Biological Systems Engineering


Date of this Version



Transactions of the ASABE Vol. 58(2): 261-269


Copyright 2015 American Society of Agricultural and Biological Engineers


The purpose of this study was to develop and evaluate the flow rate, spray pattern, and droplet spectra characteristics of an actively controlled variable-orifice nozzle at constant carrier pressures. A commercially available variable- orifice nozzle (VariTarget) was modified to allow for direct electromechanical control of the metering stem. The modified system was tested at five carrier pressures ranging from 138 to 414 kPa and five metering stem (and thus orifice) positions. The metering stem position range was chosen because it provided a linear response in flow rate at each carrier pressure. Flow rate testing indicated a turndown ratio of 2.4:1 at each carrier pressure, with a total turndown ratio of 4.8:1 across the range of carrier pressures using the selected metering stem positions. Spray pattern testing indicated acceptable coefficients of variation for the metering stem positions and carrier pressures for nozzle spacings of 38.1 and 51.0 cm. Droplet spectra test results showed that the particle sizes remained in the range of extremely coarse to ultra coarse for all metering stem positions and carrier pressures. Orifice control using the modified system resulted in slightly larger droplet sizes compared to the original spring-actuated nozzle; however, the potential for spray drift would be reduced. The results of this study show that active control of the VT nozzle metering stem could provide potential for improvements in pesticide application. Nozzle flow rates could be controlled via the proposed system with little negative effects on spray pattern or droplet spectra. In addition to compensating for sprayer ground speed changes, a system consisting of these nozzles could potentially be used to solve application errors generated from sprayer turning movements.