The Principle Operation of a Laboratory Faucet Dual Check Vacuum Breaker – Backflow Prevention Device – Backflow Prevention Backsiphonage Condition Check Valve Failure
If the supply pressure becomes sub-atmospheric, and the force loaded first check valve does not close, the atmospheric vent will open allowing air into the supply line and break the vacuum and eliminating the siphon. The force loaded second check valve will close preventing potable water from entering the potable water system. The LFDC is providing protection under a backsiphonage condition.
If the supply pressure becomes sub-atmospheric, and the force loaded first check will close tight and the atmospheric vent will open allowing air into the supply line and break the vacuum and eliminating the siphon. If the second check valve will not close tight the first check valve and atmospheric vent will be open preventing potable water from entering the potable water system. Water may discharge from the atmospheric vent during this condition. The LFDC is providing protection under a backsiphonage condition.