102 Module 8 • Water pipe systems (up to 50 mm diameter) Screwed (threaded) plastic pipe joints


Te two parts that are to be joined have threads at each end and are merely screwed into each other. Te threads must obviously not be tightened as much as steel threads, as they could strip. An example of a threaded joint is shown in Figure 8.4.


Figure 8.4 Flanged plastic pipe joints


Flanged joints are as common as with steel pipes. Te joint is reliable and simple to make. Te flanges are attached to the end of the pipes to be joined either by screwing them on or by having a ridge on the pipes between the flange and pipe end. Te flanges are then pushed on from the other side and then drawn towards each other with draw bolts as shown in Figure 8.5.


Figure 8.5 8.5


Thermoplastic piping [for example Polyvinyl Chloride (PVC)]


Tis type of plastic becomes pliable when heated and can then be worked into desired shapes and angles. Te process can be repeated over and over again. It is used for piping, ducts etc. It can also be used as an insulator around a conductor. Polyethylene (PE), in contrast, is not suitable for piping but is used for sheeting.


Termosetting plastic


Termosetting plastic piping, like all products made from this type of plastic, is much harder than thermoplastics and threads can even be cut into them. Tey are ridged and do not bend easily.


Tis material can be used for other purposes like electric fittings, fuse boxes, switches, plugs, light bulb holders etc. as it can resist much higher heat. It cannot, however, be re-used as it undergoes a chemical change that cannot be reversed. It cannot be melted down and re-used like thermoplastic. Epoxies can be used with glass fibre to construct structures like canoes and motor car bodies.


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