sizing air lines

[Deleted User]

We have a customer that wants us to install an air system to operate the tools there mechanics use. How do you size up the piping? Is it by CFM?

Brad White_185

Compressed Air

Hi Mike-

CA piping is sized by CFM typically (Imperial units) and by pressure drop across the line from source to terminal (tool).

Say a tool uses 3.2 CFM and requires 100 PSIG at the tool. You work backwards, segment by segment as your piping delivers that flow rate (plus a percentage of upstream capacity also moving along).

You add your pressure losses plus a margin for "bounce" (my term for the sudden pressure drop when a tool kicks on unless you have a larger receiver) and that is your compressor filter/dryer outlet pressure or receiver pressure to be maintained.

Typically, I size CA piping (for as often as I do which is not often at all!) for a pressure loss of not over 10 PSIG or 15 percent, whichever is less.

In other words, if I need 100 PSIG as the highest pressure at the furthest tool, I size the piping for a drop of not more than 10 PSIG, that being less than 15% or 15 PSIG.

Not saying this is the only way, it is just the way I was taught.

There are sizing charts (I think ASPE publishes them as CA is usually a plumbing specialty along with medical gasses for example.

Typically you size it segment by segment as you would for any flow piping or ductwork. Know the CFM and pressure for each tool used and how they accumulate along the mains.

Unless this is a manufacturing facility, there is a LOT of diversity on such a system. In other words, the chance of all tools drawing air at the same time is probably insignificant.

One technique I use to conserve pipe size is to make a "loop" rather than a dead-ended main. This allows a reduction in pipe size because the air is coming from two directions usually.

Other factors which are important to know: How clean and how dry the air needs to be. You may have to buy a drier and filter set, oil separator and other goodies. Some process air has to be oil-free (probably not a mechanic's shop), but the tools may need 5 micron filters for example.

Hardly the last word on anything, but some idea of how it is done.

Hope this helps!

Brad

Tony Conner_2

Sizing Compressed Air LInes

We've just moved, so most stuff is still in boxes, but I'm sure there's a line sizing table in the "Pocket Ref". I also believe there's a table giving typical CFM air requirements for various pneumatic tools.