Air Line Sizing with Respect to Air Outlet Size on the Compressor

by Mark A.
(Chicago)

Hi,
I have a question relating to air-line / plumbing. In the air-lines page I read the quotes about small air lines causing turbulence and pressure robbing:
"There’s no such thing as too large a compressed air line. A common error in compressed air systems is line sizes too small for the desired air flow." And "Undersized piping restricts the flow and reduces the discharge pressure, thereby robbing the user of expensive compressed air power."
I am looking for a compressor that is roughly in the 3-5HP / 60Gal / <$1000 range. All of the compressors I have seen in this range have a 3/8” or 1/2” air outlet size. So my question is, doesn’t going from 1/2” to your filter / regulator / manifold and then out to like a 2” pipe cause quite a bit of pressure drop and turbulence? Why don’t the compressor manufacturers just make the air outlet ports like 3” and make the consumer downsize to whatever they may need?
From what I have read on this site I have no doubt that I have come to the right place for an answer! Look forward to hearing back,

--Mark

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Bill says...

Howdy Mark. Thanks for your kind words.

The discharge port size on a compressor is generally the right size to handle the maximum CFM rating of that compressor. Going bigger than that provides no benefit to the user, and increases, possibly, the cost to the compressor manufacturer.

In terms of air mains in a shop, you will have read that I'm a strong proponent for large storage, and remote compressed air storage to allow your compressed air time to cool and de-water naturally.

If you decide to plumb from a 1/2" discharge port on the compressor to a 2" air main, there will be some initial turbulence as the mains fill, but from then on, that will self limit. It depends on the CFM requirements of the tool being used as to how fast that 3" main is drawn down, the same for the compressor tank, and the frequency with which the compressor cuts in as a result.

I don't know how much 2" pipe you are considering, but instead of looking at it just as a pipe, consider it as a longitudinal air tank.

Bigger is better, especially if you are hoping to power high demand air tools.

Hope this helps.

Cheers,

Bill