| 摘要 |
PURPOSE:To return sticking of a control valve-spool to a normal state in a short time by adding a hydraulic actuator for shearing a chip, which is operated on judging that a valve gets out of order and independent of control valve driving force. CONSTITUTION:There is provided an actuator for shearing a chip, which is connected to a hydraulic power source and adapted to operate a control valve spool 5. Further there are provided a position sensor 7 for the control valve- spool 5 driven in response to an input signal and a valve sticking decision device 3 adapted to compare output of the position sensor 7 with an input signal and generate an output signal when both do not correspond to each other. Further an output signal of the valve sticking decision device 3 is conducted to a control valve 2 to operate a chip shearing actuator 1 at the time of sticking of the control valve-spool 5. In this arrangement, sticking of the control valve-spool 5 can be returned to a normal state in a short time.
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