| 摘要 |
A butterfly valve for controlling the flow of fluid within a bore, including a butterfly and at least one ring extending at least one of substantially and completely around a perimeter of the butterfly and adapted to develop an expansion force in the radial direction when the at least one ring is in a contracted state with respect to the radial direction, wherein the at least one ring is secured to the butterfly in the contracted state and radial expansion due to the developed expansion force of the at least one ring is effectively restrained, wherein the butterfly valve is adapted to operate, when placed in a bore, without friction or substantially without friction between the at least one ring and the bore when the butterfly valve is placed in a closed position within the bore.
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