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Compressor Capacity

We recommend a F.A.D. of 1 litre per second at 5.5 bar (80psi) available at delivery unit. Although some manufacturers recommend 0.8 – 0.9 litres per second, it is our experience that this can be inadequate in certain circumstances. A slight amount of over capacity also improves the duty cycle of the compressor and adds considerably to the service life of the machine.

Free air delivery (FAD) is a standardized measure of the capacity of an air compressor.
To calculate the free air delivery of a compressor firstly the pressure and temperature at the inlet of the compressor are needed. Then the pressure and temperature of the outlet air along with the volume discharged are also measured. The output volume of the air is referenced back to inlet conditions using the Ideal Gas Law.

V1 = (V2 x p2 xT1) / (T2 x p1


The value of V1 is the free air delivery of the compressor.
The standard method for measuring free air delivery is given in the Standard ISO 1217, annex C.