| 摘要 |
PURPOSE:To improve reliability by providing the first orifice, having a predetermined flow quantity area, to be arranged in the second oil path while the second orifice, having a flow path area smaller than this predetermined flow quantity area, to be arranged in a flow path reaching a drain circuit from the second solenoid valve. CONSTITUTION:When both the first and second solenoid valves 151, 152 are turned off causing a trouble and improper operation, working fluid is supplied to a cylinder chamber 53 in a head side through the first orifice 61 and discharged to a drain side from the cylinder chamber 53 through the second orifice 62. Here because the first orifice 61 forms its flow path area A1 larger than a flow path area A2 of the second orifice 62, by suitably setting both the flow path areas, a pressure of oil in the cylinder chamber 53 in the head side can be set to an arbitrary value. Consequently, in case of turning off both the solenoid valves 151, 152, when the flow path areas A1, A2 are set in a manner wherein a pressure of oil is obtained so as to move a servo cylinder slowly in either one direction, a fail safe function operates.
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