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An atmospheric vacuum circuit breaker prevents contaminated water from flowing back through a water system. It includes an inlet, outlet, and vent with a holding valve and must be installed vertically and at least six inches higher than the water system outlet.
An atmospheric vacuum circuit breaker (AVB), also called an atmospheric type vacuum circuit breaker, prevents contaminated water from flowing back through a water system and contaminating clean water. The atmospheric vacuum breaker valves open and close in response to pressure in the water line, to ensure that water only flows in the correct direction. Some applications of AVBs include sprinkler and sprinkler systems, commercial dishwashers, and water systems with hose outlets.
Atmospheric vacuum breakers include an inlet, outlet, and vent with a holding valve. The inlet and outlet are perpendicular to each other, while the vent and valve gasket are placed around the inlet, so it can be sealed when needed. The AVBs are installed in line with the water supply line, close to the inlet control for the system. If your system has multiple input controls, you must install an AVB on each one.
Under normal operating conditions, water flows into and out of the atmospheric vacuum breaker. The valve seal is open to allow flow through the system. This is because the system has positive pressure, i.e. the pressure forces the water in the normal direction of flow for the system.
When negative pressure (pressure that pushes water in the wrong direction) begins to build up in the system, a condition called siphoning occurs. This causes the flow in the water system to reverse. If there is no valve to prevent backflow, used and contaminated water will flow back into the system and pollute the clean water supply. When an atmospheric vacuum breaker is installed, however, negative pressure in the system passes through the AVB vent and forces the valve seal closed, obstructing the flow of contaminated water. The vent also allows air to enter the system and restore the correct pressure.
AVBs are simple and inexpensive types of backflow prevention devices, but they also have some limitations. An atmospheric vacuum breaker must be installed vertically and at least six inches higher than the water system outlet to function properly. Also, it cannot be subjected to more than 12 hours of continuous pressure or the valve seal may become blocked. Not only does this mean that the system shouldn’t run for more than 12 hours at a time, it also means that no valves can be installed downstream of an AVB, as they put pressure on it, even when the system is not running.
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