Minimum CFM for a spray gun


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Old 05-13-06, 11:39 PM
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Minimum CFM for a spray gun

Hey all,

First, I searched the forum quite a lot and read the air compressor sticky but could not find the answer for this one.

I am looking to buy a set of air compressor and a spray gun. My immediate task is to repaint my motorcycle fuel tank, maybe later to repaint the fairings. I think the biggest project I may have is painting a small bike trailer.

You guys sure live well, from the posts I read you can buy a decent air compressor for quite good prices. Here in Australia however, I can only afford something like 2HP/30L air compressor (yes, liters, not galons), anything bigger than that is quite expensive.

The air compressor I mentioned (2HP/30L) claims to have a free air delivery of 5.4CFM and 7.1CFM pump displacement. Is that enough for small scaled painting jobs?

I can stretch a bit more and get a bigger compressor (2.5HP/40L) with free air delivery of 6.1CFM and 8CFM pump displacement. Do you think it makes a huge difference? Does it worth the extra bucks?

Would appreciate your help, and sorry if my post is a bit long.


Cheers,

Ronen
 

Last edited by slepax; 05-14-06 at 12:45 AM.
  #2  
Old 05-14-06, 05:17 AM
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I am also looking tword spray outfit . how about HVLP ?

Ive been Reading some good things on another forum about the one at Harbor freight for less than 100.
 
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Old 05-14-06, 05:50 AM
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Welcome Ronen!

What would be the deciding factor in selecting a compressor would be the air consumption of the gun.
You would need to match one to the other.
Here is a link to Coleman's site where they list the capacities of their spray guns.
I would believe their recomendation to not use the cheaper guns for automotive finishing which is what you want to do.
On this side of the world we have a compressor size limitation for use on our normal 15 amp 120 volt electrical recepticle of about 6 cfm.
This cfm capacity is often a size that begins to be usefull.

I have an import HVLP gun and it works fairly well but you really have to watch the cfm ratring to not run out of air.
I looked at two Harbor Freight guns.
One listed "5.9 cfm low air" which must mean the minimum compressor size and another showed 9.5 to 14.8 cfm!
Another thing you have to be carefull of is the idea of buying a bigger gun than the compressor can handle and then thinking you can wait while the compressor builds up pressure or a small compressor with a larger capacity storage tank.
For spraying automotive type paints you need to lay down the paint in a continuous motion.
An undersized compressor when it runs excessively will begin to heat the air tank which will make moisture more prone to condensing in the hose, leading to water problems.

The bottom line with air compressors is the bigger the better.
 
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Old 05-14-06, 06:59 AM
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heres the item I was refering to

http://www.harborfreight.com/cpi/cta...emnumber=44677

getting some good reveiws on another board

I see it " Sprays light, medium and heavy stain, varnish, and latex."

so maybe it wouldnt work for your appliction
 
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Old 05-14-06, 07:14 AM
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Thanks for the reply Greg.

So from what you say I understand there are mainly two golden rules:
1. Make sure to match the spray gun CFM to the compressor delivery CFM.
2. The bigger the better.

Of course the second one is not a rule but more of a recommendation ..

Your answer got me thinking and raised some more questions, with your permission:

Different spray guns require different CFM, why? I could understand if the difference was just 1-2 CFM, but some requires 12 CFM and some just 4. What are the factors that make CFM requirement in spray guns?

Just to make sure I got the math right. If my compressor delivers 5CFM at 100PSI, assuming I use a 5CFM gun at 25PSI, does it mean I have 4 minutes of constant spraying?

Sorry if it turned out too long again ..

Originally Posted by mango man
heres the item I was refering to

http://www.harborfreight.com/cpi/cta...emnumber=44677

getting some good reveiws on another board

I see it " Sprays light, medium and heavy stain, varnish, and latex."

so maybe it wouldnt work for your appliction
Thanks for the help mango man, but I am in Australia and it will be too difficult ordering this tool. Besides, I am not sure it can handle all of my requirements (primer, painting, clear coat, etc).
 
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Old 05-14-06, 07:48 AM
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The best starter "auto" painting gun kit I've run across is this one


(image courtesy of eastwoodco.com)

The specs are
Devilbiss Paint Gun Starter Kit - Devilbiss offers a smarter alternative to no-name guns. This set includes a large HVLP gravity spray gun with 1.3mm fluid tip for top coats, extra 1.8mm fluid tip for primers and heavier materials and a 600 cc (20 oz) gravity cup (requires 13 cfm at 30 psi); mini- HVLP detail spray gun with a 1.0mm fluid tip, 130 cc (4 oz) gravity cup (requires 8 cfm at 30 psi), tool kit and accessories. Packaged in blow-molded case with handle.
Spray Gun Specifications
30 psi inlet pressures delivers 10 psi air cap pressure at 13 cfm air volume. Air inlet: 1/4"NPS
Touch Up Spray Gun Specifications
30 psi air cap pressure at 8 cfm air volume. Air inlet:1/4"NPS
I'm not good at the math, but you would want a compressor that could run these guns with no problems
...even if you do not use these, the one(s) you use should be similar

The kit is available at Eastwood Co. and other places I'm sure
 
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Old 05-14-06, 02:16 PM
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Devilbiss is a top name you can't go wrong with.
The cfm rating of the compressor you buy would be determined at the pressure you will be operating at.

It's difficult to offer specific model recomendations because we do not know what retail stores are available to you.
Budget is a deciding factor but I would lean to spending more on the compressor and less on the tools.
I have a DeVilbiss auto spray gun and it works great but purchased an offshore HVLP gravity feed gun and it works great also.

The "bigger is better" comment could be considered half way between a rule and a recommendation.
If you are spraying automotive paints water in airline is a common curse.
One major contributor to this is an undersized compressor.
As I explained, if you are doing a paint job where the compressor runs continuously, the air tank will warm up. As the tank warms up less moisture will condense there and wind up condensing in the air line and at the gun nozzle.
A filter type drier will help but they don't get it all and if the drier warms up they do very little.

Give us your budget and some links of where you can shop and maybe someone can spend some money for you.
 
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Old 05-15-06, 12:16 AM
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I was thinking to buy something just like that Devilbiss Paint Gun Starter Kit. It's a bit cheaper, so it has only one gun with two nozzles (14mm and 20mm), all the rest is the same except for the fancy box.

The kit I am after requires 9CFM, so I am a bit reluctant buying it because I am not sure the compressor can deliver that much air.

Originally Posted by GregH
Give us your budget and some links of where you can shop and maybe someone can spend some money for you.
Can I just give you my address and you will send me the money?
 
 

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