Application Equipment, Calibration, and Application Procedures
Nozzle choice drives the spray
Flat-fan nozzles give broadcast coverage; even flat-fan for banding; hollow-cone for canopy penetration and finer droplets; flood and deflector tips for coarse, low-pressure, low-drift work near sensitive areas; air-induction tips for large drift-resistant droplets. Droplet size shrinks as pressure rises, so never use pressure to change rate.
Calibration math
GPA = (5940 x GPM) / (MPH x nozzle spacing in inches). The 5940 constant converts units; memorize it. Because GPA is inversely related to speed, doubling speed halves the rate. Flow varies with the square root of pressure - quadrupling pressure doubles flow.
The 1/128-acre method
1/128 acre = 340 square feet (about 18.5 x 18.5 ft), and 128 fl oz = 1 gallon, so ounces collected while spraying that area equal gallons per acre. For a hand sprayer: mark 340 square feet, time the walk, then spray water into a bucket for that same time; ounces caught equals GPA.
Field checks and procedures
Check the pattern with water on pavement, replace worn tips (10% over output means 10% overapplication), agitate thoroughly, run a jar compatibility test before tank mixing, and triple-rinse equipment. Keep the boom level at the labeled height; skipping or overlapping causes streaks.
Worked example
Desired 20 GPA at 10 mph with 20-inch nozzle spacing: GPM per nozzle = (20 x 10 x 20) / 5940 = 0.67 gpm. Select the tip that delivers 0.67 gpm at your chosen pressure, then verify output in the field.