PVC conduit :
Conduit systems made from PVC are being used increasingly by the building industry as a direct replacement for steel. PVC conduit has several advantages in the building industry as it is adoptable equally to factory prefabrication or site installations. It is incorporated both in constructional slabs and dry partition walls. Cost saving is substantial. (e.g., 1/3 of the total cost when steel conduit is used).
The nominal sizes specified are 16 mm, 20 mm, 25 mm, and 32 mm outside diameter. The circular conduit is produced in two wall thicknesses, heavy gauge and light gauge. The light gauge is suitable for suspending ceilings and where it is immediately buried in concrete. A wide range of fittings, connectors and boxes are available.
The nominal sizes specified are 16 mm, 20 mm, 25 mm, and 32 mm outside diameter. The circular conduit is produced in two wall thicknesses, heavy gauge and light gauge. The light gauge is suitable for suspending ceilings and where it is immediately buried in concrete. A wide range of fittings, connectors and boxes are available.
Flexible conduit, produced in 15 m coil length is made from corrugated rigid PVC.
Plastic are insulating materials and it is vitally important to take the following precautions when plastic pipes and fittings are installed.
“no attempt should ever be made to use plastic pipework as a means of earthing electrical equipment or as providing part of an earth path”.
Accessories and fittings for PVC piping:
Plastic pipes are now relatively common for cold water system and handling gases for the following reasons:
· Excellent strength to weight ratio.
· Non-rusting.
· Smooth surface and therefore unobstructed water flow.
· Good mechanical strength.
· Attractive appearance as they are available in different colour shades.
· Hygienic.
· Low moisture absorption and good resistance to chemical attack.
· A wide range of fittings in rigid PVC is available.
· Available in sizes from 10 mm to 150 mm diameter with normal to heavy gauge material.
The fittings available are even more impressive than the pipes themselves. Some examples of fittings are as follows:
Fig.
Fig.
PVC Pipe Fittings
· Elbows – 450, 900
· Tee
· Caps
· Couplings
· Reducing couplings
· Reducing bushings
· Socket flange
· Unions
· Plugs
· Plug valves
· Ball valves
· Siphons and so on,
All the fittings have socket designed for gap filling solvent cement jointing. The ‘methyl – ethyl ketone’ is used as solvent material.
Many times pipe ends are heated and enlarged to a suitable size to form a socket and other pipe end may be inserted.
‘Welding’ of two pipes together is the simples method of joining. Two ends of pipes are first cut square and the surfaces are kept in contact with hot plate for short time. The two ends are then pushed together and held under pressure for a minute or two until the weld has cooled. The temperature for welding polythene and PVC are approximately 1100C and 1500C respectively. This technique can be applied only in certain cases and not when the pipe has already been placed in position. In this case a more normal method of welding is used, similar to metal welding. Welding rods of 2 mm to 3 mm diameters can be used. The only equipment required is a special welding torch heated by gas or electricity. The use of this welding technique allows pipes to be joined together and flanges or T-junctions to be made. This method is widely used for joining lengths of large pipes on site.
Fig.
PVC Pipe Joints
‘Cementing’ is one to the commonest and simplest methods of making a joint, which does not require specialized equipment, except suitable cements. In effect, a spigot and socket joint is manufactured. The outside of spigot and inside of socket must be cleaned of grease and dust. A coat of cement is then applied to each surface and allowed to dry. A second coat is then applied, using a brush. Minimum of 6 hours is recommended but 24 hours would be better.
