The Principle Operation of a Hose Connection Dual Check Valve Vacuum Breaker – Backflow Prevention Device – Backflow Prevention Backsiphonage Condition
When water is introduced into the HCDCV and there is a downstream demand, the first check valve opens and the water pressure closes the atmospheric vent. As water continues to flow through the HCDCV the second check valves opens.
If a backsiphonage condition were to occur in the inlet piping, the first and second check valves would close and the atmospheric vent would open. During a backsiphonage condition with the check valves closed tight and the atmospheric vent open allowing air into the piping system breaking the vacuum and eliminating the siphon, the HCDCV is providing protection.
If a backsiphonage condition were to occur in the inlet piping and the check valves were fouled open and did not close drip tight, the atmospheric vent would open breaking the vacuum and eliminating the siphon. The HCDCV is providing protection.