| 摘要 |
PURPOSE:To prevent a seal member such as a piston ring or the like from being worn and damaged, by providing a slide contact force limiting mechanism for allowing the slide contact force against the opposing surface to be substantially zero when the abrasion of the seal member reaches a predetermined value. CONSTITUTION:A plurality of through-holes 11 as a slide contact for limiting mechanism are formed in each piston ring 4a, piercing through the latter in the thicknesswise direction, so that they are positioned within the associated annular groove 3 in a normal condition. Accordingly, when the amount of abrasion of one piston ring 4a reaches a predetermined value, the spaces on both sides of the ring 4a are communicated with each other through the holes 11 so that the pressure differential between both sides becomes substantially zero, and therefore, the pressing force of the piston ring 4a fitted in the annular groove 3, against a cylinder 1 also becomes substantially zero so that the abrasion is no more progressed. Thus, it is possible to prevent the life of the seal device from being shortened due to abrasion and damage of a specific seal member, thereby it is possible to make the life of the seal device longer.
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