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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

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.

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1. A proportional control pneumatic cylinder comprising: a housing having a bore provided therein that includes first and second portions having different diameters, a first port that communicates with the first portion of the bore, and a second port that communicates with the second portion of the

1. A proportional control pneumatic cylinder comprising: a housing having a bore provided therein that includes first and second portions having different diameters, a first port that communicates with the first portion of the bore, and a second port that communicates with the second portion of the bore;a piston disposed within the housing and defining first and second air spaces within the first and second portions of the bore, respectively, of the housing, the piston having a first surface area that is exposed to the first air space, the piston having a second surface area that is exposed to the second air space and that is approximately equal to the first surface area, the piston being movable relative to the housing between a first position, a second position, and a center position located between the first and second positions; anda mechanism biasing the piston in the center position. 2. The proportional control pneumatic cylinder defined in claim 1 wherein the first surface area and the second surface area differ by no more than 5%. 3. The proportional control pneumatic cylinder defined in claim 1 wherein the first surface area and the second surface area differ by no more than 33%. 4. The proportional control pneumatic cylinder defined in claim 1 wherein the first surface area and the second surface area have different shapes. 5. The proportional control pneumatic cylinder defined in claim 1 wherein the first surface area is generally circular in shape and the second surface area is generally annular in shape. 6. The proportional control pneumatic cylinder defined in claim 1 wherein the mechanism biasing the piston in the center position includes a spring that is disposed about the piston and within the housing. 7. The proportional control pneumatic cylinder defined in claim 1 wherein the mechanism biasing the piston in the center position includes a spring that reacts between the piston and the housing when the piston is moved from the center position. 8. The proportional control pneumatic cylinder defined in claim 1 further including a source of pressurized air that selectively communicates with the first and second ports through a pneumatic control valve that is operated by a control lever, and wherein movement of the piston is approximately proportional to movement of the control lever. 9. The proportional control pneumatic cylinder defined in claim 1 further including a source of pressurized air that selectively communicates with the first and second ports through a pneumatic control valve that is operated by a control lever such that movement of the control lever in a first direction causes movement of the piston in a first direction and movement of the control lever in a second direction causes movement of the piston in a second direction, and wherein movement of the piston in both the first and second directions is approximately proportional to movement of an actuating lever in both the first and second directions. 10. The proportional control pneumatic cylinder defined in claim 1 wherein the housing includes a first housing portion and a second housing portion, and wherein the mechanism biasing the piston in the center position includes a spring that is reacts between the piston and the first and second housing portions when the piston is moved from the center position. 11. A combined hydraulic pump valve and proportional control pneumatic cylinder comprising: a hydraulic pump valve including a valve housing supporting a hydraulic valve associated with a hydraulic pump, the hydraulic valve including a valve spool that is movable between a first position, a second position, and a center position located between the first and second positions for controlling the operation of the hydraulic pump; anda proportional control pneumatic cylinder including a cylinder housing having a bore provided therein that includes first and second portions having different diameters, a first port that communicates with the first portion of the bore, and a second port that communicates with the second portion of the bore; a piston connected for movement with the valve spool and disposed within the cylinder housing and defining first and second air spaces within the first and second portions of the bore, respectively, of the cylinder housing, the piston having a first surface area that is exposed to the first air space, the piston having a second surface area that is exposed to the second air space and that is approximately equal to the first surface area, the piston being movable relative to the cylinder housing between a first position, a second position, and a center position located between the first and second positions; and a mechanism biasing the piston in the center position. 12. The combined hydraulic pump valve and proportional control pneumatic cylinder defined in claim 11 wherein the first surface area and the second surface area differ by no more than 5%. 13. The combined hydraulic pump valve and proportional control pneumatic cylinder defined in claim 11 wherein the first surface area and the second surface area differ by no more than 33%. 14. The combined hydraulic pump valve and proportional control pneumatic cylinder defined in claim 11 wherein the first surface area and the second surface area have different shapes. 15. The combined hydraulic pump valve and proportional control pneumatic cylinder defined in claim 11 wherein the first surface area is generally circular in shape and the second surface area is generally annular in shape. 16. The combined hydraulic pump valve and proportional control pneumatic cylinder defined in claim 11 wherein the mechanism biasing the piston in the center position includes a spring that is disposed about the piston and within the cylinder housing. 17. The combined hydraulic pump valve and proportional control pneumatic cylinder defined in claim 11 wherein the mechanism biasing the piston in the center position includes a spring that is reacts between the piston and within the cylinder housing when the piston is moved from the center position. 18. The combined hydraulic pump valve and proportional control pneumatic cylinder defined in claim 11 further including a source of pressurized air that selectively communicates with the first and second ports through a pneumatic control valve that is operated by a control lever, and wherein movement of the piston is approximately proportional to movement of an actuating lever. 19. The combined hydraulic pump valve and proportional control pneumatic cylinder defined in claim 11 further including a source of pressurized air that selectively communicates with the first and second ports through a pneumatic control valve that is operated by a control lever such that movement of the control lever in a first direction causes movement of the piston in a first direction and movement of the control lever in a second direction causes movement of the piston in a second direction, and wherein movement of the piston in both the first and second directions is approximately proportional to movement of an actuating lever in both the first and second directions. 20. The combined hydraulic pump valve and proportional control pneumatic cylinder defined in claim 11 wherein the housing includes a first housing portion and a second housing portion, and wherein the mechanism biasing the piston in the center position includes a spring that is reacts between the piston and the first and second housing portions when the piston is moved from the center position.