Principles of naval engineering - Historic Naval Ships Association

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.