Nozzles and droplet size — the variable that changes spray results the most

Nozzles are the cheapest part of the spray system, but they have the biggest effect on the results.

What is droplet size?

The droplets leaving a nozzle are not all one size but spread over a range. The figure people usually talk about is the median size of that range. Different nozzles give different size ranges.

Small droplets

They cover surfaces better for the same volume, because one drop breaks into many small drops that stick to the leaves more evenly. They suit jobs where the product needs to contact a lot of surface. But small droplets drift on the wind much more easily, and evaporate faster in hot, dry air.

Large droplets

They fall quickly, drift less and cope better with wind. They suit windy conditions or products that should not be allowed to float around. But they cover less surface for the same volume.

A simple rule for choosing

Stronger wind: choose larger droplets. Very hot, dry weather: also choose larger droplets, because small droplets will evaporate before reaching the crop. Only jobs needing high coverage in still air are suited to small droplets.

Nozzle types found on agricultural drones

Flat-fan nozzles give a band-shaped spray, are easy to aim, and the droplet size can be changed by changing the nozzle size.
Rotary (centrifugal) nozzles use a spinning disc to fling the liquid out, adjust droplet size with rotation speed and give more uniform droplets, but have moving parts that need maintenance.

Care that keeps spray results consistent

Nozzles wear with use. When worn, the opening gets wider and the flow rate rises while the figure on the screen stays the same. The result is using more product than intended without realising it. Check the real flow rate from time to time by timing and measuring the water.

Even one blocked nozzle leaves a streak in the spray swath that you cannot see while flying, but it becomes obvious when the crop shows uneven symptoms several days later. Checking before every flight is therefore always worth it. Important note This article explains general principles. It is not a recommendation for any specific chemical. Suitable mixing rates and timing differ by substance, crop, growth stage and field conditions. Always treat the product label as the authority, and ask our staff or an agricultural specialist before deciding.