| 摘要 |
PROBLEM TO BE SOLVED: To secure a flow amount of pressure oil to be supplied to respective actuators in a hydraulic driving device even in the case where load pressure of the actuator related to an upstream side directional changeover valve is high, while the load pressure of the actuator in related to a downstream side directional changeover valve is low. SOLUTION: A parallel passage 22 branched from a discharge passage 2a of a hydraulic pump 2 is connected to a downstream side of a check valve 23b on a flow passage connected to a supply port of a directional changeover valve 4b, as a passage for supplying pressure oil to the downstream side directional changeover valve 4b, other than a center bypass passage 7 for tandem- connection. The parallel passage 22 is then parallely connected to an upstream side directional changeover valve 4a. A pressure control valve 8 for controlling pressure difference across the directional changeover valve 4a is arranged on the parallel passage 22, as an auxiliary control valve for controlling a flow amount of the pressure oil passing through the parallel passage 22 according to an operation rate of an operation lever 6y for controlling the downstream side directional changeover valve 4b.
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