| 摘要 |
PURPOSE:To make it possible to change-over the pressure of low pressure oil into a high pressure with no use of an electrically control means, by providing such an arrangement that a flow passage switching device automatically actuates a ram means to highly pressurize the latter when low pressure oil for moving a hydraulic piston to a position just before a clamping position is filled and the supply of the low pressure oil is stopped. CONSTITUTION:When low pressure oil is fed from a port 22 communicated with a hydraulic pressure source S, the low pressure oil is filled in the right side chamber 21b of a cylinder 21 and in the inside of a plunger 25 so that the plunger 25 reaches the left side position. Then, the low pressure oil flows into a cylinder chamber 12, and is fed to a predetermined clamping means. When the low pressure oil is filled in the predetermined clamping means, the feed thereof is automatically stooped, and an urging means 40 which has been contracted, pushes the plunger 25 toward its original position. The low pressure oil in the right side chamber 21b flows into the left side chamber 21a of the cylinder 21 through a choke 31 so that the plunger 25 is pushed back to its original position, and therefore, a port 23 is communicated with the port 22. At this stage the low pressure oil pushes out a ram means 13 so that the low pressure oil filled in the cylinder chamber 12 is gradually increased in its pressure, and then acts on a hydraulic clamping means to apply a predetermined clamping force to a workpiece.
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