Symmetrical Multi-foil Shields for reducing Spray Drift

In this study, two symmetrical multi-foil shields were designed to minimise spray drift in both upwind and downwind travel directions. One shield was a symmetrical double foil that induced direct air assist (an air jet acting directly on the spray droplets), while the other shield was a symmetrical triple foil that induced both direct air assist and an air curtain (an air jet forming a pneumatic shield in front of or behind the spray nozzle). Wind tunnel experiments were conducted to compare the effectiveness (in terms of drift reduction) of these shields with an upwind-oriented double foil shield, using two different nozzles (8001 and 8003), three levels of pressures (138, 276, and 414 kPa), and an average wind tunnel air speed of 6·2 m s−1. A previous study of nine spray shields (that were similar in concept to shields that are commercially available) showed that the best performance in terms of drift reduction was achieved by a double foil shield. This shield, however, was more effective in an upwind than in a downwind travel direction because only in the upwind travel did the shield induce an airflow that formed an air curtain to suppress drift. Although all three shields reduced drift significantly compared to unshielded spraying, overall performances were significantly different from each other (probability P<0·05). The best performance in terms of drift reduction was achieved by the symmetrical triple foil shield (61%), followed by the symmetrical double foil shield (55%), and then the double foil shield (48%).