Patent ID: 7134644

Claim:
A compressed air balancer for raising, holding and lowering a load, comprising a cable drum which is rotatable and displaceable along its axis of rotation for rolling up and unrolling a cable holding the load, a housing which includes a cylindrical casing and two end closure covers, a piston which is subjected to the effect of gas pressure and which is displaceable axially in the housing; and a ball thread transmission which includes a ball rolling spindle and a ball nut and which converts an axial movement of the piston into a rotary movement and axial movement of the cable drum, characterized in that an external running surface of the piston is formed by an internal surface of a tube which is fitted in the form of an internal sleeve into the cylindrical casing and that provided between the tube and the piston is at least one external piston ring which is subjected to the effect of gas pressure from an inside of the piston ring to reduce friction between the piston ring and internal surface of the tube.