Shields to reduce spray drift
Des boucliers pour réduire la dérive
Résumé
The effects of several spray-boom shield designs and "low-drift" nozzles on spray drift are presented. Results are based on experiments conducted in a wind tunnel. Performances of all experimental shields were evaluated under two spray pressures (0·15 and 0·3 MPa), and two air velocities (2·75 and 4·80 m/s) in the wind tunnel. The distance to the centre of mass of the spray pattern from the nozzle (Dc) was used to characterize spray drift from different shield and nozzle combinations. Dc values resulting from different shields and nozzles were compared with the Dc value from a standard flat-fan nozzle with no shield. A smaller Dc value is desirable because it indicates that more spray is deposited near the nozzle and there is less material available for drift. All nine shields tested during this study effectively reduced Dc. Even the least effective shield design produced a 13% reduction in the Dc value. A double-foil shield produced the best spray-deposit result with a reduction of 59% in Dc compared with the same nozzles spraying without the shield. The shields were effective even when used with nozzles with higher flow rates (producing a smaller percentage of spray volume in small droplets). However, the use of larger capacity nozzles reduced drift more than smaller capacity nozzles with even the most effective shield. Low-drift (LD) nozzles without a shield provided reductions in Dc ranging from 20 percent to 67 percent when compared with the Dc from a 0-611/min standard flat-fan (SFF) nozzle operating under identical conditions. The reduction in Dc with the 0·611/min SFF nozzles operating with shield 2 (the best shield) was twice as high (59% versus 27%) as that from same capacity LD nozzles operating without a shield. However, the reduction in Dc from low-capacity LD nozzles without a shield was twice that of the SFF nozzles of the same capacity operating with shield 5/1 (the shield with the worst performance). Without a shield, LD nozzles at higher flow rates are no more advantageous in reducing drift than SFF nozzles of similar flow rate
Cet article présente les l'effet de boucliers anti-dérive et de buses à faible dérive ("low drift") sur la dérive d'un pulvérisateur à rampe. Les résultats ont été obtenus à partir d'essais dans un tunnel de dérive. La distance de déport du centre de gravité de la répartition, Dc, est utilisée pour caractériser la dérive dans les différentes configurations. Même pour la configuration de bouclier la moins efficace, on obtient une réduction du Dc de 13%. Sans bouclier, les buses à faible dérive, utilisées à fort débit, ne sont pas plus avantageuses que des buses à fente normales utilisées au même débit