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Rating of Air Compressors and Air Equipment
The most common terms rating air flow capacity are ICFM, FAD, ANR, SCFM or nl/min
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There is no universal standard for rating air compressors, air equipment and tools. Common terms are:
- CFM
- ICFM
- ACFM
- FAD
- ANR
- SCFM
- nl/min
CFM
- CFM (Cubic Feet per Minute) is the imperial method of describing the volume flow rate of compressed air. It must be defined further to take account of pressure, temperature and relative humidity - see below.
ICFM
- ICFM (Inlet CFM) rating is used to measure air flow in CFM (ft3/min) as it enters the air compressor intake .
ACFM
- ACFM (Actual CFM) rating is used to measure air flow in CFM at some reference point at local conditions. This is the actual volume flow rate in the pipework after the compressor.
FAD
- FAD (Free Air Delivery) (f.a.d) is the actual quantity of compressed air at the discharge of the compressor. The units for FAD are CFM in the imperial system and l/min in the SI system. The units are measured according the ambient inlet standard conditions ISO 1217 - 1 bar abs and 20oC.
- 1 m3/min (f.a.d) = 1000 liter/min (f.a.d) = 1000 dm3/min (f.a.d) = 16.7 l/s (f.a.d) = 16.7 dm3/s (f.a.d) = 35.26 ft3/min (f.a.d)
ANR
- ANR (Atmosphere Normale de Reference) is quantity of air at conditions 1.01325 bar absolute, 20oC and 65% RH (Relative Humidity).
SCFM
- SCFM (Standard CFM) is the flow in CFM measured at some reference point but converted back to standard or normal air conditions (Standard Reference Atmosphere) 14.4 psia, 80oF and 60% RH (Relative Humidity).
nl/min
- nl/min is the flow in l/min measured at some reference point but converted to standard or normal air conditions 1.01325 bar absolute, 0oC and 0% RH (Relative Humidity).
ISO 1217
- standard reference ambient conditions - temperature 20oC, pressure 1 bar abs, relative humidity 0%, cooling air/water 20oC, and working pressure at outlet 7 bar absolute.
Example - Rating a Compressor
A typical rating of a compressor may look like this
| FAD (CFM) | Description |
| 11.1 cfm @ 7.5 Bar | The Free Air Delivery from the compressor is 11.1 CFM at 7.8 Bar |
| 8.2 cfm @ 10 Bar | The Free Air Delivery from the compressor is 8.2 CFM at 10 Bar |
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Related Topics
- Gas and Compressed Air - Gas properties, capacities of pipelines, sizing of relief valves - air, LNG, LPG and more
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Related Documents
- Air Compressors - Maximum Air Flow Inlet Pipe - Inlet pipe size and maximum air flow
- Air Tools and Air Consumption - Average air requirement of some common air tools
- Compressed Gas and Air - Storage Volumes - Calculate the storage volume of compressed air or gas
- Pressure and Maximum Content of Water in Saturated Air - Air pressure and maximum content of water in saturated air
- SCFM versus ACFM and ICFM - Actual air compressor capacity (ACFM) versus standard air capacity (SCFM) and inlet air capacity (ICFM)
- Types of Air Compressors - Reciprocating, rotary screw and rotary centrifugal air compressors
