Compressed Air Calculations

Because PULSAIR uses compressed air or gas to operate, it is helpful to understand how the volume of compressed air is calculated.

A standard cubic foot of air is the amount of air in one cubic foot of space at 70 degrees F and 14.7 PSIA, i.e. standard atmospheric conditions. Since pressure gauges do not register atmospheric pressure, 14.7 PSIA equates to 0 PSIG. Because this is approximately the way air exists in nature, air at atmospheric conditions is also called "free air". Therefore, 1 Standard Cubic Foot of air is the same as I cubic foot of free air.

A tank with a volume of 4 cubic feet holds 4 Standard Cubic Feet of air at atmospheric pressure (0 PSIG). If we inject air into the tank until the internal pressure is 44.1 PSIG, we have 4 cubic feet of air at 44.1 PSIG. How many Standard Cubic Feet of air is this?

Answer: Divide 44.1 by 14.7 = 3. This means that at 44.1 PSIG each cubic foot will contain three atmospheres plus the original 1 atmosphere that existed before pressurizing, or a total of 4 atmospheres. Multiply 4 cubic feet of volume by 4 atmospheres = 16 Standard Cubic Feet of air.

If we inject more air and double the pressure to 88.2 PSIG, the same math tells us we have 28 Standard Cubic Feet of air in the 4 cubic foot tank (88.2/14.7 = 6 atmospheres + 1 atmosphere = 7 atmospheres x 4 cu. ft = 28 SCF).

By using this standard unit of measurement we greatly simplify discussions and calculations of air volumes.