Atomization Physics: High Volume vs. High Pressure

For decades, the standard for applying finish was high pressure. Compressors would blast air at 40-60 PSI, shattering paint into a fine mist. While effective at atomization, the physics of high pressure created a chaotic, turbulent cloud. The air, moving faster than the paint, would bounce off the substrate, carrying a significant percentage of the coating with it. This is known as “overspray,” and it represents a massive inefficiency.

High Volume Low Pressure (HVLP) technology flips this equation. Instead of using pressure (PSI) as the primary energy source for atomization, it uses volume (CFM - Cubic Feet per Minute). By delivering a large mass of air at low pressure (typically 4-10 PSI at the cap), HVLP systems gently place the coating on the surface, relying on the Bernouilli principle rather than brute force.

The Bernouilli Principle in Spray Guns

Atomization in an HVLP gun occurs at the air cap. A high volume of air rushes past the fluid nozzle tip. According to Bernouilli’s principle, this high-velocity air creates a low-pressure zone directly in front of the nozzle. This pressure differential sucks the paint out of the cup (or allows it to be pushed by cup pressure) and into the airstream.

Because the air pressure is low (under 10 PSI), the paint droplets are not accelerated to violent speeds. They exit the gun in a soft, controlled cloud. This low velocity means the droplets don’t “bounce” when they hit the target; they stick. This is the fundamental physics behind the superior finish quality of HVLP.

Transfer Efficiency: The HVLP Advantage

The efficiency of a spray system is measured by “Transfer Efficiency”—the percentage of paint that actually lands on the part versus floating away as mist. * High Pressure Guns: Typically 30-40% efficiency. * HVLP Systems: Typically 65-80% efficiency.

This doubling of efficiency has profound economic and environmental implications. It means using half as much material to cover the same area, and releasing half as many VOCs (Volatile Organic Compounds) into the shop air. For expensive finishes like automotive clears or high-end lacquers, the system pays for itself in material savings alone.

Case Study: The Non-Bleed T70 Gun

The Fuji Spray 3003-T70 Q3 Platinum system pairs its turbine with the T70 Non-Bleed Spray Gun. In the realm of turbine guns, “bleed” status is a critical mechanical distinction.

• Bleed Guns: Air flows continuously through the nozzle, even when the trigger is released. This constant jet can blow dust around the shop and dry out the paint on the nozzle tip (tip dry).
• Non-Bleed Guns (T70): The trigger controls both the air and the fluid. Air only flows when you are spraying. This prevents dust disturbance and keeps the nozzle wet and ready. The T70 achieves this via an internal valve assembly that shuts off the turbine air at the gun, a feature that requires a turbine with a relief valve or bypass to prevent back-pressure damage.

Air Cap Geometries: Shaping the Fan

The T70 gun utilizes a high-precision air cap (Standard #3, 1.3mm) to shape the atomized cloud. Small holes in the “horns” of the air cap direct jets of air inward, flattening the round stream of paint into a fan pattern.

The Pattern Control Knob on the T70 allows the user to adjust the volume of air flowing to these horns. By manipulating the aerodynamics, the user can dial the spray from a small circular spot (for detail work) to a wide, flat fan (for broad surfaces) instantly. This adjustability is purely aerodynamic, requiring no changing of parts.

Turbine Staging: 2-Stage vs 3-Stage Power

The power of the atomization is determined by the turbine’s “stages”—essentially, how many fans are stacked in series. The Q3 Platinum features a 3-Stage Turbine. * Stage 1: Intakes air and accelerates it. * Stage 2: Compresses the accelerated air. * Stage 3: Further compresses the air, boosting the pressure to approximately 6.5 PSI.

This 3-stage power provides the necessary energy to atomize thicker, modern water-based coatings that would clog or spit in a weaker 2-stage system. It strikes the ideal balance between the raw power needed for atomization and the low pressure needed for control.

Conclusion: Precision in the Air

HVLP is not just a different way to spray; it is a smarter way. By respecting the physics of fluid dynamics, systems like the Fuji Spray Q3 Platinum achieve a level of control that brute-force high-pressure systems cannot match. Through the integration of 3-stage turbine power and precise non-bleed gun engineering, it puts the paint exactly where it belongs: on the project, not in the air.