GB837017A - Improvements in or relating to hydraulic lifting apparatus - Google Patents

Abstract

837,017. Hydraulic lifting jacks. WEBER, E. Jan. 24, 1957, No. 2637/57. Class 78 (3). An hydraulic jack in which a lifting cylinder 3 moves over a fixed piston 4 is operated by a pump 2 mounted in the upper part of a housing 1 secured to the cylinder 3. The housing surrounds the cylinder, with some clearance, at its lower end and engages the load through an upper surface 37 and a surface 70 mounted on the outside wall. In the form shown the housing 1 is of square section and is attached to the cylinder 3 by a block 12 supporting the pump 2 which is operated by a hand lever attached to a shaft 25. The pump draws fluid from the space between the cylinder 3 and the housing 1, and feeds it under pressure into the cylinder 3. A manually operated discharge valve 19 for lowering the jack and a pressure relief valve are provided. The latter may take the form shown diagrammatically in Fig. 8, where the slide 80 moves to the right as pressure builds up in the lifting cylinder passage 59<SP>1</SP>, until a reduced centre portion 80<SP>1</SP> allows fluid to escape from the pump cylinder 21<SP>1</SP> to the intake passage 51<SP>1</SP>. The jack may be made invertible by providing a second intake pipe above the block 12, which does not completely fill the cross-section of the housing 1, and a rotating or sliding valve to select the appropriate intake pipe. Alternatively the intake pipe may be flexible and have its end weighted down, the gap in the block 12 being sufficiently large to allow the weighted end to pass through. The pump may have two cylinders, one of which may be larger than the other, and one of which may be adapted to become inoperative when a certain fluid pressure is exceeded.