Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUT 



the relationships between the auxiliary exhaust 

 system and the main and auxiliary steam 

 systems. 



STEAM ESCAPE PIPING 



Steam escape piping is installed to provide 

 an unobstructed passage for the escape of steam 

 from boiler safety valves and from the relief 

 valves installed on steam-driven auxiliaries. A 

 line is also provided from the auxiliary exhaust 

 system to the escape piping to allow the aux- 

 iliary exhaust to unload to atmosphere if the 

 pressure becomes excessively high. Steam es- 

 cape piping is usually shown on the same plans 

 or drawings as the ones that show the auxiliary 

 exhaust piping. 



GLAND SEAL AND GLAND 

 EXHAUST SYSTEMS 



Gland sealing steam is supplied to the shaft 

 glands^ of propulsion turbines and turbogen- 

 erator turbines to seal the shaft glands against 

 two kinds of leakage: (1) air leakage into the 

 turbine casings, and (2) steam leakage out of 

 the turbine casings. These two kinds of leakage 

 may seem contradictory; however, each kind 

 of leakage could occur under some operating 

 conditions if the shaft glands were not sealed. 



Pressures in the gland seal system are low, 

 ranging from about 3/4 psig to 2psig, depending 

 upon the conditions of operation. Gland exhaust 

 piping carries the steam and air from the tur- 

 bine shaft glands to the gland exhaust condenser, 

 where the steam is condensed and returned to 

 the condensate system. 



On most ships, gland sealing steam is sup- 

 plied from the auxiliary exhaust system, although 

 on some ships it is supplied from the 150-psi 

 auxiliary steam system. In either case, the 

 steam is supplied through reducing valves or 

 reducing stations. Figure 9-19 illustrates a 

 typical gland seal and gland exhaust system for 

 propulsion turbines on an older type of destroyer. 



CONDENSATE AND FEED SYSTEMS 



Condensate and feed systems include all the 

 piping that carries water from the condensers 



6shaft glands are devices for holding various kinds 

 of packing at the point where the shaft extends through 

 the turbine casing. Shaft glands and shaft gland pack- 

 ing are discussed in chapter 12 of this text. 



to the boilers and from the feed tanks to the 

 boilers. The condensate system includes the 

 main and auxiliary condensers, the condensate 

 pumps, and the piping. The boiler feed system 

 includes the feed booster pump, the main feed 

 pump, and the piping required to carry water 

 from the deaerating feed tank to the boilers. 

 Together, the condensate and feed systems 

 begin at the condenser and end at the economizer 

 of the boiler. 



It is a little hard to say whether the deae- 

 rating feed tank is part of the condensate system 

 or part of the boiler feed system, since the 

 tank is generally taken as the dividing line be- 

 tween the two systems. The water is called 

 condensate between the condenser and the 

 deaerating feed tank. It is called feed water or 

 boiler feed between the deaerating feed tank 

 and the economizer of the boiler. Since the 

 condensate and feed systems actually form 

 one continuous system, the terms feed system 

 and feed water system are quite commonly 

 used to include both the condensate system 

 and the boiler feed system. 



Four main types of feed systems have been 

 used on naval ships: (1) the open feed system, 

 (2) the semiclosed feed system, (3) the vacuum- 

 closed system, and (4) the pressure-closed sys- 

 tem. The development of these systems, in the 

 sequence listed, has gone along with the deve- 

 lopment of boilers. As boilers have been de- 

 signed for higher operating pressures and 

 temperatures, the removal of dissolved oxygen 

 from the feed water has become increasingly 

 inportant, since the higher pressures and tem- 

 peratures accelerate the corrosive effects of 

 dissolved oxygen. Each new type of feed system 

 represents an improvement over the one before 

 in reducing the amount of oxygen dissolved or 

 suspended in the feed water. 



Since practically all modern naval ships 

 have pressure- closed feed systems, this is 

 the only type discussed here. Pressure- closed 

 systems are used on all naval ships having 

 boilers operating at 600-psi and above; they 

 are also used on some ships that have lower 

 boiler operating pressures. 



In a pressure- closed system, all condensate 

 and feed lines throughout the system (except 

 for the very short line between the condenser 

 and the suction side of the condensate pump) 

 are under positive pressure. The system is 

 closed to prevent the entrance of air. A pres- 

 sure-closed system is shown in figure 9-20. 



213 



