| 摘要 |
This invention refers to a backwater barrier for a well comprising a valve seat (5) located at the end of the inlet pipe (2) and a ball (8) located below the seat, which can move with the water level in a vertical direction. In current devices, the ball (8) becomes dirty very quickly by contaminants floating on the surface of the water, causing the ball to seal less tightly against the seat. This defect can be eliminated by giving the ball (8) an off-centre point of gravity, so the same part of the ball (8) is always above the surface of the water and presses against the seat (5).<IMAGE>
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