air valves in pipeline systems serve two primary functions. The first is the release of accumulated air that comes out of solution within a pressurized pipeline. This air will result in bubble formation, which will gather at localized high points along the pipeline profile. This air accumulation will occur when the bubble’s buoyancy is greater than the energy to convey the bubble with the liquid. air valve used to release this free air is known as an air release valve.
The second function of an air valve is to admit air into the system when the internal pressure of the pipeline drops below atmospheric pressures. By admitting air into the pipeline as the internal vacuum condition develops, the magnitude of the vacuum pressure can be reduced and as a result help prevent the pipeline from experiencing excessive deflection and/or collapse as well as help prevent the formation of a full vacuum condition in which vapor cavities may form from the fluid vaporizing. The air valve used in this situation is an air & vacuum valve. The air & vacuum valve is also used to discharge large volumes of air from the pipeline system when the pipeline is initially filled and after water column separation.