High-volume, low-pressure (HVLP) paint guns provide many advantages over their low-volume, high-pressure, gravity-fed brethren. For example, HVLP paint guns cut down on lost paint and "fog" caused by high air pressure, providing more coverage per quart of paint than high-pressure guns. Many body shops and hobbyists also say that it is easier to put a clean coat of paint on sheet metal and car parts with an HVLP paint gun than it is with a high-pressure gun. One problem that plagues professional painters and hobbyists alike is matching a compressor to their paint gun, or vice versa.
Examine the owner's manual of your HVLP paint gun for the specified CFM@PSI measurement the gun needs to function properly. The useful thing about HVLP paint guns is that they can run on relatively low pressure, but you must make sure to select a compressor that is within the pressure range of your gun. Normally, this is quoted as CFM@30PSI, 40PSI or 90PSI (example: 25CFM@90PSI).
Contact a few compressor manufacturers' help desks for more information regarding CFM ratings for your HVLP paint gun and some of their compressor options. Have the CFM rating for your paint gun available, and ask specifically if the compressors' ratings are similar to the ratings you are looking for. If they are more than 15 percent different, find a different compressor or manufacturer.
Find the highest possible CFM rating that your HVLP paint gun will be running on (this can normally be found in the owner's manual as well). Multiply the highest CFM rating by 50 percent. Add this number to the total CFM required. The number you come up with will be the highest rating of air compressor you should be looking for, as CFM ratings within 15 percent of this number will allow you to run your tools without over-taxing the compressor.
Check to see if your HPLV spray gun can operate on the CFM rating you determined in Step 2 by either testing a gun/compressor setup or by contacting the manufacturer of your paint gun and compressor manufacturers to inquire as to their compatibility. If you are satisfied that your compressor rating will provide the type of performance you are looking for, determine your budget and begin shopping around for the best deal on an air compressor within your specified CFM rating. Remember, it doesn't have to match your specs exactly, but it should be close.
Purchase the compressor and try the gun out on a small project to see if the spray looks satisfactory. If the compressor cannot handle the gun, now is the time to return for a larger model (since your compressor should still be under warranty).