Determining the ideal pipe size for your system often doesn’t get the attention it deserves. Unfortunately, failing to properly plan your distribution channel can result in a higher than desired velocity, and therefore a reduction in system pressure.

How Pipe Size Affects Pressure

The more narrow a pipe is, the higher the speed (velocity) the air will need to travel in order to get to the demand side. Think of putting your thumb on the end of a hose to visualize this concept. However, (and here is the complicated part that requires more space than is permitted in this article) as velocity increases, the pressure decreases. Therefore, to ensure you do not have unnecessary pressure drops downstream, you will want to ensure you have the proper pipe size/velocity.

What Velocity Do I Want?

Ideally in your main header, you do not want your velocity to exceed 20 fps. Downstream, closer to point of use, this can be slightly higher, but still you do not want to exceed 31 fps.

ExampleA system outputting 500 CFM, @ 100PSIG.

• Using an improperly sized 2″ pipe, velocity will be 48.9 fps, with a pressure drop of 19.2 psi (per 1,000 ft of pipe).
• The same mass going through a 3″ pipe will have a velocity of 21.7 fps, with a pressure drop of only 2.34 psi (per 1,000 ft of pipe).

Calculate the Ideal Pipe Size

To determine the ideal pipe size for your system, you will want to know (1) peak CFM flowing through the pipe, (2) gauge pressure in pipe.

If you want the long equation for determining pipe size, shoot us an email. Otherwise, use our Pipe Size Calculator to automatically calculate the ideal pipe size.