How To Use Compressed Air Paint Spray Guns by William Rice

This tutorial is written for the person who either has little spraying experience, or none at all. First off, while I have painted cars, from primer, to base coat, special effects pigments and final multiple clear coats, I do NOT consider myself a PRO painter. I am a very good painter of overall spray applications. What I want you to know is, YOU can be as well!

You can apply a reasonably good to very good coating of the Vivilon line of clear coatings in very little time IF you can read and spend a tiny amount of time practicing. Read ALL of this article, follow the procedures I outline diligently and Practice for 30 minutes to an hour. Once you have the gun set up optimally, practice will build muscle memory to coordinate hand and eye to develop a "sweet spot" combination of proper distance, speed of travel, proper overlap and hand position. That's ALL there really is to spray painting: Speed,  Position, Overlap and Distance. A simple acronym S.P.O.D.

After reading and following all the directions listed herein, if you still have any problems achieving a first class finish with VIVILON, consult the VIVILON Trouble Shooting Guide at the end of this article. Learning to Spray Can Really Be FUN!!

NOTE: This guide covers ONLY spraying with compressed air. If you are spraying with airless or electrostatic equipment, although some information will be useful to you, the bulk of this guide will not. We believe the majority of users will be applying VIVILON with compressed air equipment, as we have for almost thirty years. We think we are reasonably competent to give advice in that area. So, with those caveats, read on.

There are three things that have to work together correctly to produce a quality finish:

    * the right air compressor and air delivery system
    * the right spray gun
    * the right technique

 

The first two you can buy. Technique has to be learned through PRACTICE. We will give you starting guides and concepts on how the equipment works and how to adjust for painting variables. This will give you both a theoretical and practical foundation of knowledge. However, there is simply no substitute for the real world understanding that comes from the repeated experience of actually spraying.

Practice can make anyone at least good, if not perfect. Practice offers the ability to use your commonsense to interpret what you see happening... and make the appropriate correction to adjust or fine tune the result to your satisfaction. This process will become easier, faster and more instinctual as your experience increases. I keep repeating Practice because that's REALLY the part of the process that's fun and leads to having PRIDE in what you can do with a spray gun.

If at anytime your efforts don't produce a quality finish, remember there is always a reason the final result didn't turn out the way you desired. If you start with the fact that these products have performed well tens of thousands of times for thousands of different applicators just like yourself, you can logically assume that using the knowledge contained herein to analyze your results will give you both the explanation for what happened and the necessary method(s) to correct it.

Now Lets get started!

1. The Right Compressor & Air Delivery System

YOUR AIR SUPPLY:

Volume of Air

Every spray gun has different requirements for both operating pressure expressed in P.S.I. (Pounds per Square Inch) and volume of air, expressed in terms of the C.F.M. (Cubic Feet per Minute). Very much like Watts and Amps in Electricity. It is CRITICAL that your air compressor be capable of delivering the amounts of BOTH your spray gun requires. Before you begin trying to spray any product, make sure that your gun and compressor are in sync with each other. A compressor that delivers more C.F.M. than your spray equipment requires is most desirable. One that delivers less is not acceptable. We cannot emphasize enough that you simply cannot get your gun to produce a fine finish if your air source is undersized. Why? Because there simply will not be enough air to allow you to finely atomize the coating. The results will be a smaller than optimal fan pattern and a rough or textured finish, often described as "orange peel" (see glossary).

First, go to the product manual for your air compressor and look at the specifications for Delivered CFM. This is the CFM and PSI the compressor puts out at its air valve. The amount actually delivered to your gun will be less. Why? Because the resistance factor of air being pushed down the air hose will increase and conversely the volume and pressure of air available will decrease the longer the air hose is to supply your gun.

For example, if a compressor delivers say 14.7 CFM @125 PSI, we know air supply shouldn't be a problem for a gun that requires 13.2 CFM at the gun. Even allowing for a drop off in CFM and PSI as explained above, the gun will be capable of optimum performance. In addition, because this compressor is delivering its CFM @ 125 PSI, and the gun only uses 45 PSI., you have plenty of air to spare. Why, because CFM delivered by an air compressor goes DOWN as PSI goes up and goes UP as PSI goes down.

But, if a gun requires 15.8 CFM, there is NO way to get a fine finish from the gun. So if this is the compressor you are going to own, rent or buy, look for a gun that requires less volume of air.

Quality of Air

Once you know that your compressor can provide the amount of air needed, you must make sure the quality of that air is acceptable. Spraying requires Clean (oil free) and Dry (water free) air.

The air tank must be drained of any residual water both before you begin spraying; and periodically thereafter. You also need to check the compressor's built in filter(s) designed to remove any dirt, oil or water contaminants to determine that they are both clean and functional. Having passed both these checks, your air supply should reliably meet your needs. But, we recommend having a final air filter installed at the gun itself. The price of a good quality air filter (about $30-$50) is minimal compared to the cost of repairing a paint problem that could be caused by not having one. For a single use, a disposable filter is about $8.

2. The Right Spray Gun

YOUR SPRAY EQUIPMENT:

For a Beginner or DIY sprayer, the choice between conventional and HVLP and siphon, gravity or pressure feed guns are not critical. Get whatever gun you can afford that can put out a good pattern If you can't afford a really professional gun, rent one or buy one at a knock-off like Harbor Freight or Northern Tools. There IS a difference; but, if you only intend to spray one item and throw it away (a boat, car, trailer, etc.) just get as good as you can afford.

But, just so you know, we will give you a description of the different types and varieties. First you need to decide on conventional or HVLP technology. At present, if you do not operate in one of the HVLP compliant states, you are free to choose whichever technology best suits your needs. What are the advantages to each system?

Conventional

1) Conventional sprayers will produce a wider wet pattern spray from a greater distance, for theoretical increased speed of application.

2) Typically, gun on gun comparisons will show a slightly reduced air requirement for conventional guns. This is because of the reduction valving in an HVLP to reduce the inlet air to the air cap air.

3) They are often slightly less expensive than their HVLP counterpart.

4) They also will require less CFM, thereby reducing the size of compressor required.

HVLP

HVLP stands for High Volume Low Pressure. It reverses the concept of a conventional which could be called HPLV, High Pressure Low Volume.

1) The HVLP guns produce a softer spray pattern.

2) Less bounce-back. This is mainly attributable to the low pressures at which they operate.

For instance, a conventional gun with 45 psi entering the gun will use all 45 psi to atomize the coating. Exiting the air cap at 45 psi will naturally impart more velocity to the sprayed material causing it to bounce-back when it strikes the object surface.

3) The HVLP gun greatly reduces both the perceived and real overspray effect that results in material waste for conventional guns. (See Transfer Efficiency in the Glossary).

In contrast, the same 45 psi supplied to the HVLP gun will result in no more than 10 psi exiting the air cap. (Indeed, 10 psi at the air cap is the legal limit to qualify for designation of a gun as HVLP). This reduced air pressure is the mechanism by which material waste is reduced and transfer efficiency increased.

How much? HVLP proponents will tell you 30%-50%. Is that real? Definitely, the answer is yes and no. Why? Because, yes, a HVLP gun may well be able to produce a transfer efficiency of 65%-85%, as opposed to 35%-50% for conventional.That's real for the well made guns.

However, the reality is that there are high quality conventional guns engineered to be capable of transfer efficiencies so close to those of less expensive HVLP, that unless you are a very experienced operator, the material savings will be minimal. Figure in the speed advantage from a wider effective spray fan; and, we believe, it could become a toss up. The only discernible advantage (other than compliance in those states that require it) is the reduced overspray and fogging perceived by those in the spray area. Obviously, in some situations, this will be the deciding factor in choosing HVLP compliant equipment.

Kind Of Spray Gun

After you have made the choice between conventional and HVLP technologies, you need to choose a generic type of gun that not only meets your needs for the type of jobs you intend to do; but, is comfortable as well. Your choices are siphon guns, gravity guns and pressure feed guns. Each has advantages and disadvantages.

Siphon Guns

Siphon feed guns have a cup (usually one quart or liter size) hanging under the gun body. They deliver product to the air cap to be atomized by creating a vacuum which sucks the product up a tube inside the cup. This is the least efficient method of product supply and accounts for the fact that the product needle-tip and air cap combinations (the parts through which the material is delivered for atomization) on siphon feed guns will always be the largest of any type to spray a given coating. It is also the reason that siphon feed guns will require slightly higher air pressure to operate properly. The reason for this is the air efficiency loss created by the need to use some air to create a vacuum for product delivery.

We believe the only advantage to the siphon gun lies in its slightly easier refill. It is the gun most people would think of if asked to describe a paint gun. However, as new, higher solids coatings have been introduced, siphon guns have lost market share, particularly in the auto refinish market. The more popular choice is becoming the gravity gun.

Gravity Gun

Gravity guns have a cup resting on top of the body and supply product, as you have probably guessed, by means of gravity, into the air cap below. The product needle/tip and air cap combinations are smaller and required air is less. They are more efficient than siphon spray guns, easier to use in close quarters; and, once you get used to them, more comfortable to use. The only drawback is the need to have a special stand or rack to hold them for refills.

Pressure Feed Gun

Pressure feed guns are the most efficient guns you can own. There are two types of pressure guns. The first (more common) type uses a pressure pot of various sizes, 2 quarts up to 20 gallons or more), to hold larger amounts of coating ready to be delivered to the air cap by means of fluid pressure.

This pressure pot has two outlet hoses attached to it. On two-quart cup set ups, this hose is usually 6 feet long. Sufficient to allow full arm extension from its placement on the sprayers belt. On larger pot set ups, the hoses usually start at 25 feet in length and go up from there to suit the operator. However, remember that the longer the hose, the greater the fluid and air resistance. In our experience, while theoretically the sky's the limit, (if you have a big enough compressor) the maximum practical length for these hoses is 100 feet.

What do they do? One hose delivers atomizing air to the air connector on the gun (just as with both the siphon and gravity guns). The other hose delivers material from the pot to the air cap under pressure. It functions by means of diverting the compressed air supply into the pot, where the path of least resistance for the coating is to go up the pot's internal pick up tube and out the fluid line into the front of the gun. This allows for the smallest product needle-tip and air cap requirement of any gun and provides the convenience of not only having a full 360 degree spraying orientation (because there is no cup positioning to worry about); but, also being able to spray extended amounts of material without needing to stop for refills. The only drawbacks are the higher initial cost (because of the need to buy the pressure pot and hoses) and the need to coil and uncoil the hoses moving job site to job site. We consider these issues minor and recommend a pressure feed system for both production fine finish work (i.e. auto-truck refinishing) and large scale applications (i.e. buildings) as well.

Hybrid Gun

The other type is a hybrid between either a siphon cup AND a pressure feed. These guns function by diverting a portion of the inlet air to a pressurized cup attached below the gun's body. There is only a small diverter air hose (1/4 inch diameter) involved instead of two large hoses. Most guns are either on or off , while others have an adjustment valve to fine tune the amount of air pressure going to the cup. The most important thing to remember, if you choose one of these hybrids, is to always release the pressure BEFORE opening the lid. REMEMBER, even though you may have disconnected the air from the gun, the pressure cup is STILL pressurized. There is a pressure relief screw valve or pull release on the top of the cup. Make sure you open this and listen for the quick hiss of air release before unscrewing this lid. If you don't, Imagine Your Surprise!

The most important thing to remember if you choose a standard pressure pot (before you do anything else) is learn where its pressure relief valve is and ALWAYS check to make sure it is fully functional BEFORE attaching your air supply to the pot. Why? Because each pot is only rated for a specific pressure (usually about 50-80 PSI). If your air supply is delivering substantially more than this "safe" amount, your pressure relief valve is the only thing keeping the pot from "banana peeling" with explosive force. Forget the mess this would make. You could very easily be seriously injured. Like everything else, the valve works IF IT IS KEPT CLEAN. MAKE SURE THAT IT IS.

Once you have chosen your gun type, you need to understand how it works. To start, we will explain what each of the controls allow you to do.

The Gun Controls

Product Needle Valve

This control knob is at the back of the gun above the handle grip. It works by means of restricting the trigger's travel distance which in turn controls how much product is allowed to enter the air cap to be atomized into a spray. Turning it clockwise reduces product flow. A counter clockwise rotation increases product flow. Ideally, you would have a needle-tip-air cap set the exact size necessary to allow the product needle to be wide open whenever you desired an optimum sized spray pattern. Remember, the lower the viscosity of the coating, the more you would need to turn in the product valve. The more viscous the product, the more you would open it up.

Obviously, you (as an end user) can't increase the viscosity of a coating; but, you can easily decrease it by carefully thinning (within the recommended limits) with a suitable solvent. However, if a coating's viscosity is too greatly at variance from your chosen size set, you will have to buy a separate set that will spray that higher or lower viscosity. Of course, all VIVILON coatings are formulated to spray well with one matched set of fluid needle, nozzle and air cap as recommended in our product data sheets.

Fan Control

This is a round knob extending from either the side of the gun or the top control on the back of the gun. Different guns place it in different configurations. Consult your product manual for location. It is essentially an air diverter for the fan horns on the air cap. When opened (counter clockwise turning) it allows air to exit the holes on either side of the air horn creating a flat fan effect by pushing the product exiting the front of the air cap together and spreading it at the same time. When closed (clockwise turning) it creates a round (cone) type pattern because there is no air to disturb the flow of atomized coating exiting the round orifice in the center of the air cap. Therefore, the pattern remains conical. (On some older guns that don't have a fan control valve, you need to turn the air cap so the horns are diagonal to the face of the gun to achieve the cone pattern). The fan control is used to adjust the width of your pattern (the farther you open it the larger will be the spread of the fan) to accomplish the type of pattern you desire.

Typically, you would adjust the fan to give you the widest wet edge-to-wet edge pattern possible. Why? Because you want to have as much wet area as possible without any (for lack of a better term) half-wet or dry area. Why? Because you want to reduce the amount of your overlapping from one pass to the next to the smallest amount possible consistent with the laying down of a uniform continuous coating. In short, you want to reduce wasted overspray to the smallest amount possible to save both in material, as well as, time required to complete the job.

The air micrometer is directly under the product needle valve or  at the bottom of the gun handle next to the air attachment. It can be turned only one way, clockwise up to 90 degrees. The farther you turn it, the less air it will allow to enter the gun.

This has two purposes. First, if you don't have an air regulator and gauge attached at the air inlet, you can control your air with the built in micrometer. Even if you use an attached regulator & gauge, the built in air micrometer functions as a back up to let you continue working, if for any reason your regulator should fail. Second, (you probably will never use it for this reason) if you are doing a precise color blend, some painters like to make very small adjustments to air pressure with the built in.

Air Cap 

This is the head of the gun with horns (wings, if you prefer) on the side that sits inside the ring that screws onto the front of the gun. It allows you to adjust the direction of your fan pattern. If you want to spray in a vertical motion (up and down) align the horns vertically. This produces a horizontal pattern that is wider than it is tall. If you want a horizontal spray motion (back and forth) align the horns horizontally. This produces a vertical pattern that is taller than it is wide. (See Diagram 1) Always test spray your gun away from the surface you intend to paint to make sure the air horns are set the way you want BEFORE starting to spray. The holes you see in the cap determine the atomization capability of the gun. Therefore, it is imperative that the horns, like all other parts of the gun, be kept absolutely clean. If you experience a degraded spray pattern, blockage in these airways is the first place to look.

DIAGRAM 1


Horizontal Fan Horns Produce A Wide Tall Pattern


Vertical Fan Horns Produce A Wide Flat Pattern

 

 

3. Spray Technique

Consistent production of a uniform wet film on a sprayed object is dependent not only upon your ability to adjust the gun properly by using the controls we have just discussed; but, also, upon three additional variables. First, you need to keep the gun the proper distance from the object surface AND ALWAYS keep that distance uniform. What do we mean by the terms proper and uniform? For most conventional sprayers, a good starting point is10-12 inches from the surface. For HVLP, it is more in the 5-7inch area. (Remember, we use less pressure with HVLP so the atomized coating doesn't travel as far.) When do you depart from or adjust these starting points? When you are spraying outside on a slightly windy day, you want to be closer to the surface so the wind doesn't blow your material away before it has a chance to reach the surface. Also, you want to be closer if you are doing anything that requires low air pressure, such as touch ups and detail lines (see discussion of these techniques below).

Uniform refers to keeping the gun always at right angles to the surface and at the same distance so that all areas will receive the same amount of coating. (See Diagram 2) Standing stationary in front of the object area and moving your outstretched arm back and forth or turning your wrist or elbow at the ends of each pass (called arcing; see Paint Glossary) results in more material being applied in the center of the arc than at the ends. (See Diagram 3) While there are some limited situations where an uneven or non-uniform paint application is desirable to deliberately produce lighter and darker surface areas, spray arcing in normal practice will give uneven results. How can you achieve a uniform spray pattern?

DIAGRAM 2

CORRECT  
INCORRECT

 


INCORRECT

Stand in front of and parallel to the surface to be sprayed. Keep your feet a shoulders width apart. Make sure there are no obstructions on the floor in your intended path of horizontal travel. (We realize that seems obvious, until you see a sprayer trip over tools, air hoses or other obstacles while concentrating on spraying the surface in front of him.)

Stand away from the surface at least 18 inches, but within an easy comfortable reach of the spray area. Mentally block off the area you intend to spray with a defined right and left side which will mark the beginning and end points of each pass. Hold your arm outstretched with your wrist locked. Move your body (not your arm) side to side as you spray. In other words, to complete your spray pass from left to right in front of you, move your torso from left to right. As you go farther down the surface, start to crouch while moving (swaying or rocking) left to right. (If you have ever seen an Olympic speed skater move, minus the forward motion, you have a pretty good idea of what this looks like.) If you are spraying a curved area, you will need to move the gun out away from the apex of the curve in order to maintain the desired uniform distance from the surface.

Next, you need to understand the importance of properly triggering the gun. This means how far back you pull the trigger to initiate your gun's spraying mode. Pull back on the trigger just a little bit, and air will come out to create a low-grade blower. Pull a little farther and material will mix with the air to form an atomized coating. The density of this coating is increased the farther you pull back. Therefore, for a consistent pattern you must pull back the same amount (usually but not always the full extent of travel) throughout the pass. To achieve a uniform pattern, start to fully trigger the gun just after the pass (the motion of your spraying) begins and release it just before your motion ends. Just like learning to clutch and shift a manual transmission, this soon becomes second nature.

The final variable for you to consider is, your judgment of the proper speed of travel. This refers to the speed at which you spray a pattern left to right or up and down. The slower you move, the more material you will deposit on the surface. Just like all other adjustments, (whether to gun control set up, distance from the surface, coating evaporation rate or viscosity) test your pattern on a test board, or inconspicuous area of the surface you intend to spray. DO NOT proceed to spray the job UNTIL you have produced a satisfactory TEST spray pattern, with all variables properly adjusted and accounted for to produce the exact result you want to deliver. If mistakes are to be made, make them where they don't count.

THE BEST WAY TO UNDERSTAND WHAT EACH OF THE CONTROLS (AIR, FAN, FLUID NEEDLE AND FLUID PRESSURE ON PRESSURE FEED SYSTEMS), DOES TO THE SIZE, SHAPE, VELOCITY AND INTENSITY OF A SPRAY PATTERN, IS TO ADJUST EACH OF THEM INDIVIDUALLY FROM FULLY OPEN TO FULLY CLOSED, SPRAYING A TEST PATTERN AT EACH OF SEVERAL DIFFERENT SETTINGS AND DISTANCES FROM THE TEST SURFACE. IF YOU DO THIS, YOU WILL STOP GUESSING AND START KNOWING A LOT SOONER.

Tips & Tricks:

Just a few ideas for your consideration. How do you adjust your gun to spray a fine line, like a border frame to reduce or eliminate your need for masking? First, reduce both your product flow and air pressure. Turn off your fan air so you have a conical pattern. Experiment with your pattern. Continue to reduce product and air, move closer or farther away (closer will reduce pattern size) until you get the size line you desire.

How do you spray in cold temperatures? First, you increase the coating evaporation rate by adding a compatible faster evaporating (sometimes referred to as "hot") solvent). If, however, you don't have these solvents (or don't have enough available), you may want to use a technique called tack and fill. Essentially what you do is spray a light mist coat on the surface and let it dry until it gets "tacky". Then come behind this mist coat with a full coat to fill in a uniform full film coat. The tacky mist coat will act to hold the full topcoat to keep it from sagging and running. Once again, everything you try for the first time, you'll need to experiment with until you get it down pat.

As you gain more experience and become more comfortable with the use of a spray gun, you'll develop your own ideas and techniques for doing things that you can adapt to special needs or circumstances you may encounter. Don't be afraid to experiment. You might surprise yourself after all.

 

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