The effects on the atomization process with respect to droplet spectra were investigated for three pump systems (a rotary vane pump, a piston pump, and a diaphragm pump) and compared with an air pressure system. The test substances evaluated were water, Ortho X-77 (0.0625% and 0.5%), Windfall and Nalcotrol polymers, and two placebo (blank) insecticides (an emulsifiable concentrate and a wettable powder). All formulations were tested at field rates. All work was done using a TeeJet XR8004VS flat fan nozzle, and a Hardi 1553-12 hollow cone nozzle with a grey swirl. The effect of recirculation of the formulations on the eventual droplet spectra was also investigated. All other spraying parameters were kept constant. Droplet spectra were assessed along the long axis of the spray pattern using an Aerometrics PDPA-100 system, and a Velmex “Unislide” xyz-positioner.
Results indicate that droplet spectra of formulations containing polymers shift significantly with time of recirculation: Dv0.5 decreased by as much as 300 μm for Nalcotrol. The time taken for the Dv0.5 to stabilize depended upon pump type. Water, Ortho X-77, and the two blank formulations remained unaffected by pump type or recirculation. The effect of different mixing regimes prior to atomization was also investigated for Windfall and Nalcotrol.