| 摘要 |
Durability of a seal member is improved by reducing a surface pressure thereon. A seal mechanism 24 is provided between a backpressure plate 16 and a holder 17 so as to surround an orbiting backpressure chamber 18 . The seal member 24 comprises a seal attachment groove 25 , a seal member 26 and a Y-shaped packing 27 . The seal attachment groove 25 is stepped on its outer circumference side to define a shallow bottom portion 25 B. The seal member 26 includes, on its outer circumference side, a cutout portion 26 D matching the shallow bottom portion 25 B. The Y-shaped packing 27 is disposed between a deep groove peripheral wall 25 C of the seal attachment groove 25 and the cutout portion 26 D of the seal member 26 , and a backpressure chamber 28 is defined on a reverse surface 26 B side of the seal member 26 . By this arrangement, a slide surface 26 A of the seal member 26 can be larger than an effective area of the backpressure side of the seal member 26 . Thereby it is possible to reduce a difference between a load Ff acting on the slide surface 26 A and a load Fb acting on the reverse surface 26 B.
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