GB902079A - Improvements in valves for controlling the flow of fluid - Google Patents

Abstract

902,079. Fluid-pressure servomotor-control systems; valves. MERCIER, J. Aug. 15, 1958, No. 26340/58. Class 135. An hydraulic system comprising a pump delivering pressure-liquid to the system and a pump unloading valve, includes a control valve having movable first and second valve members wherein the first valve member moves to a predetermined position when the pressure in the system reaches a predetermined upper value to slightly open a valve passage connecting the pump unloading valve with the valve outlet and the second valve member is rapidly urged by resilient means when the first valve member reaches its predetermined position to fully open the valve passage to unload the pump. As shown in Fig. 1, a control valve 21 comprises a first movable member 34 including a piston 35 loaded by a spring 36 and subjected to the pressure in a utilization conduit 6 through a branch 48 and a second movable member 26 slidable on the first member. The second member includes a spring-loaded piston 26a slidable in a chamber 23 between an adjustable abutment cap 29 and the bottom of the chamber 23 and is provided with a port 30 in its base. Pressure liquid delivered by the pump 2 besides passing to the conduit 6 through a check valve 5 also passes to the underside of a piston 8 of a pump unloading valve 7 and through a restriction 16 to the chamber 23 and to a chamber 20 above the piston 8 to assist a spring 13 to close the valve 7. On pressure in the conduit 6 reaching a value determined by the spring 36 the member 34 is moved leftwardly to uncover a radial port 38 therein so that pressure in the chamber 23 is relieved through axial and radial ducts 37, 39 in the member 34 and a line 46 to sump 1 and the inlet side of the pump whence spring 28 immediately urges the piston 26a and member 26 rightwardly to fully open the port 38 and quickly allow the escape of pressure liquid from the chambers 20, 23 to open the valve 7. As soon as the pressure in the conduit 6 falls to a predetermined lower value, the piston 35 begins to move rightwardly to close the port 38. Pressure then builds up in the chambers 23, 20 so that the piston 26a moves against the abutment cap 29 and the valve 7 closes. In another embodiment, the first movable member comprises a piston valve 64, Fig. 4, controlling a port 78 connected to the line in which the restriction 16 is located and the second movable member comprises a loose ball valve 82 loaded by a spring 83 which controls a port 81 through the piston valve. The ball 82 coacts with a rod 94 which engages at its other end a ball 91 loaded by a spring 90 and engageable with an adjustable seat 89 in a screw-threaded cap 88 to adjust the upper and lower pressure limits at which the valve operates. On pressure in the conduit 6 and branch 48 rising above a value determined by spring 65, the piston valve 64 moves leftwardly taking the ball 82 with it to first close the port 78 to cut off the supply of pressure liquid to the chamber 20 of the unloading valve 7 and press the ball 91 on its seat 89. On further increase in pressure the rod 94 unseats the ball 82 to connect the chamber 20 through the port 81. and line 46 to the sump 1 and the inlet side of the pump 2 to open the valve 7. In a modification, the first movable member comprises a hollow piston member 102, Fig. 7, having a pair of opposed valve ports 81, 104, alternately opened and closed by the loose ball valve 82. Normally the ball 82 urged by a spring 103 closes the port 81 and opens the port 104 so that pressure liquid through the branch 48 is supplied to a chamber 111 to act on a piston 108 in opposition to a spring 109. The piston through its rod 107 and a link 106 holding a rotary plug valve 105 in a position to connect the pump delivery to the conduit 6. On pressure in the conduit rising to a value determined by the spring 65 the piston member 102 is moved leftwardly to close the port 104 and open the port 81 so that the chamber 111 is connected to sump whence the valve 105 is rotated to unload the pump. The ball 91, spring 90 and cap 88 may be replaced by a screw-threaded extension of the rod 94 which coacts with a screw-threaded cover to adjust the position of the rod 94 and the operating pressures.