# compressed air flow thru sch 40 pipe
**URL:** https://boards.straightdope.com/t/compressed-air-flow-thru-sch-40-pipe/21758
**Category:** Factual Questions
**Created:** [June 8, 2000, 3:04pm UTC](https://boards.straightdope.com/t/compressed-air-flow-thru-sch-40-pipe/21758 "2000-06-08T15:04:14Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@Burnsman2000](https://boards.straightdope.com/u/Burnsman2000)
#### Post date: [June 8, 2000, 3:04pm UTC](https://boards.straightdope.com/t/compressed-air-flow-thru-sch-40-pipe/21758/1 "2000-06-08T15:04:14Z")
what size sch40 galvanized pipe should i use for 100scfh 90psig compressed air
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### Author:  [@Steve-o](https://boards.straightdope.com/u/Steve-o)
#### Post date: [June 8, 2000, 3:16pm UTC](https://boards.straightdope.com/t/compressed-air-flow-thru-sch-40-pipe/21758/2 "2000-06-08T15:16:11Z")
It’s gonna depend on the velocity you want. If the velocity of the air is not important, your size is not going to matter much (use what is available, cheap or easy to work with), as 100scfh at 90psig is going to be easy to attain with just about any size pipe.
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### Author:  [@cornflakes](https://boards.straightdope.com/u/cornflakes)
#### Post date: [June 8, 2000, 3:18pm UTC](https://boards.straightdope.com/t/compressed-air-flow-thru-sch-40-pipe/21758/3 "2000-06-08T15:18:35Z")
I dunno, but I doubt that the pipe size will be a limiting factor. I’ve got a air compressor piping guide that specs 1/2" iron for a 5HP two-stage compressor, that probably puts out ~15CFM @ 125-175PSI. I’m sure that the skin effects are similar with or without the zinc plating and should be minimal in any case.
If no one else can help, ask the valve supply that you’re buying the fittings from. I’ve seen formulas for this in the backs of catalogs before…
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### Author:  [@JonF](https://boards.straightdope.com/u/JonF)
#### Post date: [June 8, 2000, 4:38pm UTC](https://boards.straightdope.com/t/compressed-air-flow-thru-sch-40-pipe/21758/4 "2000-06-08T16:38:21Z")
For stuff like this, nothing beats Flow of Fluids through Valves, Fittings, and Pipe, Technical Paper number 410, Engineering Division, Crane Co. You can buy it on paper (US$30) or CD-ROM (a bit pricy, US$245 for the cheapest version) at [Crane Valves](http://www.cranevalves.com/).
I’d take a shot at solving your problem using it, but there’s far too little information in your original post.
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### Author:  [@Padeye](https://boards.straightdope.com/u/Padeye)
#### Post date: [June 8, 2000, 4:40pm UTC](https://boards.straightdope.com/t/compressed-air-flow-thru-sch-40-pipe/21758/5 "2000-06-08T16:40:13Z")
It depends on the length of the run. If it’s just a short run to a manifold or drier 1/2" should not be a problem but if you’re making long distribution runs make it as large as possible, at least 3/4" Small pipe will make a differenc in air delivery.