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.
