| 摘要 |
PURPOSE:To secure high controllability by putting aiding pressure, when an operating lever is operated beyond a dead zone, into sub-pilot chambers which are provided at a control valve. CONSTITUTION:A control valve 3 is provided with pilot chamber 3A, 3B and sub-pilot chambers 3a, 3b, and a hydraulic pump 7 is connected to pilot chambers 3A, 3B through solenoid-controlled pressure-reducing valves 5A, 5B and also connected to sub-pilot chambers 3a, 3b through a changeover valve 8, when an operating lever is operated beyond a dead zone, the changeover valve 8 is changed, and aiding pressure is added to sub-pilot chambers 3a, 3b. By this, pilot pressure through slow starting-up solenoid-controlled pressure- reducing valves 5A, 5B is aided, and a spool-stroke of the control valve 3 is adjusted in a wide area of lever operation, and consequently high controllability can be secured.
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