How To Join Plastic Pipes

Plastic piping has several advantages over copper: it is less prone to "furring up"; it won't burst if water freezes in it; and it offers good insulation - though it should still be lagged to improve it further. Its disadvantage is that it cannot withstand high temperatures. Do not use plastic pipe within 380mm (15in) of a boiler; link it to a copper pipe at that point (using special adaptors). Because it will melt, you cannot solder joints with a blowtorch. And because it is rigid, plastic pipe cannot he bent like copper tubing.

Instead, where a pipe needs a change of direction, bends and elbows will need to be inserted. Although they are not as small as capillary joints, they have the advantage of being easy to fit.

To make joints watertight, a variety of methods are used with plastic pipes. When using solvent welds, follow the manufacturer's instructions and use only the recommended solvents and lubricants. Straight runs of pipes can be joined with a socketed connector and then solvent welded, fusing the

pipe and connector into a solid unit. There are also push-fit systems, some with a rubber seal in each socket that holds the pipe in place in the connector. These are for use with waste systems which are not under pressure.

Other push-fit systems are designed for use with supply pipes, where water is under pressure. An '0'-ring seals in the water as usual, but a metal grab ring behind the seal has barbed teeth pointing in one direction. The pipe can slide in, but can't be pulled out again.

Measure & Cut

Measure the length of pipe needed and allow a little extra to fit into the sleeve of the connector. Cut the pipe with a fine-toothed hacksaw, making sure the cut is square. Revolve the pipe away from you as you cut. Smooth off any burrs with a file. Push the pipe into the sleeve to test for fit, then mark where the sleeve comes up to on it with a pencil (as the guide for applying solvent). Key the outside of the pipe with fine abrasive paper. Following the manufacturer's instructions, paint solvent onto the end of the pipe up to your drawn guideline.

Push home the join

As soon as the solvent has been applied, push the pipe into the socket. Follow the manufacturer's instructions - some suggest that you twist the pipe a little to spread the solvent evenly. Align the joint correctly and leave for the recommended time. The solvent works by dissolving the surface of the 'mating' components. As it evaporates, the joint and pipe are 'welded' together into one piece of plastic to make the join completely watertight. However, you will have to wait some time before you can run water through these joins.

Sink, Bath & Basin Traps

In order to dismantle them easily, sink, bath and basin traps - the 'U'-shaped pipe that stops waste water returning back up into the sink or bath - are connected to the pipe work by compression joints that incorporate a rubber ring or washer to make the joint watertight. Like any other washer, these can degrade over time, and require replacing. Replacement washers are widely available, but make sure you buy the correct size.

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