The Principle Operation of a Hose Bibb Vacuum Breaker Backflow Prevention Device – Continuous Pressure and Backpressure
The HBVB shall only be installed where spillage of water will not cause damage. The HBVB is not suitable for continuous pressure conditions therefore, downstream shut-off valves should not be used unless the spigot valve is closed and the downstream pressure is released. Continuous pressure shall mean twelve (12) hours of use in a twenty-four (24) hour period. The HBVB should not be subjected to continuous pressure because the atmospheric vent diaphragm may stick in the vent openings, making the potable water system vulnerable to backflow hazards.
The HBVB shall only be used on systems where the only source of low head back pressure comes from an elevated hose equal to or less than 10 feet in height. Outlet pressures greater than 10 feet in height or 5 psi (10 feet X 0.043 psi/Ft. = 4.3 psi) is not acceptable.