| 摘要 |
PURPOSE:To enable an operating piston to return optionally to an original position, by connecting an alternating pressure chamber to a drained oil tank through a closable open passage. CONSTITUTION:When an alternating pressure chamber 2a is connected to a drained oil tank through a closable open passage 5, the pressure of the chamber 2a drops, a spool 2 is moved leftward by the remaining pressure of pressure oil in an oil feed passage 24, and the pressure of the passage 24 drops. The drop in the pressure of the passage 24 is detected by a pressure switch to restart a hydraulic pump to resume the feed of pressure oil. The pressure oil enters into constant pressure chambers 2b, 4b so that the pressure oil in the alternating pressure chamber 4a of a cylinder 3 is sent out to the drained oil tank. As a result, an operating piston 4 is moved and stopped in an original position.
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