| 摘要 |
PROBLEM TO BE SOLVED: To facilitate the fine operation of a lifted load by reducing a flow rate of a hydraulic actuator to the amount of operation of an operating lever in a crawler crane. SOLUTION: This control circuit switches a mode selector switch 14 to a fine hoist operation mode contact 15 side and switches a solenoid-operated directional control valve 10 to a position where a choke comprising passing resistances r1 and r2 is incorporated. Next, when an operating lever 2 is tilted to a windup side A, pressure oil from a pilot pump 7 passes through a remote control valve 3 to the solenoid-operated directional control valve 10 where the pressure of the pressure oil is distributed according the ratio of the passing resistance r1 to r2 before being delivered to a directional flow control valve 5. By this, the amount of opening of the directional flow control valve 5 can be suppressed. Thus, the pressure oil delivered.from a hydraulic pump 8 is flow-controlled by the directional flow control valve 5 to feed less oil to a hydraulic actuator 6, and the fine windup operation of a lifted load by the hydraulic actuator 6 can be performed.
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