Pneumatics 101

NORMAL AIR vs. FREE AIR

Air is commonly measured in cubic feet, but the actual amount of air in a cubic foot depends on pressure and temperature. Therefore, it is necessary to create a standard cubic foot of air. For most industrial applications, a standard cubic foot of air is considered to have the following features:

Pressure = 1 atmosphere (14.7 psi)
Temperature = 20 degrees Celsius (68 F)
Relative Humidity = 36 percent

Of course the idea of "normal air" is usually only an ideal. We typically must deal with "free air," or, air we encounter in everyday life. However, the features of free air are close enough to those of "normal air" so that changes are not necessary for the small differences.

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