GB605209A - Hydraulic jack - Google Patents

Abstract

605,209. Hydraulic jacks. PAGE, H. E. Nov. 9, 1945, No. 29990. Convention date, Nov. 10, 1944. [Class 78 (iii)] A hydraulic jack adapted for rapid engagement with the load comprises a body formed with a ram cylinder 6, a reservoir R and two coaxial pump cylinders 62, 63 of different diameters. The small cylinder 63 is connected with a valve bore 15 having gravity-seated balls 74 and 75 controlling communication with the ram cylinder and reservoir respectively, and lifting at the pressure and suction strokes of the pump piston. The large cylinder is connected with a second valve bore 10 similarly provided with check valves 67 and 68. Valve 68 is adapted to be unseated by a pressureactuated plunger 70 when the pressure in the ram cylinder rises to a predetermined value determined by a return spring 69, there being a communication 23 from behind the plunger to the ram cylinder. During initial operation of the pump, with the ram unloaded, both pump cylinders are effective to bring the ram rapidly up to the load when the consequent rise in pressure causes the plunger 70 to unseat valve 68, so placing the larger pump cylinder in permanent communication with the reservoir so that the smaller high pressure pump cylinder is then alone effective to raise the load. In the particular construction shown the ram is of the double lift type and has inner and outer telescopic sections 33 and 31, the passage to the cylinder space of the outer section in which the inner one works being controlled by a check valve 49 unseated by a fixed abutment 50 when the ram is retracted. Retraction is effected by screwing out a valve 80 controlling a direct passage 26 from ram cylinder to reservoir. The twin pump plunger 60a, 60b is actuated against a return spring 87 by either of two cams 85, 86 on a rock shaft 82. One cam is larger and gives a longer stroke than the other, and selection is effected by the direction in which shaft 82 is worked, or by changing the handle 92 to an alternative and diametrically opposite socket in a boss on the shaft.