Operation Principle of Pressure Reducing Valve
These are used to limit the pressure in part of the circuit to a value lower than that required in the rest of the circuit. The pressure reducing valve is a normally open valve which throttles or closes to maintain constant pressure in the regulated line. Direct-acting pressure reducing valves are available for low flow rates up to about 45 l/m and pressures up lo 210 bar; they can be supplied with or without a reverse-flow check valve. Pressure-reducing valves may be:
(a) Non-relieving, i.e. they do not limit any pressure increase downstream of the valve set up by an external force.
(b) Non-relieving, i.e. they do not limit any pressure increase downstream of the valve set up by an external force.
Figure 1 shows a direct-acting pressure-reducing valve. The valve is biassed open by the spring. Pressure is sensed at the outlet port and fed to the end of the spring-loaded spool. As pressure in the secondary circuit rises, the valve tends to close against the spring pressure. Flow through the small bleed hole in the spool to the spring chamber and drain prevents the valve closing completely, thus averting a pressure build up in the downstream circuit.
Figure 1. Direct-acting pressure-reducing valve.
Pilot-operated (two-stage) pressure-reducing valves are used for higher flow rates and in general give better regulation of pressure with flow.
The action of pressure-reducing valves always generates heat energy because of the throttling effect. This heat generation must be taken into account when considering their application. Where two separate pressures are continuously required in a circuit, a two-pump system may prove a better solution than one using pressure-reducing valves. This will depend upon the flow and pressures required.