Principles of naval engineering - Historic Naval Ships Association

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