Your site: altitude, air temperature, humidity (sea level, 20 °C, dry)
Ambient pressure: kPa (standard atmosphere).
Your flow converted to each reference basis
How it’s calculated
Every basis is the same amount of dry air at a different pressure and temperature (ideal gas). The volume scales with absolute pressure and absolute temperature; water vapour in humid reference air is taken out first.
Q2 = Q1 × (p1 − RH1·psat) / (p2 − RH2·psat) × T2 / T1
Pressure
FAD, Nl/min and SCFM are not the same number
A flow in litres or cubic feet means nothing without the conditions it's measured at. Compressor datasheets give FAD: the air at the compressor inlet, at 1 bar and 20 °C. Normal litres (Nl, Nm³) are at 0 °C, and cold air is denser, so the same air takes up about 8% less volume. Standard cubic feet (SCFM) sit in between.
| Basis | Reference conditions | 1 litre FAD equals |
|---|---|---|
| FAD (ISO 1217) | 1 bar(a), 20 °C, dry | 1 l |
| Normal, DIN 1343 (Nl, Nm³) | 1.013 bar(a), 0 °C, dry | 0.92 Nl |
| Normal, ISO 8778 ("ANR") | 1 bar(a), 20 °C, 65% RH | 1.02 Nl |
| SCFM | 14.696 psi(a), 60 °F, dry | 0.97 standard l |
| Standard air (ASME) | 14.7 psi(a), 68 °F, 36% RH | 0.99 standard l |
The flow in the pipe is much smaller again: at 7 bar the air is compressed about 8 times (absolute pressure: 8.013 / 1.013).
So if a machine needs 350 Nl/min, look for a compressor with at least 380 l/min (13.4 cfm) FAD. Makers of pneumatic components often mean ISO 8778 when they write Nl/min; if the datasheet doesn't say, ask.
The full explanation: Free Air Delivery (FAD).