If I trigger a complete refill cycle, it cranks for 4 minutes, 21 seconds (your figures) to build pressure from 0 p.s.i. to 135 p.s.i.

Divide the tank volume in gallons by 7.48 (1 cu-ft = 7.48 gallons) to get the tank volume in cubic feet. Thus the tank volume is 60 gallons / 7.48 gal/cu-ft = 8.021 cubic feet.

In units of atmospheres of pressure (ATA), since 1 ATA = 14.7 psi, these start and stop pressures are 0 ATA and 9.18 ATA, respectively. So the compressor adds 9.18 ATA of pressure during the cycle.

When a compressor pumps one "CFM" (cubic foot per minute), that means it sucked in one cubic foot of "free air" (air at atmospheric pressure).

Thus in one cycle, the rate at which air is being pumped into the tank, is the pressure rise times the volume of the tank, or 8.021 cubic feet * 9.18 ATA = 73.66 cubic feet per 4 minutes and 21 seconds. To proportion the time down to one minute, to get the pumped volume per minute, multiply by 60/261, or 73.66 * 60/261 = 16.93 CFM (at 135 psi).

There will be some variances considering temperature, relative humidity, and how accurate the compressor shutoff is calibrated assuming 1050 RPM. So, if you want to find out how long or what the CFM is for a slower RPM drumroll please, do a simple ratio!

What does all the math mean? Your quoted numbers are conservative for this compressor. Finally, someone gets it. Congratulations.

Last Edited on 8-Mar-2007 1:06 PM