Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NA7AL ENGINEERINGCONTROLPILOTto the condenser. The unloading pressure can beadjusted by turning an adjusting screw, therebychanging the force exerted on the actuating valvediaphragm.Thermostatic Recirculating Valves38.125Figure 14-26.—Arrangement of control pilot anddiaphragm control valve for supplying reducedpressure steam.UNLOADING VALVES.- An automaticunloadingvalve (also called a dumping valve) is installedat each main and auxiliary condenser.The function of the unloading valves is to dischargesteam from the auxiliary exhaust line tothe condensers whenever the auxiliary exhaustline pressure exceeds the design operating pressure.An automatic unloading valve is shown infigure 14-27. Auxiliary exhaust steam is ledthrough valve A to the top of the actuating valvediaphragm. The actuating valve is double seated,and one side is open when the other is closed.When the auxiliary exhaust line pressure is lessthan the pressure for which the unloading valveis set, the upper seat is closed and the lower seatis open. The valve is thus held by the diaphragmspring. Steam passes into the line through valveB and goes under the unloading valve diaphragm.The pressure acting on this diaphragm holds theunloading valve up and closed. If the auxiliary exhaustpressure exceeds the pressure of the actuatingvalve diaphragm spring, the diaphragmis forced downward and the lower seat closeswhile the upper seat opens. This makes a directconnection between the top and the bottom of theunloading valve diaphragm through the actuatingvalve. The equalized pressure on the diaphragmallows the auxiliary exhaust pressure to force theunloading valve down and steam is thus unloadedThermostatic recirculating valves are usedin systems where it is necessary to recirculatea fluid in order to maintain the temperature withincertain limits. Thermostatic recirculatingvalves are designed to operate automatically.The thermostatic recirculating valve shownin figure 14-28 is used to recirculate condensatefrom the discharge side of the main air ejectorcondenser to the main condenser. 5 The valve isactuated by the temperature of the condensate.When the condensate temperature becomeshigher than the temperature for which the valveis set, the thermostatic bellows expands and automaticallyopens the valve, allowing condensateto be sent back to the condenser.Valve ManifoldsA valve manifold is used when it is necessaryto take suction from one of several sources andto discharge to another unit or several units ofthe same or a separate group. One example of amanifold is shown in figure 14-29. This manifoldis used in the fuel oil filling and transfersystem, where provision must be made for thetransfer of oil from any tank to any other tank, tothe fuel oil service system, or to another ship.The manifold valves are frequently of the stopchecktype.Remote Operating GearRemote operating gear is installed to providea means of operating certain valves from distantstations. Remote operating gear may be mechanical,hydraulic, pneumatic, or electric.Some remote operating gear for valves isused in the normal operation of the valves. Forexample, the propulsion turbine throttle valvesare opened and closed by a series of reach rodsand gears. In the fireroom, remote operatinggear is used to operate the forced draft blowers,to adjust the constant-pressure pump governoron the fuel oil service pump, and to lift safetyvalves by hand.^Air ejector assemblies are discussed in chapter 13of this text.384