PVC Pipe and Tubing

Basics

Rigid pipe sizes are designated by a nominal diameter, meaning by name only. For example, a 1/2" pipe does not measure 1/2" on the outside nor on the inside, it is just a nominal distinction. There are various wall thicknesses available in pipe that allow the pipe to be used in different applications. This is designated by the schedule of the pipe. The OD of a pipe does not change between schedules, only the ID. Therefore, the OD of a 1/2" pipe is the same whether it is schedule 20 or schedule 80. Pipe connections are often made with threaded fittings but can also be made with socket fittings (welded for iron pipe, solvent-weld for PVC). A 1/2" coupling will fit on ANY 1/2" pipe, regardless of its schedule.

Tubing is designated by both the OD and ID and are actual measured dimensions. If only one dimension is given, it will be the OD. For example, 1/2" PVC tubing will have an outside diameter of 1/2". Most frequently though, both the OD and ID are given and these values are important to know when selecting various tubing connectors.

Tubing can either be rigid or flexible and both types have associated fittings. Compression fittings and quick-connect fitting are both used on rigid tubing and are sized according to the OD of the tube. Barb fittings are used on flexible tubing and are selected according to the ID of the tube.

Types of PVC Fittings

There are many types of fittings that are available to connect PVC pipes.  Pipes and fittings can be either threaded or unthreaded.  Fittings that join pipes must correspond, i.e. a threaded pipe can only connect to a threaded elbow, not an unthreaded one.   Check out this Wikipedia guide that explains the different types of pipe fittings.

Sealing PVC Pipe Fittings

In order to prevent leaks, it is often necessary to seal connections between a pipe and its fitting.  

To seal a threaded connection, wrap pipe tape around the external threaded 3 or 4 times and twist the components back together.  Pipe tape can be found in one of the main tool drawers.

To seal an unthreaded connection, make sure you have a clean surface.  Wipe off any dirt and remove rough edges they may have resulted from cutting. Use a wrench to open the PVC Primer and Cement.  When not in use, these must be sealed well to prevent from drying out.  Apply PVC Primer to BOTH the pipe and fitting where the two will make contact.  Allow the primer to dry for about 15 seconds.  Then apply PVC cement evenly to the same location, insert the fittings, give the pipe a twist to remove any air bubbles and to distribute the cement evenly and hold for about 15 seconds.  Don't forget to put the lid back on the primer and cement and tighten it back with a wrench.