Components, systems and materials › Water and drainage components › Air valve
Air valve
What it is
An air valve is a fitting on a pipeline that releases trapped air while the main fills and during operation, and admits air when the main drains, protecting it from vacuum.
Where it is used
High points, changes of gradient and long uniform grades on water transmission and pumping mains, and on sewage force mains with special designs.
How it works
A float sits in a chamber. When air collects, the water level falls, the float drops and opens the orifice so air escapes; when water arrives, the float rises and seals. Large orifices handle bulk air during filling and admit air quickly during draining or a pipe burst, preventing collapse of thin pipes. A small orifice releases air pockets that accumulate under pressure.
Types
- Single small-orifice valves for releasing air under pressure
- single large-orifice (kinetic) valves for filling and draining
- double or combination valves with both orifices
- sewage air valves designed to resist fouling
Materials
Cast or ductile iron body, stainless steel or plastic floats, rubber seals; isolating valve below.
Locations come from the pipeline profile drawn against the hydraulic grade line: at every high point, at intervals on long rising or falling grades and at changes in slope. Orifice size is chosen for the filling and draining rates. Trapped air reduces pipe capacity and can cause surges, so correct location matters as much as size.
Installation and QA steps
- Mark high points on the longitudinal section.
- Install on a tee with an isolating sluice valve in a ventilated, drained chamber.
- Fill the main slowly and confirm air release.
- Inspect and clean floats and seals periodically.
- Stuck or leaking floats
- chambers flooded so the valve draws in dirty water
- valves missing at high points causing air locks
- undersized valves leading to vacuum collapse
Related
Generic description for education. We do not name, endorse or compare manufacturers or products.
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