| 摘要 |
PURPOSE:To perform secure dust-proofing and elongate the lifetimes of devices inside a case by independently performing respective two-stage operations in one case that the pressure of a little quantity of air is exhausted and in the other case that the pressure of large quantity of air is exhausted. CONSTITUTION:A check valve body 10 is provided in the exhaust port 9 of a case 1 and a dust cover 3 in such a way as to be always pressed against the opening seat 7 of the exhaust port 9 by means of a coil spring 4. When a little quantity of air is exhausted in the normal state, all the air quantity to be exhausted is exhausted from a small slot 2 formed in the check valve body 10. Meanwhile, when a large quantity of air is exhausted in the drive state, the check valve body 10 is lowered to be opened by the balance action between the tension of the coil spring 4 and force caused by an exhaust back pressure.
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