A HVLP (High Volume, Low Pressure) spray gun uses a high volume of air going through the gun to atomise the primer instead of high pressure. The low pressure coming out of an HVLP gun applies much more primer on the vehicle instead of in the air. So you save paint and save money… however, you do need to set up the gun to atomise primer correctly. There are three steps to get right…
Step 1 - AIR SUPPLY
HVLP guns require a high volume of air (cfm – Cubic Feet per Minute) to operate. The directions for your gun will tell you the minimum cfm it needs to operate correctly. It’s not enough for you compressor to build up pressure, it has to be able to produce enough pressure constantly. Set your compressor to 90 psi output.
You also need to set the air pressure where it enters the gun via s small regulator which attaches to the base of your gun.
You will also need an air dryer. If you have any water or oil in your air lines, it will ruin your work. It is advisable to put a small disposable one on the end of your gun.
Step 2 - CHOOSE THE RIGHT CAP, TIP & NEEDLE FOR YOUR PRIMER SPRAY JOB
Because primer is thicker than body paint and clear coat, it is recommended you use a 1.8mm tip and air cap when applying primer.
Step 3 - SET UP
You need to re set your gun every time you use it. Variances in humidity, temperature, etc will affect how your run shoots that day…
Tape a piece of masking paper on the wall. This is for your spray test.
Now you set your pressure at the gun inlet. Use your air regulator with gauge that you have attached to the gun. You want to set it with the trigger pulled. To begin, set it at 50 psi. Close the air volume control knob (usually located beside where the air hose enters the gun) and with the trigger pulled, open it to the point where the air volume starts to stay the same, and then stop. That sets your air pressure and volume. Now open up the fan control know (located on the top or the side of the gun) all the way, and you can then turn it down a little. What you are aiming for is a fan about 15cm tall with the gun about 15cm from the surface. 15cm x 15cm!
You are now ready to test!
Hold your fun at the paper on the wall like you are going to paint it. Hold it at 15cm and pull the trigger all the way in for a split second, then close it. What you show see now is a cigar-shaped pattern on the paper. Turn your fan control knob in until you get it 15cm tall at 15cm from the paper. That sets your fan control.
Now leave it alone! If you change the psi at the cap, you will need to start set up over again!
Now hold your gun about 20 to 22cm from the paper. This is the distance you want to spray at. Your pattern will now be longer since you are further away from the paper. Test again. The centre should be fully covered without any runs. If you do have runs, you are probably too close or holding the trigger for too long.
What you want to achieve is the smallest paint droplets possible without losing full coverage.
To do this, you turn in your material knob little by little. You can also achieve the same outcome by raising the air pressure slightly. When you get fine drops with full coverage, you’re there!
Here are some excellent Spray Guns to choose from:
DeVilbiss GTI Prolite Gravity Gun Blue 1.2mm/1.3mm L/Edition Roberlo 50yr w 600mL Pot