Re: New HVLP gun
I have a compressor that puts out 13 cfm at 90 will it work with a gun that need 19 cfm at 29 psi? Or what will it do?
The 13 CFM, is that at 90 PSI or the 40PSI figure for your compressor? If it is the 90 PSI figure then your compressor may produce around 16-17 CFM at 40 PSI (but keep in mind that 40 PSI at the tank is not the same as 40PSI at the end of a hose if trying to push 19 CFM through a hose as that is a lot of air without a fair bit of pressure behind it or a large diameter hose. Also keep in mind that there is a pressure drop at each pressure regulator and typically there is a regulator set at 90-100 PSI at the tank (or drop) and another set to the 29-40 PSI installed right at the spray gun to ensure a stable and predictable pressure at the gun (note that a spray gun rated at 29 PSI may actually require an inlet pressure of 40 PSI, so read its manual to find the recommended pressure setting at the spray gun. For that reason you are still better off using the 90 PSI figure when shopping for a HVLP spray gun.
If you absolutely had to you could do smaller projects provided you have a very large tank to serve as a pre-charged air reservoir to buy you some time, but at 19 CFM your spray gun may move too much finish for small projects. Plus, if you run out of pressurized air in the middle of your job the finish will not atomize properly which may make a mess of things. Consider that an 80 gallon air tank can deliver about 20 cubic feet of air when discharged from 150 PSI to 50 PSI (which is about as far as you could possibly fall on tank pressure), any difference between the spray gun's demand and your air compressor's ability to produce air must be made up for by the air tank alone unless you can break up your job into smaller sections to allow the tank to recharge for a few minutes. With a 6 CFM deficit (19-13=6) you could perhaps get up to 3 minutes (20/6) of spraying in before pressure dropped too far with an 80 gallon reserve tank, but that is an optimistic figure as you may need more pressure to meet the 19CFM requirement at the end of your hose or your tank may be smaller or your spray gun may actually require more than 19 CFM (many air accessories require more than their advertised air volume as the stated CFM is often based upon an assumed duty cycle ratio that may, or may not, match your actual usage). Depending upon the tank pressure you actually need to ensure adequate air volume and pressure at your spray gun, that 3 minute figure may drop to as little as 1 minute -- something to be aware of before hand.
You can get smaller HVLP spray guns that are much better matched to your air compressor and that would be, by far, the better way to go unless this hypothetical spray gun happens to be free (in which case, experiment to see what you can get away with). If you stick with a gun whose demands can be met, or very nearly so, by the 90 PSI CFM capacity of your compressor then you can be assured that you will never run out of pressure or volume while spraying, ensuring you will always have adequate air pressure and volume at the end of your length of hose. For your purposes, look for a HVLP spray gun rated no more than the 12-14 CFM range and you should have no issues, but ask for more than that and you may find that the setup does not meet with your expectations.
Good luck!
