An Atmospheric Vacuum Breaker (AVB) is a backflow prevention device that incorporates which features to prevent backsiphonage?

• A. An atmospheric vent with a check valve
• B. A pressure relief valve
• C. A diaphragm and spring assembly
• D. A check valve only

Answer: (A)

An Atmospheric Vacuum Breaker protects the potable water supply by using two features together: an atmospheric vent and a check valve. When the downstream line experiences a vacuum, the atmospheric vent opens to the air, allowing air to enter and break any siphon that might pull contaminated water back into the supply. The check valve then prevents any water from flowing backward into the supply once pressure normalizes. A pressure relief valve isn’t part of this mechanism, and a diaphragm and spring assembly describes different backflow devices. A check valve alone can stop backflow under some conditions but cannot reliably prevent backsiphonage without the vent to break the siphon.