| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for cooling a hydraulic cylinder used under a high-temperature environment not by a water cooling system but by a working oil itself, and to prevent degradation of a seal member of the hydraulic cylinder. SOLUTION: A front cylinder chamber 11 of a double acting cylinder 1 is connected to a back cylinder chamber 12 via a bypass circuit 30 with a relief valve 32, a check valve 33 and an orifice 31 interposed in series. The cracking pressure of the relief valve 32 is set to be larger than the pressure in the front cylinder chamber 11 in the maximum load condition when a rod is retracted, and the check valve 33 is opened by opening the relief valve 32. At the retraction limit of a piston 3, the pressure of the front cylinder chamber 11 is larger than the cracking pressure of to open the relief valve 32, new working oil is fed to allow the whole or a part of the working oil in the front cylinder chamber 11 to flow out from the back cylinder chamber 12 to a discharge 26 side through the bypass circuit 30.
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