Patent GB-952595-A (GB)
Title: Hydraulic systems
Inventor: HANCOCK KENNETH GEORGE
IPC: F15B13/08
Filed: 1959-09-04
Abstract: 952,595. Fluid-pressure apparatus. ELECTROHYDRAULICS Ltd. Sept. 1, 1960 [Sept. 4, 1959], No. 30336/59. Heading F1P. [Also in Division F2] An hydraulic system for actuating one or more services, such as may be required in an industrial fork-lift truck or in coal mine decking arrester gear, comprises a pump 1 for supplying liquid under pressure from a tank to the system, and control means consisting of a selector mechanism SL2 having a valve body 10 in which is slidable a valve 13 having intercommunicating internal passages 23, 24, 25, one of which 23 is in permanent register with a first port 9 in the valve body, the valve body having second and third ports 5, S2 connected to the pump and a service to be operated, respectively, the third port, when the valve is moved to a selected position, being put into communication with a relay valve R which has an apertured spring- loaded member R2 and is hydraulically connected to the first port 9, the delivery line 2 from the pump, and a line R4 to the tank. As shown, two selector mechanisms SL1, SL2 are provided controlling the supply to service ports SI, ... S4, the selector mechanisms in association with the relay valve controlling the output from the pump in accordance with the requirements of the system and permitting the service selected to be operated initially at a slow speed and then at a rapid speed. The flow from the pump passes through the line 2 and the aperture in the member R2 to a line 8 connected to the first port 9 of selector SL2 and, when the valve 13 is in its central position, to an outlet 26 and the port 9 and outlet 26 of the selector SL1 to the tank. With the valve 13 in the central position, the pressure differential across the member R2 caused by the flow to the tank moves the member against its spring to uncover the line R4 so that the pump discharges at low pressure. The pump is also connected by a line 3 and one-way valves 4, 6 to ports 5, 7 in the valve bodies, the ports being isolated when the valves are in their neutral position. When the valve 13 of selector SL2 is moved to the left by a handle 14, a land 29 restricts the flow through the port 9 to reduce the pressure differential across the member R2 which is moved by its spring to partially close the outlet R4 so increasing the delivery pressure of the pump. Continued movement of the valve brings the port S1 into communication with an outlet 28 so that, if the port S1 is connected to the exhaust side of a double-acting jack, fluid therefrom can flow to the tank. Further movement of the valve brings the passage 24 into register with the port S2, which is connected to the pressure side of the jack, and the land 29 closes the connection between the ports 9, 26 so that only a small flow of fluid passes through the member R2 which thus moves to close the outlet R4 and the pump delivers at a pressure determined by the load and the restriction in the aperture and passages, the fluid passing through the port 9, one-way valve 22 and passages 21, 24 to the port S2 and the jack which is operated at slow speed. When the valve is moved to its furthest left-hand position, the port S2 is brought into communication with the port 5 and the passage 24 is closed to stop flow through the relay valve so that the maximum output of the pump is applied to the jack to effect rapid movement thereof. The land 16 to the right of the passage 24 may be shaped to progressively open the port S2. Movement of the valve 13 in the opposite direction reverses the direction of operation of the jack. The selector mechanism SL1 can be operated when the selector mechanism SL2 is in use to supply fluid at the maximum discharge to either port S3 or S4. More than two selector mechanisms may be coupled in series in the system. A relief valve 12 limits the maximum pressure in the system. In an alternative embodiment, the relay valve is connected between the tank and the selector mechanisms and the one-way valve 22 is dispensed with in the passage 21. The slow initial movement of the jack is controlled by the flow from the exhaust side thereof passing through the passages in the selector valve to the relay valve so that both following and opposed loads on the jack may be controlled. Specification 952,597 is referred to.