| 摘要 |
PROBLEM TO BE SOLVED: To reduce the occurrence of leakage, to suppress consumption of a piston ring, and to attain a high vacuum by arranging a seal in a piston ring groove. SOLUTION: A seal groove is formed in the surface, extending at right angles with the central line of the cylinder 1, of a piston ring groove and sealants 4 and 8, such as an O-ring, is inserted therein. When a piston 2 is moved downward, a piston ring 6 is pressed against the cylinder 1 side and the piston 2 is moved in such a state that a resistance force is exerted thereon, As a result, an O-ring 4 is compressed, and leakage through a gap between the piston ring 6 and the piston 2 is prevented from occurring by means of a seal 4. Reversely, when the piston 2 is moved upward, the piston ring 6 is pressed against a gap 7 and leakage is prevented from occurring by means of the O-ring 8. As a result, leakage from an upper vacuum chamber 13 to a lower vacuum chamber 9 amounts to a total of a gap 3→a gap 12→a gap 3 and a gap 3→a gap 10→a gap 3, and leakage through the inner surface of the piston ring does not occur and a high vacuum is generated.
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