Cylinder Air Consumption

Cylinder Air Consumption calculations are quite complex.

To begin, you either know already, or you are about to find out, that Pi equals approximately 3.14.

I say Pi is 3.14 approximately because we understand that 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.

Hope you'll understand :-) !

Why Pi?

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.

Retraction Uses Less Air

Yes, it is true that the retraction stroke of a single rod air cylinder will use less volume of compressed air than the extension of that same air cylinder. The reason is that part of the surface area on the retract side of the piston is taken up by the piston rod. That means less room on the retract side for air.

For simplicity's sake in determining air cylinder consumption though, I have chosen to ignore that difference.

Area Of A Circle

Our example will be a 2.5" bore air cylinder.

A 2.5" bore cylinder will have: 3.14 x r2(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.

One More Step

You still have to allow for the compression ratio, a factor that affects the flow and volume of air under pressure.

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...

I've just had developed and made available here a quick cylinder air consumption calculator.

Don't forget, for manufacturer specific cylinder air consumption numbers, you can certainly ask the air cylinder manufacturer too.