Len
01-22-2006, 10:01 PM
Since there has been a little confusion about HVLP I pulled this explanation from an old archive to better explain the difference.
There are two things that differentiate conventional from HVLP spray guns.
1. "Transfer Efficiency” means the percentage of material that goes from the cup to the surface being sprayed. HVLP needs to transfer 65% or more of the material to the surface.
2. Pounds per square inch (PSI) of air pressure measured at the "air cap" of the spray gun. The air cap is the part that surrounds the fluid tip where the paint comes out. Less than 10 PSI is required (behind the air cap) for a gun to be HVLP. This cap pressure usually doesn't need to be measured because it's controlled by adjusting the inlet pressure and the correct inlet pressure will result in the correct cap (outlet) pressure.
The old "conventional" spray guns atomized well but transferred as little as 25 to 40% of the material to the surface while having a pressure 20, 30 or more PSI at the air cap. The latest technology is the "compliant" spray guns that meet legal requirements in many states because they transfer 65% or more of the material to the surface but they have a pressure at the cap that exceeds the 10 PSI so they cannot be called HVLP.
There are pros and cons to all the variables because when you increase performance in one area you suffer in another. For instance when you decrease the pressure with HVLP you also decrease the ability of the air to break up the paint into very small droplets. At the other end of the equation when you increase pressure you generate better atomization but you lose transfer efficiency because the increase air generates effects that cause the paint to go into the air and not on the surface.
The compliant guns have a lower pressure than conventional but not as low as the HVLP. With the better engineering these compliant guns are better in some ways and not as good in other ways when compared to both conventional and HVLP.
Judging which spray gun to purchase is almost like judging which car to drive; you want to calculate....
1. Fuel consumption or in the case of the spray gun its "air consumption" meaning CFM needed to power the tool. Will your compressor keep up?
2. "Performance" Will it fit you needs? Will it generate the result you want?
3. "Cost" Does it fit your budget? If you spend too little you could possibly get an inferior tool and if you spend too much you may be waisting your money.
I find that a "good" HVLP spray gun will atomize well and be much easier to handle while a compliant gun will move faster, atomize better but won't handle as well as the HVLP. What this means to the user is that the results with compliant may be smoother and faster but they probably won't be as consistent as HVLP, especially for the painter that doesn't paint frequently to boost their skill level.
With reduced pressure at the cap you generate less of an "air pillow" on the surface which means that the changing angle of the gun doesn't drastically effect the result on surface like it does with higher pressure at the cap and a more dense air pillow.
Personally I really like the consistent results from my HVLP gun because I tend to polish most of my work and, since I'm no longer a production shop that needs to meet deadlines on my jobs, I don't need a gun the applies the paint quickly. With their consistency HVLP guns tend to generate much less overly wet or dry areas that result in dull spots and runs while making the material go a long way with it's good transfer efficiency. I also find that it's a lot easier for me to generate a high quality job with a little orange peel followed by polishing than it is to generate a good job that has runs and dry spots needing repair. However, if you're looking for speed as well as meeting the legal requirements for a paint shop business in your area OR you're painting daily OR have a limited air supply it may be wise to look at compliant or conventional spray guns. There's something for everyone.
There are two things that differentiate conventional from HVLP spray guns.
1. "Transfer Efficiency” means the percentage of material that goes from the cup to the surface being sprayed. HVLP needs to transfer 65% or more of the material to the surface.
2. Pounds per square inch (PSI) of air pressure measured at the "air cap" of the spray gun. The air cap is the part that surrounds the fluid tip where the paint comes out. Less than 10 PSI is required (behind the air cap) for a gun to be HVLP. This cap pressure usually doesn't need to be measured because it's controlled by adjusting the inlet pressure and the correct inlet pressure will result in the correct cap (outlet) pressure.
The old "conventional" spray guns atomized well but transferred as little as 25 to 40% of the material to the surface while having a pressure 20, 30 or more PSI at the air cap. The latest technology is the "compliant" spray guns that meet legal requirements in many states because they transfer 65% or more of the material to the surface but they have a pressure at the cap that exceeds the 10 PSI so they cannot be called HVLP.
There are pros and cons to all the variables because when you increase performance in one area you suffer in another. For instance when you decrease the pressure with HVLP you also decrease the ability of the air to break up the paint into very small droplets. At the other end of the equation when you increase pressure you generate better atomization but you lose transfer efficiency because the increase air generates effects that cause the paint to go into the air and not on the surface.
The compliant guns have a lower pressure than conventional but not as low as the HVLP. With the better engineering these compliant guns are better in some ways and not as good in other ways when compared to both conventional and HVLP.
Judging which spray gun to purchase is almost like judging which car to drive; you want to calculate....
1. Fuel consumption or in the case of the spray gun its "air consumption" meaning CFM needed to power the tool. Will your compressor keep up?
2. "Performance" Will it fit you needs? Will it generate the result you want?
3. "Cost" Does it fit your budget? If you spend too little you could possibly get an inferior tool and if you spend too much you may be waisting your money.
I find that a "good" HVLP spray gun will atomize well and be much easier to handle while a compliant gun will move faster, atomize better but won't handle as well as the HVLP. What this means to the user is that the results with compliant may be smoother and faster but they probably won't be as consistent as HVLP, especially for the painter that doesn't paint frequently to boost their skill level.
With reduced pressure at the cap you generate less of an "air pillow" on the surface which means that the changing angle of the gun doesn't drastically effect the result on surface like it does with higher pressure at the cap and a more dense air pillow.
Personally I really like the consistent results from my HVLP gun because I tend to polish most of my work and, since I'm no longer a production shop that needs to meet deadlines on my jobs, I don't need a gun the applies the paint quickly. With their consistency HVLP guns tend to generate much less overly wet or dry areas that result in dull spots and runs while making the material go a long way with it's good transfer efficiency. I also find that it's a lot easier for me to generate a high quality job with a little orange peel followed by polishing than it is to generate a good job that has runs and dry spots needing repair. However, if you're looking for speed as well as meeting the legal requirements for a paint shop business in your area OR you're painting daily OR have a limited air supply it may be wise to look at compliant or conventional spray guns. There's something for everyone.