| 摘要 |
A hydraulic jack comprises a base having a vertically disposed cylindrical member attached thereto. A cylindrical movable member is mounted on the fixed member and is vertically movable relative thereto. The base is provided with passages therethrough which are connected in communicating relation to a source of fluid under pressure, such as a reservoir and pump. The fixed and movable members define a pair of variable chambers, each of which is connected in communicating relation with one of the passages by a restricted orifice to reduce the flow of fluid to and from the chambers. When one of the chambers is pressurized, the movable member is raised and will support a load engaged thereby. When the other chamber is pressurized, the movable member is lowered. Fluid in the chambers is prevented from returning to the reservoir by valve elements. A valve actuator is operated by fluid pressure and selectively opens each passage to permit the return of fluid to the reservoir. Relief valves permit the escape of fluid from each chamber when a predetermined pressure is exceeded because of thermal expansion, or excess load.
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