| 摘要 |
PROBLEM TO BE SOLVED: To attain reduction of working man-hours, reduction of a cost, and even improvement in strength of a piston rod in addition thereto, when an internal drain type lift cylinder is manufactured. SOLUTION: In the point of time when hydraulic oil, leaking from a hydraulic oil chamber 18 to a part 20 between two oil seals 15, 16 provided in a slide contact surface of a piston 5, reaches a prescribed accumulated pressure, for returning the leaking oil to the side of the operating chamber 18, a check valve 22 making the part 20 between these oil seals 15, 16 communicate with the hydraulic oil chamber 18 by a return oil path 21 provided in the piston 5 to have a relief function for this return oil path 21 is interposed.
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