GB1462621A - Hydraulic units - Google Patents

Abstract

1462621 Hydraulic jacks TANGYE EPCO Ltd 8 Feb 1974 [24 Jan 1973] 3512/73 Heading F1D A hydraulic unit, Fig. 1, for operating a jack, extends rapidly until the load is contacted and then extends slowly with increased force. Liquid is drawn from a reservoir 34 by a pump 39 and passes past balls 36, 37 into a chamber 24 from which it extends a piston 62. The latter moves the cylinder 10 relative to the piston 14 until an increase in pressure occurs due to the load being contacted. During this extension liquid is drawn into a chamber 29 from the reservoir 34 through a check-valve 28. When pressure in the chamber 29 reaches a predetermined value a spool 48, Fig. 2, moves against a spring 49 and allows a ball 46 to lift off a seat in a port 45. When this occurs liquid from the pump flows through the port 45 and passages 61,31 into the chamber 29 to extend the unit. Pulling a rod 51 outwards allows liquid to return to the reservoir from chamber 44 through bores 56, 57, 52 and 59. If the operating pressure rises too high the rod 51 is moved thereby so that liquid can escape through the passage 59.