Nozzles for Spray Drift Control Drift potential can be minimized even when it is necessary to use small nozzle capacities by selecting nozzle types that produce larger Volume Median Diameter (VMD) droplets and a lower percentage of small droplets. VMD’s produced by nozzles of identical flow rates (size 11003) which produce coarser droplets than an XR TeeJet and then larger droplets in sequence; TT/TTJ60, AIXR, AITTJ60, AI and TTI. TTI nozzles produce the coarsest droplet size spectrum of this group. When operating at a pressure of 3 bar (50 PSI) and 7 km/h (5 MPH) ground speed, the application rate is 200 l/ha (20 MPH). At the same time, the observation is that the VMD increases significantly from the XR to the TTI. This shows that it is possible to cover the entire droplet size spectrum from very fine to extremely coarse droplets by using different types of nozzles. While susceptibility to drift decreases when droplets become larger, the number of droplets available may lead to less uniform coverage. To compensate for this drawback and for the chemical to be effective, it is necessary to apply the optimum pressure range specified for a particular type of nozzle. If applicators comply with the parameters set by the manufacturers, they will always cover 10–15% of the target surface on average, which is not least attributed to the fact that less drift translates into more effective coverage. Figure 4 shows the VMD curves by nozzle type indicating the optimum pressure ranges for the individual nozzles which should be selected with respect to both effective drift control and effect of the chemical. When the focus is on drift control, TT, TTJ60 and AIXR are operated at pressures of less than 2 bar (29.5 PSI). Yet, where
maximum effect is critical, the nozzles are operated at pressures between 2 bar (29.5 PSI) and 3.5 bar (52 PSI) or even higher in specific conditions. These pressure ranges do not apply to AI and TTI, which operate at less than 3 bar (43.5 PSI) when drift control is
critical and always at 4 bar (58 PSI) and 7 bar (101.5 PSI) and even 8 bar (116 PSI) when the emphasis is on chemical affect. Therefore, for applicators to select the correct nozzle size it is necessary to consider the spray pressure at which a chemical is most effective. With
this, they simply have to reduce pressure and ground speed to comply with statutory buffer strip requirements. It is down to the conditions prevailing at the individual farm (location of the field, number of water bodies, type of chemical applied, etc.) whether they should choose a TeeJet nozzle that reduces drift by 50%, 75% or 90%. On principle, applicators should use 75% or 90% drift control nozzles (extremely coarse droplets) only when spraying near field boundaries and 50% or less TeeJet nozzles in all other areas of the field. While the classic XR TeeJet orifice provides two functions; metering the volume flow rate and distributing and creating the droplets, all other nozzle types discussed above
use a pre-orifice for metering while distribution and droplet creation takes place at the exit orifice. Both functions and devices relate to each other with respect to geometry and spacing and interact with respect to the droplet size produced. The TT, TTJ60, AITTJ60 and TTI nozzles force the liquid to change direction after it has passed the pre-orifice, forcing it into a horizontal chamber and to change direction again into the nearly vertical passage in the orifice itself (global patent). The AI, AITTJ60, AIXR and TTI air induction nozzles operate on the Venturi
principle, where the pre-orifice generates a higher-velocity stream, aspirating air through the side holes. This specific air / liquid mix creates more coarse droplets that are filled with air, depending on the chemical used.
Summary
Successful drift management centers on sound knowledge about drift contributing factors and the use of drift control, TeeJet nozzles. To strike a sound balance between successful chemical application and environmental protection, applicators should use approved broadcast TeeJet nozzles that are classified as drift control and operate these within the pressure ranges that ensure chemical effectiveness; i.e. set nozzles to 50% drift control or less. The following list shows all the relevant factors that need to be considered, optimized or applied to achieve effective drift control:
Source : Teejet
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