| 摘要 |
Manhole covers with a seal against surface water or backwater have two functions to perform. They have to absorb the traffic loads and they have to soundly seal the manhole. However, this is only accomplished when the locks of the cover are properly operated. If this is not the case, the mounting of the cover is not safe for traffic. If the cover seal is arranged in the cover periphery and the sealing surface is made "negative" in the frame, i.e. in an undercutting manner, a vertical force component is obtained which presses the cover downwards onto the seating. This ensures that the cover is always in a position which is safe for traffic.
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