GB913322A - Fluid control valves - Google Patents

Abstract

913,322. Fluid-pressure servomotor systems; valves. CLARK EQUIPMENT CO. July 26, 1961 [Feb. 6, 1961], No. 26999/61. Class 135. A valve body 10, Fig. 1, has a supply port 18, a return port 26 and a pair of manually-actuable spool valves 13, 15, each controlling a double-acting ram, the working spaces of which are connected to grooves 30, 32 and 34, 36, respectively, intersecting the spool bores. With the spools in the centralized position shown the ports 18, 26 are in direct communication. Spool 13 is centralized by spring 76 whilst spool 15 is held in any selected position by a detent comprising opposed spring-loaded pins 126 in a spool extension engageable with one of four annular grooves 118, 120, 122, 124. Between each groove 30, 32, Fig. 2, and the ram is a valve 150, 152, each consisting of a movable hollow-cylindrical closure 162 with a conical seating surface 163 slidable between hollow retainers 164, 180, the former incorporating a number of calibrated orifices 174. The space within the closure 162 communicates with the associated groove 30 or 32 by a pilot valve 176 having a stem 182. Upon moving the spool 13 to the left a shoulder 184 contacts the stem 182 so tilting and/or lifting the pilot valve 176, whereby the fluid in the interior of the closure 132 enters groove 30 and flows to the return port 26. After the pilot valve has unseated the higher pressure acting on the conical surface 163 lifts the closure 162 and connects the groove 30 directly with the ram; the orifices 174 are sealed by the closure 162 when the latter is fully opened to prevent chattering. When the spool is returned to the neutral position shown, fluid from the ram enters the interior of the closure 162 by way of an orifice 190, with which co-operates a ball valve 192 on the retainer 180; the closure interior is also open to the ram via grooves 186 in the retainer 180 and the orifices 174. Concomitantly the supply pressure in groove 32 firstly unseats pilot valve 176<SP>1</SP> and then closure 162<SP>1</SP>. Both valves 150, 152 return to the closed position shown when the spool is again centralized. Upon the spool 13 being urged to the right the roles of valves 150, 152 are reversed. To ensure that the ram moves at an equal rate in both directions, the path to the return port from the chamber 154 in which valve 150 is disposed includes a check valve 234. In a modification, the valves 150, 152 are formed by a hollow cylindrical closure 244, Fig. 4, with a conical sealing surface 246, the closure being spring-loaded and slidable over a retainer 248 with a single orifice 252 therein. The pilot valve may have a plane rather than a conical sealing surface or may consist of a ball closure directly engaging the spool. Ports 18, 26 may also be interconnected by a relief valve 40, Fig. 1, comprising a sleeve 193, housing a hollow movable closure 196, urged on to its seat 198 by a spring 200 abutting a partition 202, so preventing communication between ports 206, 204; the port 204 opens via an orifice 208 to the interior of the closure 196, which latter also leads to port 26 by a tubular member 210 and passages 212, 414, the member being supported by the partition 202 and having an orifice 216 therein normally closed by a ball 218 loaded by an adjustable spring 220. When the pressure in the port 20 and hence in the closure 196 is sufficient to unseat the ball 218 the pressure differential across the closure 196 is altered such that the latter is opened by the supply pressure.