GB594140A - Improvements in or relating to valves - Google Patents

Abstract

594,140. Fluid-pressure servomotorcontrol systems. PUGH, C. A., BOOTH, D. G., ROUGH, R. W., and PLESSEY CO., Ltd. Dec. 18, 1944, No. 25339., [Class 135] A hydraulic valve for maintaining the pressure in a hydraulic system within preset limits and eliminating the necessity for the supply pump working continuously at full pressure, includes an adjustable pilot valve which enables both the upper and lower limits of the pressure to be varied independently. As shown, an inlet 3 communicates, through a Chamber 2 and check valve 30, with an outlet 4, and a low-pressure byepass 5 is controlled by a main valve 7, adjustably loaded by a spring 8 and adapted to be opened by pressure liquid admitted to a chamber 16 through a passage 32 under the control of the pilot valve. The pilot valve comprises a spring-loaded sleeve 17 slidably mounted in a bore 10, and carrying a needle valve member 21, loaded at one end by an adjustable spring 22 and at the other end by a light spring and being subjected, through a passage 31, to the pressure on the outlet side of the check valve. The relative strengths of the spring 18 loading the sleeve 17 and of the spring 22 are so selected that, under the influence of increasing pressure in the chamber 2, the sleeve moves against its ..spring whilst the needle valve remains seated, the sleeve ultimately engaging an adjustable abutment 20, after which the needle valve opens to admit pressure liquid to the chamber 16, at a pressure determined by the compression of the spring 22 during the movement of the sleeve. Thus, the upper limit of pressure may be varied by axial adjustment of the abutment 20. When the main valve is open, and the pressure in the chamber 2 is reduced, causing the check valve to close, the sleeve 17 is returned, by its spring, to its initial position, but the needle valve is retained open by the pressure of liquid acting through the passage 31, on the plunger 25, until this pressure falls to the lower limit as determined by the adjustment of the spring 22. A restricted passageway 36 in the main valve permits of the escape of pressure liquid from the chamber 16 when the needle valve closes.