I asked this on another formum also and never got any answers.
Someone tell me if I am doing this right. I have a cheap gun that needs 8.4 CFM @ 40 psi. Note: some expensive guns need 12-15. I am assuming that 8.4 is volume at 1 atm, is that correct?
Looking at the example in the link above;
http://www.truetex.com/aircompressors.htm
25 gallons = 3.342245989 cu ft
At 14.7 psi 1 cu. ft. in the tank contains 1 cu. ft. of air @ 14.7 psi so the tank in the example contains 3.34
At 40 psi 1 cu. ft. in the tank contains 2.72 cu. ft. of air @ 14.7 psi so the tank in the example contains 9.09
At 85 psi 1 cu. ft. in the tank contains 5.78 cu. ft. of air @ 14.7 psi so the tank in the example contains 19.33
At 102 psi 1 cu. ft. in the tank contains 6.94 cu. ft. of air @ 14.7 psi so the tank in the example contains 23.19
So I start at 102 psi the tank contains 23.19 cu. ft. (of air @ 14.7 psi) and I use up the air at a rate of 8.42 cu ft per minute down to a pressure of 40 psi where the tank contains 9.09 cu ft.
So 23.19 - 9.09 = 14.1 cu ft and using it at 8.4 CFM it would last 1 minute and 40 seconds so this compressor is inadequate?