GB705388A - Improvements in and relating to control valves for fluids - Google Patents

Abstract

705,388. Fluid-pressure servomotors; fluidactuated valves. SELF-CHANGING GEAR CO., Ltd., and MILLER, A. A. Feb. 13, 1952 [Feb. 16, 1951], No. 3795/51. Class 135 A piston valve comprises a movable closure member 3 having a pair of interconnected pistons 4, 5 of different diameters reciprocable in a cylinder 2 having a stepped bore 7, 8, the space 26 enclosed by the cylinder between the step thereof and the larger piston 4 being constantly in communication with an outlet, so that any variation in the pressure at the port due to an initial movement of the member 3 causes a biasing force to be imposed on the member to urge it in the direction of the initial movement. The pistons control fluid supply and exhaust ports 9, 11 respectively, outlet ports 13 communicating with a fluid operated device, e.g. a servomotor. The cylinder is mounted in a housing 1 to which supply, exhaust and outlet lines 10, 12, 14 respectively, are connected. The valve is operable manually e.g. by levers or push-rods, or by pressure fluid in chambers 16 and 18, e.g. under the control of a governor or control device 30, as described in Specification 665,610. The annular area due to the difference in diameters of the pistons constitutes a biasing surface subject to the pressure in the space 26. Thus, when the closure member is being moved to connect the servomotor with the supply, piston 5 closes ports 11 and piston 4 opens ports 9, the increased pressure in space 26 causing the member 3 to snap to fully open position. Similarly, when moving the closure member in the opposite direction, piston 4 closes ports 9 and piston 5 opens ports 11, the biasing force thus being removed whereby a biasing spring 27 snaps the closure member to fully closed position to connect the servomotor to exhaust. The spring 27 may provide a force equal, e.g. to half the biasing force due to supply pressure on the annular area.