The Principle Operation of an Atmospheric Vacuum Breaker Backflow Prevention Device – Backflow Backsiphonage – Check Valve Not Holding Tight
If a backflow backsiphonage condition were to occur in the inlet or supply piping and the upstream shut-off valve were open, the float disc would drop downward, and if operating properly would form a check valve between the potable and non-potable systems. As the float disc dropped, the air inlet port would open allowing air to enter the piping system through the air inlet port preventing non-potable from siphoning into the potable water system. If the float disc is fouled open and cold not drop down completely to form a check valve, the air inlet port would open allowing air to enter the air inlet port breaking the vacuum affect. The AVB is providing protection during a backsiphonage condition since the float disc dropped sufficiently to open the air inlet port. If the float disc did not drop sufficiently to open the air inlet port because the seat disc stuck or adhered to the air inlet port, the AVB would not be providing protection. Because the float disc may fail, a certified tester should inspect the internal parts the AVB at least annually or more frequently if necessary.
