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 produce droplets in the medium to coarse range, but offer reduced spray drift. This category is rapidly becoming the standard nozzle for combinable crop spraying. The 2010 HGCA* Nozzle chart indicates the relative droplet size of different AI nozzles at 3 bar. 

The new classification shows that only those AI nozzles with the smallest droplets are likely to be effective in the majority of applications. Bear in mind that a droplet which is just 20% larger (VMD) will have just half as many droplets. This is shown visually in the water sensitive paper trial photos (left).

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.  GuardianAIR 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.