Abstract: A proportional control pneumatic cylinder as an air actuator device for a hydraulic pump valve having a valve spool moving in a bore in a valve housing. The device having an actuator housing attachable to the valve housing and having a bore carrying a piston coaxially secured to an end of the valve spool. The device provided with spaced openings in the actuator housing which communicate with the bore therein to introduce air to act on opposite sides of the piston, and factory pretensioned biasing means for normally urging the piston and spool to a center closed position. Surface areas on opposite sides of the piston are approximately equal so that piston movement is approximately proportional to movement of an actuating lever of an air supplying pneumatic control valve over the majority of the range of travel of the actuating lever for both raised and lowered positions.

Abstract: A three position fluid powered actuator including a cylinder having a first end, a second end and an intermediate plate, the first end and intermediate plate having coaxial openings therein, a piston reciprocally positioned within the cylinder between the second end and the intermediate plate, a piston rod affixed to the cylinder and sealably and slidably received in the opening in said first end. The piston rod has a reduced diameter portion between said cylinder first end and the intermediate plate. Positioned on the reduced diameter portion of the piston rod is a pair of spring followers each abutting against the shoulder formed at each end of the intermediate portion and between the followers is a compressed spring. When fluid pressure is applied to the cylinder to either side of the piston, the piston is moved, compressing the spring. When the fluid pressure is removed, the spring returns the piston to the intermediate position.