There are two classes of spray guns in common use: old-fashioned pressure siphon feed guns, and gravity feed high-volume low-pressure (HVLP) spray guns. Although there are still a few high-pressure guns in use, the EPA's new Paint Rule has mandated the use of HVLP equipment in the motor collision and repair industry. HVLP spray guns offer three significant advantages over the older types: reduced paint consumption, lower emissions leading to healthier work conditions and better quality finishes. Nevertheless, proper fan pattern, paint delivery volume and atomising pressure adjustments are necessary for optimal results.
- Skill level:
- Moderately Easy
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Things you need
- Air compressor
- Masking tape
Fill the spray gun with paint and turn the compressor on. Attach a sheet of newspaper to the wall with masking tape.
Adjust the direction of the fan pattern by loosening the large knurled nut on the front of the gun. Twist the nozzle "horns" to either the horizontal or vertical position to achieve the desired fan direction best suited to the job at hand. Re-tighten the knurled nut.
Turn the fan pattern knob on the back of the spray gun clockwise all the way in -- this is usually the top knob. Back the adjusting knob out by two full counterclockwise turns.
Hold the gun vertically, about 18 inches from the paper. Spray a full width test pattern smoothly across newspaper. Pivot your wrists to ensure that the nozzle remains about 18 inches from the surface and at 90 degrees to the paper at all times.
Adjust the pattern by screwing the adjustment knob clockwise to decrease the width, or counterclockwise to lengthen it. Keep adjusting and deliver further passes until you have achieved the desired pattern.
Inspect the surface for smoothness; if you detect an "orange peel" effect, it means that paint is congealing before reaching the surface due to poor atomisation.
Adjust the air pressure knob on the side of the gun clockwise to increase atomising pressure and counterclockwise to reduce it. Monitor the gauge on the side of the spray gun while doing so, until you reach 25 psi atomising pressure.
Reduce the atomising pressure progressively while applying test sprays until you reach the lowest possible setting consistent with a smooth orange-peel free surface; This is usually somewhere between 18 and 25 psi.
Tips and warnings
- Protect yourself by wearing a face mask and latex gloves while spray painting.
- All of the above adjustments depend on the brand of paint used, the type of surface you are painting, relative humidity, and air movement. In addition, changing one setting may call for compensating adjustments to the other two settings. However, once initial spray gun set-up is done correctly, changing paint type and weather conditions will only call for minor adjustments.
- Ensure that the upper and lower edges of the spray pattern are still wet after each horizontal test pass. Apart from insufficient paint volume, too fast speed-to-distance of travel will leave the edges dry and powdery without proper paint-to-surface adhesion.
- Reducing spray delivery volume is an essential part of HVLP spray gun adjustment. To do this, turn the lower paint flow adjusting knob clockwise to reduce the volume of paint delivered, or counterclockwise to increase the delivery volume. Keep increasing the paint delivery volume slightly until the edges of the spray pattern remain moist immediately after the run. Reduce the spray delivery volume slightly if paint starts running down the middle of the spray pattern during the test run.
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