| 摘要 |
PROBLEM TO BE SOLVED: To prevent wear caused by the movement of a backup ring of a double seal and to dispense with retrieving the oil to a drain chamber. SOLUTION: A rod seal 33 and backup ring 34 are accommodated in an internal circumferential groove 32 at a rod guide 23 of a hydraulic cylinder 22 to form a double seal on the high pressure side, an oil seal 24 is provided on the low pressure side, and between them an oil sump 31 is formed. The oil sump 31 communicates with a part of groove 32 on its cylinder 2 side via oil paths 37 and 38, and the path 37 is provided with a check valve. When the pressure of the oil passed through the rod seal 33 and stored in the oil sump 31 becomes higher than the internal pressure of the cylinder 2, the check valve is opened to cause the oil to flow into the groove 32. The backup ring 34 is pressed always toward the upper guide 27 by the internal pressure of the cylinder 2 or oil sump 31 and is free from risk of moving. Because the oil in the oil sump 31 is returned to the cylinder 2, a drain chamber is not necessary.
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