| 摘要 |
First and second walls form first and second openings, respectively, which face each other in spaced, substantially coaxial relation. A device surrounding the first opening, for establishing and breaking fluid communication between the openings, comprises an inflatable ring which, when inflated, seals against the second wall around the second opening to complete a fluid flow path between the openings, and a circular body located in said flow path coaxially of the ring. When deflated, the ring bears sealingly against said body to prevent flow through the first opening.
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