GB492716A - Improvements in or relating to hydraulic jacks - Google Patents

Abstract

492,716. Fluid-pressure jacks. UTZ, H. March 23, 1937, No. 8568. [Class 78 (iii)] In a hydraulic jack of the kind comprising a combined jack cylinder and pump unit, the pump piston or a member connected thereto operates a check-valve when in its most advanced position to release fluid from the jack cylinder and allow it to pass to the reservoir through a passage formed in the piston or piston rod, the passage having one end terminating just behind the pressure surface of the piston and its other end connecting with the reservoir when the piston is in its most advanced position. In the embodiment shown in Fig. 1, the jack member 4 is actuated by means of a pump comprising a piston 5 and cylinder 2 mounted in a reservoir 1, the piston being operated by a lever 9. When it is desired to lower the jack, the piston 5 is depressed to its lowest position whereby a projection 13 opens a check-valve 11 to permit liquid to return through a chamber 14 communicating with a recess 12 which comprises a flat formed on the piston and is connected with the interior of the reservoir. A passage 16 in the piston connects the reservoir with the atmosphere when the piston is depressed to its lowest position. To prevent accidental release of the liquid during the lifting operation, the handle 15 which may be attached by either of its ends to the lever 9, is provided at one end with a collar which engages the top of the reservoir to prevent the piston being fully depressed until the handle is reversed. Instead of the recess 12, a channel may be bored in the piston. Alternatively, the channel may be provided by having the piston mounted on a rod of smaller diameter. The load-engaging means on the jack comprises a bracket, Fig. 4, clamped round the body of the jack and comprising a channel part 20 which engages beneath a downwardly projecting edge on, for example, the chassis of a vehicle to be lifted.