Which situation is the atmospheric vacuum breaker applicable for?

The atmospheric vacuum breaker is specifically designed to protect against back siphonage in non-pressurized systems. Its primary function is to prevent contaminated water from being siphoned back into the potable water supply. In scenarios where intermittent service is present, an atmospheric vacuum breaker can effectively perform its role, as it breaks the vacuum created when the pressure in the system drops, allowing air to enter and preventing backflow.

In the context of the other scenarios, continuous service under pressure would not allow the vacuum breaker to function properly because it is not designed to handle sustained pressure situations. Similarly, back pressure conditions require different mechanisms, such as pressure vacuum breakers or reduced pressure zone devices, as they address the additional complexities of maintaining pressure that could lead to backflow. Lastly, while the atmospheric vacuum breaker is effective in preventing back siphonage, it does not provide a suitable solution for continuous flow applications since it relies on the absence of pressure to operate correctly. Thus, intermittent service represents the appropriate application for an atmospheric vacuum breaker.