Atmospheric Vacuum Breaker is:

• A. A device that introduces air from the atmosphere into the waterline to break the back siphon when pressure drops.
• B. A device that uses two check valves with a differential valve.
• C. A physical gap between water source and fill line.
• D. A device that reduces pressure in the line.

Answer: (A)

An atmospheric vacuum breaker allows air to enter the water line to stop back siphoning when the line pressure drops. This prevents contaminated water from being drawn back into the potable supply by breaking the siphon with an air intake from the atmosphere. It’s a simple device used on irrigation systems to protect the water supply, opening to vent air whenever pressure falls below atmospheric and closing when pressure returns to normal so it doesn’t let contaminants in.

Other options describe different concepts not used by this device: a setup with two check valves and a differential valve is a more complex backflow preventer, not an atmospheric vent; a physical air gap is a different anti-siphon method not specific to this device; and something that reduces pressure in the line would not prevent backflow and could create problems.