Abstract: A quarter turn actuator comprises a body (10) defining side-by-side cylinders (11 and 12), a piston (13) in each cylinder having in one side thereof a recess in which is provided a rack (15), a pinion (16) mounted in the body and engaging the racks on the pistons, a source for supplying compressed air to the cylinders and an air distribution system interconnecting each end of each cylinder with the other end of the other cylinder. The body (10) is preferably molded of plastic material and the cylinders are lined. The pistons may also be molded plastic material.