The world of plumbing dimensions can be very deceptive to the trainee or the weekend amateur, for example a 7/8 inch plastic pipe is really called a ½ inch pipe as its inside diameter is ½ inch and this how plumbers see them. It is also reffered to as the nominal size and the one that suppliers are asked for. There has to be a system that allows different pipes to be used in many different guises so that everything was of a standard measurement. The old system of pipe measurement was called ‘Imperial’ and was used for many years in engineering until 1971, when the metric system was introduced. Here is some brief information about the metric and imperial measurements for pipework: Firstly, all the copper and stainless steel pipes used in plumbing today are made and supplied in a metric sizes, but many old pipes still exist in homes that were fitted years ago. These will be imperial. Feltham Plumbers are trained in imperial and metric. Lets compare the equivalent dimensions: 15mm=1/2in, 22mm=3/4in, 28mm=1in. The difference is quite obvious, but, metric pipe is measured by its external diameter while imperial pipework is measured by its internal diameter. The difference is only small, but can cause some real problems when trying to join two types of pipework together. If it is a soldered joint, an exact fit is critical. You can buy imperial to metric adaptors which are necessary when joining 22mm pipe to its imperial opposite and these adaptors are convenient when you are working with 28mm pipes or with thick walled 1/2in pipework. A Feltham Plumber is trained to know the difference between metric and imperial. These type of adaptors are not required when using compression fittings If you were joining 22mm to 3/4in plumbing, slip an imperial olive on the 3/4in pipework. Typically, 15mm (1/2in) pipework is used for the water supply to basins, kitchen sinks, washing machines, some showers, and radiator flow and returns. However, 22mm (3/4in) pipework is used to supply baths, high output showers, hot water cylinders and main central heating circuits, and 28mm (1in) pipe for bigger heating installations.
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