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HVLP USING COMPRESSED AIR - Conversion HVLP Spray Guns

by Editor 22. June 2018 11:35

By: Bill Boxer, Modern Finishing Products, Inc.
 
Last month we explored turbine/turbospray HVLP. There is a second HVLP format that utilizes a modified spray gun that complies with codes that define HVLP (less than 10psi at the air cap/nozzle) allowing these spray guns the title HVLP. These spray guns came about soon after HVLP was defined as a compliant technology initially based on the turbine/turbospray technology.
 
Spray gun manufacturers not ready to immediately commit to turbine/turbospray technology along with early limitations of turbine/turbospray systems found ways to modify conventional compressed air spray guns to comply with the 10psi limitation rule. Early entries into the marketplace left a bit to be desired along with continuous and numerous modifications. As time progressed, design improvements removed the issues and resistance to HVLP spray guns utilizing compressed air with consistent performance and desired atomization. Today, they are an accepted format and compliance with HVLP spray finishing codes. These spray guns are also known as HVLP Conversion Spray Guns.
 
Unlike turbine/turbospray technology which is fairly standard between manufacturers other than appearance, spray gun features and market philosophy, HVLP conversion spray guns come in all shapes and sizes, all designed to meet compliance rules. Internal and external design of these spray guns vary widely depending on the manufacturer.
 
While this article is not a commentary on conversion spray gun design or what is right or wrong or is it “actually” HVLP, I would rather comment on a few features and the positives and negatives of HVLP utilizing compressed air as opposed to the alternative HVLP turbine/turbospray systems. At the end of the day it is all about higher transfer efficiency and where mandated, air quality compliance.
 
In visiting many spray finishing shops over the years one of the things I consistently noted was the spray finisher trying to utilize HVLP conversion spray guns like they used their conventional compressed air spray guns and here in lies one of the issues. Most often I found the spray finishing technician exceeding the recommended inlet pressure settings to keep the HVLP spray gun at the designated 10psi or less thereby operating the spray gun out of compliance and defeating the primary goal of higher transfer efficiency, paint savings and reduced VOC’s in the environment. What is the answer? Better education in using HVLP Conversion Spray Guns.
 
Another question that comes up regarding HVLP Conversion Spray Guns: “Are they equally efficient as the alternative turbine/turbospray technology?” In the early 2000’s I was involved in a program to evaluate HVLP tubine/turbospray technology and HVLP spray guns for compressed air. Turbine/turbospray technology proved to be the most consistent and highest overall transfer efficiency. HVLP Conversion Spray Guns utilizing compressed air were more efficient than conventional compressed air spray guns but not quite as efficient than turbine/turbospray systems. I should note that the HVLP Conversion Spray Guns were operated within compliance guidelines.
 
There are a few additional points to note regarding HVLP Conversion Spray Guns for compressed air.

  1. Oil/water in the air lines are still an issue and require efficient oil and water filters to avoid contamination issues.
  2. Internal spray gun design is critical to achieving efficient atomization at the reduced air cap/nozzle pressure.
  3. Most, if not all HVLP Conversion Spray Guns for compressed air require a significant size air compressor (3hp/20gal tank is minimum) with adequate air storage to ensure not running out of air and the need to wait for the compressor restore air.

 
The last question that comes up: How do I select an efficient HVLP Conversion Spray Gun to utilize your own compressor?
 
Here is my personal guideline: If a spray gun can operate on both a turbine/turbospray system and an air compressor, the utilized air is being converted in a similar manner thereby producing the highest efficiency possible assuming the operator keeps within the recommended compliance guidelines. This is not to say that other HVLP spray gun design will not provide efficient results. They absolutely will. It’s on the operator to utilize the spray gun to its maximum efficiency.
 
To conclude: We all desire the highest possible finishing results for our spraying applications. Who doesn’t want a cleaner working environment, higher efficiency, paint savings and the ensuing financial savings. Each paint shop and applications are different. For many an HVLP spray gun for compressed air is a wise choice and for others an HVLP turbine/turbospray finishing systems is right. Speaking with a knowledgeable source with valued information can help you make the best choice.
 
 Learn more about this topic during Bill's session "HLVP Turbospray Technology, Past-Present-Future" at the IWF 2018 Education Conference.

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