| 摘要 |
PROBLEM TO BE SOLVED: To improve workability and operability by controlling the cylinder operating speed of at least part of hydraulic cylinders via pressure oil discharge quantity control, and providing a discharge quantity adjustment section on a pressure oil discharge path. SOLUTION: Discharge quantities of first and second main pumps 9, 10 are reduced by selecting the crane work mode with a work mode selector switch 37, thereby the pressure oil feed quantities to hydraulic actuators 14-18 are reduced. When a boom and an arm are operated to the descent side while the crane work mode is selected, the pilot pressures fed to boom and arm control valves 21, 22 and boom and arm descent preventing valves 40, 47 are reduced by third solenoid proportional pressure reducing valves 41, 48, thereby the discharging speed of the oil discharged into an oil tank 12 from a boom cylinder 16 and an arm cylinder 17 via the valves 21, 22, 40, 47 is slowed.
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