This type of equipment pressurizes and stores air to be converted to power. The power of an air compressor is measured in horsepower (HP) and cubic feet of air per minute (CFM). Positive displacement air compressors include piston type, rotary screw, and vane compressors. A centrifugal compressor is a negative displacement air compressor. Most industrial air compressors produce pressurization of approximately 100 pounds per square inch (psi).