GB594586A - Hydraulic jacks - Google Patents

Abstract

594,586. Hydraulic jacks. PAGE, H. E. Nov. 28, 1944, No. 23725. Convention date, Nov. 23. 1943.[Class 78(iii)] A hydraulic jack comprises a body in which a piston under the action of a spring ,is slidable in one direction, while upon application of pressure to a pressure chamber for the piston, the latter is forcibly moved in the same direction in which the spring acts thereon, and includes a pump for alternate connection with a pressure reservoir and the pressure chamber for the piston, said pump effecting protractive and retractive movements of the piston, while the spring effects protractive movement of the piston rotative to the body in the absence of action of the pump. A hydraulic unit, Fig. 2, consists of a body 11 with an inner end portion 11a pivotally mounted between side plates 5 by a cross pin 12. The body comprises a cylinder 15 with which a piston 16 is slidably mounted. The piston has a longitudinal bore housing a compression spring 22 tending to push the piston 16 outwards. The piston is held in the position illustrated by means of fluid pressure bearing on an annular shoulder 26 in an annular chamber 25 surrounding the piston. When the pressure in the annular chamber is released, the spring forces the piston outwards, tilting a lifting arm 6, and causing it to engage the load. Further lifting is effected by pumping fluid into the cylinder 15 from a reservoir R through a valve, Fig. 3. The pumping is effected by a small piston 36 moving in a cylinder 35. The piston is actuated by a lever H having at its end a yoke 37 pivoted at 38 to the side plates 5. The pivot 38 carries two arms 37a which are connected to two fork arms 39 which in turn are connected to the piston 36. Fluid drawn from the reservoir R passes through the valve 42, Fig. 3, controlled by a spindle 55. When fluid is drawn from the reservoir R into' the cylinder 35, it passes through a passageway 63 and past a poppet 75. On the pressure stroke of the piston 36, this fluid is forced past a ball valve 71 and through a passageway 81a into the cylinder 15 thus forcing the piston 16 outwards. To lower the jack, the valve 42 is rotated and by a cam 49 unseats the poppet 75 and ball valve 71 thus releasing the pressure in the cylinder 15. In this position of the valve, pumping of the piston 36 causes fluid to pass from the reservoir, past a poppet 67 and a ball valve 65, into the annular chamber 25, thus forcing the piston 16 back into its cylinder 15.