| 摘要 |
<p>The pneumatic shutter includes a circular plate (15) of diameter slightly less than the internal diameter of the inspection chamber (4). This plate includes a channel formed around its edge, housing an inflatable ring which is similar to a tyre. The shutter also includes at least three retractable fingers (24a) linked to a central mechanism. By rotation of a control, the fingers may be moved radially outwards towards the inner surface of the drain chamber, locating the shutter in the centre and preventing it being lifted from its seating. With the tyre inflated, a seal is formed to enable pressure testing of the drainage system. <IMAGE></p> |
