| 摘要 |
The valve is of the type having a body and a butterfly valve closure member. One of these parts has an annular sealing element which is retained in a cavity with which it defines an annular chamber. The other part has an annular surface for contacting the sealing element when the valve is closed. A conduit puts the chamber in communication with the upstream side of the closure member when the latter is in its valve closing position. According to the invention, an exhaust conduit is provided for putting the chamber in communication with the downstream side of the closure member when, and only when, the closure member is not in its valve closing position.
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