What is the difference between Free Air Delivery (FAD) and **SCFM?
Free Air Delivery is the actual CFM your compressor puts out. To measure Free Air Delivery you start with an EMPTY tank and you pressurize your compressor to the final fill pressure you want and then you open the tank valve. (You want to measure the time to fill the tank not the compressor, separators and purifier) You fill the tank to the desired pressure and measure how long it took. Then you divide the Cubic feet of the tank by the minutes it took to fill it. For instance a 80 Cu. Ft. SCUBA tank that takes 23 minutes to fill from empty puts out 3.48 CFM actual. **SCFM starts with a partially filled tank and fills it the divides the time as if it filled an empty tank. A confusing way to make poor performance look better. Generally **SCFM numbers are approximately 35% more than actual. 4.3 **SCFM = 2.78 actual FAD approximately So 3.48 FAD is much more actual CFM than 4.3 **SCFM which is well under 3 actual FAD.
