- 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's 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 pounds per square inch.
The determining factor in choosing a compressor is this cfm. Consider what your typical cfm demands will be by checking the cfm specs on your air tools, blaster, spray guns, etc. Be sure to choose a compressor that's capable of delivering sufficient cfm, at the rated psi, that will supply the highest air volume using the tool you have or will require. Using air tools that exceed the cfm rating of the compressor will cause the compressor to run constantly, overworking and overheating 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 tool's 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, including, but not limited to:
-- Construction: Single-stage vs. 2- or 3-stage; piston vs. screw-type vs. diaphragm; radial or inline.
-- Number of fittings and connectors, their IDs, hose IDs and length: Adding fittings and connectors, using 3/8” vs. 1/2” fittings, or using a longer hose will dramatically reduce available cfm.
-- Atmospheric conditions: Barometric pressure, humidity and ambient air temperature.
In short, it's 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.