Application Equipment, Nozzles, and Calibration
Match the nozzle to the job
- Flat fan (standard/even): broadcast spraying, best at 50% overlap.
- Extended-range flat fan: good over varied pressures.
- Drift-reduction / air-induction flat fan: larger droplets, less fine spray.
- Hollow cone: better penetration and coverage in dense canopy (fungicides, insecticides).
- Full cone: banding and directed sprays.
- Flood/off-center: low pressure, high volume, often turf or soil.
Nozzle spacing and boom height are tied to spray angle: 110° tips are commonly run at about 20-inch spacing and 15–20 inches above the target to achieve proper overlap. Higher pressure makes finer droplets and more drift; a worn tip increases flow and changes pattern - replace tips when flow exceeds the rated output by 10% or the pattern is visibly streaked. The relationship is: GPM per nozzle = (GPA × MPH × nozzle spacing in inches) / 5940.
Worked example
A boom has 110° flat fans on 20-inch spacing, running at 4 mph, and you want 20 GPA. GPM = (20 × 4 × 20) / 5940 = 1600/5940 = 0.27 gpm per nozzle. Now check the catalog at your target pressure - if the nearest tip delivers 0.30 gpm, either accept the slight rate increase or change pressure/speed. Recalibrate after any speed, pressure, or nozzle change.
Calibration methods
1/128 acre method: mark 340 ft², time the pass, catch one nozzle for that time - ounces caught equal GPA when nozzle spacing matches the swath. The formula method above is portable and widely tested. Always calibrate with clean water first, verify with a timed output check, and recheck mid-season.
Traps
Questions that raise pressure to increase coverage without mentioning drift, or that ignore tip wear, are wrong choices.
Rule of thumb: change one variable at a time - speed, pressure, or tip - then recalibrate.