As part of figuring that out, you either know already, or you are about to find out, that Pi equals approximately 3.14. I say Pi is approximately 3.14 because the number actually has been solved out to 2,000,000 places past the decimal point, and the number is still growing! I opted not to put all the numbers available behind the 3.14 here.
We need to know what Pi means to help figure out cylinder compressed air consumption. To do that we first need to determine the surface area of the piston inside the air cylinder. Then, if we multiply that surface area by the working stroke we'll get that cylinder air volume.
For simplicity's sake in determining air cylinder consumption though, I have chosen to ignore that difference.
The formula to use to determine the area of a circle is:
or, 3.14 x the radius squared
Our example will be a 2.5" bore air cylinder.
A 2.5" bore cylinder will have: 3.14 x r2 ( which is 1.25 x 1.25) or, 4.90 square inches of surface area on the piston face.
We will make the stroke 10". That means that this cylinder holds 4.9 x 10, or 49 cubic inches of compressed air.
If we extend and retract this cylinder one cycle that is a total of 98 cubic inches of air we would need for one extension and one retraction.
98 cubic inches of air x 10 complete cycles per minute = 980 cubic inches of air consumed per minute
Therefore, 980 cu inches divided by 1728 = .6 cubic feet of air.
My rule of thumb:
That being the case, this cylinder (2.5" bore x 10" stroke - 10 cycles per minute) will need approximately 3 CFM of compressed air to run continuously.
Since 1 HP of compressor motor generates about 4 CFM at 90 PSI, you can see that the use of air cylinders will quickly eat up compressor capacity. On a high speed machine with multiple cylinders, air consumption can be staggering.
Or, if you required detailed and accurate air cylinder air consumption figures, figure on getting help from and engineer, or, contact the air cylinder manufacturer. That'll get you the straight goods their air cylinder air consumption.