Im trying to calculate the filling time of an air receiver. Air receiver will not be supplying air when its filling.

I was trying to use following formula:

T = Vr (P2 – P1) Po (Acfm)

Where: T is time required – min. Vr is tank (or system) volume-cu ft. (cu ft = gal/7.48) Po is atmospheric pressure – psiA P1 is initial tank pressure – psiA (*) P2 is final tank pressure – psiA (*)

Acfm is CFM air delivered by the compressor during the pump-up pressure change

I wanted to know this Acfm value will be Actual ft3/min at compressor suction?

Or at the point where it enters receiver. Actual ft3/min values will differ. Do we use

Acfm or scfm for this formula. Kindly advise?