Pressure:operated rotary drive unit - has pistons with racks and antifriction components bearing against cylinder walls

摘要

The pressure-operated rotary drive unit has a cylinder containing two pistons (20), each with an integral rack (19). The portion of each piston containing the rack supports one or more components (24) of elastomer or synthetic resin having a low coefficient of friction. This bears against the adjacent portion of the cylinder wall (10), thus counteracting any tendency for the rack to move away from the pinion (18) or each other, as the pistons move together or apart. The components can be accommodated in grooves in the pistons and from which they protrude, situated in portions of the pistons curved to match the adjacent cylinder wall.