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Conversion HVLP; What's Different

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Forum topic by bilyo posted 04-17-2019 12:17 AM 801 views 0 times favorited 31 replies Add to Favorites Watch
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bilyo

661 posts in 1466 days


04-17-2019 12:17 AM

I currently have a couple of regular small capacity spray guns. Neither uses more than a 1 mm spray tip. I’ve used these a few times with mixed success. I’m not what you would call a spray gun expert. If I were to buy a conversion gun like the HF purple one, what differences would I experience? Use is mostly for small detailed work with finishes like shellac, poly, etc.


31 replies so far

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pintodeluxe

5918 posts in 3176 days


#1 posted 04-17-2019 04:18 AM

HVLP conversion guns are great, and quite a bargain too. I have several. I prefer the Wood River gun over the HF version. It just atomizes a little better.

Whatever you get, make sure to include a pressure regulator at the gun. It gives you better control of the incoming pressure. I set mine at 35 psi at the gun. 1.4-1.8 mm are common needle and nozzle sizes.

Once you get good with a spray gun you’ll never go back to a brush or rag.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

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bruc101

1337 posts in 3905 days


#2 posted 04-17-2019 05:04 AM

I’m with Willie on this one. It’s been many years since Ive wiped a finish on. I’ve been pulling the trigger on spray guns for at least 50 years and would only do a wipe on if that was the only and last resort.

Get you a hvlp gun and and play play play and test with it until you’re getting the finish you want.

Use water and cardboard to test the spray patterns and some of the setups on your gun.

-- Bruce Free Plans https://traditionalwoodworking.org

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MrUnix

7361 posts in 2562 days


#3 posted 04-17-2019 06:19 AM

For decades, I used a bunch of different higher end suction and pressure feed guns. One day I picked up one of those purple HF HVLP guns for what I thought was a ’one use and toss it’ paint job. That was years ago and I still have it – because it just keeps putting out a great spray and is super easy to clean. I’d say splurge the $10 and give it a try!


(good until the end of the month)

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

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Rich

4419 posts in 952 days


#4 posted 04-17-2019 08:57 AM

Air pressure at the gun is important, so while you’re at HF, grab one of the pressure regulators and fittings to attach it to the gun’s air input. They also have a model of the purple gun that comes with the regulator attached.

It’s much easier than trying to guestimate the pressure drop based on hose length and diameter. You also don’t have to remember to adjust the pressure output at the compressor each time. You can leave it set high and adjust the gun.

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

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bilyo

661 posts in 1466 days


#5 posted 04-17-2019 02:07 PM

Pardon me for being persistent. I get that you like the HVLP gun. But why? How is it different? If you had two guns side by side set up with their optimal settings, what differences would you see or feel?
BTW, I do use the regulator at the gun.

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YesHaveSome

155 posts in 622 days


#6 posted 04-17-2019 04:13 PM

I just got one of the HF guns with the regulator on Sunday. I had been using a Critter (https://www.amazon.com/Critter-Spray-Products-22032-Siphon/dp/B00006FRPJ) but it was too tempermental. I’ve used the HF gun the last couple of nights putting some polycrylic on a shop storage cabinet. It’s worked incredibly well. Highly recommend for the price.

-- But where does the meat go?

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pintodeluxe

5918 posts in 3176 days


#7 posted 04-17-2019 04:34 PM



Pardon me for being persistent. I get that you like the HVLP gun. But why? How is it different? If you had two guns side by side set up with their optimal settings, what differences would you see or feel?
BTW, I do use the regulator at the gun.

- bilyo

Less overspray than a traditional spray gun. Better finish because it’s being deposited more gently. On the old high pressure guns I felt like the finish was hitting the surface so hard that a lot of it bounced back. It created an orange peel effect and a certain roughness that was tough to sand out.

The HVLP conversion guns don’t suffer from these problems, as long as they’re set up correctly and the fluid is thin enough.

Good luck with it.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

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LeeRoyMan

83 posts in 90 days


#8 posted 04-17-2019 05:03 PM

HVLP conversion guns aren’t much different than any other gun. The “HVLP” doesn’t mean much if you still have to blow 35lbs air pressure to make it work.

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ocean

158 posts in 1196 days


#9 posted 04-17-2019 05:03 PM

I agree with pinto. Softer spray and less bouncing back at you, wasting less finish. Get a gun with regulator as others have said. Put in some practice time with different finishes, different finishes, different pressure settings. You will love it. I have been using one for over 15 years, I’ll never go back.

-- Bob, FL Keys

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Rich

4419 posts in 952 days


#10 posted 04-17-2019 08:45 PM


HVLP conversion guns aren t much different than any other gun. The “HVLP” doesn t mean much if you still have to blow 35lbs air pressure to make it work.

- LeeRoyMan

That’s where the conversion comes in. Yes you put 35 or 40 PSI in, but internally it converts it to a low pressure high output flow. That’s also why they require more CFM to drive them.

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

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Aj2

2207 posts in 2161 days


#11 posted 04-17-2019 08:54 PM

What size compressor are you guys using with your guns?

-- Aj

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OSU55

2253 posts in 2353 days


#12 posted 04-17-2019 09:03 PM



Pardon me for being persistent. I get that you like the HVLP gun. But why? How is it different? If you had two guns side by side set up with their optimal settings, what differences would you see or feel?
BTW, I do use the regulator at the gun.

- bilyo


If you mean vs a suction cup gun, less cfm because a vacuum doesnt have to be created. Vs a gravity feed high pressure gun, better atomization through design of the tip and air cap that doesnt require as hi of velocity of the air, resulting in more efficient transfer of finish/less overspray. This also applies vs a suction gun.


HVLP conversion guns aren t much different than any other gun. The “HVLP” doesn t mean much if you still have to blow 35lbs air pressure to make it work.

- LeeRoyMan

Well, a quality hvlp is usually limited to 30 psi gun inlet, for a cap pressure of 10 psi. I run mine from ~10 psi for air brush type detail stuff, and rarely need to go over ~25 psi with straight waterborne finishes. Tip/needle size also plays a large role. The cheaper guns dont have the tip/needle size selections, as well as lesser designed air caps, so that gets made up for with higher pressure which then starts to defeat the purpose.

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bilyo

661 posts in 1466 days


#13 posted 04-17-2019 10:37 PM

Thanks for the comments. Very helpful info.

I purchased the purple HF gun today. After cleaning all the junk out of it, I’ve only had a chance to run some tinted alcohol through it. it seems to work fine. I do have a couple of questions maybe you can help me with:

The instructions are rather brief regarding the adjustment screw adjacent to the air inlet at the base of the handle. It appears that after setting the inlet pressure, this screw will fine tune the internal air flow (pressure? volume?). I started out opening this adjustment about 1-2 turns and then with the inlet pressure set to 25 #, I can adjust the spray to about that of an air brush. This is with very thin material of course. Does that sound like the correct procedure? Anything I’m missing?

I have an in line desiccant/filter that I will put in line just ahead of the pressure gauge. There is no indication of correct flow direction. I assume it doesn’t matter.

View TungOil's profile

TungOil

1211 posts in 858 days


#14 posted 04-18-2019 01:39 AM

I have a Devilbiss conversion gun. I run 10 psi when spraying stain, 20 psi for water borne finishes. I bring full line pressure into a filter then regulator mounted to the gun. You should experience less overspray with the conversion gun.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

View CaptainKlutz's profile

CaptainKlutz

1238 posts in 1857 days


#15 posted 04-18-2019 02:07 AM

Anything I m missing?
- bilyo

Maybe?
Am not a spray expert, have used enough different spray guns over years to help a little?

All the adjustments at gun are intended to help control the FLOW RATE and PATTERN of material from the tip. Some settings control deposition rate, some control the spray width/pattern, But they are ALL inter-related and can not be set independently.

Making things more challenging is gun settings are based on material viscosity. Every combination of tip size and fan cap has a optimum range for viscosity; where the patterns are smooth/repeatable/controllable with gun controls. When get outside of optimum viscosity range, settings get very touchy or just don’t control flow very well.
Using plain solvent to test a gun with large tip intended for higher viscosity material will not really show you how all adjustments are related, and solvent settings will not work for actual material.

Highly suggest you get a couple of med/large card board boxes, and the material you intend to spray, then play with the gun. This will be only way to see the differences in spray pattern, drop size, and how controls work. :)

I own/use famous HF purple gun. One challenge with HF gun is it comes with one tip/cap, and other sizes are only obtained by calling HF parts department. So out of the box, you need to learn what viscosity it likes to spray. Can offer simple example of how I use HF gun?
Can spray Arm-R-Seal straight from can, but it is too thick and gun controls won’t allow thin enough film to stop runs. Thinning it 10-15% (Naptha in cold weather, Paint thinner/stoddard solvent in summer) and it sprays properly. In dry and very hot weather, have to add some retarder with thinner to really slow evaporation to control orange peel with thin films. Same applies for water based finishes, must have proper viscosity for spraying. I typically use acetone, alcohol, or blend of both for WB finish thinner (water evaporates too slow and needs to be distilled/free of minerals).

So one key to learning how to spray properly, is learning about viscosity of materials plus solvent compatibility, and how to thin material to get desired results. There are tremendous number of suppliers, and forum sites that offer information on solvents used for spray finishing. The most relevant are those for lacquer, or automotive forums discussing 2 part poly urethane materials. Here is one example to complexity of solvents for spraying:
https://thefinishingstore.com/blogs/news/127175747-understanding-solvents-part-iii-laquer-thinner

Hope this helps.

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

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