Calculator inputs
Formula used
The calculator estimates the tip orifice using an orifice-flow model: Q = Cd · A · √(2ΔP / ρ). It then converts the orifice diameter into thousandths of an inch and snaps to a common standard size.
- Q is target flow rate (m³/s).
- Cd is the discharge coefficient.
- A is the orifice area (m²) and ΔP is pressure (Pa).
- ρ is coating density (kg/m³).
- Effective viscosity applies a temperature adjustment and a practical safety factor.
How to use this calculator
- Select your coating type used on outdoor garden projects.
- Enter viscosity in seconds using any consistent cup method.
- Set your working pressure and the target flow rate.
- Choose distance and the fan width you want on the surface.
- Press calculate, then use the tip code as a starting point.
- Fine-tune pressure and speed to reduce runs and overspray.
Example data table
| Coating | Finish | Viscosity (s) | Flow (L/min) | Pressure (psi) | Fan @ 12" | Suggested tip |
|---|---|---|---|---|---|---|
| Wood stain | Fine | 25 | 0.9 | 1400 | 8" | 409–413 |
| Outdoor paint | Medium | 50 | 1.6 | 2200 | 10" | 515–517 |
| Primer | Coarse | 70 | 2.2 | 2600 | 12" | 621–623 |
These ranges are practical starting points. Always follow your sprayer and coating manufacturer guidance.
Why tip sizing matters outdoors
A sprayer tip controls film build, edge definition, and waste. In gardens, wind, textured lumber, and uneven masonry amplify mistakes. An undersized orifice starves flow, forcing slow passes and dry spray. An oversized orifice floods surfaces, causing runs on pickets and drips under planter rims. Correct sizing improves transfer efficiency, reduces rework, and helps coatings cure uniformly.
Balancing flow, pressure, and fan pattern
The calculator links your target flow and working pressure to an equivalent orifice area. Higher pressure raises atomization but also increases bounce-back on rough fencing. Wider fans cover faster, yet require steady overlap to avoid striping. Long hoses and fine strainers can drop pressure, so measure pressure at the gun when possible. Matching flow to your walking speed keeps wet edges intact on long rails and trellis panels.
Viscosity and temperature effects
Viscosity changes with product choice and temperature. Cooler mornings thicken many exterior coatings, demanding slightly larger tips or higher pressure to maintain flow. Hot afternoons thin materials, increasing sag risk, so smaller tips or reduced pressure can help. The tool applies a temperature-based viscosity adjustment plus a safety factor to keep selections practical. Filtering thick coatings reduces clogs and stabilizes the fan.
Reading common tip codes
Most tips use a simple code. The first digit approximates fan width at twelve inches, while the last two digits represent orifice thousandths of an inch. For example, 517 indicates about a ten inch fan and a 0.017 inch orifice. Selecting the nearest standard size keeps results compatible with common hardware. Narrow fans help lattice and tight corners, while wider fans speed flat panels.
Field checks for cleaner results
Start with the suggested tip and spray a short test board. If the pattern has tails, raise pressure slightly or replace a worn tip. If the center is heavy, reduce flow or choose a smaller orifice. Maintain a constant distance, keep the gun square, and use fifty percent overlap for consistent coverage.
FAQs
1) How do I pick a starting flow rate?
Use your sprayer’s pump rating and the coating’s coverage goal. For thin stains, start near 0.8–1.2 L/min. For exterior paints, 1.3–1.9 L/min is common. Increase only if you can maintain a wet edge.
2) What if my coating comes out gritty or dusty?
That usually indicates dry spray from too little material or too much distance. Reduce distance, raise flow slightly, or choose a larger orifice. Also check that the coating is not over-thinned and that filters are clean.
3) Why does the calculator ask for fan width and distance?
Fan width depends on distance and tip angle. Converting your desired fan to an equivalent fan at 12 inches helps select the first digit of a common tip code, keeping choices consistent across setups.
4) Should I change the tip for primer versus topcoat?
Often, yes. Primers are frequently thicker and need a larger orifice to avoid starvation. Many topcoats spray cleaner with a slightly smaller orifice for better atomization. Always verify with a quick test spray.
5) How does temperature affect my selection?
Cooler temperatures increase effective viscosity, which can reduce flow and create tails. Warmer temperatures lower viscosity, increasing run risk. Adjust pressure or tip size modestly, and re-test whenever conditions change.
6) When should I replace a tip?
Replace when the fan looks uneven, the pattern develops heavy edges, or your material use rises noticeably. Worn tips enlarge the orifice, increasing flow and overspray. A simple timed-output check can confirm wear.