Determination of Droplet Size Characteristics of Locally Manufactured Nozzles for Knapsack Sprayers

Droplet formation in spray nozzles primarily depends on nozzle design, while droplet size is of critical importance in crop protection due to the varying optimal ranges required for different target pests. In practice, locally manufactured brass nozzles are commonly used in orchard and knapsack sprayers, largely because of their low cost. However, most of these nozzles are produced without undergoing any research and development process, and their ability to generate droplet sizes suitable for effective pest management has not been scientifically verified. The present study aimed to evaluate the spray characteristics of brass hollow cone nozzles with different designs, which are widely sold in the domestic market but lack technical data in the literature beyond orifice size. Four nozzles were tested: two with an orifice diameter of 1.5 mm and two with 1.2 mm. Each nozzle was operated at pressures of 300, 400, and 500 kPa, with three replications and a spraying duration of 60 seconds. Droplet size distributions were measured using a laser diffraction analyzer, and volumetric parameters DV0.1, DV0.5, DV0.9, together with span values, were recorded. The results showed that although flow rates closely matched theoretical expectations, droplet sizes varied significantly between nozzles of similar orifice diameters, indicating that internal design strongly influences spray performance. Notably, one nozzle consistently produced coarser droplets, while others generated finer sprays, and Relative Span values demonstrated clear differences in uniformity. These findings highlight that nozzle performance cannot be assessed based solely on nominal orifice size and emphasize the necessity of systematic evaluation to ensure effective pest control and minimize environmental risks.