GB750121A - Improvements in and relating to hydraulic systems and combined unloading and relief valves therefor - Google Patents

Abstract

750,121. Hydraulic machines ; valves. ELECTRAULIC PRESSES, Ltd. May 4, 1951 [April 1, 1950], No. 8210/50. Classes 69 (2) and 135. An hydraulic system supplying pressure liquid to two independently-operated motors 11, 12, Fig. 1, actuating, e.g., a die-casting machine, comprises two motor-driven hydraulic pumps 31, 32 discharging into a common manifold 21 on opposite sides of a non-return valve 34, valves 19, 20 controlling the flow of pressure liquid to and from the motors, and a combined unloading and relief valve 36 having a spring-loaded plunger 62 operable by the pressure in that part of the manifold receiving both pump deliveries, so that with both pumps working and the control valves closed, the pressure builds up in the manifold to move the plunger to a position to unload one of the pumps whilst the other pump maintains the pressure in the manifold up to the closed valves, any substantial fall in the manifold pressure due to operation of one or both valves causing the return of the plunger to re-load the unloaded pump until the manifold pressure is restored. In one application, the check valve 34, together with a check valve 35 in a passage 87, Fig. 3, between the pump 32 and the valve 20 are housed in a casing 44 with the spring-loaded plunger 62 of the combined unloading and relief valve. The plunger 62 urged downwardly by a spring 63 slides in a ported sleeve 45 and is subjected on its underface to pressure in a first delivery passage or manifold 77 communicating through a valve inlet 75 with the pump 31 of small capacity and high pressure and through the check valve 34 and a second valve inlet 52 with the pump 32 of large capacity and low pressure. The sleeve is formed with lower sloping ports 59 connecting the passage 77 through an annular recess 58, and passages 60, Fig. 2, with a second delivery passage 90, upper sloping ports 56 connecting the passage 77 through annular recess 54 and passages 60A with exhaust, ports 55 connected to the recess 54 and ports 51 connecting the second inlet 52 with an exhaust outlet 53. With both control valves 19, 20 in closed position rendering their respective motors 11, 12 inoperative, pressure liquid from the pump 31 passes up to the control valve 19 and from the pump 32 up to the control valves 19 and 20 through the check-valves 34 and 35 respectively. On initial build-up of pressure in the passage 77 the plunger 62 is raised to uncover the ports 59 to supplement the supply to the valve 20 until the pressure in the passage 90 is the same as that in the passage 77. Further increase in pressure then raises the plunger 62 to uncover the ports 51 to unload the pump 32, the check valves 34, 35 then closing to maintain the pressure in the system which is maintained by the pump 31 supplying direct to the valve 19 and through the ports 56 to the valve 20. If the pump 31 is more than sufficient to make up losses and the pressure still rises, ports 56 will be partially uncovered to connect the pump 31 to exhaust to regulate the pressure in the system. On movement of the valve 19 to admit pressure liquid above the ram 15 of the motor 11 the ram moves outwardly and pressure in the system falls until the ram reaches the end of its stroke to close the mould. Pressure again builds up to unload the pump 32 and regulate the supply from the pump 31. The valve 20 is then moved to admit pressure liquid above the ram 16 of the motor 12 which moves outwardly to inject material into the mould. On reaching the end of its stroke pressure in the system will again build up and both rams will remain in their full stroke positions until the valves 19, 20 are moved in reverse sequence to move the rams inwardly. Return movements of the plunger 62 may be dampened by a leaky fit between the spring abutment plate 64 and the chamber 41, which is filled with oil, and a non- return valve 106. In a modification, a pressure regulating valve 113, Fig. 10, and a chock valve 114 are fitted in parallel between a valve 19a and motor 11a and similarly a pressure-regulating valve 111 and a check-valve 112 between a valve 20a and motor 12a to limit the maximum pressures that may be applied to the motors. A non-return check valve 110 may be fitted adjacent the motor 11a to insure against blowback of pressure liquid in the event of the mould tending to open during the injection operation. An accumulator 115 and a non- return check 116 may also be fitted in the line to the control valve 20a.