A little about spay gun set up and use.

As I said before, these things are nothing more than tools, but we need to use the best tool for the job at hand. I will tell you gun technology and ease of use has improved dramatically with the advent of the HVLP guns. By the way, HVLP stands for "high volume, low pressure".

I think confusion comes in on both sides of the name. A lot of people when they see "High Volume" they think it refers to the amount of paint delivered. What it actually refers to is "high volume" of air. In the older style guns, air pressure was the main component to setup, but with HVLP guns "volume" of air is the most important. Volume of air, refers to the amount of air required. rather than pressure (they are two distinct things). In a conventional gun if we run 30 PSI at the gun inlet, we will have about 30 PSI at the gun cap. In a HVLP gun we may have 30 PSI at the inlet, but only 10 PSI at the cap. This is a major distinction in how paint is delivered between the two types of guns. In short, the most significant difference we see is less paint going into the air (lost) with the a HVLP gun. HVLP guns are very efficient in paint delivery. One very important issue is having a compressor that can deliver enough volume of air for the HVLP gun we are using. Most full sized HVLP guns require a lot more volume of air than a small home compressor can deliver. Check the CFM (cubic feet per minute) rating of your gun as well as your compressor to see if you have enough air volume.

Also confusion comes about in the name "low pressure". As I mentioned above, in an HVLP gun, the amount of air at the cap is what the name refers to, not the inlet pressure. We may still need to run our HVLP gun at 30 or more PSI at the inlet, just like conventional guns. One thing that is very important on HPLV guns is not to exceed the inlet pressure for the design of the gun. In most cases, the inlet pressure is stamped on the side of the gun. It is also important to set our air pressure with the trigger pulled, after the pressure drops.

Another distinction is painting distance. With a conventional gun we may be painting 8 to 10 inches from the surface, but we may be down to as little as four inches with an HVLP gun. I think painting too far from our surface is a major mistake made with HVLP guns. Now keep in mind, every gun is going to have a proper working distance, based on the gun itself as well as setup. If we run more pressure, the working distance is going to increase and the other way around.

One great trick to determine the proper working distance for any given gun and setup is to pull the trigger for full air, but not to release any paint. Put your free hand in front of the gun and draw it toward the tip of the gun. At the point we hear a distinct difference in sound is the sweet spot (distance) that we will achieve the best paint atomization. At that distance the gun is producing the finest mist of paint. If we go further (greater distance from our surface) the paint mist will start to accumulate into larger drops. I have seen this in my own painting by staying too far away from the surface can result in a grainy texture to the surface. This shows up a lot in shooting primer.

One other area that is very important is tip and needle size in our gun. We can't effectively shoot all forms of paint with the same size tip and needle. As a general rule we want to shoot primers at around a 1.8 to 2.0 tip size. Most base coats can be shot with a 1.4 tip and clears at 1.3 to 1.4. Keep in mind, these tip sizes are for a full sized conventional gun. I personally use a small detail gun to shoot base coats. With this gun I run a tip size of 1.0 that works perfect for the HOK paints I shoot.

The bottom line is it all comes down to set up and experimentation. One thing to do t check your gun is to shoot it at a piece of cardboard or a box. It's better to have it wrong on the box instead of on your plane.