GB1040299A - Improvements in or relating to fluid pressure operated devices - Google Patents

Abstract

1,040,299. Pneumatic hoists; load balancing. GLOBE PNEUMATIC ENGINEERING CO. Ltd. Oct. 22, 1963 [Oct. 23, 1962], No. 39993/62, Headings B8B and B8H. A pneumatic hoist is so arranged that when a load is held suspended it may be easily and repeatedly adjusted vertically within the lifting range of the hoist by upward or downward manual force exerted directly on the load by an operator. As shown the hoist comprises a piston 1, with a piston rod 2, slidable in a cylinder D. A further piston 4 slides in a cylinder 3 and has a spring 5 so rated that the piston 4 will not rise to its upper limit unless the hoist is loaded beyond its lifting capacity. To lift a load it is attached to a hook 2a and a control handle 47a pulled to depress a spool valve R in a device B to connect pressure air from a duct 20 via a restrictor 48, spool valve R, duet 51, spool valve L and duct 52 to below the piston 1 in the cylinder D. At the same time a chamber 24 in a device C is connected to the atmosphere via port 28, port 50, spool valve R, duct 53 and restrictor 54. A clamp 23 on the piston 4 is thus released, assumes a position determined by the load and the spring 5, and in so doing adjusts the position of a valve 9 in a pressure regulating device A via a lever 8a, a plunger 8, a spring 10 and a diaphragm 14. A pressure P2 is thus transmitted to both sides of a diaphragm 32 in the device B. On release of handle 47a spool valve R1 rises and the load ceases to rise, being held stationary by the pressure P2 transmitted from port 12 of device A. Mains pressure is again transmitted to part 28 to force clamping block 23 against the piston 4. This balanced state is shown in Fig. 3. From this condition if an operator applies a manual downward force on the load the resulting increase in pressure below the piston 1 is transmitted via port 52, spool valve L, duct 51, spool valve R, port 39 and duct 40 to a chamber 33 forcing the diaphragm 32 off a port 31 allowing some air to escape past a ball-valve 25 through an exhaust port 30 to the atmosphere. Releasing the manual pressure allows the condition of balance to be resumed at the new position. If, however, an upward manual pressure is applied to the load the pressure below the piston 1 falls, a ball valve 37 opens allowing extra pressure air into the system so that on release of the manual pressure the condition of balance is resumed.