The Principle Operation of a Hose Bibb Vacuum Breaker Backflow Prevention Device – Backflow Prevention
As the water flow begins, the check valve opens and allows the diaphragm seal to close off the atmospheric vent. The atmospheric vent is closed during a flow condition and the check valve is open. Supply pressure forces the spring loaded check valve to open and at the same time forces the diaphragm to seal against the atmospheric vent openings.
When the water supply is turned off, the HBVB vents to the atmosphere. During a no-flow condition the spring loaded check valve is closed. When the check valve closes, it seals against the diaphragm opening the atmospheric vent introducing air downstream water system.
When zero-pressure or backsiphonage conditions exist, the spring pulls the check valve closed and simultaneously pushes the diaphragm away from the atmospheric vent which, opens the vent allowing air to be introduced into the piping system breaking the vacuum condition and eliminating the backsiphonage. The HBVB is providing protection and preventing non-potable from entering the potable water system during a backsiphonage condition as long as the atmospheric vent opens properly and the HBVB is installed in conformance with specified plumbing standards.