Making a compression joint

To make a compression joint, you need a pair of grips, adjustable wrenches or open-ended spannei-s, and either a tin of jointing compound or a roll of PTFE tape. The latter is a plastics compound – the PTFE stands for PolyTetraFluoroEthylene – which you wrap around the joint threads to make them watertight.

Make sure the pipe ends to be joined with the fitting are both clean and slightly bevelled. Dismantle the fitting to remove the capnuts and sleeves and place these in order on the piping – setting the sleeves about 12mm -from the pipe-ends. If your sleeves are tapered, position them with the slope towards the fitting. If you are using jointing compound, apply this to the inside of each capnut before slipping it on to the pipe-end.

Each pipe in turn is pushed home against the internal stop of the fittings while the capnut is tightened by hand. Apply PTFE tape or jointing compound to the male thread on the fitting before you do this. While you are tightening, be sure not to disturb the seating of the sleeves.

As each capnut is tightened, the sleeve – or compression ring as it is sometimes called – bites into the pipe beneath and spreads out against the nut to form a watertight seal. The degree of tightening is important. Although it is not possible to be precise – follow the manufacturer’s suggestion if in doubt – a turn or so after hand-tight is normally sufficient. Overtightening can cause severe problems.

Where imperial size piping is being attached to a metric fitting or length of piping, the use of additional sealant and tightening is normally quite sufficient to make up for the small differences. In the case of non-manipulative joints careful matching of sleeve and pipe sizes is necessary – you can buy size adaptors – and the advice of your local supplier or professional is worth seeking.

Compression fittings

A large variety of compression fittings is available , enabling all kinds of pipe installation to be tackled. But for simple projects, you should stick to the basic ones – elbows, tees, slow bends. If possible, incorporate these into a plan before you visit your builders’ or plumbers’ merchant. He should then be able to advise you on whether or not your plan is practical and on possible improvements.

When connecting such a fitting, think of it as two, ordinary, compression joints and assemble each ‘side’ as described.

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