Patent GB-594631-A (GB)
Title: Hydraulic jack
IPC: B66F3/42
Filed: 1945-08-21
Abstract: 594,631. Hydraulic jacks. PAGE, H. E. Aug. 21, 1945, No. 21375. Convention date, Aug. 21, 1944. [Class 78(iii)] A hydraulic jack comprises a swingable load-lifting arm 12 movable in response to the movement of a piston 11 in a cylinder 10 and hydraulic fluid pressure generating means for moving the piston during load lifting movement. of the arm, hydraulic means for imparting a limited preliminary outward movement of the piston to cause movement of the arm into initial contact with the load comprising an auxiliary pressure chamber 25 in the cylinder to which an inwardly facing annular surface of the piston is exposed, a body providing a surge chamber' 40 having a valve controlled outlet 73 communicating with the auxiliary pressure chamber and a valve controlled inlet 90, 88 communicating with the pressure chamber means and a compression spring 44 urging the plunger in the surge chamber 40 in a direction to yieldably oppose admission of fluid under pressure to it through the inlet and to force fluid under pressure from the surge chamber 40 to the auxiliary pressure chamber. The jack which is mounted on wheels has a main pressure chamber 22 and an annular auxiliary chamber 25. A hydraulic unit which may be readily removed or replaced in the body of the jack comprises two companion blocks, a bore 31 having a rotatable shaft 35, a surge chamber 40 with compression spring 44 and a pumping cylinder 41 with pumping piston 47 and pressure generating chamber 48. Conduit 56 communicates with chamber 48 and through conduit 70 communicates with main pressure chamber 22 through branch 71 and, through branch 76, which communicates with conduit 77, communicates with chamber 25. Formed half on one block and half in the other are three passageways 56, 57, 58, having valve chambers with valves 66, 67, 68, communicating with bore 31 and with the reservoir R through post 60. At each suction stroke piston 47 draws fluid from reservoir R through port 60 through bore 31 past check valve 66 and on the first pressure stroke forces 'fluid into the auxiliary chamber 25 through ports 70, 76, 77 past check valve 78 to raise arm 12 into contact with the load. On lifting at each pressure stroke of piston 47, valve 73 is unseated against the pressure of spring 74 and fluid is forced into chamber 25, through port 70 and pressure is stored in surge chamber 40. When the load is raised lever 49 is freed by rotating cam shaft 35 until cam 80 unseats valve 66. To lower the load further rotation is effected, cam 81 unseating valve 67 to release pressure from chamber 25 and cam 82 unseats valve 68 to release pressure from chamber 22. First lowering of the arm is effected by means of spring 18. After the first operation surge chamber is charged with fluid under pressure and the lifting arm may be automatically brought rapidly into contact with the load by rotating cam -shaft 35, to bring cam 91 into engagement with stem of valve 88 to unseat it, the fluid is forced into the auxiliary chamber 25 and when the cam 91 disengages stem of valves 88 to seat it, the surge chamber becomes recharged to force fluid into main chamber 22. Specification 594,595 is referred to.