New and Old Ways in Plumbing
Plastics used in plumbing have many advantages, but supply services must be limited to providing cold water and not connected in any way to the domestic hot water. Plastics are light to handle, easy to use, reliable in operation and virtually imperishable. Also, they are often less obtrusive than metal tube, where the pipework is exposed.
Plastics have an application for practically every purpose in plumbing. The exception is for the distribution of hot water, though plastics which are suitable for use with hot water have been produced. The two obstacles here are the high cost of plastic materials able to handle hot water, and design considerations. Plastics expand considerably at higher temperatures. Very careful design and installation would be necessary to allow for this high expansion factor or ‘coefficient’.
Plastics are lighter to handle than metal and have a predictably longer life and greater reliability than some metals.
Another advance is that electrolytic corrosion, which can occur in hard-water areas, particularly if copper and galvanized steel are used together, cannot occur where plastics are used.
PVC also has better insulation characteristics than metal and creates virtually no problems of condensation on pipe. As PVC is a good thermal insulator, water in pipes will not readily freeze. However, normal insulation practice should be followed in exposed situations, and pipework below the ground should be installed below the frost line.
There are no bore restrictions from build-up of hardness of scale. PVC also has excellent noise-absorption qualities.
PVC pipes must not, however, be used for cold down services, to hot-water cylinders or calorifiers or for cold-feed services for heating systems.
PVC pipe is widely used in domestic plumbing. Its high rate of thermal expansion, in common with all plastics, has to be carefully and adequately accommodated.
Up to about 30m of pipe is needed to provide cold-water services for an average house. These services can be used in conjunction with other plastics – soil and waste service and plastic storage cisterns.
Fittings used with plastic are about half the cost of those used for copper or stainless steel, but comparatively more are needed. Bends cannot reliably be formed in plastic as they can with metal pipe, and elbow fittings are needed. Plastic pipe can be bent, using a blow torch or hot-air gun, but some degree of skill is needed to do this successfully.
It is cheaper to plumb with plastic and in many ways simpler. Because of the correspondingly greater pipe bores, compared with the internal sizes of copper and stainless steel, smaller pipe can be used, which reduces comparative costs still further.
Where 13mm pipe is needed in copper, 10mm uPVC pipe can normally be used, as PVC also provides greater flow rates, with lower frictional resistance, than metal pipework, because of its smoother bore.
PTFE tape, wound three times in an anti-clockwise direction round the thread, both seals and lubricates the joint.
Where it is necessary to connect plastic pipes to metal fittings – such as taps, ball valves and adaptors, these are joined by components which are an integral part of the adapting fitting or with PVC fittings reinforced with metal bands.
10. November 2011 by admin
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