What is the purpose of HVLP spray guns?
An HVLP Spray Gun is an air powered tool used to deliver (spray out) paint using a a high volume of air at low pressure. The spray gun is designed to aerosolize or atomize the paint by breaking it up into very small particles and then mixing it with the outgoing air. This paint/air mixture is then blown out through a nozzle. The optimal mixture for paint to air is usually about 2 to 1. The purpose of the gun is to achieve a fine spray of paint/air, resulting in an even application on the intended surface.
There are two distinct types of HVLP paint sprayers, turbine HVLP spray guns and air compressor driven HVLP guns. Turbine HVLP guns, as the name suggests use a turbine motor to move fins that produce large volumes of air and move it at low pressure through the gun. These are expensive pieces of equipment and their use is confined mostly to professionals. Air compressor driven HVLP guns are far more common and are the type most people recognize. This is the type of spray gun we will cover.
HVLP spray guns are often used in automotive painting, sheet metal painting, cabinetry, furniture making and repair, or similar applications that require a fine finish. Most HVLP guns can use a wide variety of paints including latex, enamel, lacquer, clear coat and primer. Some spray guns are made for only one specific type of paint and some spray guns are designed to be able to adjust to different paint types. This adjustment has to do with the width of the nozzle opening. The thicker the paint being used, the larger the nozzle orifice needs to be.
The whole point behind using a low pressure approach to applying the paint is to reduce the amount of paint being used to only what is needed to cover the surface being painted. When too much paint is used, the result is called "overspray". Because HVLP spray guns are able to reduce this overspray, they are said to have a high "transfer efficiency". In other words, the gun transfers just enough paint to the surface to be effective, but not too much to produce a splatter and waste. The result is a smooth and even coat of paint.
Paint Spray gun Selection and operation questions
- What kind of air compressor is required?
You will need a compressor powerful enough to drive you gun. Most air compressors designed for air tools should be able to drive your HVLP spray gun. The important thing to remember is that the air requirements listed on the gun are what the gun needs delivered to it, not what the compressor is required to put out. The best way to make sure what is present at the guns intake, is to use a spray gun with a built in gauge.
- How long of a hose will I need?
Hose length depends on how far you want to work for the compressor. Just remember, the longer the hose, the higher the compressor output will need to be to compensate for the added air volume in the system
- How do I set up the gun?
Turn the compressor on and open the outgoing valve part way until you have some pressure in the system. Pull the trigger on the gun to see what the pressure at the gun is. Then adjust the valve at the bottom of the gun until you have the gun pressure you need. Then you will need to adjust the flow level to achieve the mixture that you need. The adjustment know for this is at the front of the gun where the paint comes out. Test the pattern the gun is making by doing a few test sweeps on scrap paper.
- How do I apply the paint?
Sweep the gun back and forth is smooth strokes. You should have smooth even coverage with no running paint. If your paint is clumping up or running, adjust the mix at the front of the gun.
Remember to always use respirator when using you HVLP spray gun. Make sure the cartridge you are using is designed for paint fumes and particles. Use goggles or other suitable eye protection.
Common Terms and abbreviations associated with HVLP spray guns
- HVLP: This stands for High Volume Low Pressure. It refers to the fact that the guns uses a high volume of air (HV), and delivers it at low pressure
- PSI: This stands for Pounds Per Square Inch. This is the pressure at which the air is moving. Remember that the PSI can, and probably will be different at different points in the cycle. The psi measurement coming out of the compressor will likely NOT be the psi at the gun.
- CFM: Cubic Feet per Minute. The rate at which air is being moved.
- Overspray: When too much paint is atomized and blown toward the target surface
- Transfer Efficiency: Limiting the amount of paint leaving the gun so only the amount needed hits the painting surface.
- ID: Internal diameter. The width of the inside of the air hose.
- OD: Outside diameter. The width of the outside of the air hose.
- NPT: National Pipe Thread. The style of the threaded connection of the ends of the air hose and on the inlet of the spray gun.