| 摘要 |
A valve for controlling or preventing fluid flow has a shut-off element controllably movable in an axial direction between a first position corresponding to a fully open condition of the valve and a second position corresponding to a fully closed condition of the valve, a valve seat with which the shut-off element is capable of fluid-tight sealing engagement when in the said second position, drive means operatively connected to the shut-off element and capable of controllably transmitting a drive to the shut-off element to effect the said controlled movement thereof towards one of either of the said first and second positions thereof, said drive means including a connecting member transmitting the drive to the shut-off element, the shut-off element moving relatively to said connecting member in said axial direction when driven by said drive means, and furthermore being moved axially when said connecting member is moved axially, a housing defining a chamber, a diaphragm within said chamber and having a central region attached to said connecting member and a peripheral region attached to said housing, whereby the diaphragm supports said connecting member and is capable of moving said connecting member, and thereby also said shut-off element in the axial direction in response to pressure differences across the diaphragm, and control means capable of controlling the said pressure differences across the diaphragm and operable, when the said drive means is operative and when the said drive means is inoperative, to control the said movement of the diaphragm. The pressure difference is so controllable that (1) at least when the said drive means is operative, the diaphragm is urged away from the valve seat, and (2) at least when the said drive means is inoperative, the diaphragm is urged towards the valve seat.
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