The Principle Operation of a Laboratory Faucet Dual Check Vacuum Breaker – Backflow Prevention Device – Backflow Prevention Backpressure Condition Check Valve Failure
The LFDC can resist backflow backpressure caused by the head pressure developed in an elevated hose. The second check valve is the primary protection when backpressure is present. If backpressure were to occur due to an elevated hose, the second check valve would close tight. During a backpressure conditions with the second check valve closed tight, the first check valve would be open and the atmospheric vent would be closed. The LFDC is providing protection.
If the second check valve was fouled open, the first check second check valve would close tight causing the atmospheric vent to open. Water may discharge out of the opened atmospheric vent during a backpressure condition. Since the first check valve is closed tight and the vent is open the LFDC is providing protection.
