I've noticed the topic of compressor size and CFM is of heavy focus in conversations when it comes to painting. In pondering the subject, I've come to a point where I'm willing to be the guy that say's "what's behind it?".

HVLP. High volume, low pressure.

Google says" High volume low pressure (HVLP) is similar to a conventional spray gun using a compressor to supply the air, but the spray gun itself requires a lower pressure (LP). A higher volume (HV) of air is used to aerosolise and propel the paint at lower air pressure".

So, past the point of the venturi effect and sucking product into an exiting stream of atomized droplets, now it's a high volume in the gun that pushes product to aid in atomization? Is that correct?

Getting past that point, doesn't it come down to fluid viscosity, pressure to push, and atomization on exit? Key point being atomization of the fluid?

I'm left to wonder if maybe the "no substitute for cubic feet per minute" couldn't be replaced with this is what happening and how you adjust for it?


I know...looks like farm equipment spraying. But it still comes down to droplets.

I mentioned early on I'm a welder not a painter, although the two hold a degree of similarities, I know I can still join metal with a small welder. And I did spray my first car with an undersized compressor, acrylic enamel. Three tone. I know, white hides a lot. Honestly, I still have the car. While I doubted my abilities to do smooth body work or smooth paint in a garage even after all I read, it turned out nice. It will one day go back to original black. You might notice the small dent in front of the door handle. Size of a soft ball? For good reason. A week after it was painted it took the hit, lol. It's still in the door. Part of the memories.


And a base coat clear on another before upgrading the compressor for increased air supply capacity to run air tools. I know hand sanding.

It was however not lost to me the key points of atomization during the application of paint products. This was before the days of internet. Hot rod magazines and living to learn. So, I'm not offering opinion from more then that basis.



I don't in my opinion think it's all about the size of compressor and CFM? More the material viscosity, ratio of product to air, distance from the surface and speed of travel that makes the difference in applying a uniform coating?
Isn't CFM similar to a welder duty cycle in that aspect? I may not be able to spray product non stop, but couldn't I spray product in short applications and still expect respectable results if the gun is set for proper atomization of the product and it's viscosity when sprayed? I think so? But I'm no expert and I'm assuming lots.

As I said, I've been pondering it for a bit? I'm thinking as a novice wanna be painter, what makes the difference in a quality application of product isn't having a high out put compressor, or expensive gun, it's seemingly how the gun is set that makes the difference? Droplets to a surface.

I'm not saying a large air supply isn't beneficial, or a quality gun won't atomize better. But I've paid attention when you guys have talked spraying product, put into practice what I've learned along the way, flow coats, wet coat, misting...I'm picking up enough to ask more and deeper questions?

While my limited experience suggests from what I've read and put into practice, proper mixing for flow, and settings of air to product ratio, combined with how far away and how fast or slow I move decides coverage and making the difference between success and mess more so then the size of the compressor or the quality of gun? Is this wrong?
The latter mentioned compressor size and gun quality offering a sustained air supply and improvement in atomization consistencies, doesn't change the basis for atomization and the way it reacts hitting a surface, how it flows, blends and holds on till it dries.

Anyways, my 2 cents in the conversation. For the record, I apply the same principles to welding, or with rephrasing, I apply the same principles of practice to the deposition of metal in the same way. How small a droplet, how fluid the droplet becomes, the force it's transfered, how viscous it's become, what it does or how it reacts hitting the surface, followed by does it spread and flow, or collect and run? And how fast must I move, to what depth away, to control and prevent the occurrence?
Sounds alot like painting to me?
I said my piece. Time to get something done. I'm reminded "they" will learn in spite of us. Internet sure has shortened the curve.

Have you read the articles in the Info Center?
There are a few discussing atomization.

'68 Coronet R/T wrote:Have you read the articles in the Info Center?
There are a few discussing atomization.

Actually I had, and for reader reference I'll included the link.
https://www.autobody101.com/content/art ... omization/

"Most all basic issues dealing with HVLP can be applied to conventional guns, atomization is atomization."
This was the key point I was trying to make. What size is the droplet? A given size of droplet will change coverage dependent on the distance from the panel. BB's may not give the coverage marbles will if sprayed to far away.

"You have two things that help you with this process, air and solvent."
Getting into the nitty gritty, the solvent reduces viscosity allowing for the air to be "slapping" those drops into finer droplets with less force required to do so. If my understanding is correct, the small fluid tip allows then for a greater air accumulation to accomplish this task? Example a light pressurization of the room will feel like a slight breeze by the open door the air exits?


"The thinner (less viscosity) you get the PSPR or the more air you have at the fluid tip of the gun the more it will break up the PSPR. The target for you is getting the perfect balance needed."

I think the soup needs more salt? Could be the soup has excess broth? The relationship between the fluid state and pushing the fluid is as mentioned finding the balance.

"And with HVLP guns there is less air at the cap to break up the PSPC, proper air supply and gun setup is more important than ever."

What's more important? Air supply, gun or set up? Each play a role in making it happen. I'm taking out a kidney, what's more important? The scaple, operating room, or the sharpness of the blade? Could be whether or not it was sterilized?


"An HVLP gun requires more VOLUME of air to operate (the V in HVLP, High Volume Low Pressure). Now you may notice that your HVLP gun is adjusted at maybe the same PSI as an old conventional gun, around 50 lbs at the gun (many HVLP guns are set at much lower though) so where is the "Low" in PSI they are talking about? It is at the actual air cap where the air and paint come out. An HVLP gun has only 10 lbs at the cap while a conventional has upwards of 50! So the VOLUME of air (CFM, Cubic Feet per Minute) is the key to proper atomization with an HVLP. "


Correct me if I'm wrong but, are compressors not rated for sustained capacity? Meaning, the valve open, air flowing, how much will it keep pumping? If I'm not painting a semi trailer but a kids wagon, in that context, a small capacity compressor will still allow for proper air mixtures, or the ability to atomize properly will it not?

"So atomization is the key, but why? Why can't you just lay it out wet and let it "flow", as an old painter will say. Picture a jar full of bb's, they will represent well small, atomized droplets of PSPC. The gaps in between the bb's is solvent. Now picture a jar filled with marbles, they will represent large, poorly atomized droplets of PSPC. The gaps in between are, you guessed it, solvent. "

Admittedly, I liked the analogy up to the point of solvent being the gaps in between. I'm calling BS. It suggests a greater separation then I've ever experienced? How about if you said for a given droplet size the distance closer or further away will tighen or spread the bonding of droplet edges to provide a uniform coverage and even surface finish?

"If you apply your PSPC in large poorly atomized droplets, what you will have is a film full of solvent. This can and will cause slow curing, shrinkage and dieback (the loss of gloss in the hours and days after application). "

Some where between BB's and marbles. I take a shot gun shell and count pellets, what will change the damage is the amount of pellets over distance and the charge of powder to propel them. It still falls back to how large and how many droplets are created during the atomization of the fluid, and some of that will be based on the viscosity of the fluid. I would tend to agree that solvent segregation from product is a combination of ratio in proportion to product and flash time in thinner/reducer evaporation.

"Basically you want the smallest fluid tip that will still allow you to PSPC the particular part you are PSPCing keeping the entire thing wet and in a fair amount of time. In other words a 1.0 tip would be beautiful for clearing one fender, but would be lousy to paint a complete."

This conversation started in regards to compressor size. I'm thinking it's also a good time to call it quits. Why, has to do with as buddy mentioned, are we doing a complete or one fender? Almost like asking how many thousands of an inch is that paint? How atomized is the paint? Can you describe what you saw that dark night of December 16th?

"Turn in the material knob to make the droplets smaller (and or raise the air pressure). The balance you need to attain is the smallest droplet size possible before you loose the coverage desired. In other words if you turn in the material knob too far, not enough material will be coming out to cover the panel! "

Forgive me asking, but at some point, moot as it may be, isn't distance away a factor for variances when spraying showing up as the same issue in coverage?

"Now, you'll notice that I said, "raise the pressure to the gun", while earlier I said to set it to manufactures specs. We are talking a very small adjustment. It is a fine balance in material to air ratio and a little more air than specified is okay."

That's a personal perspective. What's a little more? OOOO0000oooo....? I don't wish to beat a dead horse and in agreement a larger high CFM out put compressor has advantages in supplying ample air. What I will stand behind to argue is atomization of the fluid is more important them compressor size, although the latter if increased will allow atomization to remain with consistency for a longer period of time.

So, like using a spray can, how well you shake the can, how warm it is when sprayed, will make a difference. But the big one will be the size of droplet from the tip, the distance away, followed by the speed you move across the panel when spraying giving coverage,
I sure tend to simplify the complicated?
Some older computer drawing programs had a spray gun feature. You could change droplet size, and resulting coverage. I'm no expert. But I'm pretty adaptable to what I have to work with and still obtaining acceptable results from my limited education in the area of painting.
It wasn't my intention to muddy the water of conversation, and with thanks appreciate being part of the discussion.

The original question asked was "Whats the minimum Air Compressor I can use for HVLP?"
I'd now be inclined to say, well my son, it depends...?



This isn't a poke or jab guys...it's just funny. Fit in the context of atomization, I think it fits! 64 if you relax. LMAO!

I used to think there was no substitute for cubic inches until I met a guy on the street running a 66 Chevelle sedan with a 4bbl headered inline 6, 4 speed standard and 4:11 gears. I liked it so much I did a 65 with a 305 4 speed and 5:56 gears. Block to block fun.

The 79 Nova Ralley Sport I repainted B/C was the daily untill I was rear ended at a set of lights. Old guy supposedly had a heart attack. He lived, car didn't, I still hurt. Organ donor. You might fail to notice the detail, but the stripe scallop thing and lettering was all paint no sticker. Car magazines and thinking I could.

The little compressor that did.

The end.