| 摘要 |
A reservoir chamber (13) is defined between the cylinder (1) and the sleeve (4), and a check valve (15) is provided on the path (14) communicating the reservoir chamber (13) with the pressure chamber (6). The check valve (15) closes the path (14) when pushing force is applied and the cylinder (1) and the rod (5) retract relative to each other, and thus the pushing force is buffered by hydraulic oil in the pressure chamber (6). A communicating path (16) communicating the pressure chamber (6) with the reservoir chamber (13) is formed in the rod (5), and a relief valve (18) is mounted in the communicating path (16) to keep the upper limit of the pressure in the pressure chamber (6) constant so that excessive tension is not applied by the rod (5) to the belt (41). A throttle (34) is provided on the outlet side of hydraulic oil of the relief valve (18). This keeps pressure difference between inlet and outlet of the hydraulic oil small when relief valve (18) opens, and thus prevents vibration of a valve body (23) of the relief valve (18).
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