PRINCIPLES OF NAVAL ENGINEERING 



soot blowers. On some recent ships (both 600- 

 psi and 1200-psi) the main steam system sup- 

 plies superheated steam to several other units 

 as well. For example, some carriers use su- 

 perheated steam to supply steam catapult sys- 

 tems; also, some carriers and other ships use 

 superheated steam to operate forced draft 

 blowers, main feed pumps, main circulating 

 pumps, and other auxiliaries. The soot blowers 

 are not supplied from the main steam system 

 on some ships that have 1200-psi main steam 

 systems; instead, steam for the soot blowers is 

 taken from the 1200-psi auxiliary steam system, 

 as discussed later in this chapter. 



Figure 9-12 illustrates the main steam sys- 

 tem for the forward plant (No. 1 fireroom and 

 No. 1 engineroom) of a steam-driven destroyer 

 escort. The after plant (No. 2 fireroom and No. 

 2 engineroom) main steam system is very sim- 

 ilar. 



There is one boiler in each fireroom. Each 

 boiler is provided with a boiler stop valve which 

 can be operated either locally from the fire- 

 room or remotely from the main deck. A sec- 

 ond line stop valve in each fireroom provides 

 two-valve protection for the boiler when it is 

 not in use, and permits effective isolation in 

 case of damage. This type of two-valve protec- 

 tion is standard for all boilers installed in U.S. 

 Navy ships. 



For ahead operation, the superheated steam 

 passes through a main steam strainer, a guard- 

 ing valve, and a throttle valve before entering 

 the high pressure turbine. From the high pres- 

 sure turbine, the steam passes through a cross- 

 over pipe to the low pressure turbine; then it 

 exhausts to the condenser. For astern opera- 

 tion, the superheated steam passes through the 

 steam strainer and through a stop valve; then 

 it goes to the steam chest of the astern element, 

 which is located at one end of the low pressure 

 turbine. 



The forward and after main steam systems 

 are connected by cross-connection piping be- 

 tween the forward engineroom and the after 

 fireroom. By means of this piping, either boiler 

 can be used with either or both propulsion units 

 and turbogenerators. Thus the two propulsion 

 plants can be operated either independently 

 (split-plant) or together (cross-connected). 



Note that superheated steam for the soot 

 blowers goes from the superheater outlet pip- 

 ing into a soot blower steam header. 4 Branches 

 go from the header to the individual soot blowers. 



A 600-psi main steam system is shown in 

 figure 9-13. This is the main steam system for 

 the two forward plants (No. 1 and No. 4) on a 

 heavy cruiser of the CA 139 class. Although this 

 drawing is more complicated, the system itself 

 is still basically simple. 



A 600-psi main steam system for destroyers 

 of the DD 445 and DD 692 classes is shown in 

 figure 9-14. A later modification was made on 

 these ships to provide a separate superheated 

 steam supply to the turbogenerators. With this 

 modification, this main steam system is typical 

 of most destroyers, even those that are consid- 

 erably more recent than the DD 445 and DD 692 

 classes. 



For comparison, figure 9-15 shows a 1200- 

 psi main steam system for the forward plant of 

 the frigates DLG 14 and DLG 15. Note that the 

 1200-psi main steam system does not supply 

 steam to the soot blowers but that it does supply 

 steam to the main feed pumps. In both of these 

 respects, the 1200-psi system differs from the 

 DD 445 and DD 692 main steam system described 

 above. 



AUXILIARY STEAM SYSTEMS 



Auxiliary steam systems supply steam at the 

 pressures and temperatures required for the op- 

 eration of many systems and units of machinery, 

 both inside and outside the engineering spaces. 

 Although auxiliary steam is often called "satu- 

 rated" steam, it has some degree of superheat 

 in some auxiliary steam systems. Constant and 

 intermittent service steam systems, steam 

 smothering systems, whistles and sirens, fuel 

 oil heaters, fuel oil tank heating coils, air ejec- 

 tors, forced draft blowers, and a wide variety of 

 pumps are typical of the systems and machinery 



Soot blowers are devices for removing soot from the 

 boiler firesides while the boiler is steaming. Soot 

 blowers are discussed in chapter 11 of this text. 



The term header is commonly used in engineeringto 

 describe any tube, chamber, drum, or similar piece to 

 which a series of tubes or pipes are connected in such 

 a way as to permit a flow of fluid from one tube (or 

 group of tubes) to another. In essence, a header is a 

 kind of manifold. In common usage, a distinction is 

 made 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 



