Application Equipment and Calibration
Equipment Basics
Application equipment must deliver the labeled rate uniformly and safely. Know the major types: boom sprayers, air-blast sprayers, handheld sprayers, granular spreaders, and injection/chemigation systems. Understand the components: tank, agitation, pump, pressure regulator, filters, nozzles, and boom. Nozzles control droplet size and pattern; worn or mismatched nozzles cause uneven coverage and misapplication.
Calibration Concepts
Calibration determines the actual output so you can match the label rate. Know the relationships: flow rate depends on pressure (flow varies with the square root of pressure), speed affects coverage per area, and swath width affects area treated. Learn the 1/128 acre method and the general formula: GPA = (GPM × 5940) ÷ (MPH × swath width in inches) for broadcast boom sprayers. Understand droplet size and drift: finer droplets increase drift and evaporation; coarser droplets reduce drift but may reduce coverage.
Common Traps
A classic trap is assuming doubling pressure doubles flow; it does not (flow rises with the square root of pressure). Another is calibrating with water but applying a denser formulation without adjusting. Questions may test that speed changes alter GPA inversely and that worn nozzles over-apply. Always recalibrate after nozzle changes.
Rule of Thumb
Calibrate before every season and after any equipment change; measure output, do not assume it.
Worked example: A boom sprays 20 GPM at 4 MPH with a 240-inch swath: GPA = (20 × 5940) ÷ (4 × 240) = 118,800 ÷ 960 = 123.75 GPA.