How to Select a Paint Spray-Gun Nozzle Size
Match the fluid tip to the coating—not only to whether the liquid looks thin or thick. Use the coating technical data sheet first, then confirm viscosity, air supply and the test pattern.
Updated by the SunChem Lunaris technical content team · Approximate starting ranges only
1. Quick nozzle-selection chart
Use this as a workshop starting point, not as a substitute for the coating data sheet. Formulation, solids content, temperature, reducer, gun design and desired film build can shift the correct size.
| Coating or material | Typical starting range | Common selection logic | Watch for |
|---|---|---|---|
| Thin stains, dyes and low-viscosity lacquers | 1.0–1.4 mm | Smaller tips help control fluid flow and support fine atomisation. | Too much air can create dry spray; too large a tip can make runs easier. |
| Solvent or waterborne basecoat | 1.2–1.4 mm | Fine, even droplet distribution is normally more important than high film build. | Mottling, striping or dry edges from poor overlap, distance or air balance. |
| Clearcoat and many automotive topcoats | 1.2–1.4 mm | Enough flow for a wet, even film without flooding the panel. | Orange peel if material is too viscous or atomisation is weak; runs if fluid delivery is excessive. |
| Direct gloss / single-stage topcoat | 1.3–1.5 mm | Balances finish quality with slightly higher film build. | Check the TDS because high-solids systems may specify a different setup. |
| Sealer or wet-on-wet primer | 1.3–1.5 mm | Usually lower build than a surfacer and applied as a controlled, even layer. | Uneven hiding or excessive texture from poor setup. |
| Primer-surfacer | 1.6–1.8 mm | Larger passage supports higher solids and build. | Coarse atomisation, tailing or slow flow if the tip is too small. |
| High-build primer | 1.8–2.2 mm | Allows heavier material to pass without excessive reduction. | Do not over-thin solely to force material through a small tip. |
| Sprayable filler, texture or heavy industrial coating | 2.0–2.5 mm or product-specific equipment | Large-orifice setup for very high viscosity or intentionally textured application. | Some materials require a dedicated texture gun, pressure feed or airless equipment instead of a conventional gravity gun. |
The SunChem Lunaris HVLP gravity-feed model is offered in 1.3, 1.4, 1.7, 2.0, 2.2 and 2.5 mm versions. Select the version against the coating TDS and job—not by assuming one size suits every material.
2. Coating type, solids and required film build
Nozzle size controls potential fluid delivery, but the final result also depends on needle travel, fluid adjustment, air-cap design, atomising pressure, gun speed, distance and overlap. Two coatings with similar apparent thickness can behave differently because one contains more solids or is designed to build a thicker film.
- Read the application section of the TDS: note fluid-tip range, reducer or hardener ratio, induction time, pot life, flash time and target film thickness.
- Identify the job: spot repair, small component, full panel, furniture part or large continuous surface.
- Decide whether finish or build is the priority: a fine clearcoat film and a high-build primer generally need different setups.
- Confirm the gun type: gravity HVLP, conventional, RP/compliant, pressure feed, texture gun and airless tips are not directly interchangeable.
3. Viscosity, temperature and reduction
Viscosity should be checked using the method named by the coating manufacturer. A reading such as “20 seconds” is meaningless unless the cup type and test temperature are known. DIN 4, Ford 4 and other cups do not produce directly interchangeable numbers.
| Observation during test spray | Possible cause | What to check before changing nozzle |
|---|---|---|
| Large droplets, rough texture, fan tails | Material too viscous, low atomising air, restricted air line or tip too small | Confirm TDS reduction, material temperature, pressure with trigger pulled, filter condition and hose restriction. |
| Material barely flows with fluid control open | Blocked vent/filter, thick material, small tip or partially blocked fluid passage | Clean and strain material; check cup vent and matched needle/nozzle condition. |
| Runs or sags appear very quickly | Fluid delivery too high, material over-reduced, gun too close or travel too slow | Reduce fluid, restore correct mix, increase controlled speed and confirm distance. |
| Dry, dusty finish and excessive overspray | Too much air, gun too far away, fast travel, fast reducer or hot conditions | Use TDS-approved reducer, correct distance and minimum pressure that produces a clean pattern. |
Warm material usually flows more easily than cold material. Mix and test at the temperature range specified by the coating supplier. Never add unapproved thinner simply to make a small nozzle work.
4. Compressor and air-line requirements
Tank size alone does not tell you whether a compressor can run an HVLP gun. Compare the gun’s air consumption with the compressor’s delivered air output at the working pressure. “Displacement” or peak figures can be higher than usable output.
5. Set up on a test panel
- Prepare the material. Mix exactly, observe induction time where required, and strain through a compatible paint filter.
- Start with a clean matched set. Check nozzle seating, needle movement, cup vent and air-cap holes.
- Open the fan and fluid progressively. Do not begin with every control fully open. Establish a stable fan first.
- Set pressure under flow. Pull the trigger fully and use the lowest pressure that gives a clean, even pattern within the gun and coating specification.
- Make a one-second stationary pattern test. Hold the gun perpendicular to paper or a test panel at the recommended distance. Inspect distribution, not only overall width.
- Make moving passes. Check wetness, overlap, edge build and texture using the same speed and distance planned for the job.
- Change one variable at a time. Fluid, fan, pressure, reduction, distance and speed interact; changing all at once hides the cause.
6. Spray-pattern fault diagrams
These simplified patterns show common clues. Rotate the air cap 180° when diagnosing an uneven pattern: if the defect rotates with the cap, inspect the air cap; if it stays in the same direction, inspect the fluid nozzle, needle alignment and material flow.
7. Diagnose by symptom before changing tip size
| Symptom | Likely checks | Possible correction sequence |
|---|---|---|
| Coarse droplets or orange peel | Viscosity, low air volume, pressure drop, gun too far, fast reducer, tip too small | Verify mix and temperature → check pressure under flow → inspect air line → test a TDS-approved tip. |
| Excessive overspray / dry edge | Pressure too high, distance too great, fast travel, fan too wide | Reduce to minimum clean atomisation → correct distance and speed → narrow fan if required. |
| Runs or sagging | Too much fluid, large tip, slow movement, close distance, excessive overlap | Reduce fluid → restore distance/speed → check viscosity and flash time. |
| Pressure drops during pass | Compressor output, hose restriction, small couplers, clogged filter | Check delivered CFM and duty cycle → shorten/enlarge line where appropriate → service filtration. |
| Intermittent spitting | Loose nozzle, low cup level, blocked cup vent, air entering fluid path, damaged seal | Stop spraying → clean and inspect → tighten only to manufacturer guidance → replace damaged parts. |
8. Record a repeatable workshop setup
When a test panel succeeds, record the complete system so another operator can reproduce it:
- Coating brand, product code, batch and mix ratio
- Reducer or hardener and ambient temperature
- Viscosity cup type and measured time, where specified
- Gun model, nozzle size and air-cap set
- Pressure at the gun with trigger pulled
- Fan and fluid-control position
- Distance, overlap, gun speed and number of coats
- Flash time and final result
Frequently asked questions
Should I choose 1.3 mm or 1.4 mm for clearcoat?
Both are common starting sizes. The correct choice depends on the clearcoat TDS, gun design, solids, temperature, reducer, desired film build and operator speed. A 1.4 mm setup generally allows more potential fluid flow; the controls and technique still matter.
Is 1.7 mm suitable for primer?
It is a common starting size for many primer-surfacers. High-build primers may call for 1.8–2.2 mm, while sealers may use a smaller range. Follow the product TDS.
Can I fix poor atomisation by increasing pressure?
Only within the gun and coating specification. Excess pressure can increase overspray and dry spray. First check viscosity, air volume, hose restriction, cleanliness and whether the nozzle is appropriate.
Does a larger compressor tank solve low air supply?
A larger tank adds buffering time but does not increase the compressor’s continuous delivered airflow. Compare the compressor’s delivered CFM at pressure with the gun demand.
Reference basis and next step
Typical ranges above are consistent with manufacturer selection charts and example coating data sheets, but product-specific instructions remain authoritative.
3M nozzle-selection referencePPG basecoat examplePPG primer-surfacer examplePPG clearcoat example