GB899422A - Improvements in or relating to hydraulically operated lifting apparatus - Google Patents

Abstract

899,422. Platform elevators on vehicles. BRACEWELL (HYDRAULICS) Ltd., ALLAN. Aug. 1, 1958 [May 1, 1957; May 6, 1957], Nos. 13883/57 and 14343/57. Classes 78 (3) and 78 (4). In a guided-platform hoist, movement of the platform is effected by an hydraulic ram which is controlled by means responsive to the load on the platform, and the upper limit of travel of the platform is adjustable to any position within a predetermined range. In the embodiment shown in Fig. 1, on placing a load on a platform 10, the platform moves down it, relative to the piston 20 of an hydraulic lifting ram 22 against the action of a spring 16 and an arm 42 engages an abutment 40 on a control rod 30 to move the rod down, thereby operating a valve 52 through a lever 32 to allow fluid to pass to the ram 22. At the upper limit of travel of the platform, the arm 42 engages an adjustable abutment 44 on the control rod 30 which operates the valve 52 to allow fluid to pass back to the reservoir. On removing the load, the platform rises relative to piston 20 under the action of spring 16 and moves the control rod to bring the valve 52 into a third position to allow the platform to descend. In a second embodiment, Fig. 3, on placing a load on a platform 142, mounted on a plunger 140, the platform descends against the action of a spring 143 and the plunger 140 closes channels 138 thereby preventing hydraulic fluid from passing through the hollow piston 118 of a lifting ram 110 to the reservoir 112 and so causing the piston, together with the plunger 140 and platform, to rise. At the upper limit of travel, rubber blocks 158, on a striker ring 152 adjustably mounted on rods 148 which move with the piston, engage stops 150 and build-up of pressure under the piston 118 operates an overload release valve 166. On removing the load, the platform 142 and plunger 140 rise under the action of spring 143 allowing fluid to pass through the cylinder 118 and channels 138 and 160 to the reservoir, thereby allowing the piston and platform to descend.