Kobalt Gravity Feed Spray Gun Operation
Decades ago, your "Do-It-Yourself" at home body man used syphon feed spray guns. They did great but as time went on, technology advances. For automotive painting, this was a great turn of events. HVLP spray guns were created, and painting got a little easier, and the waste of paint went down. If you paint cars, an HVLP gun is a must. In this article you will learn how to set up an HVLP spray gun and some tips.
Setting up your spray gun before shooting primer or paint is crucial. How the gun sprays, determines how well the end results will be. You could have the gun off and not get the best coats, but that creates extra work. Before you setup your gun for a paint job, you need to learn how it works first.
How An HVLP Spray Gun Works
HVLP stands for High Volume Low Pressure. Basically, any gravity feed spray gun falls under this category. These type spray guns are unlike your previous guns of the past. HVLP and Gravity Spray Guns use gravity in a cup to feed the sprayer. This means you use way less air to atomize the paint into a mist of spray. The cup sits on top of the actual spray gun. So even without air, if you squeeze the trigger with material in the gun, it will squirt.
The function of the gun is really simple. You have the cup in which you put your paint material in. The spray gun itself, has two main adjustments, normally. You have the material adjustment and the fan adjustment. The material adjustment is the needle that pulls back when you squeeze the trigger. That needle can be adjusted how far or close it is to the air cap seat. This of course is based on if you have the trigger fully open. The fan control causes the v-pattern of spray to become narrow or wide.
Unless it is a special circumstance, you want your air cap to run horizontally. When spraying a vehicle, you are always spraying left to right or right to left, back and forth. There might be times you would turn your air cap to run vertically. Perhaps a narrow width panel that is tall, although the normal way to spray is with the air car horizontal. You have control over how wide your fan will spray by adjusting the fan control.
How Does The Fan Control Work?
You will find the fan control knob usually on the side of any type spray gun. This control, adjusts the amount of air distributed throughout passages in the air cap. The cap is drilled and designed to blow air out in a way that both atomizes and creates a spray pattern. With the air blowing out the cap, creates a vacuum, pulling the material into the air stream. This then starts the atomizing effect; the cap design is what helps create the fan pattern.
There are many designs of air caps that have a different types of air passages. For general spraying, the most common cap has just the four holes, two on each air horn. However, they make some caps with smaller passages around the center hole where the material is released from.
The reason why there are a variety of different designs of air caps are for the type of painting. Some guns are setup to spray real thick material such as a primer or Gel-Coats. There are caps made for certain types of metal flakes. And then you have some that are just improvements over the general spray guns.
No matter the type of cap, you still want your fan adjusted to get the optimal coverage. You do not want a lot of over spray, nor do you want the fan too narrow. An improper adjustment can lead to dry spray to runs.
Needle And Fluid Cap
Mechanically, this can be considered a needle valve and seat, just like in a carburetor. Except, instead of having a float bowl control the needle, it is the trigger on the gun. A channel from the cup, flows material up to the fluid cap. The needle seats against and closes off the opening in the fluid cap. So even without air. If you have material in your cup and squeeze the trigger on the gun, material will come out.
The fluid cap and needle, along with the air cap, are crucial to how thick of material you can flow through the gun. This is also a crucial part of how-to set up an HVLP spray gun. Yes, part of the setup is air, material and fan adjustments. However, the fluid cap, needle and air cap are the most important part. Let's say you wanted to spray a really thick epoxy primer. You would need a larger size fluid cap, which requires a bigger needle to accommodate the cap. The air cap usually has to change to accommodate those changes, although some newer guns are not requiring this now.
Reasons to change the sizes of the fluid cap and needle are going to be material related. For thinners paints, especially ones without pearl or metallic flakes, a smaller cap would be used. You also may find that you will have to experiment with different size fluid caps. Some pearls and metallics seem to layout better with smaller caps, where others require larger ones. If you are marine spraying material like Gel-Coats, especially with that type metal flake. You will have to use large fluid caps and most likely higher air pressures.
HVLP Spray Gun Tip Assemblies
Generally, solid color paints and clear coats are applied with a 1.3mm to 1.7mm tip. For heavy primers and heavier type coatings, you would use 1.7mm to 2.2mm tips. Usually, the 1.4mm tips is what most painters use. It seems to cover most of the clears and urethane paints on today's market. However, you can get better results with some of these paint by jumping up to a 1.5mm to a 1.6mm. Often, you need to spray test panels to see what works best. Your paint viscosity has much to do with how it sprays as well.
Some of the new Devilbiss guns no longer require you to change the air cap out when you change fluid caps and needles. However, most of them do, so when you need to buy a different size, you get a kit. You do have to purchase the kits that are made for your brand gun, this is not one size fits all. The cheaper guns like what you buy at Harbor Freight, most likely will not have these assemblies available.
Most guns come with a 1.4mm tip, however, there are tip assemblies that do not up the size, but improve the spray. I have an Optima gun, but at the time I bought it, there were kits called MS Optimization Kits. Theses came with a new fluid cap, needle, and an air cap. They were redesigned with new air passages to create a better pattern and get more material out if needed. So, consider asking your gun distributor if there are any upgrades before changing the fluid tip size.
How To Set Up Your Gun To Spray Correctly
Now that you have an idea of how the mechanics of the gun works, it's time to adjust it. From what we have covered so far. You can see setting up an HVLP spray gun is more that just turning a few knobs. Once you have determined what kind of material you are going to spray and have installed the correct tip. It is now time to get a test panel and adjust your gun. A test panel can be a poster board, a spare body part or spray out card. You just need something clean to see how the spray pattern is laying out as well as the amount coming out of the gun.
If you are getting odd shaped patterns, excessive runs or a dry spray, you may need to clean your gun. Gravity guns have a little vent hole in the cap that covers the cup. If that vent hole gets clogged, the gun will spray normal for a minute and then start dry-spraying. So, ensure it is not blocked. Also inspect and ensure that the air cap has completely clear passages. If any are obstructed, this will affect the spray pattern immensely. Always clean your gun immediately after spraying paints. To ensure the best results, tear the gun down and clean each piece. Use a cleaning grade Lacquer Thinner to clean gun and all pieces. Review RodsShop full line of Auto Body Equipment and Supplies.
Adjusting How It Is Coming Out Of The Gun
Here is where you will be adjusting the material feed, the fan spray and the air pressure. Paint specs usually indicate what the best pressure to spray their paints at. Most general-purpose gravity feed guns spray best around 35 to 45psi. A true HVLP spray around 8 to 15psi. All of this depends on the paint mix, (viscosity) you are spraying and the climate conditions. That is why it is 
important to spray a test panel first before actually applying coats on a vehicle.
Although the trigger of the gun can allow you to control the amount of material coming out of the gun. You can feather how much material comes out by not pulling the trigger all the way. Feathering is usually used when you don't want to apply too much paint in specific areas. It is best to set to the material feed to the limit you want coming out at full trigger. Adjusting the fan control in conjunction with material feed is necessary to get the correct pattern you desire. If the gun doesn't seem to be spraying enough material, you may need to increase your air pressure. The alternative to increased air pressure is to thin your material.
If you are unsure if your paint is the correct thickness, you can always measure its viscosity. However, in order to measure this, you will need the viscosity specification. This spec isn't always available, you may have to consult you paint manufacturer.
Adjusting HVLP Spray Gun Material Feed
No matter if you get your spray pattern looking correct, the feed control determines thin or thick layer application. Some paints work better being applied in thin coats, while others can be applied heavier. If you crew the feed control in, that will reduce material. This means that you are spraying thinner coats. By unscrewing the control feed, you are allowing more material to come out of the gun. This will result in heavier coats.
Example
I good example of when to adjust the material feed is comparing generic paints with name brands. Axalta makes a generic line called Nason. I use Nason products a lot, they do work well. However, there are some quirks to get used too. Nason paints are seemingly thinner, almost watered down per-se. A Miata I painted, was done in Nason single stage urethane. The finished product looked like a show job, you can view HERE. But the paint was thin, so I reduced the material feed and applied thinner coats. Of course, I applied more coats than I would have with a name brand.
Axalta also makes Chromabase base-coats, and they are far thicker than Nason's base coats. Axalta and other name brands use more pigments and thicker agents in their paints. So, when I am spraying Chromabase, I can open up the feed more and lay the paint down a little heavier. Another tip about laying paints down thin or thick. If you are spraying with a paint that takes an inordinate amount of time to dry. Apply thinner coats with longer flash times. Years ago, I painted a car with NAPA paint. It was brought to me by the customer. The paint was a base-coat clear-coat. Even with the activator, it took the car to dry to the touch, almost 15 hours. All paints have improved since then but there are still some that take way too long to dry, especially farm and tractor paints.
Adjusting The HVLP Spray Gun Fan
A big part of setting up an HVLP spray gun is getting the fan just right. If the fan adjustment is opened too wide, it will create dusting, and overspray. By having the having the fan adjustment too narrow, will cause runs and bad coverage. However, there are times you may want your fan narrow to accommodate spraying in door jams or tight spaces. Anytime you might narrow your fan, you will want to reduce the amount of material.
If you are painting a panel or entire vehicle, here is your goal. You want the fan to be wide enough for optimal coverage. However, you want to keep it from creating overspray and a dry spray to each end of the fan. As seen in this image, yes, the same as the one above. This is how you need your gun to spray.
As you adjust your gun on a test panel, you will find that they're combinations of adjustments. You have to have an adequate amount of air. Although, getting the air pressure right is already in the specs of your paints. Most paints tell you the optimal air pressure to spray at. This means you need an air pressure gauge on the line supplying the air or one at the gun.
Even if you have the air pressure spec or not. Adjusting your air, with the fan width and material feed all have to adjusted. It sounds harder than it is but it's not really. Keep in mind, the material feed is designed for you to pull the trigger all the way open.
Material Feed
The material feed adjustment just stops the needle from being pulled all the way open or not. The idea is, if you are spraying an entire car. To keep the material feed constant, you will always want to pull the trigger all the way back. However, if you are painting around rounded corners or small parts. You will eventually discover that you only pull the trigger in a little here and there.
In other words, for example, if you were painting a door mirror. You wouldn't be holding the gun wide open on such a small part. Feathering the trigger in and out to control the amount of paint would be the correct method. You can watch an example of how to spray in my YouTube Video "Painting A Hood Vertical – Don't Do It" – look around time index 8:15.
In my video, you can see that I have the fan width and material feed balanced. There is not too much going on and no real overspray dusting. So, when you are testing your gun, try to get it to spray like I have it in my video.
Keep Your Gun Clean
If your gun is not kept properly clean, you can adjust it all day long and never get it right. The same video I linked above, you will see at index 2:18, the gun will not spray right. I was using a friend's gun, he never cleaned it properly. You can see in the video that it will not put enough paint on the hood. The reason why it acted like it was starving was because the vent for the cup was clogged.
Whenever your done painting, you want to tear the gun down piece by piece. You want to clean each piece and clean out all passage ways. All my guns look like new and I have painted 100's of cars and they are all at least 25 years or older. There is no excuse not to clean your gun, if that is going to be too much for you, don't paint at all.
You need a gun cleaning kit and some cleaning thinner . Ensure that you wear gloves and if you are in a small room, wear a mask. It would hurt to wear eye protect as well. Once you clean the gun, reassemble and spray a little cleaning thinner through the gun. This is to ensure that it is still spraying correctly and ready to go for the next job.
Source: https://rodsshop.org/setup-an-hvlp-spray-gun-how-to-and-tips/
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