GB911709A - Improvements in and relating to hydraulic cylinders - Google Patents

Abstract

911,709. Hydraulic apparatus; valves. AUTOMOTIVE PRODUCTS CO. Ltd. April 25, 1961 [April 25, 1960], No. 14462/60. Classes 69 (2) and 135. An hydraulic ram 4 and cylinder 3 apparatus which may operate a valve of the sliding gatetype comprises differential pistons 1, 2 associated with the ram and moved during inward movement of the ram by predetermined amounts, the relative areas of the pistons being such that a greater effort is applied to the ram during a predetermined initial portion of the inward movement of the ram than during the remainder of the stroke, outward movement of the ram being effected by causing the hydraulic fluid to act first differentially on one of the pistons and finally on one side only of the piston. The piston 1 is disposed in a largediameter portion 5 of the cylinder and is axially-movable relative to the ram on which is secured the small-diameter piston 2. The portion 5 of the cylinder is provided with ports 8, 9, port 9 being permanently connected to a drain 20, and port 8 and a port 14 being selectively connected to a source of pressure 19 or the drain by a manually-operated valve 18 and an hydraulically-operated valve 24 responsive to actuation of a pilot valve 27 by a cam 28 on the ram 4. When the ram is to be extended, for example to close the gate valve, the manually-operated valve 18 is moved to a position in which the port 14 is connected to the source 19 and the valve 24 is urged by a spring to a position in which the source is also connected to the port 8 and, by way of an annular clearance 11 and space 12, acts on the piston 2, the differential pressure acting on the piston 2 to move the vane until the cam 28 actuates the pilot valve 27 to move the valve 24 to its alternative position and connect the port 8 and space 12 to the drain, the pressure from the port 14 acting on the piston 2 to complete the stroke of the ram. The increased pressure is necessary for the final closing movement of the gate valve if the gate is wedge-shaped. To withdraw the ram, the valve 18 is moved to connect the port 14 to drain and port 8 to the source so that the area of the piston 1 is effective for the initial movement of the ram and the initial opening movement of the gate, the completion of the stroke of the ram being effected by the fluid pressure in the space 12 acting on the annular area of the piston 2.