Is an 80 mm air valve always an 80 mm valve?

How can an 80 mm air valve be a 50 mm valve?

The customer was describing the size of their branch, not the size of the valve they needed. We supplied a 50 mm air valve with an enlarged 80 mm inlet flange. It bolted straight onto the existing 80 mm branch, and the 50 mm valve had all the capacity the main needed.

Why does it matter?

If the branch size is treated as the valve size, you can be quoted the wrong product, and often a bigger, more expensive valve than the job needs.

How should I describe it in my enquiry?

Give the valve size and the branch or flange size separately. Better still, tell us the pipe diameter, what the valve needs to do and the pressure rating, and we’ll work out the valve size for you. A photo or drawing helps if the valve is already installed.

Quick tip: if you only know the branch size, say so. “80 mm branch on a 300 mm main” is far more useful to us than “80 mm air valve”.

Before you enquire, have ready: branch or flange size, main diameter, pressure rating, valve duty, and filling or draining rates if you have them.
Related reading: Which type of air valve do I need? · Why is an isolating valve supplied with an air valve?