Chapter 16. -AUXILIARY STEAM TURBINES 



arrangement which prevents excessive opening 

 or closing of the controlling valve. An interme- 

 diate diaphragm bears against an intermediate 

 mushroom which, in turn, bears against the top 

 of the lower crosshead. Steam is led from the 

 governor outlet to the bottom of the lower dia- 

 phragm and also, through a needle valve, to the 

 top of the intermediate diaphragm. A steam 

 chamber is provided to assure a continuous sup- 

 ply of steam at the required pressure to the top 

 of the intermediate diaphragm. 



Any movement of the crosshead assembly, 

 either up or down, is thus opposed by the force 

 of the steam pressure acting either on the inter- 

 mediate diaphragm or on the lower diaphragm. 

 The whole arrangement serves to prevent 

 extreme reactions of the controlling valve in re- 

 sponse to variations in pump discharge pressure. 



Limiting the movement of the controlling 

 valve in the manner just described reduces the 

 amount of hunting the governor must do to find 

 each new position. Under constant- load condi- 

 tions, the controlling valve takes a position which 



causes the main valve to remain open by the re- 

 quired amount. A change in load conditions re- 

 sults in momentary hunting by the governor until 

 it finds the new position required to maintain 

 pump discharge pressure at the new condition of 

 load. 



An automatic shutdown device has recently 

 been developed for use on main feedpumps. The 

 purpose of the device is to shut down the main 

 feed pump and so protect it from damage in the 

 event of loss of feed booster pump pressure. The 

 shutdown device consists of an auxiliary pilot 

 valve and a constant-pressure pump governor, 

 arranged as shown in figure 16-11. The governor 

 is the same as the constant-pressure pump gov- 

 ernor just described except that it has a special 

 top cap. In the regular governor, the steam for 

 the operating piston is supplied to the controlling 

 valve through a port in the governor valve body. 

 In the automatic shutdown device, the steam for 

 the operating piston is supplied to the controlling 

 valve through the auxiliary pilot valve. The aux- 

 iliary pilot valve is actuated by the feed booster 



AUXILIARY PILOT 

 VALVE 



GOVERNOR 

 (WITH SPECIAL TOP CAP) 



ACTUATING LINE 



FROM DISCHARGE SIDE 



OF MAIN FEED PUMP 



ACTUATING LINE 

 FROM DISCHARGE SIDE 

 OF FEED BOOSTER PUMP 



affi 



jT-n rrr\ 



t 



^ 



e 



STEAM INLET 



\ 



TO MAIN FEED 



PUMP 



TURBINE 



38.91 



Figure 16-11.— Automatic shutdown device for main feed pump. 



433 



