| 摘要 |
PROBLEM TO BE SOLVED: To prevent the return of a hydraulic oil into an oil tank by comprising the spring force of the magnitude enough for keeping a state that a return valve closes a return oil passage. SOLUTION: A release lever 39 is free from the control, and pressed to a stopper 41 for pushing a compression spring 40 upwardly and a return valve 38 in the opening direction. The return valve seat force is applied to a steel ball 38B, and the return valve seat force is higher than the spring force of the compression spring 40. The compression spring 40 is compressed between the release lever 39 and a push pin 38C integrally formed on the steel ball 38B. As a return oil passage 35 and an oil passage 37 are closed by the return valve 38, the internal pressure in a cylinder chamber 20 is surely increased to the pressure for operating a high pressure control valve 36. When the terminal processing work is terminated, the high pressure control valve 36 is operated, the internal pressure in the cylinder chamber 20 is suddenly lowered, and the return valve seat force becomes smaller than the spring force of the compression spring 40.
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