Improvements relating to the hydraulic valves and of the hydraulic systems using these valves

摘要

1474686 Valves SPERRY RAND Ltd 3 May 1974 [4 May 1973] 21200/73 Heading F2V [Also in Division G3] A combined compensator and unloading valve for a hydraulic system comprises a hollow plunger 6 controlling by-pass flow between an inlet 4, connected to a pressure line fed by a pump 1, and an outlet 5 connected to reservoir. The end of the plunger in contact with the valve seat is of lesser diameter than the main port in order to provide differential pressure surfaces. In the opposite end of the plunger is a sleeve 7, of cross-sectional area equal to the valve differential area, within which slides a pin 8 one end of which abuts a light spring 14 bearing against the plunger. The other end is loaded by a spring 9. The interior of the plunger is connected, via orifices 13, passageway 12 and a valve 11, with a load pressure sensing line. In operation, when an open-centre control valve 2 is in the neutral position the load pressure sensing line is substantially at reservoir pressure and the plunger valve will open at a pressure set by the light spring 14, for example at 10 p.s.i. When the system is operating the pressure within the hollow plunger is controlled by the compression of the spring 9. At pressures above that set by the spring, for example 300 p.s.i., the valve will open to maintain this maximum. A pilot relief valve 15 may be provided to open when the load pressure exceeds a safe maximum, opening of this valve reducing pressure within the plunger so that the main valve opens to by-pass the pump to reservoir. Should system pressure fall below reservoir pressure, due to an over-running load, the valve 11 will be unseated, the load sensing line isolated, and the reduced pressure at the inlet 4 applied to the interior of the plunger to open it fully to allow fluid to flow from the reservoir to meet the demand.