PRINCIPLES OF NA7AL ENGINEERING 



CONTROL 

 PILOT 



38.125 

 Figure 14-26.— Arrangement of control pilot and 

 diaphragm control valve for supplying reduced 

 pressure steam. 



UNLOADING VALVES.- An automatic un- 

 loading valve (also called a dumping valve) is in- 

 stalled at each main and auxiliary condenser. 

 The function of the unloading valves is to dis- 

 charge steam from the auxiliary exhaust line to 

 the condensers whenever the auxiliary exhaust 

 line pressure exceeds the design operating pres- 

 sure. 



An automatic unloading valve is shown in 

 figure 14-27. Auxiliary exhaust steam is led 

 through valve A to the top of the actuating valve 

 diaphragm. The actuating valve is double seated, 

 and one side is open when the other is closed. 

 When the auxiliary exhaust line pressure is less 

 than the pressure for which the unloading valve 

 is set, the upper seat is closed and the lower seat 

 is open. The valve is thus held by the diaphragm 

 spring. Steam passes into the line through valve 

 B and goes under the unloading valve diaphragm. 

 The pressure acting on this diaphragm holds the 

 unloading valve up and closed. If the auxiliary ex- 

 haust pressure exceeds the pressure of the ac- 

 tuating valve diaphragm spring, the diaphragm 

 is forced downward and the lower seat closes 

 while the upper seat opens. This makes a direct 

 connection between the top and the bottom of the 

 unloading valve diaphragm through the actuating 

 valve. The equalized pressure on the diaphragm 

 allows the auxiliary exhaust pressure to force the 

 unloading valve down and steam is thus unloaded 



to the condenser. The unloading pressure can be 

 adjusted by turning an adjusting screw, thereby 

 changing the force exerted on the actuating valve 

 diaphragm. 



Thermostatic Recirculating Valves 



Thermostatic recirculating valves are used 

 in systems where it is necessary to recirculate 

 a fluid in order to maintain the temperature with- 

 in certain limits. Thermostatic recirculating 

 valves are designed to operate automatically. 



The thermostatic recirculating valve shown 

 in figure 14-28 is used to recirculate condensate 

 from the discharge side of the main air ejector 

 condenser to the main condenser. 5 The valve is 

 actuated by the temperature of the condensate. 

 When the condensate temperature becomes 

 higher than the temperature for which the valve 

 is set, the thermostatic bellows expands and au- 

 tomatically opens the valve, allowing condensate 

 to be sent back to the condenser. 



Valve Manifolds 



A valve manifold is used when it is necessary 

 to take suction from one of several sources and 

 to discharge to another unit or several units of 

 the same or a separate group. One example of a 

 manifold is shown in figure 14-29. This mani- 

 fold is used in the fuel oil filling and transfer 

 system, where provision must be made for the 

 transfer of oil from any tank to any other tank, to 

 the fuel oil service system, or to another ship. 

 The manifold valves are frequently of the stop- 

 check type. 



Remote Operating Gear 



Remote operating gear is installed to provide 

 a means of operating certain valves from distant 

 stations. Remote operating gear may be mechan- 

 ical, hydraulic, pneumatic, or electric. 



Some remote operating gear for valves is 

 used in the normal operation of the valves. For 

 example, the propulsion turbine throttle valves 

 are opened and closed by a series of reach rods 

 and gears. In the fireroom, remote operating 

 gear is used to operate the forced draft blowers, 

 to adjust the constant-pressure pump governor 

 on the fuel oil service pump, and to lift safety 

 valves by hand. 



^Air ejector assemblies are discussed in chapter 13 

 of this text. 



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