Air operated load balancing hoist

Claim 1

An air pressure hoist having a load balancing capability, said hoist comprising: an air cylinder closed at both ends, except for a centrally disposed opening in one of its ends, said cylinder having means to support it from a structure; a piston reciprocable in said cylinder, said piston having a rod extending from one side thereof through said opening in the one end of the cylinder, to reciprocate with said piston; an air inlet passage in one end of said cylinder; at least two first sprocket means, said first sprocket means being rotatably disposed upon a portion of the piston rod which, when the rod is reciprocated with the piston, does not pass in and out of the cylinder; second sprocket means, said second sprocket means being rotatably disposed at a fixed location adjacent the outside of the one end of the cylinder having the centrally disposed opening therethrough; chain means, one end of said chain means being anchored fixedly in the vicinity of a side of the outside of said one end of the cylinder having the opening therethrough, said chain means extending from its anchor point around one of said first sprocket means, back toward and around said second sprocket means, again back toward and around the other of said first sprocket means and downwardly below said cylinder to terminate in a depending end; air control valve means, said valve means comprising an inner elongated cylindrical body and an outer sleeve slidable relative to said body, said body being secured at its upper end to the depending end of said chain to itself depend from the chain and further being disposed along a vertical axis, the lower end of said body being provided with means to carry a load; said sleeve having an air inlet port, an air outlet port and an air bleed passage to the atmosphere, said air inlet port being in communication with a source of air under pressure; said air outlet port being in communication with the air inlet passage in said one end of said cylinder; said body having air passage means whereby, when said sleeve is shifted upwardly relative to said body to a first position, said air inlet port in the sleeve is placed in communication with its air outlet port, thereby delivering air to the cylinder to drive its piston toward that end of the cylinder with the centrally disposed opening, and through the movement of the piston rod and its carrying the said first sprocket means and chain means away from the last said cylinder end, raising the dependent end of the chain means, the air control valve means and any load carried by the means to carry such load; and when said sleeve is shifted downwardly relative to said body to a second position, said air outlet port is placed in communication with said bleed passage, thereby to remove air pressure from the cylinder so that the piston may be forced back by the weight of the load on the dependent end of the chain, acting upon the first and second sprocket means, towards the opposite end of the cylinder from that having the central opening; and spring means in said air control valve to bias said sleeve to a third position intermediate said first and second positions.