Application Equipment and Calibration
Equipment basics
Know the main application systems: boom sprayers (flat-fan, hollow-cone, even-flat nozzles), airblast sprayers for orchards, granular spreaders, backpack/compressed-air sprayers, and chemigation systems with backflow prevention. Candidates should understand nozzle function: flat-fan for broadcast herbicides, hollow-cone for penetration/fine droplets, even-flat for banded work, and off-center for directed sprays.
Calibration and the math
Calibration ensures the correct volume per area. The core relationships:
- GPA = (GPM × 5940) ÷ (MPH × swath width in inches) for typical U.S. units.
- GPM per nozzle = (GPA × MPH × spacing) ÷ 5940.
- Amount of product = (rate per acre) × (acres treated).
Learn tank-mix calculations, acres covered = (tank capacity) ÷ (GPA), and how speed and pressure change output. Increasing speed lowers GPA; increasing pressure raises flow. Drift is reduced by larger droplets, lower pressure, drift-reducing nozzles, and spraying in calm conditions (avoid inversions).
Traps in questions
(1) Mixing units (gallons vs. ounces, acres vs. square feet); (2) assuming higher pressure improves coverage without increasing drift; (3) forgetting nozzle wear raises flow and changes rate; (4) ignoring swath/spacing in the formula; (5) confusing GPA (volume per acre) with product per acre.
Rule of thumb
Calibrate before every season and after nozzle changes. If you change speed, pressure, or nozzles, recalibrate - the rate changes.
Worked example
A sprayer delivers 20 GPA with a 200-gallon tank. Acres per tank = 200 ÷ 20 = 10 acres. At a labeled rate of 1 qt/acre, you add 10 quarts to a full tank.