GB680215A - Improvements in or relating to hydraulic valves - Google Patents

Abstract

680,215. Change-over valves. NATIONAL RESEARCH DEVELOPMENT CORPORATION. June 1, 1950 [June 10, 1949], No. 15566/49. Class 135. A hydraulic change-over valve of the piston type includes a hydraulic ram for returning the valve piston to its central or inoperative position when valve control means is inoperative. Thus, a changeover valve for a reversible hydraulic motor comprises a body having a bore 4 for the piston 4a the movement of which to the right or the left to control the flow of pressure liquid from an inlet port 9 to either of two ports 12, 13 is effected by hydraulic pressure on the outer end of either of the lands 5, 8. The return of the piston to its initial position is effected by the rams 37, 38 which work in bores at the ends of the piston. The supply of pressure liquid from ducts 14 communicating with the inlet port 9 to the ends of the lands 5, 8 is controlled by pilot valves 20, 21 actuated by electromagnets 2, 3 respectively. The inner ends of the rams are permanently exposed to pressure liquid through ducts 35, 36, and the spaces between the lands 5, 6 and 7, 8 are open to exhaust through ports 10, 11 in the body. If it is desired to supply pressure liquid to the port 12, the electromagnet 3 is engaged to move the pilot valve 21 to the right against a loading spring so that the liquid flows via a recess 32 in the valve 21 to the right of the land 8. The left side of the land 5 at the opposite end of the piston 4a is meanwhile open to exhaust through the pilot valve 20, the duct 26 in the body and the exhaust port 10. The movement of the piston to the left opens the port 12 to pressure liquid and the port 13 to exhaust via the port 11. At the same time the outer end of the squared shank 39 of the ram 37 buts against a plug 27 in the body. De-energization of the electromagnet 3 results in the pilot valve 21 returning to its initial position under the action of the spring and thus opening the space to the right of the land 8 to exhaust via the duct 26 and the port 11. Meanwhile, the hydraulic pressure on the inner end of the ram 38 and the reaction on the piston of the hydraulic thrust against the inner end of the ram 37 returns the piston to its initial position. The speed of the motor may be controlled by restricting the flow thereto in which case the valve body is provided with an extension 1a having a bore 60 for a spring- loaded piston valve 61, and motor ports 69, 70. The piston valve may be operated manually or, alternatively, automatically by a cam driven through reduction gearing from the motor shaft and coacting with one end of a pivoted link the opposite end of which is connected to the piston valve spindle.