Purpose of Air Valves

Excess air in a pipe can cause slower flow, pipe churning damage, cause turbulence, and increased corrosion rate.
Air valves allow excess air to escape from the pipeline while containing pipeline fluids within the pipeline during operation. They also allow air to escape from the pipes during filling.
The valves can inject air into the pipes while they are being emptied, preventing a vacuum, which would cause the pipe to collapse.

Applications of Air Valve

All fluid transport systems

Potable
Sewage
Residual
Raw water
Saltwater (reverse osmosis plants)
Acids in solution (mining).