Hoist and balancing apparatus

Claim 1

In a balancing hoist having a pneumatic control system, a hoist, means in said hoist for supporting a cable extending from said hoist adapted to be reeled into and out of said hoist to raise or lower a load attached to the end of said cable, said means comprising an expansible pressure chamber and a piston in said chamber, said chamber being adapted to receive fluid under pressure and said piston being adapted to be moved in one direction upon an increase in pressure in said expansible chamber and in the other direction upon a decrease in pressure in said expansible chamber; a source of fluid under pressure; a first fluid line connecting said source of fluid to said expansible chamber; a pilot pressure controlled main control valve in said first fluid line; a second fluid line between said source of fluid pressure and the inlet of a pilot pressure regulator; a third fluid line connecting the outlet of said pilot pressure regulator with the pilot section of said main control valve for supply of pilot pressure thereto; a fourth fluid line comprising a vent line connected to said pilot pressure regulator; a vent control means connected to the other end of said vent line, said vent control means having at least two positions selectively connectable to said vent line for venting said vent line at rates different from each other, and a third position for blocking said vent line, each of said positions applying a pilot pressure control signal to said pilot pressure regulator of different magnitudes for transmission to said main control valve to thereby selectively vary the pressure supplied to said expansible chamber by said main control valve; said vent control means including a housing having a first body portion secured to said vent line, said first body portion having a pilot pressure inlet orifice aligned and in communication with said vent line, a second body portion secured to said first body portion and rotatable relative thereto, said second body portion having angularly spaced vent means selectively adaptable to be aligned with said pilot pressure inlet orifice of said first body portion in a first and a second position, said second body portion being rotatable to a third position in which neither of said vent means of said second body portion will be aligned with said pilot pressure inlet orifice of said first body portion, said second body portion being provided with means to normally limit rotation of said second body portion relative to said first body portion between said first and second positions and to lock said second body portion in said third position, the improvement comprising said last mentioned means comprising a pin carried within said second body portion; a curvilinear slot provided in said first body portion, biasing means carried by said second body portion for urging said pin into engagement with said curvilinear slot when said second body portion is in either said firSt or second position, said curvilinear slot being entirely enclosed by said body portions whereby said pin is entirely enclosed by said body portions, said curvilinear slot having an angular dimension corresponding to the angular spacing between said vent means, said pin being provided with means for moving said pin out of said curvilinear slot for rotation of said second body portion to said third position in which neither of said vent means is aligned with said pilot pressure inlet orifice in said first body portion to thereby block fluid flow through said vent control means; and a recess within said first body portion and arcuately spaced from said curvilinear slot, said recess receiving said pin when said second body portion is moved to said third position to lock said second body portion in said third position, said biasing means urging said pin into said recess when said second body is in said third position.