GB708635A - Improvements in and relating to adjustable relief valves - Google Patents

Abstract

708,635. Fluid-pressure servomotor-control systems ; valves. ELECTRAULIC PRESSES, Ltd. Jan. 18, 1952 [Feb. 6, 1951], No. 2884/51. Class 135 A spring-loaded relief valve in which the spring is adjustably loaded by hydraulic pressure, comprises two coaxially mounted pistons independently movable within a cylinder, one piston loading the relief valve and the other being in hydraulic balance and operable from outside the cylinder, the balanced piston on movement operating valve means to control the admission and exhaust of of pressure liquid to and from the space between the pistons, to vary the pressure therein to vary the relief valve loading and re-establish the normal positional relationship between the pistons. As shown, a relief valve plunger 3 loaded by a spring 5 controls the flow of pressure liquid from an inlet 4 to an outlet 7. The spring is adjustably loaded by a loading piston 9 and a hydraulically-balanced piston 8 having a passage 10 therethrough and operable from outside the cylinder 1 by manual, electrical, mechanical or fluid-pressure means to control a double-headed valve member 19. On movement of the piston 8 towards the piston 9, the head 21 of the valve 19 is unseated to direct pressure liquid from an inlet 25 to a space 11 between the pistons. The piston 9 is thence moved downwards until the head 21 is again seated and the positional relationship between the pistons restored with an increased pressure on the loading spring. On movement of the piston 8 away from the piston 9, the head 20 of the valve 19 is unseated to exhaust pressure liquid from the space 11 through passages 17, 18a in the piston 9 and an outlet 18b. The spring then moves the piston 9 upwardly until the head 20 is again seated and the pressure on the spring 5 reduced. In a modification the valve member 19 is mounted in the piston 9 and the exhaust passages 17, 18a are formed in the piston 8.