| 摘要 |
PURPOSE:To improve safety of the circuit in the caption by reducing the relief pressure of discharge oil from a pilot pump with an operation lever set in the neutral position. CONSTITUTION:A variable relief valve 21 is connected to the discharge line 3a of a pilot pump 3, while a switching valve 20 is connected to an operation lever 7, and then the vent port of the variable relief valve 21 is connected to a tank via the switching valve 20. Accordingly, with the operation lever 7 set in the neutral position, the switching valve 20 is opened so that the vent port of the variable relief valve 21 is connected to the tank, thereby reducing the relief pressure of discharge oil from the pilot pump 3. Therefore, with the operation lever 7 set in the neutral position, it is possible to securely prevent a control valve 4 from generating mis-operation caused by the sticks or the like of solenoid valves 5a-5c, 6a-6c due to noise, interference, dust and etc., so as to improve safety.
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