Equipment Inspection, Maintenance, and Nozzle Wear
Key Takeaways
- Inspect tank, hoses, clamps, valves, pump, agitation, gauge, boom, nozzles, shields, wiring, and emergency shutoffs before pesticide is loaded.
- Strainer mesh must match the pump, formulation, nozzle orifice, and manufacturer chart; higher mesh numbers mean smaller openings and can restrict flow or trap formulation particles.
- Nozzle flow changes with the square root of pressure, so doubling flow requires four times the pressure and usually creates an unacceptable operating change.
- Compare each nozzle with a new-tip rating or known new tip at the same pressure and replace it when output or pattern exceeds the manufacturer’s wear limit; 10 percent is a common threshold.
- Clean a tip with water and a soft brush or manufacturer-approved air—never with the mouth, wire, knives, or other hard objects.
Equipment Inspection, Maintenance, and Nozzle Wear
Calibration cannot correct a leaking, clogged, or worn sprayer. Inspect and maintain equipment with clean water before mixing pesticide. Depressurize the system before opening a line, strainer, nozzle body, or pump. Wear PPE appropriate to any previous contamination even when the current tank contains water.
Pre-use inspection
Walk around the machine in a consistent sequence. Check tank integrity and lid, sight gauge, drain, hoses, clamps, valves, pump guards, agitation, regulator, pressure gauge, boom hinges and breakaways, nozzle bodies, caps, check valves, shields, wiring, lights, and emergency shutoffs. Look for rubbing hoses, corrosion, soft spots, cracks, loose fittings, and dried residue that signals a leak. Confirm that clean-water and emergency supplies are stocked.
Flush winterizing solution or old residue to a legal collection point. Never discharge it to a storm drain, ditch, well area, or unapproved ground. Verify that valves move correctly and that agitation returns enough flow without foaming or starving the boom.
Filtration
Sprayers may use a fill basket, suction strainer before the pump, pressure-line or boom strainers, and individual tip strainers. Mesh number is openings per inch, so a larger mesh number has smaller openings. Select screens from the pump and nozzle manufacturer and the formulation label. A screen too coarse allows clogs; one too fine can trap suspended formulation, restrict inlet flow, or cause cavitation.
There is no universal requirement that every sprayer use exactly 10, 50, 80, and 100 mesh at fixed locations. Large-orifice tips and suspension formulations commonly use coarser screens than small-orifice tips and true solutions. Clean screens with the system depressurized and replace damaged mesh and seals.
Pressure and flow
Nozzle flow follows the approximate square-root relation:
GPM₂ / GPM₁ = square root of (PSI₂ / PSI₁)
To double flow with the same tip, pressure must be multiplied by four. For example, 0.25 GPM at 20 psi would require about 80 psi for 0.50 GPM if the ideal relation held. That pressure may exceed the nozzle’s range and will often make smaller droplets, so change tip size or speed for a major rate adjustment.
Use a gauge whose range makes operating pressure easy to read. Compare the machine gauge with a known accurate test gauge on a maintenance schedule and whenever readings are unstable. Check pressure at boom sections because restrictions and plumbing loss can make cab and nozzle pressure differ. Use the manufacturer’s tolerance rather than a universal two-psi rule.
Nozzle flow test
Install identical clean tips, fill with clean water, set operating speed or pump drive and pressure, and allow the system to stabilize. Catch each nozzle for the same measured time in a calibrated container. Convert volume to GPM and compare every result with a new nozzle of the same model at the same pressure or with the manufacturer rating.
A 10-percent increase over new-tip flow is a common replacement threshold because wear enlarges the orifice and can distort spray. The manufacturer or employer may specify a tighter tolerance. A low-output nozzle may be clogged rather than unworn. Replace any tip with unacceptable flow or pattern. When several tips are worn, replacing the whole set usually restores uniformity, but “two tips always requires an entire set” is not a universal statute.
Example: a new tip rated 0.30 GPM at the test pressure has a 10-percent upper limit of 0.33 GPM. A measured 0.345 GPM is 15 percent high and should be replaced under that criterion.
Pattern, boom, and speed
Use a patternator, collection tray, water-sensitive paper, or a clean safe surface to evaluate distribution as appropriate. Streaks can result from damaged tips, wrong orientation, incorrect spacing or boom height, uneven pressure, blocked strainers, or boom motion. Set height from the nozzle chart for its angle and spacing; do not use one fixed height for every 80-degree or 110-degree tip.
Measure travel speed under field conditions in the intended gear and engine setting. Tire size, slip, load, and field surface can make a speedometer wrong. After changes, recalculate and recalibrate output.
Safe cleaning and shutdown
Never blow through a tip with the mouth. Never use wire, a pin, knife, nail, or metal pick; it can enlarge or score the orifice. Depressurize, remove the tip and screen, soak them in clean water or label-compatible cleaning solution, and use a soft nozzle brush or manufacturer-approved air. Replace rather than force a stubborn obstruction.
At shutdown, follow the product label and equipment manual for rinsing, neutralization when specifically authorized, freeze protection, lubrication, and storage. Record maintenance, gauge checks, tip model, measured outputs, replacements, and calibration results.
How should a clogged nozzle tip be cleaned?
A nozzle delivers 0.25 GPM at 20 psi. Under the square-root relation, what pressure would theoretically double flow to 0.50 GPM?
Using a 10-percent wear criterion, at what output does a new 0.30-GPM tip reach the upper limit?