| 摘要 |
<p>The circular ventilating flap which is rotated about an axis inside a pipeline, is made of two sheets which are joined together at a central zone by e.g. screws or welds. Both sheets are circular, and one sheet has its peripheral edge offset, connected by a flange at right angles, to form a gap against the other sheet. Into this gap is fitted a sealing ring made of a soft material such as felt, and partly projecting from it. Housed in the remaining space under this sealing ring is a loop of wire enclosed by a plastics tube.</p> |
