7.4 Nozzles: Types, Sizing & Selection

7.4 Nozzles: Types, Sizing & Selection

The nozzle is the last thing the spray mixture touches and the component with the most influence over both coverage and drift. Federal core competency area 6 covers equipment types, their advantages and limitations, and calibration; nozzles sit at the center of all three.

Pattern Types

Reading the Number

Most flat-fan tips use a four- or five-digit code:

• 8004 - 80 = 80-degree spray fan angle; 04 = 0.40 gallons per minute at the tip's rating pressure of 40 psi.
• 11002 - 110 = 110-degree fan; 02 = 0.20 GPM at 40 psi.
• 1105 - 110 = 110-degree fan; 05 = 0.50 GPM at 40 psi.

Colors also follow the ISO standard for capacity: 01 orange, 015 green, 02 yellow, 03 blue, 04 red, 05 brown, 06 grey, 08 white. Two tips of the same ISO size are interchangeable in flow across manufacturers even when the pattern differs.

Fan Angle and Boom Height

The wider the fan angle, the lower the boom can run while still achieving proper overlap - and lower booms drift less.

Follow the nozzle manufacturer's chart for the specific tip. Height is measured to the target, which is the top of the canopy for foliar work and the soil surface for soil-applied products - not to the ground in a tall crop.

Pressure: The Square Root Rule

Flow through a fixed orifice varies with the square root of pressure:

$\frac{\text{GPM}_2}{\text{GPM}_1} = \sqrt{\frac{\text{PSI}_2}{\text{PSI}_1}}$

Rearranged for pressure:

$\text{PSI}_2 = \text{PSI}_1 \times \left(\frac{\text{GPM}_2}{\text{GPM}_1}\right)^2$

To double the flow you must quadruple the pressure. Going from 30 psi to 60 psi raises flow only about 41 percent; reaching double flow from 30 psi requires 120 psi.

Two consequences:

1. Pressure is a poor rate-adjustment tool. Large rate changes should come from a nozzle size change or a ground speed change.
2. Higher pressure shifts droplets finer, increasing drift. When the goal is drift reduction, the lever moves the other way: lower pressure within the tip's range, or switch to a pre-orifice or air-induction tip.

Tip Material and Wear

Wear is invisible. An orifice erodes gradually, flow climbs, and the applicator over-applies without any pattern change to warn them.

The replacement rule

Catch output from each nozzle for a timed interval at the operating pressure and compare it with a new tip of the same size at the same pressure. Replace any tip flowing more than about 10 percent above the new-tip rate. Also replace tips whose pattern shows streaks, gaps, or an off-center fan, and replace the entire set rather than one tip, so output stays uniform across the boom.

Never clean a nozzle with a knife, wire, or nail. Use a soft brush, compressed air, or water, and soak stubborn tips. A scratched orifice is a ruined orifice.

Screens and Strainers

Match screen mesh to orifice size: coarse screens for large orifices and wettable powders, finer screens for small orifices and solutions. Too fine a screen for a suspension plugs; too coarse a screen for a small orifice lets debris through. Clean tank, line, and nozzle screens as part of every pre-application inspection.

Choosing a Nozzle in Practice

1. Start with the label. Many labels now specify a required droplet size classification or an approved nozzle list - dicamba and 2,4-D over-the-top products are the leading Ohio example.
2. Pick the pattern the job needs: flat fan broadcast, even fan for a band, cone for canopy penetration, air induction near sensitive boundaries.
3. Pick the capacity from the rate math: required GPM per nozzle equals GPA times MPH times nozzle spacing in inches, divided by 5,940.
4. Verify at the operating pressure with a catch test, not from the catalog alone.
5. Recheck periodically through the season; wear accumulates.