| 摘要 |
The invention relates to guillotine dampers, particularly to those which are used to isolate a section of ductwork without the entire system requiring to be made inoperative. Known dampers of this kind suffer from the disadvantage that a satisfactory seal is difficult to establish around the periphery of the damper blade with the result that it can be hazardous in the isolated section if the remainder of the ductwork system is carrying toxic or otherwise dangerous fluids. According to the present invention, an auxiliary seal is provided in the form of first and second sealing surfaces extending around the periphery of the plane of movement of the blade, which are urged towards each other and into sealing engagement with the blade when in its closed position by means of a frame. The frame is continuously urged to the sealing position by means of devices. Cams act on the frame and are rotatable to selectively overcome the bias of the devices and withdraw the frame to release the damper blade for opening.
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