GB865422A - Improvements in or relating to hydraulic control valves - Google Patents

Abstract

865,422. Valves. SCHLEPPERWERK NORDHAUSEN VEB. Aug. 29, 1957 [June 25, 1957], No.27241/57. Class 135. Different pressures at which hydraulic apparatus such as lifting-gear on tractors is operated can be selected by a control-valve comprising a casing 1 having an inlet 5 and pressure ports 6, 7 and 9, 10 respectively, and a return port 8, communicating with a bore accommodating a rotatable and longitudinally-slidable hollow piston valve member 2 having passages adapted to co-operate with these ports for delivery of pressure liquid to, and its exhaust from, the apparatus, means such as a manual shift lever 4 rotatably associated with the piston valve and operative to move it longitudinally to control such delivery and exhaust, the piston carrying a spring-loaded relief valve plunger 3 which co-operates with longitudinallyspaced relief ports 11, 13 in the piston, the arrangement being that the port 11 is covered or uncovered by the casing 1 in two longitudinal operating positions of the piston valve whilst the relief port 13 is always uncovered, whereby a different relief or operating pressure is selected in each of the longitudinal operating positions. Spaced passages 17, 18, respectively, in the piston co-operate with the pressure ports 6, 7 and 9, 10, respectively, in the two longitudinal positions and similarly spaced passages 15 cooperate with the return port 8. In each longitudinal position there are three rotational working positions of the shift lever 4 corresponding respectively to a position in which the control valve delivers pressure liquid to the apparatus, a neutral or " hold " position, as shown, in which the apparatus is hydraulically isolated by the valve and a pressure pump connected to the inlet 5 delivers to the return port 8 and a position in which the control valve exhausts pressure liquid from the hydraulic apparatus through the passages 15. These passages are extended longitudinally by restricted grooves 16 co-operating with the pressure ports 6, 7 and 9, 10 so that the apparatus is exhausted gradually, e.g. a raised load on a tractor is lowered slowly.