GB918102A - Improvements in or relating to fluid pressure system unloading valves - Google Patents

Abstract

918,102. Fluid-pressure servomotor control systems. HYDRAULIK A.S. April 8, 1959 [April 12, 1958], No. 11843/59. Class 135. A pump unloading valve for a fluid-pressure system including a fluid-pressure motor 13, Fig. 1, controlled by a manual control valve 12 and pressure and return conduits 11, 14 connected respectively to the outlet and inlet sides of a pump 10, comprises a valve body 15 having inlet and outlet chambers 16, 17, a check valve 20 and an unloading valve 22 controlling communication between the chambers. The valve 22 comprises a main valve member 25, Fig. 2, slidable in a fixed sleeve 24 and loaded by a light spring 30 and a pilot valve member 33 slidable in an axial bore in the main valve member, loaded by an adjustable spring 37 and guided in the base 29 of a second fixed sleeve 28 supported by a body cover 31. Pressure of the liquid in the inlet chamber 16 is transmitted through an interchangeable orificed plug 43, Fig. 3, the axial bore 33a and a lateral port 44 in the pilot valve member to a space 24a to act on the larger rear face of the main valve member to urge the main valve member assisted by the spring 30 leftwardly to close lateral ports 26 in the sleeve 24. On pressure in the inlet chamber overcoming the loading of the spring 37, the pilot valve member 33 moves rightwardly to unseat a conical shoulder 34 and unmask lateral pilot valve member ports 45 and recesses 46 to allow the escape of liquid from the space 24a and rightward movement of the main valve member to uncover the ports 26 and unload the pump. Movements of the pilot valve member 33 to more or less unmask the ports 45 and recesses 46 will constantly adjust the pressure in the space 24a to maintain pump discharge pressure substantially constant. Interchangeability of the orificed plug 43 permits of variation in the time taken for the valve to be returned to its closed position.