Operator terms · Water
What is an air relief valve?
An air relief valve, also called an air release valve, automatically lets trapped air escape from a water main. Air collects at high points in a pipeline and can block flow or cause surges, so the valve vents it to keep water moving smoothly.
Last reviewed 2026-08-03
Why air is a problem
Air rises and collects at the high points of a pipeline. A pocket of trapped air can shrink the space for water, reduce flow, throw off meter readings, and set up pressure surges when it moves.
Where it is installed
Air relief valves are placed at the high points where air gathers. When air builds up, the valve opens and vents it; when water fills the space again, it closes. This keeps the line full of water, not air.
Common questions
- What does an air relief valve do?
- It vents trapped air out of a water main automatically.
- Where does air collect in a pipeline?
- At the high points, where an air relief valve is installed.
- Why is trapped air bad?
- It can block flow, skew meters, and cause pressure surges.