If you've been shopping around for PVC you may have heard the term “schedule”. Despite its deceiving title, schedule doesn't have anything to do with time. A PVC pipe’s schedule has to do with the thickness of its walls. Maybe you've seen that schedule 80 pipe is slightly more costly than schedule 40. Though the outside diameter of a schedule 80 pipe and a schedule 40 pipe are the same, 80 pipe has thicker walls. This standard of measuring pipe came from a need to have a universal system for referring to PVC. Since different wall thicknesses are beneficial in different situations, the ASTM (American Society for Testing and Materials) came up with the schedule 40 and 80 system for classifying the two common types.
Both schedule 40 and 80 PVC are used widely around the world. Each one has its benefits in different applications. Schedule 40 pipe has thinner walls, so it is best for applications involving relatively low water pressure. Schedule 80 pipe has thicker walls and is able to withstand higher PSI (pressure per inch). This makes it ideal for industrial and chemical applications. To give you an idea of the size difference, 1” schedule 40 PVC pipe has a .133” minimum wall and 450 PSI, while schedule 80 has a .179” minimum wall and 630 PSI.
As mentioned earlier, both 80 and 40 pipe have the exact same outside diameter. This is possible because schedule 80’s extra wall thickness is on the inside of the pipe. This means schedule 80 pipe will have a slightly more restricted flow – even though it may be the same pipe diameter as an equivalent schedule 40 pipe. This difference in design makes schedule 40 and 80 pipes incompatible with one another. When beginning a project it is important you choose PVC parts that all have the same schedule. This will ensure your parts fit together properly. Generally, schedule 40 pipe is white in color, while schedule 80 is often gray to distinguish it from 40. PVC is available in many colors though, so be sure to check labels when purchasing.
So what schedule PVC do you need? If you plan to take on a home repair or irrigation project, schedule 40 PVC is probably the way to go. Even schedule 40 PVC is capable of handling impressive pressure, and it is likely more than adequate for any home application. You’ll also save yourself a little money sticking with schedule 40, especially if you plan on using large diameter parts. If your job will be industrial or chemical in nature, you probably want to use schedule 80. These are applications that will likely cause higher pressure and stress on the material, so thicker walls are imperative.