Achieving good spray coverage

For typical arable spraying operations, there are two types of nozzle to choose from; Conventional and Air-Included.

For conventional flat fan sprays spray quality varies according to nozzle size (flow in l/min) and pressure - with larger sizes and lower pressures producing larger droplets. The spray quality for each nozzle size/pressure is defined by BCPC International Spray Classification System from very fine to very coarse. Spray manufacturers indicate the optimum spray quality on their product labels.

Air Inclusion nozzles tend to be larger in size than conventional, but offer improved wetting capability due to their slower velocity and impact. No classification system has yet been agreed for Air Inclusion nozzles (It is 'work in progress' in an HGCA funded project*.

Tests carried out Guardian Air nozzles have shown that they produce much smaller droplets than other Air Inclusion nozzles. This means that for a given volume of spray there are twice as many droplets.

The images above show spray patterns on water sensitive paper; The top image is of the AIXR nozzle, the middle image the Bubblejet and the bottom is Guardian Air. The 1 bar comparison shows the differences in droplet number very clearly, click for full results.

More droplets means better spray coverage so more spray reaches the target.  Guardian Air nozzles are recommended by Syngenta for many spray applications and have already become the standard spraying nozzle for many farmers.

Droplets per ml of spray

Guardian Air: 56,000 droplets per ml of spray
Billerciay Bubblejet: 34,000 droplets per ml of spray
Teejet AIXR: 34,000 droplets per ml of spray

Based on a calculation from droplet VMD averaged over 2 sizes at 3 bar pressure (025 and 05):

* HCGA Project ref: RD-2006-3273 - Optimising pesticide use in arable agriculture by improving nozzle selection based on product efficacy to give optimised use and improved spray drift control. The project has already concluded that: "Measurements with commercially available air-induction nozzles have confirmed that those with an equivalent specification in terms of flow rate and spray angle at a given pressure give large differences in the droplet size distribution generated."