| 摘要 |
PURPOSE:To reduce a shock by communicating a secondary pressure chamber with the first adjustment chamber through two oil passages, and closing one of the oil passages with the movement in such an direction as enlarging the volume of the first adjustment chamber of a free piston. CONSTITUTION:The first adjustment chamber 39 is demarcated from the second adjustment chamber 40 by slidably engaging a free piston 38 between a casing C and the outer periphery of a relief housing 30. A secondary pressure chamber 8 is communicated with the first adjustment chamber 39 through the first and the second oil passages 43, 44. The second oil passage 44 is so constructed as to be closed when the free piston 38 is moved in such a direction as enlarging the volume of the first adjustment chamber 39. Accordingly, the preset pressure of a cross over type relief valve can be changed through three steps like firstly from a low pressure, secondly to a middle pressure, and at last to a high pressure, so that a shock becomes less than that of the conventional device in which the pressure changes all at once from a low pressure to a high pressure.
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