PRINCIPLES OF NAVAL ENGINEERING 



But steam is used throughout the ship in a 

 good deal of machinery, equipment, and piping 

 which does not exhaust either to a condenser or 

 to the auxiliary exhaust system. Therefore, 

 steam and fresh water drain systems are pro- 

 vided so that water can be recovered and put 

 back 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 the 

 ship. The systems of piping which carry the wa- 

 ter to the feed systems, and also the water car- 

 ried in the systems, are known as drains. 



On ships built to Navy specifications, there 

 are four steam and fresh water drain systems 

 which recover feed water from machinery and 

 piping: (1) the high pressure steam drainage sys- 

 tem, (2) the service steam drainage system, (3) 

 the oil heating drainage system, and (4) the fresh 

 water drain collecting system. In addition, a 

 fifth system is provided for collecting contami- 

 nated drains which cannot be returned to the feed 

 system. These five systems are described in the 

 following paragraphs. 



The high pressure steam drainage system 

 generally includes drains from superheater 

 headers, throttle valves, main and auxiliary 

 steam lines, steam catapults (on carriers), and 

 other steam equipment or systems which operate 

 at pressures of 150 psi or above. On many ships, 

 the high pressure drains are led directly into 

 the deaerating feed tank. On some newer ships, 

 the high pressure drains go intothe auxiliary ex- 

 haust line just before the auxiliary exhaust steam 

 enters the deaerating feed tank. In either case, 

 of course, the high pressure drains end up in the 

 same place— that is, in the deaerating feedtank. 



The service steam drainage system collects 

 uncontaminated drains from low pressure (below 

 150 psi) steam piping systems and steam equip- 

 ment outside of the machinery spaces. Space 

 heaters and equipment used in the laundry, the 

 tailor shop, and the galley are typical sources of 

 drains for the service steam drainage system. 

 On some ships, these drains are discharged into 

 the most convenient fresh water drain collecting 

 tank. On other ships, particularly on large com- 

 batant ships such as carriers, the service steam 

 drains discharge to special service steam drain 

 collecting tanks located in the machinery spaces. 

 The contents of the service steam drain collec- 

 ting tanks are discharged to the condensate sys- 

 tem; in addition, each tank has gravity drain con- 

 nections to the fresh water drain collecting tank 



and to the bilge sump tank located in the same 

 space. 



Note that the service steam drainage system 

 collects only clean drains which are suitable for 

 use as boiler feed. Contaminated service steam 

 drains (such as those from laundry presses, for 

 example) are discharged overboard. 



The oil heating drainage system collects 

 drains from the steam side of fuel oil heaters, 

 fuel oil tank heating coils, lubricating oil heaters, 

 and other steam equipmentusedtoheat oil. Since 

 leakage in the heating equipment could cause oil 

 contamination of the drains, and so eventually 

 cause oil contamination of the boilers, these 

 drains are collected separately and are inspected 

 before being discharged to the feed system. 



The oil heating drains are collected in oil 

 heating drain mains and are then discharged to 

 inspection tanks. In ships that have separate en- 

 ginerooms and firerooms, there is one inspec- 

 tion tank in the fireroom and one in the engine- 

 room. On ships that have machinery rooms, 

 rather than firerooms and enginerooms, each 

 machinery room has one or more inspection 

 tanks for the oil heating drains. The inspection 

 tanks have small gage glasses or glass strips 

 along the side to permit inspection of the drains. 

 The inspection tanks normally discharge to the 

 deaerating feed tank, but they have connections 

 which allow the drains to be discharged to the 

 fresh water drain collecting tank. 



The fresh water drain collecting system, 

 often called low pressure drain system, collects 

 drains from various piping systems, machinery, 

 and equipment which operate at steam pressures 

 of less than 150 psi. As previously noted, both the 

 service steam drainage system and the oil 

 heating drainage system can discharge to the 

 fresh water drain collecting tank, although they 

 normally discharge more directly to the feed 

 system. In general, the fresh water drain collec- 

 ting system collects gravity drains (open-funnel 

 or sight-flow drains), turbine gland seal drains, 

 auxiliary exhaust drains, air ejector after con- 

 denser drains, and a variety of other low pres- 

 sure drains that result from the condensation of 

 steam during the warming up or operating of 

 steam machinery and piping. 



Fresh water drains are collected in fresh 

 water drain collecting tanks located in the ma- 

 chinery spaces. The contents of these tanks may 

 enter the feed system in two ways: they may be 

 drawn into the condenser by vacuum drag, or in 

 some installations they may be pumped to the 



220 



