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Minimum CFM for priming?

Depends ...

On the gun and primer you're planning on using. There are several different systems, each of which has it's own requirements. Additionally, every gun setup is slightly different, if using a HVLP system you really need to have a regulator mounted on the gun itself, and review the manufacturer's recommendations.
 
CFM is really an issue of whether your compressor can keep up with your gun. If you spray agressively it could be an issue. If you take a lot of breaks, no issue. Set your sprayer up as you would spray; No fluid. Pull the handle and watch for the pressure at the gun to drop more than a few PSI. That will tell you the limits of your compressor.

Most paints use a 1.3 or 1.4 tip. Many 2K primers (high solids) are best sprayed with 1.8 tips. The data sheet for your primer should recommend a tip size and possibly PSI for spraying.

Larry
 
Like others said, it depends on your gun. The gun I last used (DeVilbiss FinishLine), it needed 13CFM continuous. That goes down if you take breaks.

If you're priming the whole exterior in one go, you'll need all 13 CFM. If you are doing smaller pieces at a time and don't need to maintain a wet edge over large areas, you can probably get away with as low as half that.

Tip size doesn't affect anything related to the compressor. But it is important to match it to your paint TDS.

Compressor tank size just controls how long you have until the compressor kicks in. If it won't keep up then you will need to stop spraying until it catches up. With my 80 gal tank, that was about 10s of spraying. HVLP use a LOT of air.
 
Ken,

When beginning my airplane build, I decided early on I would not attempt painting the exterior of the aircraft myself. However, I did want to prime all the parts and also spray the interior.

As such, I really did not want to be forced to purchase a really large air compressor that was capable of providing the 7 - 13 CFM most of the really nice professional spray guns require. So I looked around for spray guns that did fine work on only 5 CFM ... which my air compressor could keep up with.

Ended up choosing the Eastwood Concours spray gun which uses 4.5 to 5 CFM with 30 psi at the cap. Very pleased with my decision. I used a 1.4 mm nozzle to spray the Akzo primer and 1.8 mm nozzle for the the Sherwin-Williams Jet Flex water reducible used on the interior.

The gun also supports the De Vlilbiss DeCups disposable cups and lids system ... which is nice because it allows the gun to spray upside down (which was great to have occasionally) and it cuts down a little time on gun cleanup (but not that much).

Happy building,
 
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