The Principle Operation of a Laboratory Faucet Dual Check Vacuum Breaker – Backflow Prevention Device – Backflow Prevention Backsiphonage Condition
During normal flow conditions with a demand downstream, the two force loaded checks valves are open. The atmospheric vent in a flow condition is closed by the supply pressure acting on the atmospheric vent diaphragm. If the supply pressure becomes sub-atmospheric, the force loaded first check valve will close due to internal spring pressure. The atmospheric vent will open allowing air into the supply line, breaking the vacuum and eliminating the siphon effect. 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.