The Principle Operation of an Atmospheric Vacuum Breaker Backflow Prevention Device – Backflow Backsiphonage
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 forming a check valve and the air inlet valve would open allowing air to enter the piping system through the air inlet port preventing non-potable from siphoning into the potable water system. The AVB is providing protection during a backsiphonage condition since the float disc dropped freely forming a check valve between the potable and non-potable systems and the opening the air inlet port interrupting the siphon between the non-potable and potable water systems. If the float disc did not function properly, causing the air inlet port to remain closed; the AVB would not provide protection. Because the float disc may fail, a certified tester should inspect the AVB at least annually or more frequently as necessary.
