Technical Info: Compressed Air Data

Compressed Air Data Conversion Data Cover Per Gallon Decimal Equivalents Friction of an Air Hose Friction of Air in Pipes

General Conversion Micronic Particles Pressure Drop Viscosities Wire Screen Filter Data

When a pump uses 10 cfm at 100 psi, it is using 10 cubic feet per minute of free air that has been compressed to 2.46 cubic feet at 100 psi. The pump is then actually using 2.46 cubic feet at 100 psi, but the measurement of its consumption is on the basis of "free air" taken into the compressor of 10 cfm.

Compressed air is measured on the basis of the volume used per unit of time (cubic feet per minute) at a given pressure (psi). The reference to volume of compressed air is always a measurement of air in its free state, i.e. atmospheric condition.

The description above illustrates the economical benefit of operating a pump at the lowest air pressure that will adequately meet the needs of pump output.

Compressed air is not unlike flowing fluids in that pressure is lost in transmission piping and hoses. The following chart aids in choosing piping and hose to minimize pressure drop in air lines.

CFM of Free Air 1/2 inch - 80 lb 1/2 inch - 100 lb 1/2 inch - 125 lb
10 0.46 0.38 0.31
20 1.74 1.42 1.17
30 3.84 3.13 2.54
40 6.93 5.55 4.53
50 10.7 8.65 7.01
60
70
80
90
100
125
150
175
200
250