| 摘要 |
A pilot operated, control valve providing for two speed operation of a hydraulic jack in a first direction, the control valve including centering spring means for resisting movement of its spool in either direction and additional spring means for resisting movement of the spool in the first direction in order to establish two operating positions of the spool corresponding to the two speeds of operation for the jack, the first operating speed being accomplished by communicating the rod end of the jack with a drain and simultaneously communicating a source of fluid under the pressure with a head end of the jack, the second operating speed being accomplished by communicating both ends of the jack with the pump, a pilot valve being manually operable to regulate the control valve and having first and second springs to indicate the operating position of the control valve spool and the corresponding speed of operation for the jack in the first direction.
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