In essence, an HVLP spray gun is still an air spray gun as it uses air as its primary atomization force. Both HVLP and conventional air spray guns use the same two components of compressed air, pressure and volume but in different quantities. The pressure, which is normally noted in terms of pounds per square inch or PSI and volume, which is noted in terms of cubic feet per minute, are both necessary for either gun to work.
Originally HVLP guns where designed to use extremely high volumes of CFM that were generated by turbines rather than compressors. These turbines delivered, in some cases, hundreds of CFM but very little pressure. In order to remain competitive with the turbine HVLP guns, the manufacturers of the traditional air spray guns soon figured out how to convert their guns to HVLP using compressed air rather than turbine air. Today HVLP guns are as common as the old conventional guns.
HVLP technology proved that if you used a lot of volume of air instead of a lot of pressure like conventional guns did, you could not only atomize coatings but also do so more efficiently. The efficiency improvement was mostly related to the fact that the atomized paint particles traveled at a slower speed than paint particles that were atomized with high air pressure. We refer to this characteristic as spray particle velocity. The higher the velocity of the paint particle the lower the efficiency would be.
I like to use the analogy of a tennis ball and a cement wall. The paint particle is representative of the atomized paint particle and the wall represents the substrate being coated. The harder you throw the ball against the wall, the further the ball bounces from the wall. During air spray atomization the paint particle can travel at speeds greater than 30 feet per second or FPS. When the same coating is atomized with HVLP technology, the FPS drops to 10 to 23 FPS. The slower the particle velocity, the less bounce back and over spray, the more efficient the technology will be.
In addition to spray particle velocity, another characteristic that affects guns that use a lot of volume of air such as HVLP is air damming. Here I like to use the analogy of a 2′ high by 2′ wide by 2′ deep box and blocks that are 1′ high by 1′ wide by 1′ deep. In this scenario the box is the inside of a cabinet and the blocks represent a cubic foot of air from your gun. Try to imagine these blocks of air as they exit the spray gun and enter the box. When you spray into the box you are filling it with the blocks of air. The inside area of the box can only hold 8 cubic feet or 8 blocks, but the gun you are using is putting out 20 cubic feet per minute or 20t blocks per minute.
The result is that within seconds you are …
