Spring-loaded reducing valve

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Special-purpose valves

Engineman 3 - Basic Engine Mechanics

Internal pilot-actuated pressure-reducing valve

SPRING-LOADED REDUCING VALVES.-One type of spring-loaded reduc-ing valve is shown in figure 13-27. These valves are used in a wide variety of appli-cations. Low-pressure air reducers, auxiliary machinery cooling-water reducing stations, and some reduced-steam system reducers are of this type. The valve simply uses spring pres-sure against a diaphragm to open the valve. On the bottom of the diaphragm, the out-let pressure (the pressure in the reduced-pressure system) of the valve forces the disk upward to shut the valve. When the out-let pressure drops below the set point of the valve, spring pressure overcomes the out-let pressure and forces the valve stem down-ward, opening the valve. As outlet pressure increases, approaching the desired value, the pressure under the diaphragm begins to overcome

Figure 13-27.-Pressure-reducing (spring-loaded) valve.

spring pressure. This forces the valve stem upward, shutting the valve. Downstream pressure can be adjusted by removing the valve cap and turning the adjusting screw, which varies the spring pressure against the diaphragm. This particular spring-loaded valve will fail in the open position in the case of a diaphragm rupture.