Which type of air valve do I need?

What does each type of air valve do?

There are three main types, and each one does a different job:

• Small orifice (air release valve): lets out the small amounts of air that build up while the main is running under pressure.
• Large orifice (air and vacuum valve): pushes out large volumes of air while the main is filling, and lets air back in if the pressure drops below atmospheric, for example when the main drains.
• Double orifice (combination valve): does both jobs in one valve.

Why doesn’t the connection size decide it?

Two air valves with the same flange can do completely different jobs. If you choose by connection size alone, you can end up with a valve that fits perfectly but can’t cope with the duty. Where you know the filling and draining rates, we can size the valve against them.

So which one do I need?

Choose a small orifice valve to release air under pressure, a large orifice valve for filling and vacuum protection, or a double orifice valve if you need both. On most pipelines, a double air valve is the safest all-round choice. If you’re not sure of the conditions, send us the details and we’ll check the duty with you.

Is this just for water mains?

No. Any long pumped main collects air at its high points, whether it’s on a water network, a factory, a quarry or a data centre site.

Quick tip

If you’re not sure what you need, send us the pipe size, working pressure and a rough profile of the main. We’ll recommend the type and where to fit it.

Before you enquire, have ready: pipe diameter, working pressure, what the valve needs to do, flange or thread type, and a photo of the existing valve if you’re replacing one.

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Related reading:

• Is an 80 mm air valve always an 80 mm valve?
• Why is an isolating valve supplied with an air valve?
• Trapped air on industrial water mains