What is a key feature of an Atmospheric Vacuum Breaker?

An Atmospheric Vacuum Breaker is designed to protect against back-siphonage in irrigation systems. A key feature of this device is its incorporation of a float check valve. This float check valve is crucial because it allows air to enter the system during a vacuum condition, preventing a negative pressure that could cause contamination by drawing water back into the supply lines.

When the pressure drops in the system, such as during system shutdown or when there's a sudden demand for water, the float within the breaker will drop. This action opens the valve to allow atmospheric pressure to equalize. This is essential for maintaining system integrity and protecting potable water supplies from potential contamination due to back-siphonage.

The other options highlight various features that may be seen in other types of plumbing or irrigation devices but do not accurately represent the primary working mechanism of an Atmospheric Vacuum Breaker. For instance, constant pressure or functioning well under back pressure do not apply to its purpose, and the presence of two check valves is characteristic of other devices like double check valve assemblies, not atmospheric vacuum breakers.