Plastic pipe and fittings can now be used for hot water supplies and central heating. They are easy to work with and allow the DIY plumber to tackle a wide range of jobs.
Over the last twenty years plastic has become the most popular plumbing material for above and below ground drainage, for rainwater collection and disposal, and for subsoil drainage. In the form of black polythene tubing it has also become a material widely used for water transportation on camping sites and farms. In the home, however, it has not proved popular. Although this lack of interest can partly be attributed to the conservatism of plumbers and householders, the main reason has been that up until now the plastic pipes that have been available have been suitable for cold water supplies only.
This has meant that plumbers, who have had no choice but to use copper or some other metal for the hot water or central heating system, have almost always tended to use the same material when dealing with the cold water system. Householders have doubted the ability of plastic pipework to do a good, life-long job, and have also tended to resist its use on grounds of taste: quite simply, in places where pipework is exposed to view the combination of plastic and copper (or stainless steel or iron) is not one that is very pleasing to the eye. Now, however, all this has changed. Recently the National Water Council (NWC) gave its approval to two proprietary systems of plastic plumbing, one made out of polybutylene and the other of chlorinated polyvinyl chloride (CPVC), both of which can now be used for cold and hot water supply as well as for wet central heating systems. These two rival plumbing systems should hold a special appeal for the DIY enthusiast and – now that they have gained the NWC’s approval – there is nothing to prevent them gaining widespread acceptance.
The advantages of plastic pipework
The most obvious advantage is the lightness of the pipework, which makes for ease of handling, but the most important benefit is the ease wrth which plastic can be cut and joined. This means that the level of skill you require to undertake a particular plumbing task is greatly reduced, as is the amount of time you require to carry it out. Both systems are also strong and durable, more resistant to frost than a traditional plumbing system and, unlike the latter, not subject to corrosion.
Last but not least, they are competitively priced. Plastic pipes are less vulnerable to frost because plastic is a poor conductor of heat compared to metal (which means that, unlike metal, it provides a certain amount of insulation), and because it has greater elasticity. This means that plastic pipes are not only less likely to freeze than metal ones, but also that in the event of their doing so they are much less likely to burst.
The greater degree of insulation that plastic provides also brings other benefits: it results in less heat being lost from pipe runs between radiators (or between the hot water cylinder and the hot taps),, as well as meaning that less insulation is necessary for pipework that needs to be protected against the cold. Plastic pipes aren’t subject to corrosion for the simple reason that plastic isn’t attacked by the water supply.
Electrolytic corrosion, which results in the build up of hydrogen gas and black iron oxide sludge (magnetite) and can ultimately lead to leaky radiators and early pump failure, is therefore far less of a problem when a central heating system is fitted with plastic pipes. This also means that plastic is a safer material to use for your drinking water supply pipes than metal, the use of which can, under some circumstances, present a health risk. One final point to be borne in mind before you replace metal pipes with plastic ones is that plastic is a non-conductor of electricity. This means that all-plastic plumbing systems cannot be used to earth a domestic electricity supply. You can obtain both polybutylene and CPVC tubing in the 15mm, 22mm and 28mm (1 in) diameters commonly used in domestic hot and cold water supply and in small-bore central heating.
However, in other respects – particularly as regards the flexibility of the two different types of tubing and methods of cutting and jointing – the two systems differ. So, before you undertake a plumbing task using plastic pipes and fittings, you’d do well to consider which system best suits your particular application. Polybutylene tubing Polybutylene tubing is brown in colour and naturally flexible; in this respect it differs from CPVC tubing, which is rigid. As well as being available in 3m (10ft) lengths in all three diameters, it is also obtainable as a 100m (39.0ft) coil in the 15mm (1/2in) size, and as a 50m (195ft) coil in the 22mm size.
This flexibility, and the long lengths in which the tubing is available, is particularly useful as it cuts down the time you need to spend on installation, and reduces the number of fittings necessary (which means less cost). You can thread polybutylene pipes under floors and between joists with minimal disturbance, their flexibility also allowing you to take them through apertures and round obstacles that would otherwise present serious difficulties. You can bend the tubing cold to easy bends with a minimum radius of eight times the pipe diameter; 15mm (1/2in) tube can therefore be bent to a minimum radius of 120mm and 22mm to a minimum radius of 176mm (7in). You must, however, provide a clip on either side of the bend to secure it. The flexibility ‘of polybutylene tubing means that inside of the fittings, brushing in the direction of the pipe.
It is usually necessary to apply two coats to ABS pipes and fittings. The second coat should be brushed on quickly before the first has dried. Push the pipe fully home into the fitting (some, but not all, manufacturers suggest that this should be done with a slight twisting action). Remove excess solvent cement and hold the assembled joint securely in position for about 30 seconds. If hot water will be flowing through the pipe, don’t use it for 24 hours to give time for the joint to set completely.
Joining ring-seal types
Preparation for ring-seal or push-fit jointing is similar to that for solvent welding. The pipe end must be cut absolutely squarely and all the burr removed. You should draw a line round the cut end of the pipe 10mm from its end and chamfer back to this line with a rasp or shaping tool, then clean the recess within the push-fit connector’s socket and check that the sealing ring is evenly seated. One manufacturer supplies sealing rings separately, and they should be inserted at this point.
The pipe end should now be lubricated with a small amount of petroleum jelly and pushed firmly into the socket past the joint ring.
Push it fully home and mark the insertion depth on the pipe with a pencil. Then withdraw it by 10mm (which is the allowance made for expansion). The expansion joint that is inserted into long straight lengths of solvent-welded waste pipe consists of a coupling with a solvent-weld joint at one end and a push-fit joint at the other. As with solvent-weld jointing, individual manufacturers may give varying instructions. Some, for instance, advise the use of their own silicone lubricating jelly.
Where the manufacturer supplies instructions it is best to follow these exactly.
PVC pipe can be bent by the application of gentle heat from a blow-torch, but this technique needs practice and it is best to rely on purpose-made fittings. Sockets are used for joining straight lengths of pipe, tees for right-angled branches, and both 90° and 45° elbows are usually available. If you need to reduce the diameters from one pipe to another you can use reducing sockets These are really sockets within sockets which can be welded together, one taking the smaller diameter pipe and the other the larger. Soil outlet pipes from WCs are joined in the same way; they are merely bigger – usually 100mm (4in) – in diameter. Sockets work in the same way, but the branch junction with the main soil stack must be of a specially ‘swept’ design.