GB927572A - Improvements relating to hydraulic control valves - Google Patents

Abstract

927,572. Valves. FAIREY CO. Ltd. Jan. 5, 1960 [Jan. 15, 1959], No. 1579/59. Class 135. A valve 10, Fig. 1, controlling fluid flow to a double-acting jack connected to delivery passages 11, 12 in the jack body 13, is mounted on the latter, and includes a pair of platens 15, 16 having opposed, parallel plane bearing-surfaces 17, 18, polished to a standard optical flat and spaced by rings 19 similarly polished. Platen 15 has a central inlet port 20 connected to a high-pressure inlet 22, and alternative delivery ports 23, 24 connected to passages 11, 12 respectively; the platen 16 is provided with alternative delivery ports 29, 30, also connected to passages 11, 12 respectively, and situated opposite ports 23, 24. The closure member is in the form of a slide 35, Fig. 3, comprising an annular sleeve mounted between the platens to move perpendicularly to the sleeve axis, the annular end faces of the slide 35 constituting bearing surfaces. When the slide is moved in either direction from the closed position shown it progressively uncovers one of delivery ports 23, 29 or 24, 30, Fig. 1, to connect them with the inlet 22 via the central opening in the slide, and at the same time closes the other pair of delivery ports. The slide 35 has end lugs with keyways by means of which operating and balancing spindles 39, 40 are attached thereto, and a return passage, not shown, is connected to the annular spacer 45 outside the slide but between the platens. Each annular end surface of the slide is formed with a circumferential band 50, Fig. 3, of 50-60 micro-inches depth leading to a step 52 of 0.052 inch radial width, the distance across the steps 52 at each end of the slide being less than the height of the rings 19, Fig. 1, so that the slide has a limited end float between the platens. In use there will be a continuous seepage of fluid outwardly across the bands 50, 52, Fig. 3, between the slide and the platens and draining into the spaces 45, so providing a lubricating film and on which the slide floats and producing a self-centering action tending to return the slide to its central position between the platens. Any foreign bodies in the fluid enter the relieved bands and give rise to an hydraulic force which lifts the slide and increases the effective gap between the platen and trapped body whereby the latter may be forced into the space 45. The step 52 may also incorporate an outer relieved band 54. In another form the delivery ports 71, 72, Fig. 6, in the upper platen are blind and communicate with the two delivery ports 73, 74 in the lower platen via cross bands 75, 76 in the slide so balancing the hydraulic forces acting on the two ends of the slide and by seepage across the blind ports 71, 72, increases the total flow through ports 73, 74. Each end face of the slide is provided with a pair of inset arcuate relieved bands. The slide may be replaced by a piston closure of dumbbell shape.