Evaluation of the Spray Droplet Size Spectra of Drift-reducing Agricultural Spray Nozzle Designs

Aims: To evaluate the spray droplet size spectra of several different agricultural spray nozzles using laser diffraction technology.

Place and Duration of Study: This study was conducted at the United States Department of Agriculture – Agricultural Research Service Aerial Application Technology Research Unit facility in College Station, Texas during April 2014.

Methodology: The spray droplet size spectra of five agricultural spray nozzles utilizing different designs were evaluated in a low-speed wind tunnel. These designs included standard flat-fan, pre-orifice, and air-induction designs. This wind tunnel was equipped with a laser diffraction sensor to analyze spray droplet diameters. A solution of 0.25% v/v nonionic surfactant in water was used to simulate the solution characteristics of many pesticide sprays.

Results: Due to the precision of the droplet sizing equipment, many significant differences in droplet size spectra were detected among all nozzle designs. Increases in median droplet diameters as great as 265% were observed between drift reducing nozzles and standard flat-fan nozzles. Additionally, decreases in the production of drift-prone droplets (≤ 100 μm in diameter) as great as 97.3% were observed with the use of drift reducing designs.

Conclusion: Nozzle designs that utilized a pre-orifice resulting in larger median droplet diameters and fewer droplets of very small diameter. Additional reductions in spray drift potential were achieved with nozzles that utilized an air induction design in conjunction with a pre-orifice.