iscalled the tube sheet. Notice that the tube sheetis thicker than the wrapper sheet. The extrathickness is required in the tube sheet to ensureadequate strength of the tube sheet after theholes for the generating tubes have been drilled.The ends of the drum are enclosed with drumheadswhich are welded to the shell, as shown infigure 10-4. One drumhead contains a manholewhich permits access to the drum for inspection,cleaning, and repair.WRAPPERSHEETTUBEFigure 10-3.— Boiler steam drum.SHEET38.19The steam drum either contains or is connectedto many of the important fittings andinstruments required for the operation andcontrol of the boiler. These fittings and controlsare discussed separately in chapter 11 of thistext.Water drums and water headers equalize thedistribution of water to the generating tubes andprovide a place for the accumulation of loosescale and other solid matter that may be presentin the boiler water. In drum-type boilers, thewater drums and water headers are at theDRUMHEAD38.20Figure 10-4.—Drumhead secured to steam drumshell.235

PRINCIPLES OF NAVAL ENGINEERINGbottom of the boiler. Water drums are usuallyround in cross section; headers may be round,oval, or square. Headers are provided withaccess openings of the type shown in figure10-5. Water drums are usually made with manholessimilar to the manholes in steam drums.HEADERFigureHANDHOLE PLATENUTGASKET38.2110-5.—Header handhole and handholeplate.Generating and Circulating TubesMost of the tubes in a boiler are generatingor circulating tubes. There are four main kindsof generating and circulating tubes: (1) generatingtubes in the main generating tube bank; (2)water wall tubes, (3) water screen tubes, and(4) downcomers. The tubes are made of steelsimilar to the steel used for the drums andheaders. Most tubes in the main generatingbank are about 1 inch or 1 1/4 inches in outsidediameter. Water wall tubes, water screen tubes,and the two or three rows of generating tubes nextto the furnace are generally a little larger.Downcomers are larger still, being on the averageabout 3 to 11 inches in outside diameter.Since the steam drum is at the top of theboiler and the water drums and headers are atthe bottom, it is obvious that the generating andcirculating tubes must be installed more or lessvertically. Each tube enters the steam drum andthe water drum (or water header) at right anglesto the drum surfaces. This means that all tubesin any one row are curved in exactly the sameway, but the curvature of different rows is notthe same. Tubes are installed normal to thedrum surfaces in order to allow the maximumnumber of tube holes to be drilled in the tubesheets with a minimum weakening of the drums.However, nonnormal installation is permitted ifcertain advantages can be achieved in designcharacteristics.What purpose do all these generating andcirculating tubes serve? The generating tubesare the ones in which most of the saturatedsteam is generated. The water wall tubes serveprimarily to protect the furnace refractories,thus allowing higher heat release rates thanwould be possible without this protection. However,the water wall tubes are also generatingtubes at high firing rates. Water screen tubesprotect the superheater from direct radiant heat.Water screen tubes, like water wall tubes, aregenerating tubes at high firing rates. Downcomersare installed between the inner and outercasings of the boiler to carry the downward flowof relatively cool water and thus maintain theboiler circulation. Downcomers are not designedto be generating tubes under any conditions.In addition to the four main types of generatingand circulating tubes just mentioned,there are a few large superheater support tubeswhich, in addition to providing partial support forthe steam drum and for the superheater, serveas downcomers at low firing rates and as generatingtubes at high firing rates.Since a modern boiler is likely to containbetween 1000 and 2000 tubes, some system oftube identification is essential. Generating andcirculating tubes are identified by LETTERINGthe rows of tubes and NUMBERING the individualtubes in each row. A tube row runs fromthe front of the boiler to the rear of the boiler.The row of tubes next to the furnace is row A,the next is row B, the next is row C, and soforth. If there are more than 26 rows in a tubebank, the rows after Z are lettered AA, BB, CC,DD, EE, and so forth. Each tube in each row isthen designated by a number, beginning with 1at the front of the boiler and numbering backtoward the rear.The letter which identifies a tube row isoften preceded by an R or an L, particularlyin the case of water screen tubes, superheatersupport tubes,and furnace division wall tubes.When an R or an L is used AFTER the regularletter and number identification of atube, it mayindicate either that the tube is bent for a righthandor left-hand boiler or that the tube isstudded or finned on the right-hand side or onthe left-hand side.236

Chapter 10- PROPULSION BOILERSFigure 10-6 shows a Boiler Tube RenewalSheet for a double-furnace boiler and illustratesthe method used to identify tubes.The water wall tube row is not identified bya letter in figure 10-6. The tubes in this row areoften identified by the letter W and a followingletter which indicates the type of tube or itsposition in the row. Still another letter (an R oran L) may be added to indicate that the tube isstudded or finned on the right-hand side or onthe left-hand side.The tubes which screenthe superheater fromdirect radiant heat are identified in figure 10-6as the LA, LB, and LC rows. Within each row,the individual tubes are numbered: LA-1, LA-2,LA-3, and so forth.Figure 10-6 identifies the superheater supportand drum support tubes as the LD row.Note that these are NOT superheater tubes.The superheater tubes in this boiler, as inmostboilers, are installed horizontally. The superheatersupport tubes and the drum support tubesare installed vertically; they are identified asLD-1, LD-2, LD-3, and so forth.The first row of division wall tubes is identifiedin figure 10-6 as the LE row. The secondrow of division wall tubes may be identified asthe LF row or as the D row. Identification oftubes in this row is usually made by using therow identification (LF, D, or whatever rowidentification is used for the particular boiler)followed by a letter to indicate the type of tubeor its position in the row; still another letter(an R or an L) may be added to indicate that thetube is studded or finned on the right-hand sideor on the left-hand side.Tubes in the main generating bank are identifiedby lettering the rows and numbering theindividual tubes, as shown in figure 6-6. Thetwo rows nearest the saturated-side furnace areslightly larger than the rest of the generatingtubes; they serve as water screen tubes. Thesetwo rows are often called the RA and the RBrows. Individual tubes in these rows are identifiedby number in the same way that the rest ofthe generating tubes are identified.Note that the superheater tubes are alsoidentified in figure 10-6. Identification of superheatertubes is discussed in the section thatdeals with superheaters.The discussion of boiler tube identificationgiven here is based on one particular type ofboiler— that is, a double-furnace boiler. Thesame general principles of tube identificationapply to most other drum-type boilers now innaval use, but the details of tube identificationare necessarily different in different types ofboilers.SuperheatersMost propulsion boilers now in naval servicehave convection-type superheaters, with waterscreen tubes installed between the superheaterand the furnace to absorb the intense radiantheat and thus protect the superheater.Most convection-type superheaters haveU-shaped tupes which are installed horizonallyin the boiler and two headers which are installedmore or less vertically at the rear ofthe boiler. One end of each U-shaped tube entersone superheater header, and the other endenters the other header. The superheater headersare divided internally by one or more divisionplates which act as baffles to direct theflow of steam. In some cases the superheaterheaders are divided externally as well as internally.Figure 10-7 illustrates some convectiontypesuperheater arrangements that are usedon double-furnace boilers. Part A is apian viewof the superheater tubes, showing how the tubesenter the headers. Part B shows a superheaterin which each header is divided into two sections,and illustrates the flow of steam throughthe superheater. Part C illustrates the flow ofsteam through a superheater in which one headerhas one internal division and the other headerhas two internal divisions. As may be seen fromfigure 10-7, the steam makes several passesthrough the furnaces. The number of passes isdetermined by the number of header divisionsand by the relative locations of the steam inletand the steam outlet.The superheater tubes are installed so thattheir U-shaped ends project forward toward thefront of the boiler. In a double-furnace boiler,the superheater tubes project forward into aspace between the water screen tubes and sometubes called furnace division wall tubes . Thesuperheater tubes and the surrounding waterscreen and division wall tubes are thus togetherthe dividing line between the superheater-sidefurnace and the saturated-side furnace. In asingle-furnace boiler, the superheater tubesproject forward into a space in the main bankof generating tubes. The tubes between thesuperheater tubes and the furnace serve aswater screen tubes.Some recent boilers have walk- in or cavitytypesuperheaters. In this type of superheater,237

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Chapter 10- PROPULSION BOILERSSUPERHEATERHEADERS^jSATURATEDSTEAMo oo o o " INLET1DRAINhave U-shaped tubes. Others, such as the oneshown in figure 10-8, have W- shaped tubes.A few boilers of recent design have vertical,rather than horizontal, convection-type superheaters.In these boilers, the U-bend superheatertubes are installed almost vertically,with the U-bends near the top of the boiler; thetubes are approximately parallel to the mainbank of generating tubes and the water screentubes. Two superheater headers are near thebottom of the boiler, running horizontally fromthe front of the boiler to the rear.Superheater tubes are generally identified byloop number, name of tube bank, and number oftube within the bank. In the case of horizontalsuperheater tubes, as shown in figure 10-6, youcount from the bottom toward the top to get thetube number. In the case of vertical superheatertubes, you count from the front of the boilertoward the rear.DesuperheatersOn boilers with noncontrolled superheaters,all steam is superheated, but a small amount ofsteam is redirected through a desuperheaterline, the desuperheater can be located in eitherthe water drum or the steam drum, most generallythe desuperheater will be found in thesteam drum below the normal water level. Thepurpose of the desuperheater is to lower thesuper-heated steam temperature back to orclose to saturated steam temperature for theproper steam lubrication of the auxiliary machinery.The desuperheater is most generallyan "S" shaped tube bundle that is flanged to thesuperheater outlet on the inlet side and theauxiliary steam stop on the outlet side.Economizers38.23Figure 10-7. — Convection-type superheater(double-furnace boiler).an access space or cavity is provided in themiddle of the superheater tube bank. The cavity,which runs the full length and height of thesuperheater, greatly increases the accessibilityof the superheater for cleaning, maintenance,and repair. Some of the walk- in superheatersAn economizer is installed on practicallyevery boiler used in naval propulsion plants.The economizer is an arrangement of tubesinstalled in the uptake space from the furnace;thus the economizer tubes are heated by therising gases of combustion. All feed water flowsthrough the economizer tubes before enteringthe steam drum, and the feed water is warmedby heat which would otherwise be wasted ascombustion gases pass up the stack. In general,boilers operating at high pressures and temperatureshave larger economizer surfaces thanboilers operating at low pressure and temperatures.239

PRINCIPLES OF NAVAL ENGINEERINGREAR OF BOILERSUPPORT CHANNELSPLAN VIEWVERTICAL CENTERLINEOF WATER DRUM\ELEVATIONFigure 10-8.— Arrangement of W-tube walk-in superheater.38.27Economizer tubes may be of various shapes.Most commonly, perhaps, they are a continuousloop of U-shaped elements from inlet to outletheader. Almost all economizer tubes have somesort of metal projections from the outer tubesurface. These projections, which are of aluminum,steel, or other metal, are shaped in variousways. Figure 10-9 shows a U-bend economizertube with aluminum gill rings that are circularin cross section. Other types of projections inuse include rectangular fins and star-shapeddisks. In all cases, the projections serve to extendthe heat transfer surface of the economizertubes on which they are installed.38.28Figure 10-9.— U-bend economizer tubewith aluminum gill rings.240

Chapter 10- PROPULSION BOILERSFuel Oil BurnersAlmost all fuel oil burners used on navalpropulsion boilers are mounted on the boilerfront. Special openings called burner cone openingsare provided in the furnace front for theburners.The two main parts of a fuel oil burner arethe atomizer assembly and the air register assembly.The atomizers divide the fuel oil intovery fine particles; the air registers permitcombustion air to enter the furnace in such away that it mixes thoroughly with the finelydivided oil. In addition to the atomizer assemblyand the air register assembly, a fuel oil burnerincludes various valves, fittings, connections,and (on new construction) burner safety deviceswhich prevent spillage of oil when an atomizerassembly is removed from the burner while theburner root valve is still open.ATOMIZERS.— Three main kinds of atomizersare now in use on naval boilers. Straightthrough-flowatomizers are used on most boilers.Return-flow atomizers are used on many ofthe newer ships, particularly those equipped withautomatic combustion controls. Steam-assistatomizers are used on boilers in some of thenewest ships.A fuel oil burner with a straight-throughflowatomizer is shown in cross section infigure 10-10. Figure 10-11 shows how burnersof this type look when installed at the boilerfront.INNER CASINGOUTER CASINGAIR DOOR HANDLESTATIONARY^!AIR FOILSGOOSE NECKBURNER CONE OPENING |,Hi-YOKEDISTANCE PIECEMOVABLE AIR DOORSINNER CASINGBURNER(SIDE VIEW)OUTER CASING(BOILER FRONT)BURNER BARRELBURNER COVER PLATEAIR DOOR HANDLEATOMIZER VALVEBURNER(FRONT VIEW)38.69Figure 10-10.— Cross-sectional view of fuel oil burner with straight-through-flow atomizer.241

|IPRINCIPLES OF NAVAL ENGINEERINGIn a straight-through-flow atomizer, all oilpumped to the atomizer is burned in the boilerfurnace. The fuel oil is forced through theatomizer barrel at a pressure between 125 and300 psi. With this type of atomizer, the firingrate is controlled by changing the number ofburners in use, the fuel oil pressure, and thesize of the sprayer plates.A straight-through-flow atomizer assemblyconsists of a goose neck, a burner barrel (alsocalled an atomizer barrel), a nozzle, a sprayerplate, and a tip. These parts are shown infigure 10-12. The fuel oil goes through thenozzle, which directs the oil to the groovesof the sprayer plate. These grooves are shapedso as to give the oil a high rotational velocityas it discharges into a small cylindrical whirlingchamber in the center of the sprayer plate.The whirling chamber is coned out at the endand has an orifice at the apex of the cone. Asthe oil leaves the chamber by way of the orifice,it is broken up into very fine particleswhich form a cone-shaped foglike spray. Astrong blast of air, which has been given awhirling motion in its passage through theburner register, catches the oil fog and mixeswith it. The mixture of air and oil enters thefurnace and combustion takes place.Figure 10-11. — Fuel oil burnersboiler front.38.70installed onGOOSE NECKINOZZLEIiTOMIZERSSEMBLYSPRAYER PLATE 1^^38.71Figure 10-12.— Parts of a straight-throughflowatomizer assembly.The sprayer plates most commonly usedare called standard sprayer plates. Two typesof standard sprayer plates are shown in figure10-13. Standard sprayer plates may be eitherflat-faced or dished and rounded, and they mayhave four, six, or eight oil grooves. Standardsprayer plates with four grooves are mostcommon.Now that the Defense Department has authorizedthe conversion to a new distillate fuel(NSDF), sprayer plates for burning this type offuel will be of the 6, 4, and 3 slot type. Sizeswill also be changed as the viscosity of thenew fuel is less than that of Navy Special fueloil (NSFO). Therefore, each class of ship willneed the correct size sprayer plates to permitthem to burn the correct amount of fuel for fullpower and overload conditions.In a return-flow (also called a variablecapacity)atomizer, part of the oil supplied tothe atomizer is burned in the boiler furnace andpart is returned. Several types of return-flowatomizers are in use. One type (Todd) is designedto operate with a constant fuel oil supplypressure of 300 psig and a minimum returnpressure of 25 psig. Another return-flow atomizer(Babcock & Wilcox) operates with avariable fuel oil supply pressure (up to 1000psi) and a variable return pressure, StLIl anothertype (also Babcock & Wilcox) operates witha constant supply pressure of 1000 psi and avariable return pressure.The return-flow atomizer shown in figure10-14 operates with a constant fuel oil supply242

Chapter 10- PROPULSION BOILERSSPRAYER ATOMIZER DISTRIBUTOR NOZZLEPLATE NUT HEAD BODYDISHED AND ROUNDED FACEOIL LEAVING WHIRLING OIL RETURNORIFICE CHAMBEROILSUPPLY38.74Figure 10-13.—Two kinds of standard sprayerplates.pressure. The amount of oil burned in the furnaceis controlled by regulating the oil returnpressure. The supply oil enters through thetube-like opening down the middle of the atomizerbarrel and passes through the sprayer plate.The tangential slots or grooves in the sprayerplate cause the oil to enter the whirling chamberwith a rotary motion. As the oil reaches thereturn annulus, centrifugal force causes a certainamount of the oil to enter the return annulis.The amount of oil thus returned is determinedby the back pressure in the return line;the back pressure is in turn determined by theextent to which the return line control valve isopen. The oil which is not returned emergesfrom the orifice in the form of a hollow conicalspray of atomized oil. The amount of oil burnedis the difference between the amount of oil suppliedand the amount returned.The straight-through-flow atomizers and thereturn-flow atomizers just described are bothconsidered to be mechanical atomizers of thepressure type. The steam-assist atomizer, nowin use on some new ships, operates on differentprinciples. The fuel oil enters a steam-assistatomizer at relatively low pressure and is veryfinely atomized by a jet of steam. Combustion airis supplied by forced draft blowers, just as it isin other installations.A steam-assist atomizer has two supply linescoming into it, one for fuel oil and one for steam.These two lines make the atomizer look a gooddeal like a return-flow atomizer. However, thesteam-assist atomizer does not return any fueloil; instead, all oil supplied to the atomizer isburned in the boiler furnace. Sprayer plates andother parts are somewhat differently shaped insteam-assist atomizers than they are in38.75Figure 10-14.—Return-flow atomizer.straight-through-flow atomizers and returnflowatomizers.One reason why steam-assist atomizers havenot been used for naval propulsion boilers untilquite recently is that they use a considerableamount of steam which cannot be recovered andreturned to the feed system. However, they havesome advantages that tend to make up for thisdisadvantage. A major advantage is that the firingrange of steam-assist atomizers is muchgreater than the firing range of other types ofatomizers. This characteristic makes thesteam-assist atomizer particularly useful fornaval service, since it means that large changesof load can be made merely by varying the fueloil supply pressure, without cutting burners inand out. The fuel oil supply pressure can bevaried between 8 and 350 psi.AIR REGISTERS.— The main parts of an airregister are (1) the movable air doors, (2) thediffuser, and (3) the stationary air foils. Theseparts are shown in figure 10-10. The movableair doors allow operating personnel to open andclose the register. When the air doors are open,air rushes in and is given a whirling motion bythe diffuser plate. The diffuser thus serves tomake the air mix evenly with the oil, and alsoto prevent flame being blown back from theatomizer. The stationary air foils guide themajor quantity of air and cause it to mix withthe larger oil spray beyond the diffuser.Furnaces and RefractoriesA boiler furnace is a space provided for themixing of air and fuel and for the combustion ofthe fuel. A boiler furnace consists of a more orless rectangular steel casing which is lined on243

PRINCIPLES OF NAVAL ENGINEERINGthe floor, front wall, side walls, and rear wallwith refractory material. The refractory liningserves to protect the furnace casing and to preventloss of heat from the furnace. Refractoriesretain heat for a relatively long time and thushelp to maintain the high furnace temperaturesrequired for complete and efficient combustionof the fuel. Refractories are also used to formbaffles which direct the flow of combustiongases and protect drums, headers, and tubesfrom excessive heat.There are many different kinds of refractorymaterials. The particular use of each type isdetermined by the chemical and physical characteristicsof the material in relation to therequired conditions of service. Refractoriescommonly used in the furnaces of naval propulsionboilers include firebrick, insulatingbrick, insulating block, plastic fireclay, plasticchrome ore, chrome castable refractory, hightemperature castable refractory, air-settingmortar, and burner refractory tile.Casings, Uptakes, and SmokepipesIn modern boiler installations, each boileris enclosed in two steel casings. The inner casingis lined with refractory materials, and theenclosed space constitutes the furnace. Theouter casing extends around most of the innercasing, with an air space in between. Air fromthe forced draft blowers is forced into the spacebetween the inner and the outer casings, andfrom there it flows through the air registersand into the furnace.The inner casing encloses most of the boilerup to the uptakes. The uptakes join the boiler tothe smokepipe. As a rule, the uptakes from twoor more boilers connect with one smokepipe.Both the inner and the outer casings of boilersare made of steel panels. The panels maybe flanged and bolted together, with gasketsbeing used at the joints to make an airtightseal, or they may be welded together. The casingsare made in small sections so they can beremoved for the inspection and repair of boilerparts.Saddles and SupportsEach water drum and water header restsupon two saddles, one at the front of the drumor header and one at the rear. The upper flangesof the saddle are curved to fit the curvature ofthe drum or header, and are welded to the drumor header. The bottom flanges, which are flat,rest on huge beams built up from the ship'sstructure. The bottom flange of one saddle isbolted rigidly to its support. The bottom flangeof the other saddle is also bolted to its support,but the bolt holes are elongated in a fore-andaftdirection. As the drum expands or contractsbecause of temperature changes, the saddlewhich is not rigidly fastened to the supportaccommodates to the changing length of thedrum by sliding backward or forward over thesupport. The flanges which are not rigidly fastenedare known as boiler sliding feet .AirheatersSome boilers of recent design have steamcoilairheaters to preheat the combustion airbefore it enters the furnace. A typical steamcoilairheater consists of two coil blocks, eachcoil block having three sections of heating coilsin a single casing. Each individual section hasrows of copper-nickel alloy tubes, helicallywound with copper fins. Airheaters used in thepast on some older naval ships were installedin the uptakes and the combustion air was preheatedby the combustion gases; these airheatersthus utilized heat which would otherwise havebeen wasted. The use of these older airheaterswas discontinued in naval ships because the savingof heat was not considered sufficient to justifythe added space and weight requirements.The new steam-coil airheaters use auxiliaryexhaust steam as the heating agent; they are installednear the point where the combustion airenters the double casing.Fittings, Instruments, and ControlsThe major boiler components just describedcould not function without a number of fittings,instruments, and control devices. These additionalboiler parts are merely mentioned herefor the sake of completeness; they are taken upin detail in chapter 11 of this text.Internal fittings installed in the steam drummay include equipment for distributing the incomingfeed water, for separating and drying thesteam, for giving surface blows to remove solidmatter from the water, for directing the flow ofsteam and water within the steam drum, and forinjecting chemicals for boiler water treatment.In addition, many boilers have desuperheatersfor desuperheating the steam needed for auxiliarypurposes.244

Chapter 10- PROPULSION BOILERSExternal fittings and instruments used onnaval boilers may include drains and vents;sampling connections, feed stop and checkvalves; steam stop valves; safety valves; sootblowers, watergage glasses and remote waterlevel indicators; pressure and temperaturegages; superheater temperature alarms; superheatersteam flow indicators; smoke indicators;and various items used for the automatic controlof combustion and water level.TYPES OF PROPULSION BOILERSNow that we have examined the basic componentsused in most naval propulsion boilers,let us put these components together, so tospeak, to see how they are arranged to form thetypes of boilers now used in the propulsion plantsof naval ships. The order of presentation ismore or less historical, starting with theheader-type boiler (which is probably the oldestboiler design still in service), going on todouble-furnace boilers and to both older andnewer types of single-furnace boilers, and endingwith the recently installed pressurizedfurnaceboiler.Header-Type BoilersSectional header boilers, commonly calledheader-type boilers, are installed in manyauxiliary ships. The basic design of this type ofboiler is shown in figures 10-15 and 10-16.Header-type boilers normally operate at 450to 465 psig and are designed for a maximumsuperheater outlet temperature of 740° to 750° F.In capacity, they range from about 25,000 toabout 40,000 pounds of steam per hour.Header-type boilers are sometimes referredto as cross-drum boilers because many of themwere designed to be installed with the steamdrum athwartships rather than fore and aft. However,some header-type boilers are not of thecross-drum type.Header-type boilers are also referred tooccasionally as side-fired boilers. This termis used to indicate the location of the burnerswith respect to the position of the steam drum.However, the term "side-fired" tends to bemisleading because the surface of aboiler alongwhich the burners are installed is generally regardedas the front of the boiler. In this discussion,we will take as the front of the boiler thesurface along which the burners are installed.From this point of view, then, the steam drum isinstalled lengthwise along the top of the boilerfront.The header-type boiler gets its name fromthe header sections which are connected by thegenerating tubes. There may be 12, 14, or 16 ofthese header sections, depending upon the sizeof the boiler. Half of the header sections areinstalled under the steam drum, at the front ofthe boiler. The other half are installed at therear of the boiler, at a somewhat higher level.The header sections are installed at a slightangle fromthe vertical, leaning somewhat towardthe front of the boiler. The angle of inclinationof the headers allows the straight generatingtubes (which enter the headers normal to theheader surfaces) to slope slightly upward fromthe front of the boiler toward the rear, thus allowingfree natural circulation within the boiler.The header sections installed under thesteam drum at the front of the boiler are knownas downtake headers. Each downtake header isconnected to the steam drum by a short downtakenipple. The lower end of each downtakeheader is connected to the junction header(sometimes called the mud drum ) by a shortnipple.The header sections installed at the rear ofthe boiler are known as uptake headers. Eachuptake header is connected to the steam drumby a large circulator tube which enters thesteam drum slightly above the normal waterlevel.As shown in figures 10-15 and 10-16, thegenerating tubes in this type of boiler arestraight rather than curved. The generatingtubes connect the downtake headers at the frontof the boiler with the uptake headers at the rearof the boiler.The superheater consists of U-bend tubes,an upper superheater header, and a lower superheaterheader. The superheater tubes are installedat right angles to the generating tubes,between the main bank of generating tubes andthe water screen tubes.The steam drum of a header-type boilerusually has a manhole at each end. The steamdrum contains the internal fittings, including adesuperheater.The furnace of a header-type boiler has fourvertical walls and a flat floor. The side wallsare water cooled, being covered by water walltubes which form a part of the circulation systemof the boiler. There are two water walldowntake headers, one at each corner of theboiler front, installed vertically in the space245

PRINCIPLES OF NAVAL ENGINEERINGDRY PIPEECONOMIZERCIRCULATOR TUBES(FROM UPTAKE HEADER)STEAM SOOTBLOWER ELEMENTSUPTAKEHEADERSRISER TUBES FROMWATER WALL( SIDEWALL)UPTAKE HEADERSUPERHEATEROUTLETGENERATINGTUBESSUPERHEATERACCESS DOORJUNCTION HEADER(MUD DRUM)SUPERHEATERTUBESFURNACEACCESS DOORBOTTOM BLOWVALVE CONNECTIONWATER WALL(ISIDEWALL)TUBESWATER WALL( SIDEWALL )DOWNTAKEHEADERSUPERHEATERHEADERSSUPERHEATERSCREEN TUBESiV';sirr:i^£asi^s^^*;;j-:'; :'i-3Siiv ir: '.Figure 10-15.— Cutaway view of header-type boiler.38.33Xbetween the inner and the outer casing. Twovertical water wall uptake headers are similarlyinstalled at the two rear corners of theboiler. The water wall tubes are rolled into adowntake header at the front and an uptake headerat the rear; they are arranged on the sameslope as the generating tubes.Water is supplied to the water wall downtakeheaders from the junction header. Steam andwater rise through the water wall tubes to theuptake headers, and then through the riser tubesthat connect the uptake headers to the steamdrum.As may be seen in figures 10-15 and 10-16,an economizer is located behind the steam drum,in the way of the combustion gas exit.The boiler is completely enclosed in aninsulated steel casing, and an outer casing is246

Chapter 10- PROPULSION BOILERSECONOMIZER TUBESSTEAM DRUMDOWNTAKE NIPPLEGENERATING TUBESDOWNTAKE HEADERAIRINTAKESUPERHEATER TUBESWATER SCREEN TUBESJUNCTION HEADER(MUD DRUM)WATER WALLDOWNTAKE HEADERWATER WALL UPTAKE HEADERWATER WALL TUBESFigure 10-16.— Side view of header-type boiler.38.34installed in such a way as to form an air chamberbetween the inner and outer casings. The airinlet is at the rear of the boiler; an air ductbeneath the furnace floor connects the front airchamber and the rear air chamber. The doublecasedair chambers at the sides of the boiler areconnected directly to the cold air inlet so that anair pressure is maintained in these side chambersat all rates of operation. Removable casingpanels are located at various points to permitaccess for cleaning, inspection, and repair.summary, we may consider the header-Intype boiler as one which, on the basis of theclassification methods given earlier in this chapter,has the following characteristics: It is awater-tube boiler with natural circulation of thefree (not accelerated) type. It has sectionalheaders instead of water drums, and so is calleda "header-type" boiler instead of a drum-typeboiler. It has only one furnace—but the term"single-furnace boiler" is never applied toheader-type boilers, possibly because such identificationhas not been needed. It is not apressurized-furnace boiler. It does not havecontrolled superheat. It operates at a pressureof 450 to 465 psig; however, header-type boilersare quite often referredtoas "400-psi boilers."247

PRINCIPLES OF NAVAL ENGINEERINGDouble- Furnace BoilersDouble-furnace boilers (also called M-typeboilers) are installed on most older destroyersand on many other combatant ships. Theseboilers are designed to carry a steam drumpressure of approximately 615 psig and to generatesaturated steam at approximately 490° F.The saturated steam for auxiliaries goes directlyfrom the steam drum to the auxiliary steamsystem; all other steam goes through the superheater.Double-furnace boilers are designed invarious sizes and capacities to suit differentinstallations. They range in capacity from about100,000 to about 250,000 pounds of steam perhour at full power.Figure 10-17 shows the general arrangementof a double-furnace boiler. The same type ofboiler is shown in sectional view infigure 10-18and in cutaway view in figure 10-19.One of the two furnaces in this boiler is usedfor generating saturated steam; the other is usedfor superheating the saturated steam. Becauseeach of the two furnaces can be fired separately,thus allowing control of superheated steam temperatureover a wide range of operating conditions,the double-furnace boiler has long beencalled a "superheat control boiler." As notedpreviously, however, the control of superheat isnot necessarily related to the number of furnaces.Therefore we will refer to this boiler asWATER WALLHEADERMAIN STEAMWATERDRUM38,36Figure 10-17.— General arrangement of doublefurnaceboiler.a double-furnace boiler, rather than as a superheatcontrol boiler, even though the boiler showndoes in fact have controlled superheat.Since each furnace has its own burners, thedegree of superheat can be controlled by proportioningthe amount of fuel burned in thesuperheater-side furnace to the amount burnedin the saturated-side furnace. When burners arelighted only on the saturated side, saturatedsteam is generated; when burners are lightedon the superheater side as well as on the saturatedside, the saturated steam flowing throughthe superheater becomes superheated. The degreeof superheat depends primarily upon (1) thefiring rate on the superheater side, and (2) therate of steam flow through the superheater.However, the rate of steam flow through thesuperheater is basically dependent upon the firingrate on the saturated side. Therefore wecome back again to the idea that the degree ofsuperheat depends primarily upon the ratio ofthe amount of oil burned in the superheater sideto the amount burned in the saturated side.The flow of combustion gases in the doublefurnaceboiler is partly controlled by gas baffleson one row of water screen tubes and on onerow of division wall tubes, as shown in figure10-18. The gas baffles on the water screentubes direct the combustion gases toward thesuperheater tubes and also deflect the combustiongases away from the steam drum and thewater screen header. The baffles on the divisionwall tubes by the saturated-side furnacekeep the saturated-side combustion gases fromflowing toward the superheater tubes, thusprotecting the superheater when the superheaterside is not lighted off. In addition, the baffleson the division wall tubes deflect combustiongases from the superheater side up toward thetop of the saturated side, thus allowing thegases to pass toward the uptake without disturbingthe fires in the saturated- side furnace.The double-furnace boiler has a steam drum,one water drum, one water screen header, andone water wall header. All these drums andheaders run from the front of the boiler to therear of the boiler. Most of the saturated steamis generated in the main bank of generatingtubes on the uptake side of the boiler; most ofthese tubes are 1 inch in outside diameter, but afew rows of 2- inch tubes are installed on the sideof the tube bank nearest the furnace. The evaporationrate is much higher in the 1-inch tubesthan in the 2-inch tubes, since the ratio of heattransfersurface to the volume of contained water248

Chapter 10- PROPULSION BOILERSAIRINLET@@®@®@@@@@@®®® @®@®®@@®@@@@® ®@@@@@@@@@@(-/@ @@@@®@@@@@®@fc@@@®® ®®@@@@@C@@@@@@@@@@@@@®@® @®®@@®®@®@@®@@@®®@@®@@®@@©@©@@®@®@®GENERATINGTUBES*- ECONOMIZERAIRINLETOUTER^CASINGOUTER'CASINGINNER .CASINGINNERCASINGWATER WALLHEADERSUPERHEATER-SIDE BURNERSWATERSCREENHEADERSUPERHEATER TUBES(CROSS SECTION)SATURATED-SIDEBURNERSFigure 10-18.— Double-furnace boiler (sectional view, looking toward rear wall).38.37is much greater in the smaller tubes. The largertubes are used in the rows next to the furnacebecause it is necessary at this point to providea flow of cooling water and steam sufficient toprotect the smaller tubes from the intense radiantheat of the furnaces.Double-furnace boilers have anywhere from15 to 50 downcomers, which vary in size fromabout 3 inches in outside diameter to about 7inches OD. The downcomers are installed betweenthe inner and the outer casings, as may beseen in figure 10-19.The use of large-tube downcomers and smallgenerating tubes results in extremely rapid circulationof water. Only a few seconds are requiredfor the water to enter the steam drum asfeed water, flow through the downcomers, circulatethrough the water drum or header, rise inthe generating tubes, and return to the steamdrum as a mixture of water and steam. Somenotion of the extreme rapidity of circulation maybe obtained from the fact that water in the downcomersmay flow at velocities of from 3 to 7feet per second.The economizer on a double-furnace boileris usually larger than the economizer on aheader-type boiler. As a rule, the economizeron a double-furnace boiler has about 60 U-shapedeconomizer tubes.On the basis of the classification methodsgiven earlier in this chapter, we may considerthe double-furnace boiler as one which has thefollowing characteristics: It is a water-tubeboiler with natural circulation of the acceleratedtype. It is a drum-type (rather than a headertype)boiler. It has tubes which are arrangedroughly in the shape of the letter M— hence it isoften called an M-type boiler. It has two249

PRINCIPLES OF NAVAL ENGINEERINGDRUM SAFETY VALVES ECONOMIZE!! INinSTEAM DRUMSCRUBBEI! ELEMENTSURFACE BLOWOFF PIPECYCLONE STEAM SEPARATORINTERNAL FEED PIPESTEAM COLLECTING BAFFLEAIR INLn TO VDOUBLE CASING\MODEL IN SOOT BLOWERSTEAM DRUMPROTECTION PLATESSUPERHEATED-SIDEFURNACEFURNACE PEEP HOLE SOOT BLOWERELEMENTSHIGH TEMPERATUREINSULATING BRICKSTUD TUBEWATER COOLEDSIDE WALLPLASTIC CHROME ORFDOWNCOMERWATER WALL HEADERIMPELLER PLATESATURATED-SIDEFURNACESUPERHEATERTUBE SUPPORTSBURNER, BEADEDCONEDENSE FIREBRICKHIGH TEMPERATUREINSULATING BRICKWATERDRUMUNCALCINEO DIATOMACEOUSEARTH BLOCKSBRICK BOLTWATER SCREEN HEADERPROTECTION PLATES t BAFFLE MIXBOTTOM BLOWOFFCONNECTIONBURNER AIR DOORSFUEL OIL BURNERSeECIAl OIL BURNER LIGHTING PORTAIR LOCK TYPESM-WATER WALL HEADERDRAIN CONNECTION PLASTIC CHROME OREWATER SCREEN HEADERBLOWOFF CONNECTIONDOWNCOMERSFigure 10-19.— Double-furnace boiler (cutaway view).furnaces— one for the saturated side and one forthe superheater side. It has controlled superheat.It operates at a pressure of about 615 psig, andis often called a "600-psi boiler."The most important advantage of the doublefurnaceboiler arises from the fact that theseparate firing of the superheater side allowspositive control of the degree of superheat. Inthe double-furnace boiler, it is theoretically250FURNACE ACCESS DOORSTDNTUBE WATER-COOLEDDIVISION WALL38.38Xpossible to maintain the maximum designedtemperature at the superheater outlet underwidely varying conditions of load. In a singlefurnaceboiler, where one source of heat is usedboth for generating the steam and for superheatingit, the degree of superheat increasesas the rate of steam generation increases; andhence the maximum designed temperature at thesuperheater outlet is normally reached only atfull power.

Chapter 10- PROPULSION BOILERSMost double-furnace boilers are designed tocarry a superheater outlet temperature of 850°F; this is about 100° F higher than the superheateroutlet temperature in a comparablesingle-furnace boiler, given the same quality ofmaterials for boilers, piping, and turbines. Thereason why a higher superheater outlet temperaturecan be used in a double-furnace boilerthan in a comparable single-furnace boiler is thatallowance must be made, in the single-furnaceboiler, for the maximum superheater temperatureswhich might occur under adverse conditionsof load.In spite of the advantages resulting from thecontrol of superheat, double-furnace boilers areno longer being installed in naval combatantships. Experience with these boilers has revealedcertain disadvantages which at the presenttime appear to outweigh the advantages of controlledsuperheat. Some of the disadvantages are:1. In practice, it is not possible to maintainmaximum designed superheat at low steamingrates. Only the steam for the main turbines andthe turbogenerators goes through the superheater;at low firing rates, therefore, the steamflow through the superheater is generally not sufficientto permit a high firing rate on the superheaterside. Thus under some conditions thesteam supplied to the propulsion turbines and tothe turbogenerators may be saturated or onlyvery slightly superheated. As a consequence,therefore, the double-furnace boiler is actuallyless efficient than the single-furnace boiler atlow firing rates.2. The double-furnace boiler is more difficultto operate than the single-furnace boiler,and requires more personnel for its operation.Once there is any appreciable load on the boiler,the high air pressure in the double casings and inthe furnace make it difficult and even dangerousto light burners on the superheater side. In orderto avoid this difficulty, operating personnelwould have to be able to predict the need forsuperheat and light off the burners on the superheaterside before the air pressure had becomeso high. Obviously, such prediction is not alwayspossible.3. The double-furnace boiler is heavier,larger, and generally more complex than asingle-furnace boiler of equal capacity.Single- Furnace BoilersThe older single-furnace boilers that wereinstalled on many World War II ships differ inseveral important respects from the newersingle-furnace boilers that have been installedon ships built since World War II.A single-furnace boiler of the older typeis shown schematically in figure 10-20 and incutaway view in figure 10-21. This boiler producesabout 60,000 pounds of steam per hour atfull power. At full power the steam drum pressureis about 460 psig, the superheater outletpressure is about 435 psig, and the superheateroutlet temperature is about 750° F.SUPERHEATERPROTECTIONEXHAUST VALVEECONOMIZER\Figure 10-20.— General arrangementsingle-furnace boiler.SUPERHEATERPROTECTIONSTEAM VALVEMAIN STEAMof38.39olderThis boiler does not have controlled superheat.When the boiler is lighted off, both thegenerating tubes and the superheater tubes areheated. In order to protect the superheatertubes from overheating, all steam generated inthe boiler must be led through the superheater.The saturated steam goes from the dry pipe inthe steam drum to the superheater inlet; it goesthrough the superheater tubes, out the superheateroutlet, and into the main steam line.Auxiliary steam must go through the superheater(in order to provide a sufficient steamflow to protect the superheater) but must thenbe desuperheated. Desuperheating is accomplishedby passing some of the superheatedsteam through a desuperheater, which is basicallya coil of piping submerged in the water in251

PRINCIPLES OF NAVAL ENGINEERINGIMTERNAL FEEDPIPEBAFFLE MATERIALSURFACE BLOWLINEFEED WATER OUTLETPLASTIC CHROMESUPERHEATERy/tPLASTIC FIREBRICK4ViFIREBRICKI'j INSULATING BRICKEINSULATING BLOCK2h" FIREBRICK2V!" INSULATING BRICK1 INSULATING BLOCKI PLASTIC CHROME ORE BOTTOM BLOW INSULATING BLOCKFigure 10-21.— Cutaway view of older single-furnace boiler.38.40252

Chapter 10- PROPULSION BOILERSthe steam drum. Heat transfer takes place fromthe steam in the desuperheater to the water inthe steam drum. The desuperheated steam whichpasses out of the desuperheater and into theauxiliary steam line is once again at (or veryclose to) saturation temperature.Thus far we have considered the flow ofsteam as it occurs after the boiler has been cutin on the steam line. But what happens when acold boiler is lighted off? How can the superheatertubes be protected from the heat of thefurnace after fires are lighted but before sufficientsteam has been generated to ensure a safeflow through the superheater?Various methods are used to protect thesuperheater during this critical period immediatelyafter lighting off. Very low firing ratesare used, and the boiler is warmed up slowlyuntil an adequate flow of steam has been established.Many—but not all—boQers of this typehave connections through which protective steamcan be supplied from another boiler on the sameship or from some outside source such as anaval shipyard or a tender. As shown in figure10-20, this steam comes in (under pressure)through the superheater protection steam valve.It enters the superheater inlet, passes throughthe superheater tubes, goes out the superheateroutlet, passes through the desuperheater, andthen goes into the auxiliary exhaust line by wayof the superheater protection exhaust valve.On single-furnace boilers which do not havea protective steam system for use during thelighting off period, even greater care must betaken to establish a steam flow through thesuperheater. In general, the steam flow is establishedby venting the superheater drains tothe bilges while warming up the boiler veryslowly.On the basis of the classification methodsgiven earlier in this chapter, we may considerthis older single-furnace boiler as one whichhas the following characteristics: It is a watertubeboiler with natural circulation of the acceleratedtype. It is a drum-type (rather than aheader-type) boiler. It has tubes which are arrangedroughly in the shape of the letter D—hence it is often called a D-type boiler. It hasonly one furnace. It does not have controlledsuperheat. It is often classified as a "600-psiboiler," although it actually operates at about435 psig.As previously noted, the degree of superheatobtained in a single-furnace boiler of the typebeing considered is primarily dependent uponthe firing rate. However, a number of designfeatures and operational considerations alsoaffect the temperature of the steam at the superheateroutlet.Design features that affect the degree ofsuperheat include (1) the type of superheaterinstalled—that is, whether heated by convection,by radiation, or by both; (2) the location of thesuperheater with respect to the burners; (3) theextent to which the superheater is protected bywater screen tubes; (4) the area of superheaterheat-transfer surface; (5) the number of passesmade by the steam in going through the superheater;(6) the location of gas baffles; and (7) thevolume and shape of the furnace.Operational factors that affect the degree ofsuperheat include (1) the rate of combustion;(2) the temperature of the feed water; (3) theamount of excess air passing through the furnace;(4) the amount of moisture contained in the steamentering the superheater; (5) the condition of thesuperheater tube surfaces; and (6) the conditionof the water screen tube surfaces. Since thesefactors may affect the degree of superheat inways which are not immediately apparent, let usexamine them in more detail.How does the rate of combustion affect thedegree of superheat? To begin with, we mightimagine a simple relationship in which the degreeof superheat goes up directly as the rate of combustionis increased. Such a simple relationshipdoes, in fact, exist— but only up to a certainpoint. Throughout most of the operating rangeof this boiler, the degree of superheat goes upquite steadily and regularly as the rate of combustiongoes up. Near full power, however, thedegree of superheat drops slightly even thoughthe rate of combustion is still going up. Whydoes this happen? Primarily because the increasedfiring rate results in an increasedgenerating rate, which in turn results in anincreased steam flow through the superheater.The rate of heat absorption increases morerapidly than the rate of steam flow until theboiler is operating at very nearly full power;at this point the rate of steam flow increasesmore rapidly than the rate of heat absorption.Therefore the superheater outlet temperaturedrops slightly.Suppose that the boiler is being fired at aconstant rate and that the steam is being usedat a constant rate. K we increase the temperatureof the incoming feed water, what happens tothe superheat? Does it increase, decrease, orremain the same? Surprisingly, the degree of253

PRINCIPLES OF NAVAL ENGINEERINGsuperheat decreases if the feed temperature isincreased, more saturated steam is generatedfrom the burning of the same amount of fuel.The increased quantity of saturated steam causesan increase in the rate of flow through the superheater.Since there is no increase in the amountof heat available for transfer to the superheater,the degree of superheat drops slightly.Under conditions of constant load and a constantrate of combustion, what happens to thesuperheat if the amount of excess air'* is increased?To see why an increase in excess airresults in an increase in temperature at thesuperheater outlet, we must take it step by step:1. An increase in excess air decreases theaverage temperature in the furnace.2. With the furnace temperature lowered,there is less temperature difference between thegases of combustion and the water in the boilertubes.3. Because of the smaller temperature difference,the rate of heat transfer is reduced.4. Because of the decreased rate of heattransfer, the evaporation rate is reduced.5. The lower evaporation rate causes areduction in the rate of steam flow through thesuperheater, with a consequent rise in the superheateroutlet temperature.In addition to this series of events, anotherfactor also tends to increase the superheateroutlet temperature when the amount of excessair is increased. Large amounts of excess airtend to cause combustion to occur in the tubebank rather than in the furnace itself; as a result,the temperature in the area around the superheatertubes is higher than usual and the superheateroutlet temperature is higher.Any appreciable amount of moisture in thesteam entering the superheater causes a verynoticeable drop in superheat. This occurs becausesteam cannot be superheated as long asit is in contact with the water from which it isbeing generated. If moisture enters the superheater,therefore, a good deal of heat must beused to dry the steam before the temperatureof the steam can rise.The condition of the superheater tube surfaceshas an important effect on superheaterThe term "excess air" is used to indicate any quantityof combustion air in excess of that which istheoretically required for the complete combustion ofthe fuel. Some excess air is necessary for efficientcombustion, but too much excess air is wasteful, asdiscussed in a later section of this chapter.254outlet temperature, K the tubes have soot on theoutside or scale on the inside, heat transfer willbe retarded and the degree of superheat will bedecreased.If the water screen tubes have soot on theoutside or scale on the inside, heat transfer tothe water in these tubes will be retarded. Thereforethere will be more heat available fortransfer to the superheater as the gases ofcombustion flow through the tube bank. Consequently,the superheater outlet temperature willrise.The single-furnace boiler is lighter andsmaller, for any given output of steam, than thedouble-furnace boiler. Because the singlefurnaceboiler supplies superheated steam atlow steaming rates, the overall plant efficiencyis better with this type of boiler than with thedouble-furnace boiler. The single-furnace boilerhas the further advantage of simplicity of operationand maintenance. Although the singlefurnaceboiler considered here does not havecontrolled superheat, this lack is less importantthan might have been supposed, since some ofthe theoretical advantages of controlled superheathave not been entirely realized in practice.The basic design of the single-furnace boilerhas been used increasingly. Except for experimentalboilers, no double-furnace boilers havebeen installed on combatant ships since WorldWar II. The newer single-furnace boilers operateat approximately 600 psi or at approximately1200 psi. Operating temperature at the superheateroutlet is quite commonly 950° F for the1200-psi boilers; this is 100° F higher than theoperating temperature of most double-furnaceboilers, and 200° F higher than the operatingtemperature of the older single-furnace boilers.One of the most noticeable differences betweenthe older and the newer single-furnaceboilers is the change in furnace design. Higherheat release rates are possible in the newerboilers. Although these newer single-furnaceboilers are not the type that we refer to as"pressurized-furnace" boilers, they do oftenuse a slightly higher combustion air pressurethan the older single-furnace boilers. The use ofhigher air pressure causes an increase in thevelocity of the combustion gases, and the increasedvelocity results in a higher rate of heattransfer to the generating tubes. Because of theincreased heat release rates, a newer singlefurnaceboiler is likely to have a water-cooledroof and water-cooled rear walls as well aswater-cooled side walls.

Chapter 10- PROPULSION BOILERSIn design details and in general configuration,the newer single-furnace boilers varysomewhat among themselves. Figure 10-22shows a 1200-psi boiler of the type installed onsome post World War II destroyers. Except forthe additional water-cooled surfaces, this boileris very much like the older single-furnaceboilers. In contrast, figure 10-23 shows a typeof single-furnace boiler that has been installedon some recent ships. The superheater tubesare installed vertically, rather than horizontally,between generating tubes and water screen tubes.Note, also, that there is a separate water screenheader for the water screen tubes; this featureis quite unusual in single-furnace boilers, thoughstandard for double-furnace boilers.New Types of Propulsion BoilersThe field of boiler design is by no meansstatic. Although one trend predominates— that ofusing higher pressures and temperatures—thereare almost innumerable ways in which the higherpressures and temperatures can be achieved.New types of boilers are constantly being developedand tp=^ed, and existing boiler designs arePERTINENT DATAOPERATING PRESSURE1200 PJICSTEAM TEMPERATURE950° PRATED STEAM OUTPUT133,000 LBS/HRTOTAL HEATING SURFACE 7590 SO PTFURNACE VOLUME 420 CU FTFigure 10-22.—Newer 1200-psi single-furnace boiler for post World War II destroyer.38.41255

PRINCIPLES OF NAVAL ENGINEERINGECONOMIZERSTEAM DRUMSUPERHEATERELEMENTSDOWNCOMERROOF, SIDE &REARWATERWALLTUBESCASINGBURNERSDESUPER-HEATERSADDLEWATER DRUMREFRACTORYREAR WALLHEADERSUPERHEATERHEADERSWATER SCREENHEADERSIDE WALLHEADERFigure 10-23.— Newer single-furnace boiler with vertical superheater.147.84subject to modification and improvement. Thenew types of boilers discussed here do not byany means exhaust the field of new designs;indeed, it must be emphasized that a wide diversityof design is still possible in this field.TOP-FIRED BOILERS.— A new boiler designwhich is at present being used on some auxiliaryships is the top-fired boiler. In this boiler, thefuel oil burners are located at the top of theboiler and are fired downward. The top-firedboiler utilizes certain new construction techniques,including welded walls. The boiler is ofthe natural circulation type, with a completelywater-cooled furnace. The only refractory materialthat is exposed to the gases of combustionis the refractory that is installed in cornersand in a small area around the burners. Thetop-fired boiler has an in-line generating tubebank and a vertical superheater. It is expectedthat the top-fired boiler will be much cleanerand thus require less maintenance than olderboilers of more conventional design.CONTROLLED CIRCULATION BOILERS,-ControUed (or forced) circulation boilers have256

Chapter 10- PROPULSION BOILERSbeen used for some time in stationary powerplants, in locomotives, and in some merchantships. Only a few controlled circulation boilershave been installed in the propulsion plants ofnaval ships, and of this few the majority weresubsequently removed and replaced by conventionalsingle-furnace boilers with acceleratednatural circulation. In theory, however, controlledcirculation has some very marked advantagesover natural circulation, and it isentirely possible that improved designs ofcontrolled circulation boilers may be developedfor future use in naval propulsion plants.In natural circulation boilers, circulationoccurs because the ascending mixture of waterand steam is lighter (less dense) than the descendingbody of relatively cool and steam-freewater. As boiler pressure increases, however,there is less difference between the density ofsteam and the density of water. At pressuresover 1000 psi, the density of steam differs solittle from the density of water that natural circulationis harder to achieve than it is at lowerpressures. At high pressures, controlled circulationboilers have a distinct advantage becausetheir circulation is controlled by pumps and isindependent of differences in density. Becausecontrolled circulation boilers can be designedwithout regard for differences in density, theycan be arranged ip practically any way that isrequired for a particular type of installation.Thus a greater flexibility of arrangement ispossible and the boilers may be designed forcompactness, savings in space and weight requirements,and maximum heat absorption.There are two main kinds of controlledcirculation boilers. One type is known as aonce-through or forced flow boiler; the othertype is usually called a controlled circulationor a forced recirculation boiler. In both types,external pumps are used to force the waterthrough the boiler circuits; the essential differencebetween the two kinds lies in the amountof water supplied to the boiler.In a once-through forced circulation boiler,all (or very nearly all) of the water pumped tothe boiler is converted to steam the first timethrough, without any recirculation. This type ofboiler has no steam drum, but has instead asmall separating chamber. Water is pumpedinto the economizer circuit and from there tothe generating circuit, the amount of flow beingcontrolled so as to allow practically all of thewater to "he converted into steam in the generatingcircuit. The very small amount of waterthat is not converted to steam in the generatingcircuit is separated from the steam in theseparating chamber. The water is dischargedfrom the separating chamber to the feed pumpsuction, if it is suitable for use; if it containssolid matter, it is discharged through the blowdownpipe. Meanwhile, the steam from theseparating chamber flows on through the superheatercircuit, where it is superheated beforeit enters the main steam line.Figure 10-24 shows the boiler circuits of acontrolled circulation (or forced recirculation)boiler. In this boiler, more water is pumpedthrough the circuits than is converted intosteam. The excess water is taken from thesteam drum and is pumped through the boileragain by means of a circulating pump.circuitsThis type of boiler has a conventional steamdrum which contains a feed pipe, steam separatorsand dryers, a desuperheater, and otherfittings. The boiler has an economizer, threegenerating circuits, and a superheater. Circulatingpumps, fitted as integral parts of theboiler, provide positive circulation to all steamgenerating surfaces.Both types of controlled circulation boilershave far smaller water capacity than do naturalcirculation boilers, and therefore have muchmore rapid response to changes in load. For thisreason, automatic controls are required onthese boilers to ensure rapid and sensitiveresponse to fuel and feed water requirements.PRESSURIZED-FURNACE BOILERS.-Aboiler recently developed for use in naval propulsionplants is variously known as a pressurized-furnaceboiler, a pressure-fired boiler ,a supercharged boiler , or a supercharged steamgenerating system .A pressurized-furnace boiler is shown schematicallyin figure 10-25 and in cutaway view infigure 10-26. As may be seen, the boiler isquite unlike other operational boiler types ingeneral configuration. The pressurized furnaceis more or less cylindrical in shape, with thelong axis of the cylinder running vertically. Theboiler drum is mounted horizontally, some distanceabove the pressurized furnace. The drumis connected to the steam and water elementsin the furnace by risers and downcomers, all ofwhich are external to the casing. Some boilersof this type are side-fired. Others (including theone shown) are top-fired; as may be seen in figures10-25 and 10-26, the burners are at the top257

PRINCIPLES OF NAVAL ENGINEERINGCIRCULATINGPUMPLEGEND1. ECONOMIZER INLET HEADER1. ECONOMIZER OUTLET HEADER3. SIDE WALL AND FLOOR CIRCUIT INLET HEADER4- SIDE WALL AND FLOOR CIRCUIT OUTLET HEADER5. PRIMARY EVAPORATOR AND REAR WALL CIRCUIT INLET HEADER7. LOWER SECONDARY EVAPORATOR CIRCUIT INLET HEADER8. UPPER SECONDARY EVAPORATOR CIRCUIT INLET HEADER9. SECONDARY EVAPORATOR OUTLET HEADER10. SUPERHEATER INLET HEADER11. SUPERHEATER OUTLET HEADEft6. PRIMARY EVAPORATOR AND REAR WALL CIRCUIT OUTLET HEADERFigure 10-24.— Schematic diagram of controlled circulation boiler.147.85of the pressurized furnace, firing downward intothe furnace.The burners, specially designed for thepressurized-furnace boiler, are quite unlike anywe have thus far considered. The burners aredesigned to burn distillate fuel rather than NavySpecial fuel oil. There are no air register doors.There are three burners per boiler, and eachburner includes a special type of straight mechanicalatomizer (not return-flow) which utilizesthree sprayer plates at the same time. Allthree burners are operated simultaneously, andall three sprayer plates remain in place in eachatomizer. The sprayer plates operate in sequenceto meet changing conditions of load. Thedesign of these burners allows an enormouslywide range of operation without cutting burnersin or out and without even changing sprayerplates.The generating tubes run vertically insidethe pressurized furnace. The superheater is anannular pancake arrangement inserted into thebottom of the pressure vessel. The superheateris designed to be removed without disturbing themain components of the boiler.The air compressor which supplies the combustionair under pressure is driven by a gasturbine. The air compressor and the gas turbinetogether are referred to as the supercharger .Part of the energy needed for driving the gasturbine is obtained from the combustion gasesleaving the boiler furnace. The combustion gasesexpand through the gas turbine, and some of theheat is converted into work. This is the same258

Chapter 10- PROPULSION BOILERSTOSTACKFEED WATERECONOMIZERFEED WATERCOMBUSTION AIRADDITIONALSOURCE OFPOWER FORAIR COMPRESSOR-TURBINECOMPRESSORBURNERSPRESSURE-TIGHTBOILER FURNACECOMBUSTION GASESGENERATINGELEMENTSTODE5UPERHEATERIN BOILER DRUMSUPERHEATED STEAM TO ENGINESSUPERHEATERELEMENTSFigure 10-25.— Schematic view of pressurized-furnace boiler.147.86kind of energy transformation that occurs in asteam turbine; the difference is that hot combustiongases, rather than steam, carry theenergy to the gas turbine. After the combustiongases leave the gas turbine, some of the remainingheat may be used to heat feed ^water as itflows through an economizer.There are no forced draft blowers in pressurized-furnaceboiler installations. The superchargertakes the place of the forced draftblowers, thus greatly increasing plant efficiency.The steam saved by the use of a superchargerinstead of forced draft blowers may amount to asmuch as 8 or 10 percent of boiler capacity.Altogether, a pressurized-furnace boiler isnot much more than half the size and half theweight of a conventional boiler of equal steamcapacity. A large part of this saving of space andweight occurs because the increased pressure^on the combustion gas side causes a very greatincrease in the rate of heat transfer to the waterin the tubes. Thus a smaller generating surfaceis required to generate the same amount ofsteam. Another cause of space and weight savingis that the general design of the pressurizedfurnaceboiler eliminates the need for much ofthe refractory material that is required in otherForced draft blowers for conventional boiler installationsfurnish air pressures ranging from to 10pslg. In a pressurized-furnace boiler, the air compressorsupplies combustion air at pressures rangingfrom 30 to 90 psig.259

PRINCIPLES OF NAVAL ENGINEERINGH ;--x«^

-Chapter 10- PROPULSION BOILERSA pressurized-furnace boiler may re-boilers.quire only about 2000 pounds of refractory, asagainst the 21,000 pounds or more usually requiredin a conventional boiler of equal capacity.Increased efficiency, a substantial savingin space and weight requirements, a substantialreduction in ship's force maintenance requirements,shorter boiler start-up time, and bettermaneuverability and control are the major advantagesof the pressurized-furnace boiler. Althoughsome operational and maintenance problemsdo exist with this boiler, it appears likelythat most of them can eventually be solved byincreased training of personnel, increased precisionin the erection of the boilers, and perhapscontinued refinements of design and construction.BOILER WATER REQUIREMENTSModern naval boilers cannot be operatedsafely and efficiently without careful control ofboiler water quality. If boiler water conditionsare not just precisely right, the high operatingpressures and temperatures of modern boilerswill lead to rapid deterioration of the boilermetal, with the possibility of serious casualtiesto boiler pressure parts.Although our ultimate concern is with thewater actually in the boiler, we cannot considerboiler water alone. We must also consider thewater in the rest of the system, since we aredealing with a closed cycle in which water isheated, steam is generated, steam is condensed,and water is returned to the boiler. Because thecycle is continuous and closed, the same waterremains in the system except for the water thatis lost by boiler blowdown^ and the very smallamount of water that escapes, either as steamor as water, and is replaced by makeup feed.There are two kinds of boiler blowdown: surfaceblowdown and bottom blowdown. Surface blowdown isused to remove foam and other light contaminantsfrom the surface of the water in the steam drum.Bottom blowdown is used to remove sludge and othermaterial that tends to settle in the lower parts of theboiler. Both surface blowdown and bottom blowdownmay be used to remove a portion of the boiler waterso that it can be replaced with purer makeup feed,thereby lowering the chloride content of the boilerwater. Surface blows may be given while the boiler issteaming; bottom blows must not be given until sometime after the boiler has been secured. The valves andpiping used for making surface and bottom blows arediscussed in chapter 11 of this text.Although we must remember the continuousor cyclical nature of the shipboard steam plant,we must also distinguish between the water atdifferent points in the system. This distinctionis necessary because different standards areprescribed for the water at different points. Toidentify the water at various points in the steamwater cycle, the following terms are used:Distillate or sea water distillate is the freshwater that is discharged from the ship's distillingplants. This water is stored in fresh water orfeed water tanks. All water in the steam - watercycle begins originally as distillate.Makeup feed is distillate used as replacementfor any water that is lost or removed from theclosed steam - water cycle.Condensate is the water that results from thecondensation of steam in the main and auxiliarycondensers. This water is called condensate untilit reaches the deaerating feed tank.Boiler feed or feed water is the water in thesystem between the deaerating feed tank and theboiler.Deaerated feed water is feed water that haspassed through deaerating feed tank and has hadthe dissolved or entrained oxygen removed fromit.Boiler water is the water actually containedwithin a boiler at any given moment.Sea water , the source of practically all freshwater used aboard ship, contains about 35,000parts per million (ppm) of sea salts. This isequivalent to roughly 70 pounds of sea salts perton of water. When sea water is evaporated andthe vapor is condensed in the distilling plant, theresulting distillate contains about 1.75 ppm ofsea salts, or roughly 70 pounds per 20,000 tons.In other words, distillate is actually diluted seawater— sea water that is diluted to about 1/20,000of its original concentration. It is not "purewater," In considering water problems andwater treatment, it is essential to remember thatthe basic impurity of sea water distillate wouldmake water treatment necessary even if no otherimpurities entered the water from other sources.The salts that are present in sea water— and,therefore, to a lesser extent in distillate— arechiefly compounds of sodium, calcium, and magnesium.Although makeup feed enters the tanks asdistillate, the makeup feed usually contains aslightly higher proportion of impurities than thedistillate. The difference is accounted for byslight seepage or other contamination of the261

PRINCIPLES OF NAVAL ENGINEERINGwater after it has remained in the tanks forsome time.Just as distillate is diluted sea water, sosteam condensate is basically a diluted form ofboiler water. The amount of solid matter carriedover with the steam varies considerably,depending upon the design of the boiler, tliecondition of the boiler, the nature of the watertreatment, the manner in which the boiler isoperated, and other factors. In general, condensatecontains from 1.7 to 3.5 ppm of solidmatter, or roughly 70 pounds per 20,000 to10,000 tons. Condensate may pick up additionalcontamination in various ways. Salt water leaksin the condenser increase the amount of seasalts present in the condensate. Oil leaks inthe fuel oil heaters may contaminate the condensate.Corrosion products from steam andcondensate lines may also be present in condensate.Under ideal conditions, condensateshould be no more contaminated than sea waterdistillate; under many actual conditions, it ismore contaminated.The solid content of the water (Boiler feedwater) in the system between the deaeratingfeed tank and the boiler is essentially the sameas the solid content of the condensate. The maindifference between condensate and deaeratedboiler feed is that most of the dissolved gasesare removed from the water in the deaeratingfeed tank.Practically all of the impurities that arepresent in feed water, including those originallypresent in the sea water distillate and thosethat are picked up later, will eventually findtheir way to the boiler. As steam is generatedand leaves the boiler, the concentration of impuritiesin the remaining boiler water becomesgreater and greater. In other words, the boilerand the condenser together act as a sort ofdistilling plant, redistilling the water receivedfrom the ship's evaporators. In consequence,the boiler water would become more and morecontaminated if steps were not taken to dealwith the increasing contamination.As an example, suppose that a boiler holds10,000 pounds of water at steaming level, andsuppose that steam is being generated at therate of 50,000 pounds per hour. After an hourof operation there would be approximately fivetimes as much solid matter in the boiler wateras there was in the entering feed water. Now ifwe continued to steam this boiler for another2000 to 4000 hours without using blowdownand without using any kind of boiler watertreatment, the boiler water would contain justabout the same concentration of sea salts as theoriginal sea water from which the distillate wasmade. In addition, the boiler water would containincreasingly large quantities of corrosionproducts and other foreign matter picked up inthe steam and condensate systems.If we continued to steam the boiler with thewater in this condition, the boiler would deterioraterapidly. To prevent such deterioration,it is necessary to do the following things:1. Maintain the incoming feed water at thehighest possible level of purity and as free aspossible of dissolved oxygen.2. Use chemical treatment of the boilerwater to counteract the effects of some of theimpurities that are bound to be present.3. Use blowdown at regular intervals to removesome of the more heavily contaminatedwater so that it may be replaced by purer feedwater.Although there aremany sources of boilerwater contamination, the contaminating materialstend to produce three main problems whenthey are concentrated or accumulated in theboiler water. Therefore, boiler water treatmentis aimed at controlling the three problems of(1) waterside deposits, (2) waterside corrosion,and (3) carryover.Waterside deposits interfere with heat transferand thus cause overheating of the boilermetal. The general manner in which a watersidedeposit causes overheating of a boiler tubeis shown in figure 10-27. In a boiler operatingat 600 psi, the temperature inside a generatingtube may be approximately 500° F and the temperatureof the outside of the tube may be approximately100° F higher.'' Where a watersidedeposit exists, however, the tube cannot transferthe heat as rapidly as it receives it. Asshown in figure 10-27, the inside of the tubehas reached a temperature of 800 ° F at the pointwhere the waterside deposit is thickest. Thetube metal is overheated to such an extent thatit becomes plastic and blows out into a bubbleor blister under boiler pressure.Waterside deposits that must be guardedagainst include sludge, oil, scale, corrosionThe temperatures used in this example do not applyto all situations in which a boiler tube is overheated.The exact temperatures of the inside andoutsideof thetube would depend upon the operating pressure of theboiler, the location of the tube in the boiler, the natureof the deposit, and various other factors.262

FChapter 10- PROPULSION BOILERS600 PSl600«F--500''FWATERSIDEDEPOSIT-500°38.131Figure 10-27. — Effect of waterside deposit onboiler tube.deposits, and products formed as the result ofchemical reactions of the tube metal.The term " waterside corrosion " is used toinclude both localized pitting and general corrosion.Most waterside corrosion is electrochemicalin nature. There are always someslight variations (both chemical and physical)in the surface of any boiler metal. These smallchemical and physical variations in the metalsurface cause slight differences in electricalpotential between one area of a tube and anotherarea. Some areas are anodes (positive terminals)and others are cathodes (negative terminals).Iron from the boiler tube tends to go intosolution more rapidly at the anode areas thanat other points on the boiler tube. Electrolyticaction cannot be completely prevented in anyboiler, but it can be kept to a minimum bymaintaining the boiler water at the proper alkalinityand by keeping the dissolved oxygen contentof the boiler water as low as possible.The presence of dissolved oxygen in theboiler water contributes greatly to the type ofcorrosion in which electrolytic action makespits or holes of the type shown in figure 10-28.A pit of this type actually indicates an anodicarea in which iron from the boiler tube hasgone into solution in the boiler water.General corrosion occurs when conditionsfavor the formation of many small anodes and38.138Figure 10-28.— Localized pit in boiler tubecaused by dissolved oxygen in theboiler water.cathodes on the surface of the boiler metal. Ascorrosion proceeds, the anodes and cathodesconstantly change location. Therefore, there isa general loss of metal over the entire surface.General corrosion may occur if the chloridecontent of the boiler water is too high or if thealkalinity is either too low or too high.The third major problem that results fromboiler water contamination is carryover . Undersome circumstances, very small particles ofmoisture (almost like a fine mist) are carriedover with the steam. Under other circumstances,large gulps or slugs of water are carried over.The term priming is generally used to describethe carryover of large quantities of water. Bothkinds of carryover are dangerous and both cancause severe damage to superheaters, steamlines, turbines, and valves. Whatever moistureor water is carried over with the steam bringswith it the solid matter that is dissolved orsuspended in the water. This solid matter tendsto be deposited on turbine blades and in superheatertubes and valves. Figure 10-29 shows asuperheater tube in which solid matter has beendeposited as a result of carryover. Priming, or263

PRINCIPLES OF NAVAL ENGINEERINGFigure 10-29. — Evidence of carryover insuperheater tube.38.140the carryover of large slugs of water, is particularlydangerous because it can do such severedamage to machinery. For example, priming canactually rip turbine blades from their wheels.One cause of carryover is foaming of theboiler water. Foaming occurs when the watercontains too much dissolved or suspended solidmatter. The solids tend to stabilize the bubblesand cause them to pile up instead of bursting.If a great deal of solid matter is present in theboiler water, a considerable amount of foamwill pile up. Under these conditions, carryoveris almost sure to occur.In order to counteract the effects of the impuritiesin boiler water, it is necessary to havea precise knowledge of the actual condition ofthe water. This knowledge is obtained by frequenttests of the boiler water and of the feedwater. Boiler water tests include chloride tests,hardness tests, alkalinity tests, pH tests, phosphatetests, and electrical conductivity testswhich indicate the dissolved solid content of theboiler water. 8 Feed water is tested routinelyfor chloride, hardness, and dissolved oxygen;alkalinity, pH, phosphate, and electrical conductivitytests are not normally made on feed water.The frequency of boiler water and feed watertests is specified by the Naval Ship SystemsCommand. Also, the allowable limits of contaminationare specified by the Naval Ship SystemsCommand. In general, the requirementsfor purity of boiler water become more stringentwith increasing boiler pressure.Water tests aboard ship are made by the oiland water king (usually a Boilerman), althoughcertain aspects of the preparation and handlingof the chemicals may require the supervisionof an officer. The tests require some knowledgeof chemistry and a high degree of precision inpreparing, using, and measuring the chemicals.Therefore, only personnel holding a currentcertification resulting from successful completionof a NavShips boiler water/feed water testand treatment training course may test andtreat boiler water and feed water on propulsionboilers.Some of the water tests made aboard shipgive a direct indication of just what contaminatingsubstance is present, and in just what amountit is present. In other cases, it is more importantto know what effects the contaminatingsubstances have upon the water than it is toknow what the substances are or exactly howmuch of each is present. Therefore, some watertests are designed to measure properties thewater acquires because of the presence of variousimpurities.The term chloride content really refers tothe concentration of the chloride ion, ratherthan to the concentration of any one sea salt.Note, however, that no one ship makes all of thesetests of boiler water. The types of boiler water testsrequired on any particular ship depend upon the methodof boiler water treatment authorized for that ship.264

Chapter 10- PROPULSION BOILERSBecause the concentration of chloride ions isrelatively constant in sea water, the chloridecontent is used as a measure of the amount ofsolid matter that is derived through sea watercontamination. The results of the chloride testare used as one indication of the need for blowdown.Chloride content is expressed in equivalentsper million (emp).^Hardness is a property that water acquiresbecause of the presence of certain dissolvedsalts. Water in which soap does not readilyform a lather is said to be hard.Alkalinity is a property that the water acquiresbecause of the presence of certain impurities.On ships that make alkalinity tests,the results are expressed in epm.Some ships are required to determine the pHvalue , rather than the alkalinity, of the boilerwater. The pH unit does not measure alkalinitydirectly; however, it is related to alkalinity insuch a way that a pH number gives an indicationof the acidity or alkalinity of the water. ThepH scale of numbers runs from to 14. Onthis scale, pH 7 is the neutral point. Solutionshaving pH values above 7 are define das alkalinesolutions. Solutions having pH values below 7 aredefined as acid solutions.Boiler water that is treated with phosphatesmust be tested for phosphate content . Boilerwater that is treated with standard Navy boilercompound is not tested for phosphates. Phosphatecontent is expressed in parts per million(ppm). When the phosphate content of boilerwater is maintained within the specified limits,the hardness of the water shovild be zero. Therefore,hardness tests are not required for boilerwater when phosphate water treatment is used.The test for chloride content indicates somethingabout the amount of solid matter that ispresent in the boiler water, but it indicates onlythe solid matter that is there because of seawater contamination. It does not indicate anythingabout other solid matter that may be dissolvedin the boiler water. A more accurateindication of the total amount of dissolved solidsEquivalents per million can be defined as the numberof equivalent parts of a substance per million parts ofsome other substance. The word "equivalent" hererefers to the chemical equivalent weight of a substance.For example, if a substance has a chemical equivalentweight of 35.5, a solution containing 35.5 parts permillion is described as having a concentration of 1epm.can be obtained by measuring the electricalconductivity of the boiler water, since this isrelated to the total dissolved solid content . Allships are now furnished with special electricalconductivity meters for measuring the conductivityof the boiler water. The total dissolvedsolid content is expressed in micromhos, a unitof electrical conductivity.As a regular routine, the test for dissolvedoxygen is made only on feed water, althoughoccasional testing of water in other parts ofthe system is recommended. A chemical testfor dissolved oxygen is made aboard ship. Sincethis test cannot detect dissolved oxygen in concentrationsof less than 0.02 ppm, more sensitivelaboratory tests are sometimes made as acheck on the operation of the deaerating feedtanks.When tests of the boiler water show that thewater is not within the prescribed limits, chemicaltreatment and blowdown are instituted.Several methods of chemical treatment are nowauthorized. Each method is designed to completelyeliminate hardness and to maintain thealkalinity (or the pH value) within the prescribedlimits. The method of boiler water treatmentspecified for each ship is the method that willbest perform these two functions and, at thesame time, take account of the total concentrationof solids that can be tolerated in theparticular type of boiler. The type of watertreatment authorized for any particular ship isspecified by the Naval Ship Systems Command;it is not a matter of choice by ship's personnel.Chemical treatment of the boiler water increases,rather than decreases, the need forblowdown. The chemical treatment counteractsthe effects of many of the impurities in theboiler water, but at the same time it increasesthe total amount of solid matter in the boilerwater and thus increases the need for blowdown.Each steam boiler must be given a surface blowat least once a day, and more often if the watertests indicate the need. Bottom blows are givenat least once a week, usually about an hour afterthe boiler has been secured. Bottom blows mustnot be given while a boiler is steaming. Specialinstructions for boiler blowdown are issued tocertain categories of ships.COMBUSTION REQUIREMENTSCertain requirements must be met beforecombustion can occur in the boiler furnace. Thefuel must be heated to the temperature that will265

PRINCIPLES OF NAVAL ENGINEERINGgive it the proper viscosity for atomization. Itshould be NOTED, however, that with the conversionto the new distillate fuel (NSDF), thefuel will not need to be heated as the viscosityis much lower than the fuel oil (NSFO) now beingused. The fuel must be forced into the furnaceunder pressure through the atomizers whichdivide the fuel into very fine particles. Meanwhile,combustion air must be forced into thefurnace and admitted in such a way that the airwill mix thoroughly with the finely divided fuel.And finally, it is necessary to supply enoughheat so that the fuel will ignite and continue toburn.Combustion is a chemical process whichresults in the rapid release of energy in theform of heat and light. When a fuel burns, thechemical reactions between the combustibleelements in the fuel and the oxygen in the airresult in new compounds. The combustible componentsof fuel are mainly carbon and hydrogen,which are present largely in the form of hydrocarbons.Sulfur, oxygen, nitrogen, and a smallamount of moisture are also present in fuel.In almost all burning processes, the principalreactions are the combination of the carbonand the hydrogen in the fuel with the oxygenin the air to form carbon dioxide and a relativelysmall amount of water vapor. In the absenceof sufficient air to form carbon dioxide, carbonmonoxide will be formed. A reaction of lesserimportance is the combination of sulfur andoxygen to form sulfur dioxide.Atmospheric air is the source of oxygen forthe combustion reactions occurring in a boilerfurnace. Air is a mixture of oxygen, nitrogen,and small amounts of carbon dioxide, watervapor, and inert gases. The approximate compositionof air, by weight and by volume, is asfollows:ElementOxygenNitrogen, etc.Weight(Percent)23,1576.85Volume(Percent)20.9179.09At the proper temperature, the oxygen inthe air combines chemically with the combustiblesubstances in the fuel. The nitrogen,which is 76.85 percent by weight of all air enteringthe furnace, serves no useful purpose incombustion but is rather a direct source of heatloss, since it absorbs heat in passing throughthe furnance and carries off a considerableamount of heat as it goes out the stack.When a combustion reaction occurs, a definiteamount of heat is liberated. The totalamount of heat released by the combustion of afuel is the sum of the heat released by eachelement in the fuel. The amount of heat liberatedin the burning of each of the principal elementsin fuel oil is as follows:Chem- Heat ReleasedElement ical By CombustionSymbol (BTUperlb)Hydrogen (to water). .Carbon (to carbonmonoxide)Carbon (to carbondioxide)Sulfur (to sulfurdioxide)H^CCS62,0004,44014,5404,050Notice that much more heat is liberated whencarbon is burned to carbon dioxide than when itis burned to carbon monoxide, the differencebeing 10,100 Btu per pound. In burning to carbonmonoxide, the carbon is not completelyoxidized; in burning to carbon dioxide, the carboncombines with all the oxygen possible, andthus oxidation is complete.Thus far in this discussion, we have assumedthat the oxygen necessary for combustion waspresent in the exact amount required for thecomplete combustion of all the combustible elementsin the fuel. However, it is not a simplematter to introduce just exactly the requiredamount of oxygen— no more, no less— into theboiler furnace.Since atmospheric air is the source of oxygenfor the combustion process that occurs in theboiler furnace, let us first calculate the amount ofair that would be needed to furnish 1 pound ofoxygen. By weight, the composition of air is23.15 percent oxygen and 76.85 percent nitrogen(disregarding the very small quantities of othergases present in air). To supply 1 pound of oxygenfor combustion, therefore, it is necessary tosupply 1/0.2315 or 4.32 pounds of air.Since nitrogen constitutes 76.85 percent of theair (by weight), the amount of nitrogen in this4.32 pounds of air will be 0.7685 x 4.32 or 3.32pounds. As mentioned before, the nitrogen serves266

Chapter 10- PROPULSION BOILERSno useful purpose in combustion and is a directsource of heat loss.Calculations will show that approximately14 pounds of air will furnish the oxygen theoreticallyrequired for the complete combustionof 1 pound of fuel. In actual practice, of course,the amount of air necessary to ensure completecombustion must be somewhat in excess of thattheoretically required. About 10 to 15 percentexcess air is usually sufficient to ensure propercombustion. Too much excess air serves nouseful purpose, but merely absorbs and carriesoff heat.When fuel is burned in the boiler furnace,the difference between the HEAT INPUT and theHEAT ABSORBED represents the HEAT LOSS.Heat losses may be unavoidable, avoidable, or—in some cases— avoidable only to a limited extent.Most heat losses may be accounted for,but some losses cannot normally be accountedfor.All fuel contains a small amount of moisturewhich must be evaporated and superheatedto the furnace temperature. Since the expenditureof heat for this purpose constitutes a heatloss in terms of boiler efficiency, every precautionshould be taken to prevent contaminationof the fuel oil with water.All fuel contains some hydrogen which, whencombined with oxygen by the process of combustion,forms water vapor. This water vapormust be evaporated and superheated, and in bothprocesses it absorbs heat. Consequently, althoughthe heat of combustion of hydrogen isvery great, a small heat loss occurs becausethe water vapor formed as a result of the combustionof hydrogen must be evaporated andsuperheated.Since atmospheric air is the source of theoxygen utilized for combustion in the boilerfurnace, there is bound to be some moisture inthe combustion air. This moisture must beevaporated and superheated, and therefore constitutesa heat loss.The heat loss due to heat being carried awayby combustion gases is the greatest of all theheat losses that occur in a boiler. Althoughmuch of this heat loss is unavoidable, somemay be prevented by keeping all heat-transfersurfaces clean and by using no more excess airthan is actually required for combustion.Another heat loss occurs because of incompletecombustion of the fuel. When the carbonin the fuel is burned to carbon monoxide, insteadof carbon dioxide, there is a tremendous heatloss of 10,100 Btu per pound. This should beconsidered an avoidable loss, since the admissionof a sufficient amount of excess air willensure complete combustion.Heat losses that cannot be measured orthat are impracticable to measure are (1) lossesdue to unburned hydrocarbons, gaseous or solid;(2) losses due to radiation; and (3) other lossesnot normally accounted for.FIREROOM OPERATIONSAlthough a complete discussion of fireroomoperations is beyond the scope of this text,some understandingof the major factors involvedin boiler operation may be useful.Basically, the fireroom force must controlthree inputs—feed water, fuel, and combustionair— in order to provide one output, steam. Understeady steaming conditions, when steam demandsare relatively constant for long periods of time,there is no great difficulty about providing auniform flow of steam to the propulsion turbines.But one of the special requirements of navalships is that they must be able to maneuver andto change speed quickly, and this requirementimposes upon the fireroom force the responsibilityfor making very rapid increases and decreasesin the amount of steam furnished to theengineroom. Under conditions of rapid change,boiler operation is a teamwork job that requiresgreat skill and alertness and smooth coordinationof efforts by several men.For manual operationof the boilers, a normalfireroom watch consists of one petty officer incharge of the watch; one checkman for eachoperating boiler; one burnerman for each operatingboiler front; one blowerman for eachoperating boiler; and one or more men to actas messengers and to check the operation ofthe auxiliary machinery. When automatic boilercontrols are installed, boilers may be operatedwith fewer men on watch when the controls arebeing used.When a boiler is being operated manually,the checkman controls the water level in theboiler by manual operation of the feed stop andcheck valves. The checkman stands at the upperlevel, near the feed stop and check valves, andnear the boiler gage glass. The checkman admitswater to the boiler as necessary to maintain thewater at or very near the designed water level.The check watch requires the utmost vigilanceand reliability; if any one job in the fireroom267

PRINCIPLES OF NAVAL ENGINEERINGcan be said to be more important than any other,the checkman's job is the one.One of the greatest difficulties in maintainingthe water level arises from the fact that theboiler water swells and shrinks as the firingrate is changed. As the firing rate is increased,there is an increase in the volume of the boilerwater. This increase, which is known as swell,occurs because there is an increase in the numberand size of the steam bubbles in the water.As the firing rate is decreased, there is a decreasein the volume of the water. This decrease,which is known as shrink, occurs becausethere are fewer steam bubbles and theyare of smaller size. Thus, for any given weightof boiler water, the volume varies with the rateof combustion.The problem of swell and shrink becomeseven more complex when we remember that theevaporation rate also increases as the firingrate increases and decreases as the firing ratedecreases. When the firing rate is increased,therefore, the checkman must remember tofeed more water to the boiler, even though thewater level has already risen momentarily becauseof swell. On the other hand, the checkmanmust remember to feed less water to the boilerwhen the firing rate is decreased, even thoughthe water level has already dropped. Becausethese actions may appear to be contrary tocommon sense to a person who does not understandthe concept of swell and shrink, a gooddeal of training is usually required before aman can be considered qualified to stand acheck watch.The control of combustion involves the controlof fuel and the control of combustion air.There are three ways in which the firing ratemay be increased or decreased in order to meetchanges in steam demand: (1) by increasing ordecreasing the fuel pressure, (2) by increasingor decreasing the number of burners in use, and(3) by changing the size of the sprayer plates inthe atomizer assemblies. With every change,the amount of combustion air supplied to theboiler must also be changed in order to maintainthe proper relationship between fuel and combustionair. The burnerman and the blowermanmust therefore work very closely together inorder to provide efficient combustion in theboiler furnace.The burnerman cuts burners in and out andadjusts the oil pressure as necessary to keepthe steam pressure at the required value. Theburnerman is guided by the steam drum pressuregage. Also, he watches the annunciator whichshows the signals going from the bridge to theengineroom, and in this way he can tell whatsteam demands are going to be made.On a double -furnace boiler, there are twoburnermen— one for the saturated side and onefor the superheater side. The burnerman on thesuperheater side cuts burners in and out andadjusts fuel pressure to keep the superheateroutlet temperature at the required value. Theburnerman on the superheater side is guidedby the distant-reading thermometer which indicatesthe temperature of the steam at the superheateroutlet. In addition, he must keep a closecheck on the actions of the saturated-sideburnerman so that he will always know howmany burners are in use on the saturated side.When two boilers are furnishing steam tothe same engine, the burnermen of both boilersmust work together to see that the load isequally divided between the two boilers.The blowerman is responsible for operatingthe forced draft blowers that supply combustionair to the boiler. Although the air pressure inthe double casings is affected by the number ofregisters in use and by the extent to which eachregister is open, it is chiefly determined by themanner in which the forced draft blowers areoperated. The opening, setting, or adjusting ofthe air registers is the burnerman's job; thecontrol of the forced draft blowers is the blowerman'sjob. As may be apparent, the burnermanand the blowerman must each know what theother man is doing at all times. The blowermanmust always increase the air pressure beforethe burnerman increases the rate of combustion,and the burnerman must always decreasethe rate of combustion before the blowermandecreases the air pressure.If a boiler is not being supplied with sufficientair for combustion, everyone in the fireroomwill know about it immediately. The boilerwill begin to pant and vibrate, and the fireroomforce will receive complaints of "heavy blacksmoke" from the bridge. If the boiler is beingsupplied with too much air—that is, more excessair than is required for efficient combustion—the fireroom force may or may not know aboutit immediately. White smoke coming from thesmokepipe is always an indication of largeamounts of excess air. However, a perfectlyclear smokepipe may be deceiving; itmay meanthat the boiler is operating with only a smallamount of excess air, but it may also mean thatas much as 300 percent excess air is causing268

Chapter 10- PROPULSION BOILERSenormous heat losses. The blowerman mustlearn by experience how much air pressureshould be shown on the air pressure gage forall the various combinations of different numbersof burners, different sizes of sprayerplates, and different fuel pressures.The number of men assigned to operate thefireroom auxiliary machinery varies from oneship to another, depending upon the size of theship and the number of men available. Someships may have two or more men assigned tothis duty; on other ships, the work may be doneby the petty officer in charge of the watch orby the messenger. The burnerman and theblowerman may also take care of some of theauxiliaries. The checkman must never be givenany duties other than his primary ones of watchingand maintaining the water level.All fireroom operations are supervised andcoordinated by the petty officer in charge of thewatch. The petty officer in charge of the watchsupervises all lighting off, operating, and securingprocedures. He keeps the engineroomand the engineering officer of the watch informedof operating conditions when necessary.He must be constantly alert to the slightestindication of trouble and must be constantlyprepared to deal with any casualty that mayoccur. The petty officer in charge of the watchis responsible for making sure that all safetyprecautions are being observed and that unsafeoperating conditions are not allowed to exist.FIREROOM EFFICIENCYThe military value of a naval vessel dependsin large measure upon her cruising radius,which, in turn, depends upon the efficiency withwhich the engineering plant is operated. Perhapsthe largest single factor in determining theefficiency of the engineering plant is the efficiencywith which the boilers are operated.Greater savings in fuel, with consequent increasein steaming radius of the ship, may often bemade in the fireroom than in all the rest of theengineering plant put together.The capacity of a boiler is defined as themaximum rate at which the boiler can generatesteam. The rate of steam generation is usuallyexpressed in terms of pounds of water evaporatedper hour. You should know something ofthe limitations upon boiler capacity, the significanceof full-power and overload ratings,and the procedure for checking on boiler loads.The capacity of any boiler is limited bythree factors that have to do both with the designof the boiler and with its operation. These limitations,which are known as end points , are(1) the end point for combustion, (2) the endpoint for moisture carryover , and (3) the endpoint for water circulation.Boilers are so designed that the end pointfor combustion should occur at a lower rate ofsteam generation than the end point for moisturecarryover, and the end point for moisturecarryover at a lower rate than the end point forwater circulation. Since the end point for combustionoccurs first, it is the only end point thatis likely to be reached in a properly designedand properly operated boiler. However, it shouldbe understood that it is quite possible to reachthe end points for moisture carryover and watercirculation before reaching the end point forcombustion, by using larger sprayer plates thanthose recommended by the manufacturer or bythe Bureau of Ships. In such a case, the boilermight suffer great damage before the end pointfor combustion was reached.End Point for CombustionThe process of burning fuel in a boilerfurnace involves forcing the fuel into the furnaceat the proper viscosity through atomizers whichbreak up the oil into a foglike spray, and forcingair into the furnace in such a way that it mixesthoroughly with the oil spray. The amount of fuelthat can be burned is limited primarily by theactual capacity of the equipment that suppliesthe fuel (including the capacity of the sprayerplates), by the amount of air that can be forcedinto the furnace, and by the ability of the burnerapparatus to mix this air with the fuel. Thevolume and shape of the furnace are also limitingfactors.The end point for combustion for a boiler isreached when the capacity of the sprayer plates,at the designed pressure for the system, isreached or when the maximum amount of airthat can be forced into the furnace is insufficientfor complete combustion of the fuel. If the endpoint for combustion is actually reached becauseof insufficient air, the smoke in the uptakes willbe black because it will contain particles ofunburned fuel. However, this condition should berare, since the end point for combustion isartificially limited by sprayer plate capacitywhen the fuel is supplied at the burner manifoldat designed operating pressure. As noted before,269

PRINCIPLES OF NAVAL ENGINEERINGthis artificial limitation upon combustion in theboiler furnace is the factor that would cause theend point for combustion to occur before eitherof the other two end points.End Point for MoistureCarryoverThe rate of steam generation should neverbe increased to the point at which an excessiveamount of moisture is carried over in the steam.In general, naval specifications limit the allowablemoisture content of steam leaving thesaturated steam outlet to 1/4 of 1 percent.As you know, excessive carryover can beextremely damaging to piping, valves, and turbines,as well as to the superheater of theboiler. It is not only the moisture itself thatis damaging but also the insoluble matter thatmay be carried in the moisture. This insolublematter can form scale on superheater tubes,turbine blades, piping and fittings; in somecases, it may be sufficient to cause unbalanceof rotating parts.As the evaporation rate is increased, theamount of moisture carryover tends to increasealso, due to the increased release of steambubbles. Because modern naval boilers aredesigned for high evaporation rates, steamseparators and various baffle arrangementsare used in the steam drum to separate moisturefrom the steam.End Point for WaterCirculationIn natural circulation boilers, circulation isdependent upon the difference between the densityof the ascending mixture of hot water and steamand the density of the descending body of relativelycool water. As the firing rate is increased,the amount of heat transferred to the tubes isalso increased. A greater number of tubes carrythe upward flow of water and steam, and fewertubes are left for the downward flow of water.Without downcomers to ensure a downward flowof water, a point would eventually be reachedat which the downward flow would be insufficientto balance the upward flow of water and steam,and some tubes would become overheated andburn out. This condition would determine the endpoint for water circulation.The use of downcomers ensures that theend point for water circulation will not be reachedmerely because the firing rate is increased.Other factors that influence the circulation in anatural circulation boiler are the location ofthe burners, the arrangement of baffles in thetube banks, and the arrangement of tubes in thetube banks.Full-power and overload ratings for theboilers in each ship are specified in the manufacturer'stechnical manual. The total quantityof steam required to develop contract shafthorsepower of the ship, divided by the numberof boilers installed, gives boiler full-powercapacity. Boiler overload capacity is usually120 percent of boiler full-power capacity. Forsome boilers, a specific assigned maximum firingrate is designated.A boiler should not be forced beyond fullpowercapacity—that is, it should not be steamedat a rate greater than that required to obtainfull-power speed with all the ship's boilers inuse. A boiler should never be steamed beyondits overload capacity, or fired beyond the assignedmaximum firing rate, except in direemergency.Checking Boiler EfficiencyIn order to check on boiler efficiency it isnecessary to compare the amount of fuel actuallyburned in a boiler with the amount thatshould be burned. This check is usually madeduring economy runs and during full-powerruns. As a rule, 4 hours are allowed for eachrun. During the run, fuel consumption is measuredat intervals of precisely 1 hour. Thismeasure, when corrected for meter error andverified by tank soundings, gives the amount offuel that is actually used.The amount of fuel that should be used underspecified conditions may be taken from tablesor curves supplied in the manufacturer's technicalmanual for the boilers or from the ship'sfuel performance tables. Since these two sourcesgive different figures for the amount of oil thatshould be burned under various conditions, it isnecessary to make a clear distinction betweenthem. The differences, incidentally, arise fromthe fact that there are two basic approaches tothe problem of checking on fuel consumption.When you are concerned only with boiler performance,you use the tables and charts from themanufacturer's technical manual; when you areconcerned with plant performance with respectto fuel consumption, you use the ship's fuelperformance tables.270

Chapter 10- PROPULSION BOILERSBOILER CASUALTY CONTROLThere are many fireroom casualties whichrequire a knowledge of preventive measuresand corrective measures. Some are major, someare minor; but all can be serious. In the eventof a casualty, the principal doctrine to be impressedupon operating personnel is the preventionof additional or major casualties. Undernormal operating conditions, the safety of personneland machinery should be given firstconsideration. Therefore, it is necessary toknow instantly and accurately what to do foreach casualty. Stopping to find out exactly whatmust be done for each casualty could mean lossof life, extensive damage to machinery, and evencomplete failure of the engineering plant. Afundamental principle of engineering casualtycontrol is split-plant operation. The purpose ofsplit-plant design is to minimize the damagethat might result from any one casualty whichaffects propulsion power, steering, and electricalpower generation.Although speed in controlling a casualty isessential, action should never be taken withoutaccurate information; otherwise the casualtymay be mishandled, and further damage to themachinery may result. Cross-connecting andintact engineering plant with a partly damagedone must be delayed until it is certain that suchaction will not jeopardize the intact one.Cross-connecting valves are provided forthe main and auxiliary steam systems and otherengineering systems so that any boiler or groupof boilers, either forward or aft, may supplysteam to each engineroom. These systems arediscussed in chapter 9 of this manual showingthe construction of the split-plant design onsome types of ships.The discussion of fireroom casualties in thischapter is intended to give you an overall viewof how casualties should be handled. For furtherinformation on casualty control, study the NavalShips Technical Manual , Chapter 9880, and thecasualty control instructions issued for eachtype of ship.Most of the casualties discussed in thischapter are usually treated in a step-by-stepprocedure, but it is beyond the scope of thischapter to give each step in handling eachcasualty. In the step-by-step procedure onestep is performed, then another, then another,and so forth. In handling actual casualties,however, this step-by-step approach will probablyhave to be modified. Different circumstancesmay require a different sequence of steps forcontrol of a casualty. Also, in handling realcasualties several steps will have to be performedat the same time. For example, maincontrol must be notified of any casualty to theboilers or to associated equipment. If "Notifymain control" is listed as the third step incontrolling a particular casualty, does this meanthat the main control is not notified until thefirst two steps have been completed? Not atall. Notifying main control is a step that canusually be taken at the same time other stepsare being taken. It is probably helpful to learnthe steps for controlling casualties in the orderin which they are given; but do not overlookthe fact that the steps may have to be performedsimultaneously.FEED WATER CASUALTIESCasualties in the control of water level includelow water, high water, feed pump casualties,loss of feed suction, and low feed pressure.These casualties are some of the most seriousones.Low water is one of the most serious ofall fireroom casualties. Low water may becaused by failure of the feed pumps, rupturesin the feed discharge line, defective checkvalves, low water in the feed tank, or otherdefects.However, the most frequent cause of lowwater is inattention on the part of the checkmanand the PO in charge of the watch, or the diversionof their attention to other duties. Thecheckman's sole responsibility is to keep thewater in the boiler at a proper level.Low water is extremely damaging to theboiler and may endanger the lives of fireroompersonnel. When the furnace is hot and thereis insufficient water to absorbthe heat, the heatingsurfaces are likely to be distorted, thebrickwork damaged, and the boiler casing warpedby the excessive heat. In addition, serious steamand water leaks may occur as a result of lowwater.Disappearance of the water level from thewater gage glasses must be treated as a casualtyrequiring the immediate securing of the boiler!It should be noted that when the water levelfalls low enough to uncover portions of thetubes, the heat transfer surface is reduced. Asa rule, therefore, the steam pressure will drop.Ordinarily a drop in steam pressure is theresult of an increased demand for steam, and271

PRINCIPLES OF NAVAL ENGINEERINGthe natural tendency is to cut in more burnersto fulfill the demand. If the drop in steam pressureis caused by low water, however, increasingthe firing rate will result in serious damageto the boiler and possibly in injury to fireroompersonnel. The possibility that a drop in steampressure indicates low water must always bekept in mind! Always check the level in thewater gage glasses before cutting in additionalburners, when steam pressure has dropped forno apparent reason.High water is another serious casualty thatis most frequently caused by the inattention ofthe checkman and the PO in charge of the watch.If the water level in the gage glass goes abovethe highest visible part, the boiler must besecured immediately.By careful observation, it is sometimes possibleto distinguish between an empty gage glassand a full one by the presence or absence ofcondensate trickling down the inside of theglass. The presence of condensate indicates,of course, an empty glass— that is, a low watercasualty. However, the boiler must be securedwhether the water is high or low. After theboiler has been secured, the location of thewater level can be determined by using thegage glass cutout valves and drain valves.Failure of a feed system pump can havedrastic consequences. Unless the pump casualtyis corrected immediately, the pump failurewill lead to low water in the boiler. In additionto the obvious dangers associated with lowwater, there are some which are equally seriousbut not so obvious. For example, low watercauses complete or partial loss of steam pressure.When steam pressure is lost or greatlyreduced, you will lose the services of vitalauxiliary machinery—pumps, blowers, and soforth. It is essential, therefore, that feed pumpcasualties be handled rapidly and correctly.If the main feed pump discharge pressureis too low, the first three things to be checkedare (1) the feed booster pump discharge pressure,(2) the level and pressure in the deaeratingfeed tank, and (3) the feed stop and checkvalves on idle boilers. A failure of the feedbooster pump will, of course, cause loss ofsuction and, therefore, loss of discharge pressureof the main feed pump. If the feed stopand check valves on idle boilers have accidentallybeen left open, the main feed pump dischargepressure may be low merely becausewater has been pumped to an idle boiler, aswell as to the steaming boiler.Some of the most likely causes of failure ofthe main feed pump are (1) malfunction of theconstant-pressure pump governor, (2) and airboundor vapor-bound condition of the mainfeed pump, (3) faulty pump clearances, and (4)malfunction or improper setting of the speedlimitinggovernor.In many installations, the feed booster pumpand the main feed pump are in the engineroom.In other installations, the feed booster pump isin the engineroom but the main feed pump is inthe fireroom. In this latter type of installation,failure of the feed booster pump will be indicatedto the fireroom force by loss of mainfeed pump discharge pressure and by the soundingof the low pressure feed alarm that isusually fitted where this type of machineryarrangement exists. The casualty to the feedbooster pump will be dealt with by engineroompersonnel, if the pump is in the engineroom;but fireroom personnel must take immediateaction to maintain a supply of feed water to theboiler.If the engineroom is unable to remedy thesituation immediately, start the emergencyfeed pump on cold suction . The emergencyfeed pump can take a hot suction from the feedbooster pump, or a cold suction from the reservefeed tanks. In standby condition, thispump should always be lined up on cold suction.If the main feed pump fails and there is nostandby pump available, start the emergencyfeed pump on hot suction and continue to feedthe boiler. If the feed also fails then it will benecessary to start the emergency feed pump oncold suction.If the emergency feed pump fails, the proceduresfor handling the casualty will varyaccording to the situation existing at the timeof the failure.In many ships, the emergency feed pump isnormally used for in-port operation, with themain feed pump in standby condition and thefeed booster pump providing a hot suction forthe emergency feed pump. Under these conditions,emergency feed pump failure can behandled by notifying the engineroom so that themain feed pump can be put on the line and usedto feed the boiler.A more difficult problem will arise if theemergency feed pump fails when it isbeingusedbecause of a previous casualty to the feedbooster pump or to the main feed pump. Underthese conditions, it may be possible to deal withthe situation by cross-connecting and using a272

Chapter 10- PROPULSION BOILERSpump in some other space to supply feed to theboiler. If the operating conditions do not allowthis solution of the problem, it will be necessaryto secure the boiler immediately in orderto prevent a low water casualty.FUEL SYSTEM CASUALTIESCasualties to any part of the fuel oil systemare serious and must be remedied at once.Common casualties include (1) oil in the fueloil heater drains, (2) water in the fuel oil, (3)loss of fuel oil suction, (4) failure of the fueloil service pump, and (5) fuel oil leaks. Itshould be noted that these casualties to the fueloil system are for ships burning NSFO. Theprocedures for ships burning other types of fuelwill differ to some extent, but not in all cases.Oil leakage from the fuel oil heaters intothe drains may cause oil contamination of thedrain lines, the reserve feed tanks, the deaeratingfeed tank, and the feed system piping andpumps. The presence of oil in any part of thefeed system is dangerous because of the possibilitythat the oil will eventually reach theboilers, where it will cause steaming difficultiesand serious damage to the boilers.Fuel oil heater drains must be inspectedhourly for the presence of oil.The presence of an appreciable amount ofwater in the fuel oil is indicated by hissing andsputtering of the fires and atomizers and byracing of the fuel oil service pump. The situationmust be remedied at once; otherwise, chokedatomizers, loss of fires, flarebacks, and refractorydamage may result.A loss of fuel oil suction usually indicatesthat the oil in the service suction tank hasdropped below the level of the fuel oil servicepump suction line. This causes a mixture ofair and oil to be pumped to the atomizers. Theatomizers begin to hiss and the fuel oil servicepump begins to race. It must be strongly emphasizedthat the loss of fuel oil suction cancause serious results. Related casualties mayinclude loss of auxiliary steam and electricpower, with the complete loss of all electricallydriven and steam-driven machinery.Failure of the fuel oil service pump cancause the same progressive series of casualtiesas those which result from loss of fuel oilsuction.Fuel oil leaks are very serious, no matterhow small they may be. Fuel oil vapors arevery explosive. Any oil spillage or leakage mustbe wiped up immediately.FLAREBACKSA flareback is likely to occur whenever thepressure in the furnace momentarily exceedsthe pressure in the boiler air casing. Flarebacksare caused by an inadequate air supplyfor the amount of oil being supplied, or by adelay in lighting the mixture of air and oil.Situations which commonly lead to flarebacksinclude: (1) attempting to light off or torelight burners from hot brickwork; (2) gunfireor bombing which creates a partial vacuum atthe blower intake, thus reducing the air pressuresupplied by the blowers; (3) forced draftblower failure; (4) accumulation of unburnedfuel oil or combustible gases in furnaces, tubebanks, uptakes, or air casings; and (5) anyevent which first extinguishes the burners andthen allows unburned fuel oil to spray out intothe hot furnace. An example of this last situationmight be a temporary interruption of thefuel supply which would cause the burners togo out; when the fuel oil supply returns tonormal, the heat of the furnace might not besufficient to relight the burners immediately.In a few seconds, however, the fuel oil sprayedinto the furnace would be vaporized, and aflareback or even an explosion might result.SUPERHEATER CASUALTIESIf the distant-reading superheater thermometerdoes not register a normal increase intemperature when the superheater is firstlighted off, the trouble may be either lack ofsteam flow or failure of the distant-readingthermometer. Lack of steam flow must be consideredas a possible cause even if the superheatersteam flow indicator (if installed) showsthat there is a flow. If the thermometer doesnot register a normal increase in temperature,secure all superheater burners.When operating with superheat, it is essentialto keep a constant check on the flow of steamthrough the superheater and on the superheateroutlet temperature. Any deviation from normalconditions must be corrected without delay.It is important to remember that a casualtyto some other part of the engineering plantmay reduce or entirely stop the flow of steamthrough the superheater, and so cause a superheatercasualty, unless appropriate action is273

PRINCIPLES OF NAVAL ENGINEERINGtaken to prevent damage. For example, acasualty to the main engines might call for asudden large reduction or even a completestoppage of steam flow. Even if the superheaterburners are secured, there will still be a needfor steam flow to protect the superheater fromthe heater of the furnace. In this event, or whenevera greater flow is required than can beobtained by ordinary means, lift the superheatersafety valves by hand to ensure a positive flowof steam through the superheater .When the superheater thermal alarm sounds,the superheater fires must be immediately decreasedto bring the temperature below alarmtemperature. Do not decrease the temperaturefurther than necessary. It is very seldomnecessary to secure all superheater burnersin order to bring the temperature down to theprescribed point.CASUALTIES TO REFRACTORIESIf brick or plastic falls out of the furnacewalls and goes unnoticed, burned casings mayresult. If brick or plastic falls out of a furnacewall, if practicable, secure all the burners.If it is not practicable to secure all the burners,secure those burners which are adjacent to thedamaged section. NOTE: It may be necessaryto continue operating the boiler until anotherboiler can be brought in on the line,CASUALTIES TO BOILERPRESSURE PARTSWhen boiler pressure parts, such as tubes,carry away or rupture, escaping steam maycause serious injury to personnel and damageto the boiler. It is urgent that the boiler be secured,relieved of its pressure, and cooled untilno more steam is generated. If a boiler pressurepart carries away or ruptures, take stepsimmediately upon discovery of the casualty, tominimize and localize the damage as much ascircumstances will allow.Gage glasses are connected to the water andsteam spaces of the steam drum. If a watergage glass carries away, the mixture of steamand water escaping from the gage connectionsmay seriously burn personnel in the area. Aball check valve in the high pressure gage linefunctions when the flow is excessive. In addition,the hazard of flying particles of glassmakes this casualty very serious. The particlesof glass could lodge in your eyes and blind you,or they could lodge elsewhere in your body andcause serious injury. If a gage glass casualtyoccurs, throw a large sheet of asbestos cloth,rubber matting, or similar material over theglass. Then take immediate action to securethe gage glass.PRECAUTIONS TO PREVENT FIRESThe following precautions must be taken toprevent fires:1. Do not allow oil to accumulate in anyplace. Particular care must be taken to guardagainst oil accumulation in drip pans underpumps, in bilges, in the furnaces, on the floorplates, and in the bottom of air-encased boilers.Should leakage from the oil system to the fireroomoccur at anytime, immediate action shouldbe taken to shut off the oil supply by means ofquick-closing valves and to stop the oil pump.2. Absolutely tight joints in all oil linesare essential to safety. Immediate steps mustbe taken to stop leaks whenever they are discovered.Flange safety shields should be installedon all flanges in fuel oil service linesto prevent spraying oil on adjacent hot surfaces.3. No lights should be permitted in the fireroomexcept electric lights (fitted with steamtightglobes, or lenses, and wire guards), andpermanently fitted smoke indicator and watergage lights. If work is being done in the vicinityof flammable vapors, or if rust-preventive compoundor metal-conditioning compound is beingused, all portable lights should be of the explosionproof type.BOILER MAINTENANCEThe engineer officer must keep himself fullyacquainted with the general condition of eachboiler and the manner in which each is beingoperated and maintained. He must satisfy himself,by periodic inspections, that the exteriorand interior surfaces of the boiler are clean;that the refractory linings adequately protectthe casing, drums, and headers; that the integrityof the pressure parts are being maintained;and that the operating condition of the burners,safety valves, operating instruments, and otherboiler appurtenances are satisfactory.274

Chapter 10- PROPULSION BOILERSThe engineer officer must assure himselfthat the idle boilers are properly secured at alltimes, and while steaming, the fuel oil used isfree of sea water, and the feed water is withinprescribed limits, free of salts, entrained oxygen,and oil.All parts of the boiler must be carefullyexamined whenever they are exposed for cleaningand overhauling, and the conditions observedmust be described in the boiler record sheetand the engineering log. All unusual cases ofdamage or deterioration discovered at any timeshould be reported to the type commander,stating in detail the extent of injury sustained,remedies applied, and the causes, if determined.If considered of sufficient importance,or technical assistance is desired from the NavalShip Systems Command, a copy of the correspondenceshould be forwarded to the NavalShip Systems Command.The requirements for fireroom maintenanceand repair are established by the PlannedMaintenance Subsystem; information on thissystem is contained in the Maintenance andMaterial Management (3-M) Manual, OPNAV43P2 Revised edition. All fireroom maintenanceshall be conducted in accordance with thissystem.275

CHAPTER 11BOILER FITTINGS AND CONTROLSThe fittings, instruments, and controls usedon naval boilers are sufficiently numerous andimportant to warrant separate discussion. Theterm boiler fittings is used to describe a numberof attachments which are installed in orclosely connected to the boiler and which arerequired for the operation of the boiler. Boilerfittings are generally divided into two classes.Internal fittings (also called internals ) are thoseinstalled inside the steam and water spaces ofthe boiler; external fittings are those installedoutside the steam and water spaces. Boilerinstruments such as pressure gages and temperaturegages are usually regarded as externalbqiler fittings. Boiler controls are special systemswhich automatically control the fuel oil,combustion air, and feed water inputs in orderto regulate the steam output of the boiler.ESTTERNAL FITTINGSThe internal fittings installed in the steamdrum usually include equipment for distributingthe incoming feed water, for giving surfaceblows, and for directing the flow of steam andwater within the steam drum. In addition, boilerswhich do not have controlled superheat havedesuperheaters for desuperheating steam neededfor auxiliary purposes; the desuperheater ismost commonly installed in the steam drum,but is installed in the water drum in some ofthe newer boilers. Internal fittings in someboilers also include equipment for injectingchemicals for boiler water treatment.The specific design and arrangement ofboiler internal fittings varies somewhat fromone type of boiler (and from one boiler manufacturer)to another. The arrangement of internalsin several boilers is therefore describedhere.Figure 11-1 illustrates atypical arrangementof internal fittings installed in the steam drumof a header-type boiler. This illustration alsoshows many of the external connections. Feedwater enters through the feed inlet (A) and flowsto the internal feed pipe (B), The feed pipe iscapped at one end. The horizontal part of thefeed pipe runs about 80 percent of the length ofthe drum, well below the normal water level.The feed pipe is perforated along the upper sideso that the feed water will be evenly distributedalong the length of the pipe.The dry pipe (C) is suspended near the topof the steam drum, along the centerline of thedrum. Both ends of the dry pipe are closed.Steam enters by way of perforations in theupper surface of the dry pipe. Thus the steammust change direction in order to enter the drypipe. Since some moisture is lost wheneversteam changes direction, the dry pipe acts asa device to separate steam and moisture. Steamleaves the dry pipe through the main steam outlet(D) and from there goes to the superheater.A few perforations in the bottom of the dry pipeallow water droplets to drain back down to thewater in the steam drum.A longitudinal baffle (N) also helps to separatemoisture from the steam before the steamenters the dry pipe. The baffle is installed insuch a way as to allow steam to flow to the drypipe but to keep moisture (and any solid matterthat might be carried over with the moisture)from entering the dry pipe.The surface blow-off pipe (E) is used to removegrease, scum, and light solids from theboiler water and to reduce the salinity of theboiler water while the boiler is steaming. Thesurface blow-off pipe is installed near the centerof the steam drum, with the upper surfaceof the pipe slightly below the normal water levelof the drum. The pipe runs almost the entirelength of the drum. Holes are drilled along thetop centerline of the pipe. One end of the pipeis blanked off. The other end is connected through276

Chapter 11-BOILER FITTINGS AND CONTROLSLONGITUDINAL SECTIONAL ELEVATIONDESIGNATION OF SYMBOLSA FEED - INLETB - FEED PIPEC - DRY PIPED - MAIN STEAM OUTLETE - SURFACE BLOW-OFF PIPEF - SURFACE BLOW-OFF NOZZLEG DESUPERHEATER INLET-H DESUPERHEATER OUTLET-J DESUPERHEATER- K - CHEMICAL FEED INLETL - CHEMICAL FEED PIPEM- SWASH PLATESN - BAFFLEP - SAFETY VALVE NOZZLESCROSS SECTIONAL ELEVATIONFigure 11-1.— Arrangement of internal fittingsheader-type boiler.in38.42the drumhead to the surface blow-off nozzle (F).When the surface blow valve is opened, the pressurein the drum forces the water above theblow-off pipe to go into the pipe through theholes on the top surface; the water from thesurface blow-off pipe then leaves the boiler byway of the surface blow valve.The desuperheater (J) is an assembly of pipelengths and return bends located below the waterlevel of the drum. The superheater steam entersthe desuperheater through the desuperheaterinlet (G), gives up its superheat to the water inthe steam drum, and then— once again at or veryclose to saturation temperature — passes throughthe desuperheater outlet (H) before entering theauxiliary steam line.The chemical feed inlet (K) is connected tothe internal chemical feed pipe (L). The chemicalfeed pipe has holes drilled in it to alloweven distribution of chemicals used for boilerwater treatment.Swash plates (M) are used to reduce thesurging or swashing of water from one end ofthe drum to the other as the ship moves. Inaddition, the swash plates act as supports forthe internal feed pipe and for the desuperheater.The safety valve nozzles (P) are not normallyconsidered internal fittings. These nozzles277

PRINCIPLES OF NAVAL ENGINEERINGconnect the safety valves (not shown) to thesteam drum.The arrangement of internal fittings in adouble-furnace boiler with controlled superheatis shown in figure 11-2. The dry pipe, the internalfeed pipe, and the surface blow line areabout the same as the corresponding fittings inthe header-type boiler; but some of the otherfittings are different.The double-furnace boiler has no desuperheater,since auxiliary steam is taken directlyfrom the steam drum without passing firstthrough the superheater.Swash plates are not required in the waterspaces of the double-furnace boiler because thistype of boiler is always installed with the longaxis of the steam drum fore-and-aft rather thanathwartships. Surging of water, therefore, isnot a particular problem.The double-furnace boiler does not have aseparate chemical feed pipe. Instead, chemicalsfor boiler water treatment come into the steamdrum with the feed water and are therefore distributedwith the feed water through the holesin the internal feed pipe.Perhaps the greatest difference in the internalfittings of the double-furnace boiler and theheader-type boiler is in the equipment providedfor the separation of moisture from the steam.In the header-type boiler, a steam baffle helpsto separate the moisture from the steam beforer^CYCLONE SEPARATORSNOZZLE PLATES OFMANIFOLD BAFFLEINTERNAL FEEDPIPEREMOVABLE APRON PLATESOF MANIFOLD BAFFLE38.43Figure 11-2.— Arrangement of internal fittingsin double-furnace boiler.the steam enters the dry pipe. In the doublefurnaceboiler, cyclone steam separators areused instead of a steam baffle. These separatorsutilize centrifugal force to separate waterand steam. There are usually 18 of these separatorsinstalled in the steam drum of a doublefurnaceboiler; half of them are installed on oneside of the drum and half on the other side.The cyclone steam separators are attachedto a manifold baffle which extends from justforward of the generating tubes to just aft ofthem. To avoid interference with boiler circulation,the manifold baffle does not reach asfar as the downcomers. The manifold bafflecurves around inside the lower half of the steamdrum, passing just below the internal feed pipeand leaving a space of about 3 inches betweenthe baffle and the steam drum. The baffle isattached to the drum by means of two flat barswhich hang from the drum, one on each side.The bars extend the full length of the baffle.Each bar contains ports or openings, and acyclone steam separator is placed over eachport.The general arrangement of the manifoldbaffle and the cyclone steam separators maybe seen in figure 11-2. Now let us examinefigure 11-3 and trace the flow of steam andwater through the steam drum. The generatingtubes discharge a mixture of steam and waterinto the space between the manifold baffle andthe steam drum. From this space, the onlypassage available for the steam and water isthrough the ports which open to the cycloneseparators. As the mixture passes through theseparators, the steam passes upward and thewater is discharged downward.The cyclone steam separator is shown in cutawayview in figure 11-4 and in plain view infigure 11-5. The mixture of steam and waterenters the separator through the inlet connection,at a tangent to the separator body. Becauseof its angle of entrance, the mixture of steamand water acquires a rotary motion. As themixture whirls around, centrifugal force separatesthe water from the steam. The water,being heavier, is thrown out toward the sidesof the separator. The steam, being lighter, tendsto remain near the center. An internal bafflefurther helps to deflect the steam to the centerand the water to the outside. The steam thenrises through the center of the separator andpasses through the scrubber element. Thescrubber consists of closely spaced corrugatedsteel plates. As the steam passes through the278

Chapter 11-BOILER FITTINGS AND CONTROLSDRY PIPESTEAMSTEAMWATERSURFACE BLOWLINEINTERNAL FEEDPIPEGENERATINGTUBESFigure 11-3.— Flow of steam and water in steam drumof double-furnace boiler.38.44scrubber, its direction is changed frequently,and with each change of direction some moistureis lost. The steam passes out of thescrubber element into the top part of the steamdrum and then enters the dry pipe.While the steam is rising, the water is fallingto the base of the separator. Stationarycurved vanes in the bottom of the separatorserve to maintain the rotary motion of the wateruntil the water is finally discharged from thebottom of the separator. Since the vanes arelocated around the periphery of a flat plate, thewater passes from the separator only aroundthe outer edge. The flat plate also serves tokeep the steam, which is in the center of theseparator, from being carried downward withthe water.A flat baffle plate is fitted at the base ofeach of the two end separators on each side.This baffle plate guides the water that is beingdischarged from the separator to the center ofthe drum, where it mixes thoroughly with therest of the water in the drum. Without such abaffle, the water from these end separatorswould tend to flow directly to the downcomersand, since it is hotter than the rest of the waterin the steam drum, it would tend to disrupt theboiler circulation.Figure 11-6 illustrates the arrangement ofinternal fittings in an older single-furnaceboiler. The internal fittings for this boiler arequite similar to those found in the double-furnaceboiler, except that the single-furnace boilerhas a desuperheater (item 5 in fig. 11-6).The internal fittings in the steam drum requireroutine maintenance and upkeep. All maintenancerequirements shall be conducted inaccordance with the Planned Maintenance Subsystemof the 3-M System.When a boiler is opened for cleaning ofwatersides, the internal fittings must be removed.The fittings are bolted into place; removingthe bolts allows you to remove thefittings. Be sure that all bolts and tools usedin removing the bolts are strictly accountedfor. When removing internal fittings, be sure toidentify them so that you will be able to reinstallthem correctly.After removing the fittings from the steamdrum, thorouglily wirebrush and clean them.Check the dry pipe, the internal feed line, andthe surface blow line to be sure that all theholes are free and clear of obstructions. Inaddition, inspect the inside of the feed line foroil accumulations; if you find any sign of oilnotify the CPO in charge of the fireroom.279

PRINCIPLES OF NAVAL ENGINEERINGmmm^ummmmmi38.45Figure 11-4.— Cutaway view of cyclone steamseparator.INLETBAFFLESTEAMWATER38.46Figure 11-5.— Plan view of cyclone steamseparator.Before reinstalling the fittings, wirebrush,clean, and hose down the steam drum. Be surethat it is clean and free of any oil or otheraccumulation.When replacing the fittings in the steamdrum, be sure that all the bolts are drawn tight.The desuperheater flanges must be thoroughlycleaned before the desuperheater is fitted intoplace and bolted. New gaskets must be installed.The flanges must be drawn up evenly and tightlyto prevent any leakage from the flanged joints.The internal fittings used in newer singlefurnanceboilers differ from those used in olderboilers and also differ among themselves. Figure11-7 shows the arrangement of fittings usedin the steam drum of a boiler on a DLG 9-15class ship. A little study of this illustrationshows several new or different features.To begin with, notice that there is no desuperheater,even though this is a single-furnaceboiler. The boiler does have a desuperheater,but it is installed in the water drum rather thanin the steam drum.Another interesting feature illustrated infigure 11-7 is the vortex eliminator. A vortexeliminator consists of a series of grid-likeplates arranged in a semicircular shape to conformto the shape of the lower half of the steamdrum. One vortex eliminator is located at thefront of the steam drum (as shown in fig, 11-7)and another is located at the rear of the drum.In each case, the eliminator is fitted over thenecks of the downcomers. The purpose of thevortex eliminators is to reduce the swirlingmotion of the water as it enters the downcomers.The arrangement of internal fittings in thesteam drum of a boiler on one of the newer destroyerescorts is shown in figure 11-8. Noticethat there are two feed pipes, each of which runslengthwise in the drum. The discharge holes aredrilled along the inner side of each feed pipe sothat the incoming feed water is discharged horizontallytoward the middle of the drum. Noticealso that the internals in this steam drum includehorizontal steam separators rather thancyclone steam separators.A horizontal steam separator is shown infigure 11-9. These separators are installed inmuch the same way as the cyclone steam separators—thatis, one row of separators is installedalong each side inside the steam drum.Each horizontal steam separator has a machinedflange which is bolted to a matching flangeattached to a girth baffle. The mixture of steam280

Chapter 11-BOILER FITTINGS AND CONTROLSSIDE VIEWEND VIEW1. DESUPERHEATER INLET2. NOZZLE PLATES OF MANIFOLDBAFFLE3. REMOVABLE APRON PLATESOF MANIFOLD BAFFLE4. CYCLONE SEPARATORS5 DESUPERHEATER TUBES6 INTERNAL FEED PIPE7 FEED NOZZLE8 STEAM SCRUBBER SUPPORT9 MAIN STEAM CONNECTION10 DRY PIPE11 STEAM SCRUBBERS12 SURFACE BLOW LINEFigure 11-6.— Arrangement of internal fittings insingle-furnace boiler.older38.47Xand water enters the separator tiirough a taperedinlet section on the side nearest the shell of thesteam drum and follows a curving path along thecurve of the separator. The steam leavesthrough the outlet orifices at each side of theseparator. The water, being heavier, continuesalong the curve of the separator and is dischargedthrough drain holes in the drain baffle.The knife edge on the drain baffle is there tominimize turbulence. A second drain bafflecurves down below the knife edge and drains offany water that might pass over the knife edge.The steam discharged from the horizontalseparators is channeled directly to the chevrondryers which are installed near the top of thedrum, as shown in figure 11-8. A number ofthese chevron dryers are installed along thelength of the steam drum. From the dryers,the steam enters the rectangular dry box whichis fitted against the top of the steam drum.The dry box acts as a chamber for the collectionof dry steam.The chemical feed pipe shown in figure 6-8is connected to a nozzle on the end of the drum.The chemical feed pipe and nozzle are used toinject chemicals for boiler water treatment whilethe boiler is in operation; they are also usedto draw samples of boiler water for testing.EXTERNAL FITTINGS AND CONNECTIONSExternal fittings and connections commonlyused on naval boilers include drains and vents,sampling connections, feed stop and checkvalves, steam stop valves, safety valves, sootblowers, blow valves, water gage glasses, remotewater level indicators, superheater steamflow indicators, pressure and temperaturegages, superheater temperature alarms, smokeindicators, oil drip detector periscopes, singleelementfeed water regulators, and other devicesthat are closely connected to the boiler but notinstalled in the steam and water spaces.Any listing of boiler external fittings andconnections tends to sound like a catalog of miscellaneousand unrelated hardware. Actually,however, all of the external fittings and connectionsserve purposes that are related toboiler operation. Some of the fittings and connectionsallow you to control the flow of feedwater and steam. Others serve as safetydevices. Still others allow you to perform operationalprocedures— removing soot from the firesides,for example, or giving surface blows—that are necessary for efficient functioning of theboiler. The instruments attached to or installed281

PRINCIPLES OF NAVAL ENGINEERINGMAIN STEAM OUTLET NOZZLEDRY PIPEHANGER BOLT ANDBOLT ANCHORSCRUBBERSCREEN PLATESURFACEBLOW NOZZLESURFACE BLOW PIPESUPPORT BARBAFFLEFRONT VORTEXELIMINATORFRONT DOWNCOMERS(TO WATER DRUM)FRONT DOWNCOMER(TO SIDEWALL HEADER)BAFFLECHEMICAL FEED PIPEFEEDWATER PIPEFigure 11-7.— Arrangement of internal fittings in newersingle-furnace boiler (DLG 9-15 class ship).38.231near the boiler give you essential information external fittings and connections, then it sconcerning the conditions existing inside the necessary to see how each item is related toboiler. To understand the purposes of the boiler operation.282

Chapter U-BOILER FITTINGS AND CONTROLSCHEVRON DRYERSDRY BOXHORIZONTAL STEAMSEPARATOR\STEAMBAFFLESOUTLETORIFICEBAFFLESCHEMICAL FEEDDESUPERHEATER INLET^DESUPERHEATER38.48Figure 11-8.— Arrangement of internal fittingsin newer single-furnace boiler (DE 1006 classship).Figures 11-10, 11-11, 11-12, and 11-13 showthe locations of many external fittings and connectionson a recent 1200-psi single-furnaceboiler. As you study the following information onexternal fittings and connections, you may find ithelpful to refer to these figures to see where thevarious units are installed on or connected tothe boiler. Remember, however, that the illustrationsshown here are for one particularboiler and that differences in boiler design leadto differences—in the type and location of externalfittings and connections. Drawings showingthe location of external fittings and connectionsare usually included in the manufacturer'stechnical manuals for the boilers on each ship.The maintenance of external fittings is ofvital importance to the proper operation of theboiler. Therefore, all maintenance shall beconducted in accordance with the PlannedMaintenance Subsystem of the 3-M System.Drains and VentsThe main part of the boiler, the economizer,and the superheater— in short, all the steam andwater sections of the boiler— must be providedwith drains and vents.38.49Figure 11-9.— Horizontal steam separator.The main part of the boiler may be drainedthrough the bottom blow valves (described laterin this chapter) and through water wall headerdrain valves. It is vented through the aircock,which is a high pressure globe valvel installedat the highest point of the steam drum. Theaircock allows air to escape when the boiler isbeing filled and when steam is first forming; italso allows air to enter the steam drum whenthe boiler is being emptied.The economizer is vented through a ventvalve on the economizer inlet piping. It isdrained through a drain line from the econonomizeroutlet header. Another drain line, thisone coming from the drain pan installed belowBasic types of valves are discussed in chapter 14 ofthis text.283

PRINCIPLES OF NAVAL ENGINEERINGECONOMIZERACCESS PANELSREMOTE WATERLEVEL INDICATORNOZZLESWATER GAGECUTOUTVALVEWATER GAGESOOT BLOWER AIRPRESSURIZINGCONNECTIONWATER GAGEDRAINCONNECTIONBURNERSTATIONARYSOOT BLOWERCONNECTIONSALINOMETERVALVEBOTTOMBLOW VALVECONNECTIONFigure 11-10. — External fittings and connections on1200-psi single-furnace boiler (front view).38. 232284

Chapter 11-BOILER FITTINGS AND CONTROLSMAIN STEAMOUTLETSUPERHEATERPILOT VALVEDRUM VENTSTEAM GAGE CONNECTIONDRUM VENTSURFACEBLOW VALVEDAMPERACCESS PANELSLIDING SADDLE(SIDE WATERWALL HEADERBOTTOM BLOW VALVES(SIDE WATERWALL HEADER)STATIONARY SADDLE(SIDE WATERWATER HEADER)Figure 11-11.— External fittings and connections on 1200-psi single-furnaceboiler (furnace side view).38.233285

PRINCIPLES OF NAVAL ENGINEERINGECONOMIZERVENT. CONN.ECONOMIZERVESTIBULE PEEPHOLESTATIONARYSOOT BLOWERCONNECTIONSDAMPERCONN. FOR AIR FLOWMEASURING DEVICEECONOMIZERVESTIBULEPEEPHOLEBLANK FLANGE(CHEMICALCLEANINGAND BOILER TESTCONNECTION)CONN.FOR AIR FLOWMEASURING DEVICEECONOMIZER DRAINOUTLETCONN.MAIN FEED PIPECONN.Figure ll-12.-E3cternal fittings and connections on 1200-psi single-furnaceboiler (economizer side view).38.234286

Chapter 11-BOILER FITTINGS AND CONTROLSECONOMIZERACCESS PANELSFEED WATERREGULATORCONNECTIONSWATER GAGECONNECTIONSDAMPERDAMPERDESUPERHEATERINLETLOWER RE/WATER WALHEADER-BOTTOM BLOW VALVES(REAR WATER WALLHEADER)SUPERHEATERINTERMEDIATEHEADER DRAINSUPERHEATERINLET a OUTLETHEADER DRAINSTATIONARYSADDLE(WATER DRUM)DESUPERHEATEROUTLETFigure11-13.— External fittings and connections on 1200-psi single-furnaceboiler (rear view).38.235287

PRINCIPLES OF NAVAL ENGINEERINGthe headers, serves as a telltale^ in the event ofhandhole leakage in the economizer.Superheater vents are installed at or nearthe top of each superheater header or headersection; superheater drains are installed at ornear the bottom of each header or header section.Thus each pass of the superheater isvented and drained.Superheater drains discharge through gravity(open-funnel) drains to the fresh water draincollecting system while steam is being raisedin the boiler. After a specified pressure hasbeen reached, the superheater drains are shiftedto discharge through steam traps^ to the highpressure drain system. The steam traps allowcontinuous drainage of the superheater withoutexcessive loss of steam or pressure.Figure 11-14 illustrates diagrammaticallythe arrangement of superheater vents and drainson a newer type of single-furnace boiler. Thisillustration also shows the superheater protectionsteam connections. Note, also, the waterdruminstallation of the desuperheater.Sampling ConnectionsIt is difficult to say just where the connectionfor drawing test samples of boiler watermay be located, since this connection is foundin different places on different types of boilers.On some boilers the sampling connection islocated at the rear of the water drum. On othersit comes off of the bottom blow line betweenthe water drum and the bottom blow valve,either at the front of the boiler or at about themiddle of the water drum. On boilers that havea chemical feed pipe in the steam drum, the testsamples may be drawn through the nozzle connectionof the chemical feedpipe. On some shipsthe surface blow line connection is used to takeboiler water samples.It is also difficult to say just what the samplingconnection may be called. On some drawingsit is identified as a test cock; on othersas a salinity cock; on others as a salinometervalve; and on still others as a water test sampleconnection.A sample cooler is fitted to the outlet sideof the sampling connection. The cooler bringsthe temperature of the sample water down belowthe boiling point at atmospheric pressure andthus keeps the water from flashing into steamas it is drawn from the higher pressure of theboiler to the lower pressure of the fireroom.Feed Stop and Check ValvesManually operated feed stop and check valvesare installed in the feed line to each boiler."*Feed stop and check valves are operated manually,with a separate handwheel for each valve.In addition, the feed check valve has remoteoperating gear so that it can be operated fromthe firing aisle. In normal operation, the stopvalve is kept fully open and the check valve isused to regulate the supply of feed water to theboiler. When automatic feed water controls arein use, both the feed stop valve and the feedcheck valve are kept fully open so that they willnot interfere with the automatic feeding of theboiler. (Similarly, the automatic feed regulatingvalve is kept fully open when the boiler is beingfed manually through the feed check valve.The feed stop and check valves shown infigure 11-15 are combined in one manifold casting.Note, however, that there are two separatevalves. In some installations the two valves arehoused in separate flanged castings which arebolted together. No matter what type of installationis used, the feed stop valve is always installedbetween the feed check valve and theeconomizer inlet.Steam Stop ValvesMain steam stop valves are used to cutboilers in on the main steam line and to disconnectthem from the line. The main steamstop valve located just after the superheateroutlet is usually called the main steam boilerstop. Figure 11-16 shows an external view ofa main steam boiler stop. Figure 11-17 showsa cross-sectional view of a globe-type mainsteam boiler stop. Gate valves instead of globevalves are used as main steam boiler stops onmany newer ships.The stop valve is a regular globe-type stop valve.The term telltale is frequently used in connectionThe so-called "check" valve is actually a stop-checkwith engineering equipment to indicate any device whichvalve which functions either as a stop valve or as ashows leakage, flow, position, or other conditions.check valve, depending upon the position of the valve3 Steam traps are discussed in chapter 14 of this text. stem.288

Chapter 11 -BOILER FITTINGS AND CONTROLSSYMBOL DESIGNATIONS- RELIEF VALVE TO BILGETEST BLOWDOWN TEST SLOWDOWNLINELINETO BILGE ANDCONTAMINATEDDRAINSTO BILGE ANDCONTAMINATEDDRAINS

PRINCIPLES OF NAVAL ENGINEERINGAuxiliary steam stop valves are smaller thanmain steam stop valves but are otherwise similar.Special turbogenerator steam stop valvescontrol the admission of steam to the turbogeneratorline.Safety ValvesFigure 11-16.— External view of mainboiler stop valve.38.52steamIn use, the main steam boiler stop is alwayseither fully open or fully closed. The valve canbe opened and closed manually at the valveitself. In some installations, it can also beclosed pneumatically at the valve. The mainsteam boiler stop can also be operated manually,by remote control cables, from a remote operatingstation; as a rule, the valve can only beclosed (not opened) from the remote station.For manual operation, the toggle operating gearshown in figures 11-16 and 11-17 provides themechanical advantage required for closing thevalve against boiler pressure.Two-valve protection for each boiler is requiredon all ships built to U. S. Navy specifications.A second steam stop valve is thereforeprovided in the main steam line just beyondthe main steam boiler stop.Each boiler is fitted with safety valves whichallow steam to escape from the boiler when thepressure rises above specified limits. Thecapacity of the safety valves installed on aboiler must be great enough to reduce the steamdrum pressure to a specified safe point whenthe boiler is being operated at maximum firingrate with all steam stop valves completelyclosed. Safety valves are installed on the steamdrum and at the superheater outlet.Several different kinds of safety valves areused on naval boilers, but all are designed toopen completely (pop) when a specified pressureis reached and to remain open until a specifiedpressure drop ( blowdown ) has occurred. Safetyvalves must close tightly, without chattering, andmust remain tightly closed after seating.There is an important difference betweenboiler safety valves and ordinary relief valves.The amount of pressure required to lift a reliefvalve increases as the valve lifts, since theresistance of the spring increases in proportionto the amount of compression. Therefore arelief valve opens slightly at a specified pressure,discharges a small amount of fluid, andcloses at a pressure which is very close to thepressure that causes it to open. Such an arrangementwill not do for boiler safety valves.If the valves were set to lift for anything closeto boiler pressure, the valves would be constantlyopening and closing, pounding the seatsand disks and causing earlyfailureof the valves.Furthermore, relief valves would not dischargethe large amount of steam that must be dischargedto bring the boiler pressure down to asafe point, since the relief valves would reseatvery soon after they opened.To overcome this difficulty, boiler safetyvalves are designed to open completely at thespecified pressure. In all types of boiler safetyvalves, the initial lift of the disk is caused bystatic pressure of the steam, just as it wouldbe in a relief valve. But just as soon as thesafety valve begins to open, a projecting lip orring of larger area is exposed for the steampressure to act upon. The increase in forcethat results from the steam pressure acting290

Chapter 11-BOILER FITTINGS AND CONTROLSOUTLET TOSTEAM LINEa^:iiINLETFROM BOILERDRAIN CONNECTIONSFigure 11-17.— Cross-sectional view of main steam boiler stop valve.38.53Xupon this larger area overcomes the resistanceof the spring, and the valve "pops"— that is, itopens quickly and fully. Because of the largerarea now presented, the valve cannot reseatuntil the pressure has become considerablysmaller than the pressure which caused thesafety valve to open.A steam drum safety valve of the huddlingchamber type is shown in figure 11-18. As thestatic pressure of the steam in the steam drumcauses the valve to open, the huddling chamber(which is formed by the position of the adjustingring) fills with steam. The steam in thehuddling chamber builds up a static pressurethat acts upon the extra area provided by theprojecting lip of the feather. The resulting increasein force overcomes the resistance of thespring, and the valve pops. After the specifiedblowdown has occurred, the valve closes cleanly,with a slight snap. The amount of tensionon the spring determines the pressure at whichthe valve will pop. The position of the adjustingring determines the shape of the huddlingchamber and thereby determines the amount ofblowdown that must occur before the valve willreseat.A steam drum safety valve of the nozzlereaction type is shown in figure 11-19. Theinitial lift of the valve occurs when the staticpressure of the steam in the drum acts uponthe disk insert with force sufficient to overcomethe tension of the spring. As the disk insertlifts, the escaping steam strikes the nozzlering and changes direction. The resulting forceof reaction causes the disk to lift higher,up to above 60 percent of rated capacity.Full capacity is reached as the result of asecondary, progressively increasing lift whichoccurs as an upper adjusting ring is exposed.The ring deflects the steam downward, and theresulting force of reaction causes the disk tolift still higher. Blowdown adjustment in this291

,SLOTSPRINCIPLES OF NAVAL ENGINEERINGCOMPRESSION SCREWRELEASE NUTLOCKING NUTLEVER PINTOP LEVERCOMPRESSIONSCREWLOCKING NUTLEVER PINTOP SPRINGWASHERDROP LEVERSPRINGBOTTOM SPRING WASHERFEATHER GUIDERETAINING RINGLOCKING SCREWSPINDLEFEATHER GUIDEFEATHERHUDDLING CHAMBERACTUAL LOCATIONOF RING PIN IS 90°TO THE RIGHTWHEN FACING THEOUTLETRING PINADJUSTINGISEAT BUSHINGy, N.P.T. FOR DRAINBASEFORWRENCHESFigure 11-18.— Steam drum safety valve (huddling chamber type).98.80type of valve is made byraising or loweringthe adjusting ring and by raising or loweringthe nozzle ring.Safety valves are always installed at thesuperheater outlet as well as on the steam drum.Superheater safety valves are set to lift justbelow, at, or just above the pressure which liftsthe steam drum safety valves, in order to ensurean adequate flow of steam through thesuperheater when the steam drum safety valvesare lifted.Most double-furnace boilers are fitted witha pressure-pilot operated superheater outletsafety valve assembly of the type shown infigure 11-20. This assembly consists of threeconnected valves: a small spring-loaded safetyvalve installed on the steam drum; an actuatingvalve installed on the steam drum; and an actuated(or unloading) valve installed on the superheater.The stem of the drum valve is connectedmechanically, by means of a lever, to the stemof the actuating valve. The actuating valve is292

Chapter 11-BOILER FITTINGS AND CONTROLSHAND LIFTING LEVER*SPINDLE1SPINDLE LOCK CLIPADJUSTING RINGSET SCR EWADJUSTING RINGDISK INSERTFigure 11-19.— Steam drum safety valve (nozzle reaction type).29.219connected by piping to the space above the diskin the superheater actuated (or unloading) valve.The unloading valve has no spring and reliessolely on pressure differential for its operation.Normally there is a static pressure above thedisk of the unloading valve, since a small orifice(or in some designs a small clearance aroundthe disk) allows some steam at superheater outletpressure to enter the space above the disk.When the drum valve is opened by steamdrum pressure, the mechanical connection betweenthe drum valve and the actuating valvecauses the actuating valve to open also. Withthe actuating valve open, steam flows from thespace above the disk of the superheater unloadingvalve, through the actuating line, throughthe actuating valve, to atmosphere. The suddenrelief of pressure above the disk of the unloading293

IPRINCIPLES OF NAVAL ENGINEERINGDRUMVALVETOATMOSPHEREACTUATINGVALVESUPERHEATERUNLOADING(ACTUATED)VALVEFigure 11-20.— Pressure pilot-operated superheater outlet safety valve assembly.98.81valve causes that valve to open fully, so thatsteam is discharged from the unloading valveto atmosphere.Many 1200-psi single-furnace boilers, andalso some 600-psi single-furnace ones, areequipped with Crosby two-valve superheateroutlet safety valve assemblies of the type shownin figure 11-21. In an assembly of this type,both of the valves are spring loaded. Thepilot valve on the steam drum and the superheatervalve at the superheater outlet areconnected by a pressure transmitting line thatruns from thedischarge side of the drum pilotvalve to the underside of the piston that isattached to the spindle of the superheater safetyvalve. The superheater valve is set to pop at apressure about 2 percent higher than the pressurewhich causes the drum pilot valve to pop.When the drum pilot valve pops, the steam pressureis transmitted immediately through thepressure line to the piston, and the superheatervalve is thus actuated. If for any reason thedrum pilot valve should fail to open, the superheatervalve would open at a slightly higherpressure.The Consolidated three-valve superheateroutlet safety valve assembly shown in figure11-22 is used on a number of 1200-psi294

Chapter 11-BOILER FITTINGS AND CONTROLSUNLOADING LINESUPERHEATERVALVEi

PRINCIPLES OF NAVAL ENGINEERINGMANUALOPERATION-LEVERACTUATINGLINEACTUATORTO ATMOSPHEREACTUATINGVALVEATMOSPHERETO ATMOSPHEREDRUM PRESSURE SUPERHEATER OUTLET PRESSURE104.2?Figure 11-22.— Three-valve superheater outlet safety valve assembly (Consolidated).Before instructing fireroom personnel toblow tubes, the engineering officer of the watchmust obtain permission from the officer of thedeck. Under some conditions, tubes cannot beblown without covering the upper decks with soot;hence the need for obtaining permission from theofficer of the deck.Soot blowers are installed on the boiler withtheir nozzles projecting into the furnace betweenthe boiler tubes or adjacent to them. The sootblowers are arranged so that operation in theproper sequence will sweep the soot progressivelytoward the uptakes.The number of soot blowers installed, theway in which they are arranged, and the blowingarcs for each unit differ from one type of boilerto another. Figure 11-23 shows the arrangementof soot blowers used on one of the newer 1200-psisingle-furnace boilers; one of the soot blowershas a blowing arc of 220° and the others haveblowing arcs of 360° F, on this particular boiler.One common type of soot blower is shown infigure 11-24. The part of the soot blowerthat maybe seen from the outside of the boiler is calledthe head. The soot blower element, a long pipewith nozzle outlets, is the part of each sootblower that projects into the tube banks of theboiler. The soot blower shown in figiire 11-24 isoperated by an endless chain; when the chain ispulled, the element is rotated and superheatedsteam is admitted through the steam valve. Thesteam discharges at high velocity from thenozzles in the elements. The nozzles direct thejets of steam so that they sweep over the tubes.The soot is thus loosened so that it can be blownout of the boiler.Some soot blowers are operated by turning acrank or handwheel, instead of by an endlesschain. On some recent ships, the soot blowers areoperated by pushbuttons. One pushbutton is providedfor each unit. Pressing the pushbutton^admits air to an air motor which drives the units.296

Chapter 11-BOILER FITTINGS AND CONTROLS38,57Figure 11-23.—Arrangement of soot blowerson a 1200 psi single-furnace boiler.Some soot blowers on some boilers are ofthe retractable type— that is, the element doesnot remain in the furnace all the time but insteadcan be retracted into a housing or shroudbetween the inner and outer casings.The scavenging air connection shown infigure 11-24 supplies air to the soot blowerelement and thus keeps combustion gases frombacking up into the soot blower head and piping.A hole in the outer casing allows air to enterthe other end of the scavenging air line; thus,scavenging air is blown through the soot blowerwhenever the forced draft blowers are in operation.A check valve is installed in thescavenging air piping, very near the soot blowerhead; this valve closes whenever steam is admittedto the soot blower element.Blow ValvesSome solid matter is always present inboiler water. Most of the solid matter isheavier than water and therefore settles inthe water drums and headers. Solid matterthat is lighter than water rises and forms ascum on the surface of the water in thesteam drum. Since most of the solid matteris not carried over with the steam, the concentrationof solids remaining in the boilerwater gradually increases as the boiler steams.For the sake of efficiency and for the protectionof the boiler pressure parts, it isnecessary to remove some of this solid matterfrom time to time. Blow valves and blow linesare used for this purpose.Light solids and scum are removed fromthe surface of the water in the steam drum bymeans of the surface blow line— which, as wehave already seen, is an internal boiler fitting.Heavy solids and sludge are removed by usingthe bottom blow valves which are fitted to eachwater drum and header. Both surface blowvalves and bottom blow valves on modern navalboilers are globe-type stop valves.Both the surface blow and the bottom blowvalves discharge to a system of piping calledthe boiler blow piping . The boiler blow pipingsystem is common to all boilers in any onefireroom. Guarding valves are installed in theline as a protection against leakage from asteaming boiler into the blow piping andagainst leakage from the blow piping backinto a dead boiler. A guarding valve installedat the outboard bulkhead of the fireroom givesprotection against salt water leakage into theblow piping. After passing through this guardingvalve, the water is discharged through anoverboard discharge valve (sometimes called askin valve) which leads overboard below theship's waterline. Figure 11-25 shows thegeneralarrangement of boiler blow piping for one ofthe newer single-furnace boilers.Water Gage GlassesEvery boiler must be equipped with at leasttwo independent devices for showing the waterlevel in the steam drum, and at least one ofthese devices must be a water gage glass.Some boilers have more than two devices forindicating water level. Various combinations ofwater level indicating devices are used onnaval boilers. Perhaps the most common arrangementon older boilers is two water gageglasses, one 10 inches long and one 18 incheslong. Newer boilers may have two water gageglasses and one remote water level indicatoror they may have one water gage glass andtwo remote water level indicators.Several types of water gage glasses areused on naval boilers. The older water gageglasses differ in some ways from the onesinstalled on the newer 1200-psi boilers, andgages made by different manufacturers may297

PRINCIPLES OF NAVAL ENGINEERINGSWIVEL TUBEPACKINGPACKINGELEMENTFigure 11-24.— External view of multi-nozzle soot blower.38.54vary somewhat in design details. Detailed informationon the water gage glasses installedon any particular boiler may be obtained fromthe manufacturer's technical manual.An older type of water gage glass is shownin figure 11-26. Figure 11-27 illustrates theconstruction of this gage. The frame is thecenterpiece of the assembly. Hollow stems ateach end of the frame connect with the cutoutvalves at top and bottom, thus allowing waterand steam to enter the gage. Two glass platesor strips, ground to flat parallel faces, areused in each water gage. The glass strips arebacked up by thin sheets of mica which separatethe glass from the high temperaturewater and steam. The mica sheets serve twopurposes. First, they keep the glass from becomingetched by the action of the hot waterand steam. And second, they prevent shatteringof the glass in case of breakage.The entire assembly of frame, glass strips,and mica sheets is supported between two steelcover plates which are held together by studs.Asbestos gaskets, 1/32 inch in thickness, areused on each side of the frame. Asbestos cushions,1/16 inch in thickness, are used betweenthe cover plates and the glass strips. The arrangementof cushions and gaskets is shown infigure 11-27.The drain connection shown in figure 11-26permits the water gage to be blown down andalso permits it to be drained. The regulatorconnections shown at the top and bottom ofthis gage are not found on all gages; they areinstalled only on boilers whichwerenot orignallydesigned to use feed water regulators butwhich were later fitted with the regulators.A more recent type of water gage glass isshown in figure 11-28. The gage is assembledsprings, as shown in the illustration. This typeof assembly makes it unnecessary to retorque298

Chapter 11-BOILER FITTINGS AND CONTROLSSURFACEBLOW VALVESUPERHEATERGENERATING BANK-SIDEWALLTUBESSIDEWALLHEADERBOTTOM BLOW VALVEOVERBOARDDISCHARGEVALVE-r— GUARDING\ VALVEFROM OTHER BOILERSKIN OF SHIPFigure 11-25.— Boiler blow piping for single-furnace boiler.38.58the studs after the gage has warmed up. (Noticethe numbering of studs in figure 11-28; thenumbers indicate theproper sequence of tighteningthe studs when assembling the gage.)On some boilers of recent design, a bicolorwater gage is used. Bi-color gages showRED in the portion of the glass which is filledwith steam and GREEN in the portion of theglass which is filled with WATER. The bi-colorgage glass works on the simple optical principlethat a ray of light bends (or refracts) adifferent amount when it passes through steamthan when it passes through water.Each water gage is connected to the steamdrum through two cutout valves, one at the topand one at the bottom. The bottom cutout valveconnection contains a ball-check valve. Theball rests on a holder. As long as there is299

,PRINCIPLES OF NAVAL ENGINEERING— ..

Chapter U-ROTT.KR FTTTTNr.S AND PDNTROLSCOVER PLATEASBESTOS CUSASBESTOSGASKETFRAMECOVER PLATEFigure 11-27.— Construction of older type of water gage glass.38.238measured and transmitted to an indicatingdial.The Yarway superheater steam flow indicatorresponds to the difference between superheaterinlet pressure and superheater outletpressure as these two pressures act uponseparate columns or heads of water. The generalarrangement of the Yarway superheatersteam flow indicator is shown in figure 11-29.A constant water level is maintained in thetwo head chambers (reservoirs). Both headchambers are in one casting, but the upper headchamber is located slightly above the lowerhead chamber in order to provide a slightconstant pressure differential which serves tostabilize the zero reading. Steam from thesuperheater inlet is led to the upper headchamber, and steam from the superheater outletis led to the lower head chamber. Exposedpiping connects each head chamber with theindicating unit.The interior of the indicating unit is shownin figures 11-30 and 11-31. As may be seen,the water from the upper head chamber entersthe indicating unit on one side of the diaphragm,and the water from the lower head chamberenters on the other side. The pressure fromthe upper head chamber is greater than thepressure from the lower head chamber, so thediaphragm is moved accordingly. The diaphragmis connected by a pin linkage to a deflectionplate which moves in sensitive response tothe movement of the diaphragm.301

PRINCIPLES OF NAVAL ENGINEERINGI 1SEE ENLARGED VIEWFOR BELLEVILLESPRING ASSEMBLYCOVERSTUD BOLTSGLASSASBESTOS GASKETASBESTOS GASKETMICA GASKETJ^-*^*STAMPBRASS GASKETCENTERPLATEENLARGED VIEW OFBELLEVILLE SPRING ASSEMBLY(IN SETS OF SIX SPRINGS)COVER"PLACE THIS SIDENEXT TO WATERFigure 11-28.— Recent type of water gage glass.38.239A permanent horseshoe magnet is rigidlymounted on that side of the deflection platewhich is free to move. The poles of the magnetstraddle a tubular well in which a spiral-shapedstrip armature is mounted on jeweled bearings.A counterbalanced pointer is attached to the endof the armature mounting shaft.When the deflection plate moves in responseto variations in pressure, the magnet is madeto move along the axisof the well. As the magnetmoves the spiral-shaped armature rolls in orderto keep in alignment with the magnetic field betweenthe poles of the magnet. Thus a rotarymotion is imparted to the armature mountingshaft; and the rotation of the shaft causes thepointer to move. The pointer moves over abrightly illuminated vertical dial which is dividedinto green and red zones to represent safe andunsafe operating conditions.The Jerguson superheater steam flow indicator,shown schematically in figure 11-32,consists of three main parts: (1) a datumchamber assembly, (2) a valve manifold, and(3) an indicating unit.The Jerguson indicator is essentially amercury-filled manometer with a stainless steelfloat in one leg. As the pressure differentialbetween the superheater inlet and the superheateroutlet varies, the mercury level in theinstrument changes and thereby actuates theindicating pointer. The movement of the floatin the manometer is transmitted to the pointeron the scale by means of a magnetic couplingdrive. The coupling consists of an internalmagnetic armature on the end of the float shaftand an externalyoke with magnetically energizedarms. The yoke, forming a part of the pointersystem, pivots on precision bearings in order302

Chapter 11-BOILER FITTINGS AND CONTROLSCAP^«.HEAD CHAMBERSsuperheaterX ZsuperoutletAheaterSETTLING POTS INLETDRAIN VALVESCAP98.90Figure 11-29.— General arrangement of Yarwaysuperheater steam flow indicator.to maintain alignment with the internal armatureattached to the float shaft; thus the yoke pivotsas the armature moves up and down.The datum chamber is connected by pipingto the superheater inlet and outlet connectionsand thus provides the means for impressing differentialpressure on the instrument. As notedpreviously, the pressure difference betweensuperheater inlet and superheater outlet is usedas a measure of the rate of steam flow throughthe superheater.Remote Water Level IndicatorsRemote water level indicators are used onmost ships to provide a means whereby theboiler water level may be observed from thelower level of the fireroom. The two types ofremote water level indicators discussed hereare in common use on combatant ships; othertypes may be found on auxiliary ships.The Yarway remote water level indicatorconsists of three parts: (1) a constant-headchamber which is mounted on the steam drumat or near the vertical centerline of the drumhead;(2) a graduated indicator which is usuallymounted on an instrument panel; and (3) tworeference legs that connect the constant-headchamber to the indicator. The reference legsare marked A and B in figure 11-33, whichshows the general arrangement of a Yarwayremote water level indicator.A constant water level is maintained inleg A, since the water level in the constantheadchamber does not vary. The level in legB is free to fluctuate with changes in thesteam drum water level. The upper hemisphereof the constant-head chamber is connected tothe steam drum at a point above the highestwater level to be indicated; because of thisconnection, boiler pressure is exerted equallyupon the water in the two legs. The variableleg B is connected to the steam drum at a pointbelow the water level to be indicated; becauseof this connection, the water level in leg B isequalized with the water level in the steam drum.As may be seen in figure 11-33, each legis connected by piping to the indicator. In theindicator, the two columns of water terminateupon opposite sides of a diaphragm. The indicatingunit is almost identical with the indicatingunit of the Yarway superheater steamflow indicator, previously described.The general arrangement of a Jergusonremote water level indicator is shown in figure11-34, As may be seen, the operating principlesof this device are very similar to theoperating principles of the Jerguson steamflow indicator, previously discussed.Superheater Temperature AlarmsSuperheater temperature alarms are installedon most boilers to warn operating personnelof dangerously high temperatures in thesuperheater. One type of superheater temperaturealarm is shown in figure 11-35. The bulb.303

PRINCIPLES OF NAVAL ENGINEERINGVENT ORFILLING LINESCALIBRATIONADJUSTINGSCREWZEROADJUSTINGSCREWDEFLECTIONPLATEDIAPHRAGMPOINTERHUBSEALINGPLUGMAGNETPRESSURE FROMSUPERHEATEROUTLETPRESSURE FROMSUPERHEATERINLETFigure 11-30.— Cross section of Yarway indicating unit (front view).the capillary tube, and the spiral-shaped Bourdonelement are filled with mercury. As thetemperature rises, the mercury expands andcauses the Bourdon tube to move so that anattached cantilever arm is moved toward anelectric microswitch. When the temperaturereaches a predetermined point, the cantileverarm closes the microswitch, actuating a warninglight and a warning howler.Smoke IndicatorsNaval boilers are fitted with smoke indicators(sometimes called smoke periscopes)which permit visual observation of the gasesof combustion as they pass through the uptakes.Most single-furnace boilers have onesmoke indicator installed in the uptake. Doublefurnaceboilers have two smoke indicators,30498.91one for observing the combustion gases comingfrom the saturated side and the other for observingthe combustion gases coming from thesuperheater side.A smoke indicator is shown in figure 11-36.A light bulb is installed in a lamp unit at therear of the boiler. At the front of the boiler,in direct line of sight with the lamp, is a reflectorunit which reflects the image to asecond mirror. The second mirror is locatedso that it may be seen from the fireroom.Oil Drip Detector PeriscopesSome boilers are equipped with oil dripdetector periscopes which permit inspectionof the floor between the inner and outer boilercastings, to see if oil has accumulated there.

Chapter 11-BOILER FITTINGS AND CONTROLSDIAPHRAGM PRESSURE FROMSUPERHEATER INLETPINLINKAGECALIBRATIONADJUSTINGSCREWARMATUREWELLSEALING PLUGSFigure 11-31.— Cross section of Yarway indicating unit(plan view).98.92The oil drip detector periscope operates on muchthe same principle as the smoke periscope.Pressure and Temperature GagesBoiler operation requires constant awarenessof the pressures and temperatures existingat certain locations within the boiler and inassociated machinery and systems. Operatingpersonnel depend upon a variety of pressureand temperature gages to provide them with thenecessary information. Pressure gages are installedon or near each boiler to indicate steamdrum pressure, superheater outlet pressure,auxiliary steam pressure, auxiliary exhaustpressure, feed water pressure, steam pressureto the forced draft blowers, air pressure in thedouble castings, and fuel oil pressure. Temperaturegages are installed to indicate superheatedsteam temperature, desuperheated steam temperature(if the boiler has a desuperheater),feed water temperature at the economizer inletand outlet, fuel oil temperature at the fuel oilmanifold before the boiler, and— in some shipsuptaketemperature.In some firerooms, the gages that indicatesteam drum pressure, superheater outletpressure, superheater outlet temperature, andcombustion air pressure are installed on theboiler front. As a rule, however, the indicatingunits of all pressure gages are mounted on aboiler gage board which is easily visible fromthe firing aisle. Distant-reading thermometersare also installed with the indicating unit mountedon the boiler gage board. In some installations,a common gage board is used for all the boilersin one space, instead of having separate gageboards for each boiler.Most of the pressure gages used in connectionwith boilers are of the Bourdon-tubetype, although some diaphragm-type gages andsome manometers are also used in the fireroom.The temperature gauges most commonlyused in the fireroom are direct- reading liquidin-glassthermometers and distant-readingBourdon-tube thermometers. The basic operatingprinciples of these pressure and temperaturegages are discussed in chapter 7 of this text,Single-Element Feed Water RegulatorsSingle-element automatic feed water regulatorsare installed on many boilers which arenot equipped with complete automatic feed waterand combustion control systems. Single-elementregulators, unlike the multi-element control305

PRINCIPLES OF NAVAL ENGINEERINGCONDENSATERETURN LINESSUPERHEATEROUTLETFigure 11-32.— Jerguson superheater steam flow indicator.98.96systems, are controlled by one variable only—namely, the water level variation in the steamdrum. Hence single-element regulators are notable to compensate for swell and shrink.Single-element regulators are intended primarilyfor keeping the boilers supplied withfeed water in battle or under other conditionswhen manual feeding of the boilers might becomedifficult or impossible. These regulatorsmust be cut in immediately when General Quartersis sounded. They may also be used atother times, and in fact should be used frequentlyenough to keep them in good workingorder and ready for use under emergency conditions.Single-element regulators can control thewater level within acceptable limits under relativelysteady steaming conditions, but not undersevere maneuvering conditions. Since completereliance cannot be placed on the single-elementregulator, a checkman must remain on stationand be ready to take manual control if necessarywhen the single-element regulator is in use inother than emergency conditions.A single-element automatic feed water regulatoris shown in figure 11-37. An inner tube,enclosed by a generator, is connected to theboiler steam drum through valves A. and B.Thus the water level in the inner tube is dependentupon the water level in the steam drum.306

-Chapter 11-BOILER FITTINGS AND CONTROLSBOILER CUTOUT VALVESthus increasing the pressure on the water inthe closed regulator system and expanding thebellows, which are normally compressed byspring pressure. Expansion of the bellows opensthe feed-regulating valve in the feed line andallows more water to flow to the boiler. Whenthe water level in the steam drum rises, thereverse process occurs and the feed-regulatingvalve tends to close.BOILER CONTROLSSETTLING POTS,WITH MAGNETSEQUALIZINGVALVE'INDICATORCUTOUT VALVES98.97Figure 11-33.— General arrangement of Yarwayremote water level indicator.Cooling fins attached to the pipe that carrieswater from the steam drum to the inner tubeensure that the water in the inner tube will beat a slightly lower temperature than the steamin the inner tube. Cooling fins on the generatorensure that the water and steam in the generatorwill be cooler than the water and steam in theinner tube. For a number of reasons, the transferof heat is more rapid from the steam inthe inner tube to the steam in the generatorthan it is from the water in the inner tube tothe water in the generator.As the water level in the steam drum drops,causing a corresponding drop in the water levelin the inner tube, more of the generator is exposedto the steam in the inner tube. This causesmore water in the generator to flash into steam,Automatic boiler controls consisting of independentcombustion control and feed watercontrol systems have been installed on a numberof naval ships. All indications point to anincreasing use of automatic controls, particularlyas boilers are designed for higher operatingpressures and temperatures. Many high pressureboilers require such rapid and sensitiveresponse to feed water, fuel, and combustionair demands that the use of automatic controlsis almost a necessity.The function of an automatic combustion controlsystem is to maintain the fuel input andthe combustion air input to the boiler in accordancewith the demand for steam and to proportionthe amount of air to the amount of fuel in sucha way as to provide maximum combustion efficiency.The feed water control system functionsto provide the required boiler feed andmaintain the steam drum water level at or nearnormal position (middle of the water gage glassat all steaming rates.An installed control system is quite oftensimpler in theory than one would suppose whenfirst viewing the complex assortment of componentsand tubing. To begin with, then, let uslook at the basic principles of automatic controland see how they apply to a very simple controlsystem.Any control system, simple or complex, mustperform four functions. It must:Measure something on the output side of aprocess;Compare the measured value with the desiredvalue;Compute the amount and direction of changerequired to bring the measured output valueback to the desired output value;Correct something on the input side of theprocess so that the output side of the processwill be brought back to the desired value.Measurement, comparison, computation, andcorrection—these are the basic operations307

^IPRINCIPLES OF NAVAL ENGINEERINGDATUMLEVEL TUBEHORIZONTAL RUN OFAT LEAST 2 FEETREOUIREDvIDATUM COLUMNSHUTOFF VALVE[XF^TOBOILERDATUMCOLUMNNWL MARKNORMAL WATERLEVELHORIZONTAL RUN OF ATLEAST 2 FEETREQUIRED,DATUM COLUMNSHUTOFF VALVE.TO BOILERTO WASTE C^GAGE SHUTOFF S. Y--J'VALVEJTO WASTEGAGE SHUTOFF VALVEEQUALIZING VALVESOLID FLOATMERCURYMAGNETIC FINGERSGAGEFigure 11-34.— Jerguson remote water level indicator.98.98performed by a control system. Taken together,they constitute a closed loop of action andcounteraction by which some quantity or conditionis measured and controlled. The closedcontrol loop is often called a feedback loop ,since it requires a feedback signal from somethingon the output side of the process to somethingon the input side of the process. The closedloop concept is illustrated in figure 11-38.Now let us examine a simple automatic controlsystem such as the one shown in figure 11-39. The process being controlled is a heatexchange process in which steam is used to heatcold water. The two inputs, steam and coldwater, produce one output— hot water at somedesired temperature. Such a process could becontrolled by various kinds of automatic controlsystems— electrical, hydraulic, pneumatic,308

Chapter 11-BOILER FITTINGS AND CONTROLSADJUSTER FORSETTING ALARMTEMPERATURE

PRINCIPLES OF NAVAL ENGINEERINGTOP SHUTOFF VALVEGENERATOR IKKER TUBEGENERATOR OUTER TUBECOPPER TUBE ENDAT GENERATORINNERTUBE COOLINGFINSFigure 11-37.— Single-element feed water regulator.38.184the position of the vane in a nozzle-and-vaneassembly located in the transmitter.A set point knob is linked in some way tothe nozzle of the nozzle-and-vane assembly, sothat the setting of the set point knob affects theposition of the nozzle. The set point knob ispositioned to represent the desired temperatureof the hot water output.The nozzle-and-vane assembly is the comparingand computing device in this pneumatictransmitter. Since the position of the Bourdontube affects the position of the vane and thesetting of the set point knob affects the positionof the nozzle, the distance between the nozzleand the vane at all times represents a comparisonof the actual measured value (Bourdon tube)and the desired value (set point knob). Thedistance between the tip of the nozzle and thevane is responsible for the computation of theamount and direction of change that must bemade in the position of the steam valve, since:(1) the rate of air flow from the nozzle dependsupon the distance between the nozzle andthe vane; and310

^—Chapter 11- BOILER FITTINGS AND CONTROLS

-PRINCIPLES OF NAVAL ENGINEERINGfCORRECTIONSTEAM INPUTSTEAMVALVE(FINALCONTROLELEMENT)— (CLOSED LOOP)COLD WATER INPUTTHE HEAT EXCHANGEPROCESSMEASUREMENT\VALVEMOTOROPERATOR

Chapter 11-BOILER FITTINGS AND CONTROLSappropriate loading pressures or control pressures;the air pressure suppliedfor this purposeis called supply pressure .It is not necessary to take up the operatingprinciples of the various pneumatic units, providedwe remember their basic function: todevelop, transmit, and receive pneumatic signalsin the form of variable air pressures. We shouldalso have some idea of the specific functionsserved by the various kinds of pneumatic unitslisted below.Transmitters . In general, a transmitter maybe defined as an instrument that produces a pneumaticsignal (in the form of variable air pressure)proportional to one of the basic variablesin the controlled process.Relays . A relay is a pneumatic device thatreceives one or more pneumatic signals, altersor combines signals in various ways, and producesan output signal which goes to one ormore other pneumatic units. There are severaldifferent kinds of relays: ratio relays, Standatrols,rate relays, selective relays, and limitingrelays. The specific functions of these units willbecome apparent later, as we trace the sequenceof events in the boiler control system.Control Drives . A power unit that mechanicallypositions valves or dampers in accordancewith the amount of control pressure receivedis called a control drive.Control Valve . A control valve is a valveused to control the flow of fluid in a line. Thecontrol valve is positioned by a control drivein accordance with control pressure. In otherwords, a control valve is the final controlelement.Selector Valves . A selector valve is a pneumaticinstrument that provides selection ofmanual or automatic control of the system componentsthat follow it. A selector valve alsoprovides a means for manual control of the system.Figure 11-40 shows the control relationshipsin the combustion control system and the feedwater control system. The relationship of themajor components is illustrated schematicallyin figure 11-41. Using this schematic diagramas a guide, we will trace the sequence of eventsin order to arrive at an understanding of thebasic control relationships. Notice that each unitin figure 11-41 is identified by a Bailey number(and in some cases by a name). The numbersand names are given in the legend for figure11-41 and are used in the following discussion.It is important to remember that a pneumaticunit may have more than one pneumaticsignal coming into it and that it may transmita penumatic signal to more than one unit. Indescribing the sequence of events, it is sometimesnecessary to ignore some signals whilefollowing others through to their final conclusion.But the system functions as a whole, not as aseries of isolated or separate events. Thismeans that a great many signals are beingtransmitted and received at any given timeand that a number of actions are taking placesimultaneously.Combusion Control System.— The combustioncontrol system maintains the energy input tothe boiler equal to the energy output by regulatingcombustion air flow and fuel flow sothat the main steam line pressure is maintainedat 1200 psig. In other words, the controlledvariable is steam pressure, the desiredvalue is 1200 psig, and the manipulated variablesare fuel flow and combustion air flow.Combustion air flow and fuel flow are readjustedin accordance with steam demand, asindicated by the measurement of steam flow.The actual measured steam flow thus providesthe system with an additional feedback signal.There are five initial signals in the combustioncontrol system: steam pressure, fuelsupply flow, fuel return flow, combustion airflow, and steam flow. Each of these variablesis measured, and pneumatic transmitters developloading pressures that correspond to themeasured values of the variables. The two fuelflow signals are combined in a fuel flow differentialrelay, as described later; in onesense, therefore, it is possible to say that thissystem has four basic signals instead of five.The combustion control system is set tomaintain the superheater outlet steam pressureat 1200 psig, with variations not exceeding±0.25 percent of the set pressure at all steamingrates. Steam pressure transmitters (Cla)measure steam pressure from the superheateroutlet of each of the two boilers and establishoutput loading pressure signals that are directlyproportional to the measured steam pressure.For the range of steam pressures being measured(900 to 1500 psig), the output loadingpressureof the steam pressure transmitter is 3 to27 psig; for the set steam pressure of 1200 psig,the steam pressure transmitter develops andtransmits a pneumatic loading pressure of 15psig. In other words, the loadingpressure variesdirectly with the applied steam pressure between313

PRINCIPLES OF NAVAL ENGINEERINGSTEAMPRESSURESTEAM FLOWAIR FLOWFUELBURNEDLOADDEMANDRELAYLIMITERAIRFLOWFUELFLOW1^STEAMFLOWDRUMWATERLEVEL\/ STEAM V(FLOW - FEE[?^WATER FLOWP"^UNBALANCE/1FEEDWATERFLOWFigure 11-40.— Control relationships, Bailey combustion control system andfeed water control system.98. 108:. 109the minimum and the maximum points of therange.The output signal from each of the steampressure transmitters is applied to the steampressure selective relay (Clb). The selectiverelay selects and transmits the higher of thetwo signals to the steam demand relay (C4al).This relay is so adjusted that its output remainsconstant when the steam pressure is constant at1200 psig.While this is going on, steam flow from eachboiler is being measured by steam flow transmitters(F2). The steam flow transmitters measurethe pressure drop across a restriction in thesteam line and extract the square root of thispressure drop. The output loading pressuresfrom the steam flow transmitters are proportionalto the square root of the pressuredrop— or, in other words, proportional to therate of flow. The output loading pressure of asteam flow transmitter ranges from 3 psig to27 psig as the steam flow ranges from minimumto maximum. The loading pressure from eachof the steam flow transmitters is applied to thesteam flow selective relay (F2b). The selectiverelay then transmits the higher of the two loadingpressures to the steam demand relay(C4al).The output steam demand signal from thesteam demand relay (C4al) passes through theboiler master selector valve (C5a). The boilermaster selector valve has no effect on the signalduring automatic operation. After passingthrough the boiler master selector valve, theoutput loading pressure from the steam demandrelay is applied to the combustion air Standatrol(C4b) and to the fuel limiting relay (C15).A measured combustion air flow signal is transmittedfrom the air flow transmitter (C3) throughthe excess air remote adjustable relay (C9),where the signal can be manually adjusted forexcess air requirements for low-load steaming,maneuvering, or soot blowing. The air flowsignal is then applied to the combustion airStandatrol (C4b).314

ITEM NO.LEGEND FOR FIGURE 11-41.

SUPERHEATEROUTLET PRESSUREGAGE:xxxxxxxxxxxxxxxxxxxxxx:FROM OTHERBOILERCIoSUPERHEATEROUTLETPRESSURETRANSMITTERSTO RECORDERRI FOR BOILER ADRUM WATER LEVELINDICATING TRANSMITTERELECTRICALCONNECTIONS TOWATER LEVEL ALARMLIGHTS, FLAME FAILUREALARM, AND CONTROLAIR FAILURE ALARMIG5-IPRESSUREGAGESIG5-4CONTROL LINEDIRECT CONNECTIONxxxxxxxxxxx:AIR SUPPLY CONNECTION •-ELECTRICAL WIRINGNO 1 BLOWERDAMPER CONTROL DRIVENO 1 BLOWERSPEED CONTROL DRIVENO 2 BLOWERSPEED CONTROL DRIVENO 2 BLOWER DAMPERCONTROL DRIVEFigure 11-41.- Schematic diagrams ot Bailey combustion and feed water control system(Facing page 314).

Chapter 11-BOILER FITTINGS AND CONTROLSUnder steady boiler loads, the output ofthe combustion air Standatrol is steady at someValue which will maintain combustion air to thefurnace at the rate required to maintain thesuperheater outlet steam pressure at 1200 psig.For each boiler, the combustion air demandsignal from C4b is applied, through a bias relay(C15a) and a rate relay (C15b), to the two forceddraft blower selector valves (C5b),The bias relay acts to maintain the minimumair flow demand signal at a value consistent withminimum blower speed and damper position. Therate relay acts in combination with the bias relayto accelerate any changes in the input steamdemand signal by providing an exaggerated loadingpressure. The rate relay may also be adjustedto decrease the effects of changes in thesteam demand signal. The exaggerated signalof the rate relay is slowly returned to normalthrough the action of a bleed valve within therate relay.Each blower selector valve (C5b) transmitsa penumatic pressure through the 3-way airtrapping valves (C6a and C7a) to the blowerspeed control drive (C6) and to the blowerdamper control drive (C7). Note that the pneumaticpressure transmitted by the selector valveis control pressure rather than loading pressure,since it goes to a control drive. The controlpressure causes the blower speed control driveand the blower damper control drive to be positionedin accordance with the demand forcombustion air. The blower selector valves(C5b) are provided with bias control knobs whichcan be used to equalize the distribution of combustionair when both blowers are in operation.The 3-way air trapping valves (C6a andC7a)function to close the forced draft blower dampersto their mechanical bottom stops and to reduceblower speed to the minimum required for stablecombustion, in the event of loss of control airsupply.The output from the air flow transmitter(C3) is also applied to the fuel limiting relay(C15). The output of the fuel limiting relay,representing fuel demand, is applied to the fuelflow-air flow Standatrol (C4a2). In the fuel flowairflow Standatrol, the signal from the fuellimiting relay (C15) is balanced against a signalrepresenting the amount of fuel burned; this"fuel burned" signal comes to the fuel flow-air,flow Standatrol (C4a2) from the fuel flow differentialrelay (C2c). The output signal of thefuel flow-air flow Standatrol (C4a2) is appliedto the fuel control valve (C8) in the return fuelline from the burners. This control pressurefrom the Standatrol C4a2 positions the fuel controlvalve so that the required amount of fuel willbe burned in order to maintain steam pressure at1200 psig at the superheater outlet. Notice thatthe amount of fuel burned is controlled by limitingthe return flow of fuel; the supply pressurein the line to the burners is fixed.Thus, far, we have been considering the combustioncontrol system as it operates when thesteam demand (steam flow from the boiler) remainsconstant. Now let us see what happenswhen there is an increase in steam demand.For simplicity, the various changes that occurare presented as a numbered list. Remember,however, that some changes may be occurringat the same time as others.1. Steam flow increases, so there is anincreased steam flow signal from the steamflow transmitters (F2) to the steam demandrelay (C4al).2. Steam pressure drops below 1200 psig,so there is a decrease in the steam pressuresignals from the steam pressure transmitters(Cla).3. The steam demand relay (C4al) is connectedso that an increased signal from thesteam flow transmitter and a decreased signalfrom the steam pressure transmitter result inan increased output loadingpressurefrom C4al.This increased loading pressure from C4al goesto the combustion air Standatrol (C4b) and to thefuel limiting relay (C15).4. The increased loading pressure fromC4al to the combustion air Standatrol (C4b)causes an increase in the output loading pressurefrom the combustion air Standatrol; theultimate effect of this increase is to increasethe control pressure to the blower damper controldrives and to the blower speed controldrives. The blowers speed up and the dampersopen wider. Actually, during this period in whichthe unbalance is just beginning to be corrected,the blowers speed up enough to allow a temporary"overfiring" rate so that the steam pressure canquickly be restored to normal.5. As the blowers begin to pick up speed, themeasured air flow signal from the air flowtransmitter (C3) to the combustion air Standatrol(C4b) and to the fuel limiting relay (C15)also increases.6. In the fuel limiting relay, the fuel demandsignal is held back to a value whichcorresponds to the value of the measured air315

PRINCIPLES OF NAVAL ENGINEERINGflow signal. Even if the steam demand signalfrom C4al is higher than the measured air flowsignal from C3, the output of C15 cannot exceedthe air flow signal during the period in which thefiring rate is increasing.7. The output signal of the fuel limiting relay(C15) is applied to the fuel flow-air flowStandatrol (C4a2). The fuel control signal— thatis, the output of the fuel flow-air flow Standatrol—begins to increase, thus closing the fuelcontrol valve and increasing the fuel supply tothe burners. Since the rate of increase in fuelflow is caused by steam demand but limited bythe measured air flow, the system can neversupply too much fuel to the burners for theamount of combustion air being supplied.8. As the steam pressure at the superheateroutlet returns to the set pressure of 1200 psig,the steam pressure transmitter signal alsorises. Increasing signals from the steam pressuretransmitters result in a decreasing loadingpressure from the steam demand relay (C4al)and decreasing control signal from the combustionair Standatrol (C4b) to the forced draftblower and damper drives (C6 and C7, respectively).This reduces the temporary "overfiring"rate previously mentioned. When themeasured air flow signal from the air flowtransmitter (C3) reaches a value which returnsthe combustion air Standatrol to balance, theoutput pressure of C4b stabilizes at a valuewhich will maintain this air flow. The outputpressure of the fuel flow-air flow Standatrol(C4a2) stabilizes in a similar way to maintainthe same rate of fuel flow to the burners. Atthis time, the main line steam pressure hasreturned to 1200 psig and the air flow and fuelflow are adjusted so as to maintain this pressureunder the new (and higher) steam demandconditions.When there is a decrease in steam demand,the system functions to slow down the forceddraft blowers, partially close the blower dampers,and open the fuel control valve so that thesupply of fuel to the burners will be decreased.After seeing how the system operates when thesteam demand is constant and when the steamdemand is increasing, it should not be too difficultto trace the signals and events that occurwhen the steam demand is decreasing.Feed Water Control System.— While the combustioncontrol system is functioning to controlcombustion air and fuel, the feed water systemis functioning to control the amount of feedwater going to the boiler.There are three elements in the feed watercontrol system: steam flow, feed water flow, andboiler drum water level. The feed water flowtransmitter (Fl) and the steam flow transmitter(F2) act together to provide a proportioningcontrol— that is, to provide a flow of feed waterthat is proportional to the flow of steam. Thedrum water level indicating transmitter (F3a)introduces a secondary signal that continuouslyadjusts the position of the feed water flow controlvalve (F6a) in order to maintain the desiredwater level in the boiler steam drum.The feed water flow transmitter (Fl) developsa pneumatic signal that is proportionalto feed water flow. This signal is applied,through a volume chamber (Fla), to the steamflow-water flow differential relay (F4-1). Theother input to relay F4-1 is the output pressurefrom the steam flow transmitter (F2). The outputpressure from F2 is applied to F4-1 throughthe transient compensating relay (C4a3); underconditions of steady steam demand, the outputsignal of C4a3 exactly duplicates the outputsignal of the steam flow transmitter (F2), butwhen there is a change in steam demand theoutput signal of C4a3 is not the same as theoutput signal of F2.The output from the steam flow-water flowdifferential relay (F4-1) is applied to the feedwater Standatrol (F4-2), where it is balancedagainst a signal from the drum water levelindicating transmitter (F3a). When the two inputsto the feed water Standatrol (F4-2) are attheir set point values, a constant pneumaticoutput pressure is transmitted from the Standatrolthrough the feed water selector valve (F5)to the feed water flow control valve (F6a). Aspring adjustment in the feed water Standatrol(F4-2) maintains the steam drum water levelat a set height.When steam demand increases, there is aproportional increase in the loading pressureoutput of the steam flow transmitter (F2) whichis transmitted to the transient compensatingrelay (C4a3). At the compensating relay, thesignal is temporarily reversed— that is, the inputsignal representing an increase in steamflow becomes an output signal representing adecrease in steam flow. This output signal fromC4a3 is applied to the steam flow-water flowdifferential relay (F4-1), which also receivesan input signal from the feed water flow316

Chapter 11-BOILER FITTINGS AND CONTROLS

PRINCIPLES OF NAVAL ENGINEERINGtransmitter (Fl). The difference in the twosignals put into the differential relay (F4-1)causes a decreased output pressure to betransmitted from the differential relay to thefeed water Standatrol (F4-2). The feed waterStandatrol therefore sends a decreased signalthrough the feed water selector valve (F5) tothe feed water flow control valve, causingthe valve to begin to close.Let us examine this point more closely.The steam demand has increased but the feedwater flow control valve is closing . Why? Becauseit is necessary to compensate for swell—the momentary increase in the volume of thewater that occurs when the firing rate is increased.As swell occurs, the pneumatic signalfrom the drum water level indicating transmitter(F3a) increases. As a result, the outputpressure of the feed water Standatrol (F4-2)begins decreasing even more rapidly, closingdown on the feed water flow control valve (F6a)and further restricting the flow of feed waterto the boiler.As the feed water flow decreases, there isa proportional drop in the pneumatic pressurefrom the feed water flow transmitter. The effectsof this pressure decrease are felt slowly,however, because of the restricting action of thebleed valve in volume chamber Fla.As the steam drum water level begins todrop, there is a proportional decrease in thepneumatic pressure from the drum water levelindicating transmitter (F3a). At the same time,the bleed valve in volume chamber F2c is decreasingthe pneumatic signal between the steamflow transmitter (F2) and the transient compensatingrelay (C4a3) and increasing the pressurein another chamber of the compensating relay.The effect of this bleed valve action is to balancethe inputs to the two chambers of the compensatingrelay so that the compensating relay outputpressure is now equal to the pressure it is receivingfrom the steam flow transmitter. Inother words, the reversing action of the transientcompensating relay (C4a3) has been stopped,and the compensating relay is now transmittinga pneumatic signal that is exactly the same as thenew (and higher) steam flow signal it receives.The increased loading pressure from thetransient compensating relay (C4a3), togetherwith the decreased loading pressure from thefeed water flow transmitter (Fl), increases theoutput pressure of the steam flow-water flowdifferential relay (F4-1). The increased outputpressure of F4-1 reverses the action of the feedwater Standatrol (F4-2) and causes its outputto increase, thus opening the feed water flowcontrol valve wider and allowing more feedwater to flow to the boiler.When the feed water flow is equal to thesteam flow, and when the steam drum waterlevel has returned to normal, the systemstabilizes and the output of the feed waterStandatrol (F4-2) stays at the higher valuewhich will maintain the new and higher rateof feed water flow.A similar (but of course reversed) seriesof events occurs when there is a decrease insteam demand. The first effect of the decreasedsteam demand is a wider opening ofthe feed water flow control valve to compensatefor shrink— that is, the decrease in thevolume of the boiler water that occurs whenthe firing rate is reduced. The final effect isa smaller opening of the feed water flow controlvalve and a reduced flow of feed water tothe boiler.MaintenanceTo ensure trouble-free operation of thecontrol system, it is important that the systembe properly maintained and calibrated atall times. Maintenance and calibration shouldbe conducted in accordance with the PlannedMaintenance Subsystem of the 3-M System.An example of maintenance actions and teststo be conducted on an Automatic Control Systemare shown in figure 11-42. Particularemphasis should also be placed on the use ofmaintenance, repair, calibration proceduresfound in the applicable manufacturer's technicalmanual. If each component is kept in a properlymaintained and adjusted condition, the need fora general overhaul or major recalibrationof thecontrol system will be minimized.NOTE: When checking the adjustments andcalibration of any component of the controlsystem the settings should not be changed exceptunder the supervision of "QUALIFIED"maintenance personnel. It is also extremelyimportant, when making adjustments to thecontrol system, that the person doing the workknow the effect adjustments have on the operationof the entire control system. In otherwords only "QUALIFIED" personnel should beallowed to perform maintenance, repair, andcalibration of any automatic control systemcomponents.318

CHAPTER 12PROPULSION STEAM TURBINESIn beginning the study of steam turbines,the first point to be noted Is that we have nowreached the part of the thermodynamic cycleIn which the actual conversion of thermalenergy to mechanical energy takes place.We know by simple observation of pressuresand temperatures that the steam leavinga turbine has far less thermal energy than Ithad when It entered the turbine. By observa -tlon, again, we know that work Is performed asthe steam passes through the turbine, the workbeing evidenced by the turning of a shaft andthe movement of the ship through the water.Since we know that energy can be transformedbut can be neither created nor destroyed, thedecrease of thermal energy and the appearanceof work cannot be regarded as separate events.Rather, we must Infer that thermal energy ha,sbeen transformed Into work—that Is, mechanicalenergy In transition.Disregarding such Irreversible energylosses as those caused by friction and by heatflow to objects outside the system, It can beshown that two energy transformations are Involved.First, there Is the thermodynamicprocess by which thermal energy Is transformedInto mechanical kinetic energy as thesteam flows through one or more nozzles.Second, there Is the mechanical process bywhich mechanical kinetic energy Is transformedInto work as the steam Impinges upon projectingblades of the turbine, thereby turningthe turbine rotor.order to understand the process by whichInthermal energy is converted Into mechanicalkinetic energy, we must have some understandingof the process that takes place as steamflows through a nozzle. The second energytransformation, from kinetic energy to work,is best understood by considering some basicprinciples of turbine design.STEAM FLOW THROUGH NOZZLESThe basic purpose of a nozzle Is to convertthe thermal energy of the steam Intomechanical kinetic energy. Essentially, this Isaccomplished by shaping the nozzle In such away as to cause an Increase In the velocity ofthe steam as It expands from a high pressurearea to a low pressure area. The nozzle alsoserves to direct the steam so that it will flowIn the right direction to Impinge upon the turbineblades.Within certain limitations, the velocity ofsteam flow through any restricted channel suchas a nozzle depends upon the difference betweenthe pressure at the Inlet of the nozzleand the pressure at the region around the outletof the nozzle. Let us begin by assumingequal pressure at Inlet and outlet. No flowexists In this static condition. Now, if wemaintain the pressure at the inlet side butgradually reduce the pressure at the outletarea, the steam will begin to flow and Itsvelocity will Increase as the outlet pressureIs reduced. However, If we continue to reducethe outlet pressure, we will reach apoint at which the velocity of steam is equalto the velocity of sound in steam . At thispoint, a further reduction in pressure at theoutlet region will not produce any further increasein velocity at the entrance to the nozzle,nor will it produce any further IncreaseIn the rate of steam flow.The ratio of outlet pressure to Inlet pressureat which the acoustic velocity (also calledthe critical flow ) Is reached 'is known as theacoustic pressure ratio or the critical pressureratio. This ratio is about 0.55 for superheatedsteam. In other words, the velocity offlow through nozzles is a function of the pressuredifferential across the nozzle, and steamvelocity will increase as the outlet pressure319

PRINCIPL5S OF NAVAL ENGINEERINGdecreases (in relation to the inlet pressure).However, no further increase in steam velocitywill occur when the outlet pressureis reduced below 55 percent of the inlet pressure.When the pressure at the outlet area ofa nozzle is designed to be higher than thecritical pressure, a simple convergent (parallel-wall)nozzle may be used. In this type ofnozzle, shown in figure 12-1, the cross-sectionalarea at the outlet is the same as the crosssectionalarea at the throat. This type of nozzleis often referred to as a nonexpanding nozzlebecause no expansion of steam takes placebeyond the throat of the nozzle.INLETREGIONTHROATOUTLETREGION147.90Figure 12-1.— Simple convergent nozzle.When the pressure at the outlet area of anozzle is designed to be lower than the criticalpressure, a convergent-divergent nozzle is usedto control the turbulence that occurs whensteam expansion takes place below the criticalpressure ratio. In this type of nozzle, shownin figure 12-2, the cross-sectional area of thenozzle gradually increases from throat to outlet.The critical pressure is reached in thethroat of the nozzle, but the gradual expansionfrom throat to outlet allows the steam to emergefinally in a steady stream or jet. Becauseexpansion takes place from the throat to theoutlet, this type of nozzle is often called anexpanding nozzle.The decrease in thermal energy of thesteam passing through a nozzle must equalthe increase in kinetic energy (disregardingirreversible losses). The decrease in thermalenergy may be expressed in terms of enthalpyaswhere- h.hi enthalpy of the entering steam, in BTUper poundh2 = enthalpy of the steam leaving the nozzle,in BTU per poundINLETREGIONFigureTHROATOUTLETREGION147.9112-2.— Convergent-divergent nozzle.The kinetic energy of the steam jet leavingthe nozzle may be determined by using theequation for mechanical kinetic energy:whereKEWV^2gKE = mechanical kinetic energy, in footpoundsW = weight of the flowing substance, mpounds per secondV = velocity, in feet per secondg = acceleration due to gravity (32.2 feetper second)Since we have taken the enthalpy per poundof the entering and departing steam, let us assume1 pound of steam per second flowing fromthe nozzle. The kinetic energy of this pound ofsteam will then be expressed by320KEA2gwhere V2 is the velocity, in feet per second,of the steam leaving the nozzle. We may nowequate the expression for the decrease in thermalenergy and the expression for the increase inkinetic energy, Thus,64.4(hj - hg) (778) ft-lbSince 1 BTU is equal to 778 foot-pounds,we have multiplied the expression for the decreasein thermal energy by 778. This putsboth sides of the equation in terms of footpounds.The kinetic energy of the steam leaving thenozzle is directly proportional to the square of

Chapter 12- PROPULSION STEAM TURBINESthe velocity. By causing an increase in velocity,therefore, the nozzle causes an increase in thekinetic energy of the steam. Thus it is clearthat our last equation has actually describedthe purpose of a nozzle by equating the decreasein thermal energy with the increase in kineticenergy.BASIC PRINCIPLES OF TURBINE DESIGNIn essence, a turbine may be thought of asa bladed wheel or rotor that turns when a jetof steam from the nozzles impinges upon theblades. The basic parts of a turbine are therotor, which has blades projecting radiallyfrom its periphery^ a casing , in which therotor revolves; and nozzles, through whichthe steam is expanded and directed. As wehave seen, the conversion of thermal energyto mechanical kinetic energy occurs in thenozzles. The second energy conversion— thatis, the conversion of kinetic energy to workoccurson the blades.The basic distinction to be made betweentypes of turbines has to do with the manner inwhich the steam causes the turbine rotor tomove. When the rotor is moved by a directpush or "impulse" from the steam impingingupon the blades, the turbine is said to be animpulse turbine. When the rotor is moved by theforce of reaction, the turbine is said to be areaction turbine.Although the distinction between impulseturbines and reaction turbines in a useful one,and one which is followed in this text, it shouldnot be considered as an absolute distinction inreal turbines. An impulse turbine utilizes boththe impulse of the steam jet and, to a lesserextent, the reactive force that results when thecurved blades cause the steam to change direction.A reaction turbine is moved primarilyby reactive force, but some motion of the rotoris caused by the impact of the steam againstthe blades.Theory of Impulse TurbinesIn discussing the manner in which kineticenergy is converted to work on the turbineblades, it is necessary to consider both theabsolute velocity of the steam and the relativevelocity of the steam— that is, its velocityrelative to the moving blades. The followingsymbols will be used in the remainder of thisdiscussion:Vi = absolute velocity of steam at bladeentranceV2 = absolute velocity of steam at bladeexitR^ = relative velocity of steam at bladeentranceRg = relative velocity of steam at bladeexitVb = peripheral velocity of bladeLet us consider, first, a theoretical elementaryimpulse turbine such as the one shown infigure 12-3, The blades of this imaginary turbineare merely flat vanes or plates. As thesteam jet flows from the nozzle and impingesupon the vanes, the rotor is moved.Assuming that there is no friction as thesteam flows across the blade, Rl must beequal to Vj^ -Vb and R2 must also be equalto Vi - Vb, since theoretically there is nochange in velocity as the steam flows acrossthe blade.It will be apparent that, in order to convertall of the kinetic energy into work, it would benecessary to design a blade from which thesteam would exit with zero absolute veolcity.This blade would be curved in the mannershown in figure 12-4, and the jet of steam wouldenter the blade tangentially rather than at anangle. As we shall see, the shape of this bladevery closely approximates the shape of theblades used in actual impulse turbines; in areal turbine, however, the steam enters theblade at an angle, rather than tangentially.When this curved blade is used, the directionof the steam is exactly reversed. Therelative velocity of the steam at the bladeentrance, Ri, is again Vi - Vb and R2 isagain Vj _ Vb. Since the direction of flow isreversed, however, absolute velocity of thesteam at blade exit is nowV2 = (Vl - Vb)= Vi - 2Vx,As previously noted, the absolute velocityof the departing steam (V2) should ideally bezero. Therefore, by transposition of the aboveequation,2Vv321

PRINCIPLES OF NAVAL ENGINEERINGIn other words, maximum work is obtainedfrom a reversing blade when the blade velocityis exactly one-half the absolute velocity of thesteam at the blade entrance.^ The maximumamount of work obtainable from a reversingblade is twice the amount obtainable from theflat vane shown in figure 12-3.In actual turbines, it is not feasible toutilize the complete reversal of steam in theblades, since to do so would require that thenozzle be placed in a position that would alsobe swept by the blades— an obvious impossibility.Furthermore, if the steam enteredthe blade tangent ially it would not be carriedthrough the turbine axially (longitudinally). However,it is only the tangential component of thesteam velocity that produces work on the turbineblades; hence the nozzle angle is made assmall as possible.As we know, the work done on the blade mustequal the total energy entering minus the totalenergy leaving. The velocity diagram for animpulse turbine shown in figure 12-5 providesa way of determining the work done on theblade in terms of the various velocities andangles.The tangential component (which is the onlycomponent that produces work) of the velocityof the entering steam isVj cos awhich is also equal toVb + Ri cos bThe tangential component of the velocity ofthe departing steam isfrom Vj^ cos a, the resultant velocity may beexpressed asor, alternatively, asVj^ cos a - V2 cos cRj cos b + R2 cos dAssuming a steam flow of W pounds persecond,andWWmass per secondforceTherefore, the force on the blade isWF, = — (Ri cos b + R2 cos d) pounds__W(Yj^ pQg 3 _y^ cos c) poundsWork is force through distance. Therefore,the rate of doing work on the blade isWkb =FfaVb= W(R^ c°^b+R2 cos d) Vjj foot-pounds^ per second= g-^'^icos a - V2 cos c) Vjj footpoundsper secondwhich isV2 cos calso equal toVjj - R2 cos dNOZZLE V,"steam jetSince entering and leaving velocities areopposed to each other if V2 cos c is in the samedirection as V^ cos a, and supplementary toeach other if V2 cos c is in the opposite directionThis statement assumes, of course, that the nozzleIs tangential to the blades. In actual impulse turbines,the maximum amount of work is done when the bladespeed is one-half the cosine of the nozzle angle timesthe absolute velocity of the entering steam.BLADES147.92Figure 12-3.—Elementary impulse turbine.322

Chapter 12-PROPULSION STEAM TURBINESThe rate of doing work on the blade mayalso be derived from consideration of thethermal energy and kinetic energy enteringthe system and leaving the system. Althoughthe actual derivations are not given here, itmay be of interest to note the relationshipsexpressed in the following equations:2 2W(Vi - V2)Wk = W (hi - h2) + 50, 000"discovered" by Newton, it is interesting tonote that the first reaction turbine— and, indeed,perhaps the first steam engine of anykind ever made—was developed by the Greekmathematician Hero about 2000 years ago.This turbine, shown in figure 12-8, consistedof a hollow sphere which carried four bentnozzles. The sphere was free to rotate on thetubes that carried steam from the boiler, below,to the sphere. As the steam flowed outandBtu per second^^ri, - W(Ri - R^ + RJ W(V? - v|)b 50, 000Btu per secondThe pressure and velocity changes that occurin the nozzle and in the blades of an impulseturbine are shown in figure 12-6. As may beseen, the pressure is the same at the entranceand at the exit of the blade; the only pressuredrop occurs in the nozzle. Figure 12-7 showsa section of an impulse turbine rotor, with theblades in place.Theory of Reaction TurbinesReaction turbines, as their name implies,are moved by reactive force rather than by adirect push or impulse. Although we commonlythink of reactive force as having beenNOZZLE147.94Figure 12-5.— Velocity diagram for impulseblading.through the nozzles, the sphere rotated rapidlyin a direction opposite to the direction of steamflow.Reaction turbines used in modern timesutilize the reactive force of the steam in quitea different way. In a modern reaction turbine,there are no nozzles as such. Instead, the bladesthat project radially from the periphery of therotor are formed and mounted in such a waythat the spaces between the blades have, in crosssection, the shape of nozzles. 2 Since theseBLADE;:^«- V5147.93Figure 12-4.— Curved impulse blade.The distinction between actual nozzles and the bladingwhich serves the purpose of nozzles in reaction turbinesis mechanical rather than functional. The previousdiscussion of steam flow through nozzles appliesequally well to steam flow through thenozzle-shaped spaces between the blades of reactionturbines.323

PRINCIPLES OF NAVAL ENGINEERINGblades are mounted on the revolving rotor,they are called moving blades .Fixed or stationary blades of the same shapeas the moving blades are fastened to the casingin which the rotor revolves; these fixed bladesare installed between successive rows of themoving blades. The fixed blades guide thesteam into the moving blade system and, sincethey are also shaped and mounted in such away as to provide nozzle- shaped spaces betweenthe blades, the fixed blades also act asnozzles. The general arrangement of the fixedand moving blades, together with the pressureand absolute velocity relationships in a reactionturbine, are shown in figure 12-9. Figure 12-10shows a section of a reaction turbine rotor withone row of moving blades and one row of fixedblades.A reaction turbine is moved by three mainforces: (1) the reactive force produced on themoving blades as the steam increases in velocityas it expands through the nozzle- shapedspaces between the blades; (2) the reactiveforce produced on the moving blades when thesteam changes direction; and (3) the push or"impulse" of the steam impinging upon theblades. Thus, as previously noted, a reactionturbine is moved primarily by reactive forcebut also to some extent by direct impulse.From what we have already learned aboutthe function of nozzles, it will be apparent thatthermal energy is converted into mechanicalkinetic energy in the blading of a reactionturbine. The second required energy transformation—thatis, from kinetic energy to work—also occurs in the blading. A velocity diagramsuch as was used to analyze the work done onimpulse blading may be similarly used to analyzethe work done on reaction blading; however, theangles and velocities are different in the twotypes of blading.Since the velocity of the steam is increasedin the expansion through the moving blades, theinitial velocity of the entering steam (V^) mustbe lower in a reaction turbine than it would bein an impulse turbine with the same blade speed(V^); or, alternatively, the reaction turbine mustrun at a higher speed than a comparable impulseturbine in order to operate at approximatelythe same efficiency.TURBINE CLASSIFICATIONAs we have seen, turbines are divided intotwo general groups or classes— impulse turbinesand reaction turbines— according to the way inwhich the steam causes the rotor to move.Turbines may be further classified accordingto (1) the manner of staging and compounding,and (2) the mode of steam flow through theturbine.Staging and CompoundingPRESSUREABSOLUTEVELOCITYNOZZLE-^BLADES38.76XFigure 12-6. — Nozzle position and pressurevelocityrelationships in an impulse turbine.Thus far in this chapter, we have more orless assumed that an impulse turbine had oneset of nozzles and one row of blading on therotor, and that a reaction turbine had one rowof fixed blades and one row of moving blades.In reality, however, propulsion steam turbinesare not this simple. Instead, they use severalrows of blading, arranged in various ways.It has been shown that the amount of thermalenergy which can be utilized in a turbinedepends upon the relationship between the velocityof the entering steam (Vi) and the bladespeed (Vb). It might seem reasonable, therefore,to think that the work output of the turbinecould only be increased by increasingVi and Vb in the proper ratio. However,mechanical considerations and problems concerningstrength of materials impose certainlimits on blade speed. In modern naval ships,the amount of available energy per pound ofsteam is so great that there is no practicableway of utilizing the major portion of it in onerow of blades. When several rows of blades are324

Chapter 12- PROPULSION STEAM TURBINESBLADES-ROTOR147.95XFigure 12-7.—Section of impulse turbine rotor(with blades).used, the steam passes through one row afteranother, and each row uses part of the energyof the steam.IMPULSE STAGE.- In an impulse turbine, astage is defined as one set of nozzles and thesucceeding row or rows of moving and fixedblades. Since the only place a pressure dropoccurs in an impulse turbine is in the nozzles,another way of defining an impulse stage is tosay that it includes the nozzles and blading inwhich only one pressure drop takes place. Asimple impulse stage is often called a Rateaustage . Turbines consisting of a single Rateaustage (fig. 12-11) are not used as propulsionturbines but are frequently used to drive smallauxiliary units.REACTION STAGE. -In reaction turbines,one row of fixed blades and its succeeding rowof moving blades are taken as constituting onestage. Since the fixed blades in a reactionturbine are comparable to the nozzles in animpulse turbine, this definition of a reactionstage may seem very similar to the definitionof an impulse stage. However, there is this139.23Figure 12-8.— Hero's steam turbine.important difference: a reaction stage includestwo pressure drops, whereas an impulse stageincludes only one.VELOCITY-COMPOUNDED IMPULSE TUR-BINE.— One way of increasing the efficiency ofan impulse turbine is by velocity-compounding—that is, by adding one or more rows of movingblades to the rotor. 3 Figure 12-12 showsan impulse turbine that has two rows of movingblades on the rotor. This type of turbine iscalled velocity-compounded because the residualvelocity of the steam leaving the first row ofmoving blades is utilized in the second row ofmoving blades. If a third row is added, thevelocity of the steam leaving the second rowis utilized in the third row. The fixed blades,Velocity-compounding can also be achieved when onlyone row of moving blades is used, provided the steamis directed in such a way that it passes through theblades more than once. This point is discussed inmore detail in chapter 16 of this text, in connectionwith helical-flow auxiliary turbines.325

PRINCIPLES OF NAVAL ENGINEERINGFIXEDBLADESENTERINGSTEAMPRESSUREVELOCITY38.77. 2XFigure 12-9.— Arrangement of fixed and movingblades and pressure-velocity relationships ina reaction turbine.which are fastened to the casing rather thanto the rotor, serve to direct the steam fromone row of moving blades to another.As may be seen in figure 12-12, the velocitycompoundedimpulse turbine has only one pressuredrop and therefore, by definition, onlyone stage. This type of velocity- compoundedimpulse stage is usually called a Curtis stage.PRESSURE-COMPOUNDED IMPULSE TUR-BINE,— Another way to increase the efficiencyof an impulse turbine is to arrange two or moresimple impulse stages in one casing. The casingis internally divided by nozzle diaphragms. Thesteam leaving the first stage is expanded againthrough the first nozzle diaphragm, to the secondstage; from the second nozzle diaphragm,to the third stage; and so on. This type of turbineis known as a pressure- compounded turbinebecause a pressure drop occurs in eachstage. Figure 12-13 shows a pressure-compoundedimpulse turbine with four stages. Apressure- compounded impulse turbine is frequentlycalled a Rateau turbine, since it is essentiallya series of simple impulse (Rateau)stages arranged in sequence in one casing.PRESSURE-VELOCITY-COMPOUNDED IM-PULSE TURBINE. -An impulse turbine whichconsists of one velocity-compounded (Curtis)stage followed by a series of pressure-ROTORMOVING BLADES38.771XFigure 12-10.— Section of reaction turbine rotor,showing fixed and moving blades.compounded (Rateau) stages is generally referredto as a pressure-velocity-compoundedimpulse turbine. Turbines of this type arecommonly used in the propulsion plants ofnaval ships.PRESSURE - COMPOUNDED REACTIONTURBINE. -Because the ideal blade speed in areaction turbine is so high in relation to thevelocity of the entering steam (V^), all reactionturbines arepressure-compounded— thatis, theyare so arranged that the pressure drop frominlet to exhaust is divided into many steps bymeans of alternate rows of fixed and movingblades. The pressure drop in each set offixed and moving blades (i.e., in each stage) istherefore small, thus causing a lowered steamvelocity in all stages and consequently a loweredideal blade velocity for the turbine as a whole.COMBINATION IMPULSE AND REACTIONTURBINE.—A combination impulse and reactionturbine employs a velocity-compounded impulse326

-Chapter 12- PROPULSION STEAM TURBINES(Curtis) stage at the high pressure end of theturbine, followed by impulse staging and thenby reaction blading. The impulse blading effectslarge pressure and temperature drops in thebeginning, with a high initial utilization ofthermal energy. The reaction blading is moreefficient at the low pressure end of the turbine.Hence the combination impulse and reactionturbine is a highly efficient machine that utilizesthe advantages of both impulse and reactionblading. Combination impulse and reaction turbinesare very commonly used as propulsionturbines.NOZZIEMode of Steam FlowTurbines may be further classified accordingto the manner in which steam flows throughthe turbine. The three aspects of steam flowconsidered here are (1) the direction of flow,(2) the repetition of flow, and (3) the division offlow.DIRECTION OF STEAM FLOW.-The directionof steam flow through a turbine may beaxial, radial, or helical. In general, the directionof flow is determined by the relative positionsof nozzles, diaphragms, moving blades,and fixed blades.Most turbines are of the axial flow type— thatthe steam flows in a direction approximatelyis,parallel to the long axis of the turbine shaft.As we have seen, the blades in an axial-flowturbine project outward from the periphery ofthe rotor.In a radial-flow turbine, the blades aremounted on the side of the rotor near theperiphery. The steam enters in such a waythat it flows radially toward the long axis ofthe shaft. Radial flow is not used for propulsionturbines, but is used for some auxiliaryturbines.In a helical-flow turbine, the steam entersat a tangent to the periphery of the rotor andimpinges upon the moving blades. The bladesare shaped in such a way that the direction ofsteam flow is reversed in each blade. Helicalflow is not used for propulsion turbines, but isused for some auxiliary turbines.REPETITION OF STEAM FLOW. -Turbinesare classified as single-entry turbines or reentryturbines, depending on the number oftimes the steam enters the blades. If the steam38.78XFigure 12-11.— Simple impulse turbine(Rateau stage).passes through the blades only once, the turbineis called a single-entry turbine. All multistageturbines are of the single-entry type.Re-entry turbines are those in which thesteam passes more than once through the blades.Re-entry turbines are used to drive some pumpsand forced draft blowers, but are not used aspropulsion units,DIVISION OF STEAM FLOW. -Turbines areclassified as single-flow or double-flow, dependingupon whether the steam flows in one directionor two. In a single-flow turbine, the steamenters at the inlet or throttle end, flows oncethrough the blading in a more or less axialdirection, and emerges at the exhaust end ofthe turbine. A double-flow turbine consistsessentially of two single-flow units mounted onone shaft, in the same casing. The steam entersat the center, between the two units, and flowsfrom the center toward each end of the shaft.The main advantages of the double-flow arrangementare (1) the blades can be shorter thanthey would have to be in a single-flow turbineof equal capacity, and (2) axial thrust is avoidedby having the steam flow in opposite directions.This second point applies primarily to reactionturbines, since impulse turbines develop relativelylittle axial thrust in any case.The turbines shown in figures 12-11, 12-12,and 12-13 are single-flow turbines. A doubleflow reaction turbine of the type used as the lowpressure turbine in some propulsion plants isshown in figure 12-14.327

PRINCIPLES OF NAVAL ENGINEERINGarrangement results in minimum stresses inthe I-beam over the complete range of turbineexpansion. The fixed end of the turbine is aft,so the motion resulting from expansion cannotbe transmitted to the reduction gears, wheredistortion and serious damage would occur ifthe after end of the turbine were free to move.Steam lines connected to the turbines arecurved, as shown in figure 12-15, to allow forexpansion of the steam line and avoid unacceptablestrains on turbine casings that couldcause distortion or misalignment.Turbine Casings38.79XFigure 12-12.— Velocity-compounded impulseturbine (one Curtis stage).TURBINE COMPONENTSAND ACCESSORIESPropulsion turbine components and accessoriesinclude foundations, casings, nozzles (orthe equivalent stationary blading), nozzle diaphragms,rotors, blades, bearings, shaft glands,gland seals, oil seal rings, dummy pistons andcylinders (on some reaction turbines), flexiblecouplings, reduction gears, lubrication systems,and turning gears.Turbine FoundationsFoundations for propulsion turbines are builtup from strength members of the hull so as toprovide a rigid supporting base. The after endof the turbine is secured rigidly to the structuralfoundation. The forward end of the turbineis secured in such a way as to allow a slightfreedom of axial movement which allows theturbine to expand and contract slightly withtemperature changes.The freedom of movement at the forwardend is accomplished by one of the two methods.Elongated bolt holes or grooved sliding seatsmay be used to permit the forward end to slideslightly fore-and-aft, as expansions and contractionoccur. Or the forward end may besecured to a deep flexible I-beam (fig. 12-15)installed with its longitudinal axis lying athwartship.When the turbine is cold, this I-beam isdeflected slightly aft from the vertical position.When the turbine is operating at maximumpower, the I-beam is deflected forward. ThisCasings for propulsion turbines are dividedhorizontally to permit access for inspection andrepair. Flanged joints on casings are accuratelymachined to make a steamtight metal-to-metalfit, and the flanges are bolted together. Somehigh pressure turbine casings are also splitvertically to facilitate manufacture, particularlywhen different alloys are used for the hightemperature inlet end and the lower temperatureexhaust end. However, these vertical joints arenever unbolted and they are usually seal welded.Each casing has a steam chest to receive theincoming steam and deliver it to the first-stagenozzles or blades. An exhaust chamber receivesthe steam from the last row of moving bladesand delivers it to the exhaust connection. Openingsin the casing include drain connections,steam bypass connections, and openings forpressure gages, thermometers, and reliefvalves.NozzlesAs previously discussed, the function of anozzle is to convert the thermal energy of thesteam into mechanical kinetic energy. Its secondaryfunction is to direct the steam to theturbine blades. Some turbines have a full arcadmission of steam; in this case, the firststage nozzles extend around the entire circleof the first row of blades. Other turbines havepartial arc admission; in this case, only asection of the blade circle is covered by thenozzles. In general, the arrangement of nozzlesin any turbine depends upon the range of powerrequirements and upon a number of designfactors.A nozzle is essentially an opening or apassageway for the steam. When we speakof nozzle construction or arrangement,328

Chapter 12- PROPULSION STEAM TURBINEStherefore, we are actually concerned with theconstruction or arrangement of the nozzleblocks in which the openings occur. In mostmodern turbines, the nozzle blocks are arrangedso that the nozzle openings occur ingroups, with each group being controlled bya separate nozzle control valve. The quantityof steam delivered to the first stage of theturbine is thus a function of the number ofnozzles in use and the pressure differentialacross the nozzles.On some auxiliary ships, hand controllednozzle valves are used in conjunction with athrottle valve to admit steam to the turbine.Any throttling of the inlet steam will reduceefficiency. To avoid throttling losses, all nozzlecontrol valves in use are opened fully beforeany additional valve is opened. Minor variationsin speed within any one nozzle control valvecombination are taken care of by the throttle.On modern combatant ships, the nozzle controlvalve arrangement shown in figure 12-16is employed. The throttle valve is omitted andsteam enters the turbine through nozzle controlvalves. Speed control is effected by varyingthe number of nozzle valves that are opened.The variation in the number of nozzle valvesis accomplished through the operation of alifting beam mechanism. The lifting beam mechanismconsists of a steel beam drilled withholes which fit over the nozzle valve stems.The valve stems are of varying lengths andare fitted with shoulders at the upper ends.When the beam is lowered, all valves restupon their seats. When the beam is raised.NOZZLES38.80XFigure 12-13.— Pressure-compoundedimpulse turbine (Rateau turbine).the valves open in succession, depending upontheir stem length— the shorter ones open first,then the longer ones.Nozzle DiaphragmsNozzle diaphragms are installed as part ofeach stage of a pressure- compounded impulseturbine. The diaphragm serves to hold thenozzles of the stage. Figure 12-17 shows atypical nozzle diaphragm. The nozzle walls aremachined, ground, and polished. The nozzles arefitted into a steel plate inner ring. An outerring fits over the outside of the nozzles. Theentire assembly is then welded together. Inorder to seal against steam leakage, labyrinthpacking (discussed later in this chapter) isused between the inner bore of the diaphragmand the rotor.Turbine RotorsThe turbine rotor carries the moving bladeswhich receive the steam. In some older turbines,the rotors were forged separately, machined,shrunk or pressed onto the shaft, and keyed tothe shaft. In most modern turbines, particularlylarge ones such as those used for ship propulsion,the rotors are forged integrally withthe shaft. Figure 12-18 shows an integrallyforged turbine rotor to which the blades havenot yet been attached.Turbine BladesThe purpose and function of turbine bladinghas already been discussed. At this point, it ismerely necessary to note that the moving bladesare fastened securely and rigidly to the turbinerotor. Figure 12-19 shows several ways offastening blades to the turbine rotor wheels.Turbine BearingsTurbine rotors are supported and kept inposition by bea rings .^ The bearings whichserve to maintain the correct radial clearancebetween the rotor and the casing are calledradial bearings. Those which serve to limitthe axial (longitudinal) movement of the rotorare called thrust bearings.Propulsion turbines have one radial bearingon each end of the rotor. These bearings are ofthe type generally known as journal bearings orsleeve bearings. The two metallic surfaces areBearings are discussed in chapter 5 of this text.329

5PRINCIPLES OF NAVAL ENGINEERINGASTERN STEAM INLETAHEAD STEAM FROMH.P. TURBINEASTERN STEAM INLETASTERNNOZZLEBLOCKFigure 12-14.— Double-flow reaction turbine.47,8Xseparated only by a fluid film of oil. Theeffectiveness of oil-film lubrication dependsupon a number of factors, including propertiesof the lubricant (cohesion, adhesion, viscosity,temperature, etc.) and the clearances, alignment,and surface condition of the bearing andthe journal. Except for the momentary metalto-metalcontact when the turbine is started,the metallic surfaces of the bearing and thejournal are constantly separated by a thin filmof oil.As previously noted, impulse turbines do not,in theory, develop end thrust. In reality, however,a small amount of end thrust is developedwhich must be absorbed in some way. Kingsburyor pivoted-shoe thrust bearings are usually usedon propulsion turbines.Shaft GlandsShaft glands are used to minimize steamleakage from the turbine casing (or air leakageinto the casing) at the points where the shaftextends through the casing. Two types of packing,carbon packing and labyrinth packing, are usedin shaft glands.Carbon packing is suitable only for relativelylow pressures and temperatures. When bothtypes of packing are used in one gland, therefore,as shown in figure 12-20, the labyrinthpacking is used at the initial high pressurearea and the carbon packing is used at thelower pressure area. Since most modem shipsutilize relatively high pressures and temperatures,most modern propulsion turbines areonly labyrinth packing.Labyrinth packing consists of rows of metallicstrips or fins. These strips are fastenedto the gland liner in such a way as to make avery small clearance between the strips and theshaft. As the steam from the turbine leaksthrough the small spaces between the packingstrips and the shaft, the steam pressure isgradually reduced.Where carbon packing rings are used, theyrestrict the passage of steam along the shaftin much the same manner as do the labyrinthpacking strips. Carbon packing rings aremounted around the shaft and are held in placeby springs. As a rule, three or four carbonrings are used in each gland; each ring isfitted into a separate compartment of the glandhousing.Gland Sealing SystemsLubricants and the oil-film theory of lubrication arediscussed in chapter 6 of this text.On propulsion turbines, the shaft glandpacking is not sufficient to entirely stop the330

.Chapter 12- PROPULSION STEAM TURBINESCURVED STEAM LINEof the steam leaking through the shaft glandpacking may be slightly higher than the pressureof the gland sealing steam. When this situationprevails, it causes a reversal in the directionof flow of the gland sealing steam. At suchtimes, the gland seal line is closed and theexcess steam is led through gland leak-offconnections to a later stage of the turbine, tothe gland exhaust condenser, or to other glandsto be used as gland seal steam. In the illustration(fig. 12-20) the excess steam leaking pastthe labyrinth packing is being led back into theeighth and twelfth stages of the high pressureturbine.AFTDEEP FLEXIBLEI-BEAMf^^^'y^^FORWARD47.12XFigure 12-15.— Foundation forpropulsionturbineflow of steam out of the turbine or to entirelyprevent the flow of air into the turbine. Forthis reason, gland sealing steam^ is broughtinto the shaft gland in the manner shown infigure 12-20. In this illustration, the gland sealingsteam enters a space between the labyrinthpacking and the carbon packing. In more recentinstallations, the sealing steam enters betweenthe segments of the labyrinth packing. Thesealing steam enters at a pressure of about 2psig (17 psia). This pressure is, of course,slightly greater than the atmospheric pressurein the engineroom.When the pressure of the gland sealing steamis greater than the pressure inside the turbinecasing, the sealing steam flows both into thecasing and into a line leading to the gland exhaustcondenser,"^ excluding all air from theturbine in the process. When a high pressureturbine is operating at high speed, the pressureDummy Pistons and CylindersThe steam passing through a multistage impulseturbine does not impart any appreciableaxial thrust to the rotor, since the pressuredrop actually takes place in the nozzles. ^ in areaction turbine, however, considerable axialthrust does result from the drop in steam pressure,since a pressure drop occurs in themoving blades as well as in the stationaryblades.In single-flow reaction turbines, this axialthrust is partially counterbalanced by the use ofa dummy piston and cylinder arrangement suchas that shown in figure 12-21. Space "A" surroundsthe inlet area of the turbine rotor andis connected by an equalizing pipe to space "B"which surrounds the outlet area of the rotor.The shoulder on the rotor, shown in figure 12-21, is under full inlet steam pressure, whilethe corresponding area on the other side of thedummy piston is under exhaust pressure. Thisdifference in pressure causes a thrust towardthe high pressure end of the turbine whichpartially counterbalances the thrust in the oppositedirection caused by the pressure dropthrough the turbine.Dummy pistons and cylinders are not requiredin double-flow reaction turbines, sincethe axial thrust caused by the pressure differentialacross one-half of the turbine is counterbalancedby the equal and opposite axial thrustin the other half of the turbine.Gland seal and gland exhaust systems are discussedin chapter 9 of this text.The gland exhaust condenser is discussed in chapter13 of this text.An equalizing hole drilled axially through each rotorwheel also helps to minimize thrust in an impulseturbine.331

PRINCIPLES OF NAVAL ENGINEERINGSTEAMINLET^J^Figure 12-16.— Arrangement of nozzle control valves.147,96Flexible CouplingsPropulsion turbine shafts are connected tothe reduction gears by flexible couplings whichare designed to take care of very slight misalignmentbetween the two units. Flexible couplingsare discussed in chapter 5 of this text.Reduction GearsFigure 12-17.— Nozzle diaphragm.96.19Reduction gears for propulsion turbine installationsare described and illustrated inchapter 5 of this text. At this point, it is importantmerely to note that turbines must operateat relatively high speeds for maximum efficiency,while propellers must operate at lower speedsfor maximum efficiency. Reduction gears areused to allow both turbine and propeller to332

9Chapter 12- PROPULSION STEAM TURBINESMain lubricating oil systems are discussed inchapter 9 of this text; the theory of lubricationis discussed in chapter 6.Turning Gears47.1 5XFigure 12-18.— Integrally forged turbine rotor(without blades).All geared turbine installations are equippedwith a motor-driven jacking or turning gear.The unit is used for turning the turbine duringwarming-up and securing periods so that theturbine rotor will heat and cool evenly. Therotor of a hot turbine, or one that is in theprocess of being warmed up, will become bowedand distorted if left stationary for even a fewminutes. The turning gear is also used forturning the turbine in order to bring the reductiongear teeth into view for routine inspectionand for making the required daily jacking of themain turbines. The turning gear is mounted ontop of and at the after end of the reduction gearcasing, as shown in figure 12-22. The brakeshown in figure 12-22 is used when it is necessaryto lock the shaft after the shaft has beenstopped.STEAM TURBINE PROPULSION PLANTSINVERTEDCIRCUMFERENTIALDOVETAILPINE TREEDOVETAILSTRADDLE-TEE147.97Figure 12-19.— Methods of fastening blades toturbine rotor wheels.operateranges.withinLubrication Systemstheir most efficient rpmProper lubrication is essential for the operationof any rotating machinery. In particular,the bearings and the reduction gears of turbineinstallations must be well lubricated at all times.The two principal types of steam turbinepropulsion plants now in use on naval ships arethe geared turbine drive and the turboelectricdrive. Direct drive installations, once in commonuse, are now practically obsolete; however,it is possible that an occasional application fordirect drive could again develop in the future.CLASSIFICATION OF PROPULSIONTURBINE UNITSNaval propulsion turbines are classified asClass A, Class B, and Class C turbines accordingto the type ship for which they are designed.Class A turbines are designed for use in submarines.Class B turbines are designed forusein amphibious warfare ships, surface combatantships, mine warfare ships, and patrol ships.Class C turbines are designed for use in auxiliaryships.Naval propulsion turbines are also classifiedaccording to design features. The six majortypes are:Reduction .gears are not used in ships having turboelectricdrive. In these ships, speed reduction isaccomplished electrically.1. Type I (single-casing unit).— The Type Ipropulsion unit consists of one or more aheadelements, each contained in a separate casingand identified as a single-casing turbine. Each333

PRINCIPLES OF NAVAL ENGINEERING,S, Li.»,..,.S»Y'' '""""I "'"I'L . „,.»,,.. TO GLAND EXHAUSTFigure 12-20.— Turbine gland.47.19XEXHAUSTDUMMYCYLINDERDUMMYPISTONSPACE "b'-^ SPACE AFigure 12-21.—Dummy piston and cylinder arrangement.47. 5Xturbine delivers approximately equal power to areduction gear.2. Type II-A (straight-through unit).— TheType II-A propulsion unit is a two elementstraight-through unit, and consists of two aheadelements, known as a high pressure (HP) elementand a low pressure (LP) element. The HPand LP elements are contained in a separatecasing and are commonly known as the HP andLP turbines, respectively. The HP and LP turbinesdeliver power to a single shaft through agear train and are coupled separately to thereduction gear. Steam is admitted to the HPturbine and flows straight through the turbine334

CENTER OF WORMGEAR AND PINIONChapter 12- PROPULSION STEAM TURBINES

PRINCIPLES OF NAVAL ENGINEERINGSeries-parallel units are being used on some ofthe more recent naval combatant vessels, suchas DEs, DDs, and CVAs.6. Type IV (cruising geared and ventedunit).— The Type IV propulsion unit consists ofa crusing element, HP element, and LP elementeachcontained in a separate casing. The cruisingturbine is connected in tandem through acruising reduction gear to the forward end ofthe HP turbine. The cruisingturbine contributespower to the propeller shaft for powers up tothe most economical point of operation, and forhigher powers it is idled in a partial vacuumand supplied with cooling steam to prevent overheating.For cruising power, steam is admittedto the cruising turbine and then exhausted to theHP turbine inlet, and thence from the HP turbineexhaust into the LP turbine through a crossoverpipe. The arrangement of the HP and LPturbine is identical to the Type II units. It ispossible to disconnect the cruising turbine to allowfor repair. Once disconnected, the HP turbinemay be placed in service.All of these six types of propelling units containan astern element for backing or reversing.An astern element is located in each end of adouble flow LP turbine casingor canbe in eitherend of each single- casing turbine or single flowLP turbine.Figure 12-23 illustrates the flow of steamin a Type IV propulsion unit when the cruisingturbine is in use; figure 12-24 illustrates theflow of steam at higher rates of operation.Astern elements in noncombatant ships areusually velocity-compounded impulse stages(Curtis stages) mounted in the exhaust end ofthe ahead turbine. Astern elements in combatantships are velocity-compounded (Curtis)stages installed at each end of the low pressureturbine. Each astern element has its own steaminlet but the admission of steam to both elementsis controlled by one astern throttle. Theastern elements exhaust through the low pressureturbine exhaust chamber to the condenser.Figure 12-25 illustrates the flow of steam forastern operation in a Type IV propulsion unit.Figure 12-26 illustrates a typical highpressureturbine. This turbine has one velocitycompoundedimpulse stage followed by elevenpressure-compounded impulse stages; hence itis a pressure-velocity-compounded impulseturbine.A low pressure double-flow turbine is shownin figure 12-27. Note the astern elements.This particular lowpressure turbine is a straightstage; the remaining seven stages are pres-reaction turbine. In some ships, double-flowpressure- compounded impulse turbines are usedas low pressure turbines.A typical cruising turbine is shown in figure12-28. This is an eight-stage impulse turbine.The first stage is a velocity-compounded (Curtis)sure-compounded (Rateau) states. The turbineis therefore a pressure-velocity-compoundedimpulse turbine.Unlike the geared turbine propulsion plants,the turboelectric drive installations have a singleturbine unit for each shaft. Figure 12-29 showsthe general arrangement of a turboelectric propulsionunit. As may be seen, the plant includesa turbine, a main generator, a propulsion motor,a direct-current generator for supplying excitationcurrent to the generator and the propulsionmotor, and a propulsion control board.Although the speed reduction is brought aboutelectrically, rather than by the use of reductiongears, the speed reduction ratio between turbineand propeller in the turboelectric drive is approximatelythe same as it is in the gearedturbine drive.One of the outstanding differences betweenthe geared turbine drive and the turboelectricdrive is that the turboelectric drive does nothave an astern element. In the turboelectricdrive, the direction of rotation of the propulsionmotor controls the direction of rotation of thepropeller. Hence there is no need to reverseturbine rotation for astern operation.PLANT OPERATIONOperating a ship's propulsion plant requiressound administrative procedures and the cooperationof all engineering departmental personnel.The reliability and the economical operationof the plant is vital to the ship's operationalreadiness.A ship must be capable of performing anyduty for which it was designed, A ship is consideredreliable when it meets all scheduledoperations and is in a position to accept unscheduledtasks. In order to do this, the ship'smachinery must be kept in good condition sothat the various units will operate as designed.In order to obtain economy, the engineeringplant, while meeting prescribed requirements,must be operated so as to use a minimumamount of fuel. The fuel performance ratiosare good overall indications of the conditionof the engineering plant and the efficiency of336

IChapter 12- PROPULSION STEAM TURBINESHIGHPRESSUREVALVES2HIGH PRESSURE STEAMV////A INTERMEDIATE PRESSURE STEAMLOW PRESSURE STEAMEXHAUST STEAMFigure 12-23,— Flow of steam in Type IV propulsionunit (cruising turbine in use).147.98the operating personnel. The fuel performanceratio is the ratio of the am.ount of fuel oil usedas compared to the amount of fuel oil allowedfor a certain speed or steaming condition.The fuel performance ratio, which is reportedon the Monthly Summary, is a general indicationof the ship's readiness to operate economicallyand within established standards. Indetermining the economy of a ship's engineeringplant, the same consideration is given to337

PRINCIPLES OF NAVAL ENGINEERING'2 HIGH PRESSURE STEAMLOW PRESSURE STEAMI IEXHAUST STEAMR°o°o°o'g|COOLING STEAMFigure 12-24,— Flow of steam in Type IV propulsionunit (cruising turbine not in use).147,99the amount of water used on board ship. Waterconsumption is computed in (1) gallons of makeupfeed per mile under way, (2) gallons of makeupfeed per hour at anchor, and (3) gallons ofpotable water per man per day.The increase or decrease in a ship's fueleconomy depends largely on the operation ofeach unit of machinery; economical operationfurther depends on personnel understanding thefunction of each unit and knowing how units are338

Chapter 12- PROPULSION STEAM TURBINESEXHAUST STEAMFigure 12-25.— Flow of steam in Type IV propulsionunit (astern operation).147.100used in combination with other units and withthe plant as a whole.Good engineering practices and safe operationof the plant should never be violated inthe interest of economy— furthermore, factorsaffecting the health and comfort of the crewshould meet the standards set by the Navy.Indoctrination of the ship's crew in methodsof conserving water is of the utmost importance,and should be given constant consideration.339

PRINCIPLES OF NAVAL ENGINEERINGCONTMLVALVE,SfSta^iiiEXHAUSTSIGHT FLOWSFLEXIBLESIGHTCOUPLINGnow.CLEARANCE INDICATORTHRUST BEARING^ .FLEXIBLE COUPLINGWASTE OIL DRAINAFTER BEARING OIL DRAINCARBON PACKING VENT \ySEALING STEAM LEAKOFF FROM H.P. PACKING\SEAUH6 STEAMLEAK-OFFSTEAM FROM CRUISING TURBINEPACKINGVENTFigure 12-26.— High pressure turbine.96.10economy measures can-Aboard naval ships,not be carried to extremes, because there areseveral safety factors that must be considered.Unless proper safety precautions are taken,reliability may be sacrificed; and in the operationof naval ships, reliability is one of the moreimportant factors. In operating an engineeringplant as economically as possible, safety factorsand good engineering practice must not be overlooked.There are several factors that, if givenproper consideration, will promote efficient andeconomical operation of the engineering plant.Some of these factors are: (1) maintaining thedesigned steam pressure, (2) proper accelerationof the main engines, (3) maintaining highcondenser vacuum, (4) guarding against excessiverecirculation of condensate, (5) maintenanceof proper insulation and lagging, (6) keepingthe consumption of feed water and potable waterwithin reasonable limits, (7) conserving electricalpower, (8) using the correct number ofboilers for best efficiency at the required loadlevels, and (9) maintaining minimum excesscombustion air to the boilers.Maintaining a constant steam pressure isimportant to the overall efficiency of the engineeringplant. Wide or frequent fluctuations inthe steam pressure or degree of superheat aboveor below that for which the machinery is designedwill result in a considerable loss ofeconomy. Excessively high temperatures willresult in severe damage to superheaters, piping,and machinery.Proper acceleration and deceleration of themain engines are important factors in the economicaloperation of the engineering plant. Afast acceleration will not only interfere withthe safe operation of the boilers but will alsoresult in a large waste of fuel oil. The officer340

.IIChapter 12- PROPULSION STEAM TURBINESASTERN STUMWinASTWM »K*DBUOE ttACTWHGROUPBUWMSTEAM INLET\ FROM H.P. TUIMNEASTERN STEAM INLHASTERN NOZZlf BLOCKASTERNN0Z21IBLOCKCARBONPACKING oGIANO6UND STEAMS£AL^^ASTERN BUDE GROUPROTOR POSITIONMICROMETEREMERGENCYOIL\f7lG0VERN0RBEARINGINLETOILBEARING&GOVERNORPUMPOIL. INLETBEARINGOIL DRAINEXHAUSTFLANGETO CONDENSERBLADE EXHAUST STEAM DRAIN EXHAUST STEAMSHIELD DEFLECTOR OEFIICTORBUDE BAFFLE GLANO \SHKLD CENTERING PM DRAINBEARING OILDRAINFigure 12-27.— Low pressure turbine(with astern elements).147,101or CPO in charge of an engineroom watch, cancontribute a great deal to the economical andsafe operation of the boilers if they use theacceleration and deceleration charts providedfor that particular propulsion plant.Acceleration and deceleration charts areposted at each main engine throttle board. Thesecharts give the exact amount of time that thethrottleman should use in changing speed. Whena speed change is ordered, the throttleman cantell instantly, by checking the chart, the minutesand seconds necessary for him to accelerateor decelerate to the new speed. Main enginecontrol has tachometers indicating the numberof rpm each shaft is doing. By means of thetachometers, the engineeringofficer of the watchcan coordinate the rpm of the shafts; if onethrottleman accelerates or decelerates toorapidly or too slowly, the engineering officerof the watch can detect the trouble and haveit corrected.Improper acceleration or decelerationwastes fuel, leads to uneconomical operation ofthe propulsion plant, and may cause operationalproblems in the fire room. Each throttlemanshould have a revolution - pressure table whichgives the approximate pressure required in thefirst stage of the high pressure turbine to developa certain rpm. By using such a table,together with the acceleration and decelerationcharts, the throttleman can make his watchstandingmuch easier and, at the same time,contribute to economical and efficient operationof the plant. There must always be completeunderstanding between the engineroom and thebridge as to how many rpm are to be maintainedfor one-third, two-thirds, standard, and fullspeed. The throttleman should never relievethe watch without knowing the rpm for thesespeeds.For most efficient turbine operation, thehighest possible vacuum must be maintainedin the condenser. Air must not be allowed toleak into the condenser, exhaust trunks, throttles,lines to air ejectors, gage lines, idlecondensate pump packing, makeup feed lines,or any other part of the system under vacuum.A steam pressure of 1/2 to 2 psi must be341

PRINCIPLES OF NAVAL ENGINEERINGFigure 12-28.— Cruising turbine.147,102maintained on the glands when the turbine is inoperation, and the gland packing must be keptin good condition. An adequate supply of watermust be maintained for the makeup feed tankso that air will not be drawn into the condenser.A combatant ship operates most of the timeat speeds far below maximum. At cruisingspeeds, only a fraction of turbine capacity isrequired. At low speeds, economy is obtainedby one of the following methods: (1) by usingcruising turbines which are designed to operateeconomically at speeds up to about 18 knots,(2) by using cruising stages in the high pressureturbine, and (3) by using turbines whichare designed so that they can be operated inseries.On ships that have a cruising turbine, thecruising combination should be used for allunderway operations requiring speeds of lessthan 18 knots. The officer of the watch (orthe petty officer of the watch) should obtainpermission from the OOD to operate on cruisingcombination whenever possible.To prevent casualties to cruising turbines,the protective devices (sentinel valve, directreadingthermometer, crossover valve lock,and thermal alarm) should be checked continuously.In order to be a good engineering officer ofthe watch, he must acquaint himself with allstanding orders and operating instructions forhis ship. These are made up for each ship and342

Chapter 12- PROPULSION STEAM TURBINESCOMBINEDFIELD aREVERSINGLEVERSPEED-GOVERNINGVALVESPROPULSIONMOTORGENERATOR-FIELDCONTACTORS\maincondenserFigure 12-29.— Diagram of turboelectric drive installation.47.2show the various plant arrangements (split plant,cross-connected steaming, cruising arrangement,etc.) for the different speeds. Eachwatchstandermust read and understand the steamingorders and any additional orders issued by theengineer officer. At this point the engineeringofficer of the watch will request permission tolight fires under the superheater if two- furnacesingle-uptake superheater control boilers is installed.On large combatant ships, there is usuallysufficient steam flow (even when steaming forauxiliary purposes) to maintain fires under thesuperheater side. However, in most installations,and particularly in destroyers, it isusually necessary to be underway and makingabout 12 knots before the fires can be lightedunder the superheater side of the boiler. When,the superheater is operating and the steam flowdrops below a safe minimum, the superheaterfires must be secured immediately. On destroyersthe superheater fires are usuallysecured when the speed of the ship drops below10 knots.From the standpoint of maintenance and repairsto the steam piping, turbine casings,and superheater handhole plates, it is notfeasible to put superheaters into operation untilit is expected that the ship's speed will bemore than 10 knots for a considerable periodof time. Furthermore, continually lighting offand securing the superheater fires will causeextensive steam leaks throughout the systemsubjected to fast changing temperature343

PRINCIPLES OF NAVAL ENGINEERINGconditions. These steam leaks will waste morefuel than could be saved by a few minutes ofsuperheat operation.The no-control, integral superheater boilercreates a different types of problem. The superheatertubes must be protected from the heat ofthe furnace in the interval during which firesare lighted but the rate of steam generation isstill insufficient to ensure a safe flow throughthe superheater. During operation, there is noproblem since all steam passes through thesuperheater and leaves the boiler at superheattemperature. After the boiler is on the line andfurnishing steam, there will be sufficient flowbecause all steam passes through the superheater.It is sometimes necessary to light off and putadditional boilers on the line, when a ship isunderway. With no-control superheat boilers, thesteps are much the same as for putting the firstboiler or boilers onthe line. With superheat controlboilers, additional precautions must betaken.When the steam lines are carrying superheatedsteam, it would be dangerous to admitsaturated steam to the lines. It is not usuallypossible to establish enough steam flow to lightoff the superheaters of the incoming boilers,until they are on the line. It is permissible tobring in the incoming boilers, without theirsuperheaters in operation, if the superheateroutlet temerature of the steaming boilers islowered to 600° F. Lowering of the superheattemperature on the steaming boilers should bestarted in time so that the cutting- in temperaturecan be reached before the incoming boilersare up to operating pressure. Except in anemergency, the temperature of the superheatersshould NOT be lowered or raised at a fasterrate than 50° F every 5 minutes.A number of other items must be checked orinspected at frequent intervals when a ship isunderway. Engineeroom personnel must be constantlyalert for abnormal pressures, temperatures,sound and vibrations.The first indication of bearing trouble isusually a rise in temperature. There is no objectionto a bearing running warm as long asthe temperature is not high enough to causedamage to the bearing. Any RAPID rise intemperature, or any increase over the normaloperating temperature, is probably a sign oftrouble. The first things to check are thequantity of lube oil and the quality of lube oil.If possible, the amount of oil going to the overheatedbearing should be increased and the flowof cooling water through the lube oil cooler should344be increased. If these measures do not reduce thebearing temperature, the unit must be stopped orslowed.A sight-flow indicator is fitted in the lube oilline of each main engine bearing and each reductiongear bearing. When the plant is in operation,each sight-flow indicator should alwaysshow a steady flow of lube oil.The rotor position indicator for each turbinemust be checked every hour and the readingmust be logged. Any abnormal reading must beinvestigated at once.Once of the first indications of engineroomtrouble is an abnormal reading on a thermometeror pressure gage. All gages should be checkedfrequently.The oil level in the main engine sump mustbe checked every hour and logged in the mainengine operating record. In addition, otherchecks should be made in between the requiredhourly checks. A rise in the oil level may meanthat water is entering the lube oil system or thatthe system is gaining oil in an abnormal manner.A drop in the oil level of the main engine sumpmay indicate a leak in the lube oil system orincorrect operation of the lube oil purifier.The water level in each operating deaeratingfeed tank should be kept between the minimumand the maximum allowable levels. If the waterlevel goes above the maximum, the tank nolonger deaerates the water. If the water level isbelow the minimum, a sudden demand for feedwater may empty the deaerating feed tank andcause cumulative casualties to the feed boosterpump, the main feed pump, and the boilers.A salinity indicator is located at or near thethrottle board in each engineroom so that engineroompersonnel can detect the entrance of saltwater into the condensate system. The salinityindicator must be checked constantly. Even avery small amount of salt in the condensatesystem will very rapidly contaminate a steamingboiler. Any abnormal reading of the salinityindicator must be investigated immediately andthe source of contamination must be found andcorrected.PLANT MAINTENANCEThe maintenance of maximum operationalreliability and efficiency of steam propulsionplants requires a carefully planned and executedprogram of inspections and preventive maintenance,in addition to strict adherence to prescribedoperating instructions and safety precautions.If proper maintenance procedures arefollowed, abnormal conditions may be prevented.

Chapter 12- PROPULSION STEAM TURBINESPreventive inspection and maintenance arevital to successful casualty control, since theseactivities minimize the occurrence of casualtiesby material failures. Continuous and detailedinspection procedures are necessary not onlyto discover partly damaged parts which mayfail at a critical time, but also to eliminate theunderlying conditions which lead to early failure(maladjustment, improper lubrication, corrosion,erosion, and other enemies of machineryreliability). Particular and continuous attentionmust be paid to the following symptoms of malfunctioning:1. Unusual noises.2. Vibrations.3. Abnormal temperatures.4. Abnormal pressures.5. Abnormal operating speeds.Operating personnel should thoroughly familiarizethemselves with the specific temperatures,pressures, and operating speeds of equipmentrequired for normal operation, in orderthat departures from normal operation will bemore readily apparent.If a gage, or other instrument for recordingoperation conditions of machinery, gives anabnormal reading, the cause must be fully investigated.The installation of a spare instrument,or a calibration test, will quickly indicatewhether the abnormal reading is due to instrumenterror. Any other cause msut be traced toits source.Because of the safety factor commonly incorporatedin pumps and similar equipment,considerable loss of capacity can occur beforeany external evidence, is readily apparent.Changes in the operating speeds from normalfor the existing load in the case of pressuregovernor-controlledequipment should be viewedwith suspicion. Variations from normal pressures,lubricating oil temperatures, and systempressures are indicative of either inefficient operationor poor condition of machinery.In cases where a material failure occurs inany unit, a prompt inspection should be made ofall similar units to determine if there is anydanger that a similar failure might occur.Prompt inspection may eliminate a wave of repeatedcasualties.Abnormal wear, fatigue, erosion, or corrosionof a particular part may be indicative of afailure to operate the equipment within its designedlimits or loading, velocity and lubrication,or it may indicate a design or material deficiency.Unless corrective action can be takenwhich will ensure that such failures will notoccur, special inspections to detect damageshould be undertaken as a routine matter.Strict attention must be paid to the properlubrication of all equipment, and this includesfrequent inspection and sampling to determinethat the correct quantity of the proper lubricantis in the unit. It is good practice to make a dailycheck of samples of lubricating oil in all auxilaries.Such samples should be allowed tostand long enough for any water to settle. Whereauxiliaries have been idle for several hours,particularly overnight, a sufficient sample toremove all settled water should bedrainedfromthe lowest part of the oil sump. Replenishmentwith fresh oil to the normal level should be includedin this routine.The presence of salt water in the oil can bedetected by drawing off the settled water bymeans of a pipette and by running a standardchloride test. A sample of sufficient size fortest purposes can be obtained by adding distilledwater to the oil sample, shaking vigorously,and then allowing the water to settlebefore draining off the test sample. Because ofits corrosive effects, salt water in the lubricatingoil is far more dangerous to a unit than is anequal quantity of fresh water. Salt water is particularlyharmful to units containing oillubricatedball bearings.An an example, the maintenance requirementswhich shall be conducted in accordancewith the 3-M System is shown in figure 12-30,(Maintenance Index Page).CASUALTY CONTROLThe mission of engineering casualty controlis to maintain all engineering services in a stateof maximum reliability, under all conditions. Tocarry out this mission, it is necessary for thepersonnel concerned to know the action necessaryto prevent, minimize, and correct theeffects of operational and battle casualties onthe machinery and the electrical and pipinginstallations of their ship. The prime objectiveof casualty control is to maintain a ship as awhole in such a condition that it will functioneffectively as a fighting unit. This requires effectivemaintenance of propulsion machinery,electrical systems, interior and exterior communications,fire control, electronic services,ship control, firemain supply, and miscellaneous345

Syitam, SubtytUm, or ComponcnlPRINCIPLES OF NAVAL ENGINEERING

Chapter 12- PROPULSION STEAM TURBINESservices such as heating, air conditioning, andcompressed air systems. Failure ofany of theseservices will affect a ship's ability to fulfillits primary objective, either directly by reducingits power, or indirectly by creating conditionswhich lower personnel morale and efficiency. Asecondary objective— which contributes considerablyto the successful accomplishment of thefirst— is the minimization of personnel casualtiesand of secondary damage to vital machinery.The details on specific casualties are beyondthe scope of this manual. Detailed informationon casualty control can be obtained from theEngineering Casualty Control Manual, the DamageControl Book, the Ship's Organization Book,and the Damage Control Bills. These publicationsmay vary on different ships, but in allcases they give the organization and the proceduresto be followed in case of engineeringcasualties, damage to the ship, and other emergencyconditions.The basic factors influencing the effectivenessof engineering casualty control are muchbroader than the immediate actions taken at thetime of the casualty. Engineering casualty controlreaches its peak efficiency by a combinationof sound design, careful inspection, thoroughplant maintenance (including preventive maintenance),and effective personnel organization andtraining. CASUALTY PREVENTION IS THEMOST EFFECTIVE FORM OF CASUALTYCONTROL.347

CHAPTER13CONDENSERS AND OTHER HEAT EXCHANGERSThis chapter deals with the major pieces ofheat transfer apparatus found in the condensateand feed system of the conventional steam turbinepropulsion plant. Heat exchangers discussedhere include the main condenser, the air ejectorcondenser, the gland exhaust condenser, the ventcondenser, the deaerating feedtank, and the auxiliarycondenser. The arrangement of piping thatconnects these units is discussed in chapter 9 ofthis text.MAIN CONDENSERThe main condenser is the heat exchanger inwhich exhaust steam from the propulsion turbinesis condensed as it comes in contact withtubes through which cool sea water is flowing.The main condenser is the heat receiver of thethermodynamic cycle— that is, it is the low temperatureheat sink to which some heat must berejected. The main condenser is also the meansby which feed water is recovered and returnedto the feed system. If we imagine a shipboardpropulsion plant in which there is no main condenserand the turbines exhaust to atmosphere,and if we consider the vast quantities of freshwater that would be required to support even oneboiler generating 150,000 pounds of steam perhour, it is immediately apparent that the maincondenser serves a vital function in recoveringfeed water.The main condenser is maintained under avacuum of approximately 25 to 28.5 inches ofmercury. The designed vacuum varies accordingto the design of the turbine installation andaccording to such operational factors as the loadon the condenser, the temperature of the outsidesea water, and the tightness of the condenser. Thedesigned full-power vacuum for any particularturbine installation may be obtained from themachinery specifications for the plant. Someturbines are designed for a full-power exhaustvacuum of 27.5 inches of mercury when the circulatingwater injection temperature is 75° F;others are designed for a full-power exhaustvacuum of 25 inches of mercury with a circulatingwater injection temperature of 75° F.It is often said that an engine can do a greateramount of useful work if it exhausts to a lowpressure space than if it exhausts against a highpressure. This statement is undeniably true, butfor the condensing steam power plant it may besomewhat misleading because of its emphasis onpressure. The pressure is important because itdetermines the temperature at which the steamcondenses. As noted in chapter 8 of this text, anincrease in the temperature difference betweenthe source (boiler) and the receiver (condenser)increases the thermodynamic efficiency of thecycle. By maintaining the condenser under vacuum,we lower the condensing temperature, increasethe temperature difference betweensource and receiver, and increase the thermodynamicefficiency of the cycle.Given a tight condenser and an adequate supplyof cooling water, the basic cause of the vacuumin the condenser is the condensation of thesteam. This is true because the specific volumeof steam is enormously greater than the specificvolume of water. Since the condenser is filledwith air when the plant is cold, and since someair finds its way into the condenser during thecourse of plant operation, the condensation ofsteam is not sufficient to establish the initial vacuumnor to maintain the required vacuum underall conditions. In modern shipboard steam plants,air ejectors are used to remove air and othernoncondensable gases from the condenser. Thecondensation of steam is thus the major causeof the vacuum, but the air ejectors are requiredto help establish the initial vacuum and then toassist in maintaining vacuum while the plant isoperating.348

Chapter IS-CONDENSERS AND OTHER HEAT EXCHANGERSWhen the temperature of the outside seawater is relatively high, the condenser tubes arerelatively warm and heat transfer is retarded.For this reason, a ship operating in warm tropicalwaters cannot develop as high a vacuum inthe condenser as the same ship could developwhen operating in colder waters.Two basic rules that apply to the operationof single-pass main condensers should be keptin mind. The first is that the OVERBOARD TEM-PERATURE should be about 10° higher than theINJECTION TEMPERATURE. The second ruleis that the condensate discharge temperatureshould be within a few degrees of the temperaturecorresponding to the vacuum in the condenser.The accompanying chart lists vacuums (based ona 30. 00- inch barometer) and corresponding temperatures.Inches of MercuryCorrespondingTemperature (°F)29.6 5329.4 6429.2 7229.0 7928.8 8528.6 9028.4 9428.2 9828.0 10127.8 10427.6 107A main condenser is shown in cutaway viewin figure 13-1. A slightly different main condenseris shown in outline drawing in figure 13-2.The operating principles of the two condensersare identical except for minor details.In any main condenser, there are two separatecircuits. The first is the vapor-condensatecircuit in which the exhaust steam enters the condenserat the top of the shell and is condensed asit comes in contact with the outer surfaces of thecondenser tubes. The condensate then falls to thebottom of the condenser, drains into a spacecalled the hot well , and is removed by the condensatepump. Air and other noncondensablegases that enter with the exhaust steam or thatotherwise find their way into the condenser aredrawn off by the air ejector through the airejector suction opening in the shell of the condenser,above the condensate level.The second circuit is the circulating watercircuit. During normal ahead operation, a scoopinjection system^ provides automatic flow of seawater through the condenser. The scoop, whichis open to the sea, directs the sea water into theinjection piping; from there, the water flows intoan inlet water chest, flows once through the tubes,goes into a discharge water chest, and then goesoverboard through a main overboard sea chest.A main circulating pump provides positive circulationof sea water through the condenser attimes when the scoop injection system is not effective—whenthe ship is stopped, backing down,or moving ahead at very low speeds.All main condensers that have scoop injectionare of the straight-tube, single-pass type.A main condenser may contain from 2000to 10,000 copper-nickel alloy tubes. The lengthof the tubes and the number of tubes depend uponthe size of the condenser; and this, in turn, dependsupon the capacity requirements. The tubeends are expanded into a tube sheet at the inletend and expanded or packed into a tube sheet atthe outlet end. The tube sheets serve as partitionsbetween the vapor-condensate circuit andthe circulating water (sea water) circuit.Various methods of construction are used toprovide for relative expansion and contraction ofthe shell and the tubes in main condensers. Packingthe tubes at the outlet end sometimes makessufficient provision for expansion and contraction.Where the tubes are expanded into each tubesheet, the shell may have an expansion joint. Expansionjoints are also provided in the scoop injectionline and in the overboard discharge line.Additional means such as flexible support feetor lubricated sliding feet are provided to compensatefor expansion and contraction differentialsbetween the shell and the condenser supportingstructure.As shown in figure 13-3, a central steam laneextends from the top of the condenser all the waythrough the tube bundle, down to the hot well. Theexhaust steam which reaches the hot well throughthis steam lane tends to be drawn under the tubebundle toward the sides of the condenser shell,in the general direction of the air cooling sections,thus sweeping out any air which wouldotherwise tend to collect in the hot well. Part ofthe steam which is drawn through the hot well^ A major advantage of scoop injection is that it providesa flow of cooling water at a rate which is controlledby the speed of the ship and hence is automaticallycorrect for various conditions. Scoop injectionis standard for naval combatant ships and for manyof the newer auxiliary ships.349

PRINCIPLES OF NAVAL ENGINEERING'RECIRCULATING f^MAKEUP FEED 'AIR EJECTOR*CONNECTION CONNECTION SUCTIONEXHAUST STEAM IFROM PROPULSION CTURBINES !CIRCULATING-WATER OUTLABSOLUTEPRESSURE GAGEVACUUM GAGECONNECTIONCONDENSATEOUTLETFigure13-1.— Cutaway view of main condenser.47.70Xunder the tube bundle is condensed by the condensatedripping from the condenser tubes. Inthis process, the condensate (which has beensubcooled by its contact with the cold tubes) tendsto become reheated to a temperature which approachesthe condensing temperature correspondingto the vacuum maintained in the hot well.The difference between the temperature of thecondensate discharge and the condensing temperaturecorresponding to the vacuum maintainedat the exhaust steam inlet to the condenser iscalled the condensate depression . One measureof the efficiency of design and operation of anycondenser is its ability to maintain the condensatedepression at a reasonably low value underall normal conditions of operation. Excessivecondensate depression decreases the operatingefficiency of the plant because the subcooled condensatemust be reheated in the feed system, witha consequent expenditure of steam. Excessivecondensate depression also allows an increasedabsorption of air by the condensate, and this airmust be removed in order to prevent oxygen corrosionof piping and boilers.Main condensers have various internal bafflearrangements for the purpose of separating airand steam so that the air ejectors will not beoverloaded by having to pump large quantities ofsteam along with the air. Air cooling sectionsand air baffles may be seen in figure 13-3.In some installations the condenser is hungfrom the low pressure turbine in such a way thatthe turbine supports the condenser. Where thistype of installation is used, sway braces are usedto connect the lower part of the condenser shellwith the ship's structure. Spring supports are350

Chapter 13-CONDENSERS AND OTHER HEAT EXCHANGERSCOoJt w u zIa X > o ui-^ (v O t. >~ K ID W ^O* o 2o I o U.O ^jujO K z " -z(/) LJ < -iZ~] 2 UJ lUOo ceosoz-

PRINCIPLES OF NAVAL ENGINEERINGAIR OFFTAKE CROSSOVER PIPES(IN EXHAUST OPENING STRUTS)STEAM LANETUBE SUPPORT PLATECONDENSER TUBESCONDENSER SHELLAIR OFFTAKETUBE PLATESTAYSCONDENSERSIDEWALLSTIFFENERSAIR BAFFLESUPPORTINGFLANGEAIR COOLINGSECTIONSUPPORTINGFLANGEAIR COOLINGSECTIONHOT WELLCAGE GLASSCONDENSATE OUTLETFigure 13-3. — Cross-sectional view of main condenser.98.33sometimes used to support part of the weight ofthe condenser so that it will not have to be entirelysupported by the turbine.Condenser performance may be evaluated bya simple energy balance which takes account ofall energy entering and leaving the condenser.In theory, the entering side of the balance shouldinclude (1) the mechanical kinetic energy of theentering steam, (2) the thermalenergy of the enteringsteam, (3) the mechanical kinetic energyof the entering sea water, and (4) the thermalenergy of the entering sea water. In theory, again,the leaving side of the balance should include (1)the mechanical kinetic energy of the leaving condensate,(2) the thermal energy of the leavingcondensate, (3) the mechanical kinetic energy ofthe leaving sea water, and (4) the thermal energyof the leaving sea water. In considering real condensers,however, the entering and leaving mechanicalkinetic energies of the sea water tendto be small and tend to cancel each other out, themechanical kinetic energy of the entering steamis so small as to be negligible, and the mechanicalkinetic energy of the leaving condensate issmall enough to disregard. With all of these relativelyinsignificant quantities omitted, the enteringside of the balance includes only the thermalenergy of the entering steam and the thermalenergy of the entering sea water, and the leavingside includes only the thermal energy of theleaving condensate and the thermalenergy of theleaving sea water.AIREJECTOR ASSEMBLIESThe function of air ejectors is to remove airand other noncondensable gases from the condenser.An air ejector is a type of jet pump,having no moving parts. The flow through the airejector is maintained by a jet of high velocitysteam passing through a nozzle. The steam istaken from the 150-psi auxiliary steam systemon most ships.The air ejector assembly (fig. 13-4) used toremove air from the main condenser usually consistsof a first-stage air ejector, an inter condenser,a second-stage air ejector, and an aftercondenser. The two air ejectors operate in series.The first-stageair ejector raises the pressurefrom about 1.5 inches of mercury absolute(condenser pressure) to about 7 inches of mercuryabsolute; the second-stage air ejectorraises the pressure from 7 inches of mercuryabsolute to about 32 inches of mercury absolute(about 1 psig).The first-stage air ejector takes suction onthe main condenser and discharges the steam-airmixture to the inter condenser, where the steamcontent of the mixture is condensed. The result-condensate drops to the bottom of the intering352

Chapter 13-CONDENSERS AND OTHER HEAT EXCHANGERSFIRST STAGEAIR EJECTORSECOND STAGEAIR EJECTORAFTERCONDENSERVENT TOATMOSPHERE(VIAEXHAUST FAN)AUX. STEAM ^ CEXHAUSTTO4 DEAERATINQTANKGLANDEXHAUSTCONDENSERCONDENSATEPUMP%-^INTERCONDENSER\:im

PRINCIPLES OF NAVAL ENGINEERINGcondenser. To avoid this difficulty, provision ismade for returning some of the condensate to themain condenser when the condensate reaches acertain temperature. As a rule, the recirculatingline branches off the condensate line just afterthe gland exhaust condenser. In most installations,the recirculating valve in this recirculatingline is thermostatically operated.VENTCONDENSERThe vent condenser is actually a part of thedeaerating feed tank, being installed in the tanknear the top. It is described separately herebecause it is functionally quite separate from thedeaerating feed tank.In the vent condenser, as in the air ejectorcondensers and the gland exhaust condenser,condensate on its way from the main condenserto the deaerating feed tank is used to cool andcondense the steam from a steam-air mixture.The vent condenser receives steam and air fromthe deaerating feed tank. The steam condensesinto water, which falls toward the bottom of thetank. The air goes to the gland exhaust condenserand is vented to atmosphere. The condensatewhich is used as the cooling medium in the ventcondenser is sprayed out into the deaerating feedtank and is deaerated before beingused as boilerfeed.DEAERATING FEED TANKThe deaerating feed tank serves to heat, deaerate,and store feed water. The water is heatedby direct contact with auxiliary exhaust steamwhich enters the tank at a pressure just slightlygreater than the pressure in the tank. Thedeaerating feed tank is usually designed to operateat a pressure of about ISpsigand to heat thewater to between 240° and 250° F.One type of deaerating feed tank is shown infigure 13-5. Condensate enters the tank throughthe tubes of the vent condenser and is forced outthrough a number of spray valves in a spray head.The spray valves discharge the condensate in afine spray throughout the steam-filled upper sectionof the deaerating feed tank. The very smalldroplets of water are heated, scrubbed, and partiallydeaerated by the relatively air-free steam.As the steam gives up its heat to the water, muchof the steam is condensed into water. Thedroplets of water (including both the enteringcondensate sprayed out from the vent condenserand the steam condensed in the deaerating feedtank) are collected in a cone-shaped baffle whichleads them through a central port, to thedeaerating unit.Steam enters the deaerating unit, picks up thepartially deaerated water, and throws ittangentiallyoutward through the curving baffles of thedeaerating unit. In this process, the water is evenmore finely divided and is throughly scrubbed bythe incoming steam. Thus the last traces of dissolvedoxygen areremovedfromthe water. Sincethe water enters the deaerating unit at saturationtemperature, having already been heated by thesteam in the upper part of the deaerating feedtank, the incoming steam does not condense toany marked degree in the deaerating unit.Therefore all (or practically all) of the incomingsteam is available for breaking up, scrubbing,and deaerating the water.The thoroughly deaerated water falls into thestorage space at the bottom of the tank, where itremains under a blanket of air-free steam untilit is pumped to the boilers. Meanwhile, the mixtureof steam plus air and other noncondensablegases travels over the spray head (where muchof the steam is condensed as it heats the incomingcondensate) and over the tubes of the ventcondenser (where more steam is condensed intowater which then goes into the deaerating unit).The air and other noncondensable gases, togetherwith a little remaining steam, goto the gland exhaustcondenser.As shown in figure 13-5, the deaerating feedtank has a recirculating connection that allowswater to be sent back to the condenser from thedeaerating feed tank. The recirculating line isused to provide a high enough condensate levelin the condenser so that the condensate pump cantake suction. The recirculating line is also usedat slow speeds and when the plant is first startedup to ensure a sufficient supply of cooling condensateto the air ejector condensers and to thegland exhaust condenser and to keep the deaeratingfeed tank at the prescribed temperature.The deaerated feed water from the deaeratingfeed tank is pumped to the boiler by the feedbooster pump and the main feed pump. The feedbooster pump takes suction from the bottom ofthe deaerating feed tank and discharges to thesuction side of the main feed pump. Thefeed booster pump provides a positive suctionpressure for the main feed pump and thus preventsthe hot water from flashing into steam atthe main feed pump suction. The main feedpump operates at variable speed in order tomaintain a constant discharge pressure under all354

Chapter 13-CONDENSERS AND OTHER HEAT EXCHANGERSVENTCONDENSERTO GLANDEXHAUSTCONDENSERCONDENSATE \RECIRCULATINGX^CONNECTION "CONDENSATEINLETAUTOMATIC CHECKVALVE CONTROLRECIRCULATINGCONNECTION TOMAIN CONDENSERVCONDENSATELEGENDSTEAMMIXTURE OF STEAM PLUS AIR ANDOTHER NONCONDENSABLE GASESWATER CONDENSED ONVENT CONDENSERDEAERATED WATERSECTION A-ATHROUGH DEAERATINGUNITFigure 13-5.— Deaerating feed tank.35538.17

PRINCIPLES OF NAVAL ENGINEERINGconditions of load. The discharge pressure of themain feed pump is considerably higher than thepressure carried in theboiler steam drum. Provisionis made for the recirculation of waterfrom the main feed pump discharge back to thedeaerating feed tank, in order to protect the pumpfrom overheating at very low capacity.SAFETY AND CASUALTY CONTROLIn the event of a casualty to a component partof the propulsion plant, the principal doctrine tobe impressed upon operating personnel is theprevention of additional or major casualties.Under normal operating conditions, the safety ofpersonnel and machinery should be given firstconsideration. Where practicable, the propulsionplant should be kept in operation by meansof standby pumps, auxiliary machinery, andpiping systems. The important thing is to preventminor casualties from becoming major casualties,even if it means suspending the operationof the propulsion plant. It is better to stopthe main engines for a few minutes than to putthem completely out of commission, so thatmajor repairs are required to place them backinto operation. In case a casualty occurs, the officeror CPO in charge of the watch should benotified as soon as possible; he in turn mustnotify the OOD if there will be any effect on theship's speed or on the ability to answer bells.LOSS OF VACUUMThe major causes of a loss of vacuum are:excessive air leakage into the vacuum system,improper functioning of the air- removal equipment,improper drainage of condensate from thecondenser, insufficient flow of circulating water,and high injection temperature.1. EXCESSIVE AIR LEAKAGE INTO THEVACUUM SYSTEM may be caused by:a. Insufficient gland sealing steam.b. Vent valve on idle condensate pumpopen.c. Loop- seal filling valve open.d. Bypass valve on drain tank open.e. Drain tank float valve stuck open.f. Taking make-up feed from empty feedbottom.g. Leakage of flanges, fittings, or valvestem packings under vacuum.2. IMPROPER FUNCTIONING OF THE AIR-REMOVAL EQUIPMENT may be due to:a. Insufficient steam to the air ejectors.b. Foreign matter lodged in the air ejectornozzle(s).c. Erosion of the air ejector nozzle, overa period of time.3. IMPROPER DRAINAGE OF CONDEN-SATE FROM THE CONDENSER may becaused by:a. Low speed of condensate pump, indicatingmalfunctioning of the pump'sspeed-limiting governor.b. Condensate pump air-bound becauseof the vent connection from the firststage being closed or not opened wide,4. INSUFFICIENT FLOW OF CIRCULATINGWATER may be caused by:a. Improper adjustment of the overboarddischarge valve (the main injectionvalve being wide open whenever thecondenser is under vacuum).b. Inadequate speed of the main circulatingpump.c. Plugged tubes, resulting from mud,shells, small fish, or kelp beingtrapped against the injection strainerbars or in the inlet water chest.d. Air trapped in condenser.5. HIGH INJECTION TEMPERATUREBasically, the injection temperature limitsthe maximum vacuum (minimum absolute pressure)obtainable in a specific plant, assuming thecondenser, associated equipment, and pipingunder vacuum to be clean and properly operated.Whenever there is a loss of vaccum, the firststep in correcting the trouble is to locate thecause of the casualty. The major possible causesare so numerous that no attempt will be made tolist the proper action required for each one. Therequired action may be very simple, suchas closing the loop seal filling valve, or it maybe much more complicated, such as leaning themain condenser or replacing air ejector nozzles.SALT WATER LEAKAGEINTO CONDENSERIf a condenser salinity indicator shows a risein the chloride content, the source of the contaminationmust be determined immediately. To locatethese sources, test the fresh water fromdifferent units in the system by checking theproper salinity indicators (if installed) and by356I

Chapter 13-CONDENSERS AND OTHER HEAT EXCHANGERSmaking chemical chloride tests. There are fourmajor causes of a salty condenser:1. Leaky tube(s) in the condenser.2. Make-up feed tank salted up.3. Low pressure drain tank salted up.4. Leaky feed suction and drain lines whichrun through the bilges.Each of the aforementioned possibilities mustbe investigated to determine the source of thecontamination and its elimination.If it is determined that there is a minor leakin the condenser and the ship's prospective arrivaltime is less than 24 hours, the affected plantwill probably be continued in operation. Isolatethe condensate system, and limit the number ofboilers on the engine involved. When operatingunder these conditions it will be necessary toblow down the boiler(s) as necessary, to keep theboiler salinity within the specified limit. However,if the leak is serious, secure the plant andlocate the leaks.If leaky tubes are found, they must beplugged so that the condenser can be kept inservice. Plugs, whicharefurnishedby the manufacturer,should be driven into the tube ends withlight hammer blows. If it becomes necessary toplug tube sheet holes after a tube has been removed,a short section of tube should be expandedinto the tube hole before the tube plug is inserted;this will protect the tube holes from damage.Plugged tubes should be renewed during thenext shipyard availability if the water chests areremoved for other work; or if more than 10 percentof the tubes are plugged, a retubing requestshould be submitted, via the type commander, toNavShips.For the procedure in locating and pluggingleaking condenser, tubes, refer to either themanufacturer's technical manual for the specificequipment or chapter 9460 of NavShips TechnicalManual.AIR EJECTOR ASSEMBLYCONTROL AND SAFETYIn order to provide for continuous operation,two sets of nozzles and diffusers are furnishedfor each stage of the air ejectors. Only one setis necessary for operation of the plant; the otherset is maintained ready for use in case of damageor unsatisfactory operation of the set in use. Thesets can be used simultaneously when excessiveair leakage into the condenser necessitatesadditional pumping capacity.Before starting a steam air ejector, the steamline should be drained of all moisture; moisturein the steam will cut the nozzles, and slugsof water will cause unstable operation.Before cutting steam into the air ejectors,make sure that sufficient cooling water is flowingthrough the condenser and that the condenserhas been properly vented.The loop seal line must be kept airtight, anair leak may cause all water to drain out of theseal.If it is necessary to operate both sets of airejectors to maintain proper condenser vacuum,air leakage is indicated. It is more desirableto eliminate the air leakage than to operate twosets of air ejectors.Unstable operation of an air ejector may becaused by any of the following: the steam pressuremay be lower than the designed amount, thesteam temperature and quality may be differentthan design condition, there may be scale on thenozzle surface, the position of the steam nozzlemay not be right in relation to the diffuser, orthe condenser drains may be stopped up.Difficulties due to low pressure are generallycaused by improper functioning or improper adjustmentof the steam reducing valve supplyingmotive steam to the air ejector assembly. It isessential that DRY steam at FULL operatingpressure be supplied to the air ejector nozzles.Erosion of fouling of air ejector nozzles isevidence that wet steam is being admitted to theunit. Faulty nozzles make it impossible to operatethe ejector under high vacuum. In some instances,the nozzles maybe clogged with grease,boiler compound, or some other deposit whichwill decrease the jet efficiency.DEAERATING FEED TANKCONTROL AND SAFETYDuring normal operation, the only controlnecessary is maintaining the proper water level.(On some of the newer ships, this is done withautomatic control valves.) If the water level istoo high, the tank cannot properly remove theair and noncondensable gases from the feedwater. A low water level may endanger the mainfeed booster pumps, the main feed pumps, andthe boilers.Deaerating feed tanks remove gases from thefeed water by using the principle that the solubilityof gases in feed water approaches zerowhen the water temperature approaches the boilingpoint. During operation, steam and water are357

PRINCIPLES OF NAVAL ENGINEERINGcomes inmixed by spraying the water so that itcontact with steam from the auxiliary exhaustline. The quantity of steam must always be proportionalto the quantity of water, otherwise,faulty operation or a casualty will result.Overfilling the deaerating tank may upset thesteam-water balance and cool the water to suchan extent that ineffective deaeration will takeplace. Overfilling the deaerating tank also wastesheat and fuel. The excess water, which will haveto run down to the condenser, will be cooled— andwhen it reenters the deaerating tank, more steamwill be required to reheat it. If an excessiveamount of cold water enters the deaerating feedtank, the temperature drop in the tank will causea corresponding drop in pressure. As the deaeratingfeed tank pressure drops, more auxiliaryexhaust steam enters the tank. This reduces theauxiliary exhaust line pressure, which causes theaugmenting valve (150 psi line to auxiliaryexhaust line) to open and bleed live steam into thedeaerating feed tank.When an excessive amount of cold water suddenlyenters the deaerating feed tank, a seriouscasualty may result . The large amount of coldwater will cool (quench) the upper area of the deaeratingfeed tank and condense the steam so fastthat the pressure is reduced throughout the deaeratingfeed tank. This permits the hot condensatein the lower portion of the deaerating feedtank and feed booster pump to boil or flash intovapor causing the booster pump to lose suctionuntil the pressure is restored and the boiling ofthe condensate ceases. With a loss of feedbooster pump pressure, the main feed pump suctionis reduced or lost entirely, causing seriousdamage to the feed pump and loss of feed watersupply to the boiler(s). Some of the newer shipshave safety devices installed on the main feedpumps which will stop the main feed pump whena partial or total loss of main feed booster pressureoccurs.The mixture of condensate, drains, and makeupfeed water, constituting the inlet water to thedeaerating tank, enters through the tubes of thevent condenser. The condensate pump dischargepressure forces the water through the sprayvalves of the spray head and discharges it in afine spray throughout the steam filled top orpreheater section of the deaerating feed tank.K a spray nozzle sticks open, or if a spraynozzle spring is broken, the flow from the nozzlewill not be in the form of a spray and the resultwill be ineffective deaeration. This conditioncannot be discovered except by analysis of thefeed water leavingthe deaerating feed tank, orby inspecting the spray nozzles.Inspection of the spray nozzles should bescheduled at frequent intervals.In most deaerating feed tanks, the manholeprovides access for the inspection of spraynozzles; other tanks are so designed that thespray nozzle chamber and the vent condensermust be removed in order to inspect the nozzles.Complete information on constructing andusing a test rig for spray valves can be found inchapter 9560 of NavShips Technical Manual.SAFETY PRECAUTIONSFOR CONDENSERSWhen opening a main condenser for cleaningor inspection, or when testing a main condenser,there are several safety precautions that mustbe observed. The following procedures and precautions,when carried out properly, will helpprevent casualties to personnel and machinery:1. Before the salt water side of a condenseris opened, all sea connections, including the maininjection valve, circulating pump suction valve,and main overboard valve, are to be closed tightlyand secured against accidental opening with wire,and tagged, DO NOT OPEN, and signed bythe person tagging the valve. This is necessaryto avoid the possibility of flooding an engineroom.Safety gates, where provided, are to be installed.2. On condenser having electrically operatedinjection and overboard valves, the electricalcircuits serving these motors are to be openedand tagged to prevent accidentally energizingthese circuits.3. Before a manhole or handhole plate is removed,drain the salt water side of the condenserby using the drain valve provided in the inletwater box. This is done to make sure that all seaconnections are tightly closed.4. If practicable, inspection plates are to bereplaced and secured before work is discontinuedeach day.5. Never subject condensers to a test pressurein excess of 15 psig.6. When testingfor leaks, do not stop becauseone leak is found. The entire surface of both tubesheets must be checked, as other leaks may exist.Determine whether each leak is in the tube jointor in the tube wall, so that the proper repairs canbe made.7. There is always a possibility that hydrogenor other gases may be present in the steam358

Chapter 13-CONDENSERS AND OTHER HEAT EXCHANGERS

PRINCIPLES OF NAVAL ENGINEERINGor the salt water side of a condenser. No openflame or tool which might cause a spark shouldbe brought close to a newly opened condenser.Personnel are not to be permitted to enter anewly opened condenser until it has beenthoroughly blown out with steam or air.8. The salt water side of a condenser mustbe drained before flooding of the steam side andmust be kept drained until the steam side isemptied.9. The relief valve (set at 15 psig) mountedon the inlet water chest is to be lifted by handwhenever condensers are secured.10. If a loss of vacuum is accompanied by ahot or flooded condenser, the units exhaustinginto the condenser must be slowed or stoppeduntil the casualty is corrected. Condensate mustnot be allowed to collect in condenser and overflowinto the turbines or engines.11. Condenser shell relief valves are to belifted by hand before a condenser is put into service,12. No permanent connection which couldsubject the salt water side to a pressure in excessof 15 psig, is to be retained between anycondenser and a water system.13. No permanent connection which couldallow salt water to enter the steam side of thecondenser, is to be retained.14. Test the main circulating pump bilge suction,when so directed by the engineer officer. Toconduct this test, it is generally necessary onlyto start the main circulating pump, open the bilgesuction line stop or check valve, and then closedown on the sea suction line valve to about 3/4closed, or until the maximum bilge suctioncapacity is obtained.MAINTENANCECondensers, heat exchangers and associatedequipment should be periodically tested and inspectedto ensure that they are operatingefficiently. Preventive maintenance is muchmore economical than corrective maintenance.All preventive maintenance should be conductedin accordance with the 3-M System (PMS Subsystem).As an example, figure 13-6 shows twomaintenance requirement cards, one for a maincondenser and the other for a deaerating feedtank. Note: These cards contain specific informationfor conducting the specified preventivemaintenance actions.360

PART IV-AUXILIARY MACHINERYAND EQUIPMENTChapter 14Chapter 15Chapter 16Chapter 17Chapter 18Chapter 19Chapter 20Chapter 21Piping, Fittings, and ValvesPumps and Forced Draft BlowersAuxiliary Steam TurbinesCompressed Air PlantsDistilling PlantsRefrigeration and Air Conditioning PlantsShipboard Electrical SystemsOther Auxiliary EquipmentThe chapters included in this part of the text deal with the auxiliarymachinery and equipment of the shipboard engineering plant. Some ofthe units and plants described here are directly related to the operationof the major units of propulsion machinery; others may be regarded assupporting systems. Major emphasis in this part of the text is on theauxiliary machinery and equipment found on conventional steam-drivenships; however, a substantial amountof the information given here appliesalso to ships with other kinds of propulsion plants.It should be noted that diesel engines, gasoline engines, and gasturbine engines-all of which may be used to drive auxiliary machineryand equipment-are not included here. These units are discussed in partV of this text.361

CHAPTER 14PIPING, FITTINGS, AND VALVESThis chapter deals with pipe, tubing,fittings,valves, and related components that make upthe shipboard piping systems used for the transferof fluids. The general arrangement and layoutof the major engineering piping systems isdiscussed in chapter 9 of this text; in the presentchapter, we are concerned with certain practicalaspects of piping system design and with theactual piping system components—pipe, tubing,fittings,and valves.DESIGN CONSIDERATIONSEach piping system and all its componentsmust be designed to meet the particular conditionsof service that will be encountered inactual use. The nature of the contained fluid,the operating pressures and temperatures ofthe system, the amount of fluid that must bedelivered, and the required rate of deliveryare some of the factors that determine the materialsused, the types of valves and fittingsused, the thickness of the pipe or tubing, andmany other details. Piping systems that mustbe subjected to temperature changes are designedto allow for expansion and contraction.Special problems that might arise—water hammer,turbulence, vibration, erosion, corrosion,and creep,! for example— are also considered inthe design of piping systems.The requirements governing the design andarrangement of components for shipboard pipingiThe term creep is used to describe a special kind ofplastic deformation that occurs very slowly, at hightemperatures, in metals under constant stress. Becausecreep occurs very slowly— so slowly, in fact,that years may be required to complete a singlecreep test—the importance of this type of plasticdeformation was not recognized in many fields ofengineering until fairly recently. Creep-resistingsteel is now used in most modern naval boilersand for most high temperature piping.systems are covered in detail by contractspecifications and by a number of plans anddrawings. The information given here is notintended as a detailed listing but merely as ageneral guide to the design requirements ofshipboard piping systems.All shipboard piping is installed in such away that it will not interfere with the operationof the ship's machinery or with the operationof doors, hatches, scuttles, or openings coveredby removable plates. As far as possible, pipingis installed so that it will not interfere with themaintenance and repair of machinery or of theship's structure. U piping must be installed inthe way of machinery or equipment which requiresperiodic dismantling for overhaul, or ifit must be installed in the way of other pipingsystems or electrical systems, the piping isdesigned for easy removal. Piping that is vitalto the propulsion of the ship is not installedwhere it would have to be dismantled in orderto permit routine maintenance on machineryor other systems. Piping is not normally installedin such a way as to pass through voids,fuel oil tanks, ballast tanks, feed tanks, andsimilar spaces.Valves, unions, and flanges are carefullylocated to permit isolation of sections of pipingwith the least possible interference to the continuedoperation of the rest of the system. Thetype of valve used in any particular locationis specified on the basis of the service conditionsto be encountered. For example, gatevalves are widely used in locations wherethe turbulent flow characteristics of othertypes of valves might be detrimental to thecomponents of the system.Unnecessary high points and low points areavoided in piping systems. Where high pointsand low points are unavoidable, vents, drains,or other devices are installed to ensure proper363

PRINCIPLES OF NAVAL ENGINEERINGfunctioning of the system and equipment servedby the system.Various joints are used in shipboard pipingsystems. The joints used in any system dependupon the piping service, the pipe size, and theconstruction period of the ship. Older navalships have threaded flanges in low pressurepiping; rolled-in joints for steel piping that istoo large for the threaded flanges; and spelterbrazedflanges for copper and brass piping. Onnew construction, welded joints are used to themaximum practicable extent in systems thatare fabricated of carbon steel, alloy steel,or other weldable material. On both older andnewer ships, flanged joints made up with specialgaskets are in use.Components welded in a piping system mustbe accessible for repair, reseating, and overhaulwhile in place; they are so located thatthey can be removed, preheated, rewelded, andstress relieved when major repairs or replacementsare necessary. Complex assemblies—for example, assemblies of valves, strainers,and traps in high pressure drain systems— aredesigned to be removable as a group if theycannot be repaired while in place and if theyrequire frequent overhaul.Flanged and union joints are placed wherethey will be least affected by piping systemstresses. In general, this means that joints arenot located at bends or offsets in the piping.Valves are designed so that they can beoperated with the minimum practicable amountof force and with the maximum practicable convenience.If a man must stand on slippery deckplates to turn a valve handwheel, or if he mustreach over his head or around a corner, he cannotapply the same amount of torque that he couldapply to a more conveniently located handwheel.Thus the location of the handwheels is an importantdesign consideration. Toggle mechanisms orother mechanical advantage devices are usedwhere the amount of torque required to turn ahandwheel is more than could normally be appliedby one man. If mechanical advantage devicesare not sufficient to produce easy operationof the valve, power operation is used.If accidental opening or closing of a valvecould endanger personnel or jeopardize thesafety of the ship, locking devices are used.Any locking device installed on a valve must bedesigned so that it can be easily operated byauthorized personnel; but it must be complexenough to discourage casual or indiscriminateoperation by other persons.Supports used in shipboard piping systemsmust be strong enough to support the weight ofthe piping, its contained fluid, and its insulationand lagging. Supports must carry the loads imposedby expansion and contraction of the pipingand by the working of the ship, and they mustbe able to support the piping with completesafety. Supports are designed to permit themovement of the piping necessary for flexibilityof the system. A sufficient number of supportsare used to prevent excessive vibration of thesystem under all conditions of operation, butthe supports must not cause excessive constraintof the piping. Supports are used forheavy valves and fittings so that the weight ofthe valves and fittings will not be entirely supportedby the pipe.PIPE AND TUBINGPiping is defined as an assembly of pipe ortubing, valves, fittings, and related componentsforming a whole or a part of a system for transferringfluids.It is somewhat more difficult to define pipeand tubing . In commercial usage, there is noclear distinction between pipe and tubing, sincethe correct designation for each tubular productis established by the manufacturer. If the manufacturercalls a product pipe, it is pipe; if hecalls it tubing, it is tubing. In the Navy, however,a distinction is made between pipe and tubing.This distinction is based on the way the tubularproduct is identified as to size.There are three important dimensions of anytubular product: outside diameter (OD), insidediameter (ID), and wall thickness. A tubularproduct is called tubing if its size is identifiedby actual measured outside diameter (OD) andby actual measured wall thickness. A tubularproduct is called pipe if its size is identifiedby a nominal dimension called iron pipe size(IPS) and by reference to a wall thicknessschedule of piping.The size identification of tubing is simpleenough, since it consists of actual measureddimensions; but the terms used for identifyingpipe sizes may require some explanation. Anominal dimension such as iron pipe size isclose to— but not necessarily identical with— anactual measured dimension. For example, apipe with a nominal pipe size of 3 inches hasan actual measured outside diameter of 3.50inches, and a pipe with a nominal pipe size of2 inches has an actual measured outside diameter364

Chapter 14. -PIPING, FITTINGS, AND VALVESof 2.375 inches. In the larger sizes (above 12inches) the nominal pipe size and the actualmeasured outside diameter are the same. Forexample, a pipe with a nominal pipe size of14 inches has an actual measured outside diameterof 14 inches. Nominal dimensions areused in order to simplify the standardizationof pipe fittings and pipe taps and threading dies.The wall thickness of pipe is identified byreference to wall thickness schedules establishedby the American Standards Association.For example, a reference to schedule 40 fora steel pipe with a nominal pipe size of 3 inchesindicates that the wall thickness of the pipe is0.216 inch. A reference to schedule 80 for asteel pipe of the same nominal pipe size indicatesthat the wall thickness of this pipe is0.300 inch. A reference to schedule 40 forsteel pipe of nominal pipe size 4 inches indicatesthat the wall thickness of this pipe is0.237 inch. As may be noted from these examples,a wall thickness schedule identificationdoes not identify any one particular wall thicknessunless the nominal pipe size is also specified.The examples used here are given merelyto illustrate the meaning of wall thicknessschedule designations. Many other values canbe found in pipe tables given in engineeringhandbooks and piping handbooks.Pipe was formerly identified as standard(Std), extra strong (XS), and double extra strong(XXS). These designations, which are still usedto some extent, also refer to wall thickness.However, pipe is manufactured in a number ofdifferent wall thicknesses, and some pipe doesnot fit into the standard, extra strong, anddouble extra strong classifications. The wallthickness schedules are being used increasinglyto identify the wall thickness of pipe becausethey provide for the identification of a largernumber of wall thicknesses than can be identifiedunder the standard, extra strong, and doubleextra strong classifications.It should be noted that pipe and tubing isoccasionally identified in ways other than thestandard ways described here. For example,some tubing is identified by inside diameter(ID) rather than by outside diameter (OD), andsome pipe is identified by nominal pipe size,OD, ID, and actual measured wall thickness.A great many different kinds of pipe andtubing are used in shipboard piping systems.A few shipboard applications that may be ofparticular interest are noted in the followingparagraphs.Seamless chromium-molybdenum alloy steelpipe is used for some high pressure, high temperaturesystems. The upper limit for the pipingis 1500 psig and 1050° F.Seamless carbon steel tubing is used inoil, steam, and feed water lines operating at775 ° F and below. Different types of this tubingare available; the type used in any particularsystem depends upon the working pressure ofthe system.Seamless carbon- molybdenum alloy steeltubing is used for feed water discharge piping,boiler pressure superheated steam lines, andboiler pressure saturated steam lines. Severaltypes of this tubing are available; the typeused in any particular case depends upon theboiler operating pressure and the superheateroutlet temperature. The upper pressure andtemperature limits for any class of this tubingare 1500 psig and 875° F.Seamless chromium-molybdenum alloy steeltubing is used for high pressure, high temperaturesteam service on newer ships. This typeof alloy steel tubing is available with differentpercentages of chromium and molybdenum, withupper limits of 1500 psig and 1050° F.Welded carbon steel tubing is used in somewater, steam, and oil lines where the temperaturedoes not exceed 450° F. There are severaltypes of this tubing; each type is specified forcertain services and certain service conditions.Nonferrous pipe and nonferrous tubing areused for many shipboard systems. Nonferrousmetals are used chiefly where their specialproperties of corrosion resistance and highheat conductivity are required. Various typesof seamless copper tubing are used for refrigerationlines, plumbing and heating systems,lubrication systems, and other shipboard systems.Copper-nickel alloy tubing is widely usedaboard ship. Seamless brass tubing is used insystems which must resist the corrosive actionof salt water and other fluids; it is available intypes and sizes suitable for operating pressuresup to 4000 psig. Seamless aluminum tubing isused for dry lines in sprinkling systems andfor some bilge and sanitary drain systems.Many other kinds of pipe and tubing besidesthe kinds mentioned here are used in shipboardpiping systems. It is important to rememberthat design considerations govern the selectionof any particular pipe or tubing for a particularsystem. Although many kinds of pipe and tubing365

PRINCIPLES OF NAVAL ENGINEERINGlook almost exactly alike from the outside, theymay respond very differently to pressures,temperatures, and other service conditions.Therefore, each kind of pipe and tubing can beused only for the specified applications.PIPE FITTINGSPipe or tubing alone does not constitute apiping system. To make the pipe or tubing intoa system, it is necessary to have a variety offittings, connections, and accessories by whichthe sections of pipe or tubing can be properlyjoined and the flow of the transferred fluid maybe controlled. The following sections of thischapter deal with some of the pipe fittings mostcommonly used in shipboard piping systems;these fittings include unions, flanges, expansionjoints, flareless fluid connections, steam traps,strainers, and valves.UNIONSUnion fittings are provided in piping systemsto allow the piping to be taken down for repairsand alterations. Unions are available in manydifferent materials and designs to withstanda wide range of pressures and temperatures.Figure 14-1 shows some commonly used typesof unions.FLANGESFlanges are used in piping systems to alloweasy removal of piping and other equipment.The materials used and the design of the flangesare governed by the requirements of service.Flanges in steel piping systems are usuallywelded to the pipe or tubing. Flanges in nonferroussystems are usually brazed to the pipeor tubing.EXPANSION JOINTSExpansion joints are used in some pipingsystems to allow the piping to expand and contractwith temperature changes, without damageto the piping. Two basic types of expansionjoints are used in shipboard piping systems:sliding-type joints and flexing-type joints,Sliding-type expansion joints include sleevejoints, rotary joints, ball and socket joints,and joints made up of some combination of thesetypes. The amount of axial and rotary motionthat can be abosrbed by any particular typeof sliding expansion joint depends upon thespecific design of the joint.Flexing-type expansion joints are those inwhich motion is absorbed by the flexing actionof a bellows or some similar device. Thereare various kinds of flexing-type expansionjoints, each kind being designed to suit therequirements of the particular system in whichit is installed. Figure 14-2 illustrates the generalprinciple of a bellows-type expansion joint.Expansion joints are not always used inpiping systems, even when allowance must bemade for expansion and contraction of the piping.The same effect can be achieved by using directionalchanges and expansion bends or loops.FLARELESS FLUID CONNECTIONSA special flareless fluid connection has recentlybeen developed for connecting sectionsof tubing in some high pressure shipboard systems.This fitting, which is generally known asthe bite-type fitting , is very useful for certainapplications because it is smaller and lighterin weight than the conventional fittings previouslyused to join tubing. The bite-type fitting is usedon certain selected systems where the tubingis between 1/8 and 2 inches in outside diameter.The bite-type fitting, shown in figure 14-3,consists of a body, a ferrule or sleeve thatgrips the tubing, and a nut. The fitting is notused in places where there is insufficient spacefor proper tightening of the nut, in places wherepiping or equipment would have to be removedin order to gain access to the fitting, or inplaces where the tubing cannot be easily deflectedfor ready assembly or breakdown of thejoint. The fitting is sometimes used on gageboard or instrument panel tubing, provided thegage board or panel is designed to be removedas a unit when repairs are required.STEAM TRAPSSteam traps are installed in steam lines todrain condensate from the lines without allowingthe escape of steam. There are many differentdesigns of steam traps, some being suitablefor high pressure use and others beingsuitable for low pressure use. In general, asteam trap consists of a valve and some deviceor arrangement that will cause the valve toopen and close as necessary to drain the condensatefrom the lines without allowing theescape of steam. Steam traps are installed at366

Chapter 14. -PIPING, FITTINGS, AND VALVES"1REGULAR STRAIGHT UNION C BRANCHUNIONELBOWUNION BULKHEADFITTING UNION RUNFigure 14-1.— Unions.11.313low points in the system or machinery to bedrained. Some types of steam traps that areused in the Navy are described here.MECHANICAL STEAM TRAPS.-Mechanicalsteam traps in common use include ball floattraps and bucket-type traps.A ball float steam trap is shown in figure14-4. The valve of this trap is connected to thefloat in such a way that the valve opens whenthe float rises. When the trap is in operation,the steam and any water that may be mixedwith it flows into the float chamber. As thewater level rises, it lifts the float and thisin turn lifts the valve plug and opens the valve.The condensate drains out and the float movesdown to a lower position, closing the valve.The condensate that passes out of the trap isreturned to the feed system.A bucket-type steam trap is shown in figure14-5. As condensate enters the trap body, thebucket floats. The valve is connected to thebucket in such a way that the valve closes as thebucket rises. As condensate continues to flow intothe trap body, the valve remains closed until thebucket is full. When the bucket is full, it sinksand thus opens the valve. The valve remainsopen until enough condensate has passed out toallow the bucket to float, thus closing the valve.THERMOSTATIC STEAM TRAPS.- Thereare several kinds of thermostatic steam trapsin use. In general, these traps are more compactand have fewer moving parts than mostmechanical steam traps.A bellows-type thermostatic steam trap isshown in figure 14-6. The operation of thistrap is controlled by the expansion of the vaporof a volatile liquid which is enclosed in a bellows-typeelement. Steam enters the trap bodyand heats the volatile liquid in the sealed bellows,thus causing expansion of the bellows. Thevalve is attached to the bellows in such a waythat the valve closes when the bellows expands.The valve remains closed, trapping steam inthe valve body. As the steam cools and condenses,367

PRINCIPLES OF NAVAL ENGINEERINGSTAINLESS STEELBELLOWSCOMPRESSION LIMITLIMITSTOPINTERNAL SLEEVEVALVE CONTROL^HV^EXTERNAL DIRTGUARDFLANGEFigure 14-2.— Bellows-typejoint.38.127Xexpansion11.312Figure 14-3.— Flareless fluid connection(bite-type fitting).the bellows cools and contracts, thereby openingthe valve and allowing the condensate to drain.IMPULSE STEAM TRAPS. -Impulse steamtraps of the type shown in figure 14-7 are usedin some steam drain collecting systems aboardship. Steam and condensate pass through astrainer before entering the trap. A circular

'Chapter 14. -PIPING, FITTINGS, AND VALVESVAPORVOLATILE LIQUIDVOLATILE LIQUIDVALVEREPLACEABLEHERMETICALLYSEALED BELLOWS(a)TRAP COLD: VALVE OPEN(b) TRAP HOT; VALVE CLOSEDFigure 14-6.— Thermostatic steam trap.11.326XLOCK NUTCYLINDER STEMCONTROLORIFICETO HIGH PRESSURE_^ORAIN SYSTEMCONTROLORIFICESTRAINERFigure 14-7.— Impulse steam trap.38.126this principle is utilized, we will consider thearrangement of parts shown in figure 14-7 andsee what happens to the flow of condensate undervarious conditions.The only moving part in the steam trap isthe disk. This disk is rather unusual in design.Near the top of the disk there is a flange thatacts as a piston. As may be seen in figure 14-7,the working surface above the flange is largerthan the working surface below the flange; theimportance of having this larger effective areaabove the flange will presently become apparent.A control orifice runs through the disk fromtop to bottom, being considerably smaller at thetop than at the bottom. The bottom part of thedisk extends through and beyond the orifice inthe seat. The upper part of the disk (includingthe flange) is inside a cylinder. The cylinder369

PRINCIPLES OF NAVAL ENGINEERINGtapers inward, so the amount of clearance betweenthe flange and the cylinder varies accordingto the position of the valve. When the valveis open, the clearance is greater than when thevalve is closed.When the trap is first cut in, pressure fromthe inlet (chamber A) acts against the undersideof the flange and lifts the disk off the valve seat.Condensate is thus allowed to pass out throughthe orifice in the seat; and, at the same time, asmall amount of condensate (called control flow)flows up past the flange and into chamber B, Thecontrol flow discharges through the control orifice,into the outlet side of the trap, and the pressurein chamber B remains lower than the pressurein chamber A.As the line warms up, the temperature of thecondensate flowing through the trap increases.The reverse taper of the cylinder varies theamount of flow around the flange until a balancedposition is reached in which the total forceexerted above the flange is equal to the totalforce exerted below the flange. It is importantto note that there is still a pressure differencebetween chamber A and chamber B. The forceis equalized because the effective area abovethe flange is larger than the effective area belowthe flange. The difference in working area issuch that the valve maintains an open, balancedposition when the pressure in chamber B is 86percent of the pressure in chamber A.As the temperature of the condensate approachesits boiling point, some of the controlflow going to chamber B flashes into steam asit enters the low pressure area. Since the steamhas a much greater volume than the water fromwhich it is generated, pressure builds up in thespace above the flange (chamber B). When thepressure in this space is 86 percent of the inletpressure (chamber A), the force exerted on thetop of the flange pushes the entire disk downwardand so closes the valve.With the valve closed, the only flow throughthe trap is past the flange and through the controlorifice. When the temperature of the condensateentering the trap drops slightly, condensateenters chamber B without flashing intosteam. Pressure in chamber B is thus reducedto the point where the valve opens and allowscondensate to flow through the orifice in thevalve seat. Thus the entire cycle is repeatedcontinuously.With a normal condensate load, the valveopens and closes at frequent intervals, discharginga small amount of condensate at eachopening. With a heavy condensate load, the valveremains wide open and allows a continuousdischarge of condensate.ORIFICE -TYPESTEAM TRAPS.-Aboardship, continuous-flow steam traps of the orificetype are used in some constant service steamsystems, oil heating steam systems, ventilationpreheaters, and other systems or services inwhich condensate forms at a fairly constantrate. Orifice-type steam traps are not suitablefor services in which the condensate formationis not continuous.There are several variations of the orificetypesteam trap, but all types have one thingin common—they contain no moving parts. Oneor more restricted passageways or orificesallow condensate to trickle through but do notallow steam to flow through. Some orifice-typesteam traps have baffles as well as orifices.BIMETALLIC STEAM TRAPS. -Bimetallicsteam traps of the type shown in figure 14-8are used on many ships to drain condensatefrom main steam lines, auxiliary steam lines,and other steam lines. The main working partsof this steam trap are a segmented bimetallicelement and a ball-type check valve.The bimetallic element consists of severalbimetallic strips2 fastened together in a segmentedfashion, as shown in figure 14-8. Oneend of the bimetallic element is fastened rigidlyto a part of the trap body; the other end, whichis free to move, is fastened to the top of thestem of the ball-type check valve.Line pressure acting on the check valvetends to keep the valve open. When steam entersthe trap body, the bimetallic element expandsunequally because of the differential responseto temperature of the two metals; the bimetallicelement deflects upward at its free end, thusmoving the valve stem upward and closing thevalve. As the steam cools and condenses, thebimetallic element moves downward, towardthe horizontal position, thus opening the valveand allowing some condensate to flow out throughthe valve. As the flow of condensate begins, agreater area of the ball is exposed to the higherpressure above the seat. The valve now openswide and allows a full capacity flow of condensate.2The principle of bimetallic expansion is discussedin chapter 7 of this text.370

Chapter 14. -PIPING,FITTINGS, AND VALVESdisks across each other in such a way as to removeany particles that have collected on themetal surfaces. Some metal- edge type filtershave magnets to aid in removing fine particlesof magnetic materials.VALVES147.104XFigure 14-8.— Bimetallic steam trap.STRAINERS AND FILTERSStrainers are fitted in practically all pipinglines to prevent the passage of grit, scale, dirt,and other foreign matter which could obstructpump suction valves, throttle valves, or othermachinery parts.Figure 14-9 illustrates three common typesof strainers. Part A shows a bilge suctionstrainer located in the bilge pump suction linebetween the suction manifold and the pump.Any debris which enters the piping is collectedin the strainer basket. The basket can be removedfor cleaning by loosening the strongbackscrews, removing the cover, and lifting thebasket out by its handle. Part B of figure 14-9shows a duplex oil strainer of the type commonlyused in fuel oil and lubricating oil lines,where it is essential to maintain an uninterruptedflow of oil. The flow may be diverted from onebasket to the other, while one is being cleaned.Part C of figure 14-9 shows a manifold steamstrainer. This type of strainer is desirablewhere space is limited, since it eliminatesthe use of separate strainers and their fittings.The cover is located so that the strainer basketcan be removed for cleaning.Metal-edge filters are used in the lubricationsystems of many auxiliary units. A metaledgefilter consists of a series of metal platesor disks. Turning a handle moves the plates orEvery piping system must have some meansof controlling the amount and direction of theflow of the contained fluid through the lines.The control of fluid flow is accomplished by theinstallation of valves.Valves are usually made of bronze, brass,iron, or steel. Steel valves are either cast orforged, and are made of either plain steel oralloy steel. Alloy steel valves are used in highpressure, high temperature systems; the disksand seats of these valves are usually surfacedwith Stellite, an extremely hard chromium-cobaltalloy.Bronze and brass valves are not used inhigh temperature systems. Also, they are notused in systems in which they would be exposedto severe conditions of pressure, vibration, orshock. Bronze valves are widely used in saltwater systems. The seats and disks of bronzevalves used for sea water service are oftenmade of Monel, a metal that is highly resistantto corrosion and erosion.Many different types of valves are used tocontrol the flow of liquids and gases. The basicvalve types can be divided into two groups,stop valves and check valves. Stop valves arethose which are used to shut off— or partiallyshut off— the flow of fluid. Stop valves are controlledby the movement of the valve stem.Check valves are those which are used to permitthe flow of fluid in only one direction. Checkvalves are designed to be controlled by themovement of the fluid itself.Stop valves include globe valves, gate valves,plug valves, piston valves, needle valves, andbutterfly valves. Check valves include ball-checkvalves, swing-check valves, and lift-checkvalves.Combination stop-check valves are valveswhich function either as stop valves or as checkvalves, depending upon the position of the valvestem.In addition to the basic types of valves, agood many special valves which cannot reallybe classified either as stop valves or as checkvalves are found in the engineering spaces.Many of these special valves serve to control371

PRINCIPLES OF NAVAL ENGINEERINGINLET FLANGESTRONGBACKCOVERBASKETHANDLEBASKETSTRAINER4 WAV PLUG COCK B OUTLET FLANGETO PUMPSUCTIONFigure 14-9.— A. Bilge suction strainer. B. Duplex oil strainer.C. Manifold steam strainer.11.329Xthe pressure of fluids and are therefore generallycalled pressure-control valves. Others areidentified by names which indicate their generalfunction— as, for example, thermostatic recir -culating valves . The following sections deal firstwith the basic types of stop valves and checkvalves and then with some of the more complexspecial kinds of valves.Globe ValvesGlobe valves are one of the commonest typesof stop valves. Globe valves get their namefrom the globular shape of their bodies. It isimportant to note, however, that other types ofvalves may also have globe-shaped bodies;hence it is not always possible to identify a globevalve merely by external appearance. The internalstructure of the valve, rather than the externalshape, is what distinguishes one type ofvalve from another.The disk of a globe valve is attached to thevalve stem. The disk seats against a seatingring or a seating surface and thus shuts off theflow of fluid. When the disk is moved off theseating surface, fluid can pass through the valve.Globe valves may be used partially open aswell as fully open or fully closed.Globe valve inlet and outlet openings arearranged in several ways, to suit varying requirementsof flow. Figure 14-10 shows threecommon types of globe valve bodies. In thestraight type, the fluid inlet and outlet openingsare in line with each other. In the angle type,the inlet and outlet openings are at an angleto each other. An angle-type globe valve isused where a stop valve is needed at a 90° turnin a line. The cross type of globe valve hasthree openings rather than two; it is often usedin connection with bypass piping.A globe-type stop valve is shown in crosssectionalview in figure 14-11. Figure 14-12shows a cutaway view of a similar (but notidentical) globe valve.Globe valves are commonly used in steam,air, oil, and water lines. On many ships, thesurface blow valves, the bottom blow valves,372

Chapter 14. -PIPING,FITTINGS, AND VALVESCROSS11.316XFigure 14-10.— Types of globe valve bodies.LIST OF PARTS |

PRINCIPLES OF NAVAL ENGINEERINGAs shown in figures 14-13 and 14-14, thegate is connected to the valve stem. Turningthe handwheel positions the valve gate. Somegate valves have nonrising stems— that is, thestem is threaded on the lower end and the gateis threaded on the inside so that the gate travelsup the stem when the valve is being opened. Gatevalves with nonrising stems are shown in figure14-13. This type of valve usually has a pointeror a gage to indicate whether the valve is inthe open position or in the closed position.Some gate valves have rising stems— that is,both the gate and the stem move upward whenthe valve is opened. In some rising stem valves,the stem projects above the handwheel whenthe valve is opened; in other rising stem valves,the stem does not project above the handwheel.A pointer or a gage is required to indicate theposition of the valve if the stem does not projectabove the handweel when the valve is inthe open position.LIST OF PARTS 1

Chapter 14. -PIPING, FITTINGS, AND VALVESin the body, the solid part of the plug blocks theports and thus prevents the flow of fluid.Plug valves are quite commonly used inconnection with auxiliary machinery. The petcocksthat are used as vents on lubricating oilcoolers for auxiliary machinery are usuallyplug valves. The three-way and four-way cocksthat allow selective routing of various fluidsare usually variations of the plug valve. Theshut off device that allows fuel oil or lubricatingoil to be diverted from one basket to anotherof a duplex strainer is often a modified plugvalve.Piston ValvesA piston valve is a stop valve that may bethought of as a combination of a gate valve anda plug valve. The piston valve consists basicallyof a cylindrical piston operating in a hollowcylinder. The piston is attached to the valvestem, and the valve stem is attached to a handwheel.When the handwheel is turned, the pistonis raised or lowered within the hollow cylinder.The cylinder has ports in its walls. When thepiston is raised, the ports are uncovered andfluid is allowed to pass through the valve.Needle ValvesNeedle valves are stop valves that are usedfor making relatively fine adjustments in theamount of fluid that is allowed to pass throughan opening. The distinguishing characteristicof a needle valve is the long, tapering, needlelikepoint on the end of the valve stem. This"needle" acts as the valve disk. The longerpart of the needle is smaller than the orificein the valve seat, and therefore passes throughit before the needle seats. This arrangementpermits a very gradual increase or decreasein the size of the opening and thus allows amore precise control of flow than could be obtainedwith an ordinary globe valve.Needle valves are used as overload nozzleson some auxiliary turbines. Needle valves areoften used as component parts of other morecomplicated valves. For example, they areused in some types of reducing valves. Mostconstant-pressure pump governors3 have needlevalves to minimize the effects of fluctuationsin pump discharge pressure. Needle valves^Constant -pressure pump governors are discussed inchapter 16 of this text.are also used in some components of automaticboiler control systems.Butterfly ValvesThe butterfly valve, shown in figure 14-15,is being used increasingly in naval ships. Thebutterfly valve has some definite advantagesfor certain services. It is light in weight, ittakes up less space than a gate valve or a globevalve of the same capacity, and it is relativelyquick acting. The butterfly valve provides apositive shutoff and may be used as a throttlingvalve set in any position from full open to fullclosed.Butterfly valves vary somewhat in designand construction. However, a butterfly-type diskand a positive means of sealing are common toall butterfly valves.The butterfly valve described and illustratedhere consists of a body, a resilient seat, abutterfly-type disk, a stem, packing, a notchedpositioning plate, and a handle. The resilientseat is under compression when it is mountedin the valve body, thus making a seal aroundthe periphery of the disk and both upper andlower points where the stem passes throughthe seat. Packing is provided to form a positiveseal around the stem if the seal formed by theseat should become damaged.To close a butterfly valve, it is only necessaryto turn the handle a quarter of a turn inorder to rotate the disk 90 degrees. The resilientseat exerts positive pressure against thedisk, ensuring a tight shutoff.Butterfly valves may be designed to meeta variety of requirements. The shipboard systemsin which these valves are now being usedinclude fresh water, salt water, JP-5, Navyspecial fuel, diesel oil, and lubricating oil.Check ValvesCheck valves are designed to permit flowthrough a line in one direction only. There arealmost innumerable examples of check valvesthroughout the engineering plant. Check valvesare used in open funnel drains, in fuel oil heaterdrains, and in various other drains. They areused in connection with many pumps, and inany line in which it is important to prevent theback flow of fluid.The port in a check valve may be closed bya disk, a ball, or a plunger. The valve openswhen the pressure on the inlet side is greater.375

PRINCIPLES OF NAVAL ENGINEERINGFigure11.319X14-16.— Swing-check valve.valves or as check valves, depending upon theposition of the valve stem. These valves areknown as stop-check valves .11.318Figure 14-15.— Butterfly valve.and closes when the pressure on the outlet sideis greater. All check valves open and closeautomatically.A swing- check valve is illustrated in figure14-16. Figures 14-17 and 14-18 show alift-checkvalve. As may be seen, the disk of the swingcheckvalve moves through an arc, while thedisk of a lift-check valve moves up and down inresponse to changes in the pressure of the incomingfluid. A good example of a ball-check valveis the discharge valve in the bimetallic steamtrap, described and illustrated earlier in thischapter.Stop-Check ValvesAs we have seen, most valves can be classifiedas being either stop valves or checkvalves.Some valves, however, function either as stopStop-check valves are shown in cross sectionin figure 14-19. As may be seen, this type ofvalve looks very much like a lift- check valve.However, the valve stem is long enough so thatwhen it is screwed all the way down it holdsthe disk firmly against the seat, thus preventingany flow of fluid. In this position, the valve actsas a stop valve. When the stem is raised, theside can be opened by pressure on the inletside. In this position, the valve acts as a checkvalve, allowing the flow of fluid in only oneThe maximum lift of the disk is con-direction.trolled by the position of the valve stem. Therefore,the position of the valve stem limits theamount of fluid passing through the valve evenwhen the valve is operating as a check valve.Stop -check valves are widely used throughoutthe engineering plant. One of the best examplesis the so-called boiler feed check valve,which is actually a stop- check valve ratherthan a true check valve. Stop- check valves areused in many drain lines; on the discharge sideof many pumps; and as exhaust valves on auxiliarymachinery.376

^iChapter 14. -PIPING.FITTINGS, AND VALVESLIST OF PARTS11.320Figure 14- 1 7. — Cutaway view of lift- checkvalve.Pressure-Control ValvesPressure- control valves are used to relieveor prevent excessive pressure, to reducepressure, and to control or regulate pressure.Several common types of pressure-controlvalves are described in the following paragraphs.RELIEF VALVES .-Relief valves are designedto open automaticially when the pressurein the line or in the machinery unit becomestoo high. There are several different types ofrelief valves, but most of them have a disk ora ball which acts against a coil spring. The springpushes downward against the disk or ball andso tends to keep the valve closed. When thepressure in the line or in the unit is greatenough to overcome the resistance of the spring,the disk or ball is forced upward and the valveis thereby opened. After the pressure has beenrelieved by the escape of fluid through the relief

PRINCIPLES OF NAVAL ENGINEERINGthe supply pressure is at least as high as the desireddelivery pressure) and regardless of theamount of reduced pressure fluid that is used.There are several kinds of spring-loadedreducing valves. The one shown in figure 14-20is used for steam service, but is very similarto spring-loaded reducing valves used for otherservices.The principal parts of the valve are (1) themain valve, an upward-seating valve which hasa piston on top of its valve stem; (2) an upwardseatingauxiliary (or controlling) valve; (3) acontrolling diaphragm; and (4) an adjustingspring.High pressure steam (or other fluid) entersthe valve on the inlet side and acts against themain valve disk, tending to close the main valve.However, high pressure steam is also led throughports to the auxiliary valve, which controls theadmission of high pressure steam to the top ofthe main valve piston. The piston has a largersurface area than the main valve disk; therefore,a relatively smallamount of high pressure steamacting on the top of the main valve piston willtend to open the main valve, and so allow steamat reduced pressure to flow out the dischargeside.But what makes the auxiliary valve open toallow high pressure steam to get to the top ofthe main valve piston? The controlling diaphragmtransmits a pressure downward upon the auxiliaryvalve stem, and thus tends to open the valve.However, reduced pressure steam is led backto the chamber beneath the diaphragm; this steamexerts a pressure upward on the diaphragm,which tends to close the auxiliary valve. Theposition of the auxiliary valve, therefore, is determinedby the position of the controlling diaphragm.The position of the diaphragm at any given momentis determined by the relative strength of twoopposing forces: (1) the downward force exertedby the adjusting spring, and (2) the upwardforce exerted on the underside of the diaphragmLIST OF PARTS |valves, sizes iand smaller may be[furnished with convexIIwELDING ENDS

Chapter 14. -PIPING, FITTINGS, AND VALVESLOCK NUTADJUSTING SCREWADJUSTING SPRINGCONTROLLING DIAPHRAGMPISTON STEAM PORTAUXILIARY VALVEPISTONHIGH PRESSURE-PORTAUXILIARY VALVESPRINGLOW PRESSUREPORTMAIN VALVE SPRING--MAIN VALVEDRAIN CONNECTIONFigure 14-20.— Spring-loaded reducing valve.47.59Xby the reduced pressure steam. These two forcesare continually seeking to reach a state of balance;and, because of this, the discharge pressureof the steam is kept constant as long as theamount of steam used is kept within the capacityof the valve.There are two types of gas-loaded (or pneumaticpressure controlled) reducing valves. Onetype, shown in figure 14-21, is designed to regulatepressure in low temperature air, water, oil,or other fluids. The other type, shown in figure14-22, is designed to regulate pressure in hightemperature steam, hot water, or other fluids.Both types of valves operate on the principle thatthe pressure of an enclosed gas varies inverselyas its volume.We will consider first the valve for low temperatureservice (fig. 14-21). In this valve, arelatively small change in the large volume withinthe dome loading chamber produces only aslight pressure variation, while the slightestvariation in the small volume within the actuatingchamber creates an enormous change inpressure. The restricting orifice connectingthese two chambers governs the rate of pressureequalization by retarding the flow of gas from onechamber to another.The dome loading chamber is charged with airor some other compressible gas at a pressureequal to the desired reduced pressure. When thechamber is loaded, and the loading valve isclosed, the dome will retain its charge almostindefinitely. When the regulator is in operation,the trapped pressure within the dome passes intothe actuating chamber through the small separationplate orifice and moves the large flexible379

PRINCIPLES OF NAVAL ENGINEERINGDOMELOADINGCHAMBERSEPARATIONPLATEORIFICEDOMESEPARATINGPLATEDIAPHRAGMPLATEPLUG{FOR EXTERNALCHARGING)DOMENEEDLEVALVEDIAPHRAGMCHARGINGCONNECTIONRELIEFVALVEPRESSUREEQUALIZINGORIFICEDIAPHRAGMPLATESPRINGACTUATINGCHAMBEROUTLETBODYNEEDLEVALVEVALVESEATVALVEVALVESPRINGCAGEFigure47.6014-21.— Pneumatic pressure controlled reducing valve for low temperature servicediaphragm. This action forces the reverse-actingvalve off its seat. The pressure enteringthe regulator is then permitted to flow throughthe open valve into the reduced pressure line.A large pressure equalizing orifice transmitsthis pressure directly to the underside of thediaphragm. When the delivered pressure approximatesthe loading pressure in the dome,and the unbalanced forces are equalized, thevalve is closed. With the slightest drop indelivered pressure, the pressure charge in thedome instantly forces the valve open, thus allowingair to pass through the valve and maintain theoutlet pressure relatively constant.The pneumatic pressure controlled reducingvalve for high temperature service (fig, 14-22)operates in much the same way as the valve forlow temperature service, except that the valvefor high temperature service.is designed in sucha way as to keep heat from the hot fluid from affectingthe gas in the loading chamber. The380

Chapter 14. -PIPING,FITTINGS, AND VALVESVALVE SPRING VALVE GUIDEGLYCERINE SEALFILLING PLUGVALVE DISKCOOLINGFINSBLEEDER VALVE CHECK VALVEAIR GAUGE AND PUMP CONNECTIONHERE11.323Figure 14-22.— Pneumatic pressure controlledreducing valve for high temperature service.loading chamber is surrounded by a finned hoodwhich conducts heat away to atmosphere.A rubber diaphragm is installed in the middleof the dome. The bottom of the diaphragm isseparated from the bottom half of the dome by afixed steel plate. The area immediately above thediaphragm communicates with the upper part ofthe dome through holes in the shrouding. The upperhalf of the dome carries a level of water forsealing; the lower half of the dome carries alevel of glycerine for sealing. The area abovethe glycerine is charged with air, which exertsa downward pressure on the glycerine and forcessome of it to go up the tube toward the diaphragm.This pressure causes the diaphragm to move upward;and, since the stem of the valve is in contactwith the diaphragm, the upward movementof the diaphragm causes the valve to open. Whenthe valve is open, steam can pass through it.From the outlet connection, an actuating lineleads back to the upper part of the dome, asshown in the illustration. Steam at the reducedpressure is thus allowed to exert a force on thetop of the water seal; this force is transmittedthrough the water and tends to move the diaphragmdownward. When the pressure of thesteam from the actuating line exceeds the loadingair pressure in the lower half of the dome, thediaphragm moves downward sufficiently to closethe valve. The closing of the valve reduces thepressure of the steam on the discharge side ofthe valve. When the pressure on the outlet sideof the valve is equal to the air pressure in thelower half of the dome, the valve takes a balancedposition which allows the passage of sufficientsteam to maintain that pressure.If the load increases, tending to take moresteam away from the valve, the outlet pressurewill be momentarily reduced. Thus, the pressureof steam on top of the diaphragm becomes lessthan the pressureof air below the diaphragm, andthe valve then opens wider to restore the pressuretonormal.If the load is reduced, this causesa momentary increase in outlet pressure; andthis in turn increases the pressure on top of thediaphragm, making it greater than the air pressurebelow the diaphragm. The diaphragm istherefore displaced downward, and the outletpressure is again restored to normal.DIAPHRAGM CONTROL VALVES WITH AIR-OPERATED CONTROL PILOTS.-Diaphragmcontrol valves with air-operated control pilotsare being used increasingly on newer ships forvarious pressure- control applications. Thesevalves and pilots are available in several basicdesigns to meet different requirements. Theymay be used to reduce pressure, to augmentpressure, or to provide continuous regulation ofpressure, depending upon the requirements of thesystem in which they are installed. Valves andpilots of very similar design can also be used forother services such as liquid level control andtemperature control. However, the discussionhere is limited to the valves and pilots that areused for pressure- control applications.The air-operated control pilot may be eitherdirect acting or reverse acting. A direct-actingair-operated control pilot is shown in figure14-23. In this type of pilot, the controlled pressure—thatis, the pressure from the dischargeside of the diaphragm control valve— acts on topof a diaphragm in the control pilot. This pressureis balanced by the pressure exerted by thepilot adjusting spring. If the controlled pressureincreases and overcomes the pressure exertedby the pilot adjusting spring, the pilot valve stemis forced down. This action causes the pilot valveto open and so to increase the amount of operating381

PRINCIPLES OF NAVAL ENGINEERINGCONTROLLED PRESSURE'AIR SUPPLYl^TO DIAPHRAGMControl valveFigure 14-23,—Air-operated control pilot.38.121Xair pressure going from the pilot to the diaphramcontrol valve. A reverse-acting pilot has a leverwhich reverses the pilot action. In a reverseactingpilot, therefore, an increase in controllingpressure produces a decrease in operating airpressure.In the diaphragm control valve, operating airfrom the pilot acts on the valve diaphragm. Thesuperstructure which contains the diaphragm isdirect acting in some valves and reverse actingin others. If the superstructure is direct acting,the operating air pressure from the control pilotis applied to the top of the valve diaphragm. Ifthe superstructure is reverse acting, the operatingair pressure from the pilot is applied to theunderside of the valve diaphragm.Figure 14-24 shows a very simple type ofdirect-acting diaphragm control valve, withoperating air pressure from the control pilot appliedto the topof the valve diaphragm. Since thisis a downward seating valve, any increase inoperating air pressure pushes the valve stemdown and tends to close the valve.Now let us look at figure 14-25. This is alsoa direct-acting valve, with operating air pressurefrom the control pilot applied to the top ofthe valve diaphragm. But the valve shown infigure 14-25 is more complicated than the oneshown in figure 14-24. The valve shown in figure14-25 is an upward seating valve, rather than adownward seating valve. Therefore, any increase382

Chapter 14. -PIPING,FITTINGS, AND VALVES'.•i?^.*h HIGHPRESSURE-^STEAM^OPERATINGAIR PRESSUREFROM CONTROLPILOTREDUCEDPRESSURESTEAMSuppose that we try it first with a direct-actingcontrol pilot. As the controlled pressure (dischargepressure from the diaphragm controlvalve) increases, increased pressure would beapplied to the diaphragm of the direct-acting controlpilot. The valve stem would be pushed downand the valve in the control pilot would be opened,thus sending an increased amount of operatingair pressure from the control pilot to the top ofthe diaphragm control valve. The increasedoperating air pressure acting on the diaphragmof the valve would push the stem down and— sincethis is anupwardseatingvalve— this action wouldopen the diaphragm control valve still wider. Obviously,this will not work. For this application,an increase in controlled pressure must resultin a decrease in operating air pressure. Therefore,we should have chosen a reverse-actingcontrol pilot rather than a direct-acting one forthis particular pressure- reducing application.It is left as an exercise to the student to tracethe sequence of events as they would occur with areverse-acting control pilot installed in the arrangementshown in figure 14-26.Figure38.123X14-24,— Direct-acting downward seatingdiaphragm control valve.OPERATINGAIR PRESSUREFROM CONTROLPILOTin operating air pressure from the control pilottends to open this valve rather than close it.As we have seen, the air-operated controlpilot may be either direct acting or reverse acting,the superstructure of the diaphragm controlvalve may be either direct acting or reverse acting,and the diaphragm control valve may beeither upward seating or downward seating.These three factors, as well as the purpose of theinstallation, determine how the diaphragm controlvalve and its air-operated control pilot areinstalled in relation to each other.To see how these factors are related, let usconsider an installation in which a diaphragmcontrol valve and its air-operated control pilotare to be used to supply reduced pressure steam.Figure 14-26 shows one arrangement that mightbe used. We will assume that the service requirementsindicate the need for a direct-acting upwardseating diaphragm control valve. What kindof a control pilot— direct acting or reverse actingwould have to be used in this installation?HIGHPRESSURESTEAMFigure38.124X14-25.— Direct-acting upward seatingdiaphragm control valve.383

PRINCIPLES OF NA7AL ENGINEERINGCONTROLPILOTto the condenser. The unloading pressure can beadjusted by turning an adjusting screw, therebychanging the force exerted on the actuating valvediaphragm.Thermostatic Recirculating Valves38.125Figure 14-26.—Arrangement of control pilot anddiaphragm control valve for supplying reducedpressure steam.UNLOADING VALVES.- An automaticunloadingvalve (also called a dumping valve) is installedat each main and auxiliary condenser.The function of the unloading valves is to dischargesteam from the auxiliary exhaust line tothe condensers whenever the auxiliary exhaustline pressure exceeds the design operating pressure.An automatic unloading valve is shown infigure 14-27. Auxiliary exhaust steam is ledthrough valve A to the top of the actuating valvediaphragm. The actuating valve is double seated,and one side is open when the other is closed.When the auxiliary exhaust line pressure is lessthan the pressure for which the unloading valveis set, the upper seat is closed and the lower seatis open. The valve is thus held by the diaphragmspring. Steam passes into the line through valveB and goes under the unloading valve diaphragm.The pressure acting on this diaphragm holds theunloading valve up and closed. If the auxiliary exhaustpressure exceeds the pressure of the actuatingvalve diaphragm spring, the diaphragmis forced downward and the lower seat closeswhile the upper seat opens. This makes a directconnection between the top and the bottom of theunloading valve diaphragm through the actuatingvalve. The equalized pressure on the diaphragmallows the auxiliary exhaust pressure to force theunloading valve down and steam is thus unloadedThermostatic recirculating valves are usedin systems where it is necessary to recirculatea fluid in order to maintain the temperature withincertain limits. Thermostatic recirculatingvalves are designed to operate automatically.The thermostatic recirculating valve shownin figure 14-28 is used to recirculate condensatefrom the discharge side of the main air ejectorcondenser to the main condenser. 5 The valve isactuated by the temperature of the condensate.When the condensate temperature becomeshigher than the temperature for which the valveis set, the thermostatic bellows expands and automaticallyopens the valve, allowing condensateto be sent back to the condenser.Valve ManifoldsA valve manifold is used when it is necessaryto take suction from one of several sources andto discharge to another unit or several units ofthe same or a separate group. One example of amanifold is shown in figure 14-29. This manifoldis used in the fuel oil filling and transfersystem, where provision must be made for thetransfer of oil from any tank to any other tank, tothe fuel oil service system, or to another ship.The manifold valves are frequently of the stopchecktype.Remote Operating GearRemote operating gear is installed to providea means of operating certain valves from distantstations. Remote operating gear may be mechanical,hydraulic, pneumatic, or electric.Some remote operating gear for valves isused in the normal operation of the valves. Forexample, the propulsion turbine throttle valvesare opened and closed by a series of reach rodsand gears. In the fireroom, remote operatinggear is used to operate the forced draft blowers,to adjust the constant-pressure pump governoron the fuel oil service pump, and to lift safetyvalves by hand.^Air ejector assemblies are discussed in chapter 13of this text.384

Chapter 14. -PIPING,FITTINGS, AND VALVESADJUSTINGSCREWMANUAL CONTROLVALVE WHEELFigure 14-27.— Automatic unloading valve.47.61XOther remote operating gear is installed asemergency equipment. For example, the boilersteam stops have remote operating gear whichcan usually be operated from the main deck orfrom the second deck, near the general quartersstation for damage control personnel of Repair5 (propulsion repair). This remote operatinggear is frequently mechanical or pneumatic,although hydraulic rem.ote operating gear isused for these valves on some ships. The pneumaticand hydraulic types of remote operatinggear for these valves allow the valves to beclosed but not opened from the remote station.Another example of emergency remote operatinggear is the gear that allows the quickclosingfuel oil valve to be closed from a remotestation in the fireroom escape trunk or from thedeck above and near the access to the space.Still other examples of emergency remote operatinggear include gear for operating somecross-connection valves, main drainage valves,and main condenser injection and overboard dischargevalves.Remote operating gear for valves includes avalve position indicator to show whether thevalve is open or closed.385

PRINCIPLES OF NAVAL ENOTNTTRPTOr.STEM HEADOVERRUN SPRINGFRAMEPACKING NUTBELLOWSBACKINGBOLANDTEFLON PACKING RINGSPRING PLATE'ACKING SPRING.OWER STEMLOAD SPRINGSCALE PLATEADJUSTING NUTSTEM ADJUSTINGASSEMBLYOVERRUN SPRINGSTEMCRANKPIN BUSHINGCRANK(SHOWN 180'OUTOPPOSITION)PINION GEARASSEMBLYTHRUST BEARINGSENSING BUL8ADJUSTING SLEEVESTEM SEATING ASSEMBLYCONNECTORPACKING BOX(SEE DETAIL)INLETPOPPETCAPFigure 14-28.-Thermostatic recirculating valve.47,175386

Chapter 14. -PIPING,FITTINGS, AND VALVESDISCHARGE STOP VALVESUCTION STOPCHECK VALVEDISCHARGEVALVESPUMPDISCHARGECONNECTIONPUMP SUCTION CONNECTIONFigure 14-29.— Valve manifold.47.63XIDENTIFICATION OF VALVES.FITTINGS, FLANGES. AND UNIONSMost valves, fittings, flanges, and unions usedon naval ships are marked with identificationsymbols of various kinds. The few valves andfittings that are made on board repair ships ortenders or at naval shipyards are usually markedwith symbols indicating the manufacturing activity,the size, the melt or casting number, andthe material. They may also be marked with anarrow to indicate the direction of flow.Commercially manufactured valves, fittings,flanges, and unions may be identified accordingto the requirements of the applicable specifications.However, many valves, fittings, flanges,and unions are now identified according to astandard marking system developed by the ManufacturersStandardization Society (MSS) of thevalves and fittings industry. Identification markingsin this system usually include the manufacturer'sname or trademark, the pressure andservice for which the product is intended, andthe size (in inches). When appropriate, materialidentification, limiting temperatures, and otheridentifying data are included.The MSS standard identification markingsare generally cast, forged, stamped, or etchedon the exterior surface of the product. In somecases, however, the markings are applied to anidentification plate rather than to the actualsurface of the product.The service designation in the MSS systemof marking usually includes a letter to indicatethe type of service and numerals to indicatethe pressure rating in psi. The letters used inservice designations are:AGLOWD-W-Vairgasliquidoilwaterdrainage, waste, and vent387

PRINCIPLES OF NAVAL ENGINEERINGWhen the primary service rating is forsteam, and when no other service is indicated,the service designation may consist of numeralsonly. For example, the number 600 marked onthe body of a valve would indicate that the valveis suitable for steam service at 600 psi. If thevalve is designed for water at 600 psi, the servicedesignation would be 600 W. Service designationsare also used in combination; for example,3000 WOO indicates a product suitable forwater, oil, or gas service at 3000 psi.Some abbreviations that are commonly usedfor material identification in the MSS systeminclude the following:ALBCSCIHFAluminumBronzeCarbon SteelCast IronCobalt- chromiumtungstenalloy (hardfacing)CU NICopper-nickel alloyNI CUNickel-copper alloySMSoft metal (lead. Babbitt,copper, etc.)CR 1313-percent chromiumsteel18 8 18-8 stainless steel18 8SMO 18-8 stainless steelwith molybdenumSHSurface-hardenedsteel (Nitralloy, etc.)Some examples of MSS standard identificationmarking symbols are given in figure 14-30.PACKING, GASKETS, AND INSULATIONPacking and gasket materials are requiredto seal joints in steam, water, gas, air, oil, andother lines and to seal connections which slideor rotate under operating conditions. There aremany types and forms of packing and gasketmaterial available commercially. To simplifythe selection of packing and gasket materialscommonly used in the naval service, engineeringpersonnel use a packing and gasket chart^showing the symbol numbers and the recommendedapplications of all types and kinds ofpacking and gasket material.The chart is identified as NavShips MechanicalStandard Drawing B-153.The symbol numbers used to identify eachtype of packing and gasket consists of a fourdigitnumber. The first digit indicates the classof service with respect to fixed and movingjoints; the digit 1 indicates a moving joint (movingrods, shafts, valve stems, etc.) and the digit2 indicates a fixed joint (flanges, bonnets, etc.).The second digit indicates the material of whichthe packing or gasket is primarily composedasbestos,vegetable fiber, rubber, metal, etc.The third and fourth digits indicate the differentstyles or forms of the packing or gaskets madefrom the material.Pressure, temperature, and other serviceconditions impose definite restrictions upon theapplication of the various kinds of packing andgasket materials. Great care must be taken tosee that the proper materials are selected foreach application, particularly when high pressuresor high temperatures are involved.Insulation is used on most shipboard pipingsystems. Insulation is actually a compositecovering which includes (1) the insulating materialitself, (2) the lagging or covering, and (3)the fastenings which are used to hold the insulationand lagging in place. In some instances,the insulation is covered by material whichserves both as lagging and as a fastening device.Insulating materials commonly used in theNavy include magnesia, calcium silicate, diatomaceoussilica, asbestos felt, mineral wool,fibrous glass, and high temperature insulatingcement. Cork, although light in weight and easyto handle, is not fire-retardant and in burningit gives off a dense, suffocating smoke; hencecork is used only in certain applications andonly after it has been treated with a fireresistantcompound.Lagging may consist of cloth, tape, or sheetmetal. Lagging serves to protect the relativelysoft insulating material from damage, to giveadded support to insulation that may be subjectedto heavy or continuous vibration, andto provide a smooth surface that may bepainted.Lagging is secured in place by sewing orby using fire-resistant adhesives, insulatingcement, or sealing compounds. The methodused to fasten the lagging in place depends uponthe type of insulation used, the type of laggingused, and the service requirements of thepiping or surfaces to be insulated.388

Chapter 14. -PIPING, FITTINGS, AND VALVES3-INCH CASTSTEELSCREWEDFITTINGSUIT-ABLE FOR WATER, OIL, OR GAS SERVICE AT1000 PSI:Manufacturer's identification . .Service designationMaterial designationB CO1000 WOGSTEELSize . 3

PRINCIPLES OF NAVAL ENGINEERINGmust be locked or wired shut and must be taggedso that they will not be opened accidentally.2. Be sure that the line is completelydrained.3. In breaking a flanged joint, leave twodiametrically opposite securing nuts in placewhile loosening the others. Then slack off onthe last two nuts. When you are sure beyondthe slightest doubt that the line is clear, removethe nuts and break the joint.4. Take all appropriate precautions to preventfire and explosion when cutting into linesor breaking joints in systems that have containedflammable fluids.5. Observe all safety precautions requiredin connection with welding, brazing, or otherprocesses used in repairing the piping.6. Before repaired piping is put back intoservice, various tests and inspections may berequired. Specific requirements for tests andinspections may be given along with instructionsfor the repair job; or you may find test andinspection requirements indicated on the plansor blueprints. If specific instructions are notgiven, consult chapter 9480 of the Naval ShipsTechnical Manual.390

CHAPTER 15PUMPS AND FORCED DRAFT BLOWERSThis chapter deals with shipboard pumps andwith the forced draft blowers used aboard manysurface ships to supply combustion air to thepropulsion boilers. In general, we are concernedhere with the driven end of the units rather thanwith the driving end; the auxiliary steam turbinesused to drive many pumps and blowers are discussedin chapter 16 of this text, and the electricmotors used to drive others are discussedin chapter 20.PUMPSAs we saw in chapter 8, the pump is one ofthe five basic elements in any thermodynamiccycle. The function of the pump is to move theworking substance from the low pressure sideof the system to the high pressure side. In theconventional steam turbine propulsion plant,"the pump" of the thermodynamic cycle is actuallythree pumps— the condensate pump, thefeed booster pump, and the main feed pump.In addition to these three pumps which are apart of the basic thermodynamic cycle, there are,of course, a large number of pumps used forother purposes aboard ship. Pumps supply seawater to the firemains, circulate cooling waterfor condensers and coolers, empty the bilges,transfer fuel oil, discharge fuel oil to theburners, supply lubricating oil to main and auxiliarymachinery, supply sea water to the distillingplant, pump the distillate into storage tanks, supplyliquid under pressure for use in hydraulicallyoperated equipment, and provide a variety ofother vital services.Pumps are used to move any substance whichflows or which can be made to flow. Most commonly,pumps are used to move water, oil, andother liquids. However, air, steam, and othergases are also fluid and can be moved withpumps, as can such substances as molten metal,sludge, and mud.A pump is essentially a device which utilizesan external source of power to apply a force to afluid in order to move the fluid from one placeto another. A pump develops no energy of its own;it merely transforms energy from the externalsource (steam turbine, electric motor, etc.) intomechanical kinetic energy, which is manifestedby the motion of the fluid. This kinetic energy isthen utilized to do work— for example, to raisea liquid from one level to another, as when wateris raised from a well; to transport a liquidthrough a pipe, as when oil is carried through anoil pipeline; to move a liquid against someresistance, as when water is pumped to a boilerunder pressure; or to force a liquid through ahydraulic system, against various resistances,for the purpose of doing work at some point.Principles and DefinitionsBefore considering specific designs of shipboardpumps, it may be helpful to examinebriefly certain basic concepts and to define someof the terms commonly used in connection withpumps.FORCE - PRESSURE - AREA RELATION-SHIPS.— When we strike the end of a bar, the mainforce of the blow is carried straight through tothe other end. This happens because the bar isrigid. The direction of the blow almost entirelydetermines the direction of the transmittedforce. The more rigid the bar, the less force islost inside the bar or transmitted outwardat right angles to the direction of the blow.When weapplypressureto theendof a columnof confined liquid, however, the pressure istransmitted not only straight through to the otherend but also equally and undiminished in everydirection. Figure 15-1 illustrates thedifferencebetween pressure applied to a rigid bar and pressureapplied to a column of contained liquid.391

PRINCIPLES OF NAVAL ENGINEERING

Chapter 15. -PUMPS AND FORCED DRAFT BLOWERSFigure 15-2. — Pressure in liquid is not affected by the shape of the vessel.147.105When the pump is installed below this level,as shown in figure 15-4, a certain amountof energy in the form of gravity head will alreadybe available when the liquid enters the pump. Inother words, there is a static pressure head , A,on the suction side of the pump. This head is partof the total input head necessary to produce theoutput head, F, that is required to raise theliquid to the top, T, of the discharge reservoir.liFORCE 1=20 LBS-PISTON 12 SO. IN.10 LBS. PER SO. INCHPISTON 220 SO. INFORCE 2 =200 LBSFttW?"rttf f t::\LLLLLL14.7Figure 15-3. — Relationship of force, pressure,and area in a simple hydraulic system.The action of the pump produces the total headdifferential . B, which can be broken down intofriction loss , C , and net static dischargehead , D. Since D_ is the vertical distance fromthe surface of the supply liquid to the surface ofthe liquid in the discharge reservoir, it is clearthat our previous definition of head would applyonly to ID. E, the total static discharge head, isthe vertical distance from the center of the pumpto the surface of the liquid in the discharge reservoir;thus, ^ is equal to D plus A.As may be seen in figure 15-4, atmosphericpressure is acting upon the free surface of thesupply liquid and upon the free surface of theliquid in the discharge reservoir. Since atmosphericpressure is exerted equally on both sidesof the pump, in this system, the two heads createdby atmospheric pressure cancel out.Now consider the case of a pump that is installeda vertical distance^ above the free surface^ofthe supply liquid (fig. 15-5). In this case,energy must be supplied merely to get the liquidinto the pump (static suction lift . A). In addition,energy must be supplied to produce the staticdischarge head , E, if the liquid is to be raisedto the top of the discharge reservoir, T. B, thetotal head differential produced by pump action,is here the total energy input. It is divided intoA on the suction side— the head required to raise393

PRINCIPLES OF NAVAL ENGINEERINGTOTAL HEADDIFFERENTIALPRODUCED BY PUMPFRICTION LOSS147.106Figure 15-4. — Pressure head (pump installedbelow surface of supply liquid).tlieCliquid to the pump— and C (friction loss) plusE ( static discharge head ) on the discharge side.Atmospheric pressure cancels out here, asbefore, except that in this case the atmosphericpressure at S^is required to lift the liquid to thepump.In both of the cases just described, we havedealt with systems which were open to the atmosphere.Now let us examine the head relationshipsin a closed system such as the one shown in figure15-6.In this system, a pump is being used to drivea work piston back and forth inside a cylinder. Wewill assume that the pump must develop a pressureequivalent to head H^ in order to drive thepiston back and forth against the resistance offered.Under this assumption, the total head differential,B^, must be produced by the pump afterthe system has begun to operate. Bis the sum ofthe friction head (or friction losses), C, and thestatic discharge head , D^. Since ^ is equal to H,D therefore produces the pressure required todo the work.Since the liquid returns to its original leveland the system is closed throughout, there willbe a siphon effect in the return pipe which willexactly balance the static suction lift, A.Therefore, atmospheric pressure plays a partin the operationof this system only when the systemis being started up, before the entire system^has been filled with liquid.At this point, we may pause and consider thevarious ways in which the term head has beenused, and attempt to formulate a definition.. Fromprevious discussion, we may infer that head is(1) measured in feet; (2) somehow related topressure; and (3) taken as some kind of a measureof energy. But what is it?NETSTATICHEADFRICTION LOSSSTATICDISCHARGEHEADi'/Ji I i cri_rTOTAL HEADDIFFERENTIALPRODUCED BYPUMPi U . i iAi i 11-147.107Figure 15-5.— Pressure head (pump installedabove surface of supply liquid).Figure147.10815-6.— Pressure head (closed system).394

Chapter 15. -PUMPS AND FORCED DRAFT BLOWERSBasically, head is a measure of the pressureexerted by a column or body of liquid because ofthe weight of the liquid. In the case of water, wefind that a column of fresh water 2.309 feet highexerts a pressure of 1 pound per square inch.When we refer to a head of water of 2.309 feet,we know that the water is exerting a pressure of1 psibecauseof its own weight. Thus, a referenceto a head of so many feet of water does imply areference to the pressure exerted by that water.The situation is somewhat different when wehave a horizontal pipe through which water isbeing pumped. In this case, the head is calculatedas the vertical distance that would correspond tothe pressure. If the pressure in the horizontalpipe is 1 psi, then the head on the liquid in thepipe is 2.309 feet. Further calculations show thata head of 1 foot corresponds to a pressure of0.433 psi.The relationship between head and energy canbe clarified by considering that (l)workisa formof energy— mechanical energy in transition; (2)work is the product of a force times the distancethrough which it acts; and (3) for liquids, the workperformed is equal to the volume of liquid movedtimes the head against which it is moved. Thusthe head relationships actually indicate some ofthe energy relationships for a given quantity ofliquid.VELOCITY HEAD. - The head required toimpart velocity to a liquid is known as velocityhead. It is equivalent to the distance throughwhich the liquid would have to fall in order to acquirethe same velocity. If we know the velocityof the liquid, we can compute the velocity headby the formulawhereHV2g= velocity head, in feetV = velocity of liquid, in feet per secondg = acceleration due to gravity (32.? feet persecond per second)In a sense, velocity head is obtained at theexpense of pressure head. Whenever a liquid isgiven a velocity, some part of the original staticpressure head must be used to impart this veloc-ity. However, velocity head does not represent atotal loss, since at least a portion of the velocityhead can always be reconverted to static pressurehead.FRICTION HEAD. -The force or pressurerequired to overcome friction is also obtained atthe expense of the static pressure head. Unlikevelocity head, however, friction head cannot be"recovered" or reconverted to static pressurehead, since fluid friction results in the conversionof mechanical kinetic energy to thermalenergy. Since this thermal energy is usuallywasted, friction head must be considered as atotal loss from the system.BERNOULLI'S THEOREM. -At any point ina system, the static pressure head will alwaysbe the original static pressure head minus thevelocity head and minus the friction head. Sinceboth velocity head and friction head representenergy which comes from the original staticpressure head, the sum of the static pressurehead, the velocity head, and the friction head atany point in a system must add up to the originalstatic pressure head. This general principle,which is known as Bernoulli's theorem , may alsobe expressed as2 2P, V P VZ +-i+_i=Z +-?+-f+[J(U -U,)-Wk-JQ]where'D 2g -^ D 2g ^ 'Z = elevation, in feetP = absolute pressure, in pounds per squarefootD = density of liquid, in pounds per cubic footV = velocity, in feet per secondg = acceleration due to gravity (32.2 feet persecond per second)J = the mechanical equivalent of heat, 778 footpoundsper BtuU = internal energy, in BtuWk =work, in foot-poundsQ = heat transferred, in BtuWhen written in this form, Bernoulli's theoremmay be readily recognized as a specialstatement of the general energy equation. Thebracketed term represents energy in transitionas work, energy in transition as heat, and the395

PRINCIPLES OF NAVAL ENGINEERINGincrease in internal energy of the fluid arisingfrom friction and turbulence. In some cases offluid flow, all elements in the bracketed term areof such small magnitude that they may be safelydisregarded.Consideration of Bernoulli's theorem indicatesthat the term pressure head , as used inconnection withpumps and other hydraulic equipment,is actually a measure of mechanical potentialenergy ; that velocity head is a measure ofmechanical kinetic energy ;and that friction headis a measure of the energy which departs fromthe system as thermal energy in the form of heator of the energy which remains in the liquid, generallyunusable, in the form of internal energy.Types of PumpsPumps are so widely used for such variedservices that the number of different designs isalmost overwhelming. As a general rule, however,it may be stated that all pumps are designedto move fluid substances from one point to anotherby pushing, pulling, or throwing, or by somecombination of these three methods.Every pump has a power end and a fluid end.The power end may be a steam turbine, a reciprocatingsteam engine, a steam jet, or an electricmotor. In steam-driven pumps, the powerend is often called the steam end . The fluid endis usually called the pump end. However, it maybe called the liquid end , the water end , the oilend, or some other term to indicate the natureof the fluid substance being pumped.Pumps are classified inanumber of differentways according to various design and operationalfeatures. Perhaps the basic distinction isbetween positive-displacement pumps and continuous-flowpumps. Pumps may also be classifiedaccording to the type of movement thatcauses the pumping action; by this classification,we have reciprocating, rotary, centrifugal, propeller,and jet pumps. Another classification maybe made according to speed; some pumps run atvariable speed, others at constant speed. Somepumps have a variable capacity, others dischargeat a constant rate. Some pumps are self-priming,others require a positive pressure on the suctionside before they can begin to operate. These andother distinctions are noted as appropriate in thefollowing discussion of specific types of pumps.RECIPROCATING PUMPS.-A reciprocatingpump moves water or other liquid by means ofa plunger or piston that reciprocates inside acylinder. Reciprocating pumps are positivedisplacementpumps; each stroke displaces acertain definite quantity of liquid, regardless ofthe resistance against which the pump is operating.The two main parts of a reciprocating pumpare the water end, which consists of a piston andcylinder arrangement and appropriate suctionand discharge valves, and the steam endl, whichconsists of another piston and cylinder and appropriatevalves for the admission and releaseof steam.Reciprocating pumps in naval service areusually classified as:1. Direct-acting or indirect-acting,2. Simplex (single) or duplex (double).3. Single-acting or double-acting.4. High pressure or low pressure.5. Vertical or horizontal.The reciprocating pump shown in figure 15-7is a direct-acting, simplex, double-acting, highpressure, vertical pump. Now let us see what allthese terms mean, with reference to the pumpshown in the illustration.The pump is direct-acting because the pumprod is a direct extension of the piston rod; thusthe piston in the power end is directly connectedto the plunger in the liquid end. Most reciprocatingpumps used in the Navy are direct-acting. Anindirect-acting pump may be driven by means ofa beam or linkage which is connected to and motivatedby the steam piston rod of a separate reciprocatingengine; or it may be driven by a crankand connecting rod mechanism which is operatedby a steam turbine or an electric motor. An indirect-actingpump might appear to have onlyone end— that is, the pump end. However, thispump, as all others, must have a power end aswell; the separate engine, turbine, or motorwhich drives the pump is the actual power end ofthe pump.The pump shown in figure 15-7 is called asingle or simplex pump because it has only oneliquid cylinder. Simplex pumps may be eitherdirect-acting or indirect-acting. A double or1 Practically all reciprocating pumps in naval use aresteam driven. However, a few low pressure, motordrivenreciprocating pumps are used for fresh water,sanitary, bilge, ballast, and fuel oil transfer services.These pumps are generally horizontal. When driven byan electric motor, reciprocating pump is usually referredto as a power pump.396

Chapter 15. -PUMPS AND FORCED DRAFT BLOWERSFigure 15-7.— Reciprocating pump.38.98397

PRINCIPLES OF NAVAL ENGINEERINGduplex pump is an assembly of two single pumpsplaced side by side on the same foundation; thetwo steam cylinders are cast in a single blockand the two liquid cylinders are cast in anotherblock. Duplex reciprocating pumps are seldomfound in modern combatant ships but were oncecommonly used in the Navy.In a single-acting pump, the liquid is drawninto the liquid cylinder on the first or suctionstroke and is forced out of the cylinder on thereturn or discharge stroke. In a double-actingpump, each stroke serves both to draw in liquidand to discharge liquid. As one end of the cylinderis filled, the other end is emptied; on thereturn stroke, the end which was just emptied isfilled and the end which was just filled is emptied.The pump shown in figure 15- 7 is double-acting,as are most of the reciprocating pumps used inthe Navy.The pump shown in figure 15- 7 is designed tooperate with a discharge pressure which ishigher than the pressure of the steam operatingthe piston in the steam cylinder. In other words,this is a high pressure pump . In a high pressurepump, the steam piston is larger in diameter thanthe plunger in the liquid cylinder. Since the areaof the steam piston is greater than the area of theplunger in the liquid cylinder, the total force exertedby the steam against the steam piston isconcentrated on the smaller working area of theplunger in the liquid cylinder; hence the pressureper square inch is greater in the liquid cylinderthan in the steam cylinder. A high pressure pumpdischarges a comparatively small volume ofliquid against a high pressure. A low pressurepump, on the other hand, has a comparatively lowdischarge pressure but a larger volume of discharge.In a low pressure pump the steam pistonis smaller than the plunger in the liquid cylinder.The standard way of designating the size ofa reciprocating pump is by giving three dimensions,in the following order: (1) the diameter ofthe steam piston, (2) the diameter of the pumpplunger, and (3) the length of the stroke. For example,a 12" x 11" X 18" reciprocating pump hasa steam piston which is 12 inches in diameter, apump plunger which is 11 inches in diameter, anda stroke of 18 inches. Thus the size designationindicates immediately whether the pump is a highpressure pump or a low pressure pump.Finally, the pump shown in figure 15-7is classified as vertical because the steam pistonand the pump plunger move up and down. Mostreciprocating pumps in naval use are vertical;a few, however, are horizontal , with the pistonmoving back and forth rather than up anddown.The remainder of the discussion of reciprocatingpumps is concerned primarily with directacting,simplex, double-acting, vertical pumps,since most reciprocating pumps used in the Navyare of this type.The power end of a reciprocating pump consistsof a bored cylinder in which the steam pistonreciprocates. The steam cylinder is fittedwith heads at each end; one head has an openingto accommodate the piston rod. Steam inlet andexhaust ports connect each end of the steam cylinderwith the steam chest. Drain valves are installedin the steam cylinder so that water resultingfrom condensation may be drained off.Some reciprocating pumps have cushioningvalves at each end of the steam cylinder. Thesevalves can be adjusted to trap a certain amountof steam at the end of the cylinder; thus, whenthe piston reaches the end of its stroke, it iscushioned by the steam and prevented from hittingthe end of the cylinder. When the pump isoperating at high speed, the cushioning valvesare kept almost closed so that a considerableamount of steam will be trapped at each end ofthe cylinder; at low speed, the cushioning valvesare kept almost open. Some reciprocating pumpsdo not have cushioning valves.Automatic timing of the admission and releaseof steam to and from each end of the steamcylinder is accomplished by various types ofvalve arrangements. Figure 15-8 shows the piston-typevalve gear commonly used for this purpose;it consists of a main piston-type slide valveand a pilot slide valve. Since the rod from thepilot valve is connected to the pump rod by avalve-operating assembly, the position of thepilot valve is controlled by the position of the pistonin the steam cylinder. The pilot valve furnishesactuating steam to the main piston-typevalve, which, in turn, admits steam to the top orto the bottom of the steam cylinder at the propertime.The valve-operating assembly which connectsthe pilot valve operating rod and the pumprod is shown in figure 15-9. As the crossheadarm (sometimes called the rocker arm) is movedup anddownby the movement of the pump rod, themoving tappet slides up and down on the pilotvalve operating rod. The tappet collars are adjustedso that the pump will make the full designedstroke.The liquid end of a reciprocating pump has apiston and cylinder assembly similar to that of398

Chapter 15. -PUMPS AND FORCED DRAFT BLOWERS=ci rt m jziLIVESPACESTEAMSTEAM PORTFOR PILOTVALVEPISTONSTEAM PILOTVALVEPILOT VALVEOPERATING RODFigure 15-8.— Piston-type valve gear for steamendof reciprocating pump.38.99the power or steam end. The piston in the liquidend is often called a plunger . A valve chest,sometimes called a water chest, is attached tothe liquid cylinder. The valve chest contains twosets of suction and discharge valves, one set toserve the upper endof the liquid cylinder and oneto serve the lower end. The valves are so arrangedthat the pump takes suction from the suctionchamber and discharges through the dischargechamber on both the up and down strokes.An adjustable relief valve is fitted to the dischargechamber to protect the pump and the pipingagainst excessive pressure.Some reciprocating pumps have an air chamberand a snifter valve installed in the liquid end.The upper part of the air chamber contains air;the lower part contains liquid. On each stroke, theair in the chamber is compressed by the pressureexerted by the plunger. When the plunger stopsat the end of a stroke, the air in the chamber expandsand allows a gradual, rather than a sudden,drop in the discharge pressure. The air chamber,therefore, smooths out the discharge flow, absorbsshock, and prevents pounding. The sniftervalve, if installed, allows a small quantity of airto be drawn in and compressed with each stroke.If no snifter valve is installed, some provisionmay be made for charging the air chamber withcompressed air.Although reciprocating pumps were oncewidely used aboardshipfor a variety of services,their use on combatant ships is now generally399

PRINCIPLES OF NAVAL ENGINEERINGPUMP ROD-STAY RODPILOT VALVEOPERATING RODADJUSTABLETAPPET COLLARADJUSTABLETAPPET COLLAR38.100Figure 15-9.— Valve-operating gear of reciprocatingpump.restricted to emergency feed pumps, fire andbilge pumps, and fuel oil tank stripping and bilgepumps. On auxiliary ships, reciprocating pumpsare still used for a number of services, includingauxiliary feed, standby fuel oil service, fueloil transfer, auxiliary circulating and condensate,fire and bilge, ballast, and lube oil transfer.VARIABLE STROKE PUMPS.- Variablestroke (also called variable displacement) pumpsare most commonly used on naval ships as partof an electrohydraulic transmission for anchorwindlasses, cranes, winches, steering gear, andother equipment. In these applications, the variablestroke pump is sometimes referred to asthe A end and the hydraulic motor which isdriven by the A end is then called the B end. Variablestroke pumps are also used on some shipsas in-port or cruising fuel oil service pumps.Although variable stroke pumps are oftenclassifed as rotary pumps, they are actuallyreciprocating pumps of a special design. A rotarymotion is imparted to a cylinder barrel or cylinderblock in the pump by means of a constantspeedelectric motor; but the actual pumping isdone by a set ofpistons reciprocating inside cylindricalopenings in the cylinder barrel or cylinderblock.There are two general types of variablestroke pumps in common use. In the axial-pistontype, the pistons are arranged parallel to eachother and to the pump shaft. In the radial-pistontype, the pistons are arranged radially from theshaft.Figure 15-10 shows an exploded view of boththe pump end (A. end) and the hydraulic motor(B^end) of an axial-piston type of variable strokeunit. The pump usually has either seven ornine2 single-acting pistons which are evenlyspaced around the cylinder barrel^ in the mannershown in figure 15-10.The piston rods (sometimes called connectingrods) make a ball-and-socket connection with apiece called the socket ring. The socket ringrides on a thrust bearing carried by a castingcalled the tilting box or tilting block; thus thesocket ring, which revolves, is actually fittedinto the tilting box, which does not revolve. Figure15-11 shows diagrammatically the arrangementof the cylinder barrel, the socket ring, andthe tilting box. Although only one piston is shownin this illustration, the others fit similarly intothe cylinder barrel and into the socket ring.Figure 15-12 illustrates diagrammaticallythe manner in whichthe position of thetilting boxaffects the position of the pistons. (Note that thisis not a continuous cross-sectional view, sincefor illustrative purposes twopistons are shown.)In order to understand how the pumping actiontakes place, let us follow one piston as the cylinderbarrel and socket ring make one completerevolution. When the tilting box is set perpendicularto the shaft, as inpart Aof figure 15-12, thepiston does not move back and forth within itscylindrical opening as the cylinder barrel andsocket ring revolve. Thus the piston is in thesame position with respect to its own cylindricalopening when it is at the top position as it is whenthe cylinder barrel has completed half a revolutionand carried the piston to the bottom position.Since the piston does not reciprocate, there is nopumping action when the tilting box is in thisposition even though the cylinder barrel andsocket ring are revolving.2 An uneven number of pistons is always used in orderto avoid pulsations in the discharge flow.3 Note that the term cylinder barrel actually refers toa cylinder block which has cylindrical openings for allof the pistons.400

Chapter 15. -PUMPS AND FORCED DRAFT BLOWERSCYLINDER BARRELVALVE PLATETILTINGBOX CONTROLTILTING BOX_B END(HYDRAULIC MOTOR)CYLINDER BARRELSOCKET RINGDRIVESHAFTAENDFigure15-10.— Exploded view of axial-piston variable stroke pump.147.109In part B of figure 15-12, the tilting box isset at an angle so that it is farther away from thetop of the cylinder barrel and closer to the bottomof the cylinder barrel. As the cylinder barrel andsocket ring revolve, the piston is pulled outwardas it is carried from the bottom position to thetop position, and is pushed inward as it is carriedfrom the top positionto the bottom posit ion. ThusCYLINDERKEYBARRELSOCKET RINGANGLE / (THRUST ANDOF / RADIAL BEARINGSTILT Ik NOT SHOWN)UNIVERSALJOINTTILTBOXDRIVESHAFT FROMREDUCTION GEARS147.110Figure 15-11.— Diagram showing eyJoxider barrel,socket ring, and tilting box in axial-pistonvariable stroke pump.the piston makes one suction stroke (from thebottom position to the top position) and one dischargestroke (from the top position to the bottomposition) for each complete revolution of thecylinder barrel.In part C of figure 15-12, we see the tiltingbox set at a somewhat larger angle. Becausethere is more distance between the cylinderbarrel and the socket ring at the top, and lessdistance between them at the bottom, the pistonnow moves further on each stroke and thusdisplaces more liquid on the discharge stroke.Although we have considered the position ofonly one piston, it is obvious that the others arebeing similarly positioned as the cylinder barreland socket ring revolve. At any given moment,therefore, some pistons are making suctionstrokes and others are making dischargestrokes. In a nine-piston pump, for example, fourpistons will be making suction strokes, four willbe making discharge strokes, and one will be atthe end of its stroke and will therefore be momentarilymotionless.Each cylindrical opening in the cylinderbarrelhas a port in the face of the cylinder barrel.As we have seen, each port except one will beeither a suctionport or a discharge port, depend-401

PRINCIPLES OF NAVAL ENGINEERINGROTATINGCfLINOER CONNECTING ROTATINGBARREL RODS SOCKETRINGf^N0NR0TAT1NGTILTING BOXNEUTRAL POSITIONTILTING BOX SETAT AN ANGLE. TILTING BOX SET ATC A GREATER ANGLE147.111Figure 15-12. -Diagram showing how tilting box position affects position of pistons.ing upon theposition of the piston in the cylindricalopening. The face of the cylinder barrelbears against the valve plate, anonrotatingpiecewhich has two semicircular ports, one for suctionand one for discharge. When a piston is atthe top position, at the end of its suction stroke,the port for that piston is over the top land'* onthe valve plate; when a piston is at the bottomposition, at the end of the discharge stroke, theport is over the bottom land on the valve plate.Figure 15-13 shows the ports in the face of thecylinder barrel and the ports in the valve plate.When the _A end is used alone as a constantspeed,variable-capacity pump, the tilting boxis often so designed that it can be tilted in onedirection only. In this case, the flow of thepumped liquid is always in the same direction.When the A end is used as part of an electrohydraulicsystem, however, the tilting box ismost commonly designed tobe tilted in either direction;and in this case the flow of the pumpedliquid may be in either direction. Therefore, itshould be clear that the position of the tilting boxcontrols both the direction of flow and the amountof flow.Figure 15-14 shows a cutaway view of anaxial-piston variable stroke pump. Note that thisparticular pump is designed for reversible flow,since the tilting box canbe tilted in either direction.The radial-piston variable stroke pump issimilar in general principle to the axial-pistonpump just described, but the arrangement ofcomponent parts is somewhat different. In theradial-piston pump, the cylinders are arrangedradially in a cylinder body that rotates arounda nonrotating central cylindrical valve. Each cylindercommunicates with horizontal ports in thecentral cylindrical valve. Plungers or pistonsThe term land refers to the space between ports.FACE OF VALVE PLATEFACE OF CYLINDER 3ARREL147.112Figure 15-13.— Suction and discharge ports inface of cylinder barrel and in valve plate.which extend outward from each cylinder arepinned at their outer ends to slippers which slidearound the inside of a rotating floating ring orhousing.402

Chapter 15. -PUMPS AND FORCED DRAFT BLOWERSSHAFT TRUNNIONBLOCKCONNECTINGRODSOCKET RINGDIAGRAM-TILTING BLOCK POSITIONSCONTROL SHAFT38.103Figure 15-14.— Cutaway view of axial-pistonvariable stroke pump.The floating ring is so constructed that it canbe shifted offcenter from the pump shaft. Whenit is centered, or in the neutral position, the pistonsdo not reciprocate and the pump does notfunction, even though the electric motor is stillcausing the pump to rotate. If the floating ringis forced offcenter to one side, the pistons reciprocateand the pump operates. If the floatingring is forced offcenter to the other side of thepump shaft, the pump also operates but the directionof flow is reversed. Thus both the directionof flow and the amount of flow aredetermined by the position of the cylinder bodyrelative to the position of the floating ring.ROTARY PUMPS.— Rotary pumps, like reciprocatingpumps, are positive-displacementpumps. The theoretical displacement of a rotarypump is the volume of liquid displaced by therotating elements on each revolution of the shaft.The capacity of a rotary pump is defined as thequantity of liquid (in gpm) actually deliveredunder specified conditions. Thus the capacity isequal to the displacement times the speed (rpm),minus whatever losses may be caused by slippage,suction lift, viscosity of the pumped liquid,amount of entrained or dissolved gases in theliquid, and so forth.All rotary pumps work by means of rotatingparts which trap the liquid at the suction side andforce it through the discharge outlet. Gears,screws, lobes, vanes, and cam-and-plunger arrangementsare commonly used as the rotatingelements in rotary pumps.Rotary pumps are particularly useful forpumping oil and other heavy, viscous liquids.This type of pump is used for fuel oil service,fuel oil transfer, lubricating oil service, andother similar services. Rotary pumps are alsoused for pumping nonviscous liquids such aswater or gasoline, particularly where the pumpingproblem involves a high suction lift.The power end of arotary pump is usually anelectric motor or an auxiliary steam turbine;however, some lubricating oil pumps that supplyoil to the propulsion turbine bearings and to thereduction gears are attached to and driven byeither the propulsion shaft or the quill shaft ofthe reduction gear.Rotary pumps are designed with very smallclearances between rotating parts and betweenrotating parts and stationary parts. The smallclearances are necesarry in order to minimizeslippage from the discharge side back to the suctionside. Rotary pumps are designed to operateat relatively slow speeds in order to maintainthese clearances; operation at higher speedswould cause erosion and excessive wear, whichin turn would result in increased clearances.Classification of rotary pumps is generallymade on the basisof the type of rotating element.In the following paragraphs the main features ofsome common types of rotary pumps are discussed.The simple gear pump (fig. 15-15) has twospur gears which mesh together and revolve inopposite directions. One gear is the driving gear,the other is the driven gear. Clearances betweenthe gear teeth and the casing and between thegear faces and the casing are only a few thousandthsof an inch. The action of the unmeshinggears draws the liquid into the suction side ofthe pump. The liquid is them trapped in thepockets formed by the gear teeth and the casing,so that it must follow along with the teeth. On thedischarge side, the liquid is forced out by themeshing of the gears. Simple gear pumps of this403

PRINCIPLES OF NAVAL ENGINEERINGDISCHARGESUCTION38.108Figure 15-15.— Simple gear pump.type are frequently used as lubricating pumpson pumps and other auxiliary machinery.The herringbone gear pump (fig. 15-16) is amodification of the simple gearpump. In the herringbonegear pump, one discharge phase beginsbefore the previous discharge phase is entirelycomplete; this overlapping tends to give a steadierdischarge than that obtained with a simplegear pump. Herringbone gear pumps are sometimesused for low pressure fuel oil service, lubricatingoil service, and diesel oil service.The helical gear pump (fig. 15-17) is still anothermodification of the simple gear pump.Because of the helical gear design, the overlappingof successive discharges from spaces betweenthe teeth is even greater than it is in theRELIEF VALVE SUCTIONHERRINGBONEDISCHARGEFigure 15-16.— Herringbone gear pump.147. 113404

Chapter 15. -PUMPS AND FORCED DRAFT BLOWERSHELICAL GEARINTAKEFigure15-17.— Helical gear pump.147,114herringbone gear pump; and the discharge flowis, accordingly, even smoother. Since the dischargeflow is smooth in the helical gear pump,the gears can be designed with a small numberof teeth, thus allowing increased capacity withoutsacrificing smoothness of flow.The pumping gears in this type of pump aredriven by set of timing and driving gears, whichalso function to maintain the required closeclearances while preventing actual metal-tometalcontact between the pumping gears. As amatter of fact, metallic contact between the teethof the pumping gears would provide a tighter sealagainst slippage; but it would cause rapid wearof the teeth because foreign matter in the pumpedliquid would be present on the contact surfaces.Roller bearings atbothendsof the gear shaftsmaintain proper alignment and thus minimizefriction losses in the transmission of power.Stuffing boxes are used to prevent leakage at theshafts.The helical gear pump is used to pump nonviscousliquids and light oils at high speeds andto pump viscous liquids at lower speeds.Figures 15-18 and 15-19 illustrate twotypesof lobe pumps. Although these pumps look somewhatlike gear pumps, they are not true gearpumps because the rotary elements are not capableof driving each other. One rotor is poweredby the drive shaft; the other is driven by a set oftiming gears. The lobes are considerably larger405

PRINCIPLES OF NAVAL ENGINEERINGFigure147.11515-18.— Lobe pump (heliquad type).than gear teeth; as a rule, there are only two orthree lobes on each rotor.There are several different types of screwpumps. The mainpointsof differencebetweenthevarious types are the number of intermeshingscrews and the pitch of the screws. A doublescrewlow pitch pump is shown in figure 15-20,and a triple-screw high-pitch pump in figure15-21. Both of these pumps are widely usedaboard ship to pump fuel oil and lubricating oil.In the double-screw pump, one rotor is driven bythe drive shaft and the other by a set of timinggears. In the triple-screwpump, a central powerrotor meshes with two idler rotors.The rotating element in a rotating plungerpump (fig. 15-22) is a plunger which is set offcenteron a drive shaft that is rotated by thesource of power. The plunger is driven up anddown and around the chamber by the rotation ofthe shaft, in such away as to make a sliding sealwith the walls of the chamber. In moving,the plunger alternately opens and closes a passageto the discharge.Because of its valveless construction, the rotatingplunger pump is suitable for pumping oilthat may contain sand or other sediment and forpumping high viscosity liquids. The pump canproduce a very high suction lift.A moving vane pump (fig. 15-23) consists ofa cylindrically bored housing with a suction inleton one side and a discharge outlet on the otherside; a cylindrically shaped rotor of smallerdiameter than the cylinder is driven about an axisplaced above the centerline of the cylinder in sucha way that the clearance between the rotor and thecylinder is small at the top and at a maximumvalue at the bottom.The rotor carries vanes which move in and outas the rotor rotates, thus maintaining sealedspaces between the rotor and the cylinder wall.The vanes trap liquid on the suction side andcarry it to the discharge side; contraction of thespace expels the liquid into the discharge line.The vanes may swing on pivots, as shown in theillustration, or they may slide in slots in therotor.The moving vane type of pump is used for lubricatingoil service and transfer and, in general,for handling light liquids of medium viscosity.An internal gear pump is shown in figure 15-24. In the gear pumps previously described, theteeth project radially outward from the center ofthegears. In an internal gear system, the teethof one gear project outward but the teeth of theother project inward toward the center. In an internalgear pump, one gear stands inside theother.A gear directly attached to the drive shaft ofthe pump is set offcenter in a circular chamberfitted around its circumference with the spursof an internal gear. The two gears mesh on oneside of the pump chamber, between the suctionand the discharge. On the opposite side of thechamber a crescent-shaped form stands in thespace between the two gears in such a way thata close clearance exists between each gear andthe crescent.The rotation of the central gear by the shaftcauses the outside gear to rotate, since the twoFigure147.11615-19.— Two-lobe pump.406

^Chapter 15. -PUMPS AND FORCED DRAFT BLOWERSIDLERROTOR HOUSINGFigure38.105X15-20.— Double-screw low-pitch pump.are in mesh. Everything in the chamber rotatesexcept the crescent, causing liquid to be trappedin the gear spaces as they pass the crescent. Thetrapped liquid is carried from the suction to thedischarge, where it is forced out of the pump bythe meshing of the gears. As liquid is carriedaway from the intake side of the pump, the pressurethere is diminished, thus forcing otherliquid into the suction side of the pump. The directionof flow in the internal gear pump can bereversed by shifting the position of the crescent180 degrees.CENTRIFUGAL PUMPS.-Centrifugal pumpswidely used aboard ship for pumping waterareand other nonviscous liquids. The centrifugalpump utilizes the throwing force of a rapidlyrevolving impeller. The liquid is pulled in at thecenter or eye of the impeller and is dischargedat the outer rim of this impeller. By the timethe liquid reaches the outer rim of the impeller,it has acquired a considerable velocity. The liquidis then slowed down by being led through avolute or through a series of diffusing passages.As the velocity of the liquid decreases, its pressureincreases— or, in other words, some of themechanical kinetic energy of the liquid is transformedinto mechanical potential energy. In theterminology commonly used in discussion ofpumps, the velocity head of the liquid is partiallyconverted to pressure head .Figure 15-21.LOWER THRUSTPLATE47.80-Triple-screw high-pitch pump.Centrifugal pumps are not positive-displacementpumps. When a centrifugal pump is operatingat a constant speed, the amount of liquiddischarged (capacity) varies with the dischargepressure according to the relationships inherentin the particular pump design. The relationshipsamong capacity, total head (pressure), and powerare usually expressed by means of a characteristicscurve.Capacity and discharge pressure can bevaried by changing the pump speed. However,centrifugal pumps should be operated at or neartheir rated capacity and discharge pressurewhenever possible. Impeller vane angles andthesizes of the pump waterways can be designedfor maximum efficiency at only one combinationof speed and discharge pressure; under otherconditions of operation, the impeller vane anglesCharacteristics curves are generally given in themanufacturers' technical manuals or in the outline assemblydrawings of pumps.407

-PRINCIPLES OF NAVAL ENGINEERINGHOLLOW ARMSLIDE PINSUCTION-•^DISCHARGEDRIVE SHAFTDISCHARGE PORTROTATING PLUNGERECCENTRICFigure 15-22.— Rotating plunger pump.47.46and the sizes of the waterways will be too largeor too small for efficient operation. Therefore, acentrifugal pump cannot operate satisfactorilyover long periods of time at excess capacity andlow discharge pressure or at reduced capacityand high discharge pressure.It should be noted that centrifugal pumps arenot self-priming. The casing must be floodedbefore a pump of this type will function. For thisreason, most centrifugal pumps are locatedbelow the level from which suction is to be taken.Priming can also be effected by using anotherpump to supply liquid to the pump suction— as, forexample, the feed booster pump supplies suctionpressure for the main feed pump. Some centrifugalpumps have special priming pumps, airejectors, or other devices for priming.Where two or more centrifugal pumps are installedto operate in parallel, it is particularlyimportant to avoid operating the pumps at verylow capacity, since it is possible that a unit havinga slightly lower discharge pressure might bepushed off the line and thus forced into a shutoffposition.Because of the danger of overheating, centrifugalpumps can operate at zero capacity foronly short periods of time. The length of timevaries. For example, a fire pump might be ableto operate for as long as 15 to 30 minutes beforelosing suction, but a main feed pump would overheatin a matter of a few seconds if operated atzero capacity.Most centrifugal pumps— and particularlyboiler feed pumps, fire pumps, and others which408

Chapter 15. -PUMPS AND FORCED DRAFT BLOWERSFigureSWINGING TYPEMOVING VANESCYLINDERROTOR15-23.— Moving vane pump.47.47may be required to operate at low capacity or inshutoff condition tor any length of time— are fittedwith recirculation lines from the discharge sideof the pump back to the source of suction supply.The main feed pump, for example, has a recirculatingline going back to the deaerating feed tank.An orifice allows the recirculation of the minimumamount of water required toprevent overheatingof the pump. On boiler feed pumps, therecirculating lines must be kept open wheneverthe pumps are in operation.On centrifugal pumps, there must always bea slight leakoff through the packing in the stuffingboxes, in order to keep the packing lubricatedand cooled. Stuffing boxes are used eitherto prevent the gross leakage of liquid from thepump or to prevent the entrance of air into thepump; the purpose served depends, of course,upon whether the pump is operating with a positivesuction head or is taking suction from a vacuum.If a centrifugal pump is operating with a positivesuction head, the pressure inside the pumpis sufficient to force a small amount of liquidthrough the packing when the packing gland isproperly set up on. On multistage pumps, it issometimes necessary to reduce the pressure onone or both of the stuffingboxes.Thisis accomplishedby using a bleedoff line which is tappedin to the stuffing box between the throat bushingand the packing.If a pump is taking suction at or below atmosphericpressure, a supply of sealing water mustbe furnished to the packing glands to ensure theexclusion of air. Some of this water mustbe allowed to leak off through the packing. Mostcentrifugal pumps use the pumped liquid as thelubricating, cooling, and sealing medium. However,an independent external sealing liquid isused on some pumps.There are several different designs of centrifugalpumps. The two types most commonlyused aboard ship are the volute pump and thevolute turbine pump.The volute pump is shown in figure 15-25. Inthis pump, the impeller discharges into a volute—that is, a gradually widening channel in the pumpcasing. As the liquid passes through the voluteand into the discharge nozzle, a greatpartof itskinetic energy is converted into potential energy.In the volute turbine pump (fig. 15-26) theleaving the impeller is first slowed downliquidby the stationary diffuser vanes which surroundthe impeller. The liquid is forced through graduallywidening passages in the diffuser ring (notshown) and into the volute. Since both the diffuserFigure147,11715-24.— Internal gear pump.23.18.0Figure 15-25.— Simple volute pump.409

PRINCIPLES OF NAVAL ENGINEERINGREVOLVINGIMPELLERSTATIONARY OIFFUSER VANESFigure 15-26.— Volute turbine pump.23.19vanes and the volute reduce the velocity of theliquid, there is in this type of pump an almostcomplete conversion of kinetic energy to potentialenergy.Centrifugal pumps may be classified in severalways. For example, they may be eithersingle-stage or multistage, a single-stage pumphas only one impeller; a multistage pump has twoor more impellershousedtogether in one casing.In a multistage pump, as a rule, each impelleracts separately, discharging to the suction of thenext-stage impeller. Centrifugal pumps are alsoclassified as horizontal or vertical, dependingupon the position of the pump shaft.The impellers used in centrifugal pumps maybe classified as single suction or double-suction.The single-suction impeller allows liquid toenter the eye of the impeller from one directiononly; the double- suction type allows liquid toenter the eye from two directions. Single- suctionand double- suction arrangements are shown infigure 15-27. The double- suction arrangementhas the advantage of balancing end thrust in onedirection by end thrust in the other.Some of the more important centrifugalpumps used on naval ships are the main feedpump, the feed booster pump, the main and auxiliarycondensate pumps, fire pumps, freshwaterpumps, and gasoline pumps.A typical main feed pump is shown in figure15-28. This is a horizontal, high speed, turbinedrivenpump. Main feed pumps on most surfaceships operate at a dischargepressurethat is 100to 1 50 psig above the maximum steam drum pres-23.25Figure 15-27. —Single-suction and doublesuctionarrangements in centrifugal pumps.sure of the boiler. On ships having 1200-psigboilers, the discharge pressure of the main feedpumps is approximately 200 to 300 psig above thesteam drum pressure. A main feed pump mustoperate at varying speeds to maintain a constantdischarge pressure under all conditions of load.A constant-pressure pump governor" is used toregulate the admission of steam to the turbineand thus control the discharge pressure of thepump.PROPELLER PUMPS.— Propeller pumps areused on some ships for pumping water. Althoughthey are often classified as centrifugal pumps,this classification is incorrect because propellerpumps do not actually utilize centrifugal force fortheir operation.A propeller pump consists essentially of apropeller fitted into a narrow, tube-like casing.The propeller pumps the liquid by pushing it ina direction parallel to the pump shaft.Constant-pressure pump governors are discussed inchapter 16 of this text.410

Chapter 15. -PUMPS AND FORCED DRAFT BLOWERSFigure 15-28.— Main feed pump.38.109Propeller pumps must be located below oronly slightly above the surface of the liquid to bepumped, since they cannot operate with a highsuction lift.MIXED- FLOW PUMPS. -A mixed-flow pumpis one in which the pumping action occurs partlyby centrifugal force and partly by propeller action.Pumps of this type can be used to handlevery viscous liquids or liquids that contain dirt;they are better than either centrifugal pumps orpropeller pumps for these services.JET PUMPS.— Devices which utilize the rapidflow of a fluid to entrain another fluid and therebymove it from one place to another are called jetpumps. Jet pumps are sometimes not consideredto be pumps because they have no moving parts.However, in view of our previous definition of apump as a device which utilizes an externalsource of power to apply force to a fluid in orderto move the fluid from one place to another, itwill be apparent that a jet pump is indeed a pump.Jet pumps are generally considered in twoclasses: ejectors, which use a jet of steam toentrain air, water, or other fluid; and eductors,which use a flow of water to entrain and therebypump water. The basic principles of operation ofthese two devices are identical.A simple jet pumpof the ejector type is shownin figure 15-29. In this pump, steam under pressureenters chamber C through pipe A^ which isfitted with a nozzle, B. As the steam flowsthrough the nozzle, the velocity of the steam isincreased. The fluid in the chamber at point F,in front of the nozzle, is driven out of the pumpthrough the discharge line, ^ by the force of thesteam jet. The size of the discharge line411

PRINCIPLES OF NAVAL ENGINEERINGsupply a positive pressure head for pumps usedin firefighting.Pump MaintenanceHiATMOSPHERICPRESSUREPumps require a certain amount of routinemaintenance and, upon occasion, some repairwork. Pumps are so widely used for variousservices in the Navy that it is necessary to consultthe manufacturer's technical manual fordetails concerning the repair of a specific unit.Routine maintenance, however, is performed inaccordance with the Planned Maintenance Subsystem(3-M System) requirements. Figure 15-31 illustrates the planned maintenance requirementsfor one type of turbine-driven main lubeoil pump. Similar requirements are establishedfor all pumps.Safety PrecautionsThe following safety precautions must be observedin connection witiithe operation of pumps:Figure 15-29.— Jet pump (ejector type).75.283increases gradually beyond the chamber, inorder to decrease the velocity of the dischargeand thereby transform some of the velocity headto pressure head. As the steam jet forces someof the fluid from the chamber into the dischargeline, pressure in the chamber is lowered and thepressure on the surface of the supply fluid forcesfluid up through the inlet, _D, into the chamber andout through the discharge line. Thus the pumpingaction is established.Jet pumps of the ejector type are occasionallyused aboard ship to pump small quantities ofdrains overboard. Their primary use on navalships, however, is not in the pumping of waterbut in the removal of air and other noncondensablegases from main and auxiliary condensers."^An eductor is shown in figure 15-30. As maybe seen, the principle of operation is the sameas that just described for the ejector type of jetpump; however, water is used instead of steam.On naval ships, eductors are used to pump waterfrom bilges, to dewater compartments, and to1. See that all relief valves are tested at theappropriate intervals as required by the PlannedMaintenance Subsystem. Be sure that reliefvalves function at the designated pressure.2. Never attempt to jack over a pump by handwhile the throttle valve to the turbine is open orthe power is on. Never jack over a reciprocatingpump when the throttle valve or the exhaustvalve is open.Air ejector assemblies used on condensers are discussedin chapter 13 of this text. Figure 15-30.-Eductor. 47.48412

Sytlem, Subsystem, or Cempon«ntChapter 15. -PUMPS AND FORCED DRAFT BLOWERS

PRINCIPLES OF NAVAL ENGINEERING3o Do not attempt to operate a pump whileeither the speed limiting governor or the constantpressure governor is inoperable. Be sure that thespeed limiting governor and the constant pressuregovernor are properly set.4. Do not use any boiler feed system pumpfor any service other than boiler or feed waterservice, except in an emergency.FORCED DRAFT BLOWERSOn most steam-driven surface ships, forceddraft blowers are used to furnish the largeamount of combustion air required for the burningof the fuel oil. A forced draft blower is essentiallya very large fan, fastened to a shaft andhoused in a metal casing. As a rule, two blowersare furnished for each boiler; they are synchronizedfor equal distribution of load.Most forced draft blowers are driven bysteam turbines. However, some blowers for inportuse and some main blowers on auxiliaryships are driven by electric motors. Most turbine-drivenblowers are direct drive, rather thangeared; but some geared turbine drives are used.On most ships, the forced draft blowers takesuction from the space between the inner andouter stack casings and discharge slightly preheatedair into a duct that leads to the space betweenthe inner and outer casings of the boiler.are fitted with flaps in the suction ducts. In theevent of a casualty to one centrifugal blower, airfrom another blower blows back toward thedamaged blower and closes the flaps.Both horizontal and vertical propellerblowers are used in naval combatant ships. Ingeneral, single-stage horizontal blowers areused on older ships and two- stage or three- stagevertical blowers on ships built since 'VorldWarII.Balanced automatic shutters are installed inthe discharge ducts between each propellerblower and the boiler casings. These shutters arelocked in the closed position whenever the bloweris taken out of service so that the blower will notbe rotated in reverse.Figure 15-32 and 15-33 show two views of asingle-stage horizontal propeller-type blower.As may be seen, the blower is a complete unitconsisting of a driving turbine and a propellertypefan. The entire unit is mounted on a singlebed plate.The air intake is screened to prevent the entranceof foreign objects. The blower casingTypes of ForcedDraft BlowersTwo main types of forced draft blowers areused in naval ships: centrifugal blowers and propellerblowers. The main difference between thetwo types is in the direction of airflow. The centrifugalblower takes air in axially at the centerof the fan and discharges it tangentially off theouter edge of the blades. The propeller blowermoves air axially— that is, it propels the airstraight ahead in a direction parallel to the axisof the shaft. Most forced draft blowers now innaval use are of the propeller type. However,some older ships and some recent auxiliarieshave centrifugal blowers.Centrifugal blowers may be either verticalor horizontal. In either case, the unit consists ofthe driving turbine (or other driving unit) atoneend of the shaft and the centrifugal fanwheel atthe other end of the shaft. Inlet trunks and diffusersare fitted around the blower fanwheel todirect air into the fanwheel and to receive anddischarge air from the fan. Centrifugal blowers38.111XFigure 15-32.— Horizontal propeller-type blower(view 1).414

Chapter 15. -PUMPS AND FORCED DRAFT BLOWERS38.112XFigure 15-33.— Horizontal propeller-type blower(view II).merges into the disciiarge duct, and the dischargeduct is joined to the boiler casing. Diffuser vanesare installed justinfrontof the blower to preventrotation of the air stream as it leaves the blower.Additional divisions in the curving sections of thedischarge duct also help to control the flow of air.The shaft that carried both the propeller andthe turbine is a single forging. The propeller iskeyed to the shaft and held to the tapered end ofthe shaft by a nut and cotter pin. The entire assemblyis supported by two main bearings, oneon each sideof the turbine wheel, outside the turbinecasing. The main bearing at the governorend is locatedinthegovernor housing, which alsocontainsthe thrust bearing. The speed- limitinggovernor spindle and the lubricating oil pumpshaft are driven by the main shaft of the blower,through a reduction gear.High powered two- stage or three- stage verticalpropeller- type blowers are installed in recentcombatant ships. One kind of three- stagevertical propeller-type blower is shown in figures15-34 and 15-35. Figure 15-36 shows therotating assembly of the same blower. As maybe seen, there are three propellers at the fanend. Each propeller consists of a solid forgeddisk to which are attached a number of forgedblades. The blades have bulb- shaped roots thatare entered in grooves machined across the hub;the blades are kept firmly in place by lockingdevices. Each propeller disk is keyed to the shaftand secured by locking devices.38.113XFigure 15-34. — External view of three-stagevertical propeller-type blower.The driving turbine is a velocity- compoundedimpulse turbine (Curtis stage) with two rows ofmoving blades. The turbine wheel is keyed to theshaft. The lower face of the turbine wheel bearsagainst a shoulder on the shaft; a nut screwedonto the shaft presses against the upper face ofthe turbine wheel.The entire rotating assembly is supported bytwo main bearings. One bearing is just below thepropellers and one is just above the thrust bearingin the oil reservoir.The blower casing is built up of welded plates.From the upper flange down to a little below thelowest propeller, the casing is cylindrical inshape. The shape of the casing changes from cylindricalto cone-shaped and then to square; thedischarge opening of the blower casing is rectangularin shape. Guide vanes in the casing controlthe flow of air and also serve to stiffen the415

^PRINCIPLES OF NAVAL ENGINEERINGPROPELLERUt STAGEPROPELLER,2nd STAGEPROPELLER,3rd STAGEOIL BAFFLESEAL RINGSTATIONARYGUIDE VANESUPPERBEARINGEXTERNAL OIL LINETO UPPER BEARINGOIL RETURNLINESTEAMCHESTNOZZLEVALVESTATIONARYBLADINGLOWERBEARINGVISCOSITYPUMPCENTRIFUGALPUMPOIL RESERVOIR— v^PRESSUREGAGETACHOMETERTHRUSTBEARINGFigure15-35. -Sectional view of three-stage vertical propeller-type blower.41638.114

integralChapter 15. -PUMPS AND FORCED DRAFT BLOWERS38.115XFigure 15-36, —Rotating assembly for threestagevertical propeller-type blower.casing. Thepart of the casing near the propellersis made in sections and is also split verticallyto allow removal of the three propellers whennecessary. The lower part of the casing, belowthe air duct, houses the turbine. The lower partof the turbine casing is welded to the oil reservoirstructure.Although all vertical propeller blowers operateon the same principle, and although theymay look very much the same from the outside,they are not identical in all details. Perhapsthe major differences to be found among verticalforced draft blowers are in connection withthe lubrication systems. Some of these differencesare noted in the following section.Blower LubricationBecause forced draft blowers must operateat very high speeds, correct lubrication of thebearings is absolutely essential. A completepressure lubrication system for supplying oilto the bearings is an . part of everyforced draft blower. Most forced draft blowershave two radial bearings and one thrust bearing;however, some blowers have two turbine bearings,two fan bearings, and a thrust bearing.The lubrication system for a horizontalforced draft blower includes a pump, an oil filter,an oil cooler, a filling connection, relief valves,oil level indicators, thermometers, pressuregages, oil sight flow indicators, and the necessarypiping. The pump is usually turned by theforced draft blower shaft but is geared down toabout one-fourth the speed of the turbine. Thelube oil is pumped from the oil reservoir, throughthe oil filter and the oil cooler, to the bearings.Oil then drains back to the reservoir bygravity.oilSimple gear pumps were used in the lubesystems of older horizontal blowers such asthose found on DD 445 and DD 692 classes ofdestroyers. These pumps were not completelysatisfactory for this use, since a simple gearpump does not supply oil to the bearings whenthe blower is turning in the wrong direction.This is a serious disadvantage in forced draftblower installations because of the possibilitythat idle blowers may be rotated in reversewhen automatic shutters fail to close. To preventdamage to the bearings from this cause,the simple gear pumps in some horizontalblowers were replaced by a special type of gearpump that continues to pump oil, without changein the direction of oil flow, when the directionof blower rotation is reversed. This alterationhas been accomplished on many ships that havehorizontal forced draft blowers.Some vertical blowers are fitted with a gearpump and alubrication system which is generallysimilar to that just described for horizontalblowers. However, most vertical blowers havequite different lubrication systems.One type of lubrication system used on somevertical forced draft blowers is shown in figure15-37. In this system, the gear pump is replacedby a centrifugal pump and a helicalgrooveviscosity pump. The centrifugal pumpimpeller is on the lower end of the main shaft,just below the lower main bearing. The viscositypump (also called a friction pump) is onthe shaft, just above the centrifugal pump impeller,inside the lower part of the main bearing.As the main shaft turns, lubricating oilgoes to the lower bearingandfrom there, by wayof the hollow shaft, to the upper bearing. Inaddition, part of the oil is pumped directly tothe upper bearing through an external supplyline. The oil is returned from the upper bearingto the oil reservoir through an externalreturn line.In this system, the lubricating oil does notgo through the oil strainer or the oil filter onits way to the bearings. Instead, oil from thereservoir is constantly being circulated throughan external filter and an external cooler andthen back to the reservoir.The viscosity pump is needed in this systembecause the pumping action of the centrifugalpump impeller is dependent upon the rpm of theshaft. At low speeds, the centrifugal pump cannotdevelop enough oil pressure to adequatelylubricate the bearings. At high speeds, thecentrifugal pump alone would develop more oil417

-PRINCIPLES OF NAVAL ENGINEERINGUPPER BEARINGOIL GUARDOIL TOUPPER BEARINGpump of the type shown in figure 15-36; but theseblowers, like the other newer ones, have a completelyexternal oil supply to the bearings insteadof a hollow-shaft arrangement.One feature of some of the newer verticalblowers is an anti-rotation device on the shaftof the lubricating pump. This device preventswindmilling of the blower in a reverse directionin the event of leakage through the automaticshutters. The anti-rotation device is continuouslylubricated through a series of passagewayswhich trap some of the leakage from the thrustbearing.Control of Blower SpeedCENTRIFUGALPUMP IMPELLERPRESSUREGAGETACHOMETER^OILRESERVOIRTHERMOMETER38.116Figure 15-37. — Lubrication system with hollowshaftoil supply and external oil supply forvertical forced draft blower.pressure than is needed for lubrication, and theexcessive pressure would tend to cause floodingof the bearings and loss of oil from thelubrication system. The viscosity pump, whichis nothing more than a shallow helical threador groove on the lower part of the shaft, helpsto assure sufficient lubrication at low speedsand to prevent the development of excessive oilpressures at high speeds.The hollow-shaft type of lubrication systemjust described is still found on some verticalforced draft blowers. The newest verticalblowers, however, do not use a hollow shaft tosupply oil to the upper bearings. Instead, oil ispumped to the bearings through an externalsupply line, passing through an oil filter and anoil cooler on the way to the bearings. Most ofthese newer vertical blowers have a gear pumpand an additional hand pump that is used toestablish initial lubrication when the blower isbeing started. Some of the newer verticalblowers have a centrifugal pump and a viscosityForced draft blowers are manually controlledon all naval ships except those that have automaticcombustion control systems for the boilers.Speed-limiting governors (discussed inchapter 16 of this text) are fitted to all forceddraft blowers, but they function merely as safetydevices to prevent the turbine from exceedingthe maximum safe operating speed; the speedlimitinggovernors do not have any control overthe turbine at ordinary operating speeds.Manual control of blower speed is achievedby a valve arrangement that controls the amountof steam admitted to the turbines. In someblowers a full head of steam is admitted to thesteam chest; steam is then admitted to the turbineby means of a manually operated lever orhandwheel that controls four nozzle valves. Thelever or handwheel may be connected by linkagefor remote operation. The four valves areso arranged that they open in sequence, ratherthan all at the same time. The position of themanually operated lever or handwheel determinesthe number of valves that will open, andthus controls the amount of steam that will beadmitted to the driving turbine. The steam chestnozzle valve shafts of all blowers serving oneboiler are mechanically coupled so as to providefor synchronized operation of the blowers.If only one blower is to be operated, the rootvalve of the nonoperating blower must remainclosed so that steam will not be admitted to theline.In other installations, a throttle valve is usedto control the admission of steam to the steamchest. From the steam chest, the steam entersthe turbine casing through fixed nozzles ratherthan through nozzle valves. Varying the openingof the throttle valve varies the steam pressureto the steam chest and thus varies the speed of418

Chapter 15. -PUMPS AND FORCED DRAFT BLOWERSthe turbine. The same throttle valve is usuallyused to control the admission of steam to allblowers serving any one boiler. K only oneblower is to be operated, the root valve of thenonoperating blower must be kept closed.When admission of steam is controlled bythe four nozzle valve arrangement, no additionalnozzle area is required to bring the blower upto maximum speed. In the other type of installation,a special hand-operated nozzle valve isprovided for high speed operation. This nozzlevalve, which is sometimes called an overloadnozzle valve , is used whenever it is necessaryto increase the blower speed beyond that obtainablewith the fixed nozzles. As a rule, theuse of the overload nozzle valve is requiredonly when steam pressure is below normal.Checking Blower SpeedMany forced draft blowers are fitted withconstant-reading, permanently mounted tachometersfor checking on blower speed. Sometimesthe tachometer is mounted ontopof the governorand is driven by the governor spindle. The governorspindle is driven by the main shaft througha reduction gear, and therefore does not rotateat the same speed as the main shaft. However,the rpm of the governor spindle is proportionalto the rpm of the main shaft. The tachometeris calibrated to give readings that indicate thespeed of the main shaft rather than the speedof the governor spindle.Some blowers are equipped with a specialkind of tachometer called a pressure-gage tachometer. This instrument, which may be seenin figures 15-35 and 15-37, is actually a pressuregage which is calibrated in both psi andrpm. The pressure-gage tachometer dependsfor Its operation on the fact that the oil pressurebuilt up by the centrifugal lube oil pumphas a definite relation to the speed of the pumpimpeller; and the speed of the impeller, ofcourse, is determined by the speed of the mainshaft. Thus the instrument can be calibratedin both psi and rpm.Some forced draft blowers of recent designare equipped with electric tachometers whichhave indicating gages at the blower and at theboiler operating station. The electric tachometer(sometimes called a tachometer generator)consists of a stator and a permanent magnetrotor mounted at the bottom of the turbine shaft.The wire from the generator plugs into a connectorinside the sump. Another connector isprovided outside the sump for attaching the wirefrom the generator to the transformer box.Forced Draft Blower OperationForced draft blowers supply the air requiredfor combustion of the fuel oil. The amount ofair that enters the furnace is determined by theair pressure in the double casings. Althoughthe air pressure is affected by the number ofburners in use and by the amount that the airregisters are open, it is primarily determinedby the speed at which the forced draft blowersare operated. The speed of the forced draftblowers is controlled by manual adjustment ofthe blower throttle in all installations exceptthose having automatic combustion controlsystems.The forced draft blowers should be operatedin such a way as to furnish the required amountof air for the complete combustion of the fuelbeing burned. In actual practice, it is necessaryto supply just over 100 percent of theamount of air theoretically required, in orderto ensure the complete combustion of the fuel.Higher percentages of excess air are wastefulof fuel, since all air that does not actually enterinto a combustion reaction merely absorbs andcarries off heat.On the other hand, an insufficient quantity ofair for combustion is also detrimental to boilerefficiency. If there is not enough air for completecombustion, there may be a greater lossin efficiency. Or, if even less air is supplied,some of the carbon will not be burned at allbut will pass out the smokestack as black smoke.Insufficient air is also detrimental because itcauses the boiler to pant and vibrate; this is oneof the major causes of brick work failure inthe boilers.The air pressure in the double casing mustbe increased BEFORE the rate of combustionis increased, and must be decreased AFTERthe rate of combustion is decreased. There isusually little difficulty in teaching fireroompersonnel to increase the air pressure beforethe rate of combustion is increased, since failureto do so results in panting and vibrationof the boiler and in heavy smoke. It is moredifficult, however, to teach the men to decreasethe air pressure after the rate of combustionhas been decreased. However, operating theblower at a faster speed than is required forthe rate of combustion is definitely a poor419

PRINCIPLES OF NAVAL ENGINEERINGpractice, since it introduces more excess airthan is required for the combustion of the fuel.Forced Draft Blower MaintenanceForced draft blowers require relatively littlemaintenance and repair, provided they areoperated and maintained in strict accordancewith instructions given in the manufacturer'stechnical manual. A good deal of the maintenancework required in connection with blowersis related to keeping the lubrication system inproper condition. All maintenance of blowersmust be performed in accordance with the requirementsof the 3-M System.The lubricating oil in the reservoir must bekept clean. The reservoir must always befilled to the correct level with oil of the specifiedweight and grade. Oil samples must betaken routinely at the specified intervals, ormore often if you have reason to suspect thatthe oil is contaminated. When a sample showsan unusual amount of sediment or water, thisfact should be reported to the engineering officeror to the PO in charge, who may issueinstructions to change the oil. After the oilhas been drained, the inside of the reservoirshould be wiped clean.The metal-edge type of filter should becleaned at least once each watch. This is doneby giving the handle one or two complete turns.From time to time the filter should be dismantledand cleaned; this should be done wheneverthe oil is changed in the reservoir, andmore often if necessary.A common occurrence with vertical blowersis contamination of the oil with fresh water.This happens in an idle blower when leakingsteam enters the turbine casing, passes throughthe upper labyrinth seal, and impinges on theoil slinger, where it condenses and mixes withthe oil.This problem can be avoided by keepingthe steam valves (especially the exhaust -reliefvalve) in good repair. If the valves leak, theturbine casing drain of an idle blower must bekept open.Automatic shutters are not subject to anygreat amount of wear under normal operatingconditions. However, they must be kept welllubricated at all times. Some types of shuttershave Zerk-type grease fittings; others have oilholes. Be sure to use the correct lubricant.K the automatic shutters are not properly lubricated,they may stick in the open positionand then slam shut with sufficient force to causedamage to the shutters and to the toggle gear.Broken or sprung parts must be replaced inorder to ensure smooth operation of the shutters.Shutters should be inspected frequentlyto determine whether the leaves operate freelyand to be sure that they seal tightly when closed.Forced draft blowers should not be operatedif they are vibrating excessively or making anyunusual noise. Vibration may be caused by wornor loose bearings, a bent shaft, loose or brokenfoundation bolts or rivets, an unbalanced fan, orother defects. All defects should be correctedas soon as possible in order to prevent a completebreakdown of the blower.Minor repairs to blower fan blades may bemade aboard ship in case of emergency, in accordancewith procedures specified in chapter9530 of the Naval Ships Technical Manual. Majorrepairs to fan blades must NOT be made withoutspecific instructions from the Naval ShipSystems Command. As a matter of routine care,blower fan blades should be wiped down fromtime to time to remove dirt and dust. (Onerapid method of cleaning the blades of a multistageblower without any disassembly is discussedin chapter 9530 of the Naval Ships TechnicalManual .) Paint must NEVER be applied toa blower fan or to any other rotating part of theunit.When inspecting and repairing blowersequipped with anti-reverse rotation devices, becareful not to apply reverse torque to the shaft,since this could cause damage to the shaft ofthe anti-reverse rotation device.Safety PrecautionsSome of the most important safety precautionsto be observed in connection with forceddraft blowers are:1. Before starting a blower, always makesure that the fan is free of dirt, tools, rags, andother foreign objects or materials. Check theblower room for loose objects that might bedrawn into the fan when the blower is started.2. Do not try to move automatic shutters byhand if another blower serving the same boileris already in operation.3. When only one blower on a boiler is tobe operated, make sure that the automatic shutterson the idle blower are closed and locked.4. Never try to turn a blower by hand whensteam is being admitted to the unit.420

Chapter 15, -PUMPS AND FORCED DRAFT BLOWERS5. Never tie down the speed-limiting governor.Be sure it is in good operating conditionat all times. Be sure it is properlyset.6. Observe all safety precautions requiredin connection with the operation of the drivingturbine.Casualty ControlIf a forced draft blower fails, take the followingaction:1. If one blower fails when two blowers arein use, speed up the other blower.2. K only one blower is in use, secure theburners immediately to prevent a flareback.3. Start the standby blower and notify theengineroom of the casualty because of a possibleneed for a reduction in speed.4. Determine the cause of the failure andremedy the trouble as soon as possible.The rupture of a forced draft blower lube oilline is a casualty in itself, as well as one whichcan lead to blower failure. The rupture of alube oil line is discussed here separately becauseof the special hazard of fire that is involved.If a forced draft blower lube oil line isruptured, take the following action immediately.1. If two blowers are in use, secure the affectedblower and speed up the other. If onlyone blower is in use, secure the burners immediatelyto prevent a flareback. Secure theaffected blower and light off the standby blower.2. Notify the engineroom because of a possibleneed for a reduction in speed.3. Get firefighting equipment to the scene.4. Wipe up all oil that has spilled out. Flushout and wipe out the bilges as necessary.5. Repair or renew the ruptured section assoon as possible.6. Refill the reservoir with clean oil. Testthe new section; if it is satisfactory, the blowercan be returned to service.421

CHAPTER 16AUXILIARY STEAM TURBINESAuxiliary steam turbines are used to drivemany auxiliary machinery units aboard steamdrivenships. Turbine-driven auxiliaries locatedin the engineering spaces include ship's servicegenerators, forced draft blowers, air compressors,and a number of pumps such as main condensatepumps, main condenser circulatingpumps, main feed pumps, feed booster pumps,fuel oil service pumps, and lubricating oil servicepumps.In many cases, the turbine-driven auxiliariesare duplicated by electrically driven units for inportor cruising use. Although the motor-drivenunits have a comparatively high efficiency, theircapacity is not sufficient (on some ships, at least)to meet the demands of the engineering plant athigh speeds. A further advantage of auxiliary turbinesis their greater reliability; in general,there is greater possibility of interruption orloss of electric power supply than of steam supply.In addition, the use of auxiliary turbines improvesthe overall plant efficiency because exhauststeam from the auxiliary turbines can beutilized in various ways throughout the plant.The basic principles of steam turbine design,classification, and construction discussed inchapter 12 of this text apply in general to auxiliaryturbines as well as to propulsion turbines,except for specific differences noted in the remainderof this chapter.TYPES OF AUXILIARY TURBINESMany auxiliary turbines are of the impulsetype. Reduction gears are used with most auxiliaryturbines^ to increase efficiency. Sincespace requirements frequently demand relativ-Direct drive, rather than geared drive, units includeforced draft blowers, high speed centrifugal pumps,and some recent ship's service turbogenerators.ely small units, auxiliary turbines are usuallydesigned with comparatively few stages— oftenonly one. This means a large pressure drop anda high steam velocity in each stage. To obtainmaximum efficiency, the blade speed must alsobe high. With auxiliary turbines, as with propulsionturbines, reduction gears serve to reconcilethe conflicting speed requirements of the drivingand the driven units.Until about 1950, many generator turbineswere designed and installed in such a way thatthey could be operated on steam from either superheatedor saturated steam lines at full boilerpressure. Most of the other auxiliary turbines atthis time operated on saturated steam at fullboiler pressure. During the early 1950's, a fewships were built in which all auxiliary turbineswere designed to operate on steam at full superheatand full boiler pressure. On most oil-firedships built since 1953, steam at full superheatand full boiler pressure is supplied to the auxiliaryturbines for generators, main feed pumps,and forced draft blowers; the other auxiliary turbineson these ships usually operate on steam atreduced temperature and pressure (about 50° Fof superheat and 600 psig). On nuclear ships, allturbines (propulsion and auxiliary) are designedto operate on wet steam— usually, steam whichcontains about 1 percent moisture. The auxiliaryturbines on nuclear ships operate over a widepressure range which varies according to thetype of nuclear propulsion plant. For more recentnuclear submarines, the pressure range is from285 to 750 psig; on the nuclear carrier USS Enterprise,the pressure range is from approximately585 to 1025 psig under normal operatingconditions. The generator turbines usually exhaustto their own separate auxiliary condensers;on recent submarines, however, they exhaust tothe main condenser. Most other auxiliary turbinesexhaust to the auxiliary exhaust system.The auxiliary exhaust system imposes a back422

Chapter 16. -AUXILIARY STEAM TURBINESpressure which is approximately 15 psig on oilfiredships and somewhat higher on nuclearships.Most auxiliary turbines are axial flow unitswhich are quitesimilar (except for size and numberof stages) to the axial-flow propulsion turbinesdescribed in chapter 12. However, someauxiliary turbines are designed for helical flowand some for radialflow— types of flow which areseldom if ever used for propulsion turbines.A helical-flow auxiliary turbine is shown infigure 16-1. In a turbine of this type, steamenters at a tangent to the periphery of the rotorand impinges upon the moving blades. Theseblades, which . consist of semicircular slotsmilled obliquely in the wheel periphery, arecalled buckets . The buckets are shaped in such away that the direction of steam flow is reversedin each bucket, and the steam is directed into aredirecting bucket or reversing chambermounted on the inner cylindrical surface of thecasing. The direction of the steam is again reversedin the reversing chamber, and the continuousreversal of the direction of flow keepsthe steam moving helically.Several nozzles are usually installed in thistype of turbine, and for each nozzle there is anaccompanying set of redirecting buckets or reversingchambers. Thus the reversal of steamflow is repeated several times for each nozzleand set of reversing chambers.Now let us consider the classification of ahelical-flow turbine with respect to staging andcompounding, as discussed in chapter 12. It isa single-stage turbine because it has only oneset of nozzles and therefore only one pressuredrop. It is a velocity-compound turbine becausethe steam passes through the moving blades(buckets) more than once, and the velocity of thesteam is therefore utilized more than once. Thehelical-flow turbine shown in figure 16-1 mightbe said to correspond roughly to a turbine inwhich velocity- compounding is achieved by theuse of four rows of moving blades.Helical-flow auxiliary turbines are used fordriving some pumps and forced draft blowers.The arrangement of nozzles and blading thatprovides radial flow in a turbine is shown in figure16-2. Turbines of this type are sometimesused for driving auxiliary units such as pumps.As discussed in chapter 12, turbines may beclassified as single- entry or re-entry turbines,depending upon the number of times the steamenters the blading. All multistage (and hence all33.45X 38.81XFigure 16-1.— Helical-flow turbine. Figure 16-2.— Radial flow.423

PRINCIPLES OF NAVAL ENGINEERINGpropulsion) turbines are of the single- entrytype.However, some auxiliary turbines are ofthe re-entry type.Re-entry turbines are those in which thesteam passes more than once through the blading.Hence the helical-flow turbine just discussed isa re-entry turbine. A different kind of re-entryturbine is shown in figure 16-3. This turbine issimilar in principle to the helical-flow turbine,38.82XFigure 16-3.— Re-entry turbine with one reversingchamber.but it has one large reversing chamber insteadof a number of redirecting chambers. Re-entryturbines are sometimes made with two reversingchambers instead of one.The auxiliary turbine shown in figure 16-4is used to drive main condensate pumps, feedbooster pumps, and lubricating oil service pumpson many older destroyers. Note that this is aradial-flow turbine. This same design of turbineis used on some newer ships, but with improvedmetals designed to withstand higher pressures,higher temperatures, and high-impact (HI)shock.Another kind of auxiliary turbine is shown infigure 16-5. This turbine, which is usedtodrivemain condenser circulating pumps, is a verticallymounted, axial-flow, velocity- compoundedimpulse turbine. Although this type of turbine isbecoming obsolete, it is still in operation onsome older types of ships. The turbine shaft issecured to the vertical shaft of the pump. A thrustbearing, mounted integrally with tlie upper radialbearing, carries the weight of the rotating elementand absorbs any downward thrust. A throttlevalve and a double- seated balanced inlet valve(normally held wide open by the governor mechanism)admit steam to the turbine.Figure 16-6 shows an auxiliary turbine usedto drive a 400-kilowatt a-c, 50-kilowatt d-cship's service turbogenerator. The turbine is anaxial-flow, pressure- compounded unit. It exhauststo a separate auxiliary condenser whichhas its own circulating pump, condensate pump,and air ejectors. Cooling water for the condenseris provided by the auxiliary circulating pump,through separate injection and overboard valves.In case of casualty to the auxiliary condenser,the turbine can exhaust to the main condenserwhen the main plant is in operation.The turbogenerator turbine shown in figure16-6 is so designed that it can operate on eithersaturated steam or superheated steam. Provisionis made for supplying steam to the turbineeither from the main steam line (superheated)while under way or from the auxiliary steam line(saturated) during in-port operation when thepropulsion turbines and the main steam systemare secured. The steam is admitted to the turbinethrough a throttle trip valve to the steam chest,the speed being regulated by a number of nozzlecontrol valves under the control of a governor.Because the ship's service generator mustsupply electricity at a constant voltage and frequency,the turbine must run at a constant speedeven though the load varies greatly. Constantspeed is maintained through the use of a constantspeedgovernor (discussed later in this chapter).As may be seen in figure 16-6, the shaftglands of the ship's service generator turbine aresupplied with gland sealing steam. The systemis much the same as that provided for propulsionturbines. Other auxiliary turbines in naval usedo not require an external source of gland sealingsteam since they exhaust to pressures aboveatmospheric pressure.Generator turbines vary greatly, and are notall like the one shown in figure 16-6. Forexample, one recent type of turbogenerator consistsof seven stages— one Curtis stage and sixRateau stages. This turbine is direct drive,rather thangeared; the turbine operates at 12,000rpm and so does the generator.AUXILIARY TURBINE LUBRICATIONAuxiliary turbines designed to Navy specificationshave pressure lubrication systems tolubricate the radial bearings, reduction gears.424

Chapter 16. -AUXmiARY STEAM TURBINESSECTION THRUBLADINGSECTION "A-A"Figure16-4.— Auxiliary turbine for main condensate pump, feed booster pump,and lubricating oil service pump.47.9Xand governors.^ Pressure lubrication systemsfor auxiliary turbines do not provide lubricationfor governor linkages or— except on some turbogeneratorsets— for flexible couplings; theseparts of the unit must be lubricated separately.2 Some very small commercially designed auxiliaryturbines have self-oiling bearings instead of pressurelubrication systems. A self -oiling bearing has one ortwo rings which hang on the turbine shaft and revolvewith it, although at a slower rate. On each revolution,the rings dip into an oil reservoir and carry oil aroundto the upper part of the bearing shell.A pressure lubrication system requires alube oil pump. As a rule, the lube oil pumps usedfor auxiliary units are positive-displacementpumps of the simple gear type, as discussed inchapter 15 of this text. The lube oil pump is generallyinstalled on the turbine end of a forceddraft blower unit, but may be on either the drivingor the driven end of pump units. The lube oilpumps for turbogenerators are usually driven byauxiliary gearing connected to the low speed gearshaft. Some forced draft blowers use a centrifugalpump, supplemented by a viscosity pump, forlubrication of the unit; this type of lubricationsystem is peculiar to forced draft blowers and is425

PRINCIPLES OF NAVAL ENGINEERINGCENTRIFUGAL SPEEDLIMITINGGOeNOROILDAMTHRUSTCOLLARDOUBLE POPPETSTEAM VALVEOILSCREWPUMP>\\\ss\s\\\\sv^^^H^^^EXHAUSTFigure 16-5.— Auxiliary turbine for main condenser circulating pump.47.10Xtherefore discussed in connection with theblowers, in chapter 15 of this text.The pressure lubrication system shown infigures 16-7 and 16-8 is designed for fuel oilservice pumps, fuel oil booster pumps, and lubricatingoil service pumps; however, it issimilar in principle to the lubricating systemsof many other units.In the system illustrated, the bottom sectionof the gear casing forms the oil reservoir. Thereservoir is filled through an oil filler hole inthe top of the casing and emptied through a drainoutlet at the base of the casing. The shaft, whichcarries the gear-type oil pump on one end andthe governor on the other end, is geared to thepump shaft. The pump shaft is in turn geared tothe turbine shaft.426

Chapter 16. -AUXILIARY STEAM TURBINESOPERATING LEVERCONNECTIONOPERATINGCYLINDERCONNECTION TOGOVERNOR LEVERRELIEF VALVECONTROLLINGVALVEGLAND EXHAUSTCONNECTIONgLANDFigureEXHAUST TO AUXILIARY CONDENSER16-6.— Auxiliary turbine for ship's service turbogenerator.47,11X427

PRINCIPLES OF NAVAL ENGINEERINGOIL LEVEL GAGETUBE^IDWORM WHEEL-GEAR CASINGTHERMOMETERFOUR-WAY COCKFILTERTHERMOMETERTHRUST ELEMENTBEARINGOILGOVERNORDRILLED PASSAGE-FILLER HOLE•BEARINGRELIEF VALVBEARINGS-DRILLED PASSAGEOIL PUMP AND GOVERNORDRIVE GEARS •WATER CONNECTIONSOIL DISTRIBUTORFLOW INDICATOROIL FILTER-COOLER UNITGEAR SPRAY NOZZLEOIL PUMPBEARINGSRESERVOIR DRAINWORM WHEEL SHAFT'LUBRICATED BY OIL DRAINED FROM GOVERNORFigure 16-7. — Pressure lubrication system for turbine-driven unit.38.96XThe lubricating oil passes through an oil sightflow indicator, a metal- edge type of filter, andan oil cooler. Oil is then piped to the bearingson the turbine shaft, to the governor, and to theworm gear on the pump shaft. The bearings andgear on the oil pump and governor shaft are lubricatedby oil which drains from the governorand passes back into the oil reservoir. A reliefvalve is built into the gear casing. This valveserves to protect the system against the developmentof excessive pressures.SPEED CONTROL DEVICESDifferent types of governors are used forcontrolling the speed of auxiliary turbines. Thediscussion here is limited to the constant- speedgovernor and the constant-pressure pump governor,both of which are in common naval use,"^Constant-Speed GovernorsThe constant- speed governor, sometimescalled the speed- regulating governor, is used on^ Additional governingdevices that maybe encounteredon recent ships include hydraulic or electric loadsensinggovernors, for turbogenerators, and pneumatic,hydraulic, or electric controls for main feedpumps. On ships having automatic combustion and feedwater control systems, the main feed pump controlsmay be related in some way to the boiler controls.428

Chapter 16. -AUXILIARY STEAM TURBINES--GOVERNORHIGH SPEED SHAFT(.DRIVEN BY TURBINE)OIL COOLEROIL FLOW INDICATORV^ ^'/ ^OIL FILTERFigure 16-8, — Isometric diagram of pressure lubrication system.38.97Xconstant- speed machines to maintain a constantspeed regardless of the load on the turbine.Constant- speed governors are used primarily ongenerator turbines and on air compressor turbines.A constant- speed governing system for aship's service generator turbine is shown in figure16-9. The constant-speed governor operatesa pilot valve which controls the flow of oil to anoperating cylinder. The operating cylinder, inturn, controls the extent of the opening or closingof the turbine nozzle valves.With an increased load on the generator, theturbine tends to slow down. Since the governoris driven by the turbine shaft, through reduction429

PRINCIPLES OF NAVAL ENGINEERINGuo% ua>c(UbeoU3(Uow"n.•IHH'j>>^{'i^/j/^j///j^^/'f/jjf'/^/.01ho•i-iCcv>obO•a(Up.mcouI0)3bO>f^ff^/f^^f^///fff^rfrffyff430

Chapter 16. -AUXILIARY STEAM TURBINESgears, the governor also slows. Centrifugalweights on the governor move inward as thespeed decreases, and this causes the pilot valveto move upward, permitting oil to enter the operatingcylinder. The operating piston rises and,through the controlling valve lever, the liftingbeam is raised. The nozzle valves open andadmit additional steam to the turbines.The upward motion of the controlling valvelever causes the governor lever to rise, thusraising the bushing. Upward motion of the bushingtends to close the upper port, shutting off theflow of oil to the operating cylinder; this actionstops the upward motion of the operating piston.The purpose of this follow-up motion of thebushing is to regulate the governing action of thepilot valve. Without this feature, the pilot valvewould operate with each slight variation in turbinespeed and the nozzle valves would be alternatelyopened wide and closed completely.A reverse process occurs when the load onthe generator decreases. In this case, the turbinespeeds up, the governor speeds up, the centrifugalweights move outward, and the pilot valvemoves downward, opening the lower ports andallowing oil to flow out of the operating cylinder.The controlling valve lever lowers the liftingbeam and thereby reduces the amount of steamdelivered to the turbine.Constant-Pressure Pump GovernorsMany turbine-driven pumps are fitted withconstant-pressure pump governors. The functionof a constant pressure pump governor is tomaintain a constant pump discharge pressureunder conditions of varying flow. The governor,which is installed in the steam line to the pump,controls the pump discharge pressure by controllingthe amount of steam admitted to thedriving turbine.A constant-pressure pump governor for amain feed pump is shown in figure 16-10. Thegovernors used on fuel oil service pumps, lube oilservice pumps, fire and flushing pumps, andvarious other pumps are almost identical. Thechief difference between governors used for differentservices is in the size of the upper diaphragm.A governor used for a pump which operateswith a high discharge pressure has a smallerupper diaphragm than one for a pump which operateswith a low discharge pressure.Two opposing forces are involved in theoperation of a constant-pressure pump governor.Fluid from the pump discharge, at dischargepressure, is led through an actuating line to thespace below the upper diaphragm. The pump dischargepressure thus exerts an upward force onthe upper diaphragm. Opposing this, an adjustingspring exerts a downward force on the upper diaphragm.When the downward force of the adjustingspring is greater than the upward force of thepump discharge pressure, the spring forces theupper diaphragm and the upper crossheaddown.A pair of connecting rods connects the uppercrosshead rigidly to the lower crosshead, so theentire assembly of upper and lower crossheadsmoves together. When the crosshead assemblymoves down, it pushes the lower mushroom andthe lower diaphragm downward. The lower diaphragmis in contact with the controlling valve.When the lower diaphragm is moved down, thecontrolling valve is forced down and thus opened.The controlling valve is supplied with a smallamount of steam through a port from the inletside of the governor. When the controlling valveis open, steam passes to the top of the operatingpiston. The steam pressure acts on the top of theoperating piston, forcing the piston down andopening the main valve. The extent to which themain valve is open controls the amount of steamadmitted to the driving turbine. Increasing theopening of the main valve therefore increases thesupply of steam to the turbine and so increasesthe speed of the turbine.The increased speed of the turbine is reflectedin an increased discharge pressure from thepump. This pressure is exerted against the underside of the upper diaphragm. When the pump dischargepressure has increased to the point wherethe upward force acting on the under side of theupper diaphragm is greater than the downwardforce exerted by the adjusting spring, the upperdiaphragm is moved upward. This action allowsa spring to start closing the controlling valve,which in turn allows the main valve spring tostart closing the main valve against the now reducedpressure on the operating piston. When themain valve starts to close, the steam supply tothe turbine is reduced, the speed of the turbineis reduced, and the pump discharge pressure isreduced.At first glance, it might seem that the controllingvalve and the main valve would be constantlyopening and closing and that the pumpdischarge pressure would be continually varyingover a wide range. This does not happen, however,because the governor is designed with an431

PRINCIPLES OF NAVAL ENGINEERINGADJUSTING SCREWHANDWHEELLOCK NUTADJUSTING SPRINGSTEAM CHAMBERDIAPHRAGM DISK(UPPER MUSHROOM)UPPER DIAPHRAGMACTUATING LINE FROMDISCHARGE SIDEOF PUMPINTERMEDIATE DIAPHRAGMCROSSHEAD CONNECTING ROD^^DIAPHRAGM STEM CAP(INTERMEDIATE MUSHROOM)LOWER DIAPHRAGMCYLINDER LINER __OPERATING PISTONNEEDLE VALVEDIAPHRAGM STEM(LOWER MUSHROOM)DIAPHRAGM STEM GUIDECONTROLLING VALVE BUSHINGCONTROLLING VALVECONTROLLING VALVE SPRINGSTEAM INLET^_^MAIN VALVE —^^^SS^^^t^MAIN VALVE SPRINGSTEAM OUTLET(TO TURBINE)STEM (FOR BYPASS)INDICATOR PLATEHANDWHEEL (FOR BYPASS)Figure 16-10.— Constant-pressure pump governor for main feed pump.3(432

Chapter 16. -AUXILIARY STEAM TURBINESarrangement which prevents excessive openingor closing of the controlling valve. An intermediatediaphragm bears against an intermediatemushroom which, in turn, bears against the topof the lower crosshead. Steam is led from thegovernor outlet to the bottom of the lower diaphragmand also, through a needle valve, to thetop of the intermediate diaphragm. A steamchamber is provided to assure a continuous supplyof steam at the required pressure to the topof the intermediate diaphragm.Any movement of the crosshead assembly,either up or down, is thus opposed by the forceof the steam pressure acting either on the intermediatediaphragm or on the lower diaphragm.The whole arrangement serves to preventextreme reactions of the controlling valve in responseto variations in pump discharge pressure.Limiting the movement of the controllingvalve in the manner just described reduces theamount of hunting the governor must do to findeach new position. Under constant- load conditions,the controlling valve takes a position whichcauses the main valve to remain open by the requiredamount. A change in load conditions resultsin momentary hunting by the governor untilit finds the new position required to maintainpump discharge pressure at the new condition ofloadȦn automatic shutdown device has recentlybeen developed for use on main feedpumps. Thepurpose of the device is to shut down the mainfeed pump and so protect it from damage in theevent of loss of feed booster pump pressure. Theshutdown device consists of an auxiliary pilotvalve and a constant-pressure pump governor,arranged as shown in figure 16-11. The governoris the same as the constant-pressure pump governorjust described except that it has a specialtop cap. In the regular governor, the steam forthe operating piston is supplied to the controllingvalve through a port in the governor valve body.In the automatic shutdown device, the steam forthe operating piston is supplied to the controllingvalve through the auxiliary pilot valve. The auxiliarypilot valve is actuated by the feed boosterAUXILIARY PILOTVALVEACTUATING LINEFROM DISCHARGE SIDEOF MAIN FEED PUMPGOVERNOR(WITH SPECIAL TOP CAP)ACTUATING LINEFROM DISCHARGE SIDEOF FEED BOOSTER PUMPaffijT-nrrr\t^ eSTEAM INLET\TO MAIN FEEDPUMPTURBINEFigure 16-11.—Automatic shutdown device for main feed pump.38.91433

PRINCIPLES OF NAVAL ENGINEERINGpump discharge pressure. When the boosterpump discharge pressure is inadequate, the auxiliarypilot valve will not deliver steam to thecontrolling valve of the governor. Thus inadequatefeed booster pump pressure allows the mainvalve in the governor to close, shutting off theflow of steam to the main feed pump turbine.SAFETY DEVICESSafety devices used on auxiliary turbines includespeed-limiting governors and severalkinds of trips. Safety devices differ from speedcontrol devices in that they have no control overthe turbine under normal operating conditions. Itis only when some abnormal condition occurs thatthe safety devices come into use to stop the unitor to control its speed.Speed- Limiting GovernorsThe speed-limiting governor is essentiallya safety device for variable speed units. Itallows the turbine to operate under all conditionsfrom no-load to overload, up to the speed forwhich the governor is set, but it does not allowoperation in excessof 107 percent of rated speed.It is important to note that this type of governoris adjusted to the maximum operating speed ofthe turbine and therefore has no control over theadmission of steam until the upper limit of safeoperating speed is reached.One common type of speed- limiting governoris shown in figure 16-12. This governor is usedon main condensate pumps, feed booster pumps,lube oil service pumps, and other auxiliaries inthe engineering plant. The particular speed-limitinggovernor shown here is designed for use ona main condensate pump with a vertical shaft;speed-limiting governors that operate on verymuch the same principle are used on main feedpumps and other auxiliaries that have horizontalshafts.The governor shaft is driven directly by anauxiliary shaft in the reduction gear, and rotatesat the same speed as the pump shaft. This speedis proportional to— although lower than— thespeed of the driving turbine. Two flyweights arepivoted to a yoke on the governor shaft and carryWEIGHTSFigure16-12. — Speed-limiting governor.43447.54

Chapter 16. -AUXILIARY STEAM TURBINESarms which bear on a push rod assembly. Thepush rod assembly is held down by a strongspring.Because of centrifugal force, the position ofthe flyweights is at all times a function of turbinespeed. As the turbine speed increases, theflyweights move outward and lift the arms. Asthe speed of the turbine approaches the speedfor which the governor is set, the arms liftagainst the spring tension. If the turbine speedbegins to exceed the speed for which the governoris set, the flyweights move even farther out,thereby causing the governor valve to throttledown on the steam.When the turbine slows down, as from an increasein load, the centrifugal force on the flyweightsis diminished and the governor push rodspring acts to pull the flyweights inward. Thisaction rotates the lever about its pivot and opensthe governor valve, thus admitting more steamto the turbine. The turbine speed increases untilnormal operating speed is reached.The speed-limiting governor acts as aconstant- speed governor when the turbine is operatingat or near rated speed, although itis designed only as a safety device to preventoverspeeding. The governor has no effect on thespeed of the turbine at speeds below about 95 percentof rated speed.TripsSeveral kinds of trips are used as safety deviceson auxiliary turbines.Overspeed trips are used on turbines thathave constant- speed governors. The overspeedtrip shuts off the supply of steam to the turbineand thus stops the unit when a predeterminedspeed has been reached. Overspeed trips areusually set to trip out at about 110 percent ofnormal operating speed. In the past overspeedtrips were used primarily on constant- speed turbinesand on some commercial-type variablespeedunits. Recent specifications require overspeedtrips onallnavalauxiliary turbines of over100 horsepower. Figure 16-13 shows the constructionof an overspeed trip used on turbogenerator.Back-pressure trips are installed on turbogeneratorsto protect the turbine by closing thethrottle automatically when the back pressure(exhaust pressure) becomes too high. A backpressuretrip is shown in figure 16-14.Emergency hand trips are installed on turbogeneratorsto provide a means for closing thethrottle quickly, by hand, in case of damage toEMERGENCY GOVERNORDETAILOIL PIPEBELL CRANK HANDLETRIP RODPLUNGER38.93Figure 16-13. — Overspeed trip for turbogenerator.ADJUSTINGBUSHINGLOCKNUTFigure 16-14.— Back-pressure trip.96.25435

Sif»l»m, Subiyilam, or C9nipen*nlPRINCIPLES OF NAVAL ENGINEERING

CHAPTER 17COMPRESSED AIR PLANTSCompressed air serves many purposesaboard ship, and air outlets are installed in varioussuitable locations throughout the ship. Theuses of compressed air include (but are not limitedto) the operation of pneumatic tools andequipment, diesel engine starting and control,torpedo charging, aircraft starting and cooling,air deballasting, and the operation of pneumaticcontrol systems. The systems that supply compressedair for the various shipboard needs arediscussed in chapter 9 of this text; in the presentchapter we are concerned with the equipmentused to compress the air and supply it to thecompressed air systems.Compressed air represents a storage ofenergy. Work is done on the working fluid (air)so that work can later be done by the workingfluid. Air compression may be eitlTer an adiabaticor an isothermal process. ^ Adiabatic compressionresults in a high internal energy levelof the air being discharged from the compressor.However, much of the extra energyprovided by adiabatic compression may be dissipatedby heat losses, since compressed air isusually held in an uninsulated receiver until it isused. Isothermal compression is, in theory, themost economical method of compressing air inthat it requires the least work to be done on theworking fluid. However, the isothermal compressionof air requires a cooling medium to removeheat fromthe compressor and its containedair during the compression process. The moreclosely isothermal compression is approached,the greater the cooling effect required; in a compressorof finite size, then, we reach a point atwhich it is no longer practicable to continue tostrive for isothermal compression.In actual practice, the process of air compressionis approximately isothermal when con-1 Thermodynamic processes are discussed in chapter8 of this text.sidered from start to finish, and approximatelyadiabatic when considered within any one stageof the compression process. In order to achievesome benefits from each type of process (isothermaland adiabatic) most air compressors aredesigned with more than one stage and witha cooling arrangement after each stage. Multistagingand after- stage cooling have the furtheradvantages of preventing the development of excessivelyhigh temperatures in the compressorand in the accumulator, reducing the horsepowerrequirements, condensing some of the entrainedmoisture, and increasing volumetric efficiency.The general arrangement of a multistagecompressed air plant with after-stage cooling isillustrated in figure 17-1. This illustration showsa reciprocating air compressor with two stages;however, the same general arrangement of partsis found in any type of compressed air plant thatutilizes multistaging and after- stage cooling.The accumulator shown in figure 1 7- 1 is foundin all compressed air plants, although the size ofthe unit varies according to the needs of the system.The accumulator (also called a receiver)helps to eliminate pulsations in the discharge lineof the air compressor, acts as a storage tankduring intervals whenthedemandfor air exceedsthe capacity of the compressor, and allows thecompressor to shut down during periods of lightload. Overall, the accumulator functions to retardincreases and decreases in the pressureof the system, thereby lengthening the startstop-start cycle of the compressor.COMPRESSOR CLASSIFICATIONSAir compressors are classified in variousways. A compressor may be single acting ordouble acting, single stage or multistage, andhorizontal, angle, or vertical, as shown in figure17-2. A compressor may be designed so thatONLY one stage of compression takes place437

PRINCIPLES OF NAVAL ENGINEERINGAIR INLETINTERCOOLERJAFTERCOOLERAIROUTLETCOOLINGf .WATER r"*"OUTLETCOOLING WATERINLETACCUMULATORFigure 17-1.— General arrangement of multistage compressed airplant.147.118within one compressing element, or so that morethan one stage takes place within one compressingelement. In general, compressors are classifiedaccording to the type of compressing element,the source of driving power, the method bywhich the driving unit is connected to the compressor,and the pressure developed.TYPES OF COMPRESSING ELEMENTS .-Air compressor elements may be of the centrifugal,rotary, or reciprocating types. The reciprocatingtype isgenerally selected for capacitiesbelow 1,000 cfm and for pressures of 100 psi orabove, the rotary type for capacities up to 10,000cfm andfor pressures below 100 psi, and the centrifugaltype for 10,000 cfm or greater capacitiesand for up to 100 psi pressures.Most of the compressors used in the Navyhave reciprocating elements (fig. 17-3). In thistype of compressor the air is compressed in oneor more cylinders, very much like the compressionwhich takes place in an internal combustionengine.SOURCES OF POWER. -Compressors aredriven by electric motors, internal combustionengines, steam turbines, or reciprocating steamengines. Most of the air compressors in navalservice are driven by electric motors.DRIVE CONNECTIONS.- The driving unitmay be connected to the compressor by one ofseveral methods. When the compressor and thedriving unit are mounted .on the same shaft, theyare close coupled. Close coupling is often usedfor small capacity compressors that are drivenby electric motors. Flexible couplings are usedto join the driving unit to the compressor wherethe speed of the compressor and the speed of thedriving unit can be the same.V-belt drives are commonly used with small,low pressure, motor-driven compressors, andwith some medium pressure compressors. In afew installations, a rigid coupling is used betweenthe compressor and the electric motor ofa motor-driven compressor. In a steam turbinedrive, compressors are usually driven throughreduction gears.PRESSURE CLASSIFICATION.-In accordancewith General Specifications for Ships of theUnited States Navy, compressors are classifiedas low pressure, medium pressure, or high pressure.Low pressure compressors are thosewhich have a discharge pressure of 150 psi orless. Medium pressure compressors are thosewhich have a discharge pressure of 151 psi to1,000 psi. Compressors which have a dischargepressure above 1,000 psi are classified as highpressure.Most low pressure air compressors are ofthe two- stage type with either a vertical V (seefig. 17-3) or a vertical W arrangement of438

Chapter 17. -COMPRESSED AIR PLANTSSUCTION VALVEDISCHARGE VALVE^/^^^DISCHARGE VALVECYLINDER^CYLINDER PISTONPISTONSUCTION VALVE.SUCTION VALVES,DISCHARGE VALVE DISCHARGE VALVE /discharge VALVESSUCTIONVALVEMl- V U V »SUCTION VALVE.B3RD STAGE3RD STAGED ^^^4TH STAGE1ST STAGE>rf^ J =b1ST STAGE^2ND STAGE2ND STAGE ^4TH STAGE1ST STAGE2ND STAGEFigureE17-2. — Types of air compressors: A. Vertical. B, Horizontal, C. Angle.D. Duplex. E. Multistage.47.151439

PRINCIPLES OF NAVAL ENGINEERINGcylinders. Two-stage, V-type low pressure compressorsusually have one cylinder for the first(lower pressure) stage of compression, and onecylinder for the second (higher pressure) stageof compression. W-type compressors have twocylinders for the first stageof compression, andone cylinder for the second stage. This arrangementis shown in the two- stage, three- cylinder,radial arrangement in part A of fig. 17-4,Compressors may be classified according toa number of other design features or operatingcharacteristics.INTERCOOLERINTERCOOLERUNLOADER^UNLOADERGUARDGUARDFEATHERVALVEHIGH PRESSURESUCTION2 NO STAGEPISTONLOW PRESSUREDISCHARGEi1ST. STAGEPISTON»OIL RESERVOIRFigure 17-3,— Reciprocating air compressor (vertical V, two stage, single-acting,low pressure).47.152440

Chapter 17. -COMPRESSED AIR PLANTSRECIPROCATING AIR COMPRESSORSReciprocating air compressors are sufficientlysimilar in design and operation so thatthe following discussion applies in large part toall reciprocating compressors now in naval use.Medium pressure air compressors are of thetwo-stage, vertical, duplex, single-acting type.Many medium pressure compressors have differentialpistons; this type of piston has morethan one stage of compression during each strokeof the piston. (See fig,17-4, A.)Modern air compressors are generallymotor-driven (direct or geared), liquid- cooled,four-stage, single-acting units with vertical orhorizontal cylinders. Cylinder arrangements forhigh pressure air compressors installed on Navyships are illustrated in part B of figure 17-4.Small capacity high pressure air systems mayhave three-stage compressors. Large capacity,high pressure, air systems may be equipped withfive- or six- stage compressors.Operating CycleLet us consider first the operating cycle thatoccurs during one stage of compression ina single-acting reciprocating air compressorsuch as the one shown in figure 17-3. The operatingcycle consists of two strokes of the piston:a suction stroke and a compression stroke.The suction stroke begins when the pistonmoves away from top deadcenter (TDC). Theairunder pressure in the clearance space (above thepiston) expands rapidly until the pressure fallsbelow the pressure on the opposite side of the airinlet valve. At this point the difference in pressurecauses the inlet valve to open and air is admittedto the cylinder. Air continues to flow intothe cylinder until the piston reaches bottom deadcenter (BDC).The compression stroke starts as the pistonmoves away from BDC and compression of theair begins. When the pressure in the cylinder2STAGE, 3 CYL. RADIALr^^III^^i II 1:11-^24 ^^•I 2^1^, i 2-STAGE WITH1 ^ ^ ---DIFFERENTIALPISTON4-STAGEARRANGEMENTS2-STAGE, VERTICAL, WITH2 DIFFERENTIAL PISTONSA3-STAGEARRANGEMENTSB47.153Figure 17-4.—Air compressor cylinder arrangements. A. Low and medium pressurecylinders. B. High pressure cylinders.441

PRINCIPLES OF NAVAL ENGINEERINGequals the pressure on the opposite side of theair inlet valve, the inlet valve closes. Air is increasinglycompressed as the piston movestoward TDC; the pressure in the cylinder finallybecomes great enough to force the dischargevalve open against the discharge line pressureand the pressure of the valve springs. During thebalance of the compression stroke, the air whichhas been compressed in the cylinder is discharged,at almost constant pressure, throughthe open discharge valve.The basic operating cycle just described isrepeated a number of times in double actingcompressors and in other stages of multistagecompressors. In a double-acting compressor,each stroke of the piston is a suction stroke inrelation to one end of the cylinder and a compressionstroke in relation to the other end ofthe cylinder. In a double acting compressor,therefore, two basic compression cycles arealways in process when the compressor is operating;but each cycle, considered separately, issimply one suction stroke and one compressionstroke.In multistage compressors, the basic compressioncycle must occur at least once for eachstage of compression. If the compressor is designedwith two compressing elements for thefirst (low pressure) stage, two compressioncycles will be in process in the first stage at thesame time. If the compressor is designed so thattwo stages of compression occur at the same timein one compressing element, the two basic cycles(one for each stage) will occur at the same time.Compressor ComponentsA reciprocating air compressor consists ofa compressor element, a lubrication system, acooling system, a control system, and an unloadingsystem. In addition to these basic components,the compressor has a system of connectingrods, crankshaft, and flywheel fortransmitting the power developed by the drivingunit to the air cylinder pistons.COMPRESSING ELEMENT. -The compressingelement of a reciprocating air compressorconsists of the air valves, the cylinder, and thepiston.The valves of modern compressorsareof theautomatic type. The opening and closing of thesevalves is caused solely by the difference betweenthe pressure of the air in the cylinder and thepressure of the external air on the intake valveor the pressure of the discharged air on the dischargevalve. On most compressors, a thin plate,low lift type of valve is used. A valve of this typeis shown in figure 17-5.The design of pistons and cylinders dependsprimarily upon thenumberof stages of compressionwhich take place within a cylinder. Commonarrangements of pistons and cylinders are shownin a previous illustration (fig. 17-2).Two types of pistons are in common use.Trunk pistons (fig. 17-6) are driven directly bythe connecting rods. Since the upper end of a connectingrod is fitted directly to the piston wristpin, there is a tendency for a piston to develop aside pressure against the cylinder walls. To distributethe side pressure over a wide area of thecylinder walls or liners, trunk pistons with longskirts are used. This type of piston tends to eliminatecylinder wall wear. Differential pistons(fig. 17-7) are modified trunk pistons having twoor more different diameters. These pistons arefitted into special cylinders which are arrangedso that more than one stage of compression isserved by one piston. The compression for onestage takes place over the piston crown; compressionfor theother stage or stages takes placein the annular space between the large and smalldiameters of the piston.LUBRICATION SYSTEM.- Lubrication of aircompressor cylinders is generally accomplishedby means of a mechanical force-feed lubricatorwhich is driven from a reciprocating or a rotarypart of the compressor. Oil is fed from the lubricatorthrough a separate feed line to each cylinder.A check valve is installed at the endof each feed line to keep the compressed air fromforcing the lube oil back to the lubricator. Eachfeed line is equipped with a sight glass. Lubricationbegins automatically as the compressorstarts up. The amount of oil that must be fed tothe cylinders depends upon the cylinder diameter,the cylinder wall temperature, and the viscosityof the oil.On small low pressure and medium pressurecompressors, the cylinders may be lubricated bythe splash method, from dippers on the ends ofthe connecting rods, instead of by a mechanicalforce-feed lubricator.Lubrication of the running gear of most compressorsis accomplished by a lube oil pump(usually of the gear type) which is attached to thecompressor and driven from the compressorshaft. This pump draws oil from the reservoir,as shown in figure 17-8, and delivers it, through442

Chapter 17. -COMPRESSED AIR PLANTSVALVE PLATEVALVE PLATE^GUIDESTOP PLATEFigure 17-5.— Diagram of a thin plate air compressor valve.47.154Xa filter, to an oil cooler. From the cooler, theoil is distributed to the top of each main bearing,to spray nozzles for reduction gears, and to outboardbearings. The crankshaft is drilled so thatoil fed to the main bearings is picked up at themain bearing journals and carried to the crankpin journals. The connecting rods contain passageswhich conduct lubricating oil from thecrank pin bearings up to the wrist pin bushings.As oil leaks out from the various bearings, itdrips back to the reservoir in the base ofthe compressor and is recirculated. Oil from theoutboard bearings is carried back to the base bythe drain lines.The discharge pressure of lubricating oilpumps varies, depending upon the pump design. Arelief valve fitted to each pump functions when thedischarge pressure exceeds the pressure forthe valve is set. When the relief valve opens, excessoil is returned to the reservoir.COOLING SYSTEM.— Most compressors arecooled by sea water supplied from the ship's fireand flushing system. The cooling water is usuallyavailable to each unit through at least twosources. Compressors located outside the largermachinery spaces are generally equipped with anattached circulating water pump as a standbysource of cooling water. Some small low pressurecompressors are air cooled by a fanmounted on or driven by a compressor shaft.The path of water in the cooling water systemfor a four- stage compressor is shown in figure17-9. The flow paths are not identical in allcooling water systems, but in all systems it isimportant that the coldest water be available forcirculation through the oil cooler. Valves areusually provided so that the flow of water to thecooler can becontroUedindependentlyof the restof the system. Thus the oil temperature can becontrolled without affecting other parts of thecompressor. Cooling water is then supplied to theintercoolers and the aftercooler and then to thecylinder jackets and heads. A high pressure aircompressor may require from 6 to 25 gallons ofcooling water per minute, while a medium443

PRWCTPLES OF NAVAL ENGINEERINGINLETVALVE> DISCHARGESZZZ^^ZZ^^ VALVE^lpressure air compressor may require from 10to 20 gallons per minute.As previously noted, cooling of the air is requiredfor most economical compression.Another reason for cooling the air between stagesand after the last stage is to condense any moisturethat may be present. The resulting condensateis then drained off. If the moisture is notremoved from the air, it will be carried into theaccumulator or into the air lines, where it cancause serious trouble.The intercoolers used between stages and theaftercooler used after the last stage are of thesame general construction except that the aftercooleris designed to withstand a higher workingpressure than the intercoolers. Water-cooledcoolers may be of the straight shell-and-tubetype or of the coil type. In coolers designed forair pressures below 250 psig, the air flows eitherthrough the tubes or over and around them; incoolers designed for air pressures above 250psig, the air flows through the tubes. In straightf]f\iaFigure 17-6. — Trunk Piston.47.155.147.155.2Figure 17-7.— Differential Piston.tube coolers, baffles are provided to guide the airand water. In coil type coolers, the air passesthrough the coil and the water flows around theoutside. Air-cooled coolers may beof the radiatortype or may consist of a bank of finned coppertubes located in the path of a blast of air suppliedby the compressor fan.Both intercoolers and aftercoolers are fittedwith moisture separators on the discharge sideto remove moisture (and also any oil that may bepresent) from the air stream. Various designsof moisture separators are in use; the removalof liquid may be accomplished by centrifugalforce, impact, or sudden changes in the velocityof the air stream.CONTROL SYSTEM. -The control system ofa reciprocating air compressor may include oneor more devices such as automatic temperatureshutdown devices, start-stop controls, constantspeedcontrols, and speed-pressure governors.444

Chapter 17. -COMPRESSED AIR PLANTS(^ ^TO OIL SPRAY FORTURBINE PINIONOIL TO TURBINE"PINION BEARING47.156Figure 17-8. — Lubrication system for turbine-driven high pressure air compressor.Automatic temperature shutdown devices arefitted to all recent designs of high pressure aircompressors. Such a device stops the compressorautomatically (and does not allow it torestart automatically) when the cooling watertemperature rises above a safe limit. Some compressorsare fitted with a device that shuts downthe compressor if the temperature of the airleaving any stage exceeds a preset value.Control or regulating systems for naval aircompressors are mainly of the start- stop type.With this type of control, the compressor startsand stops automatically as the accumulator pressurerises or falls to predetermined limits. Onelectrically driven compressors, the system isvery simple: the accumulator pressure operatesagainst a pressure switch that opens when thepressure upon it reaches a given limit andcloses when the pressure drops a predeterminedamount. On steam-driven compressors, theaccumulator pressure is piped to a controlvalve (also called a pilot, trigger, or aux-leakage or bleeding to atsteamis thereby permittedthe governor valve and re-iliary valve) which, when the designed cutoffpressure is reached, admits air to a plungerconnected with the turbine governor valve.This causes steam to be shut off and thecompressor to stop, When the pressure fallsto a predetermined level, the control valvecloses and the air acting upon the plungeris released bymosphere. Theto flow throughstart the turbine.Constant- speed control is a method of controllingthe pressure in the air accumulator bycontrolling the output of the compressor withoutstopping or changing the speed of the unit. Thistype of control is used on compressors that havea fairly constant demand for air, where frequentstopping and starting is undesirable.445

PRINCIPLES OF NAVAL ENGINEERINGffWTT'ffT?TT?T7Tr!TP??TW'!^T^TlT535TTrr7T!T?TrrT^'!'WTT?THIRD STAGE COOLERWATER OUTLETe—QgrFIRST STACE COOLERWATER INLET-OIL OUTLETOIL COOLERH' WATER OUTLETFigure 17-9.— Cooling water system for multistage air compressor.47,157Combined speed and pressure governors areusually furnished for compressors which aredriven by reciprocating steam engines. Neitherthe start-stop nor the constant- speed control isentirely satisfactory for this type of compressor.UNLOADING SYSTEM. -Air compressor unloadingsystems are installed for the removal ofall but the friction loads on the compressors. Anunloading system automatically removes thecompression load from the compressor while theunit is starting and automatically applies the loadafter the unit is up to operating speed. For unitsthat have the start- stop type of control, the unloadingsystem is separate from the control system.For compressors equipped with theconstant- speed type of control, the unloadingsystem is an integral part of the control system.A number of different unloading methods areused, including closing or throttling the compressorintake, holding intake valves off theirseats, relieving intercoolers to atmosphere,opening a bypass from the discharge to the intake,opening up cylinder clearance pockets, usingmiscellaneous constant- speed unloading devices,and using various combinations of thesemethods.As an example of a typical compressor unloadingdevice, consider the MAGNETIC TYPEUNLOADER. Figure 17-10 illustrates the unloadervalve arrangement. This typeof unloaderconsists of a solenoid-operated valve connectedwith the motor starter. When the compressor isat rest, thesolenoid valve is deenergized, admittingair from the receiver to the unloading mechanism.When the compressor approximates normalspeed, the solenoid valve is energized,releasing the pressure from the unloading mechanismand loading the compressor again.ROTARY-CENTRIFUGAL AIR COMPRESSORSThe one non- reciprocating type of air compressorthat is found aboard ship is variouslyreferred to as a rotary compressor, a centrifugalcompressor, or a "liquid piston" compressor.Actually, the unit is something of a mixture,operating partly on rotary principles and partly446

Chapter 17. -COMPRESSED AIR PLANTSSOLENOIDFigure 17-10.'d/;////// //!>l/////////>>IIMl///JfJ/Jj'/)EXHAUST47.15(-Magnetic typeunloader.on centrifugal principles; most accurately,perhaps, it might be called a rotary- centrifugal~compressor.The rotary-centrifugal compressor is used tosupply low pressure compressed air. Becausethis compressor is capable of supplying air thatis completely free of oil, it is often used as thecompressor for pneumatic control systems andfor other applications where oil-free air is required.The rotary- centrifugal compressor, shown infigure 17-11, consists of a round, multi-bladedrotor which revolves freely in an elliptical casing.The elliptical casing is partially filled withhigh-purity water. The curved rotor bladesproject radially from the hub. The blades, togetherwith the side shrouds, form a series ofpockets or buckets around the periphery. Therotor, which is keyed to the shaft of an electricmotor, revolves at a speed high enough to throwthe liquid out from the center by centrifugalforce, resulting in a solid ring of liquid revolvingin the casing at the same speed as the rotorbut following the elliptical shape of the casing.This action alternately forces the liquid to enterand recede from the buckets in the rotor at highvelocity.To follow through a complete cycle of oper*-ation, let us start at point A_. The chamber (1) isfull of liquid. The liquid, because of centrifugalforce, follows the casing, withdraws from therotor, and pulls air in through the inlet port. At(2) the liquid has been thrown outward from thechamber in the rotor and has been replaced withatmospheric air. As the rotation continues, theconverging wall (3) of the casing forces the liquidback into the rotor chamber, compressing thetrapped air and forcing it out through thedischarge port. The rotor chamber (4) is now fullINLETDISCHARGEINLET.PORTDISCHARGE— PORT147.119Figure 17-11.— Rotary- centrifugal compressor.447

PRINCIPLES OF NAVAL ENGINEERINGSystafli, Subsyi1«fn, or CempenenlReference PwbllcallontHigh-Pressure Air Compressorlwr*«w C«r4CMitral Hm.Malnf«n«nc« R»quir*m«n(M.(.H».RataM«lnl«n«M«AP ZZZFCHl 35 49351. Operate compressor by power.2. Blow down all air flasks, separators,and filters.3. Sample and Inspect lube oil.W-1MM20.5NoneZZPFVAl49361. Lift relief valves by hand.M-1MM30.1NoneZZZFCHl49371. Clean suction filter.2. Test inlet and outlet valves byoperation.3. Test temperacure switch by operation.4. Test automatic start and stop switchby operation.Q-1MM20.5NoneAPIZZFCHl92231. Test operation of speed- limitinggovernor and overspeed trip.2. Test operation of temperature control.Q-2MM2FN1.01.0NoneAPZZZFCHl76591. Clean lubricator reservoir.A-1FN0.3NoneAPZZDFCUOA1421. Clean and test air coolers andoil cooler.2. Inspect internal parts for wear.C-1MMlFN24.024.0NoneAPZZPFVAl49411. Test relief valves by pressure.C-2FN1.3NoneAP5Z6FTRO76521. Clean, inspect, and preserveexterior of turbine casing.C-3MM31.0C-4APIZSTTKO76561. Inspect carbon packing for wear.C-4MMlMM34.04.0C-3APSZZFPGF2894Inspect high-pressure airfor oil contamination.systemC-51^2FN1.51.5W-lMAINTtNAMCI IttOU MU•»N*V rOlM treOI {4-M)lUKUU MCE CONTROI. NUMSHA-3/16-9SFigure 17-12. — Maintenance Index Page.98.171448

Chapter 17. -COMPRESSED AIR PLANTSof liquid and ready to repeat the cycle which takesplace twice in each revolution.A small amount of seal water must be constantlysupplied to the compressor to make upfor that which is carried over with the compressedair. The water which is carried over withthe compressed air is removed in a refrigeration-typedehydrator.AIR COMPRESSOR MAINTENANCEMinimum requirements for the performanceof inspections and maintenance on high pressureair plants are shown on the maintenance indexpage figure 17-12.It is the responsibility of the engineer officerto determine if the condition of the equipment,hours of service, or operating conditionsnecessitate more frequent inspections and tests.Details for outline tests and inspections may beobtained from the appropriate manufacturer'sinstruction book or from the Naval Ships TechnicalManual.SAFETY PRECAUTIONSThere are many hazards associated with theprocess of air compression. Serious explosionshave occurred in high pressure air systemsbecause of a diesel effect. 2 Ignition temperaturesmay result from rapid pressurizationof a low pressure dead end portion of thepiping system, malfunctioning of compressoraftercoolers, leaky or dirty valves, and manyother causes. Every precaution must be taken tohave only clean, dry air at the compressor inlet.Air compressor accidents have also beencaused by improper maintenance proceduressuch as disconnecting parts while they areunder pressure, replacing parts with unitsdesigned for lower pressures, and installingstop valves or check valves in improper locations.Improper operating procedures havealso caused air compressor accidents, withresulting serious injury to personnel anddamage to equipment.In order to minimize the hazards inherentin the process of compression and in the useof compressed air, all safety precautionsoutlined in the manufacturers' technical manualand in the Naval Ships Technical Manualmust be strictly observed.2 A diesel engine operates bytakinginair, compressingit, and then injecting fuel into the cylinders, wherethe fuel is ignited by the heat of compression. Thesame effect (normally called the diesel effect ) canoccur in hydropneumatic machinery and in air, oxygen,or other gas systems, if even a very small amount of"fuel"— a smear of oil, for example, or a single cottonthread— is present to be ignited by the heat ofcompression.449

CHAPTER 18DISTILLINGPLANTSNaval ships must be self-sustaining as faras the production of fresh water is concerned.The large quantities of fresh water requiredaboard ship for boiler feed, drinking, cooking,bathing, and washing make it impracticable toprovide storage tanks large enough for more thana few days' supply. Therefore, all naval shipsdepend upon distilling plants to meet the requirementsfor large quantities of fresh water of extremelyhigh chemical and biological purity.PRINCIPLES OF DISTILLATIONAll shipboard distilling plants not only performthe same basic function but also performthis function in much the same way. The distillationprocess consists of heating sea water tothe boiling point and condensing the vaporto obtain fresh water (distillate). The distillationprocess for a shipboard plant is illustratedvery simply in figure 18-1.At a given pressure, the rate at which seawater is evaporated in a distilling plant isVAPORdependent upon the rate at which heat is transmittedto the water. The rate of heat transfer tothe water is dependent upon a number of factors;of major importance are the temperature differencebetween the substance giving up heat and thesubstance receiving heat, the available surfacearea through which heat may flow, and the coefficientof heat transfer of the substances and materialsinvolved in the various heat exchangersthat constitute the distilling plant. Additionalfactors such as the velocity of flow of the fluidsand the cleanliness of the heat transfer surfacesalso have a marked effect upon heat transfer ina distilling plant.Since a shipboard distilling plant consists ofa number of heat exchangers, each serving oneor more specified purposes, the plant as a wholeprovides an excellent illustration of manythermodynamic processes and concepts. Practicalmanifestations of heat transfer— includingheating, cooling, and change of phase— abound inthe distilling plant, and the significance of thepressure-temperature relationships of liquidsand their vapors is clearly evident. ^The sea water which is the raw material ofthe distilling plant is a water solution of variousminerals and salts. In addition to the dissolvedmaterial, sea water also contains suspendedmatter such as vegetable and animal growths andbacteria and other micro-organisms. Underproper operating conditions, naval distillingplants are capable of producing fresh water whichcontains only minute traces of the chemical andSEA WATER BRINE DISTILLATEHEAT SOURCE75.284Figure 18-1.— Simplified diagram of shipboarddistillation process.Much of the information given in chapter 8 of thistext has direct and immediate apphcation to the studyof distilling plants. Applicable portions of chapter 8should be reviewed, if necessary, as a basis for thestudy of distilling plants.450

Chapter 18. -DISTILLING PLANTbiological contaminants which are found naturallyin sea water. 2One of the problems that arises in the distillationof sea water occurs because some of thesalts present in sea water are negatively soluble—thatis, they are less soluble in hot waterthan they are in cold water. A negatively solublesalt remains in solution at low temperatures butprecipitates out of solution at higher temperatures.The crystalline precipitation of varioussea salts forms scale on heat transfer surfacesand thereby interferes with heat transfer. Innaval distilling plants, this problem is partiallyavoided by designing the plants to operate undervacuum or (in the case of one type of plant) atapproximately atmospheric pressure.The use of low pressures (and therefore lowboiling temperatures) has the additional advantageof greater thermodynamic efficiency thancan be achieved when higher pressures and temperaturesare used. With low pressures and temperatures,less heat is required to make the seawater boil and less heat is lost overboard throughthe circulating water that cools and condenses thevapor.DEFINITION OF TERMSThe manner in which the various kinds of distillingplants accomplish the distilling processcan best be understood if we first become familiarwith certain terms relating to the process.The terms defined here relate basically to alltypes of distilling plants now in naval use. Additionalterms that apply specifically to a particulartype of distilling unit are defined asnecessary in subsequent discussion.Distillation. — The process of boiling seawater and then cooling and condensing the resultingvapor to produce fresh water.Evaporation. — The first part of the process ofdistillation. Evaporation is the process of boilingsea water in order to separate it into fresh watervapor and brine.Condensation. — The latter part of the processof distillation. Condensation is the process ofcooling the vapor to produce usable fresh water.Feed.— The sea water which is the raw materialin the distillation process.Vapor.— The product of the evaporation of seawater. The terms vapor and fresh water vaporare used interchangeably.Distillate.— The product resulting from thecondensation of the fresh water vapor producedby the evaporation of sea water. Distillate is alsoreferred to as condensate , as fresh water ,asfresh water condensate, and as sea water distillate.However, the use of the term condensateshould be avoided whenever there is any possibilityof confusion between the condensate of thedistilling plant and the condensate that resultsfrom the condensation of steam in the main andauxiliary condensers. In general, it is best touse the term distillate when referring to theproduct resulting from the condensation of vaporin the distilling plant.Salinity. — The concentration of salt in water.Brine. — Water in which the concentration ofsalt is higher than it is in sea water.TYPES OF DISTILLING UNITSDistilling units installed in naval ships areof two general types. The vapor compression typeof unit is used aboard submarines and smalldiesel-driven surface craft where the daily requirementsdo not exceed 4000 gallons per day(gpd). The low pressure steam distilling unit isused aboard all steam-driven surface ships andon nuclear submarines. The major difference betweenthe two types of distilling units is in thekind of energy used to operate the unit. Vaporcompression units use electrical energy; steamdistilling units use auxiliary exhaust steam.VAPOR COMPRESSION DISTILLING UNITSIt should be noted that distilling plants are not effectivein removing volatile gases or liquids which havea lower boiling point than water, nor are they effectivein killing all micro-organisms. These points are ofparticular importance when a ship is operating in contaminatedor polluted waters, as discussed at the endof this chapter.A vapor compression distilling unit is shownin cutaway view in figure 18- 2 and schematicallyin figure 18-3. The unit consists of three maincomponents— the evaporator, the compressor,and the heat exchanger— and a number of accessoriesand auxiliaries.451

PRINCIPLES OF NAVAL ENGINEERINGDRIVE SHAFTDRIVEN SHAFT(THREE LOBE)MANHOLETUBE SHEETFUNNELINSULATIONDOWNTAKEBRINE OVERFLOW TUBEELECTRICHEATERS-DRAIN-^*-BRINE OVERFLOW OUTLETFigure 18-2.— Cutaway view of vapor compression distilling plant.75.286452

Chapter 18. -DISTILLING PLANTSEVAPORATOR. — The cylindrical shell inwnich vaporization and condensation occur iscommonly called the evaporator. The evaporatorconsists of two principal elements: the steamchest and the vapor separator.The steam chest^ includes all space withinthe evaporator shell except the space that is occupiedby the vapor separator. The steam chestis considered to have an evaporating side and acondensing side. The evaporating side includesthe space within the tubes of the tube bundle(which is located in the lower part of the evaporatorshell) and the space which communicateswith the inside of the tubes. The condensing sideincludes the space which surrounds the externalsurfaces of the tubes; this space communicateswith the discharge side of the compressor bymeans of a pipe, as shown in figure 18-3.The tube bundle is enclosed in a shell. Attop and bottom of the bundle the tube ends areexpanded into tube sheets. Most of the tubes aresmall; but a few, set near the periphery,are larger. Each of the larger tubes contains anelectric heater. As the sea water feed flowsthrough these larger tubes, it is heated to theboiling point by the heaters.The feed inlet pipe extends horizontally to thecenter of the evaporator, where it branches intoa Y. The two ends of the feed pipe turn downwardinto the downtake, as shown in figure 18-?. Seawater feed enters the evaporator through thehorizontal inlet pipe, pours into the downtake, andpasses down to the bottomheadof the evaporatorshell; from there, the feed flows upward throughthe tubes.A funnel is installed inside the downtake, atthe top. The top of the funnel is about 2 inchesabove the top of the evaporator tubes, and thebrine level in the evaporator shell is thus maintainedat this height. About one-half to twothirdsof the feed is vaporized; the remainingbrine overflows continuously into the funnel andthen into the brine overflow tube which isinstalled inside the downtake. The overflow tubeleads the brine out through the bottom ofthe evaporator shell, to the heat exchanger. Inthe heat exchanger, the brine gives up its heat andraises the temperature of the incoming feed.The vapor separator is an internal compartmentlocated at the top of the evaporator shell.3 "Steam chest" is a somewhat misleading term for aunit which is not operated by steam and which has nosteam coming into it from an external source. Althoughcalled a steam chest, it might more accurately bethought of as a "vapor chest."The separator consists of two cylindrical baffles.One cylinder extends downward from theupper head plate of the evaporator; the other extendsupward, and is fitted around the upper cylinderto form a baffle. The floor of the separatoris formedby the bottom of the outer cylinder. Thespace between the two cylinders provides a passagefor the vapor flowing from the evaporatingside of the steam chest to the suction side of thecompressor.The vapor from the boiling sea water risesup through the space between the shell wall andouter cylinder of the separator; it then flowstliedownward through the space between the cylindersof the separator and enters the separatorchamber. From the separator chamber, thevapor travels upward to the intake side of thecompressor.In the course of this roundabout passagethrough the vapor separator, the vapor is separatedfrom any entrained particles of water. Thewater drops to the floor of the separator and iscontinuously drained away. This water has a highsalt concentration, and must be continuouslydrained in order to keep it from enteringthe compressor and thus getting into the condensingside of the evaporator, where it wouldcontaminate the distillate.VAPOR COMPRESSOR.- The vapor whichflows upward from the separator is compressedby a positive-displacement compressor. Thetype of compressor discussed here has twothree-lobe rotors of the type shown in the inserton figure 18-2 and in figure 18-3. Two- lobe compressorsof the type shown in the main part offigure 18-2 were an earlier design.The two rotors are enclosed in a compacthousing which is mounted on the evaporator. Thethree lobes on each rotor are designed to producea continuous and uniform flow of vapor. The vaporenters the compressor housing at the bottom andthen passes upward between the inner and outerwalls of the housing to the rotor chamber, whereit fills the space between the rotor lobes. Thevapor is then carried around the cylindrical sidesof the housing, and a pressure is developed at thebottom as the lobes roll together. Clearances areprovided so that the rotor lobes do not actuallytouch each other and do not touch the housing.The shaft of one rotor is fitted with a drivepulley on one end and a gear on the other end.This gear meshes with a gear on the shaft of theother rotor, to provide the necessary drive forthe second rotor.453

, ,,PRINCIPLES OF NAVAL ENGINEERINGPRESSURE GAGERELIEF VALVEr BYPASS VALVEFROM-DESUPERHEATER.VAPORDRiPCOMPRESSORSEPARATORMANOMETER-VAPOR SEPARATOR DRAINCHECK VALVEDESUPERHEATER TANKFEED INLET-'VENT LINECONDENSATE3/64" ORIFICEOUTLET-STEAM CHEST VENT/^m^^^^^^^^^^^w\^^^^^^^^T"*!,BRINEOVERFLOW? li^m^mm^^'f^^^^^m^^^^^^^^^^"-TUBEHEAT VFNTEXCHANGER2^1^^OUTLETDRAINTRAPELECTRIC HEATER -J BRINE OVERFLOW OUTLET-FEED WATER 1CZD VAPOR AT ATMOSPHERIC PRESSURE 1M22 COMPRESSED VAPORFigureHEAT EXCHANGER. -The heatZl CONDENSATE^ CONCENTRATED BRINE-*- FLOW PATHS18-3.— Schematic view of vapor compression distilling plant.exchangerpreheats the Incoming sea water feed by two heatexchange processes. In one process, the seawater feed is heated by the distillate which isbeing discharged from the distilling unit to theship's tanks. In the other process, the sea waterfeed is heated by the brine overflow which isbeing discharged overboard or to the brine collectingtank.75.287The heat exchanger is a horizontal doubletubeunit. Either sea water or brine flowsthrough the inner tubes, while distillate flowsthrough the space between the inner and the outertubes.Figure 18-4 shows the construction of the heatexchanger and also illustrates the flow paths.454

'I'Chapter 18. -DISTILLING PLANTSffEDINLETDETAIL SECTION OF MMJNDTYPEA-A-ArfE[0OUTLET«NT OUTLETOVERFLOW INLETCONDENSATE INLETFEEO INLET6 5 -» 3 2 1») O O (OVERFLOW OUTLETooO O (o oo o ooOb>OO OcO OdO Oe) o o^O O @-® O OhO O I O O'CONDENSATE5 4 3 2 l»VO-O-G-O-OG-O-G-OH-G-G-O-O -O c'G-G-G-G-(V-G-G-G-GG-G--G-0-0J -G-G- G-G 'rO-O Q--COUTLETFEEDOUTLETOVERFLOW INLETVENT*INLET VENT OUTLET CONDENSATE INLETFigure 18-4.— Heat exclianger for a vapor compression distilling plant.75.288There are four distinct flow paths: feed, brineoverflow, condensate (distillate), and vent.ACCESSORIES AND AUXILIARIES.-A numberof accessories and auxiliaries are requiredfor the operation of the vapor compression distillingunit. These include feed, distillate, andbrine overflow pumps; feed regulating and flowcontrol valves; relief valves; compressor bypassvalves; rotameters; and avariety of pressure andtemperature gages.THEVAPOR COMPRESSION PROCESS.-Now that the principal parts of a vapor455

PRINCIPLES OF NAVAL ENGINEERINGcompression unit have been described, let ussummarize briefly the sequence of events withinthe unit and consider some of the factors that areimportant in the vapor compression process ofdistillation.The cold sea water feed enters the heatexchanger and is heated there to about 190°or 200 F. From the heat exchanger, the feedgoes into the evaporator. Here it flows down thedowntake and into the bottom of the evaporatorshell, then upward in the tubes. Boiling andevaporation take place in the tubes at atmosphericpressure. About one-half to two-thirds ofthe incoming feed is evaporated; the remainderflows out through the brine overflow, thus maintaininga constant water level within the evaporator.The vapor thus generated rises and enters thevapor separator, where any particles of moisturethat may bepresent are separated from the vaporand drained out of the separator. The vapor goesto the suction side of the compressor. In the compressor,distilled water drips onto the rotors andthus desuperheats the vapor as it is compressed.The vapor is compressed to a pressure of about3 to 5 pounds above atmospheric pressure, andis discharged to the space surrounding the tubesin the steam chest. As the vapor condenses onthe outside of the smaller tubes, the distillatedrops down and collects on the bottom tube plate.Every time a pound of compressed vapor condenses,approximately a pound of vapor isformed in the evaporator section; the compressorsuction is thus kept supplied with the rightamount of vaporThe distillate is drawn off through a steamtrap and flows into the heat exchanger at a temperatureof about 220° F. As it flows through theheat exchanger, the distillate gives up heat to theincoming feed and is cooled to within about 18° Fof the cold feed water temperature. Noncondensablegases, together with a small amount ofvapor, flow into the vent line and then to the heatexchanger.Meanwhile, the sea water which is not vaporizedin the evaporator is flowing continuously intothe funnel, down the brine overflow tube, and intothe heat exchanger. The temperature of this brineis about 214° F. In passing through the heat exchanger,the hot brine raises the temperature ofthe sea water feed that is entering through theheat exchanger.The entire distillation cycle is started byusing the electric heaters to bring the sea waterfeed temperature up to the boiling point and togenerate enough vapor for compressor operation.After the cycle has been started and thecompressor is adequately supplied with vapor,the normal operating cycle begins and the electricheaters are used henceforth only to providethe heat necessary to make up for heat losses.After the unit has become fully operational, then,the heat input from the heaters is only a smallpart of the total heat input.The major part of the heat input comes fromthe compression work that is done on the vaporby the compressor. The major energy transformationsinvolved in normal operation are thusfrom electrical energy (put in at the compressormotor) to mechanical energy (work done bythe compressor on the vapor) to thermal energy.The thermal energy thus supplied is used to boilthe sea water feed and keep the process going.The compression process serves anothervital function in the vapor compression distillingunit. Since the boiling point of sea water is severaldegrees higher than the boiling point of freshwater at any given pressure, the boiling sea waterin the evaporator is actually above 212° F andwould therefore be too hot to condense the freshwater vapor if the vapor were at the same pressureas the boiling sea water. By compressingthe vapor, the boiling pointof the vapor is raisedabove the boiling pointof the sea water at atmosphericpressure. Therefore the compressedvapor can be condensed on the outside of the tubesin which sea water feed is being boiled. Thisprocess would not be possible without the pressuredifference between the evaporating side andthe condensing side of the unit, and this pressuredifference is created by the compression of thevapor.STEAM DISTILLING UNITSSteam distilling plants now in naval use arepractically all of the low pressure type. They are"low pressure" units from two points of view.First, they utilize lowpressure steam (auxiliaryexhaust steam) as the sourceof energy; and second,they operate at less than atmospheric pressure.There are three major types of lowpressure steam distilling units: submerged tubeunits, flash-type units, and vertical basket units.Submerged Tube UnitsSubmerged tube distilling units range from4000 to 50,000 gallons per day in capacity. There456

-Chapter 18. -DISTILLING PLANTSare three kinds of submerged tube distillingunits: (1) the Soloshell double-effect unit,(2)thetwo-shell double-effect unit, and (3) the threeshelltriple-effect unit.The difference between double- effect unitsand triple- effect units is merely in the numberof stages of evaporation. Two stages of evaporationoccur in a double- effect unit, and three in atriple- effect unit.SOLOSHELL DOUBLE-EFFECT UNITS.Most Soloshell double- effect units have capacitiesof 12,000 gallons per day or less. However,some Soloshell units of 20,000 gpd capacity arein use.A Soloshell double- effect unit is shown schematicallyin figure 18-5 and in cutaway view infigure 18-6. The unit consists of a single cylindricalshell which is mounted with the long axisin a horizontal position. A longitudinal verticalpartition plate divides the shell into a first- effectshell and a second- effect shell. The first- effectshell contains the first effect tube bundle, avapor separator, and the vapor feed heater. Thesecond- effect shell contains the second- effecttube bundle, a vapor separator, and the distillingcondenser. A distillate cooler, not a part of themain cylindrical shell, is mounted at any convenientlocation, as piping arrangements permit.Another separate unit, the air ejector condenser,is mounted on brackets on the outside of the evaporatorshell. The air ejector takes suction on thesecond- effect part of the shell, maintaining itunder a vacuum of approximately 26 inches ofmercury. A lesser vacuum— about 16 inches ofmercury— is maintained in the first- effect shell.Steam for the distilling unit is obtained fromthe auxiliary exhaust line through a regulatingvalve. This valve is adjusted to maintain a constantsteam pressure of 1 to 5 psig in the line betweenthe regulating valve and a control orifice.The size of the opening in the control orifice determinesthe amount of steam admitted to thedistilling unit and hence controls the output ofdistilled water.steam pressure is reduced by theWhen theregulating valve, the steam becomes superheated.Since superheat has the undesirable effectof increasing the rate of scale formation,provision is made for desuperheating the steam.This is done by spraying hot water into the steamline between the control orifice and the pointwhere the steam enters the first- effect shell. Thehot water for desuperheating the steam is takenfrom the first- effect drain pump discharge.After being desuperheated, the steam passesinto the first- effect tube nest, where it heats thesea water feed that surrounds the first-effecttubes. The sea water boils, generating steamwhich is called vapor to distinguish it from thesteam which is the external source of energy forthe unit. The condensate that results from thecondensation of the supply steam is dischargedby the first- effect drain pump to the low pressuredrain system or to the condensate system and isthus eventually used again in the boiler feed system.Although the vapor generated in the firsteffectshell is pure water vapor, it does containsmall particles of liquid feed. As the vapor rises,a series of baffles above the surface of the waterbegins the process of separating the vapor andthe water particles.After passing through the baffles, the vaporenters the vapor separator. As the vapor passesaround the hooked edges of the baffles and vanesin the separator, it is forced to change directionseveral times; and with each change of directionsome water particles are separated from thevapor. The hooked edges trap particles of waterand drain them away, discharging them back intothe feed at a distance from the vapor separator.After passing through the first- effect vaporseparator, the vapor goes to the vapor feedheater. Sea water feed passes through the tubesof the vapor feed heater, and part of the vapor iscondensed asitflowsover the tubes of the heater.This distillate, together with the remaining uncondensedvapor, goes through an externalcrossover pipe and enters the tube nest of thesecond- effect shell. The remaining vapor is nowcondensed as it gives up the rest of its latent heatto the sea water feed in the second- effect shell.Since the pressure in the second- effect shellis considerably less than the pressure in thefirst- effect shell, the introduction of the vaporand the distillate from the first- effect shellcauses the sea water feed in the second- effectshell to boil and vaporize.The vapor thus generated in the second- effectshell passes through baffles just above the surfaceof the water and then goes to the secondeffectvapor separator. From the vapor separator,it passes to the distilling condenser. Thecondensing tubes nearest the incoming vapor areutilized as a feed heating section; the vapor condenseson the outside of the tubes and thus heatsthe incoming sea water feed which is circulatingthrough the tubes. The remainder of the vapor is457

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Chapter 18. -DISTILLING PLANTScondensed in the condensing section and is dischargedto the test tanks as distillate.The first- effect distillate which was used inthe second- effect tubes to boil and vaporize thefeed in the second- effect shell is dischargedthrough the second- effect tube nest drain regulatorand is led to the distilling condenser byway of a flash chamber. The flash chamber is essentiallya receptacle within which the vapor, liberatedwhen the second- effect drains are reducedto a pressure and temperature corresponding tothe distilling condenser vacuum, is separatedfrom the condensate and directed to the distillingthecondenser. As may be seen in figure 18-6,flash chamber is located just outside of the second-effect shell.The distilling condenser circulating waterpump takes suction from the sea and dischargesthe sea water through the shell of the distillatecooler (which is external to the unit) and thenthrough the tubes of the distilling condenser.Some of the cooling water is then dischargedoverboard; but a portion (which is now calledevaporator feed) goes through the feed heatingsection of the distilling condenser, through theair ejector condenser, and through thefirst- effect vapor feed heater before it is dischargedto the first- effect shell. These paths ofthe distilling condenser circulating water and theevaporator feed may be traced in figure 18-5.As previously described, some of the seawater feed in the first- effect shell is boiled andvaporized by the supply steam. The remainingportion becomes more dense and has a highersalinity than the original sea water feed; thisdenser, saltier water is called brine to distinguishit from sea water. After a certain amountof sea water feed has been vaporized in the firsteffectshell, the remaining brine is led to thesecond- effect shell through a pipe that has a manuallycontrolled feed regulating valve installedin it. When the feed regulating valve is open, thehigher pressure in the first- effect shell causesthe brine to flow from the first- effect shell to thesecond- effect shell. After the brine has been usedas feed to generate vapor in the second- effectshell, the remaining brine is discharged overboardby the brine overboard discharge pump.FIRST-EFFECTSEPARATORSECOND-EFFECTSEPARATORDISTILLINGCONDENSERVAPOR FEEDHEATERAIR BAFFLESECOND-EFFECTTUBESFIRST-EFFECTTUBESFLASHCHAMBERBRINE PUMPSUCTIONFIRST-EFFECTDRAIN REGULATORDIVISION PLATESECOND-EFFECTDRAIN REGULATORFigure18-6.— Cutaway view of Soloshell double-effect distilling plant.45947.117

PRINCIPLES OF NAVAL ENGINEERINGTWO-SHELLDOUBLE-EFFECT UNITS.-Two-shell double-effect units of 20,000 gpd capacityare used on some ships. A typical unit ofthis kindisshowninfigurel8-7.Asmay be seen,the unit consists of two cylindrical evaporatorshells, mounted horizontally, with the long axesof the shells parallel. The first- effect vapor feedheater is built into the upper part of the firsteffectshell. The distilling condenser and the distillatecooler are built into separate shells, whichare usually mounted between the two evaporatorshells. The air ejector condenser is also a separateunit, though it is mounted on one of theshells.The operation of the two- shell double- effectunit is almost precisely the same as the operationof the Soloshell double- effect unit. The flowpaths of steam, condensate, sea water, brine,vapor, and distillate may be traced out on figure18-7.THREE-SHELL TRIPLE-EFFECT UNITS.-Three- shell triple- effect distilling units aresimilar to the double-effect units previously discussedexcept that the triple- effect units have anintermediate evaporating stage.A triple- effect distilling unit is shown schematicallyin figure 18-8. Although there are severalkinds of triple-effect units, the general relationshipsshown in this illustration hold for anytriple- effect plant.A standard 20,000 gpd triple-effect unit consistsof three horizontal cylindrical shells, setside by side with their axes parallel. The firstandsecond- effect vapor feed heaters are builtinto the front end of the second- and third- effectevaporator shells. The distilling condenser iscontained within the third- effect shell. The airejector condenser and the distillate cooler arein separate shells and are mounted on thethird- effect shell.Another 20,000 gpd triple- effect design consistsessentially of three horizontal shells boltedtogether end to end, with vertical partition platesbetween each shell to separate the effects. Vaporseparators in independent shells are installed inthe vapor piping between effects and between thethird effect and the distilling condenser. Thefirst- and second- effect vapor feed heaters arein separate shells and are mounted in the pipingat the inlet to the second- effect and third- effecttube nests, respectively. The two sections of thedistilling condenser and the distillate cooler arebuilt into a single shell and independentlymounted as space and piping arrangements maypermit. The air ejector condenser is also aseparately mounted unit.A standard 30,000 gpd triple- effect unit isalso in use. This is similar to the standard 20,000gpd unit except that the 30,000 gpd unit is larger.There are two types of 40,000 gpd tripleeffectunits that may be regarded as standard,since both are widely used in naval ships. Thefirst type uses the same arrangement as thestandard 20,000 gpd triple- effect unit but has thelarger components needed for the increased capacity.The second type consists of three horizontalshells, usually mounted side by side, withaxes parallel. In this design, both vapor feedheaters and distilling condensers are builtas three independent units, each mounted separatelyoutside the evaporator shells. The airejector condenser and the distillate cooler arealso in independent shells and are separatelymounted outside the evaporator shells.Triple- effect units operate in virtually thesame way as the Soloshell and the two-shelldouble- effect units previously described, exceptthat the comparable actions in a triple- effect unitare spread out through more equipment andthrough one more effect. In a triple- effect unit,the sea water feed is piped to the first effectshell, then to the second- effect shell, and then tothe third- effect shell. Steam from the auxiliaryexhaust line is used to vaporize the feed in thefirst- effect shell; in the second- effect and thirdeffectshells, the vapor is generated by the heatgiven up by vapor generated in the previous shell.In the triple- effect units, as in the double- effectunits, this sequence of events is possible becausethe vacuum is greatest in the shell of the finaleffect and least in the shell of the first effect.Flash- Type Distilling UnitsSome recent ships are equipped with flashtypedistilling units. Although these units differsomewhat in design from the submerged tubecertain operating principles are commonunits,to both types. In particular, both the flash-typeand the submerged tube type of unit depends uponpressure differentials between the stages (or effects)to generate vapor from the sea water feed.Flash-type units consist of two or morestages. Two- stage units of 12,000 gpd capacityare installed on some recent destroyer typeships. Five-stage units of 50,000 gpd capacity areinstalled on some recent carriers.Each stage of a flash-type unit has a flashchamber, a feed box, a vapor separator, and a460

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C hapter 18. -DISTILLING PLANTSdistilling condenser. A two- stage or three- stageair ejector, a distillate cooler, and a feed waterheater are also provided. Feed water passesthrough the tubes of the distillate cooler, thestage distilling condenser, and the air ejectorcondenser. In each of these heat exchangers thefeed picks up heat. The final heating is done bylow pressure steam admitted to the shell of thefeed water heater. From this heater the feedwater enters the first- stage feed box and comesout through orifices into the flash chamber. Asthe heated feed water enters the chamber, a portionflashes or vaporizes because the pressurein the chamber is lower than the saturation pressurecorresponding to the temperature of the hotfeed. The vapor condenses on the tubes of thefirst- stage distilling condenser. The feed whichdoes not vaporize in the first chamber passes tothe second chamber. The process is repeated ineach stage and the brine remaining in the laststage is removed by the brine overboard pump.Vapor formed in each stage passes through avapor separator and into the stage distilling condenser,where it is condensed into distillate. Thedistillate passes through a loop seal on its wayto the distilling condenser of the next stage. Thedistillate pump removes the distillate from thelast stage and discharges it through the distillatecooler and the solenoid- operated dump valve tothe ship's tanks.The general arrangement of a two- stageflash- type unit is shown in figure 18-9; a fivestageunit is shown in figure 18-10. The majorcircuits are shown in each illustration.Vertical Basket Distilling UnitsSome recent ships are equipped with verticalbasket distillingunits. Aunitof thistypeis shownin figure 18-11. The unit shown has two effects;however, some units of this type have more thantwo effects.The vertical basket unit consists of two ormore evaporators, a distiller condenser, vaporfeed heaters, a distillate cooler, and air ejectors.The major difference between a vertical basketunit and a submerged tube unit is in the designof the evaporators. In the vertical basket unit,each evaporator consists of a vertical shell inwhich a deeply corrugated vertical basket is installed.Figure 18-12 shows a sectional view ofthe evaporator and basket.Low pressure steam is admitted to the insideof the first- effect basket. This steam boils thefeed water in the space between the outside ofthe basket and the shell of the evaporator. Thecondensate resulting from the condensation ofsteam drains downward and is returned to theboiler feed system. The vapor generated fromthe boiling sea water feed passes through thecyclonic separator above the evaporation section,where most of the entrained liquid particlesare removed from the vapor by centrifugal force.The vapor continues on through the second vaporseparator (called the "snail"), where the remainingwater droplets are separated from thevapor. The liquid particles from both of theseseparators drain downward and become part ofthe brine drains.The vapor generated in the first- effect shellpasses from the steam dome of the first- effectshell. It goes through the vapor feed water heaterand then enters the steam chest and evaporatorbasket of the second- effect shell. The first- effectvapor boils the second- effect feed and thuscauses the generation of second- effect vapor.The second- effect vapor goes through the cyclonicseparator and the snail in the secondeffectshell. From the steam dome, this vaporthen goes to the distilling condenser, where thevapor is condensed on the outside of the tubes.The second- effect distillate drains down and collectsin the flash tank.As the first- effect vapor is being used to boilthe second- effect feed, some of the vapor condenses.This distillate drains downward into thesecond- effect steam chest and is discharged tothe flash tank at the bottom of the distilling condenser,where it mixes with the distillate formedfrom the second- effect vapor. The distillate isremoved from the flash tank by the distillatepump and is discharged through the distillatecooler and the solenoid-operated dump valve tothe ship's tanks. Should the salinity of thedistillate exceed 0.065 epm, the dump valve automaticallydumps the distillate to the bilges.Sea water flows through the tubes of the distillatecooler and the distilling condenser, creatinga suction for the brine pump and maintaininga back pressure for the feed system. About ?5percent of the sea water passes through supplementaryheating sections in the distilling condenserto the air ejector condenser, and feedsthe evaporator shells in parallel. As the seawater passes through the air ejector condenser,it condenses the air ejector steam; the resultingcondensate drains to an atmospheric drain tank.463

TO RESERVEFEED SYSTEMINLET SEAWATER VALVEL-^^A^^^'SALT-WATERCIRCULATINGPUMPOVERBOARDSAMPLINGCONNECTION47.131Figure 18-9.— General arrangement of two-stage flash-type distilling plant.464

Chapter 18. -DISTILLING PLANTSREGULATORBYPASS LINESEPARATE SOURCE OFPURE WATER FORDE5UPERHEATER TO BEUSED WHEN STARTINGUP PLANTLEGENDDISTILLER SALT-WATERHEATER DRAIN PUMP

FEED —T§WATER KJFigure18-10.— General arrangement of five-stage flash-type distilling plant

[j]Chapter 18. -DISTILLING PLANTSORIFICE NOZZLESTEAM4500 LBS/HR5 PSICSALT WATER HEATERDRAIN PUMP—^—tSC]IXf\)SALINITY CELLORIFICEGLOBE & ANGLE VALVEGATE VALVECHECK VALVETHERMOMETERFigure 18-10.— General arrangement of five-stage flash-type plant--continued96.30467

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Chapter 18. -DISTILLING PLANTSEQUALIZERSKIRTCORRUGATEDBASKET TYPEHEATING SECTIONEVAPORATORSHELLE'g??^ STEAM SEA WATER47.127Figure 18-12.— Sectional view of evaporatorandbasket in vertical basket distilling plant.DISTILLING PLANT OPERATIONAlthough a detailed discussion of distillingplant operation is beyond the scope of this text,certain operational considerations should benoted. The factors mentioned here apply primarily(although not exclusively) to low pressuresteam distilling units.Naval distilling plants are designed to producedistillate of very high quality. The chloridecontent of distillate discharged to the ship's tanksmust not exceed 0.065 equivalents per million.Any distilling unit which cannot produce distillateof this quality is not considered to be operatingproperly.Steady operating conditions are essential tothe satisfactory operation of a distilling unit.Fluctuations in the pressure and temperature ofthe first- effect generating steam will cause fluctuationsof pressure and temperature throughoutthe entire unit. Such fluctuations may causepriming, with increased salinity of the distillate,and may also cause erratic operation of the feedand brine pump. Rapid fluctuations of pressurein the last effect tend to cause priming.To achieve satisfactory operation of a distillingunit, it is necessary to maintain the designedvacuum in all effects. When the unit is operatedat less than the designed vacuum, the heat levelrises throughout the unit and there is anincreased tendency toward scale formation.Scale fprmation is highly undesirable, sincescale interferes with heat transfer and thusreduces the capacity of the unit. Excessive scaleformation may also impair the quality of the distillate.Various methods have been used to retardscale formation in distilling units. In the past,a common method was the continuous injectionof a solution of Navy boiler compound and cornstarchinto the distilling unit. The boiler compoundtends to minimize the formation of scale,and the cornstarch tends to minimize priming.The boiler compound and cornstarch methodof treatment is not fully effective in preventingscale formation, however, and daily removal ofscale is required when this method is used. Theremoval of scale is accomplished by a procedurecalled chill shocking. For chill shocking, the unitis secured and pumped dry while it is still hot.Then cold sea v/ater is introduced, and the resultingthermal shock causes scale to flake off andfall tothebottomof the tube nest. The unit is thenpumped dry, the loose scale is removed, and theunit is filled with water and started up again.Chill shocking is an effective way of removingscale, but it is somewhat laborious and time- consuming.A particular disadvantage of the chillshocking process is that it requires each operatingdistilling unit to be out of production for anhour or more each day. This can lead to seriouswater shortages under some circumstances.A new chemical compound called HAGEVAPhas been adopted as the standard compound forevaporator feed treatment. This compound hasproved superior to the boiler compound and cornstarchpreviously used, and is now authorizedfor use in submerged tube, vertical basket, andfive-stage flash-type distilling units; it does notappear to be necessary for two- stage flash-typeunits. Where the HAGEVAP treatment is used,chill shocking is not necessary because thereis no scale formation (or practically none). Theuse of this compound requires the installation ofcertain equipment, including special pumps,tanks, and piping; authorization for such installationhas been issued, and the alteration has beenor will soon be made for all classes of shipshaving low pressure steam distilling plants(other than two-stage flash-type units).as itThe concentration of brine (or brine density ,is called) has a direct bearing on the qualityof the distillate. If the brine concentration is toolow, there will be a loss in capacity and economy.469

PRINCIPLES OF NAVAL ENGINEERINGIf the brine concentration is too high, there willbe an increase in the rate of scaling of the evaporatortube surfaces, and the quality of the distillatemay be impaired. The density of the brineoverboard discharge should normally be maintainedjust under 1.5/32, and should never exceedthis figure. Since the average sea water containsabout 1 part of dissolved sea salts to 32 parts ofwater (by weight), the brine density should be justunder 1 1/2 times that of the average sea water.Brine density is measured with a special kind ofhydrometer 4 which is called a salinometer .Salinometers as shown in figure 18-13 are calibratedin thirty- seconds, on four separatescales which indicate the salinity of the brine atfour different temperatures (110° ,115° ,120°,and 125° F),Special restrictions are placed upon the operationof distilling units when the ship is operatingin contaminated waters. Because most distillingplants operate at low pressures (andtherefore low temperatures) the distillate is notsterilized by the boiling process in the evaporatorsand may contain dangerous micro-organismsor other matter harmful to health. Allwater in harbors, rivers, inlets, bays, landlockedwaters, and the open sea within 10 miles ofthe entrance to such waters must be consideredcontaminated unless a specific determination tothe contrary is made. In other areas, contaminationmay be declared to exist by the fleet surgeonor his representatives, as local conditions maywarrant. When the ship is operating in contaminatedwaters, the distilling units must be operatedin strict accordance with special proceduresestablished by the Naval Ship Systems Command.4 Hydrometers are discussed in chapter 7 of this text.Figure 18-13. — Salinometer.47.136X470

CHAPTER 19REFRIGERATION AND AIR CONDITIONING PLANTSRefrigeration equipment is used aboard shipfor a number of purposes, including the refrigerationof ship's stores, the refrigeration ofcargo, the cooling of water, and the conditioningof air for certain spaces. The distinction betweenrefrigeration and air conditioning shouldbe noted. Refrigeration is only a coolingprocess;air conditioning is a process of treating air so asto simultaneously control its temperature, humidity,cleanliness, and distribution to meet therequirements of the conditioned spaces.REFRIGERATIONThe purpose of refrigeration is to coolspaces, objects, or materials and to maintainthem at temperatures below the temperature ofthe surrounding atmosphere. In order to producea refrigeration effect, it is merely necessary toexpose the material to be cooled to a colderobject or environment and allow heat to flow inits "natural" direction— that is, from the warmermaterial to the colder material. For example,a pan of hot water placed on a cake of ice will becooled by the flow of heat from the hot water tothe ice. We can maintain this refrigeration effectas long as the ice lasts. But no matter how muchice we have, we cannot produce a refrigerationeffect any greater than the cooling of the waterto 32° F. We cannot, for example, cause the waterto freeze by this method, since freezing wouldrequire the removal of the latent heat of fusionfrom the water after it had been cooled to 32° F;and for thisprocess we would need a temperaturedifference that does not exist when both the waterand the ice are at 32 F. When the purpose of refrigerationis theproductionof ice or the maintenanceof temperatures lower than 32 F at atmosphericpressure, it is obvious that ice is not asuitable refrigerant.Refrigeration is a process involving the flowof heat, and is therefore a thermodynamicprocess. From previous discussion in this text,we may surmise that a closed cycle^ would bemost practicable for a large-scale refrigerationsystem. When we try to visualize such a cycle,however, it may appear at first glance that thecycle will have to run backwards. Thus far inthis text, we have been primarily concerned witha closed cycle in which thermal energy (in theform of heat) is converted into mechanicalenergy (in the form of work). Now, instead ofwanting to convert heat into work, we want toremove heat from a body and we want to continueto remove heat from this body even afterits temperature has been lowered below that ofits surroundings, in order to maintain the bodyat its lowered temperature. In other words, wewant to extract heat from a cold body and dischargeit to a warm area.The question is: How can this be done, sincewe know from the secondlaw of thermodynamicsthat heat cannot, of itself, flow from a colder bodyor region to a warmer one? It is entirely possibleto extract heat from a body at a low temperatureand discharge it to a body or region ata higher temperature, provided a suitable expenditureof energy is made to accomplish this. Theenergy supplied to the refrigeration cycle forthis purpose is in the form of work (mechanicalenergy) done on the working fluid (refrigerant)Thermodynamic cycles are discussed in chapter 8 ofthis text. A closed cycle is one in which the workingfluid never leaves the system except through accidentalleakage. Instead, the working fluid undergoes a seriesof processes which are of such a nature that the fluidis returned periodically to its initial state and is thenused again.471

PRINCIPLES OF NAVAL ENGINEERINGby a compressor/ In a refrigeration cycle, therefrigerant must alte mate between low tempe raturesand high temperatures. When the refrigerantis at a low temperature, heat flows fromthe space or object to be cooled to the refrigerant.When the refrigerant is at a high temperature,heat flows from the refrigerant to acondenser. The energy supplied as work is usedto raise the temperature of the refrigerant to ahigh enough value so that the refrigerant will beable to reject heat to the condenser. This pointis discussed in more detail later in this chapter,but should be noted now since it is basic to theunderstanding of a mechanical refrigerationcycle.Because the energy transformations in arefrigeration cycle occur in an order that isprecisely the reverse of the sequence in a powercycle, the refrigeration cycle is sometimes saidto be one in which heat is pumped "uphill."This view of a refrigeration cycle is entirelylegitimate, provided the "reverse order" ofenergy transformations does not imply actualthermodynamic reversibility. True thermodynamicreversibility is here, as elsewhere inthe observable world, considered to be an impossibility.A refrigeration cycle does not giveus something for nothing. Instead, we must putenergy into the cycle in order to extract heat ata low temperature and discharge it at a highertemperature.DEFINITION OF TERMSSome of the standard terms used in thediscussion of refrigeration are defined in thissection. A few of these terms have been definedin chapter 8 of this text but are briefly notedhere because of their importance in the study ofrefrigeration.UNIT OF HEAT. -The British thermal unit(Btu) is the standard unit of heat measurementused in refrigeration, as in most other engineeringapplications. By definition, 1 Btu is equal to778.26 foot-pounds.A compressor provides the required energy in avapor-compression refrigeration cycle, which is thecycle most commonly used in naval refrigerationplants. Other kinds of refrigeration cycles use otherforms of energy to accomplish the same purposenamely,to raise the temperature of the refrigerantafter it has absorbed heat from the space or object tobe cooled.SPECIFIC HEAT.-The specific heat of asubstance is the quantity of heat required toraise the temperature of unit mass of the substance1 degree. In British systems of measurement,specific heat is expressed in Btuperpoundper degree Fahrenheit.SENSIBLE HEAT.— Sensible heat is the termused to identify heat that is reflected in a changeof temperature.LATENT HEAT OF VAPORIZATION .-Theheat required to change a liquid to a gas (or, onthe other hand, the heat which must be removedfrom a gas in order to condense it to a liquid)without any change in temperature is called thelatent heat of vaporization.LATENT HEAT OF FUSION .-The heat whichmust be removed from a liquid in order tochange it into a solid (or, on the other hand, theamount of heat which must be added to a solidto change it to a liquid) without any change intemperature is called the latent heat of fusion.REFRIGERATING EFFECT.-Since the heatremoved from an object that is being refrigeratedis absorbed by the refrigerant, the refrigeratingeffect of a refrigeration cycle isdefined as the heat gain per pound of refrigerant.REFRIGERATION TON. -The unit whichmeasures the amount of heat removal and therebyindicates the capacity of a refrigeration systemis known as the refrigeration ton. The refrigerationton is based on the cooling effect of 1 ton(2000 pounds) of ice at 32= F melting in 24 hours.The latent heat of fusion of ice (or water) isapproximately 144 Btu. Therefore, the number ofBtu required to melt one ton of ice is 144 x 2000,or 288,000 Btu. The standard refrigeration ton isdefined as the transfer of 288,000 Btu in 24hours. On an hourly basis, the refrigeration tonis 12,000 Btu per hour (288,000 divided by 24equals 12,000).It should be noted that the refrigeration tonis not necessarily a measure of the ice-makingcapacity of a machine, since the amount of icecan be made depends upon the initial tem-thatperature of the water and other factors.COEFFICIENT OF PERFORMANCE .-Thecoefficient of performance of a refrigerationcycle is essentially comparable to the thermal472

Chapter 19. -REFRIGERATION AND AIR CONDITIONING PLANTSefficiency of a power cycle. The thermal efficiencyof a power cycle is given by the equationthermal efficiency=work outputheat inputSince thermal efficiency is a function of absolutetemperature alone in the Carnot cycle,the equation may also be given asT - T^sthermal efficiency =where Tg is the absolute temperature at the heatsource and Tj- is the absolute temperature at theheat receiver.For the refrigeration cycle, the coefficient ofperformance is given by the equationcoefficient of performancerrefrigerating effectwork inputwhich, as in the power cycle, can be shown to be afunction of absolute temperature alone.THE R-12 PLANTThe refrigeration system most commonlyused in the Navy utilizes R-12 as the refrigerant.3 Chemically, R-12 is dichlorodifluoromethane(CCL2F2). The boiling point of R-12 isso low that the subtance cannot exist as a liquidunless it is confined and put underpressure; forexample, R-12 boils at -21 "F at atmosphericpressure, at 0' F at 9.17 psig, at 50 'F at 46.69psig, and at 100 °F at 116.9 psig. Because of itslow boiling point, R-12 is well suited for use inrefrigeration systems designed for only moderatepressures. It also has the advantage ofbeing practically nontoxic, nonflammable, nonexplosive,and noncorrosive; and it does notpoison or contaminate foods.The R-12 refrigeration system is classifiedas a mechanical system of the vapor-compressiontype. It is a mechanical system becausethe energy input is in the form of mechanicalenergy (work). It is a vapor-compression systembecause compression of the vaporized refrigerantis the process which allows the refrigerantIn accordance with recent policy, refrigerants usedin the Navy are no longer identified by trade names.Instead, they are identified by the letter R followed bythe appropriate number, or else they are identifiedsimply as "refrigerants." For example, the refrigerantformerly known as "Freon 12" is now identifiedeither as R-12 or simply as a refrigerant.to discharge heat at a relatively high temperature.The R-12 CycleThe basic cycle of an R-12 refrigerationcycle is shown shcematically in figure 19-1. Asan introduction to the system, it will be helpfulto trace the refrigerant through the entire cycle,noting especially the points at which the refrigerantchanges from liquid to vapor and fromvapor to liquid, and noting also the concomitantflow of heat in one direction or another.As shown in figure 19-1, the cycle has twopressure sides. The low pressure side extendsfrom the orifice of the thermostatic expansionvalve up to and including the intake side of thecompressor cylinders. The high pressure sideextends from the discharge side of the compressorto the thermostatic expansion valve.The condensing and evaporating pressures andtemperatures indicated in figure 19-1 are notstandard for all refrigeration plants, sincepressuresand temperatures are established as partof the design of any refrigeration system. Itshould be noted, also, that the pressures andtemperatures shown in figure 19-1 are theoreticalrather than actual values, even for thisparticular system. If the system were in actualoperation, the pressures and temperatures wouldvary slightly because they are dependent uponthe temperature of the coolingwater enteringthecondenser, the amount of heat absorbed by therefrigerant in the evaporator, and other factors.Liquid R-12 enters the thermostatic expansionvalve at high pressure, from thehighpressureside of the system. The refrigerant leavesthe outlet of the expansion valve at a much lowerpressure and enters the low pressure side of thesystem. Because of the relatively low pressure,the liquid refrigerant begins to boil and to flashinto vapor.thermostatic expansion valve, theFrom therefrigerant passes into the cooling coil (evaporator).The boiling point of the refrigerant underthe low pressure in the evaporator is extremelylow— much lower than the temperature of thespaces in which the cooling coil is installed.As the liquid boils and vaporizes, it picks up itslatent heat of vaporization from the surroundings,thereby cooling the space. The refrigerantcontinues to absorb heat until all the liquid hasbeen vaporized andthe vapor has become slightlysuperheated. As a rule, the amount of superheatis about 10° F.473

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Chapter 19. -REFRIGERATION AND AIR CONDITIONING PLANTSThe refrigerant leaves the evaporator as alow pressure superheated vapor, having absorbedheat and thus cooled the space. Theremainder of the cycle is concerned withdisposingof this heat and getting the refrigerant backinto a liquid state so that it can again vaporizein the evaporator and thus again absorb heat.The low pressure superheated vapor is drawnout of the evaporator to the suction side of thecompressor. The compressor is the unit whichkeeps the refrigerant circulating through thesystem. In the compressor cylinders, the refrigerantis compressed from a low pressurevapor to a high pressure vapor, and its temperaturerises accordingly.The high pressure R-12 vapor is dischargedfrom the compressor to the condenser. Here therefrigerant condenses, giving up its superheat,its latent heat of vaporization, and its heat ofcompression to the cooling sea water whichflows through the condenser tubes. The refrigerant,still at high pressure, is now a liquidagain.From the condenser, the refrigerant flowsinto a receiver, which serves as a storage placefor the liquid refrigerant. From the receiver,the refrigerant goes to the thermostatic expansionvalve and the cycle begins again.From this brief summary of an R-12 vaporcompressionrefrigeration system, it may beseen that the cycle is indeed one in which heatis "pumped uphill" as a result of the arrangementswhich cause the refrigerant to go throughsuccessive phases of expansion, evaporation,compression, and condensation.Major ComponentsThe major components of a shipboard R-12refrigeration plant are shown diagrammaticallyin figure 19-2. The primary parts of the systemare the thermostatic expansion valve, the evaporator,the compressor, the condenser, and thereceiver. Additional equipment required to completethe plant includes piping, pressure gages,thermometers, various types of control switchesand control valves, strainers, relief valves, sightflow indicators, dehydrators, and charging connections.Figure 19-3 shows most of the componentson the high pressure side of an R-12system, as actually installed aboard ship.In the following discussion of the major componentsof an R-12 system, we will treat thesystem as though it had only one evaporator,one compressor, and one condenser. As may beseen from figure 19-2, however, a shipboardrefrigeration system may (and, indeed, usuallydoes) include more than one evaporator and mayinclude additional compressor and condenserunits to provide operational flexibility and toprotect against loss of refrigerating capacity.THERMOSTATIC EXPANSION VALVE .-Thethermostatic expansion valve, shown in figure19-4, is essentially a reducing valve between thehigh pressure side and the low pressure side ofthe system. The valve is designed to proportionthe rate at which the refrigerant enters the coolingcoil to the rate of evaporation of the liquidrefrigerant in the coil; the amount depends, ofcourse, on the amount of heat being removedfrom the refrigerated space.A thermal bulb for the thermostatic expansionvalve is clamped to the cooling coil, nearthe outlet. The bulb contains R-12. Control tubingconnects the bulb with the area above thediaphragm in the thermostatic expansion valve.When the temperature at the bulb rises, the R-12expands and transmits a pressure to the diaphragm;this causes the diaphragm to be moveddownward, thus opening the valve and allowingmore refrigerant to enter the cooling coil.When the temperature at the bulb falls, thepressure above the diaphragm is decreasedand the valve tends to close. Thus the temperaturenear the evaporator outlet controlsthe operation of the thermostatic expansionvalve.EVAPORATOR.— The evaporator consists ofa coil of copper tubing installed in the space tobe refrigerated. Figure 19-5 shows some of thistubing. The liquid R-12 enters the tubing at avery much reduced pressure and the boilingpoint is therefore very much lowered. In passingthrough the expansion valve, going from thehigh pressure side of the system to the lowpressure side, some of the refrigerant boils andvaporizes because of the reduced pressure andsome of the remaining liquid refrigerant isthereby cooled to its boiling point. Then, as therefrigerant passes through the evaporator, theheat flowing to the evaporator from the surroundingair causes the rest of the liquid refrigerantto boil and vaporize.After the refrigerant has absorbed its latentheat of vaporization and all the liquid has beenvaporized, the refrigerant continues to absorbheat until it has acquired about 10° F of superheat.The amount of superheat is determined bythe amount of liquid refrigerant admitted to the475

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Chapter 19. -REFRIGERATION AND AIR CONDITIONING PLANTSFigure 19-3.— High pressure side of R-12 installation aboard ship.47.92477

PRINCIPLES OF NAVAL ENGINEERINGVALVE STEMPORTDIAPHRAGMSPRINGCHAMBER^OUTLETADJUSTMENTINLETPRESSURE ANDFLOW PATHSFigure 19-4.— Thermostatic expansion valve.168.1evaporator; and this, in turn, is controlled bythe spring adjustment of the thermostatic expansionvalve. About 10°Fof superheat is considereddesirable because it increases the efficiency ofthe plant and because it ensures the evaporationof all liquid, thus preventing liquid carryover intothe compressor.COMPRESSOR.— In a vapor- compression refrigerationsystem, the compressor is the unitthat pumps heat "uphill" from the cold side tothe hot side of the system.The heat absorbed by the refrigerant in theevaporator must be removed before the refrigerantcan again absorb latent heat in the evaporator.The only way in which the vaporizedrefrigerant can be made to give up the latentheat of vaporization that it absorbed in theevaporator is by condensation. In view of therelatively high temperature of the availablecooling medium (sea water), the only way tomake the vapor condense is by first compressingit.The vapor drawn into the compressor is atvery low pressure and very low temperature. Inthe compressor, both the pressure and the temperatureare raised. Since an increase in pressurecauses a proportional rise in temperature,and since the condensation point of a vapor isdetermined by the pressure, raising the pressureof the vaporized refrigerant provides a condensationtemperature high enoughtopermittheuseof sea water as a cooling and condensing medium.In other words, the compressor raises the pressureof the vaporized refrigerant sufficientlyhigh to permit heat transfer and condensationto take place in the condenser.In addition to this primary function, thecompressor also serves to keep the refrigerantcirculating and to maintain the required pressuredifferential between the high pressure side andthe low pressure side of the system.Many different types of compressors are usedin refrigeration systems. Figure 19-6 shows amotor-driven, single-acting, two-cylinder reciprocatingcompressor of a type commonly usedin naval shipboard refrigeration plants.CONDENSER.— The compressor dischargesthe high pressure, high temperature refrigerantvapor to the condenser, where it flows a round thetubes through which sea water is being pumped.As the vapor gives up its superheat to the circulatingsea water, the temperature of the vapordrops to the condensation point. As soon as thetemperature of the vapor drops to its condensingpoint at the existing pressure, the vapor condensesand in the process gives up the latentheat of vaporization that it picked up in theevaporator. The refrigerant, now in liquid form.478

Chapter 19. -REFRIGERATION AND AIR CONDITIONING PLANTSFigure 19-5.— Evaporator tubing.47.93is subcooled slightly below its boiling point atthis pressure to ensure that it will not flashinto vapor.A water-cooled condenser for an R-12 refrigerationsystem is shown in figure 19-7.Circulating water is obtained through a branchconnection from the firemain or by means of anindividual pump taking suction from the sea.A water regulating valve (not shown) is usuallyinstalled to control the flow of cooling waterthrough the condenser. The purge connectionshown in figure 19-6 is on the refrigerant side;it is used to remove air and other noncondensablegases that are lighter than the R-12 vapor.Most condensers used in naval refrigerationplants are water cooled. However, some smallunits have air-cooled condensers. These consistof tubing with external fins to increase the heattransfer surface. Most air-cooled condensershave fans to ensure positive circulation of airaround the condenser tubes.RECEIVER.— The receiver,shown in figure19-8, acts as a temporary storage space andsurge tank for the liquid refrigerant which flowsfrom the condenser. The receiver also servesas a vapor seal to prevent the entrance of vaporinto the liquid line to the thermostatic expansionvalve.ACCESSORIES AND CONTROLS .-In additionto the five major components just described, arefrigeration system requires a number of controlsand accessories. The most important ofthese are discussed briefly in the followingparagraphs.A dehydrator (or dryer ) is placed in theliquid refrigerant line between the receiverand the thermostatic expansion valve. In olderinstallations, such as the one shown in figure19-2, bypass valves allow the dehydrator to becut in or out of the system. In newer installations,the dehydrator is installed in the liquidrefrigerant line without any bypass arrangement.A refrigerant dehydrator is shown infigure 19-9.A solenoid valve is installed in the liquidline leading to each evaporator, Figure 19-10shows a solenoid valve and the thermostaticcontrol switch that operates it. The thermo-static control switch is connected by long flexiblecapillary tubing to a thermal bulb whichis located in the refrigerated space. Whenthe temperature in the refrigerated space dropsto the desired point, the thermal bulb causesthe thermostatic control switch to open, therebyclosing the solenoid valve and shutting off allflow of liquid refrigerant to the thermostaticexpansion valve. When the temperature in therefrigerated space rises above the desired point,the thermostatic control switch closes, thesolenoid valve opens, and liquid refrigerantonce again flows to the thermostatic expansionvalve.The solenoid valve and its related thermostaticcontrol switch serve to maintain theproper temperature in the refrigerated space.However, we may wonder why the solenoidvalve is necessary, since the thermostaticexpansion valve controls the amount of refrigerantadmitted to the evaporator. Actually, thesolenoid valve is not necessary in systemshaving only one evaporator. In systems havingmore than one evaporator, where there is widevariation in load, the solenoid valve providesthe additional control required to prevent spacesfrom becoming too cold at light loads.In addition to the solenoid valve installedin the line to each evaporator, a large refrigerationplant usually has a main liquid linesolenoid valve installed just after the receiver.If the compressor stops for any reason exceptnormal suction pressure control, the main liquidline solenoid valve closes and prevents liquidrefrigerant from flooding the evaporator andflowing to the compressor suction. Great damageto the compressor can result if liquid isallowed to enter the compressor suction.Whenever several refrigerated spaces ofvarying temperatures are to be maintainedby one compressor, an evaporator pressure479

•PRINCIPLES OF NAVAL ENGINEERINGVALVE CAGEDISCHARGEVALVEDISKSUCTIONVALVEDISKFigure 19-6.— Reciprocating compressor for R-12 refrigeration plant.47.94regulating valve is installed at the outlet ofeach evaporator except the evaporator in thespace in which the lowest temperature is to bemaintained. The evaporator pressure regulatingvalve is set to keep the pressure in the coilfrom falling below the pressure correspondingto the lowest temperature desired in that space.The low pressure cutout switch is the controlthat causes the compressor to go on oroff as required for the normal operation of therefrigeration plant. This switch is located onthe suction side of the compressor and isactuated by pressure changes in the suctionline. When the solenoid valves in the lines tothe various evaporators are closed, so thatthe flow of refrigerant to the evaporators isstopped, the pressure of the vapor in the compressorsuction line drops quickly. When thesuction pressure has dropped to the desiredpressure, the low pressure cutout switch causesthe compressor motor to stop. When the temperaturein the refrigerated space has risenenough to operate one or more of the solenoidvalves, refrigerant is again admitted to thecooling coils and the compressor suction pressurebuilds up again. At the desired pressure.480

Chapter 19. -REFRIGERATION AND AIR CONDITIONING PLANTSVAPORREFRIGERANTNLETOUTLETINLETFigure 19-7.— Water-cooled condenser for R-12 refrigeration system. A. Cutawayview.B. Water-flow diagram. C. Arrangement of head joints. D. Position of zincs.47.95the low pressure cutout switch closes, startingthe compressor again and repeating the cycle.A high pressure cutout switch is connectedto the compressor discharge line to protect thehigh side of the system against excessive pressures.This switch is very similar to the lowpressure cutout switch; however, the low pressurecutout switch is designed to close whenthe suction pressure reaches its upper normallimit, whereas the high pressure cutout switchis designed to open when the discharge pressureis too high. The high pressure cutoutswitch is normally set to stop the compressorwhen thepressure reaches 160 psi and to startit again when the pressure drops to 140 psi. Aspreviously noted, the low pressure cutout switchis the com.pressor control for normal operationof the plant; the high pressure cutout switch, onthe other hand, is a safety device only and doesnot have control of compressor operation undernormal conditions.A spring-loaded relief valve is installed inthe compressor discharge line as an additionalprecaution against excessive pressures. Therelief valve is set to open at about 225 psi;therefore, it functions only in case of failure or481

PRINCIPLES OF NAVAL ENGINEERINGCHARGINGCONNECTIONDRAIN -TOFROMEXPANSIONVALVECONDENSERFigure 19-8.— Receiver for R-12refrigeration system.47.96improper setting of the high pressure cutoutswitch. If the relief valve opens, it dischargeshigh pressure vapor to the suction side of thecompressor.A water regulating valve, as shown in figure19-11, is usually installed to control the quantityof circulating water flowing to the refrigerantcondenser. The valve is located either at theinlet to the condenser or at the outlet from thecondenser. The valve is actuated by the refrigerantpressure in the compressor discharge line;this pressure acts upon a diaphragm or a bellowsarrangement which transmits motion to thevalve stem. As the temperature of the circulatingwater increases, the temperature of therefrigerant vapor increases; this causes thepressure of the refrigerant to increase, andthereby raises the condensation point . When thisoccurs, the increased pressure of the refrigerantcauses the water regulating valve to openwider, thus automatically permitting more circulatingwater to flow through the condenser.When the condenser is cooler than necessary,the water regulating valve allows less water toflow through the condenser. Thus the flow ofcooling water through the condenser is automaticallymaintained at the rate actually requiredto condense the refrigerant under varyingconditions of load and temperature.A water failure switch is provided to stopthe compressor in the event of failure of thecirculating water supply. This is a pressureactuatedswitch, generally similar to the lowpressure cutout switch and the high pressurecutout switch previously described. If the waterfailure switch should fail to function, the refrigerantpressure in the condenser wouldquickly build up to the point where the highpressure cutout switch would function.Because of the solvent action of R-12, anyparticles of grit, scale, dirt, and metal thatthe system may contain are very readily circulatedthrough the refrigerant lines. To avoiddamage to the compressor from such foreignmatter, a strainer is installed in the compressorsuction connection. In addition, a liquid straineris installed in the liquid line leading to eachevaporator; these strainers serve to protectthe solenoid valves and the thermostatic expansionvalves.A number of pressure gages and thermometersare used In refrigeration systems. Acompound refrigerant gage is shown in figure9-12. The temperature markings on this gageshow the boiling point (or condensing point) ofthe refrigerant at each pressure; the gage cannotmeasure temperature directly. The darkpointer (which is actually red in color) is astationary pointer that can be set manually toindicate the maximum working pressure. Otherpressure gages and thermometers include awater pressure gage, installed in the circulatingwater line to the condenser, and standard thermometersof appropriate range, installed in therefrigerant lines.Refrigerant piping is normally made ofcopper. Copper is particularly good for thispurpose because it does not become corrodedby the refrigerant, the internal surface is smoothenough to minimize friction, and the tubing iseasily shaped to meet installation requirements.AIR CONDITIONINGAir conditioning is a field that deals withthe design, construction, and operation of equipmentused in establishing and maintaining desirableindoor air conditions. It is the scienceof maintaining the atmosphere of an enclosureat any required temperature, humidity, and purity.As such, air conditioning involves thecooling, heating, dehumidifying, ventilating, andpurifying of air.Aboard ship, air conditioning serves to keepthe ship's crew comfortable, alert, and physicallyfit. The temperature, humidity, cleanliness,quantity, and distribution of the conditionedair supply is a matter of vital concern.482

Chapter 19. -REFRIGERATION AND AIR CONDITIONING PLANTSCOVER PLATECARTRIDGEFITTINGSEAL PLUGDEHYDRANTSHELLDISPERSIONTUBEENDCAPFigure 19-9.— Refrigerant Dehydrator.47.97The comfort and efficiency of the crew isnot the only immediate reason for shipboardair conditioning. Mechanical cooling, heating,or ventilating must be provided for a numberof spaces for a variety of reasons. Ammunitionspaces must be kept below a certain temperaturein order to prevent deterioration of theammunition; gas storage spaces must be keptcool in order to prevent the buildup of excessivepressures in containers; electrical andelectronic equipment must be maintained atcertain temperatures, with controlled humidity,in air that is relatively free of dust and dirt.PRINCIPLES OF AIR CONDITIONINGTo achieve the objectives of air conditioning,it is necessary to take account of a numberof factors. The principal factors that areimportant in connection with air conditioningare discussed in the following sections.HUMIDITY.— The vapor content of the atmosphereis referred to as humidity. Excessivehumidity and too little humidity both lead todiscomfort and impaired efficiency; hence themeasurement and control of the moisture contentof the air is an important phase of airconditioning.The air holds varying amounts of watervapor, depending upon the temperature of theair; the higher the temperature, the greaterthe amount of moisture the air can hold. Forevery temperature there is a definite limit asto the amount of moisture the air is capable ofholding. When air attains the maximum amountof moisture which it can hold at a specifiedtemperature, the air is said to be saturated.483

PRINCIPLES OF NAVAL ENGINEERINGMAGNETIC COIBREAKAWAY PINVALVE STEMPLUNGERVALVE SEATPISTONINLET^OUTLETELECTRICALCONNECTIONSMAGNETBELLOWSCONNECTORROD—SPRINGCAPTOTHERMO-BULBSPRINGFigure 19-10.— Solenoid valve (top) and thermostatic control switch (bottom).47.98The saturation point is usually called thedew point. If the temperature of saturated airfalls below its dew point, some of the watervapor in the air must condense into water. Thedew that is visible in early morning after adrop in temperature is the result of such condensation.The sweating of cold water pipes isthe result of water vapor from the air condensingon the cold surfaces of the pipes.The amount of water vapor in the air is expressedin terms of the weight of the watervapor. This weight is usually given in grains(7000 grains : 1 pound). Absolute humidity isthe weight of water vapor (in grains) per cubic484

Chapter 19. -REFRIGERATION AND AIR CONDITIONING PLANTS168.4XFigure 19- 11.-Water regulating valve (crosssection.)PRESSUREINDICATED INBUCKTEMPERATURE INDICATEDIN REDfoot of air. Specific humidity is the weight ofwater vapor (in grains) per pound of air. Itshould be noted that the weight refers only tothe weight of the moisture which is present inthe vapor state; it does not include moisturethat may be present in the liquid state.Relative humidity is the ratio of the weightof water vapor in a sample of air to the weightof water vapor which that same sample of airwould hold if saturated at the existing temperature.This ratio is usually stated as apercentage. For example, when air is fully saturated,its relative humidity is 100 percent.When air contains no moisture at all, its relativehumidity is zero percent. When air is halfsaturated— that is, holding half as much moistureas it is capable of holding at the existingtemperature— its relative humidity is 50 percent.Relative humidity, rather than absolute humidityor specific humidity, is the factor thataffects comfort. This is true because it is therelative humidity that affects evaporation. Moisturetends to travel from regions of greaterwetness to regions of lesser wetness. If the airabove a liquid is saturated, the liquid and thevapor are in equilibrium contact and no furtherevaporation can take place. If the air above theliquid is only partly saturated, some evaporationcan take place.A specific example may illustrate the differencebetween absolute or specific humidity andrelative humidity. If the specific humidity ofthe air is 120 grains per pound and the temperatureof the air is 76' F, the relative humidityis nearly 90 percent— that is, the air is nearlysaturated. With a relative humidity of 90 percent,the body may perspire freely but theperspiration does not evaporate rapidly; hencethere is a general feeling of discomfort.If the temperature of the air is 86° F, however,with the specific humidity remainingconstant at 120 grains per pound, the relativehumidity is only 64 percent. Although theamount of moisture in the air is the same asbefore, the relatively humidity is lower becauseat 86 °F the air is capable of holding more watervapor than it can hold at 76° F. The body cantherefore evaporate excess moisture and thegeneral feeling of comfort is much greater eventhough the temperature is 10 degrees higher.Figure47.10219-12.— Compound R-12 pressure gage.TEMPERATURE. -When testing the effectivenessof air conditioning equipment and whenchecking the humidity of spaces, two different485

PRINCIPLES OF NAVAL ENGINEERINGtemperatures are usually considered. These arethe dry-bulb temperature and the wet-bulb temperature.The dry-bulb temperature is the temperatureof the air as measured by an ordinary dry-bulbthermometer. The dry-bulb temperature reflectsthe sensible heat of the air.The wet-bulb temperature is the temperatureof the air as measured by a wet-bulb thermometer.A wet-bulb thermometer is an ordinarythermometer with a loosely woven cloth sleeveor wick placed around the bulb and then wetwith water. The water in the sleeve or wick ismade to evaporate by a current of air at highvelocity. The evaporation lowers the temperatureof the wet-bulb thermometer. The differencebetween the dry-bulb temperature and thewet-bulb temperature is called the wet-bulbdepression . When the air is saturated, so thatevaporation cannot take place, the dry-bulbtemperature is the same as the wet-bulb temperature;the condition of saturation is unusual,however, and a wet-bulb depression is normallyto be expected.The wet-bulb thermometer and the dry-bulbthermometer are usually mounted side by sideon a frame. A handle or a short chain is attachedto the frame so that the thermometers may bewhirled in the air, thus providing an air currentof high velocity to facilitate evaporation. Such adevice is known as a sling psychrometer. (Seefig. 19-13.) Motorized psychrometeTi areprovided with a small motor-driven fan and drycell batteries. Motorized psychrometers aregradually replacing the sling psychrometers.An exposed view of a hand electric psychrometeris shown in figure 19-14. With either type ofpsychrometer, the wet-bulb temperature mustbe observed at intervals as the water is beingevaporated. The point at which there is no furtherdrop in temperature on the wet-bulb thermometeris the wet-bulb temperature of thespace.As may be inferred from this discussion,the wet-bulb depression is an indication thatlatent heat of vaporization has been used tovaporize the water in the sleeve or wick aroundthe wet-bulb thermometer.When the air contains some moisture but isnot saturated, the dew-point temperature islower than the dry-bulb temperature and thewet-bulb temperature is between the dew-pointand the dry-bulb temperatures. As the amountof moisture in the air increases, the differencebetween the dry-bulb temperature and the wetbulbtemperature becomes less and less. Whenthe air is saturated, the dew-point temperature,the dry-bulb temperature, and the wet-bulbtemperature are identical.AIR MOTION.— In perfectly still air,a layerof air adjacent to the body absorbs the sensibleheat given off by the body and increases in temperature.This layer of air also takes up theGRIPFigure 19-13.— A standard sling psychrometer,5.65486

Chapter 19. -REFRIGERATION AND AIR CONDITIONING PLANTSas a higher or lower temperature in conjunctionwith compensating relative humidity and airmotion.The term used to identify the net effect ofthese three factors is effective temperature.The effective temperature cannot be measuredwith any instrument, but can be found on aspecial psychrometric chart when the dry-bulbtemperature, the wet-bulb temperature, andthe air velocity are known.Although all of the combinations of temperature,relative humidity, and air motion ofa particular effective temperature may producethe same feeling of warmth or coolness, theyare not all equally comfortable or healthful.For best health and comfort, a relative humidityof 40 to 50 percent in cold weather and 50 to60 percent in warm weather is desirable. Anoverall range of 30 to 70 percent is acceptable.1.

iPRINCIPLES OF NAVAL ENGINEERINGTHERMOSTATIC SWITCH L.P. R'12 LIQUID-Figure 19-15.— Refrigerant circulating type of mechanical cooling system.47.109ducts leading to the spaces to be cooled. Therefrigerant used in this system is usually R-12.Chilled Water Circulating SystemsTwo types of chilled water circulating systemsare used for mechanical cooling aboardship. Both systems utilize chilled water as thesecondary refrigerant, but one type uses R-12as the primary refrigerant and the other usesR-11. R-12 systems use reciprocating compressors;R-11 systems use centrifugal compressors.488

IChapter 19. -REFRIGERATION AND AIR CONDITIONING PLANTSBoth types of chilled water circulating systemsoperate on the same general principle.The secondary refrigerant (chilled water) iscirculated to the various cooling coils. Heatfrom the spaces being cooled is absorbed bythe chilled water and is removed from thewater by the primary refrigerant in a waterchiller.Figure 19-16 illustrates the flow of primaryrefrigerant, secondary refrigerant, and condenserwater in an R-11 chilled water circulatingsystem which has a single-stage centrifugalcompressor. The primary refrigerant vaporgoes from the evaporator to the compressor,where it is compressed. It is then dischargedto the condenser. In the condenser, the primaryrefrigerant vapor condenses, giving up itssuperheat, its latent heat of vaporization, andits heat of compression to the cooling waterthat flows through the condenser tubes. Theliquid primary refrigerant then passes througha high pressure float valve to the cooler.The secondary refrigerant picks up heat inthe coils of the air conditioned space and carriesthis heat to the cooler. The function of thecooler is to transfer the heat from the secondaryrefrigerant to the primary refrigerant whichsurrounds the tubes of the cooler. As this heatis transferred, the liquid primary refrigerantabsorbs its latent heat of vaporization, boils,and vaporizes. The quantity of liquid refrigerantthus evaporated varies directly with theamount of heat picked up by the secondaryrefrigerant. The vaporized primary refrigerantgoes to the compressor, and the same sequenceof events is repeated in a cyclical manner.Figure 19-17 illustrates an R-11 chilledwater circulating system with a two-state centrifugalcompressor. The refrigerant vaporcoming from the cooler goes into an openingaround the hub of the first wheel of the centrifugalcompressor. The blades in the rapidlyrotating wheel impart velocity to the vapor. Thevapor is then directed to the hub of the second-AIR CONDITIONING SYSTEMCOOLING COILSS REFRIGERANTSECONDARY REFRIGERANTCONDENSER WATERCOMPRESSOR(WFigure 19-16.— Flow diagram, chilled water circulating system withsingle-stage centrifugal compressor.147.120489

iPRINCIPLES OF NAVAL ENGINEERINGCONDENSERWATER INCONDENSERWATER OUT•FLOATFLOAT35°T0 45°F47.110Figure 19-17.— Chilled water circulating system with two-stage centrifugal compressor.wheel, where it is compressed and dischargedto the condenser.Between the condenser and the cooler, theliquid refrigerant passes through an economizer.A float in the upper chamber of the economizerallo\

Chapter 19. -REFRIGERATION AND AIR CONDITIONING PLANTSVentilation is accomplished chiefly by meansof fans which supply and exhaust through ventilationduct systems. Most fans used in ductsystems are of the axial-flow type, but somecentrifugal fans are used. Bracket fans are usedto provide local circulation in certain spaces.Portable fans are used for such purposes astemporary ventilation of compartments afterpainting, exhausting toxic gases from closedspaces and tanks, and cooling hot areas aroundmachinery while repairs are being made.SAFETY PRECAUTIONSRefrigerants are furnished in cylinders foruse in shipboard refrigeration and air conditioningsystems. The following precautions must beobserved by personnel handling, using, and storingthese cylinders:1. Never drop cylinders nor permit them tostrike each other violently.2. Never use a lifting magnet or a sling(rope or chain) when handling cylinders. A cranemay be used if a safe cradle or platform isprovided to hold the cylinders.3. Caps provided for valve protection mustbe kept on cylinders except when the cylindersare being used.4. Whenever refrigerant is discharged froma cylinder, the cylinder should be weighedimmediately and the weight of the refrigerantremaining in the cylinder should be recorded.5. Never attempt to mix gases in a cylinder.6. NEVER put the wrong refrigerant into arefrigeration system! No refrigerant except theone for which the system was designed shouldever be introduced into the system. In somecases, putting the wrong refrigerant into a systemmay cause a violent explosion.7. When a cylinder has been emptied, closethe cylinder valve immediately to prevent theentrance of air, moisture, or dirt. Also, be sureto replace the valve protection cap.8. Never use cylinders for any purpose otherthan their intended purpose. DO NOT use themas rollers, supports, etc.9. DO NOT tamper with the safety devicesin the valves or cylinders.10. Open cylinder valves slowly. Never usewrenches or other tools except those providedby the manufacturer.11. Make sure that the threads on regulatorsor other connections are the same as those onthe cylinder valve outlets. Never force connectionsthat do not fit.12. Regulators and pressure gages providedfor use with a particular gas mustNOT be used on cylinders containing othergases.13. Never attempt to repair or alter cylindersor valves.14. Never fill R-12 cylinders beyond 80percent of capacity.15. Whenever possible, store cylinders in acool, dry place, in an upright position. If thecylinders are exposed to excessive heat, adangerous increase in pressure will occur. Ifcylinders must be stored in the open, take carethat they are protected against extremes ofweather. NEVER allow a cylinder to be subjectedto a temperature above 125° F.16. NEVER allow R-12 to come in contactwith a flame or red-hot metal! When exposedto excessively high temperatures, R-12 breaksdown into PHOSGENE gas, an extremely poisonoussubstance. Because R-12 is such apowerfulfreezing agent that even a very small amountcan freeze the delicate tissues of the eyes,causing permanent damage; it is essential thatgoggles be worn by all personnel who may beexposed to a refrigerant, particularly in itsliquid form. If refrigerant does get in the eyes,the person suffering the injury should receivemedical treatment immediately in order to avoidpermanent damage to the eyes. In the meantime,put drops of clean olive oil, mineral oil, orother nonirritating oil in the eyes, and makesure that the person does not rub his eyes.CAUTION: Do not use anything except clean,nonirritating oil for this type of eye injury.(NOTE: If large leaks are indicated, the soapmethod should be used to detect leaks; forminute leaks, the halide torch should be employed.)If R-12 comes in contact with the skin, itmay cause frostbite. This injury should betreated as any other case of frostbite. Immersethe affected part in a warm bath for about 10minutes, then dry carefully. DO NOT rub ormassage the affected area.R-12 is considered a fluid of low toxicity.However, in closed spaces, high concentrationsdisplace the oxygen in the air and thus do notsustain life. If a person should be overcomeby R-12 remove him IMMEDIATELY to a wellventilatedplace and get medical attention at theearliest opportunity. Watch his breathing. Ifthe person is not breathing, give artificialrespiration.491

CHAPTER 20SHIPBOARD ELECTRICAL SYSTEMSShipboard electrical systems include a greatvariety of equipment which provides numerousservices indispensable to the operation of amodern naval ship. These systems distributepower throughout the ship for offensive and defensiveweapons, the ship's movement, and shipboardhabitability. Since the systems and equipmentutilizing electric power are often underthe cognizance of a division other than theelectrical division, a joint responsibility frequentlyexists for the operation, maintenance,and repair of electrical systems and equipment.This chapter provides some information onbasic electrical theory and gives a brief descriptionof shipboard electrical systems andequipment.BASIC ELECTRICAL THEORYThe word electric is derived from the Greekword meaning amber. The ancient Greeks usedthe word to describe the strong forces of attractionand repulsion that were exhibited by amberafter it had been rubbed with a cloth. Sincescientists are still unable to define electricityclearly, and since many of the phenomena whichoccur cannot be completely explained, theoriescan only be postulated from the reactions observed.Through research and experiment, scientistshave observed and described many predictablecharacteristics of electricity and have postulatedcertain rules which are often called "laws."These laws of electricity, together with theelectron theory, are the basis for our presentconcepts of electricity.ELECTRON THEORYEvery atom is primarily an electrical systemwith high speed planetary electrons orbitingaround its nucleus. The electron, whose negativecharge forms a natural unit of electricity, isbound to the atom by the positive charge withinthe nucleus.The electrons in the outer orbits of certainelements are easily separated from the positivenuclei of their parent atoms. Should an outsideforce be applied, one of these loosely boundelectrons will be released from the parentatom, thus becoming a free electron, and travelto another atom. It is on this ability of an electronto move about from one atom to anotherthat the electron theory is based.Elements such as silver, copper, gold, andaluminum have many loosely bound electronsand are considered to be good conductors ofelectricity. In materials used as insulators,electron flow from one atom to another isrelatively non-existent, since the planetary electronsin the outer orbital shells are more tightlybound to their parent nuclei.Ordinarily an atom is most likely to be inthat state in which the internal energy is at aminimum, having a neutral electrical charge.However, if an atom absorbs sufficient energyfrom am. outside source, loosely bound electronsin the outer orbital shells will leave the atom.An atom that has lost or gained one or moreelectrons is said to be ionized . If an atom loseselectrons it becomes positively charged and isreferred to as a positive ion ; if an atom gainselectrons it is referred to as a negative ion andis said to have a negative charge. Apositive ionwill attract any free electron in its surroundingsin order to reach a neutral state.STATIC ELECTRICITYWhen two bodies have unlike charges, onepositive and the other negative, an electricalforce is exerted between the two. This force iscalled a static charge or an electrostatic force .A static charge can easily be produced bythe force of friction when two materials are492

Chapter 20. -SHIPBOARD ELECTRICAL SYSTEMSrubbed together. If the materials used are bothgood conductors, it is difficult to obtain a detectablecharge because equalizing currents willflow easily in and between the conducting materials.However, if the materials used are poorconductors (insulators), little equalizing currentcan flow and an electrostatic charge is built up.Charged BodiesOne of the fundamental laws of electricityis that like charges repel each other and unlikecharges attract each other . A positive chargeand a negative charge, being unlike, tend tomove toward each other; thus in the atom thenegative electrons are held in their orbitalshells by the positive attraction of the nucleus.The law of charged bodies may be demonstratedby a simple experiment using two pith(paper pulp) balls suspended near one anotherby threads, as shown in figure 20-1, and a hardrubber rod. If the hard rubber rod is rubbed togive it a negative charge and then held againstthe right-hand ball in part (A), the rod will imparta negative charge to the ball. The righthandball will be charged negatively with respectto the left-hand ball, and when released the twoballs will be drawn together. When the two ballstouch, they will remain in contact with eachother until the left-hand ball acquires a portionof the negative charge, at which time they willswing apart as shown in part (C) of figure 20-1.Should positive charges be placed on both balls,as shown in part (B) of figure 20-1, the ballswould also repel each other.Coulomb's Law of ChargesThe amount of attracting or repelling forcewhich acts between two electrically chargedbodies in free space depends upon the magnitudeof their charges and the distance between them.This relationship between charged bodies wasfirst discovered by a French scientist namedCoulomb. Coulomb's law of charges states thatcharged bodies attract or repel each other witha force that is directly proportional to theproduct of their charges and inversely proportionalto the square of the distance betweenthem .The practical unit of charge a body has isexpressed in coulombs . One coulomb is thecharge carried by approximately 6 x lO^^ electrons.147.121Figure 20-1.— Reaction between charged bodies.Electric Current FlowA difference of potential exists between twobodies having opposite electrostatic charges. Ifa path is provided between the two bodies, electronswill flow from the negatively charged bodyto the positively charged body until the chargeshave equalized and the difference of potentialno longer exists. This movement of electronsis called electric current . The rate of flow ismeasured in amperes . One ampere may be definedas the flow of one coulomb per secondpast a fixed point in a conductor.The force or difference in potential whichcauses electrons to flow from one charged bodyto another is called electromotive force (emf).Electromotive force is measured in volts . Onevolt may be defined as the potential differencebetween two points when one joule of work isrequired to move a one-coulomb charge betweenthese points.MAGNETISMThe relationship between magnetism andelectricity was first shown in 1819 when theDanish scientist Oersted observed that a smallcompass needle was deflected when it was passednear a wire carrying a current. About 12 yearslater, Michael Faraday discovered that moving aconductor in a magnetic field would produce anelectric current.493

PRINCIPLES OF NAVAL ENGINEERINGMagnets may be found in the natural statein the form of an iron oxide, but the majorityare produced by artificial means. Artificialmagnets may be either permanent magnets ortemporary magnets, depending upon their abilityto retain magnetic strength after the magnetizingforce has been removed.Permanent magnets are bars of hardenedsteel or other alloy which have been permanentlymagnetized. Permanent magnets are usedextensively in electrical instruments, meters,telephone receivers, and magnetos.Electromagnets are temporary magnetscomposed of soft- iron cores around which arewound coils of insulated wire. Electromagnetsare used in electric motors, generators, andtransformers. When an electric current flowsthrough the coil, the core becomes magnetized.Magnetism is a field of force exerted inspace. A magnetic field consisting of imaginarylines along which the magnetic force acts surroundseach magnet. A visual representation ofa magnetic field can be obtained by placing aplate of glass over a magnet and sprinkling ironfilings onto the glass. The filings arrange themselvesin a pattern of definite paths between thepoles, along the magnetic lines of force, asshown in figure 20-2.41.4Figure 20-2.— Magnetic field pattern around amagnet.Magnetic flux is the entire quantity of linesin a magnetic field, with gauss being the unitmeasurement of its density. One gauss is equalto one line of force per square centimeter ofmagnetic field.PRODUCING A VOLTAGEThere are six commonly used methods ofproducing a voltage. Magnetism and chemicalaction are the two methods most commonly usedaboard ship; hence the present discussion islimited to these two methods. It should be noted,however, that a voltage can also be produced byfriction, pressure, light,Voltage Produced ByChemical Actionand heat.^Chemical energy is transformed into electricalenergy within the cells of a battery. Shipboarduses of electricity from this sourceInclude power supply for emergency lighting(with dry cell batteries) and the starting of smallengines (with wet cell batteries).The most common dry cell battery consistsof a cylindrical zinc container, a carbon electrode,and an electrolyte of ammonium chlorideand water in paste form. The zinc container isthe negative electrode of the cell; it is lined witha nonconducting material to insulate it from theelectrolyte. When a circuit is formed, the currentflows from the negative zinc electrode tothe positive carbon electrode.In a common wet cell storage battery, theelectrodes and the electroljrte are altered bythe chemical action that takes place when thecell delivers current. Such a battery may berestored to its original condition by forcing anelectric current through it in the opposite directionto that of discharge.The most common wet cell storage batteryin use is the lead-acid battery having an emf of2,2 volts per cell. In the fully charged state, thepositive plates are pure lead peroxide and thenegative plates are pure lead immersed in adilute sulfuric acid electrolyte.When a circuit is formed, the chemical actionbetween the ionized electrolyte and dissimilarmetal plates converts chemical energy to electricalenergy. As the storage battery discharges,the sulfuric acid is depleted by being graduallyconverted to water, while both positive andnegative plates are converted to lead sulfate.This chemical reaction is represented by thefollowing equation, the reversibility of which isdependent upon electrical energy being addedduring the charging cycle.One device for producing a voltage by heat is thethermocouple, discussed in chapter 7 of this text.494

Chapter 20. -SHIPBOARD ELECTRICAL SYSTEMSPb + PbOg + 2H2SODISCHARGING_2PbSO^ + 2H2OCHARGINGThe capacity of a battery is measured inampere-hours . The capacity is equal to theproduct of the current (in amperes) and thetime (in hours) during which the battery is supplyingthis current to a given load. The capacitydepends upon many factors, the most importantof which are (1) the area of the plates in contactwith the electrolyte, (2) the quantity and specificgravity of the electrolyte, (3) the general conditionof the battery, and (4) the final limitingvoltage.Voltage Produced by MagnetismCONDUCTOR MOVEDDOWNCONDUCTORMOTIONCONDUCTOR MOVEDUPOne of the most useful and widely employedapplications of magnets is in the production ofvast quantities of electric power from mechanicalsources. The mechanical power may be providedby a number of different devices, includinggasoline engines, diesel engines, water turbines,steam turbines, and gas turbines. Thefinal conversion of these energies to electricityis done by generators employing the principleof electromagnetic induction.There are three conditions which must existbefore a voltage can be produced by electromagneticinduction. First, we must have amagnetic field; second, a conductor; and third,relative motion between the field and the conductor.In accordance with these conditions,when a conductor is moved across a magneticfield so as to cut the lines of force, electronswithin the conductor are forced to move; thusa voltage is produced. ,Producing a voltage by magnetic inductionis illustrated in figure 20-3. If the ends of aconductor are connected to a low-reading voltmeteror galvanometer and the conductor ismoved rapidly down through a magnetic field,there is a momentary reading on the meter.When the conductor is moved up through thefield, the meter deflects in the opposite direction.If the conductor is held stationary and themagnet is moved so that the field cuts acrossthe conductor, the meter is deflected in the samemanner as when the conductor was moved andthe field was stationary.The voltage developed across the conductorterminals by electromagnetic induction is knownas an induced emf , and the resulting current thatflows is called induced current. The inducedLEFT-HAND GENERATOR RULEFigure 20-3.— Left-hand generator rule.12.143emf exists only so long as relative motionoccurs between the conductor and the field.There is a definite relationship between thedirection of flux, the direction of motion of theconductor, and the direction of the induced emf.When two of these directions are known, thethird can be found by applying the left-hand rulefor generators . To find the direction of the emfinduced in a conductor, extend the thumb, theindex finger, and the second finger of the lefthand at right angles to each other, as shown infigure 20-3. Point the index finger in the directionof the flux (toward the south pole) and thethumb in the direction in which the conductoris moving in respect to the fields. The secondfinger then points in the direction in which theinduced emf will cause the electrons to flow.DIRECT-CURRENT CIRCUITSAn electric circuit is a complete path throughwhich electrons can flow from the negative terminalof the voltage source, through the connectingwires (conductors), through the load, andback to the positive terminal of the voltage495

PRINCIPLES OF NAVAL ENGINEERINGsource (fig. 20-4). The resistance^ of a circuit(opposition to current flow) controls the amountof current flow through the circuit. The unit ofelectrical resistance, the ohm (symbol fi), isnamed after the German physicist Georg SimonOhm, who in the 19th century proved by experimentthe constant proportionality between currentand voltage in the simple electric circuit.^-=- 12 VOLT=:LOADSOURCE1Figure 20-4.— Simple electric circuit.OHM'S LAW4.125Ohm's law is fundamentally linear and thereforesimple. It is exact and applies to d-c circuitsand devices in its basic form; in a modifiedform it may also be applied to a-c circuits.Ohm's law may be stated in words as: theintensity of the current (in amperes) in anyelectric circuit is equal to the difference inpotential (in volts) across the circuit dividedby the resistance (in ohms) of the circuit . Expressedas an equation, Ohm's law becomes1=^*Rcircuit, power is equal to the product of thevoltage and the current. Expressing the powerin watts (P), the current in amperes (I), and theemf in volts (E), the equation isThe various implications of Ohm's law maybe derived from the algebraic transposition ofthe units I, E, R, and P. A summary of the 12basic formulas which may be derived fromtransposing these units is given in figure 20-5.in each quadrant of the smaller circleThe unitis equivalent to the quantities in the same quadrantof the larger circle.Series CircuitsThe analysis of a series circuit to determinevalues for voltage, current, resistance, andpower is relatively simple. It is necessary onlyto draw or to visualize the circuit, to list theknown values, and to determine the unknownvalues by means of Ohm's law and Kirchhoff'slaw of voltages.Kirchhoff's law of voltages states that thealgebraic sum of all the voltages in any completeelectric circuit is equal to zero . In otherwords, the sum of all positive voltages must beequal to the sum of all negative voltages. Forany given voltage rise there must be an equalvoltage drop somewhere in the circuit. The voltagerise (potential source) is usually regardedIEwhereIERintensity of current (in amperes)difference in potential (in volts)resistance (in ohms)If any two of these quantities are known, thethird may be found by applying the equation.In addition to the volt, the ampere, and theohm, the unit of power frequently appears inelectric circuit calculations. In a d-c electricAll conductors have some resistance, and thereforea circuit made up of nothlngbut conductors would havesome resistance, however small it might be. In circuitscontaining long conductors, through which anappreciable amount of currentlsdrawn, the resistanceof the conductors becomes important. For the purposesof this chapter, however, the resistance of theconducting wires is neglected.Figure 20-5.—Summary of basicformulas.27.236Ohm's law496

Chapter 20. -SHIPBOARD ELECTRICAL SYSTEMSas the power supply, such as a battery. Thevoltage drop is usually regarded as the load,such as a resistor. The voltage drop may bedistributed across a number of resistive elements,such as a string of lamps or severalresistors. However, according to Kirchhoff'slaw, the sum of their individual voltage dropsmust always equal the voltage rise supplied bythe power source.The statement of Kirchhoff's law can betranslated into an equation, from which manyunknown circuit factors may be determined.(See fig. 20-6.) Note that the source voltage Egis equal to the sum of the three load voltagesEj, E2, and E3. In equation form,E = E + E + Es 1 2 3The following procedure may be used to solveproblems applicable to figure 20-6:1. Note the polarity of the source emf (Eg)and indicate the electron flow around the circuit.Electron flow is out from the negative terminalof the source, through the load, and back to thepositive terminal of the source. In the examplebeing considered, the arrows indicate electronflow in a clockwise direction around the circuit.2. To apply Kirchhoff's law it is necessaryto establish a voltage equation. The equation isdeveloped by tracing around the circuit and notingthe voltage absorbed (that is, the voltagedrop) across each part of the circuit, and expressingthe sum of these voltages according tothe voltage law. It is important that the tracebe made around a closed circuit, and that itencircle the circuit only once. Thus, a point isarbitrarily selected at which to start the trace.The trace is then made and, upon completion,13.15Figure 20-6.— Series circuit for demonstratingKirchhoff's law of voltages.the terminal point coincides with the startingpoint.3. Sources of emf are preceded by a plussign if, in tracing through the source, the firstterminal encountered is positive; if the firstterminal is negative, the emf is preceded by aminus sign.57 Voltage drops along wires and acrossresistors (loads) are preceded by a minus signif the trace is in the assumed direction of electronflow; if in the opposite direction, the signis plus.5. If the assumed direction of electron flowis incorrect, the error is indicated by a minussign preceding the current, as obtained in solvingfor circuit current. The magnitude of thecurrent is not affected.The preceding rules may be applied to theexample of figure 20-6 as follows:1. The left terminal of the battery is negative,the right terminal is positive, and electronflow is clockwise around the circuit.2. The trace may arbitrarily be started atthe positive terminal of the source and continuedclockwise through the source to its negativeterminal. From this point the trace is continuedaround the circuit to a, b, £, d, and backto the positive terminal, thus completing thetrace once around the entire closed circuit.3. The first term of the voltage equation is+Eg.4. The second, third, and fourth terms are,respectively, -Ej, -E2, -E3. Their algebraicsum is equated to zero, as follows:^2-^3^s 1Transposing the voltage equation and solvingfor Eg,^s = El+ E2 + EgSince E = IR, from Ohm's law, the voltagedrop across each resistor may be expressed interms of the current and resistance of the individualresistor, as follows:Eg = IRj + IR2 + IR3where Rj, R2, and R3 are the resistances ofresistors Rl, R2, and R3, respectively. Eg isthe source voltage and I is the circuit current.E may be expressed in terms of the circuitcurrent and total resistance as IR^. SubstitutingIR^ for Eg, the voltage equation becomesIR.= IRj + IRg + IR3497

PRINCIPLES OF NAVAL ENGINEERINGSince there is only one path for current inthe series circuit, the total current is the samein all parts of the circuit. Dividing both sides ofthe voltage equation by the common factor I, anexpression is derived for the total resistance ofthe circuit in terms of the resistances of theindividual devices:RlAA/VW-5nRt = Rl- R2 + R3Therefore, in series circuits the total resistanceis the sum of the resistances of theindividual parts of the circuit.In the example of figure 20-6, the totalresistance is 5+10+15= 30 ohms. The totalcurrent may be found by applying the equation^t 30 ^TI). = on = 1 ampereRt"^"The power absorbed by resistor R^ is I^R^,or 1^x5=5 watts. Similarly, the power absorbedby R2 is 1^ X 10 = 10 watts, and the power absorbedby R3 is l2 X 15 = 15 watts. The totalpower absorbed is the arithmetic sum of thepower of each resistor, or 5 + 10 + 15 = 30 watts.The value is also calculated by Pt = Etl^ =30 X 1 = 30 watts.Parallel CircuitsThe parallel circuit differs from the simpleseries circuit in that two or more resistors, orloads, are connected directly to the same sourceof voltage. There is accordingly more than onepath that the electrons can take. The more paths(or resistors) that are added in parallel, the lessopposition there is to the flow of electrons fromthe source. This condition is opposite to the effectthat is produced in the series circuit whereadded resistors increase the opposition to theelectron flow.As may be seen from figure 20-7, the samevoltage is applied across each of the parallelresistors. In this case the voltage applied acrossthe resistors is the same as the source voltage,Figure 20-7.— Parallel electric circuit.13.16resistance of the branch, the higher will bethe current through that branch. The individualcurrents can be foundby the application of Ohm'slaw to the individual resistors. Thus,andand^sT 30 „I1 = — = 3— = 6 amperes^1s 30 „I9 = — = rr- = 3 amperes10RrE3 Rq30301 ampereThe total current. It, of the parallel circuitis equal to the sum of the currents through theindividual branches. This, in slightly differentwords, is Kirchhoff's law. In this case, the totalcurrent isT = Ij + I2 + I„= 6 + 3 + 1 = 10 amperesCurrent flows from the negative terminal ofthe source to point a where it divides and passesthrough the three resistors to point band back tothe positive terminal of the voltage source. Theamount of current flowing through each individualbranch depends on the source voltage and on theresistance of that branch— that is, the lower theIn order to find the equivalent, or total,resistance (R^) of the combination shown infigure 20-7, Ohm's law is used to find each ofthe currents (I^, Ii, I2, and Ig) in the precedingformula. The total current is equal to the sumof the branch currents. Thus,498

Chapter 20. -SHIPBOARD ELECTRICAL SYSTEMSorEsEsRt Rl R2 R3Rt= E, (^Rl^R2 ^Rs)Both sides of this equation may be divided byEg without changing the value of the equation;therefore,Rt Rl R2 R3By means of the preceding equation the totalresistance of the circuit shown in figure 20-7may be determined. ThusRl IN SERIES WITH PARALLEL COMBINATION OF R2 AND R3Figure 20-8.— Compound electric circuit.27.237The total resistance, Rt, of figure 20-8 isdetermined in two steps. First, the resistanceR2 3 of the parallel combination of R2 andR3 isdetermined asandR 1^X+ -L+10 30_1= 10Rt 30R 2,3^2^3 3x6 18 o. ^= a — = 2 ohmsR2 R3 3+6The sum of R, „ and R- (that is, Rj isRt = ^2, 3 + Rl = 2 + 2 = 4 ohmsTaking the reciprocals of both sides,30R = Yq-=3 ohmsA useful rule to remember in computing theequivalent resistance of a d-c parallel circuitis that the total resistance is always less thanthe smallest resistance in any of the branches.In addition to adding the individual branchcurrents to obtain the total current in a parallelcircuit, the total current may be found directlyby dividing the applied voltage by the equivalentresistance, R,, For example, in figure 20-7:Es^0I^=—-=-p= 10 amperesRtThree or more resistors may be connectedin series and parallel combinations to form acompound circuit. One basic series-parallel circuitcomposed of three resistors is shown infigure 20-8,If the total resistance, Rt, and the sourcevoltage. Eg, are known, the total current. It,may be determined by Ohm's law. Thus, infigure 20-8,andE . = I,R. = 5 X 2 = 10 voltsab t 1E. = LRo , z 5 X 2 = 10 voltsbe t 2,0According to Kirchhoff's voltage law, thesum of the voltage drops around the closed circuitis equal to the source voltage. Thus,orEab + Eijc - Eg10 + 10 = 20 voltsIf the voltage drop Ebc across R2 3— that is,the drop between points b and c— is known, thecurrent through the individual branches may bedetermined as^bc 10Rr3.333 amperes499

)PRINCIPLES OF NAVAL ENGINEERINGandEbc^3 =Rr10 = 1. 666 amperesAccording to Kirchhoff's current law, thesum of the currents flowing in the individualparallel branches is equal to the total current.Thus,orl2 + ^3 = It3. 333 + 1. 666 = 5 amperes (approx.The total current flows through Rl; at pointb it divides between the two branches in inverseproportion to the resistance of the branches.Twice as much goes through R2 as through R3because R2 has one-half the resistance of R3.Thus, 3.333 (or two-thirds of 5) amperes flowthrough R2; and 1.666 (or one-third of 5) amperesflow through R3.WHEATSTONE BRIDGEA type of circuit that is widely used for precisionmeasurements of resistance is the Wheat -stone bridge . The circuit diagram of a Wheatstonebridge is shown in figure 20-9. Rl, R2,and R3 are precision variable resistors, andR^is the resistor whose unknown value is to bedetermined. The galvanometer, G, is insertedacross terminals b and d to indicate the conditionof balance. When the bridge is properlybalanced, there is no difference in potentialacross terminals b and d_and the galvanometerdeflection, when the switch is closed, will bezero. Should the bridge become unbalanced dueto a change in resistance of R^, the differenceof potential between terminals b anddwLll causea deflection in the galvanometer.When this type of circuit is used as a componentof a resistance thermometer, Rx is thetemperature-sensing element. The resistance ofRjj varies directly with the temperature; thus achange in temperature results in an unbalancedbridge and a deflection of the galvanometer.DIRECT-CURRENT GENERATORSA d-c generator is a rotating machine thatconverts mechanical energy into electrical energy.This conversion is accomplished by rotatingan armature, which carries conductors, ina magnetic field, thus inducing an emf in theconductors.A d-c generator (fig. 20-10) consists essentiallyof a steel frame or yoke containing thepole pieces and field windings; an armature consistingof a group of copper conductors mountedin a slotted cylindrical core; a commutator formaintaining the current in one direction throughthe external circuit; and brushes with brushholders to carry the current from the commutatorto the external load circuit.The frame, in addition to providing mechanicalsupport for the pole pieces, serves as aportion of the magnetic circuit in that it providesa path for the magnetic flux between thepoles.CAP SCREWFOR MOUNTINGPOLE PIECEFIELD POLEANDFIELD COREARMATURECOMMUTATOR12.251Figure 20-9.— Wheatstone bridge circuitdiagram.Figure 20-10.—A d-c generator.73.161500

GENERATING A VOLTAGEChapter 20. -SHIPBOARD ELECTRICAL SYSTEMSThe field \windings of ad-c generator receivecurrent either from an external d-c source ordirectly across the armature, thus becomingelectromagnets. They are connected sothattheyproduce alternate north and south poles and, whenenergized, they establish magnetic flux in thefield yoke, pole pieces, air gap, and armaturecore, as shown in figure 20-11.The armature is mounted on a shaft and isrotated through the field by an outside energysource (prime mover). Thus we have a magneticfield, a conductor, and relative motion betweenthe two— which, it will be remembered, are thethree essentials for producing a voltage by magnetism.If the output of the armature is connectedacross the field windings, the voltageand the field current at start will be smallbecause of the small residual flux in the fieldpoles. However, as the generator continues torun, the small voltage across the armature willcirculate a small current through the field coilsand the field will become stronger. In a selfexcitedgenerator, this action causes the generatorvoltage to rise quickly to the proper valueand the machine is said to "buildup" its voltage.The simplest generator armature winding is aloop or single coil. Rotating this loop in a magneticfield will induce an emf whose strengthis dependent upon the strength of the magneticfield and the speed of rotation of the conductor,A single-coil generator with each coil terminalconnected to a bar of a two-segmentmetal ring is shown in figure 20-12. The two41.10Figure 20-12.— Single-coil generatorwith commutator.segments of the split ring are insulated fromeach other and the shaft, thus forming a simplecommutator which mechanically reverses thearmature coil connections tothe external circuitat the same instant that the direction of generatedvoltage reverses in the armature coil.The emf developed across the brushes ispulsating and unidirectional. Figure 20-13 is agraph of the pulsating emf for one revolution ofa single-loop armature in a 2-pole generator.A pulsating direct voltage of this characteristic(called ripple ) is unsuitable for most applications.In practical generators, more coils andmore commutator bars are used to produce anoutput voltage waveform with less ripple. FigureFIELDWINDING27.248.1 41.10Figure 20-11.— Magnetic circuit of a 2-pole Figure 20-13.— Pulsating voltage from a singlegenerator,coil armature.501

PRINCIPLES OF NAVAL ENGINEERING20-14 shows the reduction in ripple obtained bythe use of two ci -Is instead of one. Since thereare now four commutator segments and onlytwo brushes, the voltage cannot fall any lowerthan point A; therefore, the ripple is limited bythe rise and fall between points A and B. By addingstill more armature coils, the ripple can bereduced still more.u.o111oREVOLUTIONS41.9Figure 20-14.— Voltage from atwo-coilarmature.TYPES OF D-C GENERATORSD-c generators are usually classified accordingto the manner in which the field windingsare connected to the armature circuit (fig. 20-15).A separately excited d-c generator is indicatedin part A of figure 20-15. In this machinethe field windings are energized from a d-csource other than its own armature.Self-excited d-c generators may be of threetypes, as indicated in part B of figure 20-15.A shunt generator has its field windings connectedparallel with the armature, whereas thefield windings of a series generator are connectedin series with the armature. The compoundd-c generator employs both shunt andseries field windings.The d-c generator most widely used in theNavy is the stabilized shunt generator , whichemploys a light series field winding on thesame poles with the shunt field windings. Thistype of generator has good voltage regulationcharacteristics and at the same time ensuresgood parallel operation.VOLTAGE CONTROLVoltage control is either manual or automatic.In most cases, the process involveschanging the resistance of the field circuit,thus controlling the field current which permitscontrol of the terminal voltage. The major differencebetween the various voltage regulatorsystems is merely the method by which thefield circuit resistance is controlled.DIRECT-CURRENT MOTORSThe construction of a d-c motor is essentiallythe same as that of a d-c generator. Thed-c generator converts mechanical energy intoelectrical energy, and the d-c motor convertsthe electrical energy into mechanical energy.A d-c generator may be made to function as amotor by applying a suitable source of directvoltage across the normal output electricalterminals.There are various types of d-c motors,depending upon the way in which the field coilsare connected. Each type has characteristicsthat are advantageous under given load conditions.Shunt motors have the field coils connectedin parallel with the armature circuit. This typeof motor, with constant potential applied, developsvariable torque at an essentially constantspeed, even under changingload conditions. Suchloads are found in drives for such machine shopequipment as lathes, milling machines, drills,planers, and shapers.Series motors have the field coils connectedin series with the armature circuit. This type ofmotor, with constant potential applied, developsvariable torque but itsspeedvaries widely underchanging load conditions. The speed of a seriesmotor is low under heavy loads but becomesexcessively high under light loads. Series motorsare commonly used to drive electric cranes,hoists, and winches.Compound motors are a compromise betweenshunt and series motors, having one set of fieldcoils in parallel with the armature circuit andanother set of field coils in series with the armaturecircuit. The compound motor developsan increased starting torque over the shunt motorand has less variation in speed than the seriesmotor.502

Chapter 20. -SHIPBOARD ELECTRICAL SYSTEMSLOAOQSHUNTSERIESCOMPOUND(A)SEPARATE EXCITATION(B)SELF EXCITATIONFigure 20-15.— Types of d-c generators.147.122The operation of a d-c motor depends on theprinciple that a current-carrying conductorplaced in, and at right angles to, a magneticfield tends to move at right angles to the directionof the field. A convenient method of determiningthe direction of motion of a currentcarryingconductor in a magnetic field is byuse of the right-hand motor rule for electronflow (fig. 20-16). Extend the thumb, index finger,and second finger of the right hand at rightangles to each other, with the index fingerpointed in the direction of the flux (toward thesouth pole) and the second finger pointed in thedirection of electron flow. The thumb then pointsin the direction of motion of the conductor withrespect to the field.ALTERNATING-CURRENT THEORYJust as a current flowing in a conductorproduces a magnetic field around the conductor,the reverse of this process is true. A voltagecan be generated in a circuit by moving a conductorso that it cuts across lines of magneticforce or, conversely, by moving the lines offorce so that they cut across the conductor. Ana-c generator utilizes this principle of electromagneticinduction to convert mechanical energyinto electrical energy.In the case of alternating current, electronsmove first in one direction andtheninthe other.Thus the direction of the current reversesperiodically and the magnitude of the voltage isconstantly changing. This variation in current isrepresented graphically in sine waveform infigure 20-17.The vertical projection (dotted line in fig.20-17) of a rotating vector may be used torepresent the voltage at any instant. Vector Ej^^represents the maximum voltage induced in aconductor rotating at uniform speed in a 2-polefield (points 3 and 9). The vector is rotatedcounterclockwise through one complete revolution(360°). The point of the vector describes acircle. A line drawn from the point of the vectorperpendicular to the horizontal diameter of thecircle is the vertical projection of the vector.The circle also describes the path of theconductor rotating in the bi-polar field. Thevertical projection of the vector represents thevoltage generated in the conductor at any instantcorresponding to the position of the rotatingvector as indicated by angled. Angle ^representsselected instants at which the generatedvoltage is plotted. The sine curve plotted at the12.143Figure 20-16.—Right-hand motor ruleforelectron flow.503

PRINCIPLES OF NAVAL ENGINEERINGFigure 20-17.— Generation of sine-wave voltage.41.19right of the figure represents successive valuesof the a-c voltage induced in the conductor asit moves at uniform speed through the 2-polefield, because the instantaneous values of rotationallyinduced voltage are proportional to thesine of the angled that the rotating vector makeswith the horizontal.The sine wave in figure 20-17 represents onecomplete revolution of the armature or onevoltage cycle. The frequency of a-c voltage ismeasured in cycles per second (cps) and maybe determined by the following formula:whererpmP: frequencyf = P X rpm120(in cps; according to theNational Bureau of Standards SpecialPublication 304, frequency in cyclesper second in the International Systemsof Units is expressed as Hertz (H2).One hertz equals one cycle per second.)revolutions per minutenumber of poles in the generatorA generator made to deliver 60 cps, andhaving two field poles, would need an armaturedesigned to rotate at 3600 rpm.PROPERTIES OF A-C CIRCUITSResistance, the opposition to current flow,has the same effect in an a-c circuit as it doesin a d-c circuit. However, in the application ofOhm's law to a-c circuits, other propertiesmust be taken into consideration.Inductance is that property which opposesany change in the current flow and capacitanceis that property which opposes any change involtage. Since a-c current is constantly changingin magnitude and direction, the propertiesof inductance and capacitance are always present.The amount of opposition to current flow inan inductive circuit is referred to as its inductivereactance, Xj^. The value of inductive reactance(in ohms) depends on the inductance of the circuitand the frequency of the applied voltage. Expressedin equation form,X^ :27rfL504

Chapter 20. -SHIPBOARD ELECTRICAL SYSTEMSwhere•71fLinductive reactance, in ohms3.1416frequency, in cycles per secondinductance, in henrys-rVWV\rH(^\\The current flowing in a capacitive circuitis directly proportional to the capacitance and tothe rate at which the applied voltage is changing.The rate at which the voltage changes is determinedby the frequency. The value of the capacitivereactance, Xq, is inversely proportional tothe capacitance of the circuit and the frequencyof the applied voltage. Thus,IRwhere127rfCX -X 'TTfc= capacitive reactance, in ohms= 3.1416= frequency, in cycles per second= capacitance, in faradsThe effects of capacitance and inductance inan a-c circuit are exactly opposite. Inductivereactance causes the current to lag the appliedvoltage and capacitive reactance causes the currentto lead the applied voltage. These effectstend to neutralize each other, and the combinedreactance is the difference between the individualreactances.The total opposition offered to the flow ofcurrent in an a-c circuit is the impedance , Z.The impedance of a circuit, expressed in ohms,is composed of the capacitive reactance, theinductive reactance, and the resistance.The effects of capacitive reactance, inductivereactance, and resistance in an a-c circuit canbe shown graphically by the use of vectors. Forexample, consider the series circuit shown inpart A of figure 20-18.The vector representation of the reactancesis shown in part B of figure 20-18. Because theinductive reactance and the capacitive reactanceare exactly opposite, they are subtracted directlyand the difference shown in part C offigure 20-18 as capacitive reactance. The resultantis found vectorially by constructing aparallelogram, as shown in part D of figure20-18. The resultant vector is also the hypotenuseof a right triangle; therefore,Z= \/r2 + (Xc -Xl)2Figure20-18.— Vector solution of an a-ccircuit.In accordance with Ohm's law for a-c circuits,the effective current through a circuit isdirectly proportional to the effective voltage andinversely proportional to the impedance. Thus,whereI = -^I = current, in amperesE = emf, in voltsZ = impedance, in ohmsA-C GENERATORSMost of the electric power for use aboardship and ashore is generated by alternatingcurrentgenerators.A-c generators are made in many differentsizes, depending upon their intended use. Forexample, any one of the generators at BoulderDam can produce millions of volt-amperes, whilegenerators used on aircraft produce only afew thousand volt-amperes.Regardless of size, however, all generatorsoperate on the same basic principle: a magneticfield cutting through conductors, or conductorspassing through a magnetic field. Thus allgenerators will have at least two distinct setsof conductors. They are (1) a group of conductors505

PRINCIPLES OF NAVAL ENGINEERINGin which the output voltage is generated, and(2) a group of conductors through which directcurrent is passed to obtain an electromagneticfield of fixed direction. The conductors in whichthe output voltage is generated are always referredto as the armature windings . The conductorsin which the electromagnetic fieldoriginates are always referred to as the fieldwindings .In addition to the armature and field, theremust also be relative motion between the two.To provide this relative motion, a-c generatorsare built in two major assemblies— the statorand the rotor. The rotor rotates inside thestator. The rotor may be driven by any one ofa number of commonly used prime movers,including steam turbines, gas turbines, and internalcombustion engines.TYPES OF A-C GENERATORSIn the revolving-armature a-c generator,the stator provides a stationary electromagneticfield. The rotor, acting as the armature, revolvesin the field, cutting the lines of force,producing the desired output voltage. In thisgenerator, the armature output is taken throughsliprings and thus retains its alternating characteristics.For a number of reasons, the revolvingarmaturea-c generator is seldom used. Itsprimary limitation is the fact that its outputpower is conducted through sliding contacts(sliprings and brushes). These contacts aresubject to frictional wear and sparking. Inaddition, they are exposed, and thus liable toarc-over at high voltages. Consequently, revolving-armaturegenerators are limited toapplications of low power and low voltage.The revolving-field a-c generator (fig. 20-19) is by far the most commonly used type. Inthis type of generator, direct current from aseparate source is passed through windings onthe rotor by means of sliprings and brushes.This maintains a rotating electromagnetic fieldof fixed polarity (similar to a rotating bar magnet).The rotating magnetic field, following therotor, extends outward and cuts through thearmature windings embedded in the surroundingstator. As the rotor turns, alternating voltagesare induced in the windings, since magneticfields of first one polarity and then the othercut through them. Since the output power istaken from stationary windings, the output maybe connected through fixed terminals directlyARMATURE WINDINGSSTATORft-COUTPUT TERMINALS147.124Figure 20-19.— Essential parts of a rotatingfielda-c generator.to the external loads, as through terminals Tland T2 in figure 20-19. This is advantageousbecause there are no sliding contacts and thewhole output circuit is continuously insulated,thus minimizing the danger of arc-over.Sliprings and brushes are still used on therotor to supply direct current to the field; theyare adequate for this purpose because the powerlevel in the field is much lower than in the armaturecircuit.THREE-PHASE GENERATORSThe three-phase a-c generator has threesingle-phase windings spaced so that the voltageinduced in each winding is 120° out of phasewith the voltages in the other two windings. Aschematic diagram of a three-phase statorshowing all the coils becomes complex and isdifficult to understand. A simplified schematicdiagram, showing all the windings of a singlephase as one winding, is given in figure 20-20.The rotor is omitted for the sake of simplicity.The waveforms of voltage are shown to theright of the schematic. The three voltages are120° apart and are similar to the voltages thatwould be generated by three single-phase a-cgenerators whose voltages are out of phase byangles of 120°. The three phases are independentof each other.Rather than have six leads come out of thethree-phase alternator, one of the leads from506

Chapter 20. -SHIPBOARD ELECTRICAL SYSTEMSSIMPLIFIED SCHEMATIC AND WAVE FORMSWYE CONNECTION DELTA CONNECTION27.244Figure 20-20.— Three-phase a-c generator.each phase may be connected to form a commonjunction. The stator is then called a wye -connected or star-connected stator. The commonlead may or may not be brought out of themachine. If it is brought out, it is called theneutral . The simplified schematic diagram (fig.20-20) shows a wye-connected stator with thecommon lead not brought out. Each load is connectedacross two phases in series. Thus, R^)-,is connected across phases A and B in series,R^f. is connected across phases A and C inseries, and R]-,^, is connected across phases Band C in series. Thus the voltage across eachload is larger than the voltage across a singlephase. The total voltage, or line voltage, acrossany two phases is the vector sum of the individualphase voltages. For balanced conditions,the line voltage is 1.73 times the phase voltage.Since there is only one path for current in aline wire and the phase to which it is connected,the line current is equal to the phase current.A three-phase stator can also be connectedso that the phases are connected end to end, asshown in figure 20-20. This arrangement iscalled a delta connection . In the delta connection,the line voltages are equal to the phasevoltages. The line currents are equal to thevector sum of the phase currents. The line currentis equal to 1.73 times the phase current,when the loads are balanced.VOLTAGE REGULATIONWhen the load on an a-c generator is changed,the terminal voltage varies with the load. Theamount of variation depends on the design ofthe generator and on the amount of reactancefrom the inductive or capacitive loads. Underpractical shipboard operating conditions, theload varies widely with the starting and stoppingof motors.The only practicable way to regulate thevoltage output of an a-c generator is to controlthe strength of the rotating magnetic field. Thestrength of the electromagnetic field may bevaried by changing the amount of current flowingthrough the coil, which is done by connectinga rheostat in series with the coil. Thus, voltageregulation in an a-c generator is accomplishedby varying the field current. This allows a relativelylarge a-c voltage to be controlled by amuch smaller d-c voltage and current.Since manual adjustment of a-c voltage isnot practicable when the load fluctuates rapidly,automatic voltage regulators are used. The constructionand operating principles of voltageregulators varies; however, the essential functionof any voltage regulator is to use the a-coutput voltage, which the regulator is designedto control, as a sensing influence to control theamount of current the exciter supplies to itsown control field.TRANSFORMERSA transformer (fig. 20-21) is an a-c devicethat has no moving parts and that transfersenergy from one circuit to another by electromagneticinduction. The energy is always transferredwithout a change in frequency but usuallywith changes in voltage and current. A step-uptransformer receives electrical energy at onevoltage and delivers it at a higher voltage, Astepdown transformer receives electricalenergy at one voltage and delivers it at a lowervoltage. Transformers are not used on directcurrent.The conventional constant -potential transformeris designed to operate with the primaryconnected across a constant-potential sourceand to provide a secondary voltage that is substantiallyconstant from no load to full load.Various types of small single-phase transformersare used on shipboard equipment. Inmany installations, transformers are used onswitchboards to step down the voltage for indicatinglights. Low-voltage transformers areincluded in some motor control panels to supplycontrol circuits or to operate overload relays.Other common uses include low-voltage supply507

PRINCIPLES OF NAVAL ENGINEERINGCOIL AND CORE ASSEMBLYFigure 20-21,— Single-phase transformer.147.125for gunfiring circuits, special signal lights, andhigh-voltage ignition circuits.The typical transformer has two windingswhich are electrically insulated from each other.These windings are wound on a common magneticcircuit made of laminated sheet steel.The principal parts are the core , which providesa circuit of low reluctance for the magneticflux; the primary winding , which receives theenergy from the a-c source; and the secondarywinding , which receives the energy by mutualinduction from the primary and delivers it tothe load.When a transformer is used to step up thevoltage, the low-voltage winding is the primary.When a transformer is used to step down thevoltage, the high- voltage winding is the primary.The primary is always connected to the sourceof the power; the secondary is always connectedto the load. It is common practice to refer to thewindings as the primary and the secondary,rather than as the high-voltage and the lowvoltagewindings.The operation of the transformer is basedon the principle that electrical energy can betransferred efficiently by mutual induction fromone winding to another. When the primary windingis energized from an a-c source, an alternatingmagnetic flux is established in the transformercore. This flux links the turns of bothprimary and secondary, thereby inducing voltagesin them. Because the same flux cuts bothwindings, the same voltage is induced in eachturn of both windings. Hence the total inducedvoltage in each winding is proportional to thenumber of turns in that winding. That is,'1 NiE2where E-^ and E2 are the induced voltages in theprimary and secondary windings, respectively,N2508

Chapter 20. -SHIPBOARD ELECTRICAL SYSTEMSand Ni and N2 are the number of turns in theprimary and secondary windings, respectively.In ordinary transformers, the induced primaryvoltage is almost equal to the applied primaryvoltage; hence, the applied primary voltage andthe secondary induced voltage are approximatelyproportional to the respectivenumber of turns inthe two windings.A-C MOTORSA-c motors are manufactured in many differentsizes, shapes, and ratings for use in awide variety of applications. Since this discussioncannot possibly cover all aspects of allkinds of a-c motors, it will be limited to thepolyphase induction motor. Information on othertypes of motors may be found in Basic Electricity, NavPers 10086-A, and in various manufacturers'technical manuals.The induction motor is a widely used type ofa-c motor because it is simple, rugged, andinexpensive. It consists essentially of a statorand a rotor; it can be designed to suit mostapplications requiring constant speed and variabletorque.The stator of a polyphase induction motorconsists of a laminated steel ring with slots onthe inside circumference. The stator windingis similar to the a-c generator stator windingand is generally of the two-layer distributedpreformed type. Stator phase windings are symmetricallyplaced on the stator and may be eitherwye connected or delta connected.Most induction motors used by the Navy havea cage-type rotor (fig. 20-22) consisting of alaminated cylindrical core with parallel slots inthe outside circumference to hold the windingsin place. The rotor winding is constructed ofindividual short circuited bars connected to endrings.In induction motors, the rotor currents aresupplied by electromagnetic induction. Thestator windings contain two or more out-oftime-phasecurrents which produce correspondingmagnemotive forces which establish a rotatingmagnetic field across the air gap. Thismagnetic field rotates continuously at constantspeed, regardless of the load on the motor. Thestator winding corresponds tothe primary windingof a transformer.The induction motor derives its name fromthe fact that mutual induction (transformeraction) takes place between the stator and therotor under operating conditions. The magnetic77.77Figure 20-22.— Cage-type induction motor rotor.revolving field produced by the stator cutsacross the rotor conductors, thus inducing avoltage in the conductors which causes rotorcurrent to flow. Hence, motor torque is developedby the interaction of the rotor currentand the magnetic revolving field.POWER DISTRIBUTION SYSTEMThe power distribution system is the connectinglink between the generators that supplyelectric power and the electrical equipment thatutilizes this power to furnish the various servicesnecessary to operate the ship. The powerdistribution system includes the ship's servicepower distribution system, the emergency powerdistribution system, and the casualty power distributionsystem.Most a-c power distribution systems on navalships are 450-volt, three-phase, 60-cycle,three-wire systems. The lighting distributionsystems are 115-volt, three-phase, 60-cycle,three-wire systems supplied from the powercircuits through transformer banks. On someships, the weapons systems, some I.C. circuits,and aircraft starting circuits receive electricalpower from a 400-cps system.SHIP'S SERVICE POWERThe ship's service power distribution systemis the electrical system that normally supplieselectric power to the ship's equipment and machinery.The switchboards and associated generatorsare located in separate engineeringspaces to minimize the possibility that a singlehit will damage more than one switchboard.509

PRINCIPLES OF NAVAL ENGINEERINGThe ship's service generators and distributionswitchboards are interconnected by bus tiesso that any switchboard can be connected to feedpower from its generator to one or more of theother switchboards. The bus ties also connecttwo or more switchboards so that the generatorplants can be operated in parallel (or the switchboardscan be isolated for split-plant operation).In large installations, power distribution toloads is from the generator and distributionswitchboards or switchgear groups to load centers,to distribution panels, and to the loads,or directly from the load centers to some loads.On some ships, such as large aircraft carriers,a system of zone control of the ship'sservice and emergency power distribution isprovided. Essentially, the system establishes anumber of vertical zones, each of which containsone or more load center switchboardssupplied through bus feeders from the ship'sservice switchgear group. A load center switchboardsupplies power to the electrical loadswithin the electrical zone in which it is located.Thus, zone control is provided for all powerwithin the electrical zone. The emergencyswitchboards may supply more than one zone,depending on the number of emergency generatorsinstalled. Figure 20-23 shows the ship'sservice and emergency power distribution systemin a large aircraft carrier.In smaller installations (fig. 20-24) the distributionpanels are fed directly from thegenerator and distribution switchboards. Thedistribution panels and load centers (if any) arelocated centrally with respect to the loads theyfeed to simplify installation. This arrangementalso requires less weight, space, and equipmentthan if each load were connected to a switchboard.At least two independent sources of powerare provided for selected vital loads throughautomatic bus transfer equipment. The normaland alternate feeders to a common load run fromdifferent ship's service switchboards and arelocated below the waterline on opposite sides ofthe ship to minimize the possibQity that bothwill be damaged by a single hit.The lighting circuits are supplied from thesecondaries of 450/115-volt transformer banksconnected to the ship's service power system.In large ships, the transformer banks are installedin the vicinity of the lighting distributionpanels, at some distance from the generatorand distribution switchboards. In small ships,the transformer banks are located near thegenerator and distribution switchboards andenergize the switchboard buses that supply thelighting circuits.EMERGENCY POWERThe emergency power distribution system isprovided to supply an immediate and automaticsource of electric power to a limited number ofselected vital loads in the event of failure of theship's service power distribution system. Theemergency power system, which is separate anddistinct from the ship's service power distributionsystem, includes one or more emergencydistribution switchboards. Each emergencyswitchboard, supplied by its associated emergencygenerator, has feeders which run to the bustransfer equipment at the distribution panels orloads for which emergency power is provided.The emergency generators and switchboardsare located in separate spaces from those containingthe ship's service generators and distributionswitchboards. As previously noted, thenormal and alternate ship's service feedersare located below the waterline on oppositesides of the ship. The emergency feeders arelocated near the centerline and higher in theship (above the waterline). This arrangementprovides for horizontal separation between thenormal and alternate ship's service feedersand vertical separation between these feedersand the emergency feeders, thereby minimizingthe possibility of damaging all tluree types offeeders simultaneously.The emergency switchboard is connected byfeeders to at least one and usually to two differentship's service switchboards. One of theseswitchboards is the preferred source of ship'sservice power for the emergency switchboardand the other is the alternate source. Theemergency switchboard and distribution systemare normally energized from the preferredsource of ship's service power. If both the preferredand the alternate sources of ship's servicepower fail, the diesel-driven emergencygenerator starts automatically and the emergencyswitchboard is automatically transferredto the emergency generator.When the voltage is restored on either thepreferred or the alternate source of the ship'sservice power, the emergency switchboard isautomatically retransferred to the source thatis available (or to the preferred source, if voltageis restored on both the preferred and thealternate sources). The emergency generator510

II XIkGIIHI\^I\Chapter 20. -SHIPBOARD ELECTRICAL SYSTEMSr ni Ii^o „ '^Iox* lU||ujI Q! I-j^Sn trf^ ^EMER GEN & BUSTRANSF SECT NO 3'^1000 KW. 450 VOLT,60'^. 3 EMERGENCYDIESEL GENERATOR©1500 KW, 450 VOLT,G ) 60~, 3^ SHIPS SERVICETURBOGENERATOREMERGENCY GENERATOR ROOM NO. 3SHORE TERMINAL BOXES PORT-CDO111 \n3iABUS TIE 8. DISTSECT NO. 7GEN BUS TIE &DIST SECT NO 7BUS TIES. DIST GEN BUS TIE iSECT NO 6 DIST SECT NO. 6SWITCHBOARD ROOM NO, 7SWITCHBOARD ROOM NO. 6MACH ROOM NO, 3MACH ROOM NO. 2 AUX MACH ROOM NO. 2SWITCHBOARD ROOM NO. 8rmGEN BUS TIES. BUS TIE 8. DISTDIST SECT NO 8 SECT NO. 8^L,(*,¥lSWITCHBOARD ROOM NO, 5GEN BUS TIE & BUS TIE & DISTDIST SECT NO 5 SECT NO 5.?-CDdhSHORE TERMINAL BOXES STBO77.164Figure 20-23.— Ship's service and emergency power distribution system in a large carrier.511

IAnI (1i^''IPRINCIPLES OF NAVAL ENGINEERINGrt Ir.j4' Nkill'I'L.rr^ 'TJ-tEMERGENS BUSTRANSF SECT NO. 2lisL JEMERGENCY GENERATOR ROOM NO. 2r^f"1rI_I_ J._GEN BUS TIE &OISTSECT NO 3T_Y_YJBUS TIE &OISTSECT NO 3jSWITCHBOARD ROOM NO. 3MACH ROOM NO. 4MACH ROOM NO. IAUX MACH ROOM NO 1SWITCHBOARD ROOM NO. 4oGEN BUS TIE 8.OIST SECT NO. iPBUS TIE&DISTSECT NO. 4j. * II «LTJ:l.._i II.SHORE TERMINAL BOXES STBDCD CDFigure 20-23.— Ship's service and emergency power distribution systemin a large carrier.— Continued.65.54.2512

Chapter 20. -SHIPBOARD ELECTRICAL SYSTEMSX.o•ac_oBuCO(1ICSl1o(Mu-kzDili;:i[^N=ii513

PRINCIPLES OF NAVAL ENGINEERINGmust be manually shut down. Hence, the emergencyswitchboard and distribution system arealways energized either by a ship's servicegenerator or by the emergency generator.Therefore, the emergency distribution systemcan always supply power to a vital load if boththe normal and the alternate sources of theship's service power to this load fail. Theemergency generator is not started if the emergencyswitchboard can receive power from aship's service generator.A feedback tie from the emergency switchboardto the ship's service switchboard (fig.20-24) is provided on most ships. The feedbacktie permits a selected portion of the ship'sservice switchboard load to be supplied fromthe emergency generator. This feature facilitatesstarting up the machinery after majoralterations and repairs and provides power tooperate necessary auxiliaries and lighting duringrepair periods when shore power and ship'sservice power are not available.CASUALTY POWERThe casualty power distribution system isprovided for making temporary connections tosupply electric power to certain vital auxiliariesif the permanently installed ship's service andemergency distribution systems are damaged.The casualty power system is not intended tosupply power to all the electrical equipment inthe ship but is confined to the facilities necessaryto keep the ship afloat and to get it awayfrom a danger area. The system also supplies alimited amount of armament, such as antiaircraftguns and their directors, that may benecessary to protect the ship when in a damagedcondition. The casualty power system for riggingtemporary circuits is separate and distinctfrom the electrical damage control equipment,which consists of tools and appliances for cuttingcables and making splices for temporaryrepairs to thepermanently installed ship's serviceand emergency distribution systems.The casualty power system includes portablecables, bulkhead terminals, risers, switchboardterminals, and portable switches. Portablecables in suitable lengths are stowed in convenientlocations throughout the ship. The bulkheadterminals are installed in watertightbulkheads so that the horizontal runs of cablescan be connected on the opposite sides to transmitpower through the bulkheads without the lossof watertight integrity. The risers are permanentlyinstalled vertical cables for transmittingpower through the decks without impairingthe watertight integrity of the ship. A riserconsists of a cable that extends from one deckto another with a riser terminal connected toeach end for attaching portable cables.CONTROL AND SAFETY DEVICESThe distribution of electric power requiresthe use of many devices to control the currentand to protect the circuits and equipment.Control devices are those electrical accessorieswhich govern, in some predeterminedway, the power delivered to any electrical load.In its simplest form, the control applies voltageto (or removes it from) a single load. In morecomplex control systems, the initial switch mayset into action other control devices that governthe motor speeds, the compartment temperatures,the depth of liquid in a tank, the aimingand firing of guns, or the direction of guidedmissiles.Switchboards make use of hand-operated(manual) switches as well as electrically operatedcontrols. Manually operated switches arethose familiar electrical items which can beoperated by motions of the hand, as with apushing, pulling, or twisting motion. The typeof action required to operate the manuallyoperated switch is indicated by the names ofthe controls—push-button switch, pull-chainswitch, or rotary switch.Automatic switches are devices which performtheir function of control through therepeated closing and opening of their contacts,without requiring a human operator. Limitswitches and float switches are representativeautomatic switches.The Navy uses many different types ofswitches and controllers, which range from thevery simple to the very complex. A typical a-cacross-the-line magnetic controller is shownin figure 20-25.The simplest protective device is a fuse,consisting of a metal alloy strip or wire andterminals for electrically connecting the fuseinto the circuit. The most important characteristicof a fuse is its current-versus-timeor "blowing" ability. Three time ranges forexistence of overloads can be broadly definedas fast (5 microseconds through 1/2 second),medium (1/2 second to 5 seconds), and delayed(5 to 25 seconds).514

Chapter 20. -SHIPBOARD ELECTRICAL SYSTEMSFigure 20-25.— A-c magnetic controller.77.73X515

PRINCIPLES OF NAVAL ENGINEERINGNormally, when a circuit is overloaded orwhen a fault develops, the fuse element meltsand opens the circuit that it is protecting. However,all fuse openings are not the result ofcurrent overload or circuit faults. Abnormalproduction of heat, aging of the fuse element,poor contact due to loose connections, oxides orother corrosion products forming within the fuseholder, and unusually high ambient temperatureswill alter the heating conditions and thetime requiredfor the element to melt.A more complex type of protective deviceis the circuit breaker. In addition to acting asprotective devices, circuit breakers perform thefunction of normal switching and are used toisolate a defective circuit while repairs arebeing made.Circuit breakers are available in manytypes; some may be operated both manuallyand electrically, while others are restricted toone mode of operation. Figure 20-26 shows acircuit breaker which may be operated eithermanually or electrically. When operated electrically,the operation is usually in conjunctionwith a pilot device such as a relay or switch.Electrically operated circuit breakers employan electromagnet, used as a solenoid, to trip arelease mechanism that causes the breakercontacts to open. The energy to open the breakeris derived from a coiled spring, and the electromagnetis controlled by the contacts in a pilotdevice.Circuit breakers designed for high currentshave a double-contact arrangement, consistingof the main bridging contacts and the arcingcontacts. When the circuit opens, the main contactsopen first, allowing the current to flowthrough the arc contacts and thus preventingburning of the main contacts. When the arccontacts are open, they pass under the frontof the arc runner, causing a magnetic field to beset up which blows the arc up into the arcquencher and quickly opens the circuit.SYNCHROS AND SERVOMECHANISMSSynchros, as identified by the Armed Forces,are a-c electromagnetic devices which are usedprimarily for the transfer of angular-positiondata. Synchros are, in effect, single-phasetransformers in which the primary-tosecondarycoupling may be varied by physicallychanging the relative orientation of these twowindings.FLEXIBLE CONNECTIONFigure 20-26.— Circuit breaker.^«< ARC QUENCHERSOVERCURRENT TRIP27.73Synchro systems are used throughout theNavy to provide a means of transmitting theposition of a remotely located device to oneor more indicators located away from the transmittingarea.Part A of figure 20-27 shows a simplesynchro system. When the handwheel is turned,an electrical signal is generated by the synchrotransmitter and is transmitted through interconnectingleads to the synchro receivers. Thesynchro receivers will always turn the sameamount and direction and at the same speed asthe synchro transmitter.Part B of figure 20-27 shows the same typeof system using mechanical linkage. As may bereadily seen, mechanical systems are impracticablebecause of the need for associated belts,pulleys, gears, and rotating shafts.Synchro systems are widely used for inputcontrol of electromechanical devices (servomechanisms)that position an object in accordancewith a variable signal. The essentialcomponents of a servomechanism system arethe input controller and the output controller.The input controller provides the means,either mechanical or electrical, whereby the516

Chapter 20. -SHIPBOARD ELECTRICAL SYSTEMSSYNCHROTRANSMITTERNTERCONNECTINGLEADSHANDWHEELRECEIVERSINDICATORDIALSHANDWHEELRECEIVERSINDICATORDIALS(B)Figure 20-27.— Simple synchro system.72.38human operator may actuate or operate a remotelylocated load.The output controller of a servomechanismsystem is the component (or components) inwhich power amplification and conversion occur.This power is usually amplified by vacuumtubeor magnetic amplifiers and then convertedby the servomotor into mechanical motion ofthe direction required to produce the desiredfunction.Figure 20-28 shows a simplified block diagramof a servomechanism. When the shaft ofthe input controller is rotated in either direction,a voltage is induced in the rotor of thecontrol transformer. This voltage is fed to theamplifier, where it is sent through the necessary517

PRINCIPLES OF NAVAL ENGINEERINGstages of amplification, and drives the servomotor.DEGAUSSING INSTALLATIONSA ship is a magnet because of the presenceof magnetic material in its hull and machinery.A ship is therefore surrounded by a magneticfield which is strong near the ship and weak at aconsiderable distance from the ship. As a shippasses over a point on the surface of the earth,the magnetic field of the ship is superimposedupon the magnetic field of the earth, thus tendingto distort the earth's field around the ship. Ifthe ship is close to a magnetic mine or torpedo,the distortion caused by the ship's field willactivate the firing mechanism to detonate themine or torpedo.Degaussing equipment is installed aboardship to neutralize the disturbance of the earth'smagnetic field caused by the ship, and thus toreduce the possibility of detonating a magneticmine or torpedo. A shipboard degaussing installationconsists of one or more coils of electriccable in specific locations inside the ship's hull,a d-c power source to energize these coils, anda means of controlling the magnitude and polarityof the current through the coils. Compasscompensatingequipment, consisting of compensatingcoils and control boxes, is also installedas a part of the degaussing system, to compensatefor the deviation effect of the degaussingcoils on the ship's magnetic compasses.Naval ships are tested periodically at magneticrange stations to determine the configurationof the ship's magnetic field. SensitiverOUTPUT CONTROLLEROUTPUT

Chapter 20. -SHIPBOARD ELECTRICAL SYSTEMSwork on electrical equipment should be performedonly by duly authorized and assignedpersons.When any electrical equipment is to beoverhauled or repaired, the main supply switchesor cutout switches in each circuit from whichpower could possibly be fed should be securedin the open position and tagged. The tag shouldread: "This circuit was ordered open for repairsand shall not be closed except by directorder of." The name given is usuallythe name of the person directly in chargeof the repairs. After the work has been completed,the tag or tags should be removed bythe same person.The covers of fuse boxes and junction boxesshould be kept securely closed except when workis being done. Safety devices such as interlocks,overload relays, and fuses should never bealtered or disconnected except for replacements.Safety or protective devices must neverbe changed or modified in any way without specificauthorization.Fuses should be removed and replaced onlyafter the circuit has been deenergized. When afuse blows, it should be replaced only with afuse of the correct current and voltage ratings.When possible, circuit should be carefullychecked before the replacement is made, sincethe burned-out fuse is often the result of acircuit fault.519

CHAPTER 21OTHER AUXILIARY EQUIPMENTIn addition to the shipboard auxiliary machinerydescribed in previous chapters of this text,there are a number of other units of machinerythat are essential to the operation of a ship andwhich are directly or indirectly of concern toengineering department personnel. Such auxiliarymachinery includes steering gears andtheir remote control equipment, elevators,winches, capstans, windlasses, and catapults.Some of this machinery may be located withinthe engineering spaces of the ship; but many ofthe units are located outside the engineeringspaces and are sometimes referred to as out -side machinery .ELECTROHYDRAULIC TRANSMISSIONSome shipboard auxiliary machinery mustoperate at variable speeds over a considerablerange. In addition, there must be close controlof speed between minimum and maximum limits.Many auxiliary machines operate with a highstarting torque and must be capable of acceleratingto maximum speed very quickly. Tomeet these requirements, the electrohydraulictransmission is used on naval ships. Since theelectrohydraulic transmission is utilized inmore than one type of auxiliary machine, it isdiscussed first.Electrohydraulic transmissions are usedfordriving or controlling machinery such as steeringgears, gun turrets, anchor windlasses, boatand airplane handling equipment, capstans,hoists, and certain shipboard valves. Someelectrohydraulic transmissions are designed todeliver rotary motion; others are designed todeliver reciprocating motion.An electrohydraulic transmission designedto deliver rotary motion to an auxiliary machineconsists basically of an electric motor, a hydraulicpump, a hydraulic motor, and piping toallow the flow of fluid from and to the pumpthrough the motor. The pump is of the variabledisplacement reversible type^; it is sometimescalled the A-end of the transmission. A complexmachinery system may include one or morepumps and one or more motors. The hydraulicmotor of an electrohydraulic transmission issimilar in design to the pump, except that themotor is usually of fixed displacement. Occasionally,to provide very wide speed variation,the motor may also be of the variable displacementtype. A hydraulic motor for use in anelectrohydraulic transmission is shown in figure21-1.The components, control equipment, andpiping system for an electrohydraulic transmissionused to drive a winch are illustratedin figure 21-2. The transmission illustrated istypical of those designed to deliver rotarymotion to various types of shipboard auxiliarymachinery.The pump is driven at constant speed by anelectric motor. The hydraulic motor is drivenby the fluid under pressure, and the auxiliarymachine is driven by the mechanical output ofthe motor. By controlling the variable output ofthe pump, the direction and speed of rotation ofthe motor can be controlled; therefore, thedirection and speed of motion utilized in theoperation of the auxiliary machine can be controlled.The flow of fluid under pressure from thepump to the motor exerts force on the faces ofthe pistons open to the valve port receiving thefluid under pressure. This force on the pistonresults in a thrust component along the axis ofrotation of the socket ring and a turning componentat right angles to the thrust component.Operating principles of variable displacement pumpsare discussed in chapter 15 of this text.520

Chapter 21. -OTHER AUXILIARY EQUIPMENTSOCKET RINGOUTPUTSHAFTPISTON(ONE OF 9)FIXED TILTVALVE PLATECYLINDER BARRELFROM A-ENDTO A-ENDFigure 21-1.— Hydraulic motor for electrohydraulic transmission.110.23(See fig. 21-3.) the turning component rotatesthe socket ring. The rotation of the socket ringcauses the cylinder barrel and output shaft ofthe motor to rotate, and thereby provides therotary motion utilized to drive a machine.When reciprocating motion is required, asin the case of a steering gear (fig. 21-4), themotor of an electrohydraulic transmission isreplaced by a piston or plunger. The completehydraulic assembly of which the plungeris a part is commonly called a ram. Theforce of the hydraulic fluid from the pumpcauses the movement of the piston or plunger.The tilting box in the pump can be controlledeither locally (as on the anchor windlass) or byremote control (as on the steering gear).STEERING GEARSThe steering gears installed on naval shipsare of two types: electromechanical and electrohydraulic.Most modern naval ships have steeringgears of the electrohydraulic type; however,electromechanical steering gears are also describedbriefly.ELECTROMECHANICAL STEERING GEARElectric motors were first introduced asprime movers of steering gears on combatantships to serve in case of failure of the steamsteering engines, at one time the only primemover used. Electric motors were used lateras the primary source of power, with steam asa reserve. Steam is no longer used as a primemover for steering gears. The use of electromechanicalsteering gear is now limited to smallnoncombatant vessels.The principles of operation are about thesame for all designs of electromechanical steeringgear. Any differences that exist are chieflyin the manner in which the driving motor isconnected to the tiller and the method by whichthe motor is controlled. The motor may drivethe tiller by means of gears and a quadrant, aright- and left-hand screw assembly (fig. 21-5),or by means of wire rope from a drum. In thegear and quadrant type, the steering engine islocated in the steering gear room; in the wirerope and drum type, it may be installed in anearby machinery space.521

PRINCIPLES OF NAVAL ENGINEERINGPUSH BUTTON MASTER(RESET aEMERGENCY RUNSTARTSTOP)BRAKEAPPLIEDBRAKERELEASEDEMERGENCYDRUM BRAKEFigure 21-2.— Electrohydraulic transmission.147.128The steering motor control may be either ofthe follow-up or the nonfolloiw-up type. In thenonfollow-up type, the motor is controlled by amaster controller at the steering station. Whenthe master controller is brought to neutral,dynamic braking action takes place to slow downthe motor; the motor is finally brought to restand held by a magnetic brake.In the follow-up type of control, the followupfeature is incorporated in a contact ringassembly in the steering stand. The rings makecontact with rollers which control the circuits tocontractors on the control panel. Movement of thesteering wheel rotates the contact rollers in theproper direction to start the motor. Motion of thesteering motor is transmitted through shafting tothe contact ring assembly, which follows up themotion of the rollers. By this action the rudder ismoved an amount proportional to the rotation ofof the steering wheel.Most wire rope and drum type steeringgears utilize a follow-up control arrangement.The follow-up motion is transmitted from thesteering gear to the steering stand by meansof shafting, bevel gears, and flexible couplings.In most electromechanical installations, theshafting connecting the steering engine to thewheel is utilized not only to provide follow-upcontrol to the steering stand but also to providea means for steering by hand from the pilothouse if power is lost.ELECTROHYDRAULIC STEERING GEARSteering gearnaval ships areinstallations on most modernof the electrohydraulic type.522

Chapter 21. -OTHER AUXILIARY EQUIPMENTTURNCOMPONENTSOCKET RING83.82Figure 21-3.— Thrust and turning componentsin hydraulic motor operation.The development of this type of steering gearwas prompted primarily by the large momentaryelectric power requirements for electromechanicalsteering gears—particularly for ships oflarge displacement and high speed, with attendantincreased rudder torques.Electrohydraulic steering gears in use includevarious types of equipment. Some shipboardinstallations have double hydraulic ramsand cylinders; others have single-ram arrangements.(See figs. 21-4 and 21-6.)STEERING GEAR ARRANGEMENTS. -Onlythe pump of the previously described electrohydraulictransmission is used in electrohydraulicsteering gears. Axial-piston variable displacementpumps are used inmost installations;radial-piston pumps are used in some.The pumps are connected by piping to theram cylinders of the steering gear. Two pipesfrom each pump are united at a main transfervalve. The transfer valve is a multiportedvalve which permits the ram cylinders to beconnected to either pump while the pipes fromthe other pump are connected for bypassing.Various methods are used for connecting thehydraulic rams to the tiller. The arrangementsdepend on the design and on the space availablefor the installation. Two common arrangementsare shown in figures 21-4 and 21-6.Typical cruiser steering gear installationsinclude two rams set fore and aft, one on eitherside of the rudder stock. The rams operate therudder through a double yoke tiller fitted withsliding blocks.The gear illustrated in figure 21-6 is typicalof those installed on destroyers. The installationincludes a single ram set athwartship. The ramoperates the rudder through a single yoke tillerfitted with a sliding block.Some cruiser steering gear installations havetwo rams set fore and aft but located forwardfrom the rudder stock (fig. 21-4). The rams areconnected to the tiller by connecting links andpins. Some ships are equipped with twin ruddersand an independent steering gear for eachrudder. Carriers and auxiliary ships may haveany one of the above-mentioned steering geararrangements.PRINCIPLES OF OPERATION.—Regardlessof the type of equipment (double ram or singleram, axial pump or radial pump) included inelectrohydraulic steering installations, the principlesof operation are basically the same. Thedischarge volume and direction of flow from thevariable displacement pumps are controlled bythe operation of the tilting block in the pump.This control is accomplished mechanically bymeans of trick wheels in the steering gearroom, and by remote control from one or moresteering stations.Any movement, right or left, of the controlfrom any of the various steering stations placesthe hydraulic pump on stroke and causes thepump to supply liquid under pressure to thehydraulic rams, resulting in a correspondingright or left movement of the rudder. Thisrudder movement actuates the follow-up gearwhich in turn immediately acts to return thepump control to neutral but does not accomplishthis until the assigned rudder position has beenattained. The rudder is held in the assignedposition by a hydraulic lock until another movementis originated at the steering station.EMERGENCY STEERINGSYSTEMS.-Allnaval combatant and auxiliary ships equippedwith electrohydraulic steering gears are alsoequipped with an auxiliary steering gear. Thisemergency steering system generally consistsof a relief and shuttle valve, hand-operatedhydraulic pump, and the piping, valves, andfittings necessary to complete the system. Theemergency equipment is installed in or near thesteering gear compartment.523

PRINCIPLES OF NAVAL ENGINEERINGSELF SYNCHRONOUSRECEIVERPLANETARYDIFFERENTIAL GEARFigure 21-4.— Arrangement of a double-ram electrohydraulic steering gear.47.139XTo prevent the pressure developed by thehand pump from causing motoring or leakagethrough the main hydraulic units, the pipingfrom the emergency pump to the main hydraulicsystem is so arranged that the highpressurestop valves may be closed. Theemergency pump is usually connected to themain hydraulic system in a manner wherebyall ram cylinders will be in use. Since it isnecessary to block off the emergency systemunder normal steering gear operation, the emergencylines are usually connected to the drainvalves to eliminate the necessity of additionalhigh pressure valves.Some ships are equipped with a dual emergency,submersible steering system. The purposeof this system is to provide emergencysteering by means of either electric motor orhand power in event of failure of the mainsystem. This emergency gear, with drivingmotor integrally mounted, is located in thesteering gear compartment of the ship. Handoperation is accomplished by use of a remotelylocated crank stand connected to theunit by shafting.REMOTE CONTROLS - Electrohydraulicsteering gears may be controlled from remotesteering stations (1) electrically by either apilot motor and its controller or by a synchronoustransmission; (2) hydraulically bymeans of a telemotor system; or (3) mechanicallyby means of wire rope. (See subsequentsection on remote control systems.)Only a few pilot motor control systems arein use; the majority of naval ships utilize eithersynchronous transmission or hydraulic telemotorsystems.In control arrangements for electrohydraulicsteering gears, the trick wheel and the receiverof the control system, either synchronous receiver,hydraulic telemotor receiver, or pilotmotor, are geared to and actuate the pump controlcam through one end of a differential to putthe pump on stroke. The follow-up acts throughthe opposite end of the differential to reverse themovement of the cam and to take the pump offstroke. The differential control unit and cam areso arranged that the control unit may lead therudder by the full amount of rudder travel.REMOTE CONTROL SYSTEMSFOR STEERING GEARControl of the steering gear from the steeringwheel on the bridge may be accomplishedby any of the following remote control systems.524

iChapter 21. -OTHER AUXILIARY EQUIPMENTBRAKE OPERATING ROD DRIVING NOT3 \ LINKPEDESTALTO DECKSECUREDRUDDER^YOKE^ BRAKE BAND'RUDDER STOCKTRANSMISSION SHAFTFROM STEERING ENGINEFigure 21-5. —Right-and-left screw steering gear.47.140XELECTRICAL SYSTEMS. -Steering gearcontrol systems of the electrical type are dividedinto two general types— the direct current pilotmotor type and the alternating current synchronoustransmission type. The direct currentpilot motor type is no longer used on newconstruction.The direct current pilot motor type ofremote control consists of a small reversibledirect current motor which is connected throughthe differential gear to the control shaft of avariable displacement hydraulic pump. The controlof the pilot motor is effected by means of amagnetic contactor control panel located adjacentto the motor and through master controllerslocated at remote control stations. The motoris equipped with a magnetic brake which promptlystops and holds the motor when the mastercontroller is returned to the neutral position.The alternating current synchronous transmissiontype of remote control consists ofinterchangeable receiving and transmitting unitswhich are, in reality, small wound rotor inductionmotors with interconnected three-phaserotor windings; their stator windings are connectedto the same alternating current supply.When the transmitter rotor is turned, the receiverrotor turns at the same speed and inthe same direction.The transmitters are located in steeringstands at remote control stations such as thepilot house, conning tower, central station,etc., and are mechanically connected throughgearing to the wheels. A transmitter at one ofthe remote stations is electrically connected toa receiver in the steering room. Where morethan one remote steering station is provided,as on cruisers and carriers, a switch is providedfor selecting the desired control station.Indicating lights are provided on the steeringstands and at the selector switch to indicate theselected circuit and the power available.The receiver is connected to the control shaftof the variable displacement hydraulic pumpthrough a differential. On large hydraulic unitswhere the torque required to stroke the pump isgreater than the torque that can be exerted bythe receiver, the stroke is controlled through anauxiliary hydraulic servosystem. In installationsinvolving the use of a servosystem, the synchronousreceiver actuates a pilot valve whichcontrols the flow of oil, under pressure, toand from a power cylinder. The direction andamount of motion of the power piston controlsthe stroke of the main pump which actuates therudder.Electrical control circuits from the transmitterselector switch (from the pilot houseselector switch in the case of destroyers andauxiliary vessels) to the steering gear compartmentare installed in duplicate. Drum-typeselector switches, one in the steering room andone located at the terminus of the duplicate runof control circuits, are provided for selectingthe port or starboard cable. When independentsynchronous receivers are provided for each525

PRINCIPLES OF NAVAL ENGINEERINGAUTOMATIC BYPASSVALVESTEERING WHEELON AFTER DECK HOUSE .TRANSMIHER UNIT,||_SLSTEERING WHEELON BRIDGEELECTRIC CONTROlISYSTEMTRANSMIHER UNITCRANK FOR HAND OPERATIONOF PORT PUMPPORTRUNNING ELEC. MOTORWORM WHEELRECEIVING UNITt>«f>mi!mfl>.TRANSFER SWITCH TRANSMITSCURRENT THROUGH EITHERCABLE OR EITHER TRANSMIHERTO RECEIVER AS SELEOEDf*' TRICK WHEEL FORHAND CONTROLSTBD.CniNDER.AUTOMATIC BYPASS VALVEsuppLyRETURNSTARBOARDIDLE ELEaRICMOTORWORMWHEEL^^WORMSPIRAL GEARSH-HFigure 21-6.— Single-ram electrohydraulic steering gear.27.83Xsteering gear, an additional switch is providedin the steering room for selecting the properreceiver.HYDRAULIC TELEMOTOR SYSTEM. -Atelemotoris a hydraulic device by means of whichthe motion of the steering gear is controlledfrom the pilot house. In general, telemotorsystems are employed for remote steeringcontrol where it is impractical to provide anelectrical synchronous transmission systemand where the length of runs of shafting orwire rope and the paths for such shafting orropes would make the use of these types ofmechanical controls impracticable.The hydraulic telemotor system consists ofone or more transmitters located at remotesteering stations connected by piping to areceiver or receivers located in the steeringengineroom. Each transmitter unit is either aa pair of cylinders or a fixed-delivery pistontypepump connected so that movement of thesteering wheel causes fluid to flow through thesystem, resulting in a corresponding movementof the plungers in the receiver unit. Thereceiver unit is connected by suitable means tothe pump control or valve operating mechanismof the steering engine. The principal componentsof a hydraulic telemotor control system areshown schematically in figure 21-7.WIRE ROPE SYSTEM.-This type of remotecontrol is found in some small ships. Thesteering engine control mechanism is connectedto the wheel by wire ropes. The system has thedisadvantages of requiring long leads involvinglarge friction loads; of the ropes being vulnerableto gunfire above decks; of impairing watertightintegrity by passage of the cables throughbulkheads and decks; and of requiring a526

Chapter 21. -OTHER AUXILIARY EQUIPMENTPILOT HOUSESTEERIt4G WHEELINDICATOR LIGHTSTO PILOT HOUSE TOPSTEERING STATIONDISENGAGE CLUTCH WHENSTEERING FROM PILOTHOUSE TOPHELM ANCLE INDICATORDIMMER KNOB AND SWITCH IELECTRIC HELM ANGLE RECEIVERENGAGE CLUTCH WHEN STEERINGFROM PILOT HOUSE TOPSTEERING CONSOLE(IN PILOT HOUSE)ELECTRIC CABLE TO HELMANGLE TRANSMITTERLIQUID LEVEL GAGE(TRUE LOCATION ON OPPOSITE SIDE)BYPASS VALVE LEVERAUTO STEERINGINTERLOCK SWITCHBYPASS VALVEHYDRAULIC PUMP(CUTAWAY TO SHOWPISTONS, AND TILTED PLATE)HYDRAULIC CYLINDERADJUSTABLE STOPHELM ANGLE TRANSMITTERRACK AND PINION(IN STEERING GEAR COMPARTMENT)FILLING OR CHARGINGCONNECTIONFigure 21-7.— Hydraulic telemotor control system.47.142X527

PRINCIPLES OF NAVAL ENGINEERINGcomparatively great amount of time for maintenance,ELECTROHYDRAULIC ELEVATORSMany naval ships are equipped with electrohydraulicelevators which are used to handleairplanes, bombs, freight, mines, torpedoes,ammunition, and other material. Electrohydraulicelevators may be divided into two generaltypes: the direct plunger lift and the plungeractuatedwire rope lift.DIRECT PLUNGERLIFT ELEVATORS.-The platform of the direct plunger lift typeelevator is raised and lowered by direct connectionunder the platform, with one or morevertical hydraulic rams. Oil from a high pressuretank is directed into the ram during thehoisting operation. Lowering is accomplishedby the oil being discharged from the rams intoa low pressure tank. Pressure is maintainedin the high pressure tank by means of twoelectrical variable displacement pumps, whichtake suction from the low pressure tank. Oneof the pumps is capable of maintaining elevatoroperation atreduced speed. Two electric sumppumps keep the volume of oil in the pressuresystem within specified limits.Special control valves (operated by pilotvalves or a motor) in the pressure and exhaustlines regulate elevator speeds by varying theamount of oil admitted to or discharged fromthe rams. Positive stops and mechanical locks,interlocked with the elevator control system,enable the platform to be stopped, locked, andheld in position at deck level. An equalizersystem maintains the platform at uniform levelunder conditions of unequal loading. Automaticquick-closing valves in the oil line prevent anunrestricted fall of the elevator.PLUNGER-ACTUATED WIRE ROPE LIFTELEVATORS.— The primary difference betweenthe direct plunger lift elevator and the plungeractuatedwire rope lift elevator is that thelatter type is raised by wire rope fastened tothe platform at two or four symmetricallylocated points. Most hydraulic airplane elevatorsare of the plunger-actuated wire rope lift type.The wire ropes in an airplane elevator, througha series of sheaves, are actuated by a horizontalhydraulic ram located beneath the hangar deck.Hydraulic bomb elevators differ fromplunger-actuated wire rope lift elevators in thatthe hoisting wire ropes are wound on drumsdriven through reduction gears by the hydraulicmotor. Raising, lowering, or speed changes areaccomplished by varying the stroke of thevariable delivery pump through differentialgearing. Hydraulic accumulators are not usedwith hydraulic bomb elevators,WINCHESA winch is a deck machine used for hoistingor hauling loads. The main components of awinch are a wire rope drum (or drums), a reductiongear train, and a power unit. Somewinches are provided with one or two gypsyheads for handling manila or other fiber lines.Most ships constructed before World War IIwere provided with steam-powered winches, afew of which remain in naval service. DuringWorld War II, Auxiliary ships were providedwith winches powered by either alternating ordirect-current electric motors. On modernships, a-c electric drive winches are used.Figure 21-8 shows an a-c electric motor drivewinch.Where stepless speed control between zeroand design maximum is required, a variablespeed hydraulic transmission is included betweenthe electric motor and the gear train onthe same bed frame. The variable speed hydraulictransmission consists of a variablevolume pump connected by high pressure tubingto a hydraulic motor, which is usually of thefixed-displacement type. The fluid output fromthe pump passes through the motor and returnsto the pump in a closed circuit, and the speed ofthe motor varies as the volume of fluid from thepump varies. The speed and direction of rotationof the motors are obtained through a manuallyoperated lever control at the pump or at a remotestation. Figure 21-9 shows a typical electrohydraulicwinch.One type of steam-driven winch is illustratedin figure 21-10. The winch illustrated is equippedwith two gypsy heads (1), one mounted at eachend of the main drive shaft, and a single hoistingdrum (10), The drum is provided with astandard type of brake band (3) with a foot-operatedcontrol and ratchet lock. The winch isdriven by a two-cylinder, single-expansion,double-acting reciprocating engine. The driveis by means of a train of spur gears, A gearshift is provided to give two drive speeds.The clutch mechanism consists of a sleeve(11) which is keyed to the crankshaft (12) and528

Chapter 21. -OTHER AUXILIARY EQUIPMENTSPEEDCONTROLBOXELECTRICBRAKEFigure 21-8.— A-C electric motor drive winch.80.149provided with a shifter yoke which is operatedby a lever (7) located near the reverse valve(9). When this lever is moved to the left, theposition shown in part A of figure 21-10, thepinion which is integral with it is engaged withthe gear (2) on the intermediate shaft. This isthe "compound gear" position and gives a slowerdrum speed with an increase in available linepull. When the shifter lever (7) is moved to theright, the driving sleeve is shifted to the right.This disengages the pinion from the intermediateshaft gear (2) and engages the square jawclutch (13) and pinion which is always in meshwith the main drive gear. This gives a directdrive from the crankshaft to the main shaft, andis called the "single gear" position. The "singlegear" gives a higher-drum speed for a givenengine speed, but with a decrease in the availableline pull.The speed and direction of rotation of theengine is controlled by a hand lever (14). Withthe winch in compound gear, the drum turns tolift a load when the hand lever is raised. Withthe lever in this position, a spool type valvepasses steam from the reverse valve (9) throughthe two top horizontal pipe lines (5) to thecylinders where it drives the engine. The twolower pipes (4) are exhaust lines. When the leveris lowered below the horizontal position, thedirection of steam flow is reversed and theengine turns in the opposite direction, thuslowering the load. On some winches, the handlever is provided with an automatic latch forholding it in the horizontal, or neutral position.529

PRINCIPLES OF NAVAL ENGINEERINGROPE DRUM^ROPE DRUM BAND BRAKE-DOUBLE CLUTCHROPE DRUM_^SPUR GEARSL.H WORM DRIVEGYPSY HEADHYDRAULIC MOTORAC ELECTRICMOTORFigure 21-9.— Typical electrohydraulic winch.47.145For all other positions, the lever must be heldin position for the desired speed.CAPSTANSA capstan is a spool-shaped, vertical revolvingdrum used for heaving in on heavymooring lines. When a capstan is used to haida load, as in mooring, several turns of mooringline are placed around the capstan head. Amanpower strain is then taken on the free endof the line.Maintaining the strain causes the lineto bind on the capstan head, which in turn haulsthe load.A capstan head may be a component part ofan anchor windlass. Since the shaft for a capstanhead is vertical, a capstan is always free of thefair lead problem which is often present inconnection with gypsy heads which are mountedon horizontal shafts. A line leads fair to acapstan from any horizontal direction. Capstansthat are not components of anchor windlassesare usually electrically powered.ANCHOR WINDLASSESA windlass is a piece of deck machineryused primarily for paying out and heaving inan anchor chain. A wildcat (drum) may bemounted vertically or horizontally at the endof the windlass shaft for handling the anchorchain. The wildcat is usually fitted with whelpsto engage the anchor chain. On the windlassthere may also be a capstan head or warpinghead (concave drum) for handling lines. Avertical-shaft anchor windlass with capstanhead is shown in figure 21-11.All anchor windlasses were formerlypowered by steam, and some windlasses onauxiliaries still use steam as the source ofpower. Small combatant ships have electricallypowered windlasses; larger combatant shipshave vertical -shaft windlasses with electrohydraulictransmission. Hand-operated windlassesare in use, but they are found only on smallships where the weight of the anchor gear issmall enough to be handled in a reasonable530

Chapter 21. -OTHER AUXILIARY EQUIPMENT47.144Figure 21-10.— Steam-operated winch. (A) Plan view. (B) Side view. (C) Reversingthrottle valve.531

PRINCIPLES OF NAVAL ENGINEERINGFRICTION BRAKEHANDWHEEL(WEATHER DECK)GEAR CASINGMOTOR BRAKE-ANCHORCHAIN3.224XFigure 21-11.— Vertical-shaft anchor windlass.time and without excessive effort on the partof operating personnel,CARRIER CATAPULTSThe efficiency of an aircraft carrier dependsupon the speed of its airplane launching operations.Therefore, a compact and efficient devicefor getting all airplanes into the air within a shorttime is needed. This requirement is met by themodern carrier catapult. The catapult permitscontrolled application of a predetermined amountof power at any desired instant. Through thecontrolled power of the catapult, the plane on thecatapult is safely accelerated from a standstillto flying speed within the limited space availableon the flight deck of a carrier.The type of catapults used during World WarII and through the Korean incident were of thepneumatic-hydraulic type. Catapults of this typeadequately met launching requirements, but thegradual increase in the weight of newly designedaircraft and the attendant higher launchingspeeds continually necessitated the developmentof larger and heavier catapults. By 1950,the size and weight of the pneumatic-hydraulictype catapult had increased to a point whereany further increase would be impracticable.British investigation of steam as the sourceof power for catapults attracted the attentionof U. S. Navy officials; the Navy's powerfulsteam catapult of today is the result of basicBritish research.^ The present discussion dealsonly with the steam catapult.The major components of a steam catapultare shown schematically in figure 21-12.During the operational cycle of the steamcatapult, the plane is first spotted astride thecatapult slot slightly aft of the shuttle. Theairplane is coupled with the shuttle by meansof the bridle which slips over the shuttle hookand over the hooks mounted on the undersideof the airplane frame. The airplane is anchoredto the deck by means of the holdback devicewhich is released at the moment of launch.The grab, attached to the shuttle, pushes forwardafter the bridle is attached so that theshuttle puts tension on the bridle.When the airplane is ready to be launched,with its engines running at full power, thelaunching valves are opened and steam is admittedto the after side of each piston. Theresulting accelerating force combined with theengine thrust causes a calibrated "breaking"link in the holdback to part and the grab releasesthe shuttle. The sliuttle and airplane arefree to be moved forward by the acceleratingforce.At the end of the launching run, the planeis airborne and the bridle is automaticallyreleased from the hook. The brake stops thepiston-shuttle assembly. The grab, drivenby the retracting engine, now moves along thetrack, hooks the shuttle, and returns it to thelaunching or battery position.The principal component of the steam catapultis a cylinder-piston assembly—two power cylindersand two pistons per catapult. Thespear-tipped pistons, which in the launchingFor greater detail on the history and operation ofthe steam catapult, see The Steam Catapult, NavAer00-80T-69.532

Chapter 21. -OTHER AUXILIARY EQUIPMENTTOWING BRIDLEHOOKPOWERPISTONS SHUTTLE CYLINDERS BRAKEL LFigure 21-12.— Major components of a steam catapiolt.47.146operation are forced at high speed throughthe cylinders by steam pressure, are solidlyinterconnected by means of a connector shapedlike an inverted T. The vertical leg of theinverted T extends upward through a slot inthe flight deck, and serves as the hook towhich the aircraft towing bridle is connected.The piston connector is attached to the shuttle.The shuttle is a small roller -mounted carwhich moves, during the launch, on tracks installedjust under the flight deck. (See fig. 21-13.)Power to drive the shuttle and its airplaneload comes from expanding steam piped to thecatapult from the main boilers of the ship. Thissteam is placed under pressure in large tankscalledaccumulators or receivers—located underthe launching engine on the hangar deck.From the receivers, the steam is transferredFigure 21-13.— Shuttle-connector-piston assembly for steam catapult.147.131533

PRINCIPLES OF NAVAL ENGINEERINGat the moment of launch into the power cylinders.Steam pressure acts directly on thepistons and propels the piston- shuttle assemblythrough the cylinders. A sealing strip closes theslot in each cylinder as the pistons are drivenforward, thus preventing the escape of steamfrom the cylinder slots through which the connectormoves.Prior to a launch, the engines of an airplanemust be operating at full power. A holdbackdevice is utilized to prevent the airplane frombeing moved forward by the thrust of its ownengines, until the time of launch. The holdbackdevice hooks into a fitting in the flight deck.The piston-connector-shuttle assembly isstopped at the end of its launching run by a waterbrake. The brake consists of two cylinders ofwater locatedco-axially with the power cylindersat the forward end of the catapult. The spear tipsof the pistons ram into the water-filled cylinders.As the spear tips penetrate the water, pressurebuilds up and stops the assembly. (See fig. 21-14.)The principal unit in the shuttle retractionand tensioning systems is the grab. This unit isessentially a spring-loaded latch mounted on awheeled frame just aft of the shuttle. The grabis driven along the shuttle track through a systemof cables by hydraulic force. The hydraulic retractionengine consists of two cylinders. In onecylinder, hydraulic pressure is converted intothe mechanical motion of a piston rod which isinstalled in this cylinder. The other cylinder isan accumulator in which hydraulic liquid isstored under pressure. The motion of the pistonrod is transmitted to a device called a crossheadto which the drive cables of the grab are attached,(See fig. 21-15.)Prior to a launch, the grab is moved forwardby a hydraulic cylinder-piston assembly. Thisassembly is located aft of the grab. (See fig.21-16.) When liquid is introduced into the cylinder,the piston pushes the grab forward. Thegrab, in turn, exerts force on the shuttle so thatit moves forward enough to place tension on thetowing bridle which connects the shuttle to theairplane. When the launch is made, the grab releasesthe shuttle and it is driven through thepower cylinders of the catapult by steam pressure.After the launch is made, the grab isM^-^-

pChapter 21. -OTHER AUXILIARY EQUIPMENT^••u—;L*'giw

System, SubtyUem, or ComponentPRINCIPLES OF NAVAL ENGINEERING

Chapter 21. -OTHER AUXILIARY EQUIPMENT

..PRINCIPLES OF NAVAL ENGINEERINGSYSTEMAuxiliaryCOMPONENTAnchor WindlassM. R. NUMBERA-5 W-1SUB-SYSTEMWinches, Capstans,Cranes and AnchorHandlingIC 1%.OCSCRIPTION1. Inspect oil levels.2. Test operate windlass.SAFETY PRECAUTIONSRCI. ATEO M. R.NoneRATESMM3TOTAL M/VtM/H0.30.3ELAPSED TIME:0.31. Observe standard safety precautions.2. De-energize circuit and tag "Out Of Service."3. Ensure wildcat is disengaged before starting windlass.TOOLS. PARTS. MATERIALS. TEST EQUIPMENT1. Oil, Symbol 2190 TEP6 Funne 12. Oil, Symbol 2135 H7. 8" Adjustable wrench3. Oil, Symbol 2110 H8. Safety tag4. Flashlight5. RagsPROCEDUREPreliminarya. De-energize circuit and tag "Out Of Service."Inspect Oil Levels .a. Inspect oil level in main gearcase, power unitgear reducer, and hydraulic system storage tank.Proper oil level is at top mark on gauge rod.Replenish gearcase and reducer with oil, Sjmibol2190 TEP; replenish hydraulic system with oil.Symbol 2135 H.b. Inspect oil level in power brake storage tank.Proper level is at center line on gauge. Replenishwith oil. Symbol 2110 H.WARNING: Ensure wildcat is disengaged before startingwindlass2. Test Operate Windlass .a. Remove safety tag and energize circuit.b. Operate unit; inspect for proper operation.LOCATION1 July 1965Figure 21-18. —Maintenance Requirement Cards— continued. 98. 176538

Chapter 21. -OTHER AUXILIARY EQUIPMENTdriven along the track by the retraction engine,hooks onto the shuttle, and returns it to thelaunching position.AUXILIARY EQUIPMENT OPERATION,MAINTENANCE AND SAFETYThe operation and safety pertaining to auxiliaryequipment should be in accordance withNavShips Technical Manual and/or the instructionsposted on or near each individual piece ofequipment. All maintenance actions, tests, andinspections should be accomplished in accordancewith the 3-M System (PMS Subsystem).Figure 21-17 (Maintenance Index Page) showsthe minimum maintenance requirements for asteering gear. Examples of maintenance requirementsfor two types of auxiliary equipmentare shown in figure 21-18. Note that the MaintenanceRequirement Cards list safety precautionsto be observed, the tools, parts, materials,and test equipment required, and give the proceduresto follow when performing the specifiedmaintenance.539

PART V-OTHER TYPES OF PROPULSIONPLANTSChapter 22Chapter 23Chapter 24Chapter 25Diesel and Gasoline EnginesGas TurbinesNuclear Power PlantsNew Developments in Naval EngineeringThe conventional steam turbine propulsion plant, although widely used,is by no means the only propulsion plant in naval use. Chapter 22 dealswith internal combustion engines of the reciprocating type— diesel andgasoline. Chapter 23 discusses the increasingly important gas turbineengine. Chapter 24 takesupthenuclearpower plant— a plant which utilizesthe steam turbine as a prime mover but which employs the nuclear reactorrather than the conventional boiler as a source of heat for the generationof steam. Chapter 25providesabrief survey of new developments in navalengineering and indicates some of the areas in which future developmentsmay change the nature of our present shipboard engineering plants.541

CHAPTER 22DIESEL AND GASOLINE ENGINESMuch of the machinery and equipment discussedin the preceding chapters utilizes steamas the working fluid in the process of convertingthermal energy to mechanical energy . This chapterdeals with internal combustion engines, inwhich air (or a mixture of air and fuel) servesas the working fluid. The internal combustionengines considered are those to which thethermodynamic cycles of the open and heatedenginetypes^ apply. In engines which operateon these cycles, the working fluid is taken intothe engine, heat is added to the fluid, theenergy available in the fluid is utilized, andthen the fluid is discarded. During the process,thermal energy is converted to mechanicalenergy. The purpose of this chapter is to presentthe basic theory and the fundamentalprinciples underlying the energy conversionin internal combustion engines, and the functionsof the engine parts, accessories, and systemsessential for the conversion. No attempt ismade to describe design, construction, models,etc., except as necessary to make the theory ofoperation and the function of components readilyunderstandable.Internal combustion engines are used extensivelyin the Navy, serving as propulsionunits in a variety of installations such as ships,boats, airplanes, and automotive vehicles. Ehginesof the internal combustion type are alsoused as prime movers for auxiliary machinery.Internal combustion engines in a majority ofthe shipboard installations are of the reciprocatingtype. In relatively recent years, enginesof the gas turbine type have been placed in Navyservice as power plants. Gas turbine engines arediscussed in chapter 23 of this text.Thermodynamic cycles are discussed in chapter 8 ofthis text.RECIPROCATING ENGINESMost of the internal combustion enginesin marine installations of the Navy are of thereciprocating type. This classification is basedon the fact that the cylinders in which theenergy conversion takes place are fitted withpistons, which employ a reciprocating motion.Internal combustion engines of the reciprocatingtype are commonly identified as diesel and gasolineengines. The general trend in navy serviceis to install diesel engines rather than gasolineengines unless special conditions favor the useof the latter.Most of the information on reciprocatingengines in this chapter applies to diesel andgasoline engines. These engines differ, however,in some respects; the principal differenceswhich exist are noted and discussed,Basic PrinciplesThe operation of an internal combustionengine of the reciprocating type involves theadmission of fuel and air into a combustionspace and the compression and ignition of thecharge. The resulting combustion releases gasesand increases the temperature within the space.As temperature increases, pressure increasesand forces the piston to move. This movement istransmitted through a chain of parts to a shaft.The resulting rotary motion of the shaft isutilized for work; thus, heat energy is transformedinto mechanical energy. In order forthe process to be continuous, the expandedgases must be removed from the combustionspace, a new charge admitted, and then theprocess repeated.In the study of engine operating principles,starting with the admission of air and fuel andfollowing through to the removal of the expandedgases, it will be noted that a series of events543

PRINCIPLES OF NAVAL ENGINEERINGtakes place. The term cycle identifies thesequence of events that takes place in thecylinder of an engine for each power impulsetransmitted to the crankshaft. These eventsalways occur in the same order each time thecycle is repeated. The number of events occurringin a cycle of operation will dependupon the engine type—diesel or gasoline. Thedifference in the events occurring in the cycleof operation for these engines is shown in thefollowing table.The events and their sequence in a cycleoperation for a:DIESEL ENGINEINTAKE of airCOMPRESSION of airINJECTION of fuelIGNITION AND COM-BUSTION of chargeEXPANSION ofREMOVAL of wastegasesGASOUNE ENGINEINTAKE of fuel and airCOMPRESSION of fuelairmixture.IGNITION and COM-BUSTION of chargeEXPANSION of gasesREMOVAL of wasteThe principal difference, as shown in thetable, in the cycles of operation for diesel andgasoline engines involves the admission offuel and air to the cylinder. While this takesplace as one event in the operating cycle of agasoline engine, it involves two events indiesel engines. Thus, insofar as events areconcerned, there are six main events takingplace in the diesel cycle of operation and fivein the cycle of a gasoline engine. This is pointedout in order to emphasize the fact that theevents which take place and the piston strokeswhich occur during a cycle of operation are notidentical. Even though the events of a cycleare closely related to piston position and movement,all of the events will take place duringthe cycle regardless of the number of pistonstrokes involved. The relationship of eventsand piston strokes is discussed later under aseparate heading.The mechanics of engine operation is sometimesreferred to as the mechanical or operatingcycle of an engine; while the heat process whichproduces the forces that move engine parts maybe referred to as the combustion cycle . A cycleof each type is included in a cycle of engine operation.Mechanical CyclesIn the preceding section, the events takingplace in a cycle of engine operation wereemphasized. Little was said about piston strokesexcept that a complete sequence of events wouldoccur during a cycle regardless of the number ofstrokes made by the piston. The number ofpiston strokes occurring during any one seriesof events is limited to either two or four, dependingupon the design of the engine; thus, the4-stroke cycle and the 2-stroke cycle. Thesecycles are known as the mechanical cycles ofoperation.Four- and Two-Stroke Cycles.— Both typesof mechanical cycles are used in diesel andgasoline engines. However, most large gasolineengines in Navy service operate on the4-stoke cycle; a greater number of dieselengines operate on the 2-stroke than on the4-stroke cycle. The relationship of the eventsand piston strokes occurring in a cycle of operationinvolves some of the differences betweenthe 2-stroke cycle and the 4-stroke cycle.RELATIONSHIP OF EVENTS AND STROKESIN A CYCLE .—A piston stroke is the distance apiston moves between limits of travel. Thecycle of operation is an engine operating on the4-stroke cycle involves four piston strokes— intake,compression ,power , and exhaust . In thecase of the 2-stroke cycle, only two strokesapply—power and compression .A check of the previous table listing theseries of events which take place during thecycles of operation of diesel and gasoline engineswill show that the strokes are named tocorrespond to some of the events. However,since six events are listed for diesel enginesand five events for gasoline engines, it is evidentthat more than one event takes place duringsome of the strokes, especially in the case ofthe 2-stroke cycle. Even though this is the case,it is common practice to identify some of theevents as strokes of the piston. This is becausesuch events as intake, compression, power andexhaust in a 4-stroke cycle involve at least amajor portion of a stroke and, in some cases,more than one stroke. The same is true ofpower and compression events and strokes in a2-stroke cycle. Such association of events andstrokes overlooks other events taking place544

Chapter 22. -DIESEL AND GASOLINE ENGINESduring a cycle of operation. This oversightsometimes leads to confusion when the operatingprinciples of an engine are being considered.This discussion points out the relationshipof events to strokes by covering the number ofevents occurring during a specific stroke, theduration of an event with respect to a pistonstroke, and the cases where one event overlapsanother. The relationship of events to strokescan be shown best by making use of graphic representationof the changing situation occurring ina cylinder during a cycle of operation. Figure22-1 illustrates these changes for a 4-strokecycle diesel engine.The relationship of events to strokes is morereadily understood, if the movements of a pistonand its crankshaft are considered first. In part Aof figure 22-1, the reciprocating motion andstroke of a piston are indicated and the rotarymotion of the crank during two piston strokes isshown. The positions of the piston and crank atthe start and end of a stroke are marked "top"and "bottom, " respectively. If these positionsand movements are marked on a circle (part B,fig 22-1) the piston position, when at the top ofastroke, is located at the top of a circle. Whenthe piston is at the bottom of a stroke, the pistonposition is located at the bottom center of thecircle. Note in parts A and B of figure 22-1 thatthe top center and bottom center identify pointswhere changes in direction of motion take place.In other words, when the piston is at top center,upward motion has stopped and downward motionis ready to start or, with respect to motion,the piston is "dead."The points which designate changes in directionof motion for a piston and crank arecommonly called top dead center (TDC) andbottom dead center (BDC).If the circle illustrated in B is broken atvarious points and "spread out" (part C, fig.22-1), the events of a cycle and their relationshipto the strokes and how some of the eventsof the cycle overlap can be shown. TDC andBDC should be kept in mind since they identifythe start and end of a stroke and they are thepoints from which the start and end of eventsare established.By following the strokes and events as illustrated,it can be noted that the intake event startsbefore TDC, or before the actual down stroke(intake) starts, and continues on past BDC, orbeyond the end of the stroke. The compressionevent starts when the intake event ends, but theupstroke (compression) has been in processsince BDC. The injection and ignition eventsoverlap with the latter part of the compressionevent, which ends at TDC. The burning of thefuel continues a few degrees past TDC. Thepower event or expansion of gases ends severaldegrees before the down (power) stroke endsat BDC. The exhaust event starts when the powerevent ends and continues through the completeupstroke (exhaust) and past TDC. Note the overlapof the exhaust event with the intake event ofthe next cycle. The details on why certainevents overlap and why some events are shorteror longer with respect to strokes will be coveredlater in this chapter.From the preceding discussion, it can beseen why the term "stroke" is sometimes usedto identify an event which occurs in a cycle ofoperation. However, it is best to keep in mindthat a stoke involves 180° of crankshaft rotation(or piston movement between dead centers) whilethe corresponding event may take place during agreater or lesser number of degrees of shaftrotation.The relationship of events to strokes in a2-stroke cycle diesel engine is shown in figure22-2. Comparison of figures 22-1 and 22-2 revealsa number of differences between the twotypes of mechanical or operating cycles. Thesedifferences are not too difficult to understand ifone keeps in mind that four piston strokes and720° of crankshaft rotation are involved in the4-stroke cycle while only half as many strokesand degrees are involved in a 2-stroke cycle.Reference to the cross-sectional illustrations(fig. 22-2) will aid in associating the event withthe relative position of the piston. Even thoughthe two piston strokes are frequently referredto as power and compression, they are identifiedas the "down stroke" (TDC to BDC) and "upstroke" (BDC to TDC) in this discussion in orderto avoid confusion when reference is made to anevent.Starting with the admission of air, (1) figure22-2, we find that the piston is in the lower halfof the down stroke and that the exhaust event (6)is in process. The exhaust event started (6') anumber of degrees before intake, both startingseveral degrees before the piston reached BDC.The overlap of these events is necessary inorder that the incoming air (1') can aid inclearing the cylinder of exhaust gases. Note thatthe exhaust event stops a few degrees before theintake event stops, but several degrees after theupstroke of the piston has started. (The exhaust545

PRINCIPLES OF NAVAL ENGINEERINGTOP CENTER

Chapter 22. -DIESEL AND GASOLINE ENGINES(2')COMPRESSION(6')EXHAUST(]) SCAVENGINGFigure 22-2.— Strokes and events of a 2-stroke cycle diesel engine.54.20AX547

-PRINCIPLES OF NAVAL ENGINEERINGpermits the burned gases to enter the exhaustmanifold. As the piston moves downward, the intakeports are uncovered (!') and the incomingair clears the cylinder of the remaining exhaustgases and fills the cylinder with a freshair charge (1); thus, the cycle of operation hasstarted again.Now what is the difference between the 2-and 4-stroke cycles? From the standpoint of themechanics of operation, the principal differenceis in the number of piston strokes taking placeduring the cycle of events. A more significantdifference is the fact that a 2-stroke cycleengine delivers twice as many power impulsesto the crankshaftfor every 720° of shaft rotation.(See fig. 22-3.)Diagrams showing the mechanical cycles ofoperation in gasoline engines would be somewhatsimilar to those described for diesel enginesexcept that there would be one less event takingplace during the gasoline engine cycle. Since airand fuel are admitted to the cylinder of a gasolineengine as a mixture during the intake event, theinjection event does not apply.The figures shown here representing thecycles of operation are for illustrative purposesonly. The exact number of degrees before orafter TDC or BDC that an event starts and endswillvary between engines. Information on suchdetails should be obtained from appropriatetechnical manuals dealing with the specific enginein question.Combustion CyclesTo this point, the strokes of a piston and therelated events taking place during a cycle ofoperation have been given greater considerationthan the heat process involved in the cycle. However,the mechanics of engine operation cannotbe discussed without dealing with heat. Suchterms as ignition, combustion, and expansion ofgases, all indicate that heat is essential to acycle of engine operation. So far, particulardifferences between diesel and gasoline engineshave not been pointed out, except the number ofevents occurring during the cycle of operation.Whether a diesel engine or a gasoline engine,the 2- or the 4-stroke cycle may apply. Then,one of the principal differences between thesetypes of engines must involve the heat processutilized to produce the forces which make theengine operate. The heat processes are sometimescalled combustion or heat cycles.The three most common combustion cyclesassociated with reciprocating internal combustionengines are the Otto cycle , the true dieselcycle, and the modified diesel cycle .FOUR STROKE CYCLEDOWNSTROKE (POWER)|UPSTROKE (EXHAUST)|DOWNSTROKE(INTAKE)|UPSTROKE (COMPRESSION)-ONE REVOLUTION OF CRANKSHAFT --ONE REVOLUTION OF CRANKSHAFT- 360°-INJECT lON-IGN ITION-COMBUSTION -Figure 22-3.— Comparison of the 2- and 4-stroke cycles.54.19:.20X548

Chapter 22. -DIESEL AND GASOLINE ENGINESReference to combustion cycles suggests anotherimportant difference between gasoline anddiesel engines— compression pressure. Thisfactor is directly related to the combustion processutilized in an engine. Diesel engines have amuch higher compression pressure than gasolineengines. The higher compression pressure indiesels explains the difference in the methods ofignition used in gasoline and diesel engines.Compressing the gases within a cylinder raisesthe temperature of the confined gases. Thegreater the compression, the higher the temperature.In a gasoline engine, the compressiontemperature is always lower than the point wherethe fuel would ignite spontaneously. Thus, theheat required to ignite the fuel must come froman external source— spark ignition. On the otherhand, the compression temperature in a dieselengine is far above the ignition point of the fueloil; therefore, ignition takes place as a resultheat generated by compression of the air withinthe cylinder— compression ignition.The difference in the methods of ignition indicatesthat there is a basic difference in the combustioncycles upon which diesel and gasolineengines operate. This difference involves thebehavior of the combustion gases under varyingconditions of pressure, temperature, and volume.Since this is the case, the relationship ofthese factors is considered before the combustioncycles,RELATIONSHIP OF TEMPERATURE, PRES-SURE, ANDVOLUME.-The relationship of thesethree conditions as found in an engine can beillustrated by considering what takes place in acylinder fitted with a reciprocating piston. (Seefig. 22-4.)Instruments are provided which indicate thepressure within the cylinder and the temperatureinside and outside the cylinder. Considerthat the air in the cylinder is at atmosphericpressure and that the temperatures, inside andoutside the cylinder, are about 70°F. (See fig.22-4A.)If the cylinder is an airtight container and aforce pushes the piston toward the top of thecylinder, the entrapped charge will be compressed.As the compression progresses, thevolume of the air decreases , the pressure increases, and the temperature rises (see B andC). These changing conditions continue as thepiston moves and when the piston nears TDC(see D) we find that there has been a markeddecrease in volume and that both pressure andtemperature are much greater than at the beginningof compression. Note that pressure hasgone from to 470 psi and temperature has increasedfrom 70° to about 1000° F, These changingconditions indicate that mechanical energy,in the form of work done on the piston, has beentransformed into heat energy in the compressedair. The temperature of the air has been raisedsufficiently to cause ignition of fuel injected intothe cylinder.Further changes take place after ignition.Since ignition occurs shortly before TDC, thereis little change in volume until the piston passesTDC. However, there is a sharp increase inpressure and temperature shortly after ignitiontakes place. The increased pressure forces thepiston downward. As the piston moves downward,the gases expand, or increase in volume,and pressure and temperature decrease rapidly.The changes in volume, pressure, and temperature,described and illustrated here, are representativeof the changing conditions within thecylinder of a modern diesel engine.The changes in volume and pressure in anengine cylinder can be illustrated by diagramssimilar to those shown in figure 22-5, Suchdiagrams are made by devices which measureand record the pressures at various piston positionsduring a cycle of engine operation. Diagramswhich show the relationship between pressuresand corresponding piston positions arecalled pressure-volume diagrams or indicatorcards . Examples of theoretical and actual pressure-volumediagrams are used in this chapterwith the description of combustion cycles.On diagrams which provide a graphic representationof cylinder pressure as related to volume,the vertical line P on the diagram (fig.22-5) represents pressure and the horizontalline V represents volume. When a diagram isused as an indicator card, the pressure line ismarked off in units of pressure and the volumeline is marked off in inches. Thus, the volumeline could be used to show the length of thepiston stroke which is proportional to volume.The distance between adjacent letters on eachof the diagrams represents an event of a combustioncycle— that is, compressionof air, burningof the charge, expansion of gas, and removalof gases.The diagrams shown in figure 22-5 providea means by which the Otto and true diesel combustioncycles can be compared. Reference tothe diagrams during the following discussion ofthese combustion cycles will aid in identifying549

PRINCIPLES OF NAVAL ENGINEERINGFigure 22-4.— Volume, temperature, and pressure relationships in a cylinder.75.4the principal differences existing between thecycles. The diagrams shown are theoreticalpressure-volume diagrams. Diagrams representingconditions in operating engines aregiven later. Information obtained from actualindicator diagrams may be used in checkingengine performance.OTTO (CONSTANT-VOLUME) CYCLE.-Intheory, this combustion cycle is one in which550

Chapter 22. -DIESEL AND GASOLINE ENGINEScompressed air, some of the fuel ignites, thenthe rest of the charge burns. The expansion ofthe gases keeps pace with the change in volumecaused by piston travel; thus combustion is saidto occur at constant pressure (represented byline BC).OTTO CYCLE DIESEL CYCLE75.5Figure 22-5.— Pressure-volume diagramsfor theoretical combustion cycles.combustion, induced by spark ignition, occursat constant volume. The Otto cycle and its principlesserve as the basis for modern gasolineengine designs.Compression (see line A-B, figure 22-5) ofthe charge in the cylinder is adiabatic. Sparkignition occurs at B, and, due to the volatilityof the mixture, combustion practically amountsto an explosion. Combustion, represented byline BC, occurs (theoretically) just as the pistonreaches TDC. During combustion, there is nopiston travel; thus there is no change in the volumeof the gas in the cylinder. This accounts forthe descriptive term, constant volume. Duringcombustion, there is a rapid rise of temperaturefollowed by a pressure increase which performsthe work during the expansion phase, representedby line CD. The removal of gases, represented byline DA, is at constant volume.TRUE DIESEL (CONSTANT-PRESSURE)CYCLE.— This cycle may be defined as one ininduced by compression ig-which combustion,nition, theoretically occurs at a constant pressure.Adiabatic compression (represented byline AB, fig. 22-5) of the air increases its temperatureto a point where ignition occurs automaticallywhen the fuel is injected. Fuel injectionand combustion are so controlled as to giveconstant-pressure combustion (represented byline BC). This is followed by adiabatic expansion(represented by line CD) and constant volume(represented by the line DA).In the true diesel cycle, the burning of themixture of fuel and compressed air is a relativelyslow process when compared with the quick, explosive-typecombustion process of the Ottocycle. The injected fuel penetrates theMODIFIED COMBUSTION CYCLES.- Thepreceding discussion covers the theoreticalcombustion cycles which serve as the basis formodern engines. In actual operation, modernengines operate on modifications of the theoreticalcycles. However, characteristics of thetrue cycles are incorporated in the cycles ofmodern engines. This is pointed out in the followingdiscussion of examples representing theactual cycles of operation in gasoline and dieselengines.The following examples are based on the 4-stroke mechanical cycle since the majority ofgasoline engines use this type of cycle; thus, ameans of comparing the cycles found in bothgasoline and diesel engines is provided. Differencesexisting in diesel engines operating on the2- stroke cycle are pointed out.The illustrations in figures 22-6 and 22-7represent the changing conditions in a cylinderduring engine operation. Some of the events areexaggerated in order to show more clearly thechange which takes place and, at the same time,to show how the theoretical and actual cyclesdiffer.The compression ratio situation and a pressure-volumediagram for a 4- stroke Otto cycleis shown in figure 22-6. Illustration A showsthe piston on BDC at the start of an upstroke,(In a 4- stroke cycle engine, this stroke couldbe either that identified as the compressionstroke or the exhaust stroke.) Notice that inmoving from BDC to TDC (illustration B), thepiston travels 5/6 of the total distance ab. Inother words, the volume has been decreased to1/6 of the volume when the piston was atBDC. Thus, the compression ratio is 6 to 1.Illustration C shows the changes in volumeand pressure during one complete 4- strokecycle. Note that the lines representing the combustionand exhaust phases are not straight asthey were in the theoretical diagram. As in thediagram of the theoretical cycle, the verticalline at the left represents cylinder pressure inpsi. Atmospheric pressure is represented by ahorizontal line called the atmospheric pressureline. Pressures below this line are less thanatmospheric pressures, while pressures above551

PRINCIPLES OF NAVAL ENGINEERINGTOTAL VOLUMEAT TOO.il==:TOTAL VOLUMEAT B DC.A -START OF UPSTROKE(COMPRESSION OR EXHAUST)B-START OF OOWNSTROKE(POWER OR INTAKE)14.7-ONE-HALF CRANKSHAFT REVOLUTION -— TOTAL VOLUME (BDC)C-CYCLEDIAGRAMFigure 22-6.— Pressure-volume diagram, Otto 4-stroke cycle.54.19Bthe line represent compression. The bottomhorizontal line provides a means of representingcylinder volume and piston movement. Thevolume line has been divided into six partswhich correspond to the divisions of volumeshown in illustration A. Since piston movementand volume are proportional, the distance betweenO and 6 indicated the volume when thepiston is at BDC, and the distance from O to 1the volume with the piston at TDC. Thus, thedistance from 1 to 6 corresponds to total pistontravel and units of the distance may be used toidentify changes in volume resulting from thereciprocating motion of the piston.The curved lines of illustration C representthe changes of both pressure and volume whichtake place during the four piston strokes ofthe cycle. To conform to the discussion on therelationship of strokes and events (see fig.22-1), the cycle of operation starts with intake.552

Chapter 22. -DIESEL AND GASOLINE ENGINESTDCBDCATMOSPHERICPRESSURELINEFigure 22-7.— Pressure-volume diagram, diesel 4-stroke cycle.54.19CIn the case of Otto cycle, this event includesthe admission of fuel and air. As indicatedearlier, the intake event starts before TDC,or at point a, illustration C. Note that pressureis decreasing and after the piston reaches TDCand starts down, a vacuum is created whichfacilites the flow of the fuel-air mixture intothe cylinder. The intake event continues a fewdegrees past BDC, ending at point b. Since thepiston is now on an upstroke, compression takesplace and continuesuntil the piston reaches TDC.Note the increase in pressure (xtox') and the decreasein volume (f to x). Spark ignition at cstarts combustion which takes place very rapidly.There is some change in volume since thephase starts before and ends after TDC.There is a sharp increase in pressure duringthe combustion phase. The relative amountis shown by the curve cd. The increase inpressure provides the force necessary to drivethe piston down again. The gases continue toexpand as the piston moves toward BDC, andthe pressure decreasesas the volume increases,from d to e. The exhaust event starts a fewdegrees before BDC, ate, and the pressure dropsrapidly until the piston reaches BDC. As thepiston moves toward TDC, there is a slight dropin pressure as the waste gases are discharged.The exhaust event continues a few degrees pastTDC to point g so that the incoming chargeaids in removing the remaining waste gases.The modified diesel combustion cycle is onein which the combustion phase, induced by compressionignition, begins on a constant-volumebasis and ends on a constant -pressure basis.In other words, the modified cycle is a combinationof the Otto and true diesel cycles. Themodified cycle is used as the basis for thedesign of practically all modern diesel engines.An example of a pressure-volume diagramfor a modified 4-stroke cycle diesel engine isshown in figure 22-7. Note that the volume lineis divided into 16 units, indicating a 16 to 1compression ratio. The higher compressionratio accounts for the increased temperaturenecessary to ignite the charge. By comparingthis illustration with illustration C of figure22-6, it will be found that the phases of thediesel cycle are relatively the same as those ofthe Otto cycle, except for the combustion phase.Fuel is injected at point c and combustion isrepresented by line cd. While combustion in the553

PRINCIPLES OF NAVAL ENGINEERINGOtto cycle is practically at constant-volumethroughout the phase, combustion in the modifieddiesel cycle takes place with volume practicallyconstant for a short time, during which periodthere is a sharp increase in pressure, until thepiston reaches a point slightly past TDC. Then,combustion continues at a relatively constantpressure, dropping slightly as combustion endsat d. For these reasons, the combustion cycle inmodern diesel engines is sometimes referredtoas the constant-volume constant-pressure cycle.Pressure-volume diagrams for gasoline anddiesel engines operating on the 2-stroke cyclewould be similar to those just discussed, exceptthat separate exhaust and intake curves wouldnot exist. They do not exist because intake andexhaust occur during a relatively short intervalof time near BDC and do not involve full strokesof the piston as in the case of the 4-stroke cycle.Thus, a pressure-volume diagram for a 2-strokemodified diesel cycle would be similar to a diagramformed by f-b-c-d-e-f of figure 22-7. Theexhaust and intake phases would take place betweene and b with some overlap of the events.(See fig. 22-2.)The preceding discussion has pointed outsome of the main differences between engineswhich operate on the Otto cycle and those whichoperate on the modified diesel cycle. In brief,these differences involve (1) the mixing of fueland air, (2) compression ratio, (3) ignition, and(4) the combustion process.Action of Combustion Gases on PistonsEngines are classifiedinmany ways. Mentionhas already been made of some classificationssuch as those based on (1) the fuels used (dieselfuel and gasoline), (2) the ignition methods (sparkand compression), (3) the combustion cycles(Otto and diesel), and (4) the mechanical cycles(2-stroke and 4-stroke). Engines may also beclassified on the basis of cylinder arrangements(V, in-line, opposed, etc.), the cooling media(liquid and air), and the valve arrangements(L-head, valve-in head, etc.). The manner inwhich the pressure of combustion gases actsupon the piston to move it in the cylinder ofan engine is also used as a method of classifyingengines.The classification of engines according tocombustion-gas action is based upon a considerationof whether the pressure created by thecombustion gases acts upon one or two surfacesof a single piston or against single surfaces oftwo separate and opposed pistons. The twotypes of engines under this classification arecommonly referred to as single-acting andopposed-piston engines.SINGLE-ACTING ENGINES. -Engines of thistype are those whichhave one piston per cylinderand in which the pressure of combustion gasesacts only on one surface of the piston. This is afeature of design rather than principle, for thebasic principles of operation apply whether anengine is single acting, opposed piston, ordouble acting.The pistons in most single-acting enginesare of the trunk type (length greater thandiameter). The barrel or wall of a piston ofthis type has one end closed (crown) and oneend open (skirt end). Only the crown of a trunkpiston serves as part of the combustion spacesurface. Therefore, the pressure of combustioncan act only against the crown; thus, with respectto the surfaces of a piston, pressure is singleacting . Most modern gasoline engines as well asmany of the diesel engines used by the Navy aresingle acting.OPPOSED-PISTON ENGINES.-With respectto combust ion- gas action, the term opposedpiston is used to identify those engines which havetwo pistons and one combustion space in each cylinder.The pistons are arranged in "opposed"positions—that is, crown to crown, withthecombustionspace in between. (See fig. 22-8.) Whencombustion takes place, the gases act against thecrowns of both pistons, driving them in oppositedirections. Thus, the term "opposed" not onlysignifies that, with respect to pressure and pistonsurfaces, the gases act in "opposite" direction,but also classifies piston arrangement within thecylinder.In modern engines which have the opposedpistonarrangement, two crankshaft (upper andlower) are required for transmission of power.Both shafts contribute to the power output of theengine. They may be connected in one of twoways; chains as well as gears have been usedfor the connection between shafts. However,in most opposed-piston engines common to Navyservice, the crankshafts are connected by avertical gear drive. (See fig. 22-8.)The cylinders of opposed-piston engines havescavenging air ports located near the top. Theseports are opened and closed by the upper piston.Exhaust ports located near the bottom of thecylinder are closed and opened by the lowerpiston.554

,AIRChapter 22. -DIESEL AND GASOLINE ENGINESUPPERCONNECTINGRODVERTICAL-GEAR DRIVEINJECTORUPPERCRANKSHAFTUPPERPISTONSCAVENGINGPORTSOMBUSTIONCHAMBEROpposed-piston engines used by the Navyoperate on the 2-stroke cycle. In engines of theopposed-piston type, as in 2-stroke cycle singleactingengines, there is anoverlapof the variousevents occurring during a cycle of operation. Injectionand theburningof the fuel start during thepart of the compression event and extendlatterinto the power phase. There is also an overlap ofthe exhaust and scavenging periods. The eventsin the cycle of operation of an opposed-piston,2-stroke cycle diesel engine are shown in figure22-10.Modern engines of the opposed-piston designhave a number of advantages over single-actingengines of comparable rating. Some of theseadvantages are: less weight per horsepowerdeveloped; lack of cylinder heads and valvemechanisms (and the cooling and lubricatingproblems connected with them); and fewermoving parts.Functions of ReciprocatingEngine ComponentsLOV^ERPISTONLOWERCONNEOTNG?RODEXHAUSTPORTSLOV^ERCRANKSHAFT75.8Figure 22-8.— Cylinder and related partsopposed-pistonengine.Movement of the opposed pistons is such thatthe crowns are closest together near the centerof the cylinder. When at this position, the pistonsare not at the true piston dead centers. This isbecause the lower crankshaft operates a fewdegrees in advance of the upper shaft. Thenumber of degrees that a crank on the lowershaft travels in advance of a correspondingcrank on the upper shaft is called lower cranklead. This is illustrated in figure 22-9.The design of most internal combustion enginesof the reciprocating type follows much thesame general pattern. Though engines are notall exactly alike, there are certain features commonto all, and the principal components of mostengines are similarly arranged. Since the generalstructure of gasoline engines is basically thesame as that of diesel engines, the followingdiscussion of the engine components appliesgenerally to both types of engines. However, differencesdo exist and these will be pointed outwhereever applicable.The principal components of an internalcombustion engine may be divided into twoprincipal groups—parts and systems. The mainparts of an internal combustion engine may befurther divided into structural parts and movingparts. Structural parts, for the purpose of thisdiscussion, include those which, with respectto engine operation, do not involve motion;namely, the structural frame and its componentsand related parts. The other group of engineparts includes those which involve motion. Manyof the principal parts which are mounted withinthe main structure of an engine are moving parts.Moving parts are considered as those which convertthe power developed by combustion in thecylinder to the mechanical energy that is availablefor useful work at the output shaft.The systems commonly associated with theengine proper are those necessary to make555

''PRINCIPLES OF NAVAL ENGINEERINGRIGHT HAND ROTATIONENGINEINNER OEAO CENTERINNER DEAD CENTERLEFT HAND ROTATIONENGINE,LEFT HAND -"^-^^ RIGHT HANDROTATION ENGINE "*1 l2Vt.l2t* ROTATION ENGINELOWER CRANK LEAD ^Figure 22-9.— Lower crank lead, opposed-piston engine.75. 9X556

Chapter 22. -DIESEL AND GASOLINE ENGINES2- STARTINJECTION3-ENDINJECTION4-EXPANSION 5-SCAVENGING 6-SUPERCHARGEFigure 22-10.— Events in operating cycle of an opposed-piston engine.75.10combustion possible, and those which minimizeand dissipate heat created by combustion andfriction. Since combustion requires air, fuel,and heat (ignition), systems providing each maybe found on some engines. However, since adiesel engine generates its own heat for combustionwithin the cylinders, no separate ignitionsystem is required for engines of this type. Theproblem of heat, created as a result of combustionand friction, is taken care of by two separatesystems— cooling and lubrication. The functionsof the parts and systems of engines which operateon the principles already described are discussedbriefly in the following paragraphs.MAIN STR UCTURAL PAR TS. -The main purposeof the structural parts of an engine is tomaintain the moving parts in their proper relativeposition. This is necessary if the gas pressureproduced by combustion is to fulfill itsfunction.The term frame is sometimes used to identifya single part of an engine; in other cases, itidentifies several stationary parts fastened togetherto support most of the moving engineparts and engine accessories. For the purposeof this discussion, the latter meaning will beused. As the load-carrying part of the engine,the frame of the modern engine may includesuch parts as the cylinder block, crankcase,bedplate or base, sump or oil pan, and endplates.The part of the engine frame which supportsthe engine's cylinder liners and heador heads is generally referred to as the cylinderblock. The blocks for most large enginesare of the welded-steel type construction. Blocksof small high-speed engines may be of the enbloc construction. In this type construction, theblock is cast in one piece. Two types of cylinderblocks coming to Navy service are shown infigures 22-11 and 22-12. The block shown infigure 22-11 is representative of blocks designedfor some large engines with in-line cylinder arrangement.The block illustrated infigure 22-12is representative of blocks constructed forsome engines with V-type cylinder arrangement.The engine frame part which serves as ahousing for the crankshaft is commonly calledthe crankcase. In some engines, the crankcaseis an integral part of the cylinder block (seefig. 22-11), requiring an oil pan, sump, or base557

PRINCIPLES OF NAVAL ENGINEERINGCYLINDERHEAD STUDCYLINDERLINER BOREFigure 22-11.— Cylinder block with in-line cylinder arrangement.75.14XSCAVENGING AIRCHAMBERSTRANSVERSE FRAME MEMBERUPPER DECKPLATECAMSHAFT POCKETLOWER DECKPLATE75.16Figure 22-12,— An example of a V-typecylinder block construction.to complete the housing. In others the crankcaseis a separate part and is bolted to the block.In large engines of early design, the supportfor the main bearings was provided bya bedplate. The bedplate was bolted to thecrankcase and an oil pan was bolted to thebedplate when a separate oil pan was used.In some large engines of more modern designthe support for main bearings is provided by apart called the base. Figure 22-13 illustratessuch a base, which is used with the block shownin figure 22-11. This type base serves as acombination bedplate and oil plan. This baserequires the engine block to complete the framefor the main engine bearings. Some crankcasesare designed so that the crankshaft and the mainbearings are mounted and secured completelywithin the crankcase.Since lubrication is essential for properengine operation, a reservoir for collecting andholding the engine's lubricating oil is a necessarypart of the engine structure. The reservoir maybe called a sump or an oil pan , depending uponits design, and is usually attached directly to558'

Chapter 22. -DIESEL AND GASOLINE ENGINESUPPER BEARINGSHELLNUMBER 10MAIN BEARINGLOWER BEARINGSHELLFRAME TOBASE BOLT^icating oil;tion outlet|0N SYSTEMOUTLETBASESHIMSSTUD NUTMOATING OIL)ER INLETLUBRICATIBYPASSLTRATiONSYSTEM INLETFigure 22-13.— Engine base.75.20Xthe engine. However, in some engines, the oilreservoir may be located at some point relativelyremote from the engine; such engines may be referredto as dry sump engines.In the engine base shown in figure 22-13,oil sump is an integral part of the base or crankcase,which has functions other than just beingan oil reservoir. Many of the smaller engines donot have a separate base or crankcase; instead,they have an oil pan, which is secured directlyto the bottom of the block. In most cases, an oilpan serves only as the lower portion of the crankshafthousing and as the oil reservoir.Some engines have flat steel plates attachedto each end of the cylinder block. End platesadd rigidity to the block and provide a surfaceto which may be bolted housings for such partsas gears, blowers, pumps, and generators.Many engines, especially the larger ones,have access openings in some part of the engineframe. (See fig. 22-11.) These openings permitaccess to the cylinder liners, main and connectingrod bearings, injector control shafts.and various other internal engine parts. Accessdoors (sometimes called covers or plates ) forthe openings are usually secured with handwheelor nut-operated clamps and are fitted withgaskets to keep dirt and foreign material out ofthe engine's interior.The cylinder assembly completes the structuralframework of an engine. As one of the mainstationary parts of an engine, the cylinder assembly,along with various related workingparts, serves to confine and release the gases.For the purpose of this discussion, the cylinderassembly will be considered as consisting of thehead, the liner, the studs, and the gasket. (Seefig. 22-14.)The design of the parts of the cylinder assemblyvaries considerably from one type ofengine to another. Regardless of differences indesign, however, the basic components of allcylinder assemblies function, along with relatedmoving parts, to provide a gas- and liquid-tightspace.559

PRINCIPLES OF NAVAL ENGINEERING-CAMSHAFT•CYLINDER HEADHOLDDOWN NUT— CYLINDER HEADWATERSEAL RINGWATER FERRULECOPPER GASKET•CYLINDERBLOCKCYLINDERLINERCOOLING WATERiINLETFigure 22-14.— Principal stationary parts of a cylinder assembly.75.24XThe barrel or bore in which an enginepiston moves back and forth may be an integralpart of the cylinder block or it may bea separate sleeve or liner. The first type,common in gasoline engines, has the disadvantageof not being replaceable. Practicallyall diesel engines are constructed with replaceablecylinder liners.Six cylinder liners of the replaceable typeare shown in figure 22-15. These liners illustratesome of the differences in the designof liners and the relative size of the enginesrepresented.The liners or bores of an internal combustionengine must be sealed tightly to form the combustionchambers. In most Navy engines, except560

Chapter 22. -DIESEL AND GASOLINE ENGINESafv^BOALCO_539FM 38D81/8 GM 278A GM 268A GM 6-71 NAVYFigure 22-15.— Cylinder liners of diesel engines.75.25for engines of the opposed-piston type, thespace at the combustion end of a cylinder isformed and sealed by a cylinder head whichis a separate unit from the block. (See fig.22-14.)A number of engine parts which are essentialto engine operation may be found in orattached to the cylinder head. The cylinder headmay house intake and exhaust valves, valve guidesand valve seats, or only exhaust valves and relatedparts. Rocker arm assemblies are frequentlyattached to the cylinder head. The fuel injectionvalve is almost universally in the cylinderhead or heads of a diesel engine, while thespark plugs are always in the cylinder head ofgasoline engines. Cylinder heads of a dieselengine may also be fitted with air starting valves,indicator and blow down valves, and safetyvalves.The number of cylinder heads found onengines varies considerably. Small engines ofthe in-line cylinder arrangement utilize onehead for all cylinders. A single head servesfor all cylinders in each bank of some V-typeengines. Large diesel engines generally haveone cylinder head for each cylinder. Someengines use one head for each pair of cylinders.In most cases, the seal between the cylinderhead and the block depends principally upon thestuds and gaskets. The studs, or stud bolts,secure the cylinder head to the cylinder block.A gasket between the head and the block iscompressed to form a seal when the head isproperly tightened down. In some cases, gasketsare not used between the cylinder head andblock; the mating surfaces of the head and blockare accurately machined to form a seal betweenthe two parts.PRINCIPAL MOVING PARTS.-In order thatthe power developed by combustion can be convertedto mechanical energy, it is necessary forreciprocating motion to be changed to rotatingmotion. The moving parts included in the conversionprocess, from combustion to energyoutput, may be divided into the following threemajor groups: (1) the parts which have onlyreciprocating motion (pistons), (2) the partswhich have both reciprocating and rotatingmotion (connecting rods), and (3) the partswhich have only rotating motion (crankshaftsand camshafts).The firsttwo major groups of moving partsmay be further grouped under the single headingof piston and rod assemblies. Such an assemblymay include a piston, piston rings, piston pin,connecting rod, and related bearings.561

PRINCIPLES OF NAVAL ENGINEERINGAs one of the principal parts in the powertransmitting assembly, the piston must be sodesigned and must be made of such materialsthat it can withstand the extreme heat andpressure of combustion. Pistons must also belight enough to keep inertia loads on relatedparts to a minimum. The piston aids in thesealing of the cylinder to prevent the escapeof gas and transmits some of the heat throughthe piston rings to the cylinder wall. In additionto serving as the unit which transmitsthe force of combustion to the connecting rodand conducts the heat of combustion to thecylinder wall, a piston serves as a valve inopening and closing the ports of a two-strokecycle engine. The nomenclature for the parts ofa typical trunk type piston is given in figure22-16.Piston rings are particularly vital to engineoperation in that they must effectively performthree functions: seal the cylinder, distribute andcontrol lubricating oil on the cylinder wall, andCOMPRESSIONRING GROOVESAND LANDSPISTON HUBBUSHING75.47Figure 22-16.— Piston nomemclature.transfer heat fromthepistontothecylinderwall.All rings on a piston perform the latter function,but two general types of rings— compression andoil— are required to perform the first two functions.There are numerous types of rings in eachof these groups, contructed in different waysfor particular purposes. Some of the variationsin ring design are illustrated in figure 22-17.In trunk-type piston assemblies, the connectionbetween the piston and the connecting rod isusually the piston pin (sometimes referred to asthe wrist pin ) and its bearings. These partsmust be of especially strong construction becausethe power developed in the cylinder istransmitted from the piston through the pin tothe connecting rod. The pin is the pivot pointwhere the straight-line or reciprocating motionof the piston changes to the reciprocating androtating motion of the connecting rod. Thus, theprincipal forces to which a pin is subjected arethe forces created by combustion and the sidethrust created by the change in direction ofmotion. (See fig. 22-18.)The connecting link between the piston andcrankshaft or the crankshaft and the crossheadof an engine is the connecting rod . In order thatthe forces created by combustion can be transmittedto the crankshaft, the rod changes thereciprocating motion of the piston to the rotatingmotion of the crankshaft.Most marine engines in Navy service use thetrunk-type piston connected directly to the connectingrod.The camshaft is a shaft with eccentric projection,called cams, designed to control theoperation of valves, usually through variousintermediate parts as described later in thischapter. Originally cams were made as separatepieces and fastened to the camshaft. However,in most modern engines the cams are forged orcast as an integral part of the camshaft.To reduce wear and to help them withstandthe shock action to which they are subjected,camshafts are made of low-carbon alloy steelwith the cam and journal surfaces carburizedbefore the final grinding is done.The cams are arranged on the shaft toprovide the proper firing order of the cylindersserved. The shape of the cam determines thepoint of opening and closing, the speed of openingand closing, and the amount of the valvelift. If one cylinder is properly time, theremaining cylinders are automatically in time.All cylinders will be affected if there is a changein timing.562

Chapter 22. -DIESEL AND GASOLINE ENGINESA- DIAGONALLY-CUT COMPRESSION RING B-LAP-JOINT COMPRESSION RINGC-OIL RING D- SLOTTED OIL RINGE-THREE PIECE OIL RINGFigure 22-17.— Types of piston rings.75.51The camshaft is driven by the crankshaftby various means, the most common being bygears or by a chain and sprocket. The camshaftfor a 4-stroke cycle engine must turn at onehalfof the crankshaft speed; while in the 2-strokecycle engine, it turns at the same speed as thecrankshaft.The location of the crankshaft in variousengines differs. Camshaft location depends onthe arrangement of the valve mechanism. Thelocation of a camshaft is shown in figure 22-14.One of the principal engine parts which hasonly rotating motion is the crankshaft . As one ofthe largest and most important moving parts inan engine, the crankshaft changes the movementof the piston and the connecting rod into the rotatingmotion required to drive such items asreduction gears, propeller shafts, generators,pumps, etc. As a result of its function, thecrankshaft is subjected to all the forces developedin an engine.While crankshafts of a few larger enginesare of the built-up type (forged in separatesections and flanged together), the crankshaftsof most modern engines are of the one-piecetype construction. A shaft of this type is shownin figure 22-19. The parts of a crankshaft maybe identified by various terms; however, thoseshown in figure 22-19 are common in the technicalmanuals for most of the engines used bythe Navy.The speed of rotation of the crankshaft increaseseach time the shaft receives a powerimpulse from one of the pistons; and it thengradually decreases untilanother power impulseis received. These fluctuations in speed (theirnumber depending upon the number of cylindersfiring in one crankshaft revolution) would resultin an undesirable situation with respect to thedriven mechanism as well as the engine;therefore,some means must be provided to stabilizeshaft rotation. In some engines this is accomplishedby installing a flywheel on the crankshaft;in others, the motion of such engine parts asthe crankpins, webs, lower ends of connectingrods, and such driven units as the clutch,generator, etc., serve the purpose. The needfor a flywheel decreases as the number ofcylinders firing in one revolution of the crankshaftand the mass of the moving parts attachedto the crankshaft increases.A flywheel stores up energy during the powerevent and releases it duringthe remaining eventsof the operating cycle. In other words, when the563

PRINCIPLES OF NAVAL ENGINEERING^ tt-^

Chapter 22. -DIESEL AND GASOLINE ENGINESI. MAIN BEARING JOURNAL- FRONT2. COUNTERWEIGHT3. MAIN BEARING JOURNAL-INTERMEDIATE4. CONNECTING ROD JOURNAL- NO. 35. MAIN BEARING JOURNAL- REAR6. BOLTING FLANGE -TIMING GEAR7. DOWEL- FLYWHEEL8. RING GEAR9. RETAINING BOLT HOLE10. DOWEL HOLEI I. PULLER SCREW HOLE12. FLYWHEEL13. LUBRICATING OIL HOLESFigure 22-19.— One-piece six-throw crankshaft with flywheel.75.81Xare finished, are commonly referred to as theintake and exhaust systems . These systems areclosely related and, in some cases, are referredto as the air systems of an engine. A crosssectionalview of the air systems of one typeof high-speed diesel engine is shown in figure22-20.The following information on air systemsdeals primarily with the systems of diesel engines;nevertheless, much of the informationdealing with the parts of diesel engine air systemsis also applicable to most of the partsin similar systems of gasoline engines. However,the intake event in the cycle of operationof a gasoline engine includes the admission ofair and fuel as a mixture to the cylinder. Forthis reason, the intake system of a gasolineengine differs, in some respects, from that ofa diesel engine. (See subsequent section on fuelsystems.)A discussion of the air systems of deiselengines frequently involves the use of two termswhich identify processes related to the functionsof the intake and exhaust systems. These termsscavengingand supercharging— and the processesthey identify are common to many moderndiesel engines.In the intake systems of all modern 2-strokecycle engines and some 4-stroke cycle engines,a device, usually a blower, is installed to increasethe flow of air into the cylinders. Thisis accomplished by the blower compressing theair and forcing it into an air box or manifold(reservoir) which surrounds or is attached tothe cylinders of an engine. Thus, an increasedamount of air under constant pressure is availableas required during the cycle of operation.The increased amount of air available as aresult of blower action is used to fill the cylinderwith a fresh charge of air and, during theprocess, aids in clearing the cylinder of thegases of combustion. This process is calledscavenging . Thus, the intake system of someengines, especially those operating on the 2-stroke cycle, is sometimes called the scavengingsystem. The air forced into the cylinder565

PRINCIPLES OF NAVAL ENGINEERINGSEA WATER INLETEXHAUSTfflIDINLET PIPEFLEXIBLEPIPEEXHAUSTSILENCER^:*P> EXHAUST ANDSEA WATEROUTLETIBiOWATER LINEWATERJACKETOVERBOARDDISCHARGEEXHAUSTMAN! FOLDAIR INTAKEPORTSTAKESILENCERAIRBOXAIRSCREENFigure 22-20.-Air systems of a 2-stroke cycle engine.75.151Xis called scavenge ( or scavenging ) air and theports through which it enters are called scavengeports .The process of scavenging must be accomplishedin a relatively short portion of the operatingcycle; however, the duration of the processdiffers in 2- and 4-stroke cycle engines. In a2-stroke cycle engine, the process takes placeduring the later part of the downstroke (expansion)and the early part of the upstroke (compression).Ina4-stroke cycle engine, scavengingtakes place when the piston is nearing and566

Chapter 22. -DIESEL AND GASOLINE ENGINESpassing TDC during the latter part of an upstroke(exhaust and the early part of a downstroke (intake).The intake and exhaust openings are bothopen during this interval of time. The overlapof intake and exhaust permits the air from theblower to pass through the cylinder into theexhaust manifold, cleaning out the exhaust gasesfrom the cylinder and, at the same time, coolingthe hot engine parts.Scavenging air must be so directed, when itenters the cylinder of an engine, that the wastegases are removed from the remote parts ofthe cylinder. The two principal methods bywhich this is accomplished are sometimes referredto as port scavenging and valve scavenging.Port scavenging may be of the direct (orcross-flow) loop (or return), or uniflow type.(See fig. 22-21.)An increase in air flow into cylinders of anengine can be used to increase power output,Ln addition to being used for scavenging. Sincethe power of an engine is developed by the burningof fuel, an increase of power requires morefuel; the increased fuel, in turn, requires moreair,since each pound of fuel requires a certainamount of air for combustion. Supplying more airto the combustion spaces that can be suppliedthrough the action of atmospheric pressure andpiston action (in 4-stroke cycle engines) orscavenging air (in 2-stroke cycle engines) iscalled supercharging .In some 2-stroke cycle diesel engines, thecylinders are supercharged during the air intakesimply by increasing the amount and pressureof scavenge air. The same blower is usedfor supercharging and scavenging. Whereasscavenging is accomplished by admitting airunder low pressure into the cylinder while theexhaust valves or ports are open, superchargingis done with the exhaust ports or valves closed.This latter arrangement enables the blower toforce air under pressure into the cylinder andthereby increase the amount of air availablefor combustion. The increase in pressure resultingfrom the compressing action of theblower will depend upon the engine involved,but it is usually low, ranging from 1 to 5 psi.With this increase in pressure, and the amountof air available for combustion, there is a correspondingincrease in the air-fuel ratio and incombustion efficiency within the cylinder. Inother words, a given size engine which is superchargedcan develop more power than the samesize engine which is not supercharged.Supercharging a 4-stroke cycle diesel enginerequires the addition of a blower to the intakesystem since the operations of exhaust and intakein an unsupercharged engine are performedPORT DIRECT SCAVENGING VALVE UNIFLOW SCAVENGING UNIFLOW PORT SCAVENGINGFigure 22-21,— Methods of scavenging— diesel engines.75.152567

PRINCIPLES OF NAVAL ENGINEERINGby the action of the piston. The timing of thevalves in a supercharged 4-stroke cycle engineis also different from that in a similar enginewhich is not supercharged. In the superchargedengine the intake-valve opening is advanced andthe exhaust-valve closing is retarded so thatthere is considerable overlap of the intake andexhaust events. This overlap increases power,the amount of the increase depending upon thesupercharging pressure. The increased overlapof the valve openings in a supercharged 4-stroke cycle engine also permits the air pressurecreated by the blower to be used in removinggases from the cylinder during the exhaustevent. How the opening and the closing of theintake and exhaust valves or ports affect bothscavenging and supercharging, and the differencesin these processes as they occur insupercharged 2- and 4-stroke cycle engines,can be seen by studying the diagrams in figure22-22.As in the case of the diagrams used in connectionwith the discussion of engine operatingprinciples, the circular pattern in figure 22-22represents crankshaft rotation. Some of theevents occurring in the cycles are shown interms of degrees of shaft rotation. However,the numbers (of degrees) shown on the diagramsare for purposes of illustration and comparisononly. When these diagrams are being studied,it must be kept in mind that the crankshaft of a4-stroke cycle engine makes two complete revolutionsin one cycle of operation while the shaftin a 2-stroke cycle engine makes only one revolutionper cycle. It should also be rememberedthat the exhaust and intake events in a 2-strokecycle engine do not involve complete pistonstrokes as they do in a 4-stroke cycle engine.Even though the primary purpose of a dieselengine intake system is to supply the air requiredfor combustion, the system generallyhas to perform one or more additional functions.In most cases, the system cleans the air andreduces the noise created by the air as it entersthe engine. In order to accomplish the functionsof intake, an intake system may include an airsilencer, an air cleaner and screen, an air boxor header, intake valves or ports, a blower, anair heater, and an air cooler. All of these partsare not common to every intake system. Anintake system in which only a silencer, a screen,a blower, an air box, and intake ports providea clean supply of air, with minimum noise, tothe combustion spaces is shown in figure 22-20.FOURSTROKECYCLETWOSTROKECYCLET.D.C.B.D.C.54.19:.20BFigure 22-22.—Scavenging and supercharging indiesel engines.The system which functions primarily to conveygases away from the cylinders of an engineis called the exhaust system . In addition to thisprincipal function, an exhaust system may bedesigned to perform one or more of the followingfunctions: muffle exhaust noise, quenchsparks, remove solid material from exhaustgases, and furnish energy to a turbine-drivensupercharger. The principal parts which maybe used in combination to accomplish the functionsof an engine exhaust system are shown infigures 22-20 and 22-23.568

Chapter 22. -DIESEL AND GASOLINE ENGINESSILENCERINTAKEAIR;f i. ^Figure 22-23. — Intake and exhaust systems.75.167XOPERATING MECHANISMS FOR SYSTEMPARTS AND ACCESSORIES.-Tothis point, considerationhas been given only to the main engineparts— stationary and moving— and to twoof the systems common to internal combustionengines. At various points in this chapter,reference has been made to the operation ofsome of the engine parts. For example, it liasbeen pointed out that the valves open and closeat the proper time in the operating cycle andthat the impellers or lobes of a blower rotateto compress intake air. However, little569

PRINCIPLES OF NAVAL ENGINEERINGconsideration lias been given to the source ofpower or to the mechanisms which cause theseparts to operate.In many cases, the mechanism which transmitspower for the operationof the engine valvesand blower may also transmit power to partsand accessories which are components of variousengine systems. For example, such itemsas the governor; fuel, lubricating, and waterpumps; and overspeed trips, are, in some engines,operated by the same mechanism. Sincemechanisms which transmit power to operatespecific parts and accessories may be relatedto more than one engine system, such operatingmechanisms are considered here before theremaining engine systems are discussed.The parts which make up the operating mechanismsof an engine may be divided into twogroups: the group which forms the drive mechanismsand the group which forms the actuatingmechanisms . The source of power for the operatingmechanisms of an engine is the crankshaft.As used in this chapter, the term drivemechanism identifies the group of parts whichtakes power from the crankshaft and transmitsthat power to various engine parts and accessories.In engines, the drive mechanismsdoes not change the type of motion, but it maychange the direction of motion. For example,the impellers or lobes of a blower are drivenor operated as a result of rotary motion whichis taken from the crankshaft and transmitted tothe impellers or lobes by the drive mechanism,an arrangement of gears and shafts. While thetype of motion (rotary) remains the same, thedirection of motion of one impeller or lobe isopposite to that of the other impeller or lobeas a result of the gear arrangements withinthe drive mechanism.A drive mechanism may be of the gear,chain or belt type. Of these, the gear type isthe most common; however, some engines areequipped with chain assemblies, A combinationof gears and chains is used as the drivingmechanism in some engines.Some engines have a single drive mechanismwhich transmits power for the operation of engineparts and accessories. Inother cases, theremay be two or more separate mechanisms.When separate assemblies are used, the onewhich transmits power for the operation of theaccessories is called the accessory drive . Someengines have more than one accessory drive.A separate drive mechanism which is used totransmit power for the operationof engine valvesis generally called the camshaft drive or timingmechanism .The camshaft drive, as the name implies,transmits power to the camshaft of the engine.The shaft, in turn, transmits the power througha combination of parts which causes the enginevalves to operate. Since the valves of an enginemust open and close at the proper moment(with respect to the position of the piston) andremain in the open and closed positions fordefinite periods of time, a fixed relationshipmust be maintained between the rotational speedsof the crankshaft and the camshaft. Camshaftdrives are designed to maintain the properrelationship between the speeds of the two shafts.In maintaining this relationship, the drive causesthe camshaft to rotate at crankshaft speed in a2-stroke cycle engine; and at one-half crankshaftspeed in a 4-stroke cycle engine.The term actuating mechanism, as used inthis chapter, identifies that combination of partswhich receives power from the drive mechanismand transmits the power to the engine valves.In order for the valves (intake, exhaust, fuelinjection, air starter) to operate, there must bea change in the type of motion. In other words,the rotary motion of the crankshaft and drivemechanism must be changed to a reciprocatingmotion. The group of parts which, by changingthe type of motion, causes the valves of an engineto operate is generally referred to as thevalve actuating mechanism . A valve-actuatingmechanism may include the cams, cam followers,push rods, rocker arms, and valvesprings. In some engines, the camshaft is solocated that the need for push rods is eliminated.In such cases, the cam follower is a part of therocker arm. (Some actuating mechanisms aredesigned to transform reciprocating motion intorotary motion, but in internal combustion enginesmost actuating mechanisms change rotarymotion into reciprocating motion.)There is considerable variation in the designand arrangement of the parts of operating mechanismsfound in different engines. The size ofan engine, the cycle of operation, the cylinderarrangement, and other factors govern the designand arrangement of the components aswell as the design and arrangement of the mechanisms.Three types of operating mechanismsare shown in figures 22-24, 22-25, and 22-26.The mechanisms which supply power for theoperation of the valves and accessories of gasolineengines are basically the same as those570

Chapter 22. -DIESEL AND GASOLINE ENGINESCOUNTER-WEIGHTEDCAMSHAFT ANDBALANCE SHAFTDRIVE GEARSBLOWERDRIVEGEARIDLERGEARFLYWHEELPILOTSCRANKSHAFT GEARFigure 22-24.— Camshaft and accessory drive.75,98Xfound in diesel engines. Some manufacturersutilize mechanisms consisting primarily of chainassemblies, while others use gears as the primarymeans of transmitting power to engineparts. Combination gear-chain drive assembliesare used on some gasoline engines.ENGINEFUEL SYSTEMS.-The method ofone of the majorgetting fuel into the cylinder isdifferences between gasoline and diesel engines.As pointed out earlier, fuel for gasoline enginesis mixed with air outside the cylinder and themixture is then drawn into the cylinder and compressed.On the other hand, fuel for dieselengines is injected or sprayed into the combustionspace after the air is already compressed.The equipment which supplies fuel to the cylindersof a gasoline engine would necessarily bedifferent from that of a diesel engine.There are several types of fuel injectionsystems in use. The function of each type is,however, the same. The primary function of a571

PRINCIPLES OF NAVAL ENGINEERINGFigure 22-25.— Valve-actuating mechanism.75.101X572

Chapter 22. -DIESEL AND GASOLINE ENGINESENGINE CONTROL GOVERNORPINIONOVERSPEEDGOVERNOI?GOVERNOR GEARGOVERNOR DRIVE GEARTACHOMETER GENERATORCAMSHAFT SPROCKETCAMSHAFT DRIVE GEARENGINE SPEED)GOVERNOR DRIVE GEARCAMSHAFT GEARn.12.13.14.15.16.17.18.19.PUMP DRIVE GEARKNEE SPROCKETWATER PUMP GEARDRIVING CHAINCRANKSHAFT SPROCKETCLAMP RINGCHAIN TIGHTENERIDLER SPROCKETTACHOMETER GEARFigure 2-26.— Camshaft and accessory drive mechanism.75.111X573

PRINCIPLES OF NAVAL ENGINEERINGfuel injection system is to deliver fuel to thecylinders, under specified conditions. The conditionsmust be in accordance with the powerrequirements of the engine.The first condition to be met is that of theinjection equipment. The quantity of fuel injecteddetermines the amount of energy available,through combustion, to the engine. Smoothengine operation and even distribution of theload between the cylinders depend upon thesame volume of fuel being admitted to a particularcylinder each time it fires, and upon equalvolumes of fuel being delivered to all cylindersof the engine. The measuring device of a fuelinjection system must also be designed to varythe amount of fuel being delivered as changesin load and speed vary.In addition to measuring the amount of fuelinjected, the system must properly time injectionto ensure efficient combustion, so maximumenergy can be obtained from the fuel.Early injection tends to develop excessive cylinderpressures; and extremely early injectionwill cause knocking. Late injection tends todecrease power output; and, if extremely late,it will cause incomplete combustion. In manyengines, fuel injection equipment is designed tovary the time of injection, as speed or loadvaries.A fuel system must also control the rate ofinjection. The rate at which fuel is injected determinesthe rate of combustion. The rate ofinjection at the start should be low enough thatexcessive fuel does not accumulate in the cylinderduring the initial ignitiondelay (before combustionbegins). Injection should proceed atsuch a rate that the rise in combustion pressureis not excessive, yet the rate of injection mustbe such that fuel is introduced as rapidly as ispermissible in order to obtain complete combustion.An incorrect rate of injection willaffect engine operation in the same way asimproper timing. If the rate of injection is toohigh, the results will be similar to those causedby an excessively early injection; if the rateis too low, the results will be similar to thosecaused by an excessively late injection.A fuel injection system must increase thepressure of the fuel sufficiently to overcomecompression pressures and to ensure properdistribution of the fuel injected into the combustionspace. Proper distribution is essentialif the fuel is to mix thoroughly with the air andburn efficiently. While pressure is a primecontributing factor, the distribution of the fuelis influenced in part, by "atomization" and"penetration" of the fuel. As used in connectionwith fuel injection, atomization means thebreaking up of the fuel, as it enters the cylinder,into small particles which form a mist-likespray. Penetration is the distance through whichthe fuel particles are carried by the kineticenergy imparted to them as they leave the injectoror nozzle.Atomization is obtained when the liquid fuel,under high pressure, passes through the smallopening or openings in the injector or nozzle.As the fuel enters the combustion space, highvelocity is developed because the pressure inthe cylinder is lower than the fuel pressure.The friction created as the fuel passes throughthe air at high velocity causes the fuel to breakup into small particles. Penetration of the fuelparticles depends chiefly upon the viscosity ofthe fuel, the fuel-injection pressure, and thesize of the opening through which the fuel entersthe cylinder.Fuel must be atomized into particles sufficientlysmall so as to produce a satisfactoryignition delay period. However, if the atomizationprocess reduces the size of the fuel particlestoo much, they will lackpenetration; the smallerthe particles the less the penetration. Lack ofsufficient penetration results in the small particlesof fuel igniting before they have beenproperly distributed. Since penetration andatomization tend to oppose each other, a compromisein the degree of each is necessary inthe design of fuel injection equipment if uniformfuel distribution is to be obtained. The pressurerequired for efficient injection, and, inturn, proper distribution, is dependent upon thecompression pressure in the cylinder, the sizeof the opening through which the fuel enters thecombustion space, the shape of the combustionspace, and the amount of turbulence created inthe combustion space.The fuel system of a gasoline engine is basicallysimilar to that of a diesel engine, exceptthat a carburetor is used instead of injectionequipment. While injection equipment handlesfuel only, the carburetor handles both air andfuel. The carburetor must meet requirementssimilar to those of an injection system exceptthat in the carburetor air is also involved. Inbrief, the carburetor must accurately meterfuel and air, and in varying percentages, accordingto engine requirements. The carburetoralso functions to vaporize the fuel charge andthen mix it with the air, in the proper ratio.574

Chapter 22. -DIESEL AND GASOLINE ENGINESThe amount of fuel mixed with the air must becarefully regulated, and must change with theengine's different speeds and loads. The amountof fuel required by an engine which is warmingupis different from the amount required by anengine which has reached operating temperature.Special fuel adjustment is needed for rapidacceleration. All of these varying requirementsare met automatically by the modern carburetor.Engine Ignition Systems.— The methods bywhich the fuel mixture is ignited in the cylindersof diesel and gasoline engines differ as much asthe methods of obtaining a combustible mixturein the cylinders of the two engines. An ignitionsystem, as such, is not commonly associated withdiesel engines. There is no one group of parts ina diesel engine which functions only to cause ignition,as there is in a gasoline engine. However,a diesel engine does have an "ignition system";otherwise, combustion would not take place inthe cylinders.In a diesel engine, the parts which may beconsidered as forming the ignition system arethe piston, the cylinder liner, and the cylinderhead. These parts are not commonly thought ofas forming an ignition system since they aregenerally associated with other functions such asforming the combustion space and transmittingpower. Nevertheless, ignition in a diesel enginedepends upon the piston, the cylinder, and thehead. These parts not only form the space wherecombustion takes place but also provide themeans by which the air is compressed to generatethe heat necessary for self- ignition of thecombustible mixture. In other words, both thesource (air) of ignition heat and its generation(compression) are wholly within a diesel engine.This is not true of a gasoline engine becausethe combustion cycles of the two types of enginesare different. In a gasoline engine, even thoughthe piston, the cylinder, and the head form thecombustion space, as in a diesel engine, the heatnecessary for ignition is caused by energy froma source external to the combustion space. Thecompletion of the ignition process, involving thetransformation of mechanical energy into electricalenergy and then into heat energy, requiresseveral parts, each performing a specific function.The parts which make the transformationof energy and the system which they form arecommonly thought of when reference is made toan ignition system.The spark which causes the ignition of theexplosive mixture in the cylinders of a gasolineengine is produced when electricity is forcedacross a gap formed by two electrodes in thecombustion chamber. The electrical ignitionsystem furnishes the spark periodically to eachcylinder, at a predetermined position of pistontravel. In order to accomplish this function, anelectrical ignition system must have, first ofall, either a source of electrical energy or ameans of developing electrical energy. In somecases, a storage battery is used as the source ofenergy; in other cases, a magneto generateselectricity for the ignition system. The voltagefrom either a battery or a magneto is not sufficientlyhigh enough to overcome the resistancecreated by pressure in the combustion chamberand to cause the proper spark in the gap formedby the two electrodes in the combustive chamber.Therefore, it is essential that an ignitionsystem include a device which increases thevoltage of the electricity supplied to the systemsufficiently to cause a "hot" spark in the gapof the spark plug. The device which performsthis function is generally called an ignition coilor induction coil .Since a spark must occur momentarily ineach cylinder at a specific time, an ignitionsystem must include a device which controls thetiming of the flow of electricity to each cylinder.This control is accomplished by interrupting theflow of electricityfromthe source to the voltageincreasingdevice (ignition coil). The interruptionof the flow of electricity also plays an importantpart in the process of increasing voltage.The interrupting device is generally called thebreaker assembly. A device which will distributeelectricity to the different cylinders inthe proper firing order is also necessary. Thepart which performs this function is called thedistributing mechanism. Spark plugs to providethe gaps and wiring and switches to connect theparts of the system are essential to complete anignition system.All ignition systems are basically the same,except for the source of electrical energy. Thesource of energy is frequently used as a basisfor classifying ignition systems; thus the battery-ignitionsystem and the magneto-ignitionsystem.Engine Cooling Systems.—A great amountof heat is generated within an engine duringoperation. Combustion produces the greaterportion of this heat; however, compression ofgases within the cylinders and friction betweenmoving parts add to the total amount of heat575

PRINCIPLE OF NAVAL ENGINEERINGdeveloped within an engine. Since the temperatureof combustion alone is about twice that atwhich iron melts, it is apparent that, withoutsome means of dissipating heat, an engine wouldoperate for only a very limited time. Withoutproper temperature control, the lubricating-oilfilm between moving parts would be destroyed,proper clearance between parts could not bemaintained, and metals would tend to fail.Of the total heat supplied to the cylinder ofan engine by the burning fuel, only one-third,approximately, is transformed into useful work:an equal amount is lost to the exhaust gases.This leaves approximately 30 to 35 percent ofthe heat of combustion which must be removedin order to prevent damage to engine parts. Thegreater portion of the heat which may produceharmful results is transferred from the enginethrough the medium of water; lubricating oil, air,and fuel are also utilized to aid in the cooling ofan engine. All methods of heat transfer are utilizedin keeping engine parts and fluids (air,water, fuel, and lubricating oil) at safe operatingtemperatures.In a marine engine, the cooling system maybe of the open or closed type. In the open system,the engine is cooled directly by saltwater.In the closed system, fresh water (or an antifreezesolution) is circulated through the engine.The fresh water is then cooled by salt water.In marine installations, the closed system isthe type commonly used; however, some oldermarine installations use a system of the opentype. The cooling systems of diesel and gasolineengines are similar mechanically and in functionperformed.The cooling system of an engine may includesuch parts as pumps, coolers, engine passages,water manifolds, valves, expansion tank, piping,strainers, connections, and instruments. Theschematic diagrams in figure 22-27 and 22-28show the parts and the path of water flow in thefresh- and sea-water circuits of one arrangementof a closed cooling system.Even though there are many types and modelsof engines used by the Navy, the cooling systemsof most of these engines include the same basicparts. Design and location of parts, however,may differ considerably from one engine toanother.ENGINE LUBRICATING SYSTEMS. -It isessential to the operation of an engine that thecontacting surfaces of all moving parts of anFRESH WATER PUMPEXHAUST MANIFOLD EXTENSIONATMOSPHERIC VENTDUPLEX PRESSUREGAGE^EXPANSION TANKSUPERCHARGERCONNECTIONLUBE OIL HEATEXCHANGERADAPTERTHERMOMETERFRESH WATER HEATEXCHANGERRESTRICTIONNOZZLEBOXFRESH WATER PUMP-TEMPERATURE INDICATOR-^MhERMOSTATCOUPLINGFigure 22-27.— Fresh water circuit of a closed cooling system.75.208X576

Chapter 22. -DIESEL AND GASOLINE ENGINESTHERMOMETER-- OVERBOARD DISCHARGERESTRICTIONPRESSUREGAGESEA WATER INTAKE THRUHULL FITTING AND STRAINERFigure 22-28.— Salt water circuit of a closed cooling system.75.209Xengine be kept free from abrasion and that therebe a minimum of friction and wear. If slidingcontact is made by two dry metal surfacesunder pressure, excessive friction, heat, andwear result. Friction, heat, and wear can begreatly reduced if metal -to-metal contact isprevented by keeping a clean film of lubricantbetween the metal surfaces.Lubrication and the system which supplieslubricating oil to engine parts that involve slidingor rolling contact are as important to successfulengine operation as air, fuel, and heatare to combustion. It is important not only thatthe proper type of lubricant be used, but alsothat the lubricant be supplied to the engine partsin the proper quantities, at the proper temperature,and that provisions be made to removeany impurities which enter the system. Theengine lubricating oil system is designed tofulfill the above requirements.The lubricating system of an engine may bethought of as consisting of two main divisions,that external to the engine and that within theengine. The internal division, or engine part,of the system consists principally of passagesand piping; the external part of the systemincludes several components which aid in supplyingthe oil in the proper quantity, at theproper temperature, and free of impurities. Inorder to meet these requirements, the lubricatingsystems of many engines include, externalto the engine, such parts as tanks and sumps,pumps, coolers, strainers and filters, and purifiers.These parts and their relative locationfor one type of engine are shown in figure 22-29.The engine system which supplies the oilrequired to perform the functions of lubricationis of the pressure type in practically all moderninternal combustion engines. Even though manyvariations exist in the details of engine lubricatingsystems, the parts of such a system andits operation are basically the same, whetherthe system is in a diesel or a gasoline engine.Any variance between the systems of the twotypes of engines is generally due to differencesin engine design and in opinions of manufacturersas to the best location of the component parts ofthe system. In many cases, similar types ofcomponents are used in the systems of dieseland gasoline engines.TRANSMISSION OF ENGINE POWERThe fundamental characteristics of an internalcombustion engine make it necessary,in many cases, for the drive mechanism to577

PRINCIPLES OF NAVAL ENGINEERINGCHECKVALVEtGLOBE VALVEfj^CHECK VALVE\FROM TRANSFERGLOBE VALVE-LUBRICATINGOIL PUMPITN LUBE oil COOLER TT METALjIEDGEJ GLOBE VALVESSTRAIHERFIl'tEROBE VALVE||tTO TRANSFERFLOWINDICATORN@tlilit^=lit^GLOBE VALVEFigure 22-29.— Sump-type lubricating oil filtering system.75.198Xchange both the speed and the direction of shaftrotation in the driven mechanism. There arevarious methods by which required changes ofspeed and directions may be made during thetransmission of power from the driving unitto the driven unit. In most installations the jobis accomplished by a drive mechanism consistingprincipally of gears and shafts.The process of transmitting engine power toa point where it can be used in performinguseful work involves a number of factors. Twoof these factors are torque and speed.The force which tends to cause a rotationalmovement of an object is called torque or"twist". The crankshaft of an engine suppliesa twisting force to the gears and shafts whichtransmit power to the driven unit. Gears areused to increase or decrease torque. If the rightcombination of gears is installed between theengine and the driven unit, the torque or "twist"will be sufficient to operate the drivenunit.If maximum efficiency is to be obtained, anengine must operate at a certain speed. In orderto obtain efficient engine operation, it might benecessary in some installations for the engineto operate at a higher speed than that requiredfor efficient operation of the driven unit. Inother cases the speed of the engine may haveto be lower than the speed of the driven unit.Through a combination of gears, the speed ofthe driven unit can be increased or decreasedso that the proper speed ratio exists betweenthe units.578

Chapter 22. -DIESEL AND GASOLINE ENGINESTypes of Drive MechanismsThe term indirect drive describes a drivemechanism which changes speed and torque.Drives of this type are common to many marineengine installations. Where the speed and thetorque of an engine need not be changed in orderto drive a machine satisfactorily, the mechanismused is a direct drive . Drives of thistype are commonly used where the enginefurnishes power for the operation of auxiliariessuch as generators and pumps.INDIRECT DRIVES.— The drive mechanismof most engine-powered ships and many boatsare of the indirect type. With indirect drive,the power developed by the engine(s) is transmittedto the propeller(s) indirectly, through anintermediate mechanism which reduces the shaftspeed. Speed reduction may be accomplishedmechanically (by a combination of gears) or byelectrical means.Mechanical drives include devices whichreduce the shaft speed of the driven unit, providea means for reversing the direction of shaftrotation in the driven unit, and permit quickdisconnectof the driving unit from the drivenunit.The combination ofgears which effects thespeed reduction is called a reduction gear. Inmost diesel engine installations, the reductionratio does not exceed 3 to 1; there are someunits, however, which have reductions as highas 6 to 1.The propelling equipment of a boat or a shipmust be capable of providing backing-down poweras well as forward motive power. There are afew ships and boats in \yhich backing down is accomplishedby reversing the pitch of the propeller;in most ships, however, backing down isaccomplished by reversing the direction of rotationof the propeller shaft. In mechanical drives,reversing the direction of rotation of the propellershaft may be accomplished in one of twoways: by reversing the direction of engine rotation,or by the use of reverse gears. Of thesetwo methods, the use of reverse gears is morecommonly employed in modern installations.More than reducing speed and reversing thedirection of shaft rotation is required of thedrive mechanism of a ship or a boat. It isfrequently necessary to allow an engine to operatewithout power being transmitted to thepropeller. For this reason, the drive mechanismof a ship or boat must include a means ofdisconnecting the engine from the propellershaft. Devices used for this purpose are calledclutches and couplings .The arrangement of the components in anindirect drive varies, depending upon the typeand size of the installation. In some small installations,the clutch or coupling, the reversegear, and the reduction gear may be combinedin a single unit; in other installations, the clutchor coupling and the reverse gear may be in onehousmg and the reduction gear in a separatehousing attached to the reverse-gear housing.Drive mechanisms arranged in either mannerare usually called transmissions. The arrangementof the components in two different types oftransmissions are shown in figures 22-30 and22-31.In the transmission shown in figure 22-30the housing is divided into two sections by thebearing carrier. The clutch or coupling assemblyis in the forward section, and the gear assemblyis in the after section of the housing.In the transmission shown in figure 22-31, notethat the clutch assembly and the reverse gearassembly are in one housing, while the reductiongear unit is in a separate housing (attached tothe clutch and the reverse gear housing).In large engine installations, the clutch orcoupling and the reverse gear may be combined;or they may be separate units, located betweenthe engine and a separate reduction gear; orthe clutch or coupling may be separate and thereverse gear andthe reduction gear may be combined.An assembly of the last type is shown infigure 22-32.In most geared-drive, multiple-propellerships, the propulsion units are independent ofeach other. An example of this type of arrangementis illustrated in figure 22-33.In some installations, the drive mechanismis arranged so that two or more engines drivea single propeller. This is accomplished byhaving the driving gear which is on, or connectedto, the crankshaft of each engine transmitpower to the driven gear on the propellershaft. In one type of installation, each of twopropellers is driven by four diesel engines.The arrangement of the engines, the location ofthe reduction gear, and the direction of rotationof the crankshaft and the propeller shaft in onetype of "quad" power unit are illustrated infigure 22-34.The drive mechanism illustrated includesfour clutch assemblies (one mounted to eachengine flywheel) and one gear box. The box579

PRINCIPLES OF NAVAL ENGINEERINGCAMSHAFTGEARFORWARDDISKPLUNGERREVERSEDISKSLIDINGSLEEVEIDLER GEAR Z-T'ii:THROWOUT FORKFORWARDSLEEVEREVERSESHAFTCRANKSHAFTGEARFLYWHEELBACKPLATEFLOATINGPLATE'FRONT'THROWOUTPLATEBEARINGFigure 22-30.— Transmission with independent oil system.75.245-OPERATINGLEVER-DRUM ^ BRAKE BANDINTERNALGEAR V EXTERNALPROPELLER \GEARSHAFT ,\^rfiSlREDUCTION GEAR UNIT ^ CLUTCH AND /^CRANKSHAFT GEARREVERSE GEAFHOUSINGFigure 22-31.— Clutch and reverse gear assembly with attached reduction gear unit.75.246580

Chapter 22. -DIESEL AND GASOLINE ENGINESFORWARD DRUMany time. An increase or decrease in generatorvoltage is used as a means of controllingthe speed of the propeller. Changes in generatorvoltage may be brought about by electricalmeans, by changes in engine speed, and by acombination of these methods. The controls ofan electric drive may be in a location remotefrom the engine, such as the pilot house.In an electric drive, reversing the directionof rotation of the propeller is not accomplishedby the use of a reverse gear. The electricalsystem is arranged so that the flow of currentthrough the motor can be reversed. This reversalof current flow causes the motor torevolve in the opposite direction. Thus, thedirection of rotation of the motor and of thepropeller can be controlled by manipulating theelectrical controls.REVERSE STEP-UP PINION75.247Figure 22-32.— Clutch and reverse reductiongear assembly.contains two drive pinions and the main drivegear. Each pinion is driven by the clutch orcoupling shafts of two engines, through splinesin the pinion hubs. The pinions drive the singlemain gear, which is connected to the propellershaft.Electric drives are used in the propulsionplants of some diesel-driven ships. With electricdrive, there is no mechanical connectionbetween the engine(s) and the propeller(s). Insuch plants, the diesel engines are connecteddirectly to generators. The electricity producedby such an engine-driven generator is transmitted,through cables, to a motor. The motoris connected to the propeller shaft directly, orindirectly through a reduction gear. When areduction gear is included in a diesel-electricdrive, the gear is located between the motorand the propeller.The generator and the motor of a dieselelectricdrive may be of the alternating current(a-c) type or of the direct current (d-c) type;almost all diesel-electric drives in the Navy,however, are of the direct current type. Sincethe speed of a d-c motor varies directly withthe voltage furnished by the generator, the controlsystem of an electric drive is so arrangedthat the generator voltage can be changed atDIRECT DRIVES.— In some marine engineinstallations, power from the engine is transmittedto the driven unit without a change inshaft speed; that is, by a direct drive. In adirect drive, the connection between the engineand the driven unit may consist of a "solid"coupling, a flexible coupling, or a combinationof both. A clutch may or may not be includedin a direct drive, depending upon the type ofinstallation. In some installations, a reversegear is included.Solid couplings vary considerably in design.Some solid couplings consist of two flangesbolted solidly together. In other direct drives,the driven unit is attached directly to the enginecrankshaft by a nut.Solid couplings offer a positive means oftransmitting torque from the crankshaft of anengine; however, a solid connection does notallow for any misalignment nor does it absorbany of the torsional vibrations transmitted fromthe engine crankshaft or shaft vibrations.Since solid coupling will not absorb vibrationand will not permit any misalignment, mostdirect drives consist of a flange-type couplingwhich is used in connection with a flexiblecoupling. Connections of the flexible type arecommon to the drives of many auxiliaries, suchas engine-generator sets. Flexible couplingsare also used in indirect drives to connect theengine to the drive mechanism.The two solid halves of a flexible couplingare joined by a flexible element. The flexibleelement is made of rubber, neoprene, or steelsprings. Two views of one type of flexiblecoupling are shown in figure 22-35.581

PRINCIPLES OF NAVAL ENGINEERINGOILSTRAINER^G AIR STRAINERR A NO REDUCINGVALVESA^SIBOARDFigure 22-33.— Example of independent propulsion units.75.248XTlie coupling illustrated has radial springpacks as the flexible element. The power fromthe engine is transmitted from the inner ring,or spring holder, of the coupling, through a numberof spring packs to the outer spring holder,or driven member. A large driving disk connectsthe outer spring holder to the flange onthe driven shaft. The pilot on the end of thecrankshaft fits into a bronze, bushed bearing onthe outer driving disk to center the driven shaft.The ring gear of the jacking mechanism ispressed onto the rim of the outer spring holder.The inner driving disk, through which thecamshaft gear train is driven, is fastened to theouter spring holder. A splined ring gear isbolted to the inner driving disk. This helical,internal gear fits on the outer part of the crankshaftgear and forms an elastic drive, throughthe crankshaft gear which rides on the crankshaft.The splined ring gear is split and the twoparts are bolted together with a spacer block ateach split-joint.The parts of the coupling shown in figure22-35 are lubricated by oil flowing from thebearing bore of the crankshaft gear through thepilot bearing.CLUTCHES, REVERSE GEARS, ANDREDUCTION GEARSClutches may be used on direct-driven propulsionNavy engines to provide a means ofdisconnecting the engine from the propellershaft. In small engines, clutches are usuallycombined with reverse gears and used formaneuvering the ship. In large engines, specialtypes of clutches are used to obtain specialcoupling or control characteristics, and to preventtorsional vibration.Reverse gears are used on marine enginesto reverse the direction of rotation of the propellershaft, when maneuvering the ship, withoutchanging the direction of rotation of the engine.They are used principally on relatively smallengines. If a high-output engine has a reversegear, the gear is used for low-speed operationonly, and does not have full-load and full-speedcapacity. For maneuvering ships with large582

^ 5Chapter 22. -DIESEL AND GASOLINE ENGINESO O Qc]0 OO O [ra] O OiO O [la] O O :fh17o o dilo o —Figure 22-34.— Four engines (quad unit) arranged to drive one propeller.75.249Xdirect-propulsion engines, the engines are reversed.Reduction gears are used to obtain lowpropeller-shaft speed with a high engine speed.When accomplishing this, the gears correlatetwo conflicting requirements of a marine engineinstallation. These opposing requirements are:(1) for minimum weight and size for a givenpower output, engines must have a relativelyhigh rotative speed; and (2) for maximum efficiency,propellers must rotate at a relativelylow speed, particularly where high thrust capacityis desired.Friction Clutches and Gear AssembliesFriction clutches are commonly used withsmaller, high-speed engines, up to 500 hp.However, certain friction clutches, in combinationwith a jaw-type clutch, are used withengines up to 1400 hp; and pneumatic clutches,with a cylindrical friction surface, with enginesup to 2000 hp.Friction clutches are of two general styles;the disk and the band styles. In addition, frictionclutches can be classified into dry and wettypes, depending upon whether the friction surfacesoperate with or without a lubricant. Thedesigns of both types are similar, except thatthe wet clutches require a large friction areabecause of the reduced friction coefficient betweenthe lubricated surfaces. The advantagesof wet clutches are smoother operation and lesswear of the friction surfaces. Wear resultsfrom slippage between the surfaces not onlyduring engagement and disengagement, but also,to a certain extent, during the operation of themechanism. Some wet-type clutches are filledwith oil periodically; in other clutches the oil,being a part of the engine-lubricating system,is circulated continuously. Such afriction clutchincorporates provisions which will preventworn-off particles from being carried by thecirculating lubricating oil to the bearings, gears,etc.The friction surfaces are generally constructedof different materials, one being of cast ironor steel; the other is lined with some asbestosbasecomposition, or sintered iron or bronzefor dry clutches, and bronze, cast iron, or steelfor wet clutches. Cast-iron surfaces are preferredbecause of their better bearing qualitiesand greater resistance to scoring or scuffing.583

PRINCIPLES OF NAVAL ENGINEERINGOUTERSPRING HOLDERFITTED BOLTINNERSPRING HOLDER.INE RINGOIL SLINGER?ANKSHAFTTAP BOLTPILOT BUSHINGpOUTER DRIVINGDISKTURNING RINGGEAR

Chapter 22. -DIESEL AND GASOLINE ENGINESIDLER GEARFORWARD ROTATION75.252Figure 22-36. — Forward and reverse gear trainsfor Gray Marine engines.The clutch operating lever moves the throwoutfork, which in turn shifts the sliding sleevelengthwise along the forward shaft. When theoperating lever is placed forward, the slidingsleeve is forced backward. In this position thelinkages of the spring-loaded mechanism pullthe floating pressure plate against the forwarddisk, and cause forward rotation. When the operatinglever is pulled back as far as it can go,the sliding sleeve is pushed forward. In thisposition, the floating pressure plate engages thereverse disk and back plate for reverse rotation.The clutch has a positive neutral which isset by placing the operating lever in a middleposition. Then the sliding sleeve is also in amiddle position, and the floating plate rotatesfreely between the two clutch disks. (The onlycontrol that the operator has is to cause thefloating plate to bear heavily against either theforward disk or the reverse disk, or to put thefloating plate in the positive neutral positionso that it rotates freely between the twodisks.)The reversing gear unit is lubricated separatelyfrom the engine by its own splash system.The oil level of the gear housing should neverbe kept over the high mark because too muchoil will cause overheating of the gear unit. Theoil is cooled by air which is blown through thebaffled top cover by the rotating clutch. Greasefittings are installed for bearings not lubricatedby the oil.JOE'S DOUBLE CLUTCH REVERSE GEAR.-A gear mechanism found on many power boatsis Joe's double clutch reverse gear. The installationof a typical Joe's reverse gear andclutch assembly for the Navy type DC engineis shown in figure 22-37. The drive from theengine crankshaft is taken into the clutch andreverse gear housing by an extension of thecrankshaft drive gear. The crankshaft rotationis transmitted to the reduction gear shaft throughthe clutch and the reverse gear unit.If one could open the clutch and reverse gearhousing and watch the reverse gear drum andthe reduction gear shaft while the engine is running,the following operation would be observed:When the operating lever is thrown forward,the drum and reduction gear shaft rotate in thesame direction as the engine crankshaft. Thiscauses forward rotation of the propeller.In the intermediate position of the operatinglever, the drum rotates but the reduction gearshaft remains stationary. This is the neutralsetting.Forward rotation is obtained by dual clutchaction while reverse rotation is obtained throughthe operation of the planetary gears. The unitconsists of a housing enclosing a split conicalclutch and a multi-plate friction clutch andgearing. Additional components include the collarand yoke and an outer brake band with anoperating toggle mechanism. Movement of thesliding collar selects the direction of rotation.When the operating lever is placed in theforward position, the linkage between the leverand the collar and yoke assembly slides thecollar lengthwise to the left along the reductiongear shaft. This motion operates the toggleassembly which, in turn, drives the threeplungers to the right, pressing them hard againstthe disk clutch.When the plungers are driven hard againstthe disk clutch, the disks are locked togetherby friction. This locks the drum housing to the585

PRINCIPLES OF NAVAL ENGINEERINGDISK CLUTCH-7/-BEARING CAGETOGGLE ASSEMBLY.CONECLUTCHFRONT COVERENGINE SHAFTCOLLAR ANDYOKEREDUCTIONGEAR SHAFTPROPELLERDRIVE SLEEVEENGINE SLEEVEPINION GEAR (LONG)PINION GEAR (SHORT)Figure 22-37.— Cutaway view of Joe's clutch and reverse gear.75.254propeller drive sleeve. In addition, tiie force ofthe plungers on the disk clutch is transmittedto the bearing cage, which is a cylinder containingthe reverse gear pinions. The bearingcage, in turn, is pressed against the cone clutch.Thus, the cone clutch is forced against its seatin the front cover of the gear box, clamping theclutch to the front cover by friction. Since thecone clutch is in mesh on its inner surface withthe engine sleeve, which is in turn keyed to theengine shaft, the front cover is now locked tothe engine shaft. The front cover must rotatewith the engine shaft, in the same direction.Now, since the front cover is bolted to thedrum housing, which is locked to the propellerdrive sleeve by the disk clutch, there is a completelock from the engine shaft to the reductiongear shaft. The entire assembly rotatesas a unit in the same direction as the engineshaft; this motion gives the propeller a forwardrotation.When the operating lever is thrown into thereverse position, the plungers are withdrawn.and both clutches are disengaged. At thesame time the brake band is tightened aroundthe drum, holding the drum stationary. Thebearing cage is locked to the drum. The coneclutch rotates freely out of contact with the frontcover. Then the motion from the engine shaft tothe reduction gear shaft is transmitted throughthe inner gear assembly.The reverse gear pinions are held in thebearing cage, which is stationary for reverserotation. There are three short pinions, eachin mesh with the small inner gear of the enginesleeve. The three short pinions mesh with thethree long pinions, each of which also mesheswith the propeller drive sleeve gear. Enginerotation is transmitted from the engine sleeveto the short pinions, to the long pinions, and tothe propeller drive sleeve. These pinions (geartrain) cause the reduction gear shaft to rotateopposite to the engine rotation (see arrows infig. 22-37), and give the propeller a reverserotation.586

Chapter 22. -DIESEL AND GASOLINE ENGINESNote that in figure 22-38, which shows themechanism more clearly, the gears are set forreverse rotation, and the brake band is clampedto the drum. The parts which are shaded are heldstationary by the brake band, and the remaininginternal parts, which are not shaded, rotate. (Therotation of the engine shaft and engine sleeve istransmitted directly to the cone clutch and theshort pinions. The cone clutch rotates freely outof contact with the stationary front cover. Theshort pinions drive the long pinions, which drivethe propeller drive sleeve. The latter unit iskeyed to and drives the reduction gear shaft,which rotates opposite to the engine shaft.)The reduction gear unit is bolted to thereverse gear housing, as shown in figure 22-31. It consists merely of an external gear,mounted on the reduction gear shaft, and in meshwith a larger internal gear, mounted on the propellershaft. Power is transferred, at a reducedspeed, from the smaller drive gear to the largerinternal gear.Lubrication of the clutch and reverse gearmechanism is accomplished by means of adrilled passage in the crankshaft which suppliesoil, as a spray, to the gears and other movingparts. This oil returns to the engine sump bygravity.Lubrication of the reduction gear unit isaccomplished by an external line from theengine's main oil gallery. Oil is sprayed overthe gears and moving parts to lubricate andcool them. Excess oil either drains back to theengine sump by gravity, or, where the unit isbelow the engine, returns to the sump by meansof a scavenging pump.Airflex Clutch and Gear Assembly.— On thelarger diesel-propelled ships, the clutch, reverseand reduction gear unit has to transmit anenormous amount of power. To maintain theweight and size of the mechanism as low aspossible, special clutches have been designedfor large diesel installations. One of these isthe airflex clutch and gear assembly used withsome General Motors engines on LST's.A typical airflex clutch and gear assembly,for ahead and astern rotation, is shown infigure22-32. There are two clutches, one for forwardrotation and one for reverse rotation. Theclutches are bolted to the engine flywheel bymeans of a steel spacer, so that they both rotatewith the engine at all times, and at engine speed.Each clutch has a flexible tire (or gland) on theinner side of a steel shell. Before the tires areinflated, they will rotate out of contact with thedrums, which are keyed to the forward andreverse drive shafts. When air under pressure(100 psi) is sent into one of the tires, the insidediameter of the clutch decreases. This causesthe friction blocks on the inner tire surface tocome in contact with the clutch drum, lockingthe drive shaft with the engine.The parts of the airflex clutch which givethe propeller ahead rotation are illustrated inthe upper view of figure 22-32. The clutch tirenearest the engine (forward clutch) is inflatedto contact and drive the forward drum with theengine. The forward drum is keyed to the forwardTOGGLE PLUNGER BRAKE MECHANISMASSEMBLY -^^^^>i^ /r BRAKE BANDLONG PINIONDRUMSHORT PINIONCOLLARAND YOKEREDUCTIONGEAR SHAFTPROPELLERDRIVE SLEEVEENGINE SLEEVEENGINE SHAFTFigure 22-38.— Schematic diagram of Joe's reverse gear assembly.75.255587

PRINCIPLES OF NAVAL ENGINEERINGdrive shaft, which carries the double helicalforward pinion at the after end of the gear box.The forward pinion is in constant mesh with thedouble helical main gear, which is keyed on thepropeller shaft. By following through the geartrain, you can see that, for ahead motion, thepropeller rotates in a direction opposite to theengine's rotation.The parts of the airflex clutch which givethe propeller astern rotation are illustrated inthe lower view of figure 22-32. The reverseclutch is inflated to engage the reverse drum,which is then driven by the engine. The reversedrum is keyed to the short reverse shaft, whichsurrounds the forward drive shaft. A largereverse step-up pinion transmits the motion tothe large reverse step-up gear on the uppershaft. The upper shaft rotation is opposite tothe engine's rotation. The main reverse pinionon the upper shaft is in constant mesh with themain gear. By tracing through the gear train,it may be seen that, for reverse rotation, thepropeller rotates in the same direction as theengine.The diameter of the main gear of the airflexclutch is approximately 2 1/2 times as greatas that of the forward and reverse pinions. Thus,there is a speed reduction of 2 1/2 to 1 fromeither pinion to the propeller shaft.Since the forward and main reverse pinionsare in constant mesh with the main gear, theset that is not clutched in will rotate as idlersdriven from the main gear. The idling gearsrotate in a direction opposite to their rotationwhen carrying the load. For example, with theforward clutch engaged, the main reverse pinionrotates in a direction opposite to its rotation forastern motion (note the dotted arrow in the upperview of figure 22-32. Since the drums rotate inopposite directions, a control mechanism is installedto prevent the engagement of both clutchessimultaneously.The airflex clutch is controlled by an operatinglever which works the air control housing,located at the after end of the forward pinionshaft. The control mechanism, shown with theairflex clutches in figure 22-39, directs the highpressure air into the proper paths to inflatethe clutch glands (tires). The air shaft, whichconnects the control mechanism to the clutches,passes through the forward drive shaft.The supply air enters the control housingthrough the air check valve and must pass throughthe small air orifice. The purpose of the restrictedorifice is to delay the inflation of theclutch to be engaged, when shifting from onedirection of rotation to the other. The delay isnecessary to allow the other clutch to be fullydeflated and out of contact with its drum beforethe inflating clutch can make contact with itsdrum.The supply air goes to the rotary air jointin which a hollow carbon cylinder is held tothe valve shaft by spring tension. This preventsleakage between the stationary carbonseal and the rotating air valve shaft. The airgoes from the rotary joint to the four-way airvalve. The sliding-sleeve assembly of the fourwayvalve can be shifted endwise along the valveshaft by operating the control lever.When the shifter arm on the control leverslides the valve assembly away from the engine,air is directed to the forward clutch. The fourwayvalve makes the connection between the airsupply and the forward clutch, as follows: thereare eight neutral ports which connect the centralair supply passage in the valve shaft withthe sealed air chamber in the sliding member.In the neutral position of the four-way valve, asshown in figure 22-39, the air chamber is adead end for the supply air. In the forwardposition of the valve, the sliding member uncoverseight forward ports, which connect withthe forward passages conducting the air to theforward clutch. The air now flows through theneutral ports, air chamber, forward ports, andforward passages to inflate the forward clutchgland. As long as the valve is in the forwardposition, the forward clutch will remain inflatedand the entire forward air system will remainat a pressure of100 psi.LUBRICATION.— On most large gear units,a separate lubrication system is used. Onelubrication system is shown in figure 22-40.Oil is picked up from the gear box by an electricdrivengear-type lubricating oil pump and issent through a strainer and cooler. After beingcleaned and cooled, the oil is returned to thegear box to cool and lubricate the gears. Intwin installations, such as shown in figure 22-40 a separate pump is used for each unit and astandby pump is interconnected for emergencyuse.Hydraulic Clutches or CouplingsThe fluid clutch (coupling) is widely usedon Navy ships. The use of hydraulic coupling588

Chapter 22. -DIESEL AND GASOLINE ENGINESFRICTION BLOCKSFORWAFD CLUTCHSHIFTER ARMCONTROLLEVER\NEUTRAL PORTS V)FORWARD^'ROTARY AIRJOINTSPRINGCARBON CYLINDERFORmRD PORTSAIR]SEALSFOUR-WAY VALVEEMERGENCYSHAFTAIRFITTINGORIFICECHECKAIRVALVEREVERSE PASSAGEREVERSE CLUTCHFigure 22-39.— Airflex clutches and control valves.75.257eliminates the need for a mechanical connectionbetween the engine and the reduction gears.Couplings of this type operate with a minimumof slippage.Some slippage is necessary for operation ofthe hydraulic coupling, since torque is transmittedbecause of the principle of relative motionbetween the two rotors. The power lossresulting from the small amount of slippage istransformed into heat which is absorbed by theoil in the system.Compared with mechanical clutches, hydraulicclutches have a number of advantages. Thereis no mechanical connection between the drivingand driven elements of the hydraulic coupling.Power is transmitted through the coupling veryefficiently (97 percent) without transmittingtorsional vibrations, or load shocks, from theengine to the reduction gears. This protects theengine, the gears, and the shafting from suddenloads which may occur as a result of pistonseizure or fouling of the propeller. The poweris transmitted entirely by the circulation of adriving fluid (oil) between radial passages in apair of rotors. In addition, the assembly of thehydraulic coupling will absorb or allow forslight misalignment.The two rotors and the oil-sealing cover ofa typical hydraulic coupling are shown in figure22-41. The primary rotor (impeller) is attachedto the engine crankshaft. The secondary rotor(runner) is attached to the reduction gear pinionshaft. The cover is bolted to the secondaryrotor and surrounds the primary rotor. Eachrotor is shaped like a half-doughnut with radialpartitions. A shallow trough is welded into thepartitions around the inner surface of the rotor.The radial passages tunnel under this trough(as indicated by the white arrows in fig. 22-41).589

PRINCIPLES OF NAVAL ENGINEERINGREDUCTION GEAR OIL COOLERREDUCTION GEAR OIL COOLERPORT REDUCTION GEAR STARBOARD REDUCTION GEARFigure 22-40.— Schematic diagram of reverse gear lubrication system.75.258When the coupling is assembled, the tworotors are placed facing each other to completethe doughnut (fig. 22-42). The rotors do not quitetouch each other, the clearance between thembeing 1/4 to 5/8 inch, depending on the size ofthe coupling. The curved radial passages of thetwo rotors are opposite each other, so that theouter passages combine to make a circularpassage except for the small gaps between therotors.In the hydraulic coupling assembly, shown infigure 22-42, the driving shaft is secured to theengine crankshaft and the driven shaft goes tothe reduction gear box. The oil inlet admits oildirectly to the rotor cavities, which becomecompletely filled. The rotor housing is boltedto the secondary rotor and has an oil-sealedjoint with the driving shaft. A ring valve,going entirely around the rotor housing, can beoperated by the ring valve mechanism to openor close a series of emptying holes (fig. 22-42)housing. When the ring valve is opened, the oilwill fly out from the rotor housing into thecoupling housing, draining the coupling completelyin two or three seconds. Even when thering valve is closed, some oil leaks out intothe coupling housing, and additional oil entersthrough the inlet. From the coupling housing,the oil is drawn by a pump to a cooler, thensent back to the coupling.Another coupling assembly used on severalNavy ships is the hydraulic couplingwithpistontypequick-dumping valves, .shown in figure 22-43. In this coupling, in which the operation is590

Chapter 22. -DIESEL AND GASOLINE ENGINESRING VALVEMECHANISM!SECONDARY ROTOR(RUNNER)RINGVALVESECONDARYROTORRADIALPASSAGERADIALPASSAGEPRIMARY ROTOR ^'(IMPELLER)COVER ORROTOR HOUSING'DRIVENSHAFTROTORHOUSING \\(COVERCOUPLINGHOUSINGRING VALVE-5.33Figure 22-41.— Runner, impeller, and cover ofhydraulic coupling.similar to the one described above, a seriesof piston valves, around the periphery of therotor housing, are normally held in the closedposition by springs. By means of air oil pressureadmitted to the valves, as shown in figure22-43, the pistons are moved axially so as touncover drain ports, allowing the coupling toempty. Where extremely rapid declutching isnot required, the piston-valve coupling offersthe advantages of greater simplicity and lowercost than the ring-valve coupling.Another type of self-contained unit for certaindiesel engine drives is the scoop controlcoupling, shown in figure 22-44. In couplingsof this type, the oil is picked up by one of twoscoop tubes (one tube for each direction ofrotation), mounted on the external manifold.Each scoop tube contains two passages: asmaller one (outermost) handles the normalflow of oil for cooling and lubrication, and alarger one which rapidly transfers oil from thereservior directly to the working circuit.^^RAIN75,260Figure 22-42.— Hydraulic coupling assembly.The scoop tubes are operated from the controlstand through a system of linkages. Asone tube moves outward from the shaft centerlineand into the oil annulus, the other is beingretracted.Four spring-loaded centrifugal valves aremounted on the primary rotor. These valvesare arranged to open progressively as the speedof the primary rotor decreases. The arrangementprovides the necessary oil flow for coolingas it is required. Quick-emptying pistonvalves are provided to give rapid emptying ofthe circuit when the scoop tube is withdrawnfrom contact with the rotating oil annulus.Under normal circulating conditions, oil fedinto the collector ring passes into the pistonvalve control tubes. These tubes and connectingpassages conduct oil to the outer end of thepistons. The centrifugal force of the oil in thecontrol tube holds the piston against the valveport, thus sealing off the circuit. When thescoop tube is withdrawn from the oil annulusin the reservoir, the circulation of oil will be591

PRINCIPLES OF NAVAL ENGINEERINGin*>>Bftfi3•OJiuIcofteI1•oICOCM«592

Chapter 22. -DIESEL AND GASOLINE ENGINES4 CENTRIFUGAL VALVESROTATING RESERVOIRPRIMARY ROTOR (IMPELLER:COLLECTOR RINGSECONDARY ROTOR (RUNNER)LUBE OIL FROM ENGINE 3 GPM - 10 PSILUB OIL RETURN TO ENGINE(GRAVITY)SCOOP TUBEPISTON VALVE CONTROL TUBE4 QUICK-EMPTYING PISTON VALVESFigure 22-44.— Scoop control hydraulic coupling.75.262interrupted and the oil in the control tubes willbe discharged through the orifice in the outerend of the piston housing. This releases thepressure on the piston and allows it to moveoutward, thus opening the port for rapid dischargeof oil. Resumption of oil flow from thescoop tube will fill the control tubes; and thepressure will move the piston to the closedposition.When the engine is started and the couplingis filled with oil, the primary rotor turns withthe engine crankshaft. As the primary rotorturns, the oil in its radial passages flows outward,under centrifugal force. (See arrows infig. 22-42.) This forces oil across the gap atthe outer edge of the rotor and into the radialpassages of the secondary rotor, where the oilflows inward. The oil in the primary rotor isnot only flowing outward, but is also rotating.As the oil flows over and into the secondaryrotor, it strikes the radial blades in the rotor.The secondary rotor soon begins to rotateand pick up speed, but it will always rotatemore slowly than the primary rotor because ofdrag on the secondary shaft. Therefore, thecentrifugal force of the oil in the primary rotorwill always be greater than that of the oil in thesecondary rotor. This causes a constant flowfrom the primary rotor to the secondary rotorat the outer ends of the radial passages, andfrom the secondary rotor to the primary rotorat the inner ends.The power loss in the hydraulic clutch issmall (3 percent) and is caused by friction inthe fluid itself. This means that approximately97 percent of the power delivered to the primaryrotor is transmitted to the reduction gear.The loss power is transformed into heat that isabsorbed by the oil— which is the reason forsending part of the oil through a cooler at alltimes.MAINTENANCEKeeping an internal combustion engine (dieselor gasoline) in good operating condition demandsa well-planned procedure of periodic inspection.593

.PRINCIPLES OF NAVAL ENGINEERINGadjustments, maintenance, and repair. If inspectionsare made regularly, many maladjustmentscan be detected and corrected before aserious casualty results. A planned maintenanceprogram will help to prevent majorcasualties and the occurrence of many operatingtroubles.There may be times when service requirementsinterfere with a planned maintenanceprogram. In this event, routine maintenancemust be performed as soon as possible afterthe specified interval of time has elapsed.Necessary corrective measures should be accomplishedas soon as possible; if repair jobsare allowed to accumulate, the result may behurried and incomplete work.Since the Navy uses so many models ofinternal combustion engines, it is impossibleto specify any detailed overhaul procedure thatis adaptable to all models. However, there areseveral general rules which applyto all engines.They are:1. Detailed repair procedures are listed inmanufacturers' instruction manuals and maintenancepamphlets. Study the appropriate manualsand pamphlets before attempting any repairwork. Pay particular attention to tolerances,limits, and adjustments.2. The highest degree of cleanliness mustbe observed in handling engine parts duringoverhaul.3. Before starting repair work, be sure thatall required tools and replacements for knowndefective parts are available.4. Detailed records of repairs should bekept. Such records should include the measurementsof parts, hours in use, and new partsinstalled. An analysis of such records willindicate the hours of operation that may beexpected from the various engine parts. Thisknowledge is helpful as an aid in determiningwhen a part should be renewed in order toavoid a failure.5. Detailed information on preventive maintenanceis contained in the PMS Manual for theengineering department. All preventive maintenanceshould be accomplished in accordancewith the (3-M System) Planned MaintenanceSubsystem which is based upon the properutilization of the PMS manuals. MaintenanceSYSTEMPropuls ionSUB-SVSTFMPropulsionUnitsCOMPONENTPropulsion DieselT3 - T4RELATED M.R.R-5MB cesCBipTioN AFTER 750 HOURS OF OPERATION:1. Inspect cap screws on cylinder retainersfor tightness.2. Inspect valve tappets for proper clearance.SAFETY PRECAUTIONSM.n NUMBEREID R-6RATESEN2BN3FNTOTAL M/H:2.02.02.06.0ELAPSED TIME;1. Air starting valve wired shut and tagged, "DO NOT OPEN".2. Injection pump must be in stop position when jacking engineby handTOOLS. PARTS MATERIALS, TEST EQUIPMENT1. Cover gasket H-75 PAM 108662. Torque wrench3. Socket set^. Feeler gauge5. Blowdown valve wrenchPROCEDURENOTE: To be done when engine is hot.6. Jacking bar7. Wire and tag8. NAVSHIPS 341-33931. a. Remove valve cover.b. Remove vibration damper cover plate.c. Install barring socket plate.d. Open blow down valves.e. Using torque wrench and special torquelng tool. Inspectcap screws in cylinder retainer for tightness (216inch pounds torque).f. Continue checking and adjusting torque until a completeround is made with no movement of the screws.NOTE: Working clockwise, check cap screw tightness Infollowing order 1, 5, 9, 7, 4, 2, 6, 10, 8, 3.2. a. With barring socket in place, jack engine as neededto measure each valve tappet clearance.Maximum clearance 0.15 Minimum clearance .007o. Remove barring socket plate and re-install the capscrews in vibration damper.c. Re-install vibration damper cover plate.

CHAPTER 23GAS TURBINESThe gas turbine engine, long regarded asa promising but experimental prime mover,has in recent years been developed to the pointwhere it is entirely practicable for ship propulsionand for a number of auxiliary applications.Gas turbine engines are currently installedas prime movers on minesweepers,landing craft, PT boats, air-sea rescue boats,hydrofoils, hydroskimmers, and other craft. Inaddition, the gas turbine engine is finding increasingapplication as the driving unit forship's service generators, pumps, and otherauxiliary units.Although the gas turbine engine as a typeneed no longer be regarded as experimental,many specific models of gas turbine engines arestill at least partially experimental and subjectto further change and development. The discussionin this chapter therefore deals primarilywith the general principles of gas turbineengines rather than with specific models. Detailedinformation on any specific model maybeobtained from the manufacturer's technical manualfurnished with the equipment.BASIC PRINCIPLESThermodynamic cycles are discussed in chapter 8 ofthis text.The gas turbine engine bears some resemblanceto an internal combustion engine of thereciprocating type and some resemblance to asteam turbine. However, a brief considerationof the basic principles of a gas turbine enginereveals several ways in which the gas turbineengine is quite unlike either the reciprocatinginternal combustion engine or the steam turbine.Let us look first at the thermodynamiccycles of the three engine types. The reciprocatinginternal combustion engine has an open,heated-engine cycle and the steam turbine*^ hasa closed, unheated- engine cycle. In contrast, thegas turbine has an open, unheated- engine cycle—a combination we have not previously encounteredin our study of naval machinery. The gasturbine cycle is open because it includes theatmosphere; it is an unheated-engine cycle becausethe working substance is heated in a devicewhich is separate from the engine.Another way in which the three types ofengines differ is in the working substance. Theworking fluid in a steam turbine installation issteam. In both the reciprocating internal combustionengine and the gas turbine engine, theworking fluid may be considered as being thehot gases of combustion that result from theburning of fuel in air. However, there are veryimportant differences in the way the workingfluid is used in the reciprocating internal combustionengine and in the gas turbine engine.Still other differences in the three types ofengines become apparent when we consider thearrangement and relationship of component partsand the processes that occur during the cycle.From our study of previous chapters of thistext, we are already familiar with the functionalarrangement of parts in steam turbine installationsand in reciprocating internal combustionengines. Now let us look at the relationship ofthe major components in a basic gas turbineengine, as illustrated schematically in figure23-1.In the steam turbine installation, the processesof combustion and steam generation takeInternal combustion engines are discussed In chapter22.3 Steam turbines are discussed In chapter 12 and Inchapter 16.595

PRINCIPLES OF NAVAL ENGINEERINGCOMBUSTIONCHAMBERSTARTERPROPULSIONPOWERCOUPLINGCOMPRESSOR SHAFT TURBINEATMOSPHERICAIR INTAKEEXHAUST TOATMOSPHERE147.135Figure 23-1.— Schematic diagram showing relationship of parts in single-shaft gas turbine engine.place in the boiler, while the process by whichthe thermal energy of the steam is converted intomechanical work takes place in the turbine. Inthe reciprocating internal combustion engine,three processes— the compression of atmosphericair, the combustion of a fuel-air mixture,and the conversion of heat to work— all takeplace in one unit, the cylinder. The gas turbineengine is similar to the reciprocating internalcombustion engine in that the same three processes—compression,combustion, and conversionof heat to work— occur; but it is unlike thereciprocating internal combustion engine in thatthese three processes take place in three separateunits rather than in one unit. In the gasturbine engine, the compression of atmosphericair is accomplished in the compressor; the combustionof fuel is accomplished in the combustionchamber; and the conversion of heat to workis accomplished in the turbine.Many different types and models of gasturbine engines are in use. The gas turbineengine shown in figure 23-1 is called a single -shaft type because one shaft from the turbinerotor drives the compressor and an extensionof this same shaft drives the load.The gas turbine engine shown in figure 23-2is called a split- shaft type. This engine is consideredto be split into two sections: the gasproducingsection, or gas generator, and thepower turbine section. The gas-generator section,in which a stream of expanding gases iscreated as a result of continuous combustion,includes the compressor, the combustion chamber(or chambers), and the gas-generator turbine.The power turbine section consists of apower turbine and the power output shaft. In thistype of gas turbine engine, there is no mechanicalconnection between the gas-generator turbineand the power turbine. When the engine isoperating, the two turbines produce basically thesame effect as that produced by a hydraulictorque converter. The split shaft gas turbineengine is well suited for use as a propulsionunit where loads vary, since the gas-generatorsection can be operated at a steady and continuousspeed while the power turbine sectionis free to vary with the load. Starting effortrequired for a split-shaft gas turbine engineis far less than that required for a single-shaftgas turbine engine connected to the reductiongear, propulsion shaft, and propeller.In the twin- spool gas turbine engine (fig.23-3) the air compressor is split into twosections or stages and each stage is drivenby a separate turbine element. The lowpressureturbine element drives the low pressure compressorelement and the high pressure turbineelement drives the high pressure compressor596

Chapter 23. -GAS TURBINEGAS -GENERATOR SECTIONPOWER TURBINE SECTIONCOMBUSTIONCHAMBERSTARTERCOMPRESSORSHAFTGAS-GENERATORTURBINEPOWERTURBINESHAFTPROPULSIONPOWERCOUPLINGi147,136Rgure 23-2.— Schematic diagram showing relationship of parts in split-shaft gas turbine engine.element. Like the split-shaft type, the twinspoolgas turbine engine is usually divided intoa gas-generator section and a power turbinesection. However, some twin- spool gas turbineengines are so arranged that the low pressureturbine element drives the low pressure compressorelement and the power output shaft.The basic cycle of the gas turbine engineis one of isentropic compression, constantpressureheat addition, isentropic expansion,and constant-pressure heat rejection. As thehot combustion gases are expanded through theturbine, converting thermal energy into mechanicalwork, some of the turbine work is used todrive the compressor and the remainder is usedto drive the load. The power output from theturbine is steady and continuous and, after theinitial start, self-sustaining.Although this chapter deals only with gasturbine engines which operate on the simpleopen cycle, it should be mentioned that othercycles are also of interest to designers of gasturbine engines. Among the cycles that havebeen considered (and to some extent used) arethe closed cycle, the semi-open cycle, andvarious modifications of the simple open cycle.In one such modification, known as the regen -erated open cycle , the hot exhaust gases from theturbine are passed through a heat exchanger inwhich they give up some heat to the air betweenthe compressor discharge and the inlet to thecombustion chamber. The utilization of this heatdecreases the amount of fuel required and therebyincreases the efficiency of the cycle.FUNCTIONS OF COMPONENTSAs we have seen, the three major componentsof a gas turbine engine are the compressor,the combustion chamber, and the turbine.In addition, the engine requiresanumber of othercomponents, accessories, and systems in orderto operate as a complete unit. The functions ofthe gas turbine engine components are describedin the following sections.CompressorThe compressor takes in atmospheric airand compresses it to a pressure of several597

PRINCIPLES OF NAVAL ENGINEERINGGAS-GENERATOR SECTIONPOWER TURBINESECTIONCOMBUSTIONCHAMBERCOMPRESSORSHAFT-L P ELEMENTiiTURBINEPOWERTURBINEPROPULSIONPOWERCOUPLINGLP ELEMENTSHAFT-H P ELEMENTH.P ELEMENTSTARTERHPELEMENTLPELEMENTLX3LOFigure 23-3.— Schematic diagram showing relationship ofparts in twin-spool gas turbine engine.147.137atmospheres. Part of the compressed air, calledprimary air , enters directly into the combustionchamber where it is mixed with the atomizedfuel so that the mixture can be ignited and burned.The remainder of the air, called secondary air ,is mixed with the gases of combustion. The purposeof the secondary air is to cool the combustiongases down to the desired turbine inlettemperature.Both axial-flow compressors and centrifugal(radial-flow) compressors are currently usedin gas turbine engines. There are several possibleconfigurations of these basic types, someof which are in use and some of which are inexperimental phases of development.In the axial-flow compressor the air is compressedas it flows axially along the shaft.An axial-flow compressor of good design mayachieve efficiencies in the range of 82 to 88percent at compressor pressure ratios up to8:1. At higher pressure ratios, the efficiencytends to decrease. Axial flow compressors maybe of the single-spool type, previously illustratedin figures 23-1 and 23-2, or of the twin-spooltype, as shown in figure 23-3. The gas turbineengine shown in figure 23-4 has an axial-flowcompressor of the single-spool type. Figure23-5 shows an axial-flow single-spool compressorremoved from its engine. Where twinspoolaxial-flow compressors are used, a separateturbine drives each spool, as shown infigure 23-3.The centrifugal (radial-flow) compressorpicks up the entering air and accelerates itoutward by means of centrifugal force. Thecentrifugal compressor (fig. 23-6) may achieveefficiencies of 80 to 84 percent at pressureratios of 2.5 to 4 and efficiencies of 76 to 81percent at pressure ratios of 4 to 10.The advantages of the axial-flow compressorinclude high peak efficiencies; a relatively smallfrontal area for any given air flow; and onlynegligible losses between stages, even whena large number of stages are used. The598

Chapter 23. -GAS TURBINEGAS PRODUCING SECTIONPOWER TURBINE SECTIONCOMPRESSORCOMBUSTIONCHAMBERGASPRODUCINGTURBINEACCESSORYDRIVEFigure 23-4.— Gas turbine engine with single-spool axial-flow compressor.147.138disadvantages of the axial-flow compressorinclude difficulty of manufacture, high initialcost, and relatively great weight.147.139Figure 23-5.— Single-spool axial-flowcompressor.The advantages of the centrifugal compressorinclude a high pressure rise per stage, simplicityof manufacture, low initial cost, and relativelylight weight. The disadvantages of the centrifugalcompressor include the need for a relativelylarge frontal area for a given air flow and thedifficulty of using two or more stages becauseof losses that would occur between the stages.Combustion ChamberThe combustion chamber is the componentin which the fuel-air mixture is burned. Thecombustion chamber consists of a casing, aperforatedinner shell, a fuel nozzle, and a devicefor initial ignition. The number of combustionchambers used in a gas turbine engine varieswidely; as few as one and as many as sixteencombustion chambers have been used in one gasturbine engine.The combustion chamber is the most efficientcomponent of a gas turbine engine. Efficienciesbetween 95 and 98 percent can be obtained over awide operating range. To produce such efficiencies,combustion chambers are designed to operatewith low pressure losses, high combustion599

PRINCIPLES OF NAVAL ENGINEERINGFigure 23-6.— Centrifugal (radial-flow) compressor.147.140efficiency, and good flame stability. Additionalrequirements for the combustion chamber includelow rates of carbon formation, lightweight, reliability, reasonable length of life,and the ability to mix cold air with the hot combustiongases in such a way as to give uniformtemperature distribution to the turbine blades.Only a small part (perhaps one-fourth) ofthe air which enters the combustion chamberarea is burned with the fuel. The remainder ofthe air is used to keep the temperature of thecombustion gases low enough so that the turbinenozzles and blades will not be overheated andthereby damaged.The basic types of combustion chambers incurrent use are the tubular or can-type chamber,the annular chamber, the can-annular chamber,and the elbow chamber.The tubular or can-type chamber, shown infigures 23-7 and 23-8, is used with both axialflowand centrifugal compressors. The can-typecombustion chamber consists of an outer caseor housing within which is a perforated, stainlesssteel, highly heat resistant combustionchamber liner. The combustion chamber housingis divided to facilitate liner replacement. Eachcan-type chamber has its own individual airinlet duct.Interconnector tubes (flame tubes) are a necessarypart of can-type combustion chambers.-TUMWM VKNESrHEAD or LINER-SECONDARY AM147.141Figure 23-7.— Tubular or can-type combustionchamber.600

Chapter 23. -GAS TURBINECOMBUSTIONCHAMBERHOUSINGCOMBUSTIONCHAMBERLINERCOMBUSTIONCHAMBERCOVERCOMBUSTIONCHAMBERINLET DUCTFigure 23-8,— Elements of tubular or can-type combustion chamber.147.142Since each of the combustion chambers has itsown separate burner, each one operating independentlyof the others, there must be some wayto spread the flames during starting. This requirementis met by interconnecting all thechambers so that, as the flame is started by thespark ignition plugs in the lower chambers, theflame passes through the interconnector tubesand ignites the combustible mixture in the adjacentchambers. Once ignition is obtained, thespark igniters are automatically cut off.The annular combustion chamber is moreefficient than the can-type chamber. Althoughdetails of design may vary, the annular combustionchamber consists essentially of a singlechamber which completely surrounds the engine.Fuel enters the combustion chamber through aseries of nozzles which are mounted equidistantfrom each other on a ring at the front end of thecombustion chamber; because of this arrangement,the flame is distributed evenly around theentire circumference of the combustion chamber.Diffusion of air and an efficient flamepattern are maintained by means of rows ofholes which are punched in the outer liner orbasket of the combustion chamber.The can-annular combustion chamber combinesfeatures of both the can-type chamberand the annular chamber. The can-annularchamber allows an annular discharge from thecompressors, from which the air flows to individualburners where the fuel is injected andburned.- The can-annular combustion chambersare arranged radially around the axis of theengine— the axis in this instance being the rotorshaft housing. Figure 23-9 shows the arrangementof can-annular combustion chambers.The can-annular combustion chambers areenclosed by a removable steel shroud whichcovers the entire burner section. This featuremakes the burners readily accessible for anyrequired maintenance.The can-annular combustion chambers areinterconnected by means of projecting flametubes. These flame tubes facilitate starting,as previously described in connection with thecan-type combustion chamber.Each of the can-annular combustion chamberscontains a central, bullet-shaped, perforatedliner. The size and shape of the holes aredesigned to admit the correct quantity of airat the required velocity and angle. Cutouts areprovided in two of the bottom chambers for theinstallation of the spark igniters.Each can-annular combustion chamber receivesfuel through duplex nozzles installed atthe forward end of the chamber. Guide vanesaround the fuel nozzles direct the primary airand cause it to enter the combustion chamberwith a swirling motion which mixes the fueland air and thus leads to even and completecombustion.TurbineIn theory, design, and operating characteristics,the turbines used in gas turbine enginesare quite similar to the turbines used in asteam plant. The gas turbine differs from thesteam turbine chiefly in the type of blading601

PRINCIPLES OF NAVAL ENGINEERING,. .;-• > * ^'» » T' *'^' f ^* £^*-^i^f^fSBt^^Figure 23-9. — Can-annular combustion chamber.147.143material used, the means provided for coolingthe bearings and highly stressed parts, and thehigher ratio of blade length to wheel diameterwhich is required to accommodate the largegas flow.The turbine section of a gas turbine engineis located directly behind the combustion chamberoutlet. The turbine consists of two basicelements, the stator and the rotor . Part of astator element is shown in figure 23-10; a rotorelement is shown in figure 23-11.The stator element is referred to by variousnames, including turbine nozzle vanes and tur -bine guide vanes . The vanes of the stator elementserve the same purpose as the nozzlesin an impulse steam turbine or the stationaryblading in a reaction steam turbine— that is,they convert thermal energy into mechanicalkinetic energy. The vanes of the stator elementare contoured and set at such an angle thatthey form a number of small nozzles whichdischarge the gas as extremely high speed jets.As in the case of the nozzles (or stationaryblading) of steam turbines, the increase invelocity may be equated with the decrease inthermal energy. The vanes of the stator elementdirect the flow of gas to the rotor blades at therequired angle while the turbine wheel is rotating.The rotor element of the turbine consistsof a shaft and a bladed wheel or disk. The wheelis attached to the main power transmitting shaftof the gas turbine engine. The jets of combustiongas leaving the vanes of the stator elementact upon the turbine blades and cause the turbinewheel to rotate at a very high rate of speed.The high rotational speed imposes severe centrifugalloads on the turbine wheel, and at thesame time the very high temperatures result ina lowering of the strength of the material.Consequently, the engine speed and temperaturemust be controlled to keep turbine operationwithin safe limits. Even so, the operating lifeof the turbine blading is accepted as the governingfactor in determining the life of the gasturbine engine.The turbine may be of the single-rotor typeor of the multiple-rotor type. Either single-rotor602

Chapter 23. -GAS TURBINE147.145Figure 23-11.— Rotor element of turbineassembly.147.144Figure 23-10.— Stator element of turbineassembly.or multiple-rotor turbines may be used witheither centrifugal or axial-flow compressors.In the single-rotor type of turbine, the poweris developed by one rotor and all engine-drivenparts are driven by this single wheel. In themultiple-rotor type, the power is developed bytwo or more rotors. It is possible for one ormore rotors to drive the compressor and theaccessories, while one or more other rotorsare used for the power output.Main BearingsThe main bearings in a gas turbine engineserve the critical function of supporting thecompressor, the turbine, and the engine shaft.The number and position of main bearings requiredfor proper support vary according tothe length and stiffness of the shaft, with bothlength and stiffness being affected by the typeof compressor used in the engine. In general,a gas turbine engine requires at least threemain bearings and may require six or evenmore.Several types of main bearings are usedin gas turbine engines. Ball and roller bearingshave been quite commonly used in the past, andthey are still used in many aircraft gas turbineengines. Sleeve bearings, split-sleeve bearings,floating-sleeve bearings, and slipper bearingsare commonly used in gas turbine engines designedfor marine propulsion.The slipper or pivoted-shoe type of bearinghas recently attracted considerable attention andis being used increasingly for main bearings ongas turbine engines and other high speed engines.This type of bearing is designed withrelatively large radial clearances. Since arotating object tends to rotate about its truebalance center when it is not restrained bybearings or supports, the large radial clearancesin the slipper bearings allow a kind ofself-balancing action or automatic compensation603

PRINCIPLES OF NAVAL ENGINEERINGOILSLINGER RADIAL COMPRESSOR BEARINGBEARINGRETAINERSLIPPER BEARINGTHRUST SLEEVEFigure 23-12.— Slipper bearing.147.146for balance errors to take place when the engineis operating.One type of slipper bearing is shown in figure23-12. In this type of bearing, the slipper consistsof four pivoted-shoe segments, similar tothe pivoted shoes used in Kingsbury bearings.The segments are held together loosely by awire spring.Another type of slipper bearing is shown infigure 23-13. In this type of bearing, the slipperconsists of six segments which are fastened inplace by dowel pins. This type of bearing issometimes called a fixed-pivot slipper bearing.Accessory DrivesBecause the turbine and the compressor areon the same rotating shaft, a popular misconceptionis that the gas turbine engine has onlyone moving part. This is not the case, however.A gas turbine engine requires a starting device(which is usually a moving part), some kind ofcontrol mechanism, and power take-offs.The accessory drive section of the gasturbine engine takes care of these variousaccessory functions. The primary purpose ofthe accessory drive section is to provide spacefor the mounting of the accessories requiredfor the operation and control of the engine.Secondary purposes include acting as an oilreservoir and/or oil sump and providing forFigure 23-13.— Slipper bearing(fixed-pivot type).147.147604

Chapter 23. -GAS TURBINEand housing accessory drive gears and reductiongears. The accessory drive section of a gasturbine engine is shown in figure 23-14.The gear train is driven by the engine rotorthrough an accessory drive shaft gear coupling.The reduction gearing within the case providessuitable drive speeds for each engine accessoryor component. Because the operating rpm of therotor is so high, the accessory reduction gearratios are relatively high. The accessory drivesACCESSORY DRIVEIDLER SHAFTACCESSORY DRIVEGEAR AND DRIVESHAFTACCESSORY DRIVEIDLER GEARSTARTER-GENERATODRIVESHAFTPINION SHAFTBEARINGRETAINERSLEEVEINPUT BEVELPINION ANDDRIVE SHAFTOIL PUMPDRIVE GEARUPPERHOUSINGOIL PUMPMAIN ACCESSORYDRIVE SHAFTOIL SUMPFigure 23-14.— Cutaway view of accessory drive section,147.148605

PRINCIPLES OF NAVAL ENGINEERINGare supported by ball bearings assembled in themounting bores of the accessory case.Accessories always provided in the accessorydrive section include the fuel control, withits governing device; the high pressure fuel oilpump or pumps; the oil sump; the oil pressureand scavenging pump or pumps; the auxiliaryfuel pump; and a starter. Additional accessorieswhich may be included in the accessorydrive section or which may be provided elsewhereinclude a starting fuel pump, a hydraulicoil pump, a generator, and a tachometer. Somegas turbine engines are equipped with magnetosfor ignition and these magnetos are driven fromthe accessory drive. Most of these accessoriesare essential for the operation and control ofany gas turbine engine; however, the particularcombination and arrangement of engine-drivenaccessories depends upon the use for which thegas turbine engine is designed.Engine SystemsThe major systems of a gas turbine engineare those which supply fuel, lubricating oil, andelectricity.FUEL SYSTEM.— The fuel system suppliesthe specified fuel for combustion. The componentsof a fuel system depend to some extentupon the type of gas turbine engine; however,the basic fuel oil system shown in figure 23-15may be regarded as typical of a simple fuelsystem. The engine-driven pump receives filteredfuel from a motor-driven supply pump ata constant pressure. The engine-driven fuelpump increases the pressure and forces the fuelthrough the high pressure filter to the fuel controlgovernor in the fuel control assembly. Thefuel control governor provides fuel to theFUEL PRESSUREGAGENOZZLE SHUTOFFVALVENI-(-z>zLESSTARTIf

Chapter 23. -GAS TURBINEnozzles at the pressure and volume required tomaintain the desired engine performance. At thesame time, the fuel control governor limits fuelflow to maintain operating conditions within safelimits.The fuel nozzles serve to introduce the fuelinto the combustion chamber. The fuel is sprayedinto the combustion chamber under pressure,through small orifices in the nozzles. Variouskinds of fuel nozzles are in use. Figure 23-16shows a simplex nozzle and a duplex nozzle.The simplex nozzle was used on some oldergas turbine engines. Most recent gas turbineengines use some kind of duplex nozzle. A duplexnozzle requires a dual manifold just ahead ofthe nozzles and a flow divider (before the manifold)to divide the fuel into primary and secondarystreams. The duplex type of nozzle providesa desirable spray pattern for combustionSECONDARYBFigure 23-16.— Fuel nozzles.A. Simplex. B. Duplex.147.150over twice the range of that provided by thesimplex nozzle.The fuel control assembly is the unit whichregulates the turbine rpm by adjusting fuel flowfrom the high pressure engine-driven pump tothe fuel nozzle. The major parts of the fuelcontrol assembly are shown in figure 23-17.Fuel enters the fuel control assembly and ispumped through a filter. High pressure fuel isrouted to the differential relief valve, then tothe fuel shutoff valve, and finally to the fuelnozzles.The speed setting lever on the outboard endof the governor is connected to a speed controldevice on the control console either by a cableor by an electric servomotor. At the fuel controlend, the lever is keyed to a pinion. Thispinion positions a rack which in turn controlsthe governor flyweight spring. The mechanismregulates gas producer speed according to theposition of the control lever. With the controllever in any particular position, variations fromthe preset speed are sensed by the governorflyweights and a compensating movement of thefuel control valve results. An externally adjustableneedle valve provides a constant minimumfuel flow during deceleration, when the governorvalve is closed, to prevent loss of combustion.An acceleration limiter, consisting of a needlevalve positioned by a shaft, arm, and bellows,is actuated by compressor discharge pressure.During acceleration, this mechanism controlsfuel flow to the point at which the governor flyweightmechanism and its fuel control valvetake over.LUBRICATING SYSTEM.-Because of thehigh operating rpm and the high operating temperaturesencountered in gas turbine engines,proper lubrication is of vital importance. Thelubricating system is designed to supply bearingsand gears with clean lubricating oil at thedesired pressures and temperatures. In someinstallations, the lubricating system also furnishesoil to various hydraulic systems. Heatabsorbed by the lubricating oil is transferredto the cooling medium in a lube oil cooler.The lubricating system shown in figure 23-18 has a combined hydraulic system— in thiscase, the hydraulic system is for the operationof a hydraulic clutch in a gas turbine propulsionServomechanisms are discussed in chapter 20 of thistext.607

PRINCIPLES OF NAVAL ENGINEERINGACCELERATIONLIMITERBELLOWSVENT TOATMOSPHERE— TO FUELSHUTOFF VALVEAND NOZZLES— COMPRESSORDISCHARGEPRESSUREMINIMUMFLOW VALVEGOVERNORVALVEDIFFERENTIALRELIEF VALVEACCELERATIONFLOWADJUSTING SCREWULTIMATERELIEF VALVE— ACCELERATIONLIMITER NEEDLEVALVEFROM BOOSTERPUMPFUEL PUMP FILTER PLY WEIGHTSSPEED SETTING LEVERFigure 23-17.— Schematic diagram of fuel control assembly.147,151system. The lubricating system illustrated is ofthe dry- sump type, with a common oil supplyfrom an externally mounted oil tank. The systemincludes the oil tank, the lubricating oil pump,the hydraulic oil pump, the air inlet scavengingpump, the oil temperature switch, the oil cooler,oil filters, the pressure regulating valve, thediverter valve, and a low pressure switch.All bearings and gears in the engine, accessorydrives, reduction gears, and reverse gearare lubricated and cooled by the lubricatingsystem. Also, as may be observed in figure23-18, the system illustrated here supplies oilfor the lubrication of the fuel control governor.ELECTRICAL SYSTEM.-In the gas turbineengine, the electrical system (fig. 23-19) is theprincipal means of automatic control of theengine. Electrical circuits which incorporatespeed and pressure sensing switches control thestarting and ignition sequence by opening andclosing various valves in the fuel system. Engineoperating conditions are reported by speed,pressure, and temperature operated switchesand temperature bulbs.The electrical system usually includes astarter, an ignition circuit, a control battery,and relays. In addition, it includes electrical accessoriesand control components such as thestarting and ignition control switches and relays;the panel-mounted instruments and indicatorlights for oil temperature, oil pressure, and enginerpm; and engine-mounted reporting devicessuch as fuel pressure switches, oil temperatureswitches, oil pressure switches, and thermocouples.608

Chapter 23. -GAS TURBINECMc•i-ibec m(1)as5naoOU•3afi•acCI]bcCIHuIICOa;r-t609

PRINCIPLES OF NAVAL ENGINEERINGTO RELAY PANEL TERMINALS-^rTTTTTTTTTTmI_•I «> 5a BS SO 2Z 47 49 23 21 &1 24 28 U 37 BvGlNc NO. 4•0 *• &3 se 57 10 4e 4a IS « oo 19 17 s£ 3« ENGINE NO. 37» 63 M 3S 2» 12 n 40 13 11 42 14 15 44 5 ENGINE NO. 2TO EXHAUSTTEMPERATUREINDICATOR?• 41 31 22 M 27 39 8 10 41 9 7 43 4 ENGINE NO. 15y^>y>!f^5y>jxj>yyx>!J>j ^^ngine electricalDISCONNECT PLUGIbcdepcti.dipb /hFUEL NOZZLESHUTOFF VALVEVL.JTACHOMETER(TURBINE RPM)EXHAUSTJ THERMO-COUPL EENGINE ELECTRICAL WIRING DIAGRAMTO STARTERRELAYEMERGENCY STOPFUEL PUMP STARTFUEL SUPPLY PUMPI-FUEL NOZZLESHUTOFF VALVETACHOMETER EXHAUST TEMP.INDICATOR INDICATORALARM HORNTO OTHER ENGINETACHOMETERGENERATOREXHAUSTTHERMOCOUPLEIGNITIONTEST SWITCHNOTESGROUND SYMBOLS INDICATEA COMMON RETURN WIREEXCEPT POINTS © WHICHARE ACTUALLY GROUNDEDTO TURBINE.CIRCUITS SHOWN WITH EN-CINE NOT RUNNING.Figure 23-19.— Electrical system for gas turbine engine.75.275610

Chapter 23. -GAS TURBINEThe starting and ignition circuits receivepower from storage batteries. The warning andsafety circuits receive power from the ship'spower supply panel. Power for the indicatingcircuits is self generated by thermocouplesand other units in the circuits.Ehgine StartersOf the various methods used for starting gasturbine engines, the three most common devicesare the air turbine, the hydraulic starting device,and the electric starter-generator.The air turbinestarter is a turbine-air motorwith a radial inward-flow turbine wheel assemblyand an engaging and disengaging mechanism.Compressed air is supplied to the air turbinefrom an external source.The hydraulic motor starter consists of amotor-driven hydraulic pump mounted separately.It supplies high pressure hydraulic oilto the hydraulic motor starter, which is mountedon the accessory pad along with its engagingand disengaging mechanism. The hydraulicmotor starter is quite similar to the air turbinestarter; however, the hydraulic motor starteris usually used for larger and higher horsepowergas turbine engines.The electric starter- generator is a shuntwoundd-c generator with compensating windingsand a series winding, using a 24-volt batterypower source. The generator is usually mountedon the accessory drive pad. The generator is sodesigned and controlled that it can be used as anengine starter. When the designed engine speedis reached, the starter- generator is automaticallyswitched from a starter to a generator.TRANSMISSION OF ENGINE POWERThe two main types of gas turbine engineinstallations used for ship propulsion are (1)the geared drive, and (2) the turboelectricdrive.The fundamental characteristics of the gasturbine engine make it necessary for the drivemechanism to change both the speed and thedirection of shaft rotation in the driven mechanism.The process of transmitting engine powerto a point where it can be used in performinguseful work involves a number of factors, twoof which are torque and speed. The gas turbineengine does not produce high torque, but it doesproduce high speed. Therefore, a gear train isused with most gas turbine engines to lowerspeed and increase torque. This is true inboth types of installations. In the case of thegeared drive installation, the gears are usedbetween the gas turbine engine and the propellershaft. In the case of the turboelectric drive,the gears are usually used between the gasturbine engine and the generator shaft, to reducethe rpm of the generator to a practicable operatingvalue.The propelling equipment of a boat or shipmust be capable of providing reversing poweras well as forward power. In a few ships andboats, reversing is accomplished by the use ofcontrollable pitch propellers.^ In mostvessels,however, reversing is accomplished by the useof reversing gears.Reducing the speed of rotation and reversingthe direction of shaft rotation are not the onlyrequirements of the drive mechanism of a shipor boat. It is also necessary to make some provisionfor the fact that the engine must be ableto operate at times without transmitting powerto the propeller shaft. In the electric drive,this is no problem because the transmissionof power is controlled electrically. With thegear type of drive, however, it is necessary toinclude a means of disconnecting the enginefrom the propeller shaft. Devices used for thispurpose are called clutches .The arrangement of components in a geartypedrive varies, depending upon the type andsize of the installation. In some of the smallinstallations, the clutch, the reversing gear,and the reduction gear may be combined in asingle unit. This type of arrangement is shownin figure 23-20. In other installations, the clutchand the reversing gear may be in one housing andthe reduction gear in a separate housing attachedto the reversing gear housing. Drive mechanismsarranged in either manner are calledtransmissions .GAS TURBINE ENGINES ANDJET PROPULSIONThus far, we have considered the gas turbineengine as a prime mover which delivers powerin the form of torque on an output shaft. In concludingthis chapter, it should be noted thatthe gas turbine engine also serves as the primeControllable pitch propellers are discussed in chapter5 of this text.611

PRINCIPLES OF NAVAL ENGINEERINGFIRST STAGEREDUCTION DRIVECLUTCH'SHAFTH, SELECTOR VALVE.DRIVEN PLATES (FIXED TO GEAR).DRIVING PLATESOUTPUT GEAR.sulEM^SECOND STAGEREDUCTION DRIVEJ^FORWARD DRIVEFROM —^SCAVENGE PUMPPISTON COMPRESSESCLUTCH PLATES ANDOUTPUT GEAR E DRIVEN\ TO COOLER INACTIVE ^AME DIRECTION ASPETON CLUTCH SHAFTDIVERSIONVALVECOUNTERSHAFTREVERSELEGENDDRIVEOIL AT PRESSURENON-ACTIVE OILCOOLING OILRgure 23-20.— Clutch,PETON COMPRESSES CLUTCH PLATESAND OUTPUT GEAR E DRIVEN BYCOUNTERSHAFT IN OPPOSITE DIRECTIONTO CLUTCH SHAFTreduction gear, and reverse gear arrangement.147,153612

Chapter 23. -GAS TURBINEmover in the power plants of many militaryaircraft. When so adapted, the gas turbineengine develops power by converting thermalenergy into mechanical kinetic energy in a highvelocity gas stream. The highly accelerated gasstream creates thrust which propels the aircraft.This methodof creating thrust is called thedirect reaction or jet propulsion method.The concept of thrust is basic to an understandingof jet propulsion. The concept of thrustis based on Newton's third law of motion, whichmay be stated as follows: For every acting forcethere is an equal and opposite reacting force .In the case of aircraft in flight, the acting forceis the force the engine exerts on the air massas itflows through the engine. The reacting force(thrust) is the force which the air mass exertson the components of the engine as the heatedair mass is discharged from the jet nozzle atthe rear of the airplane. In other words, thrustis not produced by the ejected air mass reactingagainst the atmosphere; rather, thrust is createdwithin the engine as the air mass flowingthrough the engine is accelerated and discharged.Engines which include the gas turbine andwhich create thrust by the direct reactionmethod are commonly identified as turbojetengines. Except for a diffuser and a differenttype exhaust system in engines of the turbojettype, the basic components of the turbojet engineare similar in design and function to the componentsof any open-cycle gas turbine engine.The function of the diffuser is to decrease thevelocity of the inlet air and to increase itspressure before the air enters the compressor.The exhaust system of aturbojet engine consistsbasically of a cone and a convergent nozzle.The exhaust cone is designed to exhaust to thenozzle the accelerated air mass which the othercomponents of the engine deliver to the cone.As the accelerated air mass flows through theconvergent nozzle, its velocity is greatly increasedand thrust is created within the engine.MAINTENANCEThe maintenance of gas turbines is thenormal function of operating activities. Cleanlinessis one of the most important basic essentialsin operation and maintenance of gas turbines.Particular care should be exercised inkeeping fuel, air, coolants, lubricants, rotatingelements, and combustion chambers clean. Periodicinspection procedures should be followedin order to detect maladjustments, possiblefailures, and excessive clearances of movingparts. All inspection and maintenance requirementsshould be accomplished in accordancewith the 3-M System (PMS Subsystem).CAUTION : Never use lead pencils for markinggas turbine hot parts, because the carboncontent of the pencil lead will cause stainlesssteel to become brittle, causing a possible failureof the parts that were marked. A greasepencil should be used in marking gas turbineparts. Do not use steel wool to clean gas turbineparts, unless the wool is stainless steel.Overhaul periods and procedures are setup by the Naval Ship Systems Command. Theseperiods and procedures are reported to theFleet through NavShips Technical Manuals and/or direct correspondence. Accurate operatinglogs should be kept on each engine so the numberof hours and operational history on each engineis readily known. These records aid in developingmeasures which improve engine reliability.613

CHAPTER 24NUCLEAR POWER PLANTSNuclear reactors release nuclear energy bythe fission process and transform this energyinto thermal energy. While we are learning moredaily about the phenomena which occur in nuclearreactions, the knowledge already gained has beenput to use in both the submarine and the surfacefleets. The Navy is now in the second decade ofthe utilization of nuclear energy for ship propulsion.Nuclear engineering is a field that is in thestage of rapid development at the present time;therefore the discussion in this chapter is limitedto the basic concepts to reactor principles. Thediscussion of nuclear physics is limited to thefission process, since all power reactors inoperation at this time use the fissioning of aheavy element to release nuclear energy.^ADVANTAGES OF NUCLEAR POWERA major advantage of nuclear power for anynaval ship is that less logistic support is required.On ships using conventional petroleumfuels as an energy source, the cruising rangeand strategic value are limited by the amountof fuel which can be stored in their hulls. Aship of this type must either return to port totake on fuel or refuel for a tanker at sea— anoperation which is time consuming and hazardous.Nuclear -powered ships have virtually unlimitedcruising range, since the refueling isdone routinely as part of a regular scheduledoverhaul. On her first nuclear fuel load, theUSS Nautilus steamed 62,562 miles, more thanhalf of this distance fully submerged. The USSEnterprise steamed over 200,000 miles beforeFor a discussion of nuclear fusion, see John F.Hogerton, The Atomic Energy Deskbook (New York:Reinhold Publishing Corp., 1963), p, 196.614being refueled. In 1963, Operation Sea Orbit, a30,000-mile cruise around the world in 65 days,completely without logistic support of any kind,proved conclusively the strategic and tacticalflexibility of a nuclear-powered task force.There are other (and perhaps less obvious)advantages of nuclear power for aircraft carriers.For one thing, tanks that would otherwisebe used to store boiler fuels can be used onnuclear-powered carriers to store additionalaircraft fuels, thus giving the ship a greaterstriking potential. Another advantage is the lackof stacks; since there are no stack gases tocause turbulence in the flight deck atmosphere,the operation of aircraft is less hazardous thanon conventionally powered ships.The fact that a nuclear-powered ship requiresno outside source of oxygen from the earth'satmosphere means that the ship can be completelyclosed off, thereby reducing the hazardsof any nuclear attack. This greatly increasesthe potential of the submarine fleet by givingit the capability of staying submerged for extendedperiods of time. In 1960 the nuclearpoweredsubmarine USS Triton completed asubmerged circumnavigation of the world, travelinga distance of 35,979 miles in 83 days and10 hours.NUCLEAR FUNDAMENTALSAt the present time there are 103 knownelements of which the smallest particle thatcan be separated by chemical means is theatom. The Rutherford-Bohr theory of atomicstructure (fig. 24-1) describes the atom asbeing similar to our solar system. At thecenter of every atom is a nucleus which iscomparable with the sun; moving in orbitsaround the nucleus are a number of particlescalled electrons. The electrons have anegative charge and are held in orbit by theattraction of the positively charged nucleus.

Chapter 24. -NUCLEAR POWER PLANTSCLECmON (•)ParticleHYDROOENAOXYCEN41.2Figure 24-1.— Rutherford-Bohr modelsof simple atoms.Two elementary particles, protons and neutrons,often referred to as nucleons, compose theatomic nucleus. The positive charge of atomicnuclei is attributed to the protons. A proton hasan electrical charge equal and opposite to that ofan electron. A neutron has no charge.The number of electrons in an atom andtheir relative orbital positions predict how anelement will react chemically, whereas thenumber of protons in an atom determines whichelement it is. An atom which is not ionizedcontains an equal number of protons and electrons;thus it is said to be neutral, since thetotal atomic charge is zero.As shown in part A of figure 24-1, thehydrogen atom has a single proton in the nucleusand a single orbital electron. Hydrogen, thelightest element, is said to have a mass ofapproximately one. The next heavier atom,that of helium (part B of fig. 24-1), had a massof four relative to hydrogen and was expectedto contain four protons. It was found that thehelium atom has only two protons instead of thefour expected; the remainder of its mass isattributed to two neutrons located in the nucleusof the helium atom. The more complex atomscontain more protons and neutrons in the

PRINCIPLES OF NAVAL ENGINEERING©A COMMON HYDROGEN B DEUTERIUM C TRITIUMFigure 24-3.— Isotopes of hydrogen.5.40(147A)the symbol of the element is the atomic massnumber; thus the superscript indicates whichisotope of the element is being referred to.The geneal symbol for any atom is thusZXAwhereX symbol of the elementZ atomic number (number of protons)A atomic mass number (sum of the numberof protons and the number of neutrons)Of the known 103 elements, there are approximately1000 isotopes, most of which areradioactive. 2 Figure 24-4 gives the nuclearcompositon of various isotopes.alpha particle or a beta particle . One ormore gamma rays may also be emitted withthe alpha or beta particle.An alpha particle (symbol a) is composedof two protons and two neutrons. It is thenucleus of a helium (2He^) atom, has an electricalcharge of +2, and is very stable. Inthe decay process to a more stable element,ElementRADIOACTIVITYAll isotopes with atomic number Z greaterthan 83 are naturally radioactive and many moreisotopes can be made artifically radioactive bybombarding with neutrons which upset theneutron-proton ratio of the normally stablenucleus.Naturally radioactive isotopes undergo radioactivedecomposition ,thereby forming lighterand more stable nuclei. Radioactive decompositionoccurs through the emission of an^For a detailed discussion of nuclear stability, seeFrancis W. Sears and Mark W. Zemansky, UniversityPhysios (3d ed.; Reading, Mass.: Addison-WesleyPublishing Company, Inc., 1964), p. 997.

Chapter 24. -NUCLEAR POWER PLANTomany unstable nuclei emit an alpha particle.The results of alpha emission can be seenfrom the following equation:92 U'238 1"^* 90Th 234In the above equation, the parent isotopeof uranium (goU ) is a naturally occurring,radioactive isotope which decays by alphaemission. Since the A and Z numbers mustbalance in a nuclear equation, and since analpha particle contains two protons, we seethat the uranium has changed to an entirelynew element.The radioactive isotope of thorium(QQTh234) produced in the above reaction further(fecays by the emission of a beta particle symbol^) as indicated in the following equation:90 Th234__^^+g^Pa234The beta particle has properties similarto an electron.3 However, the origin of thebeta particle is within the nucleus ratherthan the orbital shells of an atom. It is postulatedthat a beta particle is emitted at anextremely high energy level when a neutronwithin the nucleus decays to a proton and anelectron (beta particle). When this phenomenonoccurs, the proton stays within the nucleusforming an isotope of a different elementhaving the same mass.A radioactive isotope may go through severaltransformations of the above types before reachinga stable state. In the case of 92U238there are a total of eight alpha particles andsix beta particles emitted prior to reachinga stable isotope of lead (82Pb206),The third manner in which a naturallyradioactive isotope may reach a more stableconfiguration is by the emission of gammarays (symbol y). The gamma ray is an electromagnetictype of radiation having frequency,high energy, and a short wave length. Gammarays are similar to X-rays in that the propertiesare the same. The distinguishing factorbetween the two is the fact that gamma raysare originated in the nucleus of an atom,whereas the X-ray originates from the orbitalelectrons. In general it can be said that agamma ray is of higher energy, higher frequency,and shorter wave length than an X-ray.Frequently an isotope which emits an alphaor beta particle in the decay process willemit one or more gamma rays at the sametime, as in the case of 27^'^ > ^^ isotopethat decays by beta emission and at the sametime emits two gamma rays of different energylevels. Some radioactive isotopes reach a stablestate by the emission of gamma rays only. Inthe latter case, since gamma rays have neithermass nor electrical charge, the A and Znumbers of the isotope remain unchanged butthe energy level of the nucleus is reduced.An important property of any radioactiveisotope is the time involved in radioactivedecay. To understand the time element, it isnecessary to understand the concept of halflife. Half-life may be defined as the timerequired for one-half of any given numberof radioactive atoms to disintegrate, thus reducingtheradiation intensity of that particularisotope by one-half. Half lives may vary frommicroseconds to billions of years. At timesan isotope may be said to be "short-lived"or "long-lived", depending upon its peculiarradio-active half-life. Some half-lives of typicalelements are:ggU^^S ^ ^ gj ^ jq9 yg^j.gggU^^^ = 7.13 X 10^ years88 Ra226 = 1620 yearsFrancis W. Sears and Mark W. Zemansky, Uni -versity Physics (3d ed.; Reading, Mass.: Addlson-Wesley Publishing Company, Inc., 1964), p.986.53 I^^^ = 6.7 hours84 Po214 ^ jo-6 seconds617

PRINCIPLES OF NAVAL ENGINEERINGAs stated previously, naturally radioactiveisotopes decay bythe emission of alpha particles,beta particles, gamma rays, or a combinationthereof. In the case of induced nuclear reactionsthere are many other phenomena which mayoccur, including fission and the emission ofneutrons, positrons, nutrions, and other formsof energy.^CONSERVATION OF MASS-AND ENERGYThe conservation of energy is discussed inchapter 8 of this text. It now becomes necessaryto consider mass and energy as two phases of thesame principle. In so doing, the law of conservationbecomes:(mass + energy) before =(mass + energy) after.Fundamental to the above and to the entiresubject of nuclear power is Einstein's massenergyequation where the following relationholds:wheremCE = energy in ergs,M = mass in grams,C = velocity of light (3 X 10^° cm/sec)Mass and energy are not conserved separatelybut can be converted into each other.Several units and conversion factors whichhave become conventional to the field of nuclearengineering are listed below.1 ev (electron-volt = the energy acquired byan electron as it movesthrough a potential differenceof 1 volt1 Mev (million electronvolts)= lO^ev= 1.52 X 10-l6BtuFor detailed information on nuclear particles, referto Samuel Glasstone, Sourcebook on Atomic Energy(2d ed.; Princeton: D. Van Nostrand Company, Inc.,1958).1 amu 1.49 X 10 erg1.66 X 10 24gm931 Mev1.415 X 1013 BtuNUCLEAR ENERGY SOURCE1 amu (atomic mass unit = 1/16 of an oxygenatom (by definition)It was previously stated that the atomicmass number is the total number of nucleonswithin the nucleus. It can also be said thatthe atomic mass number is the nearest integer(as found by experiment) to the actual mass ofan isotope. In nuclear equations, the entiremass must be accounted for; therefore the actualmass must be considered.The atomic mass of any isotope is somewhatless than indicated by the sum of the individualmasses of the protons, neutrons, and orbitalelectrons which are the components of thatisotope. This difference is termed mass defect:it is equivalent to the binding energy of thenucleus. Binding energy may be defined as theamount of energy which was released when anucleus was formed from its component parts.The binding energy of any isotope may befound, as in the following example of copper(ggCu"^) which contains 34 neutrons, 29 protons,and 29 electrons. Using the values givenin figure 24-2 we find:34 X 1.00894 = 34.30496 amu29 X 1.00785 = 29.21982 amu29 X 0.00055 = 0.01595 amuTotal of component massesLess actual mass of atomMass defectConverting to energy, we find:931 Mev/amu x 0.61093Mev, or 560.8 + 63 == 63.54073 amu= 62.9298 amu= 0.61093 amuamu = 568.775838.9 Mev/nucleonThe relationship between mass number andthe average binding energy per nucleon isshown in figure 24-5.Since binding energy was released when anucleus was formed from its component parts,it is necessary to add energy to separate anucleus. In the fissioning of uranium 235, theadditional energy is supplied by bombarding thefissionable fuel with neutrons. The fissionablematerial absorbs a neutron and is converted618

—Chapter 24, -NUCLEAR POWER PLANTS238— 6zoulUozazEQ1 I 1 I I I I20 40 60 80 100 120 140ATOMIC MASS NUMBER—I160 180 200 220 240 260Figure 25-5.—Relationship between atomic mass number andaverage binding energy per nucleon.147.155into the compound nucleus of uranium-236,which fissions instantaneously.There are more than 40 different ways auranium-235 nuclei may fission, resulting inmore than 80 different fission products.^ Forthe purpose of this discussion, let us considerthe most probable fission of a uranium-235nucleus. In slightly more than 6 percent ofthe fissions, the uranium-235 nucleus will splitFor a detailed discussion on nuclear fission, referto Samuel Glasstone, Sourcebook on Atomic Energy(2d ed.; Princeton: D. Van Nostrand Company, Inc.,1958).intofragments having mass numbers of 95 and139. The following equation is typical:it235 „192^ ^o"-,95 1^39 1 .39^ 2530*where the daughter products, yttrium and iodine,are toh radioactive and decay through betaemission to the stable isotopes of molybdenum(^2^'^ ) and lanthanum (57Lal39)^ respectively.One method of determining the energy releasedfrom the above reaction is to find thedifference in atomic mass units of the daughterproducts and the original nucleus. It is alsonecessary that we account for the neutron usedto bombard the uranium-235 atom and the twoneutrons liberated in the fission process. In619

PRINCIPLES OF NAVAL ENGINEERINGthe investigation of energy released in thisreaction we find:Mass of uranium-235 atom = 235. 0439Mass of neutron= 1. 00894Original mass= 236. 05284 amuMass of molybdenum-95atom= 94.9058Mass of lanthanum- 139atom= 138.9061Mass of 2 neutrons= 2.01788Total mass of fissionfragmentsMass defect = 236. 05284 -= 235. 82978235. 829780. 22306 amu/ fissionHence,0.22306 amu/fission x 931 Mev/amu207.7 Mev/fissionThus we find that from each fission approximately200 Mev of energy is released,most of which (about 80 percent) appearsimmediately as kinetic energy of the fissionfragments. As the fission fragments slow down,they collide with other atoms and molecules;this results in a transfer of velocity to thesurrounding particles. The increased molecularmotion is manifested as sensible heat. The remainingenergy is realized from the decay offission fragments by beta particle and gammaray emission, kinetic energy of fission neutrons,and instantaneous gamma ray energy.In a nuclear reactor, the two neutronsliberated in the above reaction are available,under certain conditions, to fission other uraniumatoms and assist in maintaining the reactorcritical . A nuclear reactor is said to becritical if the neutron flux remains constant.Neutron flux is defined as the number ofneutrons passing through unit area in unittime, A neutron flux of 10^3 neutrons persquare centimeter per second is not uncommon.If the neutron flux is decreasing, the reactoris said to be subcritical; conversely, a reactoris supercritical if the neutron flux is increasing.NEUTRON REACTIONSNeutrons may be classified by their energylevels. A fast neutron has an energy level ofgreater than 0.1 Mev, an intermediate neutronin the process of slowing down possesses anenergy level between 1 ev and 0.1 Mev, athermal neutron is in thermal equilibrium withits surroundings and has an energy level ofless than 1 ev.Neutrons lose their kinetic energy by interactingwith atoms in the surrounding area.The probability of a neutron interacting withone atom is dependent upon the target areapresented by that atom for a neutron reaction.This target area (which is the probability of aneutron reaction occurring) is called crosssection . The unit of cross section measurementis barns. The size of a barn is 10""square centimeters. Four of the different crosssections that an element may have for neutronprocesses are as follows:Scattering cross section is a measure of theprobability of an elastic (billiard ball) coUisonwith a neutron. In this type of collision part ofthe kinetic energy of the neutron is imparted tothe atom and the neutron rebounds after collision.Neutrons are thermalized (reduced to anenergy level below 1 ev) by elastic collisions.Capture cross section is a measure of theprobability of the neutron being captured withoutcausing fission.Fission cross section is a measure of theprobability of fission of the atom after neutroncapture.Absorption cross section is a measure of theprobability that an atom will absorb a neutron.The absorption cross section is the sum of thecapture cross section and the fission crosssection.The cross section for any given elementmay vary with the energy level of the approachingneutron. In the case of uranium-235,the absorption cross section for a thermalneutron is 100 times the cross section for afast neutron.REACTOR PRINCIPLESA nuclear reactor must contain a criticalmass. A critical mass contains sufficient fissionablematerial to enable the reactor tomaintain a self-sustaining chain reaction, therebykeeping the reactor critical. A criticalmass is dependent upon the species of fissionablematerial, its concentration and puritythe geometry and size of the reactor, and thematter surrounding the fissionable material."For a thorough discussion of the aspects of reactordesign, see Samuel Glasstone, Sourcebook on AtomicEnergy (2d ed.; Princeton: D. Van Nostrand Company,Inc., 1958).620

Chapter 24. -NUCLEAR POWER PLANTSREACTOR FUELSThe form and composition of a reactorfuel may vary both in design and in the fissionableisotope used. Many commercial powerreactors use a solid fuel element fabricatedin plate form, with the fissionable material beingenriched uranium in combination with aluminum,zirconium, or stainless steel. Fuel elementsmay be arranged in thin sandwich layers, asshown in figure 24-6. This construction providesa relatively large heat transfer area betweenthe fuel elements and the reactor coolant.The outer cladding on the fuel elementsconfines the fission fragments within the fuelelements and serves as a heat transfer surface.Cladding materials should be resistant to corrosion,should be able to withstand high temperatures,and should have a small cross sectionfor neutron capture. Three common claddingmaterials are aluminum, zirconium, and stainlesssteel. The fuel elements may be assembledin groups, some of which may contain controlrods. Several groups of fuel elements placedwithin a reactor vessel make up the reactorcore. It is not necessary that all fuel groupswithin the reactor contain control rods.CONTROL RODSControl rods serve a dual purpose in areactor. They keep the neutron density (neutronflux) constant within a critical reactor and theyprovide a means of shutting down the reactor.The material for a control rod must havea high capture cross section for neutrons andPLATE OFCLADDINGMATERIALvi '. '?;,,-• v'.,iv >'--",: '-'.v-vjv •-'-- 'i-l-v:j-?^ -j•ri ''7~V-^\/ilt'-:-7y^ir&:^?Al^jiiLLCii_j_i.lCl.l,;ilficiZ^lj^:lJi._li:^II^l:^FUELCLADDINGCOOLANT"CHANNEL147.156Figure 24-6.—PWR fuel element.a low fission cross section. Three materialssuitable for control rod fabrication are cadmium,boron, and hafnium. Hafnium is particularlysuitable for control rods because it has arelatively high capture cross section and becauseseveral daughter products after neutroncapture are stable isotopes which also havegood capture cross sections.The control rods are withdrawn from thereactor core until criticality is obtained; thereaftervery little movement is required. It isimportant to note at this point that aftercriticality is reached, movement of controlrods does not control the power output of thereactor; it controls only the temperature ofthe reactor.Control rod drive mechanisms are so designedthat, should an emergency shutdown ofthe reactor be required, the control rods maybe inserted in the core very rapidly. A shutdownof this type is called a scram.MODERATORSA moderator is the material used to thermalizethe neutrons in a reactor. As previouslystated, neutrons are thermalized byelastic collisions; therefore, a good moderatormust have a high scattering cross section anda low absorption cross section to reduce thespeed of a neutron in a small number of collisions.Nuclei whose mass is close to that ofa neutron are the most effective in slowingthe neutron; therefore, atoms of low atomicweight generally make the best moderators.Materials which have been used as moderatorsinclude light and heavy water, graphite, andberyllium.Ordinary light water makes a good moderatorsince the cost is low; however it must befree from impurities which may capture theneutrons or add to the radiological hazards.REACTOR COOLANTSThe primary purpose of a reactor coolantis to absorb heat from the reactor. The coolantmay be either a gas or a liquid; it must possessgood heat transfer properties, have goodthermal properties, be noncorrosive to thesystem, be nonhazardous if exposed to radiation,and be of low cost. Coolants which have beenused in operational and experimental reactorsinclude light and heavy water, liquid sodium, andcarbon dioxide.621

PRINCIPLES OF NAVAL ENGINEERINGREFLECTORSIn a reactor of finite size, the leakage ofneutrons from the core becomes somewhat ofa problem. To minimize the leakage, a reflectoris used to assist in keeping the neutronsin the reactor. The use of a reflectorreduces both the required size of the reactorand the radiation hazards of escaping neutrons.The characteristics required for a reflectorare essentially the same as those required fora moderator.Since ordinary water of high purity is suitablefor moderators, coolants, and reflectors,the inference is that it could serve all threefunctions in the same reactor. This is indeedthe case in many nuclear reactors.SHIELDINGThe shielding of a nuclear reactor servesthe dual purpose of (1) reducing the radiationso that it will not interfere with the necessaryinstrumentation, and (2) protecting operatingpersonnel from radiation.The type of shielding material used isdependent upon the purpose of the particularreactor and upon the nature of the radioactiveparticles being attenuated or absorbed.The shielding against alpha particles isa relatively simple matter. Since an alphaparticle has a positive electrical charge of 2,a few centimeters of air is all that is requiredfor attenuation. Any light material such asaluminum or plastics makes a suitable shieldfor beta particles.Neutrons and gamma rays have considerablepenetrating power; therefore, shielding againstthem is more difficult. Since neutrons are bestattenuated by elastic collisions, any hydrogenousmaterial such as polyethylene or water is suitableas a neutron shield. Sometimes polyethylenewith boron is used for neutron shields, asboron has a high neutron capture cross section.Gamma rays are best attenuated by a densematerial such as lead.NUCLEAR REACTORSThe purpose of any power reactor is toprovide thermal energy which can be convertedto useful work. Several types of experimentaland operational reactors have beendesigned. They include the Pressurized WaterReactor (PWR), the Sodium Cooled Reactor,the Experimental Boiling Water Reactor, theExperimental Breeder Reactor, and the ExperimentalGas Cooled Reactor.The first full-scale nuclear-powered centralstation in the United States was the PressurizedWater Reactor (PWR) at Shippingport, Pennsylvania.The Shippingport PWR is a thermal,heterogeneous reactor fueled with enricheduranium-235 "seed assemblies" arrangedin a square in the center of the core, surroundedby "blanket assemblies" of uranium- 238 fuelelements. Figure 24-7 shows a cross-sectionalview of the PWR reactor and core. This typeof reactor can be called a converter , since theuranium-238 is converted into the fissionablefuel of plutonium-239.A schematic diagram of PWR and its associatedsteam plant with power output andflow ratings is shown in figure 24-8. Thereactor plant consists of a single reactorwith four main coolant loops; the plant iscapable of maintaining full power on threeloops. Each coolant loop contains a steamgenerator, a pump, and associated piping.High purity water at a pressure of 2000psia serves as both moderator and coolantfor the plant. At full power the inlet watertemperature to the reactor is 508° F and theoutlet temperature is 542° F.The coolant enters the bottom of the reactorvessel (fig. 24-9) where 90 percent of the waterPLACE FOREXTRA 8LANKETASSEMBLYCONTROL ROD

. STEAMChapter 24. -NUCLEAR POWER PLANTSFROM OTHERSTEAM GENERATORS'////////////////^y^ GENERATOR ^/, 60,000 - KW NET ^X OUTPUT (SLOOPS)^HEAT OUTPUT- 790 X 10« 8TU / MRFLOW . 50,400 GPMOPERATING PRESSURE= 2000 PSIDESIGN PRESSURE. 2500 PSISTEAM PRESSURE - 600 PSIAFLOW . 287,000 LBS.'HRSTEAMGENERATORSTEAMSEPARATORCONDENSATEPUMP.FLOW = 1^800 GPMVELOCITY . 30 FT/SECFEEDWATERi PREHEATER-C5c-BOILER FEED PUMPLOOP NO. 3TOOTHER STEAMGENERATORSFigure 24-8.— Schematic diagram of PWR plant.147.158Xflows upward between the fuel plates, withthe remainder bypassing the core in order tocool the walls of the reactor vessel and thethermal shield. After having absorbed heat asit goes through the core, the water leaves thetop of the reactor vessel through the outletnozzles and flows through connecting piping tothe steam generator.The steam generator is a shell-and-tubetype of heat exchanger with the primary coolant(reactor coolant) flowing through the tubes andthe secondary water (boiler water) surroundingthe tubes. Heat is transferred to the secondarywater in the steam generator, producing highquality saturated steam for the use in theturbines.The primary coolant flows from the steamgenerator to a hermetically sealed (cannedrotor) pump (fig. 24-10) and is pumped throughconnecting piping to the bottom of the reactorvessel to complete the primary coolant cycle.The pressure on the reactor vessel and themain coolant loop is maintained by a pressurizingtank (fig. 24-11) which operates underthe saturation conditions of 636° F and 2000 psia.A second function of the pressurizing tank is toact as a surge tank for the primary system.Under no load conditions the inlet, outlet, andaverage temperatures of the reactor coolant623

IPRINCIPLES OF NAVAL ENGINEERINGCONTROL DRIVEMECHANISM HOUSINGTERMINAL BOXBEUVILIE SPRINGCONTROL RODNATURAL URANIUMASSEMBLY (BLANKET)CORE CAGETHERMAL SHIELDSBOTTOM PLATEFLOW BAFFLEIMPELLERBOLTING RINGVOLUTE147.159XFigure 24-9.— Longitudinal section ofPWR reactor.147.160XFigure 24-10.—PWR main coolant pump.(A) External view. (B) Cutaway view.624

Chapter 24. -NUCLEAR POWER PLANTSare nearly equal in value. As the power increases,the average temperature remainsconstant but the inlet and outlet temperaturesdiverge. Since the colder leg of the primarycoolant is the longer, the net effect in thepressurizer is a decrease in level to makeup for the increase in density of the water inthe primary loop. The reverse holds true witha decreasing power level. Electrical heatersand a spray valve with a supply of water fromthe cold leg of the primary coolant assist inmaintaining a steam blanket in the upper partof the pressurizer and also assist in maintainingsaturation conditions of 2000 psia and636° F.coolant increases, so does the magnitude of theneutron scattering cross section. The highervalue of the scattering cross section allows thecoolant, in its capacity as moderator, to thermalizeneutrons at faster rate, supplying moreSPRAY NOZZLEPRINCIPLES OF REACTOR CONTROLReactor control principles' which are ofparticular interest to this discussion includethe negative temperature coefficient , the de -layed neutron action , and the poisoning of fuel.The term "negative temperature coefficient"is used to express the relationship betweentemperature and reactivity— as the temperaturedecreases, the reactivity increases. The negativetemperature coefficient is a design requirementand is achieved by the proper ratioof elements in the reactor, the geometry of thereactor, and the physical size of the reactor.The negative temperature coefficient makes itpossible to keep a power reactor critical withminimum movement of the control rods.The concept of negative temperature coefficientmay be most easily understood by useof an example. Assume that, in the PWR plantshown in figure 24-8, the reactor is criticaland the machinery is operating at a givenpower level. Now, if the valve is opened toincrease the turbine speed, the rate of steamflow, and the power level of the reactor, themeasurable effect with installed instrumentationis a decrease in the temperature of theprimary coolant leaving the steam generator.The decrease in temperature is small butsignificant in that it results in an increase indensity of the coolant. As the density of the^ DOMESTANDPIPEHEATERSECTIONJohn F. Hogerton, The Atomic EnergyPeskbook (NewYork: Reinhold Publishing Corp., 1963), p. 463.147.161XFigure 24-11.— Cutaway view of PWRpressurizing tank.625

PRINCIPLES OF NAVAL ENGINEERINGthermal neutrons to be absorbed in the fuel.As more neutrons are absorbed in the fuel,more fissions occur, resulting in a higherpower level and more heat being generatedby the reactor. The additional heat is removedby the reactor coolant to the secondarywater in the steam generator to compensate forthe increased steam demand by the turbine. Thetemperature of the primary coolant leaving thesteam generator increases slightly, loweringthe scattering cross section of the moderator,and the reactor settles out at a higher powerlevel.The delayed neutron action is a phenomenonthat simplifies reactor control considerably.Each fission in a nuclear reactor releases onthe average between two and three neutronswhich either leak out of the reactor or areabsorbed in reactor materials. If the reactormaterial which absorbs the neutron happens tobe the fissionable fuel, and if the neutron is ofproper energy level, another fission is likelyto result. The majority of the neutrons releasedin the fission process appear instantaneouslyand are termed prompt neutrons; butother neutrons are born after fission and aretermed delayed neutrons . The delayed neutronsappear in a time range of seconds to 3 or moreminutes after the fission takes place. Theweighted mean lifetime of the delayed neutronsis approximately 12 seconds. About 0.75 percentof the neutrons produced in the fissionprocess are delayed neutrons.Should a reactor become prompt critical(critical on prompt neutrons), it would be verydifficult to control and any delayed neutronswould tend to make it supercritical. The delayedneutrons have the effect of increasing thereactor period sufficiently to permit reactorcontrol. Reactor period is the time requiredto change the power level by a factor of e_(the base of the system of natural logarithms).A nuclear poison is material in the reactorthat has a high absorption cross section forneutrons. Some poisons are classed as burnablepoisons and are placed in the reactor for thepurpose of extending the core life; other poisonsare generated in the fission process and have atendency to be a hindrance to reactor operation.A burnable poison has a relatively high crosssection for neutron absorption but is used up inthe early part of the core life. By adding aburnable poison to the reactor, more fuel can beloaded into the core, thus extending the life ofthe core.Most of the fission products produced ina reactor have a small absorption cross section.The most important one that does have ahigh absorption cross section for neutrons isxenon- 135; this can become a problem nearthe end of core life. Xenon- 135 is a directfission product a small percentage of thetime but is mostly produced in the decay ofiodine-135 as indicated in the following decaychain:-„I^^^ 6.7hrs ..Xe^^^53 549. 2 hrs^135 „ „ ,„6 „ 135-Cs 2. X 10 yrs55'cgBaXenon- 135 has a high neutron absorptioncross section. In normal operation of thereactor, xenon- 135 absorbs a neutron and istransformed to the stable isotope of xenon- 136,which presents no poison problem to the reactor.Equilibrium xenon is reached after about40 hours of steady- state operation. At thispoint the same amount of xenon- 135 is being"burned" by neutron absorption as is beingproduced by the fission process.The second, and perhaps the more serious,effect of xenon poisoning occurs near the endof core life. As indicated by the half- livesshown in the xenon decay chain, xenon-135 isproduced at a faster rate than it decays. Thebuildup of xenon-135 in the reactor reaches amaximum about 11 hours after shutdown. Shoulda scram occur near the end of core life, thexenon buildup may make it impossible to takethe reactor critical until the xenon has decayedoff. In a situation of this type, the reactormay have to sit idle for as much astwo days before it is capable of overridingthe poison buildup.THE NAVAL NUCLEAR POWER PLANTSince many aspects of the design andoperation of naval nuclear propulsion plantsinvolve classified information, the informationpresented here is necessarily brief and generalin nature.In a nuclear power plant designed for shippropulsion, weight and space limitations andother factors must be taken into considerationin addition to the factors involved in the designof a shore-based power plant.The thermodynamic cycle of the shipboardnuclear propulsion plant is similar to that ofthe conventional steam turbine propulsion plant.626

Chapter 24. -NUCLEAR POWER PLANTSInstead of a boiler, however, the nuclear propulsionplant utilizes a pressurized water reactoras the heat source and a steam generatoras a heat exchanger to generate the steam usedto drive the propulsion turbines.The steam generator is a heat exchanger inwhich the primary coolant transfers heat to thesecondary system (boiler water) by conduction.The water in the secondary side of the steamgenerator, being at lower pressure, changesfrom the physical state of water to the physicalstate of steam. This steam then flow throughpiping to the engineroom.The engineroom equipment consists of propulsionturbines, turbogenerators, condensers,and associated auxiliaries.PROBLEMS OF NUCLEAR POWERAlthough many developmental and engineeringproblems associated with nuclear powerhave been solved to some extent, some problemsremain. A few problems that are of particularimportance in connection with the shipboardnuclear power plant are noted here briefly.The remote possibility of radiologicalhazards exists even though the radiation is wellcontained in the shipboard nuclear reactor. Toeliminate or minimize the radiological hazards,a high degree of quality control is essential inthe design, construction, and operation of nuclearpower plants. The high pressures and temperaturesused in nuclear reactors, together withthe prolonged periods of continuous operation,pose materials problems. For shipboard use,the great weight of the materials required forshielding presents still other problems.Although many of these problems may besolved by further technological developments,the problems involved in the selection andtraining of personnel for nuclear ships appearto be continuing ones. The safe and efficientoperation of a shipboard nuclear plant requireshighly skilled, responsible personnel who havebeen thoroughly trained in both the academic andthe practical aspects of nuclear propulsion. Theselection and training of such personnel is inevitablycostly in terms of time and money.627

CHAPTER 25NEW DEVELOPMENTS INNAVAL ENGINEERINGNew developments in naval engineering tendto be closely related to concepts of strategy. Insome instances, new concepts of strategy mayforce the development of new engineering equipmentto meet specific needs; in other instances,the development of a new source of power, anew engine, a new hull form, or a new propulsivedevice opens up new strategic possibilities. Inany event, engineering capability is a majorlimiting factor in strategic planning, since itdetermines what is possible and what is notpossible in the way of ship operation.In previous chapters of this text, we havebeen concerned with naval engineering equipmentcurrently installed in naval ships. But itwould be unreasonable to assume that presentachievements, impressive though they may be,are the last word in naval engineering. Practicallyeverything in the Navy— policies, procedures,publications, systems, and equipment— issubject to rapid change and development, andnaval engineering is certainly no exception. Therate of change in technological areas is increasingall the time. The officer who is just beginninghis naval career may well, in the course of afew years, see more changes in naval engineeringthan have been seen in the past half centuryor more. And, difficult though it may be, everynaval officer has a responsibility for keeping upwith new developments.Because of the increasingly rapid rate oftechnological development, it is no mean feat tokeep abreast of changes in engineering equipment.In order to keep up with new developmentsin naval engineering, it is necessary to readwidely in the literature of the field and to developa special kind of alertness for information thatmay ultimately have an effect on naval engineering.In the present chapter, we will depart fromour previous framework of the here- and-now andmention briefly a few areas which, at present,appear to offer some promise for future applicationin the field of naval engineering. With afew exceptions, the areas noted in this chapterare ones in which some actual work has beendone or in which some serious thought has beengiven to naval engineering applications. It shouldbe emphasized that this chapter is neither a completesurvey of new developments nor a crystalballtype reading of the future. Some of the areasmentioned here may turn out to have little or noapplication to naval engineering, while areas thatare not even mentioned may suddenly come intoprominence and importance.HULL FORMSMany new developments in naval engineeringhave been aimed, directly or indirectly, at increasingthe speed of ships. One approach to thisproblem is to increase the size or change thenature of the propulsion machinery— a solutionwhich, for various reasons, is not always feasible.Even when larger or better propulsion machineryis feasible, it is not always a total solutionto the problem of increased speed, since atleast some of the increased power thus providedis needed to overcome the increased resistanceof the ship at the resulting higher speed. In thecontinuing search for ways to achieve higheroperating speeds, therefore, a considerableamount of thought has been given to new hullforms which will reduce the resistance of theship as it moves through the water.A surface ship moving through the water isimpeded by various resistances, ^ chiefly thef rictional resistance of the water and the resistancethat results from the generation of wavetrains by the ship itself. Overcoming each ofFundamentals of ship resistance are discussed inchapter 5 of this text.628

Chapter 25. -NEW DEVELOPMENTS IN NAVAL ENGINEERINGthese resistances requires the expenditure ofdefinite, calculable amounts of energy; henceeach kind of resistance must be considered inconnection with efforts to increase the speed ofsurface ships.Among the interesting hull forms that havebeen developed (or at least considered) with aview to increasing surface ship speed by decreasingone or both of these resistances are thebulbous-bow form, the slender hull form, thesemi- submarine form, the hydrofoil, and thevarious forms devised to utilize an air cushionor an air bubble. Each of these forms has specificadvantages and disadvantages; the search isnot for one perfect hull form but rather for avariety of hull forms suitable for a variety offunctions.Bulbous-Bow FormsThe bulbous-bow configuration is currentlyused on most large naval ships. 2 The theory ofthe bulbous-bow form is that the bulb will generateits own system of waves which will interferewith the systems of waves formed by theship, thus reducing the resistance that resultsfrom the wave-making of the ship.Although the bulbous-bow configuration is notso very new either in theory or in application,the concept of using much larger bulbs is a fairlyrecent development. In theory, the wave- makingresistance of a ship could be substantially reducedby locating a large bulb just below the surfaceand just forwardof the bow. In reality, thereare enormous design difficulties involved, sincethe bulb must be specifically designed to interferewith complex wave trains generated by theship.Some idea of the complexity of the problemmay be obtained by tossing pebbles into a pondand observing the waves that are formed. Whentwo pebbles are tossed in together, each pebblegenerates its own systemsof waves. Under someconditions, the systems of waves tend to canceleach other out; under other conditions, they tendto enhance or amplify each other; and under stillother conditions, they interfere with each otherin a chaotic, unpredictable manner which is essentiallyuseless as far as achieving any cancellationof waves is concerned.See the discussion of stem and bow structure inchapter 2 of this text.In spite of design difficulties, the use of largebulbs is of value in the design of certain tjrpes ofships. Tests of models have shown that a shipwith a large bulb at the bow generates smallerand smoother systems of waves than a ship withoutsuch a bulb. However, this gain is not all free,since the bulb adds frictional resistance to theship.Slender ShipsA slender hull ship is basically similar to adestroyer except that, for any given displacement,the slender ship is about 30 percent longerthan the destroyer. The extra length is designedto increase speed by decreasing the wave-makingresistance of the ship. A slender ship has lessstatic stability than a comparable destroyer, dueto the narrower beam in relation to length. Also,the structural weight of the slender ship must beconsiderably greater than the structural weightof a comparable destroyer.Some slender ships have been designed utilizinga large bulb at the bow and another one at thestern. Such ships are of interest because theyhave improved longitudinal stability characteristicsas well as decreased wave- making resistance.Semi-SubmarineThe semi- submarine is still another approachto the problem of increasing speed byusing a special hull form. The semi- submarineis shaped somewhat like avery streamlined submarine.The main hull of the semi- submarineruns submerged, while surface-piercing structuresor fins (hydrofoils) at the stern increasethe dynamic stability characteristics of the vesseland provide a means for handling engine airintake and exhaust. Because the semi-submarineruns submerged, except for the fins (hydrofoils),the craft avoids both storm waves and the selfgeneratedwave- making resistance of surfaceships.HydrofoilsThe hydrofoil has been described as a crossbetween a high speed boat and an airplane. Thecraft has two modes of operation; it may run onthe surface of the water, as a conventional surfaceship, or it may fly on the foils with the hullclear of the water. When flying, the hydrofoil issupported clear of the water by the dynamic liftof the foils.629

PRINCIPLES OF NAVAL ENGINEERINGThe primary advantages of the hydrofoil formare high speed and superior seakeeping abilities.The high speed is attainable because the resistancesencountered by other shipforms are substantiallyreduced in the hydrofoil. When the hydrofoilis flying, the hull is entirely above thesurface of the water and is therefore not impededby frictional resistance or wave- making resistanceand is not disturbed by waves, swells, orchoppy surfaces that slow down other craft.At present, the hydrofoil form is not consideredfeasible for very large vessels. However,the future development of propulsion plantswith smaller specific weights^ could well extendthe tonnage range of the hydrofoil form. In fact,a "hydrofoil destroyer" has even been proposed.Several types of hydrofoil systems have beendeveloped. The Navy hydrofoil program has concentratedlargely on fully submerged subsurfacewings or foils. Control surfaces on the fully submergedfoils act like aircraft ailerons and controlthe course of the craft through the water;the foils are controlled by a height- sensing systemwhich maintains level flight. In another typeof control (incidence control) the entire foil ismoved instead of flaps. Other hydrofoil systemsinclude skids or other planing devices and surface-piercingfoils. Surface-piercing foils havea lifting area that is proportional to the amountof foil immersed.A number of hull forms have been used forhydrofoils, but most of them are basically adaptationsof conventional hull forms. The hull isrelatively long and narrow, with the length of thecraft being eight to ten times the beam. It hasbeen suggested that the catamaran'* design mayhave certain specific advantages for hydrofoils;however, this type of design is not currently usedin Navy hydrofoils except on an experimentalbasis.Although a wide variety of power plants havebeen considered for hydrofoil craft, the gas turbineand the diesel engine are the types primarilyinstalled in these craft at present. Some hydrofoilsare equipped with both gas turbines anddiesel engines."^The specific weight of a propulsion plant is thenumber of pounds of propulsion machinery requiredper shaft horsepower.4 The catamaran or twin-hull design consists of twoslender hulls which are joined together above thewaterline.A major problem in the development of hydrofoilshas centered around the transmission ofpower. When an underwater propeller is used,power must be transmitted downward from theprime mover in the hull to the propeller, whichis at a deeper level. Various solutions to thisproblem have been tried. One solution is to usean inclined shaft and an inclined prime moverwhich drives into a V-gear. Another solution isto use double right-angled gearing. To date, nosolution has been found that is entirely satisfactory.Propellers have also been a continuing problemwith hydrofoils. The cavitation encounteredat high speeds has led to numerous propellerfailures. One solution to this problem is the supercavitating(SC) propeller discussed later inthis chapter. Because of the propeller problem,other propulsion devices such as airscrews andairjet or waterjet propulsion systems have beenconsidered for use with hydrofoils.The Navy's first operational hydrofoil, USSHigh Point , PCH 1, is shown in figures 25-1 and25-2. In flight, this hydrofoil reaches speeds ofmore than 45 knots.HydroskimmersThe hydroskimmer belongs to the generalcategory of craft designed to ride on a bubble ora cushion of air. Vehicles and craft in this categoryare called ground effect machines (GEM),air cushion vehicles (ACV), or surface effectships. In general, any GEM that is designed tooperate over water is called a hydroskimmer.The hydroskimmer has been referred to as a"flying washtub,"5 and the comparison is apt.The basic principles of the hydroskimmer (and,indeed, of all ground effect machines) may begrasped by considering an inverted washtub witha fan mounted inside the tub. When the fan isturned on, the tub begins to rise off the groundas soon as the air pressure inside the tub becomessufficiently great. This, in essence, isthe principle of the hydroskimmer.In a real hydroskimmer or other GEM, the airescapes uniformly around the bottom edges of thecraft, thus providing a cushion of air which liftsthe craft evenly above the ground or the water.The air cushion is developed and maintained invarious ways, depending upon the basic design ofthe vehicle.SErwin A. Sharp, JOC. USN, "Sailing on a Bubble ofAir." All Hands . December 1960, pp. 8-11.630

Chapter 25, -NEW DEVELOPMENTS IN NAVAL ENGINEERINGAIR INTAKE AND STRUTTRUNK HOUSINGFORWARD FOILPROPELLER FOR FOILBORNEOPERATIONNACELLEPROPELLER FORHULLBORNE OPERATIONFigure 25-1. -Hydrofoil (USS High Point ,PCH1)3.88In the plenum- chamber type ,air is forceddown from the top of one chamber and allowed toescape around the edges at the bottom.In the air-curtain type ,the interior is dividedinto sections, with open air ducts between thesections. Air is forced down through the ducts toform a high pressure air cushion for the craft toride upon. Air jets, pointing downward and inward,are installed around the periphery of thecraft; the air from these jets holds the air bubblein place. In some air-curtain designs, the airjets are used only at the front and the rear. Sidewalls (called skegs ) are used to enclose the airbubble at the sides.In the water- curtain type , a scoop and a waterpump are used to form water jets (instead of airjets) around the peripheryof the craft. The waterare even more efficient than the air jets injetskeeping the air cushion under the craft. Obviously,the water- curtain design is suitable onlyfor craft operating over water.The air cushion gets the hydroskimmer intothe air, but it does not provide it with any meansof horizontal propulsion. Both airscrews andwater screws have been tried; each type has someadvantages, with the choice depending upon thenature of the vehicle and the service conditions.The hydroskimmer, although still experimentalat this stage, gives promise of being avery fast and effective craft for a variety of uses.Speeds of 80 to 120 knots are considered feasible.The hydroskimmer is being considered for suchuses as ASW craft, patrol craft, high speed transport,amphibious assault, mine countermeasurescraft, and rescue craft. The Navy's 25-ton researchhydroskimmer, SKMR-1, is shown infigure 25-3. This vessel was built with the specificaim of providing more knowledge on the preferredshapes, propulsion machinery, and propulsivedevices for this type of craft. The aircushion system for SKMR-1 is shown in figure25-4.PROPULSION AND STEERINGFor more than a hundred years, the underwaterscrew propeller has been the conventionaldevice for ship propulsion. Although the screwpropeller is in nodangerof being replaced withinthe foreseeable future, the increasing emphasison high speed ships has led to an increasing concernwith other types of propulsion devices. Someof the propulsion devices presently under developmentor consideration are mentioned here.631

PRINCIPLES OF NAVAL ENGINEERINGFigure 25-2. -Hydrofoil in flight.3.88The super cavitating (SC) propeller is a recentdevelopment that may have particular applicationto hydrofoils and other high speed ships. Thesupercavitating propeller is intended for use athigh forward speeds and high rpm, with a relativelyshallow depth of submergence. It is designedto operate under conditions of full cavitation,although it may encounter conditions ofpartial cavitation when operating at less thandesigned forward speed and rpm. Under conditionsof partial cavitation, the supercavitatingpropeller may be subject to cavitation erosionsimilar to that encountered on conventional propellers.A supercavitating propeller is designed tooperate with the suction side (back) of the bladesenclosed in avapor cavity. Because of the specialdesign of the blades, this vapor cavity collapsesfar enough downstream from the propeller bladesto prevent any cavitation effects on the face of theblades. In essence, the basic line of reasoning behindthe design of the supercavitating propelleris not to do away with or prevent cavitation butrather to accept it as inevitable at high speedsand to control it. The supercavitating propellercontrols cavitation by making sure that the cavitycollapse occurs in an area in which it can do relativelylittle damage.632

Chapter 25. -NEW DEVELOPMENTS IN NAVAL ENGINEERINGFigure 25-3. — Navy research hydroskimmer(SKMR-1).3.265Another approach to the problem of cavitationand the resulting reduction in thrust is the use ofpropeller nozzles and shrouds . Nozzles andshrouds reshape the flow of water to the propellerin such a way as to delay cavitation by increasingand "containing" the pressure aroundthe propeller. A similar reshaping of the waterflow may be obtained by the use of hydraulic jets .One "new" propulsion device is actually quiteold; although it has not recently had any majorapplication for ship propulsion, it has been usedon some torpedoes. This is the contra- rotatingpropeller , which consists of two screws turningin opposite directions. The advantage of the contra-rotating propeller design is that the afterpropeller is able to utilize some of the energyfrom the wake of the forward propeller, thusleading to higher efficiencies than are obtainablewith a single screw propeller. The contra-rotatingpropeller also offers possibleweight savings and efficiency improvements inthe propulsion machinery.One variation of the contra- rotating propellerinstallation is called a tandem propeller instal -lation .In this arrangement, one propeller is installednear the bow and the other near the stern.The propeller blades are mounted on a blade ring,with the blades projecting out through the hull.The pitch of the contra-rotating propeller bladescan be varied in such a way as to provide completemaneuverability, as well as propulsion;hence this device is actually a combination of apropulsion device and a steering device. Althoughoriginally proposed for small submersible craft,it is possible that this type of installation mayhave application for larger ships in the future.A number of other devices have been suggestedwhich combine the functions of propulsionand steering. Among these are the steeringscrew, which consists of a propeller mounted ona vertical shaft. The shaft can be rotated through360° in order to propel the vessel in any desireddirection. Other devices which combine the functionsof propulsion and steering to some extentare screw propellers arranged as bowthrustersor as stern thrusters . In each case, the screwpropeller is mounted on a horizontal shaft. Thepropeller is located within a tube which runs athwartshipthrough the bow or the stern. The propellerscan be reversed to provide thrust ineither athwarthship direction. The tubes can bearranged to be closed off when not in use.Airscrew propulsion for ships has been underinvestigation for the past few years. The primaryadvantage of the airscrew is that it provides verygreat maneuverabiltiy, particularly at lowspeeds. In a Navy test of airscrew propulsion onthe liberty ship John L. Sullivan (YAG 37), it wasfound that maneuverability at low speeds wasbetter with the airscrews than with conventionalpropulsion and steering. When approaching piersor mooring buoys, the ship was able to maneuverwithout the assistance of a tug because the airscrewsprovided the capability for applying propulsiveforce in any direction.The disadvantage of airscrew propulsion forships is that enormous airscrews would be requiredto propel even a medium- sized ship at anygreat speed. For certaintypesof craft, however,it is possible that some combination of waterscrew and airscrew propulsion may be feasible.Although none of the combined devices thusfar developed have solved all propulsion andsteering problems, there is much to recommendthe combination approach. Propulsion and steeringare very closely related; a truly effectivepropulsion and maneuvering combination shouldresult in greater simplicity and greater efficiencythan is obtainable with two separate devices.Waterjet propulsion for ships was tried outmany years ago but abandoned becauseof its relativelylow efficiency. However, the Navy hasrecently been investigating the possibility of633

PRINCIPLES OF NAVAL ENGINEERINGSTABILIZINGNOZZLESPERIPHERALNOZZLEPROPULSIONDUCTSCUSHION FAN DUCTSPILOTHOUSENOZZLECONTROL VANESFLOTATIONCOMPARTMENTSFigure 25-4.— Air cushion system for SKMR-1).3.265using the waterjet as a prime mover in smallcraft such as the one shown in figure 25-5.The general principle of waterjet propulsionis illustrated infigure 25-6. The "prime mover"consists merely of a water pump. The rotatingimpellers deliver thrust by accelerating a largevolume of water at a high velocity through a nozzle.The velocity of flow through the nozzle is directlyproportional to the flow rate and inverselyproportional to the volume of flow times the velocityof flow.One of the outstanding advantages of thewaterjet mode of propulsion is that the waterjetproduces much less underwater noise than aconventional propeller-driven craft of the samesize and general configuration. Preliminarystudies of the waterjet indicate that a comparableconventional propeller-driven craft could be detectedapproximately ten times farther away thanthe waterjet.Quite a different system of jet propulsion hasbeen suggested as a possibility for the propulsionof underwater vehicles. This propulsion system(fig. 25-7) is generally known as an underwaterramjet system . The fuel in the combustionchamber reacts with the water; hence the waterthat enters the combustion chamber may be regardedas a co-propellant. The products of thereaction are expanded through a nozzle at theafter end of the craft, thus propelling the craftforward. Although a propulsion system of thissort would have many advantages for short- rangeoperation, there are some disadvantages; onepresent disadvantage is that the system is extremelynoisy. Also, it is very inefficient exceptat very high speeds (above 80 knots).DIRECT ENERGY CONVERSIONThe production of power for ship propulsionbegins with the conversion of some stored formof energy. In all present propulsion plants, thestored energy that is the original source of powermust undergo a series of transformations beforeit can be utilized to propel the ship. We have twomajor sources of stored energy: fossil fuel andnuclear fuel. In each case the stored energy mustbe converted into thermal energy which is thenconverted into mechanical energy.'During the past few years, a considerableamount of interest has developed concerning634

Chapter 25. -NEW DEVELOPMENTS IN NAVAL ENGINEERING147.162Figure 25-5.— Small craft with waterjetpropulsion.direct energy conversions that may ultimatelyhave application to the production of power forship propulsion. This interest arises from twomajor considerations. First, the Carnot cycle^which is the thermodynamic basis for our heatengines is inherently inefficient, with the theoreticalmaximum efficiency of the cycle beingTi - T2Tllimited to where Ti is the absolute temperatureat which heat flows from the source to theworking fluid and T2 is the absolute temperatureat which heat is rejected to the receiver. Sincethe temperature of the heat receiver (the ocean)cannot be lowered, the only way to improve theefficiency of an actual cycle based on the Carnotcycle is to increase the temperature of T^. Thepast few years have seen great advances in theuse of higher Tj temperatures (e.g., boilersoperating at higher pressures in order to increasethe difference between Tj and T2), butmaterials limitations eventually impose a barrierto progress in this direction.The second reason for current interest innovel energy conversions is that the actual shipboardcycles in which stored energy is convertedto thermal energy which is then converted to work°The Carnot cycle is discussed in chapter 8 of thistext.require a great deal of equipment to performthese various energy conversions. Beginningwith an inherently inefficient cycle which cannotoperate unless a great deal of heat is "wasted"because it must be rejected to a heat receiver,we must accept even greater inefficiency becauseof the mechanical losses and miscellaneous heatlosses that inevitably occur throughout the plant.There are two major approaches to the problemof direct energy conversion. One approachis to find an energy conversion which is not basedon the Carnot cycle and is therefore not limitedby the requirement that some heat be rejectedto a low temperature heat receiver. The otherapproach is to utilize a "static" heat enginewhich is based on the Carnot cycle, and thereforesubject to its limitations, but which has no movingparts and therefore no mechanical losses.The fuel cell is an example of a device that bypassesthe Carnot cycle to make a direct energyconversion. Thermoelectric converters, thermionicconverters, and magnetohydrodynamicgenerators are examples of static heat engineswhich, although operating on the Carnot cycle,come very much closer to the maximum theoreticalefficiency of the cycle by reducing or eliminatingmechanical losses.Fuel CellsA fuel cell is a battery-type device in whichchemical energy is converted directly into electricalenergy. The reaction involves a freeenergy release, without the rejection of heat to aheat sink; hence the process is independent of theCarnot cycle and free of Carnot cycle limitations.The major parts of a fuel cell (fig. 25-8) arean anode, a cathode, and an electrolyte. The fuelis fed continuously to the anode, while the oxidantis fed continuously to the cathode. The conversionfrom chemical energy to electrical energy occursas electrons, released at the anode, flowtothe cathode.Several types of fuel cells are under investigationand development. Some operate at relativelylow pressures and temperatures, others athigh pressures andtemperatures. A wide varietyof fuels have been considered for fuel cells; hydrogen,various hydrocarbons, and methanol appearto offer particular promise for many applications,while a sodium amalgam is beingconsidered for use in certain small fuel cells.The oxidants most commonly used are air andoxygen; however, peroxides, chlorine, and othersubstances have also been tried. Electrolytes635

PRINCIPLES OF NAVAL ENGINEERINGFigure 25-6.— Principle of waterjet propulsion.147.163COMBUSTIONCHAMBERDISCHARGE ^NOZZLEFORWARD MOTION OF VESSELFigure 25-7. — Underwater ramjet propulsion system.147.164that have been used in fuel cells include potassiumhydroxide, fused salts, and liquid salts.As may be inferred, the fuel cell is simplicityitself in basic concept, and it offers thepromise of enormously greater efficiencies thancan ever be obtained through any energy conversionthat is based on the Carnot cycle. However,there are many problems to be overcome beforethe fuel cell can be regarded as a major sourceof power for applications requiring large poweroutputs.Thermoelectric ConvertersA thermoelectric converter is a device forconverting heat to direct- current electricity.The general arrangement of a thermoelectricconverter is illustrated in figure 25-9. As maybe seen, the converter is basically a thermocoupledevice in which an emf is developedthrough the application of heat to dissimilar materials.In the thermoelectric converter, one of thedissimilar materials is of the type known as anN material and the other is of the type known asa P material. Asfar as electron behavior is concerned,N and P materials react differently whenheat is applied to one end. In N materials, theapplication of heat tends to make negativelycharged free electrons move toward the cold endof the piece. In P materials, the application ofheat tends to produce positive charges toward thecold end of the piece. When heat is applied to thehot junction of a thermoelectric converter (asshown in fig. 25-9) thecoldendof the Immaterialis negative and the cold end of the P^ material ispositive. When the cold ends are connectedthrough a load, the electric circuit is complete.The efficiency of the thermoelectric converteris limited by Carnot cycle limitations.As with all Carnot cycleenergy conversions, theefficiency of the thermoelectric converter increasesas the temperature differential increases.It is believed that the maximum attainableefficiency of the thermoelectric convertermay be on the order of 25 to 30 percent, althoughefficiencies thus far achieved are not nearly sohigh.Thermionic ConvertersAnother device for converting heat to directcurrentelectricity is the thermionic converter.In its simplest form, the thermionic converter issimilar to a vacuum tube, consisting of two metalelectrodes separated by a space under vacuum.The cathode is heated, and the anode is maintainedat a lower temperature. When the cathodeis heated, electrons are thermally agitated anddriven from the cathode to the anode. Connecting636

Chapter 25. -NEW DEVELOPMENTS IN NAVAL ENGINEERINGA^Arthus neutralizing the space charge effect and allowingthe unimpeded flow of electrons. Thermionicconverters in which the space betweenelectrodes is filled with cesium vapor appear tobe promising.Because a thermionic converter must operateat an extremely high temperature in order to developany great efficiency, some thought has beengiven to utilizing the decay heat of radioactiveisotopes as the heat source. One device that hasbeen successful in laboratory tests combinesreactor fuel and the thermionic converter in oneunit, thus in effect producing a "thermionic fuelcell." It is also believed that thermionic conversionmay be suitable for solar energy conversionfor use in space.Magnetohydrodynamic GeneratorsFigure 25-8.— Fuel cell.147.165the two electrodes to a load establishes a circuitand allows the flow of electric current.The thermionic converter, like the thermoelectricconverter, is a static heat engine andis limited by Carnot cycle considerations. It isbelieved, however, that higher efficiencies canbe obtained with the thermionic converter thanwith the thermoelectric converter. One reasonfor the higher efficiencies is that the thermionicconverter typically operates at substantiallyhigher temperatures (and with substantiallygreater temperature differentials) than the thermoelectricconverter. Another reason for thehigher efficiencies is that very little thermalenergy is lost between the hot and cold terminalsbecause of the vacuum that is maintained betweenthe cathode and the anode.In itself, however, the use of a vacuum createssome significant problems in connection with thethermionic converter. As electrons pass througha space under vacuum, there is a tendency for anegative "space charge" to be built up. Thisspace charge is merely a cloud of electronswhich, after escaping the cathode, have insufficientenergy to reach the anode. As the negativespace charge builds up, electron flow is greatlydiminished. The space charge effect can be reducedby putting the electrodes extremely closetogether, but this is difficult to do except in verysmall converters. One recent approach to thisproblem is to fill the space with positive ions.The magnetohydrodynamic (MHD) generatoris still another device for converting heat to direct-current electricity. In the MHD generator,the conversion is accomplished by passing a hightemperature gas through a magnetic field. Heatingthe gas to a very high temperature ionizes thegas and makes it electrically conductive. Passingthe electrically conductive gas through a fixedmagnetic field induces an electrical voltage inaccordance with Faraday's law.©LOAD

PRINCIPLES OF NAVAL ENGINEERINGThe MHD conversion is similar to the thermoelectricconversion and the thermionic conversionin some respects but quite unlike themin others. All three conversions involve the directconversion of thermal energy into electricalenergy, without the intervening step of conversionto mechanical energy; in this sense, all threemay be regarded as "direct energy conversions."But the MHD conversion, unlike the thermoelectricand thermionic conversions, requiresa working fluid— namely, a hot ionized gas.In this respect, then, the MHD conversion issomewhat less a "direct energy conversion"than the other two processes.The major problems in connection with magnetohydrodynamicconversion arise from the factthat extremely high temperatures (in excess of4000 ° F) must be developed in order to produceionization of the gas. Obviously, such high temperaturespose materials problems. Also, it isdifficult to achieve such temperatures on thelarge scale desired for MHD generators. Nuclearreactors capable of operating at these ultra- hightemperatures are under development but are notfully operational. When chemical fuels such asoil or powdered coal are used, the desired temperaturescan be obtained only if combustiontakes place with almost pure oxygen or if thecombustion air is preheated to approximately2000° F.In spite of the temperature problem, the magnetohydrodynamicconversion process continuesto arouse great interest among scientists andengineers. It should be noted, in fact, that thetemperature problem is only one side of the coin.On the other side, the use of such high temperaturesleads to thepossibilityof thermal efficienciesfar greater than any that are even theoreticallypossible with conventional heat engines. Ithas been estimated that overall efficiencies ashigh as 50 to 60 percent may be achieved throughMHD conversion, if provision is made for utilizingthe "waste" heat of the MHD process. Theadvantage of utilizing the waste heat is enormous,since the ionized gas is at a temperature of 2500°to 3000° F when it is discharged from the generator.COMBINED POWER PLANTSIn recent years there has been a great dealof interest in the use of combined power plantsfor ship propulsion. In a combined power plant,two basically different kinds of prime movers areused to furnish propulsive power. Each type ofprime mover has its own inherent limitations, aswell as its own unique advantages; the purpose ofcombining two prime movers is to make full useof the specialadvantagesof eachand, atthe sametime, to minimize or bypass its limitations.Combined power plants are of particular interestfor naval ships because of the constantneed to reconcile conflicting operational requirements.On the one hand, a naval ship mustbe able to operate at high speeds when necessary.On the other hand, the ship must be able to cruiseeconomically at lower speeds for extended distancesand extended periods of time. "^ If the primemover is selected specifically for high speedoperation, there is normally some sacrifice ofcruising radius. If the prime mover is selectedspecifically for economical operation at cruisingspeeds, there is normally some sacrifice ofspeed capability. In most cases, then, the selectionof a prime mover represents a compromisebetween high speed capability and large cruisingradius. 8For many naval applications, it appears thatconflicting operational requirements can be reconciledby combining a base-load plant of moderateweight and high efficiency with a boosterplant of very light weight and lesser efficiency.The base- load plant is selected to meet cruisingrequirements, and should be able to go manyhours between overhauls. The booster plant willinevitably require overhauls at much shorter intervalsbut is capable of providing additionalpower for high speed operation when necessary.A combined power plant for ship propulsionusually consists of two prime movers which aremechanically connected by gearing, clutching, orboth. In some combination plants, the two primemovers have interrelated thermodynamic cyclesin which one prime mover utilizes waste heatfrom the other. In other combination plants, thethermodynamic cycles of the two prime moversare entirely separate and independent.A great many combinations of prime moversare possible, though not all combinations areequally feasible or desirable. Also, for any given^More than 80 percent of the total operating time ofnaval ships is at speeds requiring less than a third ofthe power available from the Installed plant.SThis does not necessarily apply to nuclear ships. Obviously,however, the use of nuclear power bringsabout the necessity for another set of compromises.638

Chapter 25. -NEW DEVELOPMENTS IN NAVAL ENGINEERINGcombination of prime movers, various arrangementsare possible. The three combination plantswhich at present appear to offer great advantagesfor naval ships are (1) the combined steam andgas turbine plant, known as COSAG, (2) the combineddiesel and gas turbine plant, known asCODAG, and (3) the combined gas turbine and gasturbine plant, known as COGAG. Other combinations,including some that utilize nuclear power,are also under consideration.Combined steam and gas turbine (COSAG)plants have been installed in some combatantships of the British Navy and are being investigatedby our own Navy. Figure 25- 10 illustrates thegeneral arrangement of one COSAG plant installedin a British twin-screw guided missiledestroyer; there are two such plants, each servingone propeller. Each shaft set consists ofa cross- compound steam turbine of 15,000 shafthorsepower plus two gas turbines of 7500 horsepowereach. All prime movers drive into onegear box.CX]CX]GAS TURBINESSTEAM TURBINES147.167Figure 25-10.— COSAG plant for one screw of atwin-screw ship.A slightly different arrangement of a COSAGplant is shown in figure 25-11. This plant, whichis installed in a British single-screw frigate,consists of a single casing steam turbine of12,500 shaft horsepower and one gas turbine of7500 shaft horsepower.In both of the COSAG plants illustrated, thesteam turbine installation is capable of propellingthe ship at approximately 85 percent of fullpower ship's speed, in the event of completefailure of the gas turbine unit. The ability of thegas turbines to make a rapid start allows the shipto get underway very quickly with the steam plantcold. Maneuverability (including reversing) withthe gas turbine is achieved by fairly complexgearing and clutching. Each gear box incorporatesa reversing sectionfor the gas turbine; twomanual clutches for the gas turbine, one for theboost drive and one for maneuvering; a manualclutch for the steam turbine; synchronizingclutches which automatically connect the gas turbinedrive to the main shaft; and two hydrauliccouplings which are used when maneuvering onthe gas turbine. With this arrangement, the steamturbines or gas turbines (or both) can be used forpropulsion, and maneuvering can be accomplishedeither on the astern steam turbine or onthe gas turbine and the reversing gears.STEAM TURBINECAS TURBINE147.168Figure 25-11.— COSAG plantfor one- screw ship.Combined diesel and gas turbine (CODAG)plants utilize diesels for the base- load plant andgas turbines for the booster plant. The use ofmultiple diesels and multiple boost gas turbinesmeans that the loss in ship's speed will be verysmall in the event of failure of any one or evenany two units. The ship can get underway veryquickly with either diesel or gas turbine power.The efficiency of the diesel is much higher thanthe efficiency of a steam plant, and (for smallsizes of engines) the specific weight is somewhatless. In general, CODAG plants appear to be suitablefor ships which have moderate requirementsfor cruising power,A combined gas turbine and gas turbine(COGAG) plant has been proposed. Such a plantwould combine a long-life, efficient, moderateweightgas turbine for the base load and a light,aircraft- type gas turbine for the booster load.COGAG plants have not yet been tried out becausegas turbines suitable for the base loads are stillin developmental stages.CENTRAL OPERATIONS SYSTEMAdvances in engineering technology, the use ofsolid state devices, and computer circuitry havemade possible significant automation factors inthe operation of the naval engineering installations.Much of this automation has been appliedin the area of ship control and plant surveillance.A general discussion is presented in this chapteron a portion of an automated engineering plantconsidered representative of those currentlybeing employed on naval vessels.639

PRINCIPLES OF NAVAL ENGINEERINGThe automated engineering plant is designedto bring togetlier in one location all of the majorcontrol functions and indications previously locatedthroughout the engineering spaces^ In addition,major advances made in the areas ofboiler control, turbine control, and plant surveillancehave also been incorporated in the controlsystems. Control systems such as the centraloperation system provide for direct control ofshaft speed and direction at a console located onthe bridge. These control systems are located inan enclosed Engineering Operation Station (EOS)located within the machinery plant.The Central Operations System (COS), shownin figure 25-12, as found in naval vessels, providesfor control of the electrical plant, the mainturbine, selected auxiliary equipment and surveillanceof the entire engineering plant. It utilizessolid state components in the analog and thedigital circuitry. Analog components are used inthe throttle control systems and in the input to theplant surveillance equipment. Throttle controlfeatures are provided by standard operationalamplifiers and functional generators used in aclosed loop system which maintains operation ata desired point.Information on plant conditions is provided bydigital demand displays, alarm indications, indicatinglights, meters and the printout typewriters.This is handled by a time sharing systemmade up of logic circuitry, and controlled bya sjmchronous timing generator.A substantial decrease in the number of watchstanders required to operate the engineering installationcan be achieved through the use of asystem of this type. The bridge throttle controlfeature provides the OOD with a greater feel ofthe ship as well as a faster response to desiredchanges.ENGINE ROOM CONSOLEThe engine room console (fig. 25-13) is theheart of the central operations system (COS) andis divided into five functional sections, generators,propulsion, boilers, auxiliaries, anddata logger. The desk top of the console housesthe controls and devices required to be within theoperator's reach. The vertical surface above thedesk top is used primarily for instrument displayand visual indicators. Solid state control moduleswith printed circut elements are used which canBLOCKDIAGRAMPROPULSIONPLANTCONTROL. INFORMATION" DISPLAYSENSORS. MONITOR'^ a ALARM TEMP PRESSURE. PROGRAM ^" CONTROLS""^ACTUATORSSUB-LOOPCONTROLS1-^LEVELDATAMOTOR VALVE^ LOGGERFigure 25-12.— Central operations system major units.27.344640

Chapter 25. -NEW DEVELOPMENTS IN NAVAL ENGINEERINGFigure 25-13.— Engine Room Console.27.345be easily removed from the panels by unplugging.Temperatures, pressures, and liquid levels areconverted to electrical signals by sensors locatedat various points throughout the system.Significant readings on the console aredisplayed on flush mounted electric meters.Other readings which only need to be checkedperiodically are read on digital meters (calleddigital demand display readouts). The consoleprovides monitoring of the boilers and monitoringand control of the main propulsion plant, turbogeneratorsets, main condensate pumps, lubeoil pumps, fire pumps, and other auxiliary machinery,thus, enabling the engine room operatorto observe all important operating functionswithout leaving his station. At any time a plantstatus record may be made with the data logger.The COS continually monitors key temperatures,pressures, levels and motor conditions.If any go beyond operating limits, the systemsounds an alarm to alert the operator and thealarm logger automatically records the out oflimit conditions. An alarm log review, plantstatus log and bell log printout may be obtainedat any time by pressing a push button. Selectedpoints also have individual alarm lights. A belllogger automatically records engine order telegraphsignals and responses, propellor r.p.m.,throttle control location, and throttle controlwheel position together with time and date.Generator SectionThe generator section of the engine roomconsole (fig. 25-14) provides control and monitoringof the ship service generators. Provisionsare included which enable the operator toadjust the frequency and voltage and monitor theoutput of each generator; monitor the current inthe shore power connection; open, close, or monitorthe position of generator or bus tie circuitbreakers and the shore power circuit breaker;test each switch-board busfor grounds, and controland monitor the space heaters in each generator.Propulsion SectionThe propulsion section of the engine roomconsole (fig. 25-15) contains the throttle controlsand transfer switches, engine order telegraph,shaft revolution indicator- transmitter, and thenecessary gages and indicators for monitoringthe operating conditions of the main turbines, reductiongears, and propeller shaft.The throttle control handwheel controls theposition of pilotvalves on hydraulic power actuators.The hydraulic power actuators, in turn,open or close the main steam valves to the aheadand astern turbines, thus, controlling the speedand direction of the propellor shaft. An alternateelectrical control and a direct mechanical controlof the throttle are also provided. Throttle641

PRINCIPLES OF NAVAL ENGINEERING3 999 '^2!^ ®S®5^IFK—«tSIp7 t, « -«f^ *Jfl iff \\

Chapter 25. -NEW DEVELOPMENTS IN NAVAL ENGINEERINGFigure 25-15. — Propulsion Section.27.347different functions may be displayed simultaneously.Data Logger SectionThe data logger section (fig. 25-18) consistsof plant performance data logging, alarm scanning,and bell logging equipment. The plant performancelogging equipment can be set upto print at regular time intervals and on demand,with continuous scanning of all sensor points. Abnormalconditions are printed in red by the performancetypewriter (shown on the left in fig.25-18). The bell log typewriter (on the right) recordseach engine order telegraph signal alongwith time and date, location of throttle control,throttle control wheel position, and shaft RPM asstated previously.643

PRINCIPLES OF NAVAL ENGINEERINGFigure 25-16. — Boiler Section.27.348BRIDGE CONSOLEThe bridge console provides remote controlof the throttle as stated earlier. The throttle controlhandwheel and other necessary equipmentfor control of the propulsion plant are mounted onthe left section of the console. The ship's helmand other steering and navigation equipment aremounted on the right section as shown in figure25-19.SENSORSThe sensing devices used with the automatedcontrols are in most cases improved versions ofdetectors already receiving wide usage throughoutthe fleet.644

Chapter 25. -NEW DEVELOPMENT IN NAVAL ENGINEERINGIn all cases the manufacturer's technical manualsused with the system give complete installation,operation, and maintenance instructions.Pressure SensorsPressure sensors are used to convert plantpressure to an electrical signal for furtherFigure 25-17.—Auxiliaries Section.64527.349transmission to the Engine Room Console. Twoof the main types of sensors are the pressure- tocurrenttransmitter and the pressure switchtypes.The pressure-to- current transmitter (fig.25-20) converts the applied pressure to adirectcurrent proportional to the applied pressure.This current can then be applied to a meter for

PRINCIPLES OF NAVAL ENGINEERINGFigure 25-18,— Data Logger Section.27.350remote indication. The meter is calibrated in thedesired scale (PSI). These meters are in mostapplications d.c. microammeters.The pressure switch type transmitter findsits application in the alarm circuitry on the EngineRoom Console. Herein, at a given high or lowpressure, electrical contacts within the switchhousing are actuated completing or breaking acircuit and actuating an alarm.Level SensorsThree types of level sensors are generallyemployed throughout the system. Sincepressure may be a function of level the firsttwo devices used are the two detectors mentionedunder pressure; the pressure-to- currentfor indication and the pressure switch foralarm.646

Chapter 25. -NEW DEVELOPMENTS IN NAVAL ENGINEERINGFigure 25-19. — Bridge Console.27.351An additional level switch is employed inbilges and unvented tanks. This switch is similarin operation to that described in chapter 3 as afloat switch.Temperature SensorsTemperature is measured by means of resistancetemperature detectors (RTD).TheRTD(fig. 25-21) consistsof a sensing element incasedin a protective tube. Since the electrical resistanceof the element changes with temperaturechanges, the temperature can be determined bymeasuring the resistance.For temperatures having a maximum of 600degrees F., a nickel resistance element is used.These detectors are found to be of the stem- sensitivetype, where the sensing element is locatedwithin a few inches of the stem, or the tip- sensitivetype, where the sensing element is within thetip of the detector tube which must be pressedagainst the material being measured.Above 600 degrees a platinum element is employedin the stem- sensitive element type. Currentlythis is the only application of this type element.In most applications the RTD is installed inthermo wells, bored and threaded to receive thedetector. By the use of this method the unit maybe removed from the measured component orpiping without disturbing the integrity of the component.Extra protection is also afforded to theelement in this manner.DATA SCANNER SYSTEMFigure 25-22 is a block diagram of the DataScanner system. The inputs from the sensing devicesare placed into the scanner (block 27) asanalog values. The scanner is an electronic selectorgoverned by the Synchronous Timing Generator(22), the Program Contact (23) and thePoint Drive (26). When there are no requests forthe system such as the Bell Log, Alarm Log,Status Log, or Display Triggers, the scannercontinues to check each of the inputs. K there isa request present, the scanner will go directly tothe address requested and process that signalbefore monitoring all of the addresses. Thesignals are sent to the Isolation Amplifier (28)from the scanner, and after amplification it passeson to the Analog/Digital converter (29). The647

PRINCIPLES OF NAVAL ENGINEERING(1) Differential Pressure-to-Current Transmitter(2) Pressure-to-Current Transmitter(3) Float Switch(4) Differential Pressure Switch(5) Pressure SwitchFigure 25-20.— Pressure and Level Sensors.140.92program contact, controlled by the scanner, setsup the comparison values for the signal as wellas any adjustments to the signal required duringconversion and scaling.If the information is requested and/or thepoint is in alarm, the A/D converter then transfersthe values via the Word Distributor (24) tothe scaling module. If neither of the previouslymentioned conditions exist, the scanner executesbranch back and picks up the next address andrepeats the process.After the information leaves the A/D converterit is sent to the scaling module whichscales all signals into a zero to 1000 scale. Thisinformation is in the form of pulses numberingfrom zero to 1000 according to the value of theinput signal to the A/D converter. The addressinformation is then placed in the necessary registersand along with inputs from the Real TimeClock (40) and Digital Inputs (43) and made readyto be sent to the log Printout Buffer (37) and onto the Typewriter Drive (38) for printing.648

Chapter 25. -NEW DEVELOPMENTS IN NAVAL ENGINEERING(1) Stem Sensitive RTD(2) Thermowell with Adapter(3) Tip Sensitive RTD(4) Thermowell with HolderFigure 25-21.— Resistance Temperature Detectors.140.93Information leaving the scaling module fordisplay is sent directly to the Digital Display Buffersand Readouts (44) and appear at the readoutunits on the console face.The entire operation from pick-up of the inputaddress to activation of the printout unitsrequires a time span of .0376 milliseconds. Theassembly will monitor the complete bank of 273inputs in approximately two seconds providingthere are no requests or alarms conditions presentedto the system during that time period.THROTTLE CONTROLFigure 25-23 is a block diagram of thethrottle control system. A reference input signalmay be taken from either the bridge or engineroom reference handwheel potentiometer and fedto the system. Negative voltages are used forahead speeds and positive for astern. The signalthen passes through a common operational amplifierwhere it is inverted and then goes to thecommon circuit for both the ahead and astern turbines.The function generators will accept onlya signal of a given polarity. The ahead functiongenerator accepts positive signals and the asternfunction generator negative signals. The signalto the function generator is also used as a referencesignal for the speed feedback system. Thiscircuit compares the reference and speed feedbacksignals and uses the algebraic sum as theinput to the speed error amplifier.The signal to the function generator is adjustedwithin the amplifier so that the output isequivalent to the cube of the input. This is doneto change the linear movement of the referenceto the non-linear characteristics of the throttlevalve. Inversion once again takes place in thefunction generator.The output of the function generator ismatched with the speed error signal and thethrottle position signal at the summing junctionand the algebraic sum is fed to the summing amplifier.Inversion takes place and the output controlsthe action of the SCR power package.The SCR power package will cause the pilotmotor to drive in either direction depending uponthe input. A positive input will cause the pilot649

PRINCIPLES OF NAVAL ENGINEERING

Chapter 25. -NEW DEVELOPMENTS IN NAVAL ENGINEERING>—II-Ii-d»MP>— IFigure 25-23.— Block diagram of throttle control system.140.95motor to drive in a direction to open the throttlevalve. A negative input will close the throttlevalve. The SCR power package will be inhibitedby limit switches if the motor travel exceeds apredetermined point of travel.The pilot motor positions a pilot valve in thehydraulic actuator which ports oil in the properdirection to correctly position the throttle valve.A reference signal for throttle position, whichis controlled by the pilot motor, is fed back to thesumming junction. This section cancels the inputsignal when the desired valve opening is reached.During direct electrical control of the throttle,the contacts in the throttle location switchchange the circuitry eliminating the regulatedsignal and setting up the circuitry for signalsfrom the direct throttle switches.During manual operation, the manual clutch isengaged and the hydraulic actuator is inhibited. Inaddition, the hydraulic system is vented to preventa hydraulic lock and permit the movementof the handwheel for manual throttle control.A tachometer generator on the shaft producesan output signal that is fed back as the speed651

PRINCIPLES OF NAVAL ENGINEERINGerror signaL This signal produces a rapid responsefrom the system when the engineeringplant is in the maneuvering mode. Under normalmode of plant operation the speed feedback signalis not utilized.The signals for astern throttle movement arehandled in the same manner but all of the polaritiesare reversed.In the near future we may see a substantialincrease in the automation of naval propulsionmachinery and auxiliary machinery. At the presenttime, it is entirely possible to design acompletely automated ship. Although completeautomation is an unlikely goal for the naval ship,three is little doubt that automation will increaseto some extent within the next few years.FUEL CONVERSION PROGRAMAs of this writing, the Department of Defensehas authorized the Navy to shift to an all distillatemarine diesel type fuel which will replacethe Navy Special Fuel Oil (NSFO) now in use.The shift will take place on a gradual basis overa three year period. This conversion will easethe principal adverse factors associated with theuse of Navy Special Fuel Oil such as:1. Fouling of firesides of boilers by permissibleimpurities in Navy Special Fuel Oil, principallysulphur, ash, and carbon residue.2. Decrease in ship readiness associatedprincipally with cleaning of firesides.3. High corrosion rate of above-deck equipmentassociated with exposure to products ofcombustion of Navy Special Fuel Oil.4. Substantially below average retention rateof Navy enlisted personnel who perform boilercleaning operations.Testing planned completion date 1975, ispresently taking place with diesel engines andgas turbine propulsion plants; the results of thesetests are to be evaluated for the "Single- Fuel"Navy concept, which will permit the Navy tooperate either steam diesel, or gas turbinedriven propulsion plants with one and the sametype fuel.GENERAL TRENDSIn conclusion, it may be of interest to notesome general trends in naval engineering and tohazard a few predictions concerning possiblefuture developments.we may expect continuing refinementFirst,and improvement of the machinery and equipmentnow in use. The steam turbine, the diesel engine,the gas turbine, thenuclear propulsion plant— allare capable of further development and perhapsincreased efficiency. We may reasonably lookfornew designs in boilers, turbines, reducing gears,bearings, propellers, condensers and other heatexchangers, and a wide variety of auxiliary machinery.Some improvements may be aimed atreducing mechanical losses, others at increasingthe utilization of power developed by the primemover, others at reducing noise levels, and stillothers at minimizing maintenance requirements.We may look forward to the introduction ofnew engineering materials-metals and alloys,plastics, ceramics, lubricants, and others. Wemay watch for— though not necessarily count on—a materials breakthrough that would raise theupper temperature limits of our present machinery.If it is not possible to devise new materialsto withstand ultra-high temperatures, wemay perhaps lookfor new designs that will enableus to utilize higher temperatures with some ofour present materials. We may also expect newand improved techniques for welding or otherwisejoining metals, new methods of metal formingand shaping, new methods of treating metalsto obtain desired properties, and new proceduresfor the nondestructive testing of engineering materials.In the more distant future, perhaps, we mightlook for some entirely new concepts of ship propulsion.In particular, we might expect to seeship and machinery designs tending toward theultimate goal of integrating the prime mover, thepropulsive device, the steering device, and thehull form into one coordinated unit. Designers ofships and propulsion machinery have long lookedwith envy at the fully integrated propulsion systemsof many fish, and a good deal of work hasbeen done in analyzing fish propulsion with a viewto picking up some usable ideas. One approachthat has been suggested is to effect undulation ofa flexible hull by pumping water in a sinusoidalpath through a series of compartments. Stillanother approach utilizes a series of undulatingplates. Although no type of simulated fish propulsionis even close to being operational at present,these approaches should not be dismissedas frivolous or trivial. A great deal has alreadybeen learned through biological and simulationstudies of fish propulsion.Altogether, we may expect the future to bringat least a few surprises, a few practical results652

Chapter 25. -NEW DEVELOPMENTS IN NAVAL ENGINEERINGfrom ideas which at the moment might be classi- in the field of naval engineering, and some offled as exotic if not downright ludicrous. There these ideas will doubtless find application in theis at present a great proliferation of new ideas propulsion plants of the future.653

INDEXA-c generators, 505-507Accessories and controls R-12, 479-482Adiabatic state changes, 178Air ejector assemblies, 352Alpha survey meters, 76Alternating- current theory, 503Anchor windlass, 503-532Area meters, 145Auxiliary machinery and equipment, 361Auxiliary steam turbines, 422-436safety devices, 434-436safety devices-testing, 436speed control devices, 428-434turbines-auxiliarylubrication, 424-428types of, 422-424Boiler components-Continuedfuel oil burners, 241-243furnaces and refractories, 243generating and circulating tubes, 236saddles and supports, 244superheaters, 237-239Boiler controls, 307-318Boiler fittings and controls, 276-318controls, 307-318external fittings and connections, 281-307internal fittings, 276-281Boiler maintenance, 274Boiler water requirements, 261-265Bourdon-tube elastic elements, 138-141Bridge console, 644Butterfly valves, 375Back-pressure trips, 435Ballasting systems, 225Basic mechanical units, 121-124Bearings, 93-98main line shaft, 96main thrust, 96stern tube and strut, 96-98Bellows elastic elements, 141Bernoulli's theorem, 395Beta and gamma meters, 75Bimetallic expansion thermometer, 132Bimetallic steam traps, 370Biological decontamination, 79Blower lubrication, 417Blower speed, control of, 418Boiler casualty control, 271-274Boiler components, 235-245airheaters, 244castings, uptakes, and smoke pipes, 244desuperheaters, 239drums and headers, 235economizers, 239fittings, instruments, and controls, 244Capstan, 530Carnat principle, 182Carrier catapults, 532-539Centrifugal pumps, 407-410Centrifugal purifiers, 116-118Centrifugal tachometers, 147Check valves, 375Chemical decontamination, 80Chronometric tachometers, 148Components and accessories-turbines, 328-333bearings, 329blades, 329castings, 328dummy pistons and cylinders, 331flexible couplings, 332foundation, 328gland sealing systems, 330lubricating systems, 333nozzles, 328nozzle diaphragms, 329reduction gears, 332rotars, 329shaft glands, 330654

INDEXComponents and accessories-Continuedturning gears, 333Compressed air plants, 437-449air compressor maintenance, 449compressor classifications, 437-441reciprocating air compressors, 441-446rotary-centrifugal air compressors, 446-449safety precautions, 449Compressed air systems, 226Compressor classifications, 437-441Compressor components, 442-446Compressor R-12, 478Condensate and feed systems, 213-219Condenser-R-12, 478Condensers and other heat exchangers, 348-360air ejector assemblies, 352deaerating feed tank, 354-356gland exhaust condenser, 353main condenser, 348-352maintenance, 360safety and casualty control, 356-360vent condenser, 354Constant-pressure pump governors, 431-434Control rods, 621Controllable pitch propeller, 90Controlled circulation boilers, 256Conventional steam turbine propulsion plant, 191Coulomb's law of charges, 493Damage control central, 62Damage- investigations of, 64Data scanner system, 647-649Deaerating feed tank, 354-356Degaussing installations, 518Detailed contamination, 79Development of Naval ships, 3-14Naval surface ships- modern, 7-12steam machinery, 3-7submarines, 12-14Diaphragm elastic elements, 142Diesel and gasoline engines, 543clutches, reverse gears, and reduction gears,582-593maintenance, 593reciprocating engines, 543-577transmission of engine power, 577-582Diesel oil and JP-5 systems, 225Direct-current circuits, 495-500Direct-current generators, 500-502Direct-current motors, 502Distillate fuel systems, 225Distilling plants, 450-470definitions of terms, 451Distilling plants-Continuedoperation of, 469principles of distillation, 450types of distilling units, 451-468Dosimeters, 76Double-furnace boilers, 248-251Drainage systems, 228Drive mechanisma, tjrpes of, 579-582Elastic elements, 138-143Electrical systems steering gear, 525Electrohydraulic steering gear, 522-528Electrohydraulic transmission, 520Electromechanical steering gear, 521Electron theory, 492Elevators-electrohydraulic, 528Emergency steering systems, 523Engine room console, 640-643Engineering piping systems, 195-229ballasting systems, 225compressed air systems, 226condensate and feed systems, 213-219diesel oil and JP-5 systems, 225distillate fuel system, 225drainage systems, 228exhaust systems-auxiliary, 211-213firemain systems, 226flushing systems, 228fuel oil systems, 221-225gland seal and gland exhaust systems, 213hydraulic systems, 229main lubricating oil systems, 225main steam systems, 205potable water systems, 228sprinkling systems, 228steam and fresh water drains, 219-221steam excape piping, 213steam systems-auxiliary, 206-211washdown systems, 228Engineering theory-basic, 83Evaporator-R-12, 475Exhaust systems-auxiliary, 211-213Expansion thermometers, 128-135External fittings and connectors-boilers,281-307blow valves, 297drains and vents, 283-288feed stop and check valves, 288oil drip detector periscopes, 304pressure and temperature gages, 305safety valves, 290-295sampling connections, 288single-element feed water regulators,305-307655

PRINCIPLES OF NAVAL ENGINEERINGExternal fittings and connectors- Continuedsmoke indicators, 304soot blowers, 295-297steam stop valves, 288-290superheater steam flow indicators, 300-303superheater temperature alarms, 303water gage glasses, 297-300Filled-system thermometer, 132-134Firemaln systems, 226Fireroom operations and efficiency, 267-270Fires-control of, 66-68Flooding-control of, 68-71Flushing systems, 228Force-pressure-area relationships, 391Forced draft blower operation, 419Friction clutches and gear assemblies, 583-588Friction head, 395Fuel cells, 635Fuel oil systems, 221-225Hull members- Continuedplating, 23stanchions, 25stem and bow structure, 20-21stern structure, 22upper deck and superstructure, 25Hydraulic clutches or couplers, 588-593Hydraulic telemotor system, 526Hydraulic systems, 229Impulse steam traps, 368-370Internal fittings-boilers, 276-281Isenthalpic state changes, 178Isentropic state changes, 178Isobaric state changes, 177Isothermal state changes, 178Jet pumps, 411Joe's double clutch reverse gear, 585-588Gamma meters, 75Gas turbines, 595-613basic principles, 595-597components, functions of, 597-611gas turbine and jet propulsion, 611-613transmission of engine power, 611Gate valves, 373Geometry of the ship, 29-33body plan, 31half-breadth plan, 32sheer plan, 32Gland exhaust condenser, 353Gland seal and gland exhaust systems, 213Globe valves, 372Gross decontamination, 79Gyrocompasses, 518Head meters, 145Header-type boilers, 245-248Heating and ventilation, 490Horizontal weight shift, 45-49Hull members, 18-26bilge keels, 24bulkheads, 25decks, 24double bottom, 20framing, 18-20keel, 18Langmuir theory, 113Liquid-column elements, 138Liquid-in-glass thermometers, 128-132Longitudinal bending and stresses, 17Longitudinal stability and effects of trim, 56-59calculation of change of trim, 58center of flotation, 56change of trim, 56effects of trim on transverse stability, 58flooding effects diagram, 58longitudinal stability, 57longitudinal weight addition, 58moment to change trim one inch, 57Lubricants, 114Lubrication-theory of, 112-118fluid lubrication, 112-115friction, 112lubricating oil, care of, 115-118Machinery arrangement and plant layout, 193-229engineering piping systems, 195-229methods of propulsion plant operation, 229propulsion machinery-arrangement of, 193-195Magnetohydrodynamic generators, 637Main condenser, 348-352656

INDEXMain line shaft bearing, 96Mail lubricating oil system, 225Main steam systems, 205Main thrust bearing, 96Material conditions of readiness, 63Measurement-principles of, 119-156concept of, 119fluid now, 143-146instrument accuracy, 155liquid level, 146Navy calibration program, 151-155pressure, 135-143rotational speed, 147-150specific gravity, 150systems units and standards of measurement,120-127temperature, 127-135viscosity, 150Mechanical cooling, 487-490chilled water circulating systems, 488-490refrigerant circulating systems, 487self-contained air conditioners, 490Mechanical energy, 158-161Mechanical steam traps, 367Mixed-flow pumps, 411Moderators, 621Modern Naval surface ships-development of, 7-12Navy calibration program, 151-155NBC attack-defenses against, 74-81NBC contamination-detection of, 75NBC decontamination, 77-81Needle valves, 375Neutron reactions, 620New developments in Naval engineering, 628-653central operations system 639-652combined power plants, 638direct energy conversion, 634-638fuel conversion program, 652general trends, 652hull forms, 628-631propulsion and steering, 631Nuclear energy source, 618-620Nuclear power plants, 614-627advantages of nuclear power, 614naval nuclear power plant, 626nuclear fundamentals, 614-622nuclear power-problems of, 627nuclear reactors, 622-625principles of reactor control, 625Nuclear reactors, 622-625OHM'S law, 496-500Orifice-type steam traps, 370Other auxiliary equipment, 520-539anchor windlass, 530-532capstans, 530carrier catapults, 532-539electrohydraulic elevators, 528electrohydraulic transmission, 520operation, maintenance, and safety, 539steering gears, 521-528winches, 528Overall ship survival measures, 64Overspeed trips, 435Pipe fittings, 366-386expansion joints, 366flanges, 366flareless fluid connection, 366steam traps, 366-370unions, 366Piping, fittings, and valves, 363-390design considerations, 363identification of, 387packing gaskets and insulation, 388pipe and tubing, 364-366 (366)safety, 389Piston valves, 375Plug valves, 374Positive-displacement meters, 144Potable water systems, 228Power distribution system, 509-516Pressure head, 392-395Pressurized-furnace boilers, 257-261Preventive and corrective damage control, 61-82corrective measures, 64damage control organization, 62damage control precautions, 82investigations of damage, 64material conditions of readiness, 63practical damage control, 65-74resist damage-preparations to, 61Principles of air conditioningair motion, 486humidity, 483-485sensation of cooling, 487temperature, 485Properties of A-C circuits, 504Propeller pumps, 410Propellers, 88-93blade angle, 89blade velocity, 89controllable pitch propellers, 90problems, 91-93657

PRINCIPLES OF NAVAL ENGINEERINGPropellers-continuedsize, 90thrust deduction, 90Propulsion boilers, 230-275boiler casualty control, 271-274boiler water requirements, 261-265classification, 232-235combustion requirements, 265-267components, 235-245definitions, 230-232fireroom efficiency, 269fireroom operations, 267-269maintenance, 274types of, 245-261Propulsion machinery arrangement, 193-195Propulsion plants, other types, 541Propulsion steam turbines, 319-347components and accessories, 328-333nozzles, 319-321steam turbine propulsion plant, 333-347turbine classification, 324-327turbine design-basic principles, 321-324Propulsive power-development and transmission,85-103bearings, 93-98flexible couplings, 100-103power requirements, 87propellers, 88-93propulsion shafting, 98reduction gears, 99Pump capacity, 392Pumps and forced draft blowers, 391-421forced draft blowers, 414-421pumps, 391-414centrifugal, 407-410jet, 411mixed-flow, 411propeller, 410reciprocating, 396-400rotary, 403-407variable stroke, 400-403Radiation and optical pyrometers, 134Radioactivity, 616-618Radiological decontamination, 79Reactor control, principles of, 625Reactor coolants, 621Reactor fuels, 621Reactor principles, 620Receiver-R-12, 479Reciprocating air compressors, 441-446Reciprocating engines, 543-577basic principles, 543Reciprocating engines-Continuedcombustion cycles, 548-554combustion gases on pistons, 554components, 555-577mechanical cycles, 544-548Reciprocating pumps, 396-400Reducing valves, 377Reduction gears, shafting and bearings-care of,103-109Reflectors, 622Refrigeration and air conditioning plants, 471-491air conditioning, 482-491refrigeration, 471-482safety precautions, 491Relief valves, 377Remote control systems for steering gears, 524Remote operating gear-valves, 384-386Repair parties, 62Resistance thermometers, 134Resonance tachometers, 148Rotary-centrifugal air compressors, 446-449Rotary pumps, 403-407R-12 plant, 473-482Sensors, 644-647Sentinel valves, 377Settling tanks, 118Ship design and construction, 15-33basic design considerations, 15basic ship structure, 17-26geometry of the ship, 29-33ship compartmentation, 26-29ship flotation, 16Ship propulsion and steering-fundamentals of,85-111care of reduction gears, shafting and bearrings,103-109propulsive power, development and transmissionof, 85-103resistance, 85safety precautions, 109-111steering. 111Shipboard electrical systems, 492-519A-C generators, 505-507alternating current theory, 503basic theory, 492degaussing installations, 518direct-current circuits, 495-500direct-current generators, 500-502direct-current motors, 502gyrocompasses, 518power distribution system, 509-516658

INDEXShipboard electrical systems-Continuedproperties of A-C circuits, 504safety precautions, 518synchros and servomechanisms, 516-518transformers, 507-509Single-furnace boilers, 251-255Speed-limiting governors, 434Sprinkling systems, 228Stability and bouyancy, 34-60inclining movements, 36influence of metacentric height, 38metacenter (M), 37metacentric height (GM), 38principles of stability, 34-39Stability curves, 39-42cross curves, 41effects of draft on righting arm, 39-41Stability-principles of, 34-39displacement, 34impaired stability-causes of, 59inclining experiment, 42-44KB versus draft, 35longitudinal stability and effects of trim, 56-59loose water effects of, 52-56reverse bouyancy, 36stability curves, 39-42weight shift-effects of, 44-49weight changes-effects of, 49-52Standards of measurements, 124-127Static electricity, 492-495Steam and fresh water drains, 219-221Steam distilling units, 456-468flash-type, 460-463submerged tube, 456-460vertical basket, 463-468Steam escape piping, 213Steam machinery-development of, 3-7Steam systems-auxiliary, 206-211Stern tube and strut bearing, 96-98Steam turbine propulsion plant, 333-347Stop-check valves, 376Strainers and filters, 371Stroboscopic tachometers, 149Structural damage-repair of, 71-73Submarines-development of, 12-14Synchros and servomechanisms, 516-518Thermal energy, 161-171heat, 161Thermal energy-Continuedheat transfer, 162-167heat transfer appratus, 169-171internal energy, 161sensible heat and latent heat, 167-169units of measurement, 162Thermionic converters, 636Thermocouple pyrometers, 134Thermodynamics-introduction to, 157-190carnot principle, 182cycles, 178energy, 157-171energy balance, 190energy relationship in the shipboard propulsioncycle, 188-190entropy-concept of, 181first law of, 171-173processes, 173-178second law of, 180reversibility-concept of, 179systems, 173working substances, 183-188Thermodynamics processes, 173-178flow-type of, 175-177state change-type of, 177Thermoelectric converters, 636Thermostatic recirculating valves, 384Thermostatic steam traps, 367Throttle control, 649-652Top-fired boilers, 256Transformers, 507-509Twin-disk clutch and gear mechanism, 584Unloading valves, 384Valve manifolds, 384Vapor compression distilling units,Variable stroke pumps, 400-403Velocity head, 395Vent condenser, 354Vital services-restoration of, 73Washdown. systems, 228Wheatstone bridge, 500Winches, 528Wirerope system, 526451-456659iX U.S. GOVERNMENT PRINTING OFFICE : 1979 O—299-962

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