| 摘要 |
A hydraulic actuator has a housing, a piston drive chamber in the housing, a fluid inlet into the chamber, and a piston reciprocable in the drive chamber. The piston has diametrical steps exposed to fluid under pressure to cycle the piston. A sleeve spaced from and surrounds over a length of the piston to define a return chamber therebetween. The housing has first and second seats. The first seat and a first surface of the sleeve define an exhaust valve, which has an exhaust port, for the return chamber. The exhaust port is opened and closed by reciprocating the sleeve. The second seat and a second surface of the sleeve an inlet valve for the return chamber. Reciprocating the sleeve opens and closes the return chamber to the drive chamber. The housing also has a bore through which a portion of the sleeve reciprocates to close the exhaust valve and seal the drive chamber. The piston and the sleeve are configured so that they interact hydraulically during cycling to generate hydraulic pressure changes in the return chamber. This reciprocates the sleeve between the exhaust valve and the return chamber inlet valve to cycle the piston. The piston/sleeve configuration also hydraulically cushions the piston as it travels toward the exhaust valve.
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