Intelligent Compressed Air: Distribution System Design

No matter what kind of compressor you have, or what you use compressed air for, a critical part of your system is the distribution system. My neighbor has a 5HP reciprocating compressor that sits on top of a 50 gallon tank in his garage. Unlike me, he LIKES working on cars, and has a variety of pneumatic tools, and a really nice air operated paint sprayer that he can make a car look brand new with. Anyway, his “distribution system” is a 1/2″ rubber air hose with a quick connect on the end. And that works just fine for him.

On the other end of the compressed-air-system-complexity spectrum, a large manufacturing facility may have a few (or more) compressors, and they may not even be in the same room. Today, we’re going to look at the factors that affect distribution design, and some of the “pros and cons” of those designs.

The two main types of supply systems…centralized (where there’s one single compressor room), and de-centralized (where individual compressors are located throughout the facility). There are advantages, and disadvantages to both as far as maintenance, number of operators required, controls, utilities, and noise reduction go. The main impact of these on the distribution and storage layout falls largely on distribution design. Supply headers have to be adequately sized, and plumbed, to get sufficient air flow to the farthest usage points from a centralized compressor room. Inadequate initial design, or adding load without considering flow capacity to service added load, can lead to increasing compressor discharge pressure to keep point of use pressure at the required level. De-centralized systems aren’t usually as affected…because they’re closer to their points of use by design, there’s less pressure loss through the distribution lines.

Whether the supply side is centralized or de-centralized, the advantages & disadvantages of different distribution piping layouts are similar in nature. Let’s look at a Loop design:

In this design, the compressors feed a complete loop of piping, with drops at points of use.

Since compressed air loses pressure due to friction as it flows through the distribution piping, it’s always important to design for the distance from the compressor, to the point of use, to be as short as possible. A Loop design facilitates this by allowing the air to reach any point of use from two directions…by definition, the farthest that the air has to travel is half the total length of the piping.

The other basic style of distribution layout is called “Trunk & Branch”:

In this design, the “trunk” (the horizontal line) feeds a series of “branches” (the vertical lines) to various points of use.

If the distance from the compressor(s) to the farthest point of use isn’t excessively long, a Trunk & Branch system is a lower cost alternative, because it uses less pipe. Keep in mind that line loss will necessarily create a pressure drop that steadily increases, the farther it gets from the compressor. If that means you have to use larger pipe, your installation & materials costs start to creep right back up. The larger the facility, the more sense it makes to consider a Loop design. Alternately, a de-centralized compressor layout can minimize line loss in a Trunk & Branch design too. Locating a compressor on the right-hand side of the sketch above, for example, will effectively give you the major benefit of a Loop design: allowing air to reach any point of use from both directions.

At EXAIR, our mission is to help you get the most out of our products, and your compressed air system. If you have questions, we’ve got answers – give me a call.

Russ Bowman, CCASS

Application Engineer
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