Balancing hoist

Claim 1

A BALANCING HOIST COMPRISING: A CASING CONTAINING A CYLINDRICAL BORE AND INCLUDING MEANS FOR MOUNTING THE CASING ON A SUPPORT WITH THE AXIS OF SAID BORE EXTENDING SUBSTANTIALLY HORIZONTALLY; A HOLLOW HOIST DRUM CONTAINED IN SAID CYLINDRICAL BORE FOR ROTATING IN IT AND MOVING AXIALLY ALONG IT; A HOISTING CABLE WRAPPED AROUND THE EXTERIOR OF SAID DRUM AND DEPENDING THROUGH AN OPENING IN SAID CASING; THE INNER SURFACE OF SAID DRUM BEING PROVIDED WITH AN INTERNAL FEMALE HELICAL THREAD; A BRACKET MOUNTED ON SAID CASING AND PROJECTING AXIALLY INTO SAID DRUM; A GROUP OF ROLLERS ROTATIVELY MOUNTED ON SAID BRACKET AND POSITIONED TO RIDE IN SAID HELICAL THREAD SO THAT SAID DRUM IS CAUSED TO ROTATE AS IT MOVES AXIALLY IN SAID BORE; A FIRST COVER FIXED ON AN END OF SAID BORE AND A SECOND COVER FIXED ON AN END OF SAID DRUM TO COOPERATE WITH THE WALLS OF SAID BORE TO FORM A CLOSED FLUID CHAMBER; MEANS FOR SUPPLYING PNEUMATIC PRESSURE TO SAID CHAMBER; MEANS FOR CONTROLLING AND VARYING THE PNEUMATIC PRESSURE IN SAID CHAMBER TO PROVIDE A SELECTED FORCE IN SAID CHAMBER SERVING TO BIAS SAID DRUM AXIALLY IN SAID BORE; SAID HELICAL THREAD BEING ARRANGED TO ROTATE IN ONE DIRECTION UNDER SAID FORCE; AND SAID HOISTING CABLE BEING WOUND ON SAID DRUM IN A DIRECTION SUCH THAT IT IS WOUND UP ON THE DRUM AS SAID DRUM ROTATES IN SAID ONE DIRECTION.