LVLP or HVLP Paint Gun that may work with my compressor.

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PostPosted: Sun Nov 20, 2016 8:14 pm
Hello all,
I wanted to get your expertise on something. Currently my Air Compressor is designed to run at 8.6 scfm @ 40psi and 6.4 scfm@90 psi. I am assuming that i could run a LVLP gun to lay down the epoxy primer/high build surfaces, but will not have enough airflow for the top/clear coat. I plan on upgrading to a larger unit, but that is out of the equations for the moment. What gun would you recommend that would work with this compressor currently?
Ron



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PostPosted: Sun Apr 02, 2017 11:40 am
I have same question and have read conflicting answers. One thread said to use a conventional gun at a low psi the other said use a LVLP. I'm looking for a budget gun and researching Grizzly H7667 1.5 and Spray-It SP33000 kit. Grizzy also has the HVLP H7669 1.4 which is rated 4.2-7.1 CFM. There's also the Astro EVOT LVLP series which looks good but I can't find many reviews. Hopefully someone else can chime in.

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PostPosted: Sun Apr 02, 2017 6:26 pm
The problem you are going to run into is the CFM requirement of the gun not being met by the compressor.
Compressed air is measured in two capacities, pressure and volume. Pressure is measured as Pounds per Square Inch or PSI. Volume is measured in Cubic Feet per Minute or CFM (sometimes referred to as SCFM). These are two different things and should not be confused one with another.

Air tools, including spray guns, will have the required amount of air (CFM) given at a specific operating pressure (PSI) for them to run properly. This means that your compressor must be capable of producing that much or preferably more than this amount. For example here are the Specifications for the DeVilbiss Tekna Copper:

Key Specs

Air Cap 7E7 High Efficiency Air Cap (as efficient as HVLP!)
Fluid Tips 1.3mm needle/nozzle set as well as a 1.4mm needle/nozzle set
Materials All basecoats (inc. waterborne), all clearcoats, all single-stage
Air Pressure Input pressure: 16 to 30 PSI
Spray Pattern 12 ½ inch
Air consumption 9CFM to 13CFM


Notice that two different specs are listed, Air Pressure and Air Consumption. To be safe in calculating air supply I suggest you take the high numbers so for this gun to operate properly your air compressor must produce 13 CFM at 30 PSI.

Another concern is the run time of the compressor so sizing your compressor to handle at least 15 CFM at 40 PSI is recommended. This is especially true if you plan to use an air sander or sandblaster as they required large volumes of air as well.

Remember the longer a compressor is running the hotter it gets and the more moisture it produces.

Another thing to consider is the cost of the paint and the amount of labor you have invested into your car already. Do you really want to risk it turning out crappy and having a do over?

Hopefully you have invested in a good filtration system as well. I rented a compressor once to do a quick paint job on a truck but my filtering system wasn't up to spec and the compressor spit some oil and water that ended up on my truck. :flatten:
1968 Coronet R/T


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PostPosted: Sun Apr 02, 2017 11:14 pm
'68 Coronet R/T wrote:The problem you are going to run into is the CFM requirement of the gun not being met by the compressor.


Thanks for the reply and I understand what you're saying with the Tekna Copper because the specs are over what my compressor can supply. But what about the LVLP Spray-It SP33000? The specs are as follows

Low volume and low pressure spray gun
1-piece lightweight aluminum gun body with 20 oz./0.6 l plastic cup
Able to use with small portable air compressors
Tip sizes: 1.3 mm, 1.5 mm, 1.7 mm
Air consumption 3.5 to 3.9 CFM at 30 psi
Working pressure 28-45 psi,
maximum pressure 60 psi
Fan pattern: 7 in. to 10.9 in.
Air inlet: 1/4 NPT hose connector

From the mostly good reviews I read, it sprays best at 30-32 psi. So a 5 hp compressor rated at 8.6 CFM @ 40 psi should be able to supply enough air for this gun, correct?

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PostPosted: Mon Apr 03, 2017 9:23 am
According to the specs that should work.
I don't know anything about the gun or its quality so can't comment on how it will actually perform.
There is a reason some guns are higher priced than others. SATA, Iwata, DeVilbiss and other sprays guns commonly used by professional painters are made of better quality materials and have much tighter machining tolerances.
Some machining specs will be +/- .0005" while others might be +/- .002" which is 4 times higher. When controlling airflow through tiny holes in the cap this becomes crucial.
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PostPosted: Mon Apr 03, 2017 5:23 pm
Ok thanks. Yea no way this is near pro gun quality. From what I see it looks to be the same gun Eastwood calls the Concourse LT. Same specs. I've heard it's a solid gun but the CFM is closer to 7 not 4 as advertised. Still I might give it a try. I simply can't afford a pro gun and new compressor so I've have to make due. One more question. If the CFM on this gun is almost half of what a normal HVLP gun uses (7 vs. 13), and most say you need a 60 gallon tank to paint a whole car, do you think I could I get away with a 25 gallon tank? The compressor I have now is 5 hp 25 gallon. I was thinking of adding a 10 gallon tank if needed.

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PostPosted: Mon Apr 03, 2017 8:34 pm
I know this is not what you are wanting to hear but this is the reality of what you are trying to do.

The volume of air in the tank is dependent upon the pressure setting.
A 25 gallon tank at 40 psi only holds about 12.43 Cubic Feet of air.
If you set the tank at 100 psi it will hold 26.1 Cubic Feet. (compressed air)

Now figuring 7 cfm for the gun means you will drain your compressor tank in about 1.8 minutes if tank pressure is 40 psi and trigger on gun is held open.
It would take about 3.73 minutes if tank pressure is at 100.
That may seem like a lot of time but actually your compressor will kick on as soon as the pressure drops. You will be draining 30 psi and 7 CFM of air while spraying.

Your compress says it will put out 8.6 CFM at 30 psi which means it will be running continuously shortly after you pull the trigger.

To give you a comparison here's my compressor specs.
15.6 CFM @ 100 psi
80 gallon tank set at 150 psi holds 119.95 CF of air.
Gun uses 13 CFM @ 30 psi
Tank would take 9.2 minutes to drain if gun held full open.

My compressor puts out more CFM at 100 psi than my gun uses at 30 psi, so the compressor will "catch up" and cycle off as it maintains the air pressure in the tank. This ensures that my gun always has plenty of air to operate correctly.
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PostPosted: Mon Apr 03, 2017 11:20 pm
68 has really done a thorough explanation of "why" this is a problem with these smaller compressors. I also have an LVLP gun of about those same spec.s and own a few portable compressors along with our big shop compressor. At best you can "panel" paint with one of those but that's about it. If you are going to do an overall shoot that compressor will be turned into a "rainmaker" running continuously and making plenty of moisture which will be difficult to manage.
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PostPosted: Mon Apr 03, 2017 11:23 pm
Thanks for explaining. Yeah not what I wanted to hear but I do have a better understanding of what I'm trying to do. It actually looks like it could be done if, as you said, I kept the moisture under control from the compressor running constantly. My best bet may be to borrow/rent another compressor the same size and run them in tandem/parallel. That would give me 12.8 CFM @ 90 PSI. I know that can be sketchy so I'll have to look into it more.



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PostPosted: Tue Apr 04, 2017 7:48 am
Here's a few pics of when I first shot the epoxy sealer. At the time I didn't know my compressor was undersized so I used it and a DeVilbiss Starting Line gun with a disposable desiccant canister dryer (rated for 4 months). I thought it went on good with just some orange peel and striping due to my technique as a beginner.

Image

Image

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I sprayed everything at once and compressor did run constantly. I didn't have problems until after the body work and started spraying 2K primer. Then the "rain" started and sent me looking for solutions. I figured a gun rated for my compressor would help. I now think this is when the dryer needed to be replaced even though it was only a few coats.

The real problem is I'm tapped out and the I need to have the car out of the garage by mid-May. I have a few hundred for a solution to get color on the car. I know others will read this and no one wants to give bad advice but this is an extreme case. I'm open to all suggestions. Otherwise it's off to Maaco for a $300 paint job. :oops:
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