Auto Refinisher's Questions and Answers Session

Auto Refinisher's Question & Answer Session

Q:  The auto paint store where I buy my supplies is recommending that I switch to an HVLP compliant gun.  What does HVLP mean?

A:  Well, that?s a popular question that many painters have been asking in the last few years.  To answer your question; HVLP stands for: High Volume Low Pressure.  This has to deal with the amount of air that the Spraygun requires.  HVLP compliant guns require a higher volume of air at a lower pressure.  HVLP is a government spec. that has been mandated for all Spraygun Mfgrs.  To be HVLP compliant a Spraygun must have less than 10 psi of air leaving the air cap.  Inlet pressure will vary by model and brand of the gun.  I have seen anywhere from 16-50 psi inlet pressure recommended by the different Spraygun manufacturers.  If the gun is said to be HVLP compliant it will have 10 psi or less leaving the air cap regardless of the recommended inlet pressure. It must also be at least 65% efficient .

Q:  Why should I switch?

A:  Well to be perfectly honest, if you don't like to save money you shouldn't switch.  In the answer to the previous question I said that an HVLP is 65% efficient.  In comparison, a siphon feed Spraygun is about 20-25% efficient and a regular gravity feed spraygun is about 35-45% efficient.  In laymen terms, spraying with an HVLP, at least 65% of the material you're spraying is actually going to the panel.  A siphon feed Spraygun will only put down 25% or less materiel. And likewise a gravity feed Spraygun will only put down 45% or less.  So if your average paint costs $100.00 per gallon you would save anywhere from $35-$55.

Q:  Will I have to change my spraying technique?

A:  Definitely, with an HVLP you will need to move closer to the item being painted.  Typically 8" - 10" away from surface is required.  Compared to siphon feeds, they require 10" - 12" from surface.  Also, you won't need as much overlap as a siphon feed Spraygun.  My recommendation is 15-25% overlap. With a siphon feed you needed to get at least 40-50% overlap to get a nice even job.

Q:  So do I just buy a HVLP Spraygun and start using it?

A:  No, First things first. You really need to check and make sure you have an adequate air supply. I have talked to guys that tell me they have plenty of air so I go ahead and sell them an HVLP Spraygun and come to find out later they didn't have anywhere near the recommended volume.  Now, how do you find out if you have enough air you might ask? The first step is you need to know what your compressor's scfm rating is.  If you have the paper work that came with your compressor it should tell or you may have to refer to where you bought it from. Also, sometimes on your compressor you'll find a sticker or tag giving the scfm rating at various psi. If you know what horsepower your compressor is a general rule of thumb is approximately 4 cfm per horse if the compressor is fairly new and 3 cfm per horse on an older model.  Don't trust this equation to be 100% factual information though because many compressor Mfgrs adjust their horsepower by over-sizing the pulleys. Finding out this information can sometimes be a pain but it is very important before you buy a HVLP Spraygun.

Q:  Is temperature selection more important for reducers and hardeners using HVLP?

A:  Yes and No, No on spot panel repairs.  Large repairs or full paint jobs are extremely important.  I recommend using at least 1 temperature selection higher in your reducer selection than what the paint Mfgr. recommends for the temperature that day.  (Example:  If its 72? and your Mfgr. recommends 70? temp reducer, HVLP Sprayguns will perform better with an 80?-85? temperature reducer.)

Q:  Will changing to an HVLP slow my production speed down?

A:  According to the Spraygun Mfgrs. No.  However I have talked with many Refinish Techs and most all of them say they had to slow down at first.  After the learning curve, most all of them were able to go back to painting as many cars a day as before.  Even though you're using much less air pressure with an HVLP spraygun to apply the finish you're putting on more material per pass than the average siphon feed Spraygun.

Q:  I have been told that HVLP Sprayguns must be kept pristine clean. Is there any truth to that?

A:  The truth is yes and no. Yes and no you ask? HVLP guns will spray just as well as a standard siphon feed gun will when it is dirty.  So to answer your question it would be no it is not mandatory that HVLP be kept in ?pristine? condition. However with paints now days costing well into the hundreds of dollars per gallon why would you take the chance of ruining a paint job with a dirty gun. And it?s not just with the paint. Primers now days also cost well into the hundreds of dollars as well. So a dirty gun could literally cost you a bundle. Besides the price of the gun, imagine if you will all the material you would use on any particular job that could be completely wasted if your dirty gun caused a problem. Why take the chance? In this day and age you can purchase insurance for everything. Why not purchase a good spraygun cleaning kit? It?s cheap insurance.

Q:  Why does my new HVLP gun sound so much different than my old siphon feed gun?

A:  Remember HVLP stands for high volume low pressure. Also remember that HVLP must have less than 10 P.S.I. leaving the air cap. So your new HVLP spraygun is going to emit a different sound than your old conventional siphon feed gun. I have talked with some painters that compare their old siphon feed as a high pitched hissing sound and their new HVLP as a low pitched jet engine. So don't be fooled by the sound coming from your new HVLP spraygun. If you inlet pressure is set at the manufacturers recommendation then the air cap pressure will be at or below 10 P.S.I.

Q:  I have heard other painters rave about the finish that their HVLP spraygun puts out. I have painted cars for 18 years and I tried an HVLP a few months back and I hated the thing. I just couldn't get my finish to lay out. What could I have been doing wrong?

 A:  Well, there are a number of things that could have been a problem. First of all I would check my technique. Remember I said earlier you would need to move in closer, slow down slightly, and overlap less. Secondly, I would check my air compressor's CFM. Most HVLP Sprayguns will need anywhere from 8-16 CFM at around 40-50 PSI. On average I want at least a 5 horse compressor with at least a 60 gallon air tank. This would be the bare minimum recommendation. This size air compressor with some HVLP Sprayguns would not be adequate. Thirdly and most often overlooked is air fittings and hoses. Let?s talk hoses first. With HVLP since they work off CFM instead of PSI you will need to make sure you have at least a 3/8" inside diameter air hose. Also use only the amount of air hose needed for the job (i.e. don't use 50 feet if 35 feet will work). Now for air fittings, buy only 3/8" inside diameter air fittings such as Sharpe's 8310, 8320, 8330, and 8340. Also get rid of all air restrictions that aren't absolutely necessary such as those little colored air dryer balls, air regulators, wound up unused air hose and yes even hose reels. These steps can be time consuming to fix all the little problems, but to save the most material and get the best out of your HVLP spraygun these things are very necessary.