Chapter 15. -PUMPS AND FORCED DRAFT BLOWERS 



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PISTON 



LIVE STEAM 

 SPACE 



STEAM PORT 

 FOR PILOT 

 VALVE 



STEAM PILOT 

 VALVE 



PILOT VALVE 

 OPERATING ROD 



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Figure 15-8.— Piston-type valve gear for steamendof reciprocating pump. 



the power or steam end. The piston in the liquid 

 end is often called a plunger . A valve chest, 

 sometimes called a water chest, is attached to 

 the liquid cylinder. The valve chest contains two 

 sets of suction and discharge valves, one set to 

 serve the upper endof the liquid cylinder and one 

 to serve the lower end. The valves are so ar- 

 ranged that the pump takes suction from the suc- 

 tion chamber and discharges through the dis- 

 charge chamber on both the up and down strokes. 



An adjustable relief valve is fitted to the dis- 

 charge chamber to protect the pump and the pip- 

 ing against excessive pressure. 



Some reciprocating pumps have an air cham- 

 ber and a snifter valve installed in the liquid end. 

 The upper part of the air chamber contains air; 



the lower part contains liquid. On each stroke, the 

 air in the chamber is compressed by the pressure 

 exerted by the plunger. When the plunger stops 

 at the end of a stroke, the air in the chamber ex- 

 pands and allows a gradual, rather than a sudden, 

 drop in the discharge pressure. The air chamber, 

 therefore, smooths out the discharge flow, ab- 

 sorbs shock, and prevents pounding. The snifter 

 valve, if installed, allows a small quantity of air 

 to be drawn in and compressed with each stroke. 

 If no snifter valve is installed, some provision 

 may be made for charging the air chamber with 

 compressed air. 



Although reciprocating pumps were once 

 widely used aboardshipfor a variety of services, 

 their use on combatant ships is now generally 



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