| 摘要 |
Arranged on a side of a first pump are a flow control valve for controlling a first boom cylinder, a flow control valve for an arm, said flow control valve being connected in tandem with said flow control valve and being adapted to control an arm cylinder, and a flow control valve for a second boom, said flow control valve being connected to a downstream side of the flow control valve and being adapted to control a second boom cylinder. On a side of a second pump, an additional flow control valve for the arm, said additional flow control valve being adapted to control the arm cylinder, an additional flow control valve for controlling the first boom cylinder, and a reserve flow control valve for controlling an attachment-driving actuator are connected in parallel with each other, and a shuttle valve is also arranged to output a pilot pressure, which is normally used to change over the flow control valve for the second boom, to the flow control valve for the arm, whereby the flow control valve for the arm is changed over to permit feeding hydraulic pressure from the first pump to the flow control valve for the second boom.
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