GB773142A - Improvements in and relating to fluid-pressure actuated bye-pass valves - Google Patents

Abstract

773,142. Fluid-pressure servomotor control systems; valves. ELECTRAULIC PRESSES, Ltd. Nov. 28, 1952 (Dec. 7, 1951; Sept. 15, 1952], Nos. 28701/51 and 23130/52. Class 135. A pump unloading valve comprises a main valve member 5, Fig. 1, slidable in a casing bore 3 to control flow between an inlet 10 connected to pump discharge and an outlet 11 connected to pump inlet and a pilot valve 17 controlling discharge from a chamber 15 of liquid admitted to the chamber through a small duct 16 in the valve 5 which is open to the inlet 10. The pilot valve is loaded by a spring 18 urging it away from the valve 5 and controlled by a piston 6 slidable in a cylinder 2 having an inlet port 7 and an outlet port 8. On an auxiliary valve (not shown) being actuated to supply pilot pressure liquid to the cylinder 2, the piston is urged downwardly so that the valve 17 seats on the valve 5. Pressure then builds up in the chamber 15 to move the valve 5 towards its seat followed by the valve 17. On the auxiliary valve being actuated to cut off the supply of pilot pressure liquid, liquid in the cylinder 2 flows at a controlled rate to exhaust through restricted ports 9 in an undercut portion of the piston, the piston and valve 17 moving upwardly under the action of the spring to unseat the valve 17 to discharge liquid from the chamber 15 to allow the valve 5 to open and follow-up the movement of the valve 17. In a modification, the inlet 7 and outlet 8 in the cylinder 2 are reversed, the spring 18 then being located above the piston to urge the valve 17 towards closure so that when pilot pressure liquid is admitted beneath the piston the valves 17 and 5 are unseated. A light spring 21 fitted between the piston and the valve 17 holds the valve 17 in contact with the piston. Instead of the restricted ports 9, a passage in the casing fitted with a plurality of spaced washers having small orifices connects the outlet 8 to the inlet 7. If desired, the main valve member 5 may be omitted, in which case the valve 17 controls flow between the inlet 10 and the outlet 11. To load and unload a number of pumps in sequence, several valves, one for each pump, are connected in series. The valves are then modified, the restricted ports 9 in the piston 6 are replaced by a duct 32, Fig. 4, the duct in the case of the first valve being fitted with an orificed plug 30 and in the case of the remaining valves completely closed. Lateral ports 37, 38 in the cylinder 2 lead to a passage 34 which in turn leads to an outlet 33 connected to the inlet 7 of the next valve in the series. When the piston of the first valve is nearly at the end of its downward stroke to close the valves 17, 5 to load the first pump, pilot pressure liquid is transmitted through the port 38, passage 34 and outlet 33 to the second valve whose piston is then urged downwardly to cause loading of the second pump and so on. In unloading the pumps liquid is firstly exhausted from beneath the piston of the first valve which moves upwardly to uncover the port 37 to exhaust liquid from beneath the piston of the second valve and so on. In a further modification, a plunger 39, Fig. 5, is fitted in the duct controlled by the pilot valve 17, the underside of the plunger being subjected to pump discharge pressure which when exceeded by that of the spring 18 causes the plunger to lift to unseat the valve 17 which in turn allows discharge from the chamber 15 and the opening of the main valve 5.