Compressor Selection

Many folks refer to motor horsepower and tank capacity when describing or sizing an air compressor. While these specifications are nice, consider the compressor as simply an “air pump” and it is more important to rate the ability of that “pump” to do a job. There is a common air volume requirement rating for evaluating the ability of a compressor, air tool or spray gun to perform a certain job. That is the “Cubic Feet per Minute” or “CFM” rating. As an example; this would be listed in specs as “12 CFM @ 85 PSI”. This translates into a device requiring an air volume of 12 Cubic Feet of air per Minute at a pressure of 85 PSI.

The determining factor in choosing a compressor is CFM. Consider what your typical CFM demands will be by checking the CFM requirement specs on your air tools, blaster, spray guns etc. Be sure to choose a compressor that is capable of delivering sufficient CFM at the rated PSI that will supply the highest air volume using tool you have or will require. Using air tools that would exceed the CFM rating of the compressor will cause it to run constantly which will overwork and overheat it, resulting in permanent damage.

This is also very important when choosing a tool, blasting equipment or paint gun. You want to be certain the air operated device requirements do not exceed the capabilities of your existing compressor. For example; if you have a compressor with a maximum output of 9 CFM @ 90 PSI and you are considering a blast cabinet requiring 12 CFM @ 85 PSI, the compressor will not be up to the task and the blast cabinet will not perform properly. This is also true of HVLP paint guns and other air operated tools.

Many factors will affect the actual CFM output of a particular compressor and they are but not limited to:

-     Construction – Single stage vs. 2 or 3 stage, piston vs. screw type vs. diaphragm, radial or inline.

-    How many fittings and connectors, their ID, the hose ID and length. Adding fittings and connectors and 3/8” vs ½” fitting & hose size will dramatically reduce available CFM. There is a great website that I need to find for you that provides data for pressure and CFM drop for each fitting and foot of a given hose size.

-     Atmospheric conditions – Barometric pressure, humidity & ambient air temperature.

In short, It is always best to find the highest CFM requirement of all the tools you own or ever plan to acquire then add 25% to that figure when choosing a compressor. I always use 85-95 PSI as a baseline.