RP spray guns: The best of both worlds?

April 4, 2023
Painters increasingly see the benefits of using an RP-technology spray gun for more than just clearcoat.

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What you'll learn:
  • The difference between HVLP and RP spray guns
  • Why there is a movement toward using RP spray guns
  • How newer gun designs can be matched to a painter's unique application style

When should a painter use an RP gun? The best way to answer this question is to start with what an RP is and how it’s different than an HVLP spray gun. When SATA began making spray guns for the automotive refinish industry, the technology was cutting-edge. Those spray guns are now referenced as “conventional” technology. 

The definition of a conventional spray gun can be summed up as a spray gun that relies on air pressure to achieve fine atomization. The paint products that were being used in the past were classified as low to medium solids and typically had high viscosity by today’s standards, and it was not uncommon to spray with a 1.6 or 1.8 fluid tip for both primers and topcoats. If you wanted a finish to be flatter or smoother, you had only two options. A painter could either lower viscosity with heat, commonly referred to as “hot cupping” lacquer or enamels by placing the spray gun’s siphon feed cup on a hot plate to warm the paint. Or he or she could more finely atomize the paint by cranking up the air pressure to 45-65 psi. By increasing the air pressure, the paint was atomized into smaller droplets, which resulted in a flatter, smoother finish and a better overall appearance. 

But a negative of utilizing higher air pressure to achieve finer atomization and smoother finishes is its effects on transfer efficiency. Though a painter was able to achieve a better appearance, he or she often would put more paint in the booth filters due to overspray than he or she did on the vehicle. Fast forward to more than 30 years later, and there are now rules and regulations regarding spray equipment and their operational efficiency. Just as there are regulations on the volatile organic compounds (VOCs) in paints, there are regulations that apply to spray equipment. The current regulations on spray guns are that they must not exceed 10 psi at the air cap, or if that air pressure is in excess of 10 psi, the transfer efficiency of the spray gun must meet or exceed 65 percent. South Coast Air Quality Management District (SCAQMD) is one of the leading agencies that focuses on spray equipment testing and approvals. 

Until the late 1990s, painters had used a mixed bag of both conventional and HVLP spray gun technologies. The industry’s focus on cost and material savings pushed painters to put down their old spray guns and pick up the newly introduced HVLP guns. Initially, HVLP spray guns were not welcomed with open arms.  When compared to the more conventional spray guns, the HVLP spray guns were slower, felt choked for material and really had a negative market reputation. 

The SATAjet NR 95 was the first industry-accepted HVLP spray gun. This had more to do with education than equipment. Distributors and technicians alike were finding out through paint company training that HVLP spray guns needed a higher volume of air to run them properly. Spray booths started providing “high-flow” hoses, couplers and fittings to accommodate the volume of air required to run these new spray guns. 

In 1999, SATA also introduced what we now call a “compliant” spray gun with the NR2000 RP spray gun. The new RP was introduced to have the speed and wetting of a conventional gun, with the transfer efficiency and savings of an HVLP. This new compliant spray gun met the standards of refinish equipment guidelines by focusing on transfer efficiency rather than the air pressure at the air cap. This allowed a superior atomizing spray gun that still maintained 65 percent or greater transfer efficiency. 

However, by this time, painters had also started seeing the benefits of using an HVLP over conventional spray guns for color application. Vehicle manufacturers were starting to use colors with more special effect pigments and metallic flakes. These colors required better atomization and orientation than a conventional spray gun could provide, so the HVLP spray gun really found its place spraying basecoat color. 

While HVLP spray guns were doing a great job with color, they still weren’t a painter’s first choice for clearcoat application. Even with ideal hoses and fittings, painters were still holding onto the old guns to spray clearcoat due to their speed, wetting and final appearance. This is where the new RP really impacted the industry.  In the hands of a trained technician, it could provide you with an incredibly smooth, glossy finish without sacrificing those application attributes painters expect.  It was during this time that the unwritten rule of using HVLP for basecoat and RP for clearcoat was created by the painters using the products. 

Fast forward 20 years from the RP’s first introduction, and manufacturers have continued to improve their spray guns’ performance. More painters are really seeing the benefits of using an RP-technology spray gun for more than just clearcoat. With today’s variety of paint brands and preferences, it is difficult to make a blanket statement like “RP is the best option for basecoats.” However, we are seeing a significant shift from HVLP to RP for spraying basecoat in recent years. 

How RP and HVLP technology differ

To better understand this shift, let’s look at what makes an RP different than an HVLP spray gun. An HVLP is limited to 10 psi at the air cap to perform atomization of today’s high solids paint materials. That limitation is one major contributor to why we use smaller fluid tips today than we did more than 20 years ago. A smaller stream is easier to atomize than a larger one. While that 10 psi limitation is put on the HVLP, an RP meets the rule of 65 percent or greater transfer efficiency, which allows it to utilize higher pressures at the air cap to atomize. A general rule is that an RP has 60 percent of the inlet air at the air cap. That means if both spray guns are hooked up to a hose with 29 psi inlet pressure, the HVLP has 10 psi while the RP has 18-19 psi at the air cap. What that means to a technician is that while an HVLP is an excellent choice for spraying both basecoat and clearcoat, an RP can offer improved atomization. 

As an example, the SATAjet  X5500 nozzle system offers choices of “I” and “O” patterns in both HVLP and RP, which allow a painter to customize a spray gun to his or her specific style and technique of spraying. 

Some painters prefer to be close to the panel with quick arm speed, while others prefer to be a little further back and controlled. Now, both painters have that option, and the the performance gap between an HVLP and an RP gun has never been tighter. 

Increasingly, painters use RP technology for basecoats. They are starting to see the performance of an RP, paired with the customizable pattern shapes of the X 5500 I & O nozzles make their jobs easier. The improved atomization of the RP and the pattern-shaping of the I & O nozzle set allows a painter to struggle less with difficult colors. Overall, painters are seeing improved application with an RP for both color and clearcoat. 

In today’s automotive refinish Industry, painters are being asked to do more with less every day. The proper selection of an RP technology spray gun allows a painter to achieve incredible final appearance without sacrificing material savings. 

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