| 摘要 |
PROBLEM TO BE SOLVED: To prevent the generation of an impacting sound between a piston and a back flow check valve in the case there is an air reservoir in a pipe on a downstream side of a drainage pin inserting the back flow check valve in a narrow diameter section of the piston from the outside. SOLUTION: A relief passage 25 based on a slight difference in diameters between a back flow check valve 22 inserted in a narrow diameter section 17 of a piston 18 from the outside and a water seal section 26 connected to the relief passage 25 and capable of varying area with the movement of the back flow check valve 22 are formed between both of them, the back flow check valve 22 is slowly closed by the effect of damper while releasing water in the water seal section 26 from the relief passage 25, and the generation of the impacting sound can be prevented.
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