| 摘要 |
PROBLEM TO BE SOLVED: To provide the hydraulic circuit for operating a working machine of a hydraulic excavator capable of automatically changing over from speed-up to ordinary speed of a specific actuator and vice versa to improve operability, and improving workability at composite operation of the specific actuator and the other actuator. SOLUTION: This hydraulic circuit comprises a second directional changeover valve 18 connected to a second pump 4 through a confluent changeover valve 5, a second actuator 19 controlled by the second directional changeover valve 18, and other operation detecting sensors 21, 22 detecting the second actuator 19 being operated. A controller 15 is provided, which outputs a command to an electromagnetic changeover valve 7 to connect the pilot pressure receiving part 5a of the confluent changeover valve 5 with one pilot conduit 2a of a first directional change over valve 2, when the detected signal of the other operation detecting sensors 21, 22 is not input, and outputs a command to the electrimagnetic changeover valve 7 to connect the pilot pressure receiving part 5a of the confluent changeover valve 5 to a tank 25 only while the detected signal is input, when either of the other operation detecting sensors 21, 22 is input.
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