How to measure pipework - it's complicated!

It might appear easy and straightforward, but on many occasions we are given the wrong measurements and the customer ends up with a part that is either too big or too small. Or we are given a the measurement of a part of a pump or heater and we have to guess the size of the pipwork.

So I hope to clarify how we measure components.

Imperial measurement (inches)

If we look at a standard 2" diameter pipe, the measurement is the INTERNAL diameter of the pipe.

This will then fit a buttress which has an internal diameter of around 2.375" (depending on the thickness of the pipe walls).

This will then fit into a union joint which will have an internal diameter of around 2.75". Which in turn will fit a screw thread of almost 3".

When we describe a standard Waterway Jet pump or Wet End as 2 x 2, this indicates that the inlet and outlet of the Wet End will fit 2" pipework - once we have added the union and the buttress.

Waterway Jet pumps or Wet Ends can also be described as 2.5 x 2 and are designed to be connected to 2.5" pipework for the inlet and 2" pipework for the outlet. As you can see from the Wet End below the inlet face is much wider, in comparison to the one above, to take the larger buttress fitting to connect to 2.5" diameter pipe.

Please note that we also supply 2.5" Waterway unions (mainly used with the Waterway Viper pumps) with either a tailpiece to fit 2.5" pipework or a tailpiece that can fit 2" pipework.

So far so good! - Now the complicated bit!

Metric Pipework (mm)

The majority of Spas in the world have Imperial pipework but some Spas built in Europe will have Metric pipework.

On all metric pipework, the size is the EXTERNAL diameter of the pipe.

The standard sizes of metric pipework are: 32mm, 50mm or 63mm (external diameter).

If you are unsure if your plumbing is Imperial or Metric - or if you only have a Metric ruler or tape measure, here is a table showing the standard Imperial internal diameters and the their equivalent Imperial and Metric external diameters.

This is the reason why if you require a new Pump, Wet End or Heater, we will always ask you to check the diameter of the existing inlet and outlet pipework in order that we can be sure that we are supplying you with the correct part.

Bill Norris, 16-10-2014