Pneumatic actuator

Claim 1

A pneumatic actuator having a controllable rate of displacement comprising: a. a body having fixed concentric tubular members defining an axially extending annular pneumatic chamber and a central hydraulic chamber adapted to contain hydraulic fluid; b. a sleeve engaged over the inner tubular member for axial sliding movement thereon, and having, at one end, an annular pneumatic piston operatively engaged with the pneumatic chamber, and, at the other end, means for attachment to a device to be actuated; c. means on the body to selectively introduce motive gas into the pneumatic chamber on either side of the pneumatic piston for selectively moving the sleeve in opposite directions between terminal axial positions; d. a control rod extending axially into the hydraulic chamber and having attached thereto an hydraulic piston operatively engaged with the hydraulic chamber; e. coupling means between the control rod and the sleeve for causing both the rod and the sleeve to move together as a unit during at least a portion of the movement in either direction of the sleeve between its terminal axial positions; f. hydraulic conduit means interconnecting the opposite sides of the hydraulic piston for effecting transfer of hydraulic fluid in the hydraulic chamber from one end to the other upon movement therein of the hydraulic piston; g. a control valve in the conduit means establishing a constriction for controlling the rate of flow of hydraulic fluid therein; h. relief means, effective when the sleeve and rod move as a unit in one direction only, for effecting the transfer of hydraulic fluid from one end of the hydraulic cylinder to the other independently of the control valve; and i. a boss on the end of the sleeve opposite the pneumatic piston, which boss has an axially directed aperture through which the control rod freely passes and extends beyond the boss, the coupling means comprising the free end of the boss and a stop on the rod located beyond the boss.