GB603658A - Hydraulic jack - Google Patents

Abstract

603,658. Hydraulic jacks. PAGE, H. E. Oct. 26, 1945, No. 28368. Convention date, Oct. 27, 1944. [Class 78 (iii)] A hydraulic jack, adapted for rapid engagement with the load, comprises a pump piston 10 reciprocable in a bore 6 which extends into a coaxial work cylinder 7 with a load piston 11; an auxiliary piston 12 secured to the piston 11 works in an extension of the bore 6, and a spring-controlled check valve 60 controls a passageway extending from the space 15 between the pump and auxiliary pistons to the work cylinder. Upon commencing to reciprocate the. pump piston 10 by its operating handle 20, the check valve 60 being seated, fluid in the space 15 acts on the auxiliary piston 12 to move the load piston 11 rapidly outwards. When the load is taken up, the pressure in the space 15 rises and unseats the check valve 60 so that the fluid then passes to the work cylinder 7 and acts directly on the piston 11 to lift the load. Fluid is admitted to the pump bore 15 from a reservoir R by way of a spring- loaded valve 40 which normally seats on the lower end of a sleeve 30 mounted to slide in an extension of the bore accommodating the valve. A similar valve seating on a sleeve 31 controls communication between the work cylinder and reservoir. Both sleeves are held down in operative engagement with the valves, and against springs 38, 48, by a plate 77 loaded by a spring 78. To lower the load, the plate 77 is retracted through linkage 70, 83, so allowing the sleeves to be unseated from their valves under the action of their springs 38, 48, and the fluid to return from bore 6 and cylinder 7 to the reservoir. The plate 77 is also retracted to release the pressure at the limit of outward movement of the load piston, this being effected by a finger 92 on the lifting lever rocking a lever 90 also connected with the plate. Outward movement is, however, normally limited by a stop 87.