Chapter 14. -PIPING, FITTINGS, AND VALVES 



VALVE SPRING 



VALVE GUIDE 

 VALVE DISK 



GLYCERINE SEAL 

 FILLING PLUG 



COOLING 

 FINS 



BLEEDER VALVE CHECK VALVE 



AIR GAUGE AND PUMP CONNECTION 



HERE 



11.323 



Figure 14-22.— Pneumatic pressure controlled 



reducing valve for high temperature service. 



loading chamber is surrounded by a finned hood 

 which conducts heat away to atmosphere. 



A rubber diaphragm is installed in the middle 

 of the dome. The bottom of the diaphragm is 

 separated from the bottom half of the dome by a 

 fixed steel plate. The area immediately above the 

 diaphragm communicates with the upper part of 

 the dome through holes in the shrouding. The up- 

 per half of the dome carries a level of water for 

 sealing; the lower half of the dome carries a 

 level of glycerine for sealing. The area above 

 the glycerine is charged with air, which exerts 

 a downward pressure on the glycerine and forces 

 some of it to go up the tube toward the diaphragm. 

 This pressure causes the diaphragm to move up- 

 ward; and, since the stem of the valve is in con- 

 tact with the diaphragm, the upward movement 

 of the diaphragm causes the valve to open. When 

 the valve is open, steam can pass through it. 



From the outlet connection, an actuating line 

 leads back to the upper part of the dome, as 

 shown in the illustration. Steam at the reduced 

 pressure is thus allowed to exert a force on the 

 top of the water seal; this force is transmitted 



through the water and tends to move the dia- 

 phragm downward. When the pressure of the 

 steam from the actuating line exceeds the loading 

 air pressure in the lower half of the dome, the 

 diaphragm moves downward sufficiently to close 

 the valve. The closing of the valve reduces the 

 pressure of the steam on the discharge side of 

 the valve. When the pressure on the outlet side 

 of the valve is equal to the air pressure in the 

 lower half of the dome, the valve takes a balanced 

 position which allows the passage of sufficient 

 steam to maintain that pressure. 



If the load increases, tending to take more 

 steam away from the valve, the outlet pressure 

 will be momentarily reduced. Thus, the pressure 

 of steam on top of the diaphragm becomes less 

 than the pressureof air below the diaphragm, and 

 the valve then opens wider to restore the pres- 

 sure tonormal.If the load is reduced, this causes 

 a momentary increase in outlet pressure; and 

 this in turn increases the pressure on top of the 

 diaphragm, making it greater than the air pres- 

 sure below the diaphragm. The diaphragm is 

 therefore displaced downward, and the outlet 

 pressure is again restored to normal. 



DIAPHRAGM CONTROL VALVES WITH AIR- 

 OPERATED CONTROL PILOTS.-Diaphragm 

 control valves with air-operated control pilots 

 are being used increasingly on newer ships for 

 various pressure- control applications. These 

 valves and pilots are available in several basic 

 designs to meet different requirements. They 

 may be used to reduce pressure, to augment 

 pressure, or to provide continuous regulation of 

 pressure, depending upon the requirements of the 

 system in which they are installed. Valves and 

 pilots of very similar design can also be used for 

 other services such as liquid level control and 

 temperature control. However, the discussion 

 here is limited to the valves and pilots that are 

 used for pressure- control applications. 



The air-operated control pilot may be either 

 direct acting or reverse acting. A direct-acting 

 air-operated control pilot is shown in figure 

 14-23. In this type of pilot, the controlled pres- 

 sure—that is, the pressure from the discharge 

 side of the diaphragm control valve— acts on top 

 of a diaphragm in the control pilot. This pres- 

 sure is balanced by the pressure exerted by the 

 pilot adjusting spring. If the controlled pressure 

 increases and overcomes the pressure exerted 

 by the pilot adjusting spring, the pilot valve stem 

 is forced down. This action causes the pilot valve 

 to open and so to increase the amount of operating 



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