| 摘要 |
PROBLEM TO BE SOLVED: To reliably maintain a drive piston 4 at a top dead center position before the pressure of compressed air fed in a drive cylinder 2 is sufficiently large irrespective of the operating speed of a main valve. SOLUTION: A downwardly directed cylindrical part 14 and a piston stop 6 with a recessed part 15 formed on the inner side of the cylindrical part 14 are disposed on an upper end part of the drive cylinder 2, a boss part 16 protruded from an upper surface of the drive piston 4 is stored in the recessed part 15, a lower end face of the cylindrical part 14 is tightly sealed with an upper face of the drive piston 4 to demarcate an outer circumferential side of the cylindrical part 14 from the inner side thereof, and the compressed air fed in the drive cylinder 2 is applied to the outer circumferential surface of the cylindrical part 14 to maintain the boss part 16 stored in the recessed part 15.
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