Oct 29 2024
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      1. Normal reference conditions: 101.325 kPa, 0°C (32°F), 0% RH (Normal cubic meters [Nm3])
      2. FAD (Free Air Delivery) (f.a.d) is the actual amount of compressed air delivered by the compressor, measured at its outlet port, converted to the compressor’s inlet conditions. Inlet conditions for FAD are: ambient temperature = 20oC, ambient pressure = 1 bar abs, relative humidity = 0%, water or cooling air temperature = 20oC. The units of FAD are [CFM] in the imperial system and [m3/s] in the SI system, although in Europe and outside countries using the imperial system it is popular to use units such as [m3/min, m3/hr, litres/minute, litres/second].
      3. Normal compressor flow is the actual amount of compressed air supplied by the compressor, measured at its outlet port, converted to the compressor’s normal inlet conditions. Normal inlet conditions are: 101.325 kPa, 0°C (32°F), 0% RH (Normal cubic meters [Nm3/min], [Nm3/hr], etc.)

There is no universal standard for rating air compressors, air equipment and tools. Common terms are: CFM, ICFM, ACFM, FAD, ANR, SCFM, lN/min, ISO1217:

  • 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 (Inlet CFM) rating is used to measure air flow in CFM (ft3/min) as it enters the air compressor intake.
  • 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.
  • ANR (Atmosphere Normale de Reference) is quantity of air at conditions 1.01325 bar absolute, 20oC and 65% RH.
  • SCFM (Standard CFM) is the flow in CFM measured at some reference point but converted back to Standard Reference Atmosphere conditions 14.696 psia, 60oF.
  • lN/min is the flow in litres per minute measured at some reference point but converted to normal air conditions 1.01325 bar absolute pressure, 0oC and 0% RH.
  • ISO 1217 standard reference ambient conditions – temperature 20oC, pressure 1 bar abs, relative humidity 0%, cooling air/water 20oC.
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