A sewerage backflow into the building/house will happen if a stoppage or similar problem in the municipal/street sewer, or septic system occurs causing the drainage water level to rise above the top of the building/house drain. It is under these conditions that the Flood-Gate® works.

As the sewerage backflow occurs the air trapped in the expansion chamber is compressed by sewerage backup. The pressure in the expansion chamber causes the knife gate to rise until the 4” or 6” drainage opening is completely sealed. This action occurs with a 9” head of drainage water for a 4” valve and a 14” for a 6” valve. When complete closure is obtained in the valve, all backflow is prevented from entering the building or structure.

Once the backflow subsides and the drainage water level returns to normal, the counterweight atop the expansion chamber forces the trapped air out of the chamber and into the drainage line, allowing the knife gate to lower to a full open position. Now the Flood-Gate® is ready to guard against future backflow situations.