How Are Compressors Rated?
There is no "universal" standard for rating air compressor output used by compressor manufacturers.
ICFM - rating used in measuring air as it enters the compressor intake in cfm at some reference point.
ACFM - flow in cfm measured at some reference point and based at conditions at that point
FAD - actual quantity of air compressed as measured at the discharge of the assembly package at a specific pressure.
SCFM - flow measured at some reference point but converted to a set of standard conditions. The ISO standards definition of standard air is temperature of 68°F (20C), pressure of 14.5 psia (1 bar), and dry air (relative humidity of 0%).
Normal Air - This is the average atmospheric air at sea level
with some moisture. It is defined by ASME Test Code For Displacement Compressors
as being 14.696 psiA, 68°F, 36% RH.
Care must be used to make sure performance comparisons between compressors
are made on an equal footing.
Potential Pitfalls of Failure to Apply Proper Ratings
- Lower than expected output at elevation
- Potential for seasonal shortfalls in hot and/or humid conditions
- Mismatch between plant load and compressor capacity
- Possibility of over sizing dryer and other equipment
For additional information or assistance, contact Kelly Beiermann, Nebraska Public Power District.
Note: We encourage requests from Nebraska customers. Businesses outside of Nebraska will be directed to their utility for further information.
Source: Airometrix Mfg., Inc. 1999-2003
