Low the friction which is used low for the frictional follow-up seal null

摘要

PROBLEM TO BE SOLVED: To effectively prevent gas leakage between a rod and an through-hole while reducing the manufacturing cost by mitigating the requirement of the concentricity and parallelism between the rod 11 of a free piston 1 and the through-hole 22 in a driving piston 2. SOLUTION: A circumferential groove 23 is provided in the through-hole 22 in the driving piston 2, and the low friction follow-up seal 4 formed by stacking thin-plate disks 41 is incorporated in the circular groove so that, if the concentricity and the parallelism between the rod 11 and the through hole 22 are deviated to some extent, the sealability between the low friction follow-up seal and the outer circumferential surface of the rod 11 can be secured. This constitution can thus mitigate the requirement of the concentricity and the parallelism between the rod 11 and the through-hole 22 to greatly reduce the manufacturing cost while effectively preventing gas leakage.