Air Release Valves

Air is the enemy of a pressurised pipeline. As a main is filled, air is pushed to the high points where it collects. Under working pressure these pockets restrict the bore, raise pumping costs and accelerate corrosion, and during rapid air movement they can drive damaging pressure surges. On drain-down, the reverse problem appears: without a way to admit air, a vacuum forms that can collapse thin-walled pipe or cause column separation. Air release valves manage both conditions automatically.

The main types are distinguished by orifice arrangement. A small-orifice (automatic) air valve releases the small volumes of air that come out of solution under working pressure. A large-orifice (kinetic) air valve vents the large volumes displaced during filling and admits air during draining. The combination (double-orifice) air valve does both in one body and is the usual choice on water mains. Anti-shock designs add a throttled air inlet that softens the surge as a collapsing vacuum draws air back in.

Air release valves belong at every high point on a pipeline, immediately downstream of pump stations, at gradient changes and at intervals along long horizontal runs. Sewage and wastewater duty needs purpose-built valves whose floats and seals resist fouling by solids, grease and biofilm, since a clean-water air valve would soon clog. Sizing depends on the bore, working pressure, filling rate and the pipeline profile.

Bodies are typically ductile iron with fusion-bonded epoxy coating, with stainless steel and resilient internals, to standards such as EN 1074-4 for air valves in water supply, with flanges to EN 1092. Correct sizing matters in both directions: an oversized valve may cycle needlessly under working pressure, while an undersized one cannot clear air fast enough on filling.

To specify, provide the bore, working pressure, the medium (clean water or sewage) and, where possible, the pipeline profile and filling rate. We can then recommend an orifice arrangement and a valve suited to the location.