HVLP CFM & PSI - Argh!

rmwarren

rmwarren

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Jul 11, 2010
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Somehow I must be over-complicating this. I have a 3M HG 14 HVLP gun and am trying to figure out how much compressor I REALLY need for infrequent small-midsize projects in a home shop. I have googled myself cross-eyed and cannot seem to come up with a clear answer.

I assumed there would be a simple formula, i.e. CFM/PSI times your age divided by day of the week = The Answer. Does not seem to be this straightforward.

Any not-too-technical answers?

Thanks, RMW
 
Your air compressor needs to deliver a minimum of 10 CFM (74.80 gallons per minute) @ 20 PSI.

What compressor do you have? The tank size, head, hoses/fittings and atmospheric conditions affect the output.

Flow and pressure are inversely proportional. If your compressor will deliver 5 CFM @ 100 pounds, it should easily deliver 10 CFM @ 20 pounds.

Get a water separator.

If you really want to do the math the formula is in this blog;
http://www.aircompressorworks.com/blog/index.php?mode=post&id=29

Tom
 
tjbnwi said:
Flow and pressure are inversely proportional. If your compressor will deliver 5 CFM @ 100 pounds, it should easily deliver 10 CFM @ 20 pounds.
Click to expand...

That is correct. In practice this does not work well. I have a compressor that delivers a rated 5.5cfm@ 90lbs. and it could not keep up with a gun that required 13.5cfm @ 28lbs. It ran 100% of the time with a continual loss of pressure. Most (all) 110-20 volt 20 amp compressors cannot power most HVLP guns sufficiently. There are several HVLP guns that can be powered by smaller compressors but they are usually detail guns or for spraying dye or very light viscosity coatings.

In my opinion a turbine with a pressure pot provides the cheapest solution to the problems of delivering enough CFM and pressure for the most water borne paints. Compressors capable of providing enough CFM and pressure to power a HVLP gun are expensive and or large and require 220 volts @ 30-40 amps for > 5 HP. Because water is heavier than solvents, the pressure required to get the coating to the gun to properly atomize is critical to the application of the coating.

tjbnwi said:
Get a water separator.
Click to expand...

Do you mean a filter or collector?

tjbnwi said:
http://www.aircompressorworks.com/blog/index.php?mode=post&id=29
Click to expand...

Good link thanks.
Tim
 
I don't do the quote thing as well as Tim, so heres my responses in order.

The compressor issues for a medium shop/home use is why I use a turbine. In my opinion they cannot be beat in 99% of applications. I'd like another Graco AAA but it would be for the shop only, they can be inconvenient to transport. The positive displacement piston pumps are definitely shop only.

Using a compressor for a gun I highly recommend a filter/water separator combination. I know there are at the gun line separators available, I prefer the wall mount combo units;
http://www.eastwood.com/ew-filter-separator-regulator-system.html

You're welcome.

Tom
 
Tim/Tom thanks for the responses, although it was not what I wanted to hear. I will not often use a compressor so was hoping to get by with a cheapy, there are some locally available that claim 150 PSI, with 4 SCFM @ 90 PSI & 6 SCFM @ 40 PSI. Since the drop in CFM was not linear I was afraid it would not really deliver 10 CFM @ 20 PSI.

Most likely I will just sell the gun or more probably forget about it and forego spray finishing, it's not worth the cost or space premium to buy a decent turbine.

Thanks again.

RMW
 
tjbnwi said:
What material are you spraying?

Look at a Graco hand held. The new TrueCoat 360 with the collapsable lines appears to be a nice unit. Relatively inexpensive, it may serve your purpose.
http://www.graco.com/us/en/products/contractor/truecoat-360.html

Tom
Click to expand...

I'll take a look at it, I don't have a specific product I want to spray, just stuff for misc. projects. Likely paint for interior cabinets and clear WB poly.

Thanks again.

RMW
 
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