Automotive HVLP Paint Sprayers - Spray Guns
By Dennis Bandy Copyright © 2006,07,08
Conventional pressurized spray guns operate between 40 to 60 psi (Pounds Per Square Inch). The result of this higher pressure is excessive overspray with 66% of the paint wasted. Due to the lower operating pressure of HVLP (High Volume Low Pressure) paint spray guns which is 9-10 psi, they save 30-50 percent of the paint due to less overspray. The EPA (Evironmental Protection Agency) reports that by using HVLP sprayers hazardous emissions is reduced. The HVLP gun can pay for itself quickly in material savings. In fact the HVLP spray gun is one of the most popular sprayers used in automotive painting applications.
The HVLP spray gun uses a compressor to supply the air and a regulator at the compressor that is usually set to around 30 psi and the gun is adjusted to 9-10 psi at the cap. The length of the hose will affect the pressure drop, the longer the hose the more the pressure drop. As with any spray gun it is important to use filtered dry air from an air compressor that can provide enough CFM (Cubic Feet Per Minute) so that while spraying there will be enough volume to maintain a uniform spray pattern.
The CFM is important and it can range from 7.5 to 24. There is a test to check for proper air pressure and volume coming from the air compressor. The test will determine the static air pressure at the gun and the dynamic air pressure at the gun. The air pressure drop from the compressor the gun can affect spray quality.
Checking the Pressures Using a Gauge
1. Adjust to the desired pressure with an adjustable gauge like the SHP3310, at the gun with the trigger in the off position, this is the static pressure reading.
2. Set the fan and the material control adjustment knobs in the wide-open position. Note the dynamic air pressure reading on the gauge. (The dynamic reading is checked with gun's trigger fully pulled back).
3. Check for adequate compressed air supply by maintaining the trigger position for two minutes.
If there is no pressure drop, there is enough PSI and CFM to operate that particular gun. If the gun does not have enough volume and pressure provided, do not attempt to spray because the result will not be satisfactory.
When using the HVLP spray gun compared to a conventional gun it will need to be closer to the target.
The way the HVLP works is with air restriction. There is a restrictor inside of the HVLP gun that controls the air pressure from the compressor in order to provide a lower air pressure at the air cap. The typical air cap reading is 9-10 psi., a HVLP manual might say 30 psi inlet pressure produces 10 psi air cap pressure. This is different from a conventional paint spray gun, since the conventional spray gun doesn't have an internal restrictor. That means that whatever the pressure coming in will be about the same at the air cap. HVLP guns are not suitable for spraying house paints, because house paint is too thick for this design sprayer.
With any type of spray gun, paint will become air born so a respirator, face shield and paint suit is required to protect the user. Supplied air systems use a respirator with a built in face mask that has peel off lens covers.
For more information on sprayers and spray guns, there's a great resource for searching FAQ's at one of our supplier's websites. This resource has a wealth of information, most of which applies to Astro Pnuematic, DeVilbiss, Sharpe, Steelman, Titan or any brand paint sprayer being used.