Rating Air Compressors

Overview

Engineering reference data for Rating Air Compressors in gases and compressed air.

Key Formulas

Ideal Gas Law

$PV = nRT$

Pressure × Volume = moles × gas constant × temperature.

Boyle's Law

$P_1 V_1 = P_2 V_2$

At constant temperature.

Charles's Law

$\frac{V_1}{T_1} = \frac{V_2}{T_2}$

At constant pressure.

Variables

Symbol	Description	Unit
$P$	Pressure	Pa
$V$	Volume	m³
$T$	Temperature	K
$R$	Gas constant	8.314 J/(mol·K)

Air Compressor Rating Terms

• CFM (Cubic Feet per Minute): Imperial volume flow rate of compressed air, defined at specific pressure, temperature, and humidity.
• ICFM (Inlet CFM): Air flow in CFM as it enters the compressor intake.
• ACFM (Actual CFM): Air flow in CFM at a reference point under local conditions.
• FAD (Free Air Delivery): Actual quantity of compressed air converted back to inlet conditions, typically measured per ISO 1217 (ambient temperature 20°C, pressure 1 bar abs, humidity 0%, working pressure 7 bar abs).
• ANR (Atmosphere Normale de Reference): Air at 1.01325 bar absolute, 20°C, and 65% relative humidity.
• SCFM (Standard CFM): Flow in CFM converted to standard conditions (14.696 psia, 60°F).
• nl/min: Flow in l/min converted to standard conditions (1.01325 bar absolute, 0°C, 0% relative humidity).

FAD Unit Conversions

$1 \, \text{m}^3/\text{min (f.a.d)} = 1000 \, \text{liter/min (f.a.d)} = 1000 \, \text{dm}^3/\text{min (f.a.d)} = 16.7 \, \text{l/s (f.a.d)} = 16.7 \, \text{dm}^3/\text{s (f.a.d)} = 35.26 \, \text{ft}^3/\text{min (f.a.d)}$

References

• Original Source