What FAD means
Free Air Delivery expresses compressor output as an equivalent volume at inlet or agreed reference conditions. Check the test conditions, outlet pressure and package boundaries in the datasheet. Positive-displacement compressors may be tested to ISO 1217; the abbreviation FAD alone does not replace a full test report.
Flow in the pipework is different
Air in pressurised pipework has a higher density, so the same mass occupies a smaller volume. Pipe velocity is therefore calculated from the operating volumetric flow. Comparison with catalogue FAD requires conversion between conditions, not merely changing minutes to seconds.
What to check in practice
- For a consumer's flow, verify whether it refers to free air, standard air or air at operating conditions.
- Compare compressor delivery at the same outlet pressure.
- Account for air treatment regeneration consumption in the delivered volume, unless already included in the balance.
Example scenario
The conversion 1 m³/min = 1,000 L/min ≈ 16.67 L/s applies at unchanged conditions. At 20 °C for ideal dry air, 1 m³/min at 1 bar(a) corresponds to approximately 0.125 m³/min at 8 bar(a).
What to watch out for
- Comparing FAD with theoretical intake displacement.
- Calculating velocity in a pressure pipe directly from free-air volume.
- Treating maximum delivery at a different pressure as guaranteed delivery in operation.
Does 1 m³/min always mean the same amount of air?
No. Without conditions, the figure is incomplete. The same volume at higher absolute pressure and the same temperature contains a greater mass of air. The meter and quotation must therefore use the same reference.