I'm trying to figure out how long a small 3 Gallon compressor tank will last in between the compressor kicking on and off. I know the tank volume, and cut-in/cut-out PSI, and my approximate SCF usage per minute. So can I just calculate the SCF of the tank at the cut-in and cut-out pressure, and then subtract them to get "usable SCF"?
The cut-in/cut-out pressure are the tank pressure before the regulator, which will step the pressure down 40-100 PSI. But converting to SCF should accommodate for this, right?
I'm using SCF = ACF * (tank pressure + 14.7) / 14.7 (in cubic feet and PSI units), where ACF is the actual tank volume.
Then the "usable air" = SCF_cutout - SCF_cutin?
EDIT: Concrete example:
Tank: 3 Gallons = 0.4 cubic feet (ACF)
Compressor Cut-out: 150 PSI
Compressor Cut-in: 120 PSI
Tank SCF @ 150 PSI: 4.5 cubic feet
Tank SCF @ 120 PSI: 3.7 cubic feet
"Usable SCF" = 4.5 - 3.7 = 0.8 cubic feet <-- is this correct?
RE: regulator pressure, it will be between 20-80 PSI - but the conversion to SCF should account for that, no?
Long story short, if I'm using 2.0 SCF/minute constantly, with only 0.8 SCF available in the tank between compressor cycles, then the compressor will always be on, which is bad, right?
[all this is ignoring temperature for simplicity, which I acknowledge is unrealistic]