Quarter turn actuators

A quarter turn actuator, comprising:

• a body defining two parallel spaced-apart cylinders at least partly coextensive with one another through said body,
• a transverse bore in said body which opens into each of said cylinders,
• a pair of pistons each formed of plastics material and arranged for reciprocating movement in a different one of said cylinders, each of said pistons having in its external circumferential surface said recess facing toward a transverse bore,
• at least one of said pistons being hollow defining a closed axial end face of said piston and an axial bore, the bottom of said axial bore being near said closed axial end face of the piston, said axial bore being open at the opposite end face of the piston,
• a rack embedded in a bottom wall of the recess on the external circumferential surface of each piston,
• a pinion mounted in said transverse bore in said body and engaging each of the racks embedded in said pistons for rotation in response to movement of said pistons in opposite directions,
• means for supplying compressed air to both said cylinders,
• biasing means seated in said axial bore of said at least one piston to contact the bottom of said axial bore and extending axially also to contact a part of said body facing said opposite end face of the piston for biasing the piston in a direction which causes said pinion to rotate in a desired direction in the absence of said compressed air, and
• an air distribution system interconnecting each end of each cylinder with the other end of the other cylinder for allowing said air supplying means to communicate with the interconnected ends of said cylinders in said body to enable movement of said pistons to rotate said pinion in a selected direction of rotation.