Atmospheric vacuum breakers (AVBs) are simple, inexpensive devices that prevent backflow due to back siphonage. They are designed for low-pressure, low-flow applications and are not suitable for high-pressure or high-flow systems. AVBs are also not designed to prevent backpressure, which can occur when the system pressure exceeds the supply pressure. In contrast, other types of backflow preventers, such as double check valves and reduced pressure zone (RPZ) assemblies, are designed to prevent both back siphonage and backpressure.