| 摘要 |
In a cup seal, the hydraulic pressure in a first hydraulic chamber (6) causes a first seal portion (21e) of an outer lip portion (21c) to closely contact to a bottom wall (20a) of a recessed portion (20) and causes a second seal portion (21f) of a base portion (21a) to closely contact to a rear surface (20b) of the recessed portion (20). A double seal due to the first and second seal portions (21e) and (21f) reliably prevents the leakage of a brake fluid from the first hydraulic chamber (6). If the pressure becomes negative in the first hydraulic chamber (6), the tip portion of the outer lip portion (21c) deflects inward and the outer peripheral end of the base portion (21a) deflects forward. Therefore, the brake fluid in the reservoir flows into the first hydraulic chamber (6) through the gaps among the second and first seal portions (21f), (21e) and the wall surface of the recessed portion (20) to maintain fluid-feeding performance.
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