GA Air Release Valves work by exhausting small amounts of air which collect at high points when the system is flowing and under pressure. As small quantities of air bubbles enter the valve, they displace the liquid within the valve and lower the float.
When the float drops, the valve seat opens and exhausts the collected air into the atmosphere. Once the air is released, the liquid level in the valve rises, lifts the float, and closes the valve.
Air Release Valves are used on water transmission lines and sewage force mains, at or slightly downstream of peaks and high points.