Rapid Initial Air Vents: VA series
When water is pumped through the system, the initial air inside the piping is pushed into the air vent by the pressure of the flow. The float remains in the lower part of the air vent, allowing the valve to remain open and air to be rapidly discharged.
After the initial air has been discharged, water begins to flow into the air vent, causing the float to rise and close the valve.
Once the valve closes, it will remain closed and will no longer discharge air even if more air flows in and the water level inside the air vent drops.
Only when the pressure inside the vent approaches vacuum conditions will the valve open again, allowing air to enter and water to drain.