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Plastic Pipe Fittings

More types of PVC fittings are sold than in any other material, and most of them are used for DWV applications. This is due to the complexity often involved in consolidating waste lines from all over the house into one main sewer pipe. Since they originate at a large variety of fixtures and drains, and converge on a limited number of soil stacks, most of which must be enclosed inside of walls, their alignment can present a challenge. Fortunately, there is a fitting to address every situation.

Fittings for plastic pipe and fittings for connecting plastic to metal pipe are available in threaded, compression and solvent weldable types. They are available in smaller diameters for pressure connections; these fittings tend to be heavier and with deeper throats. 

Threaded plastic fittings thread exactly like metal fittings. In applications where both hot and cold water will be carried, however, special transition fittings should be installed to prevent leaks caused by the different expansion rates of plastic and metals.

Solvent-weld fittings have specially formed sockets into which plastic pipe is inserted. The inside of the socket is slightly tapered, from a diameter slightly larger than the pipe OD at the entry, to a dimension at the root of the socket that is a few thousandths of an inch smaller than the pipe OD. Solvent cement is applied to the outside of the pipe end and the inside of the socket. The pipe is then pushed into the socket until it bottoms.

Pipe and fittings are bonded together by means of chemical fusion. Solvents contained in primer and cement soften and dissolve the surfaces to be joined. Once the pipe and fitting are assembled, a chemical weld occurs. This weld strengthens over time as the solvents evaporate.

The manufacturer's name or trademark is printed on each fitting, as well as the standard to which it conforms, fitting size, resin type, item identifier, mold cavity identifier, and Schedule number or DWV. It will bear a laboratory seal or mark if it's suitable for potable water.

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