GB166726A - Improved construction of hydraulic lifting or operating jack and like appliance - Google Patents

Abstract

166,726. Collis, L. A. April 26, 1920. Jacks. - In hvdraulic jacks, the passage connecting the ends of the cylinder contains a pair of valves and a piston, and the pump is connected to the passage between the two valves, the arrangement being such that, by moving the valves, the opening to the non-working end of the cylinder is reduced and the ram descends slowly. The invention is described as applied to a jack for raising the platform of a hand truck. The cylinder 3, which is of greater length than the stroke of the ram, is secured to a casting ing 2 fixed to the frame 1 of the truck, and the ram 5 is attached to the lifting platform 7. The ends of the cylinder are connected by a passage 8, 9 controlled by valves 10, 11 and a piston 20. The passage 14 connects the pump cylinder 13 to the passage 8, 9. The ball valve 10 has its seating in a plug 16 screwed into a hole in the casting 2 and is either spring-controlled or limited in its movement by a bar 15. A plug 18 is screwed into an enlargement of the hole in the casting and has a central hole of two diameters in the larger part of which is the piston 20 having grooved sides 28. The piston 20 is of two diameters and during raising of the platform has it smaller part opposite the holes 25 in the plug. The piston 20 is attached to a rod 21 having a head 24 which bears against a cam 42. The disc valve 11 is carried by a stem 26 slidably mounted in the piston. When the cam 42 is turned by depressing a pedal, the piston 20 is pressed in until the grooves 28 form the only means of communication between the passages 8, 9, and the valve 11 is opened. Towards the end of the movement of the piston 20, the stem 26 comes against the valve 10, and, forcing it off its seating, releases the fluid from the working end of the cylinder. The piston 20 is connected to a bell-crank lever mounted on the cylinder or casting 2 in the path of the platform at such a position that, when the ram reaches the end of its stroke, the lever will be rocked, and the piston 20 pressed in to release the fluid. As soon as the ram has descended a distance sufficient to release the lever, the piston 20 will be forced out by the spring 23, and the movement of the ram will stop. The plunger 12 of the pump 13 is provided with teeth 31 which mesh with a toothed sector 32 mounted on a casing 33. A toothed rod 34 passing through a gland 35 in the top of the casing 33 meshes with the sector 32 and is connected by a collar 36 to the operating- handle 37. The bent end 38 of the handle 37 is connected by a link 39 to a lug 40 on a ring 41 surrounding the gland 35.