The function of pressure reducing valve is to maintain constant pressure on its delivery side of the valve irrespective of fluctuating demand of steam. This is achieved by throttling of steam passing through the pressure reducing valve. It is generally used in low capacity boilers where it is difficult to maintain constant delivery pressure with fluctuating demand of steam. In such boilers, steam is generated at higher pressure than required by prime movers. The constructional details are shown in Figure 4.29. From boiler, high pressure steam enters the steam inlet flange via throttle valve A to steam outlet flange. The throttling is done by a spring and valve rod mechanism. When the steam passes through the throttle valve, its pressure reduces. The force exerted by spring can be adjusted by a screw F. This varies the opening of the throttle valve so that any exit pressure required can be manipulated.
Figure 4.29 Pressure Reducing Valve
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