Maintenance & Reliability · SOP
Spray Gun Pattern Test Procedure
A step-by-step methodology for verifying spray gun atomization, pattern uniformity, and fan width. Essential for coating consistency and defect prevention.
Estimated Time
15 min
Difficulty
Intermediate
Regulation
ANSI/NFPA 33
Version
1.0
Purpose
To establish a standardized procedure for testing spray gun spray pattern to ensure uniform coating deposition, minimize overspray, and reduce rework. Improves transfer efficiency and coating quality across all production paint lines.
Scope
Applies to all pneumatic spray guns used in industrial painting lines, including HVLP, LVMP, and conventional air spray systems. Covers pattern test using a spray pattern test board or paper. Does not cover electrostatic or airless spray equipment.
Safety Precautions
- Lockout/tagout pneumatic supply before performing any gun cleaning, disassembly, or adjustment.
- Wear NIOSH-approved respiratory protection, chemical-resistant gloves, and safety glasses with side shields. Solvent vapours and overspray are hazardous.
- Ensure spray booth ventilation is active and solvent vapour concentration is below 25% of Lower Explosive Limit (LEL) at all times.
Required Tools & Materials
- Spray pattern test board (white cardboard or paper, matte finish) — minimum A3 size
- Measuring tape or ruler (metric scale, 0.5 mm resolution)
- Pressure gauges calibrated for fluid and atomizing air lines
- Solvent for cleaning (compatible with coating being tested)
- Viscosity cup (Zahn #2 or Ford #4) and stopwatch
- Portable light source (LED inspection light, 500+ lumens)
- Safety goggles, nitrile gloves, NIOSH-approved respirator or fresh-air hood
Procedure: Step-by-Step
1
Verify fluid viscosity per manufacturer specifications using a viscosity cup. Record the drain time in seconds. Adjust thinner addition if outside ±2s of target.
2
Set atomizing air pressure and fluid pressure according to the gun data sheet. Typical starting point: 2.5 bar atomizing, 1.0 bar fluid. Let pressures stabilize for 10 seconds.
3
Hold the gun perpendicular to the test board at a distance of 6–8 inches (15–20 cm). Keep the gun steady and parallel to the surface.
4
Trigger the gun for 1–2 seconds to deposit a single stripe of paint on the board. Avoid overlapping strokes.
5
Immediately inspect the pattern under the light source. A correct pattern is symmetrical, has a uniform width with no tails, heavy centre, or split (dog‑bone) shape.
6
Measure the fan width using a ruler. Compare to the gun’s specified pattern width (e.g., 250 mm ±10 mm). Record the measurement.
7
If the pattern is too narrow/wide or asymmetrical, adjust the pattern control knob (fan width adjuster). Turn clockwise to narrow, counter‑clockwise to widen. Re‑test from step 3.
8
Repeat steps 3–7 until the pattern falls within tolerance. Once acceptable, flush the gun with solvent and document the final pressure settings and fan width in the equipment maintenance log.