Proper pipe joining is
key to successful systems
Take the time to properly install pipe fittings.
Thermoplastics PVC (Polyvinyl Chloride) and CPVC (Chlorinated Polyvinyl Chloride) pipe and fittings are light, flexible and tough and pro- vide exceptional corrosion resistance. Because of these and other properties, the savings that can be realized in ini- tial installation and continuing maintenance costs are substantial. The impor- tance of proper installation cannot be understated. The solvent cemented connection in thermoplastic pipe and fittings is the last vital link in a plastic pipe installation. It requires the same professional care and attention given to other compo- nents of the system. There are many techniques published covering step-by-step procedures on how to make solvent cemented joints. However, if the basic principles involved are explained, known and under- stood, a better understanding for practical application would be gained as to what techniques are necessary to suit particular applications, temperature conditions and variations in sizes and fits of pipe and fittings. To consistently make good joints, the following points should be clearly understood: • The joining surfaces must be dissolved and made soft • Sufficient cement must be applied to fill the gap between pipe and fitting • Assembly of pipe and fittings must be made while the surfaces are still wet and soft • Joint strength develops as the cement dries. In the tight part of the joint, the surfaces will tend to fuse together; in the loose part, the cement will bond to both surfaces. Penetration and softening of the pipe and fitting surfaces can be achieved by the use of a suitable primer, or by the use of both primer and cement. A suitable primer will penetrate and soften the plastic more quickly than cement alone. The primer is important to obtain sufficient softening in varying tempera- ture conditions. If the cement coatings on the pipe and in the fitting socket are wet and soft when assembly takes place, they will tend to flow together and become one cement layer. Also, if the cement is wet the surfaces beneath them will still be soft, and these softened surfaces in the tight part of the joint will fuse together. As the solvent dissipates, the cement layer and the softened surfaces will harden with a corresponding increase in joint strength. A good joint will take the required working pressure long before the joint is fully dry and final strength will develop more quickly than in the looser (bonded) part of the joint. Fig. 2 Fig. 3
To fill the loose part of the joint, sufficient cement must be applied. Besides filling the gap, adequate cement layers will penetrate the surface and also remain wet until the joint is assembled.
Fig. 1
Fig. 4
(Continued on page 28)
The basics: Making the joint
Cutting:
Pipe must be squarely cut to allow for the proper interfacing of the pipe
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