Concept reference

Air Valves and High Points

C.1Plain-language definition

Air in a pressurised main gathers where the hydraulic profile and pipe geometry let it. A small air-release orifice handles accumulated gas under pressure; an air/vacuum function moves much larger volumes while filling, draining or responding to negative pressure. “Air valve” without its required duty is an incomplete specification.

C.2Governing relation or decision logic

Placement begins with the longitudinal pipe profile and expected HGL, not fixed spacing alone. Sizing depends on gas accumulation or water filling/draining rate, differential pressure and manufacturer discharge/intake curves; compressible airflow is not safely inferred from a water K value. The governing local water/wastewater standard also sets contamination and discharge details.

C.3The failure to name

A valve can release sewage gas, liquid and aerosols at exactly the profile summit chosen for it. An undersized vacuum function may not protect the pipe during drain-down; an oversized device without controlled exhaust can allow damaging slam when water reaches it.

C.4Field review checklist

• Mark geometric and hydraulic high points for all operating conditions.
• Define release, admission and exhaust duties separately and size from stated events.
• Check pressure rating, isolation, drainage, odour/corrosion, flooding and safe maintenance access.
• Coordinate controlled filling, surge analysis and contamination protection with the valve selection.

C.5Where it fits in the course

§5.4 reads high points and three air duties; §8.5 reviews transient consequences.