There are various designs and types ofpressure-reducing valves. The spring-loadedreducer and the pilot-controlled valve arediscussed in this text.Spring-Loaded ReducerThe spring-loaded pressure-reducing valve(fig. 6-18) is commonly used in pneumaticsystems. It is often referred to as a pressureregulator.The valve simply uses spring pressure againsta diaphragm to open the valve. On the bottomof the diaphragm, the outlet pressure (the pressurein the reduced-pressure system) of the valve forcesthe diaphragm upward to shut the valve. Whenthe outlet pressure drops below the set point ofthe valve, the spring pressure overcomes the outletpressure and forces the valve stem downward,opening the valve. As the outlet pressure increases,approaching the desired value, the pressureunder the diaphragm begins to overcome springpressure, forcing the valve stem upwards, shuttingthe valve. You can adjust the downstreampressure by turning the adjusting screw, whichvaries the spring pressure against the diaphragm.This particular spring-loaded valve will fail in theopen position if a diaphragm rupture occurs.Pilot-Controlled Pressure-Reducing ValveFigure 6-19 illustrates the operation of apilot-controlled pressure-reducing valve. Thisvalve consists of an adjustable pilot valve, whichcontrols the operating pressure of the valve, anda spool valve, which reacts to the action of thepilot valve.The pilot valve consists of a poppet (1), aspring (2), and an adjusting screw (3). The valveFigure 6-19.—Pilot-controlled pressure-reducing valve.6-13
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