Ratio of Free Air to Compressed Air

Free air is air at ambient conditions at a specific location where

[LIST][*]ambient temperature[*]moisture content[*]barometric pressure[/LIST]
are stated.
[h=3]Compression Ratio[/h] [I]Compression Ratio[/I] is the ratio between [I]Discharge Pressure Absolute[/I] and [I]Suction Pressure Absolute[/I].
The compression ratio of free air - to compressed air, is indicated in the diagram below.
[h=3]Compression Ratio - Pressure [I](psi)[/I][/h] [img]http://www.egpet.net/vb/images/imported/2011/07/30.png[/img]

[LIST][*][I]1 psi = 6.9 kPa = 0.069 bar[/I][*][I]1 ncfm = 0.5 nl/s[/I][/LIST]
[h=4]Example - Converting a Compressed Air Volume to a Free Air Volume[/h] A compressed air volume flow of [I]10 acfm [/I]at [I]100 psig[/I] must be multiplied with a compression ratio approx.[I] 8[/I] to find the free air flow at atmospheric pressure.

[LIST][*]in this case approx. [U][I]80[/I][/U][I] scfm[/I][/LIST]
[h=3]Compression Ratio - Pressure (bar)[/h] [img]http://www.egpet.net/vb/images/imported/2011/07/31.png[/img]