Patent GB-705689-A (GB)
Title: Improvements in or relating to pressure actuated valve devices
Inventor: TALBOYS DAVID CHARLES
IPC: G05D16/10
Filed: 1951-05-18
Abstract: 705,689. Fluid-pressure servomotor-control systems ; valves. AUTOMOTIVE PRODUCTS CO., Ltd. May 7, 1952 [May 18, 1951], No. 11706/51. Class 135 In a pressure fluid system wherein a relief valve connects a pump to, or disconnects it from, an accumulator according to the pressure in the latter, and wherein the valve is actuated by pressure fluid under the control of a unit which is urged by the accumulator pressure against a loading spring to a position corresponding to the open position of the relief valve, the control unit includes a stepped plunger means which exposes the actuating device of the relief valve to accumulator pressure or connects it to exhaust, the arrangement being that, when the stepped plunger is in the position corresponding to the open position of the relief valve, the accumulator pressure acts on the larger area of the plunger, and when the latter is in the position corresponding to the closed position of the relief valve, the accumulator acts only on the smaller area of the plunger. In an embodiment, the pump delivery enters at port 14, flows around the closed relief valve 102, and past a non-return valve 104 to a bore 17 leading to the accumulator. Valve 102 is loaded by two springs 111, 112, of which spring 112 abuts against a piston 113 subject on its other side to accumulator pressure which has access to the piston through a passage constituted by flats on the stem 123 of a piston valve 115, a chamber 117 formed between two fixed liners 125, 126 in the bore 17, radial passages 117a leading to a groove around liner 125, a passage 118, groove 119, and a passage 121. At first, due to the lack of pressure behind piston 113, the loading effect provided by spring 112 will be negligible and valve 102 will be held closed solely by spring 111, but as the accumulator pressure rises, spring 112 will become sufficiently effective to retain valve 102 closed. Two piston valves 115, 116 of different diameters can slide in the liners 125, 126, the valves having a common loading spring 122 and their stems, which are provided with flats, being held in contact with each other by a further spring 96. As the accumulator pressure rises, it acts on the exposed area of valve 116 and, when the effect of spring 122 has been overcome, valves 115, 116 will move to shut off accumulator pressure from piston 113 and the fluid behind the latter will be vented past valve 116. This will remove the loading effect of spring 112 and pump pressure will open valve 102 so that the pump outlet is diverted to reservoir through port 15. Non-return valve 104 will also close due to the loss of pressure on the upstream side thereof. A modification is described wherein the relief valve incorporates a check valve and a chamber constituting a dashpot to slow up the opening movement of the valve. An additional relief valve of normal construction is also provided, this valve operating on failure of valve 102. In a modification of this additional relief valve, the loading spring thereof abuts against a piston subject to the air pressure in the accumulator, the spring loading thus being reduced should the air pressure in the accumulator be lost.