Elliott Equipment Corporation

In a post last week on Electrostatic Spray Guns, you may have seen my comment about the transfer efficiency of HVLP Guns being in the 20-20% range. Kind of a provocative statement, wouldn't you say? Here is how I would defend that statement.

Since HVLP guns were mandated for most finishing operations in California by the South Coast Air Quality Management District (SCAQMD) a number of years ago; most other states environemtal governing bodies have implemented similar regulations and the transfer efficiency number of 65% has been generally accepted.

The problem is; finishers are fooling themselves if they think they are really achieving that high a degree of efficiency; and are hurting themselves (and their bottom line) if they are using anywhere near that number when calculating their actual applied coating costs.

• When the tests were done many years ago that deemed HVLP Spray Guns 65% transfer efficient; one must look closely at the criteria used. Virtually any type spray gun can have an artificially high transfer efficiency rate if the test criteria are favorable enough. Consider this: if one were to use as a test substrate a 4' by 8' sheet and limit the coating viscosity and flow rate enough; with no criteria for finish quality; one can achieve virtually any transfer efficiency one desires. I am afraid that was the case when these test were done. There were no universally accepted standards used that would have allowed the test results to have universal significance under actual factory conditions. In other words; had the test substrate been 1" tubular weldments; would one expect to still see 65% transfer efficiency? That is the problem with the tests and the reason the 65% transfer efficiency claim should be viewed cautiously.

• In real world practice; HVLP guns began to be used in applications where their limitations became glaringly evident. When coating viscosity's exceeded certain ranges, or when production rates were high; HVLP guns simply could not offer acceptable atomization characteristics. At that point finishers began to try to operate the guns outside the relatively narrow range of their physical limitations and the guns became nothing more than a very expensive conventional air spray gun,. It's a simple matter of physics; when we lower the atomizing air pressure (one aspect of atomizing energy)  of a spray gun enough; even if we keep the atomizing air volume high (another aspect of atomizing energy); we quickly reach a point where there simply isn't enough physical energy available to atomize the coating satisfactorily. either the finish quality or the production rate will suffer.

Our experience has shown that HVLP Guns are a good choice on lighter viscosity coatings or where production speeds are low to moderate.  Air Assisted Airless Spray Guns are most suitable for wood products clearcoats (sealers, lacquers, paints, varnishes) and other industrial finishes where good quality atomization (Not Class A Automotive) and higher production speeds are required. Electrostatic Spray Guns-both Conventional and Air Assisted Airless will also have production speed and atomization advantages over HVLP Guns in many applications.


Now; nothing I have said in this post should be construed as telling finishers to ditch their HVLP guns. On the contrary; EPA rules are EPA rules and substantial fines can be imposed upon finishers if the equipment they use is deemed to be non-compliant. The point of this blog is more to have users of spray guns carefully consider whether HVLP guns are their best choice or perhaps have them consider one of the other compliant technologies such as Air Assisted Airless (which also have HVLP Air Caps) or Electrostatic Spray Guns.

Want to learn more? Have a different opinion?       800-823-7527