| 摘要 |
PROBLEM TO BE SOLVED: To moderate a peak pressure in a simple form by providing a hydraulic cooler in a return oil circuit from a hydraulic actuator to a tank and a first relief valve in parallel with this, and providing a second relief valve upstream of the first valve. SOLUTION: A hydraulic cooler 5 is provided in a return circuit 10, a first bypass circuit 6 is provided in parallel with this, and a first relief valve 7 is provided in the circuit 6. The cooler 5 and the circuit 6 are branched and interconnected at a point 10a on the circuit 10, a second bypass circuit 11 is branched and connected to a point 10b upstream of the point 10a near the outlet of an operation valve 3 on the circuit 10, and a second relief valve 12 is provided for this. The valve 12 is disposed upstream of the valve 7 by a pipe length L between the point 10a and the point 10b. A peak pressure generated by an operation of an actuator 2 transfers through the circuit 10 via the operation valve 3, is moderated by the valves 7 and 12, and is applied to the cooler 5. The peak pressure moderated by the valve 12 consumes energy for volume change of hydraulic fluid while it progresses through a piping 10c with a length L, and damped.
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