Questions about nozzle colour coding have arisen from the nozzle selection story featured on the cover of the February 28 issue ofGrainews. The reference in the story about colour coding was not referring to the colour of nozzle tips, but a new colour-coding system tip manufacturers are using in spray tip catalogues to highlight the changes in droplet size of a nozzle as pressure varies.
To clarify, the colour of a nozzle tip reflects the flow rate of the nozzle, not droplet size. All yellow nozzle tips put out 0.20 gallons per minute (gpm), violet puts out 0.25 gpm, blue 0.30 gpm, red 0.40 gpm, brown 0.50 gpm and gray 0.60 gpm. These flow ratings are measured at 40 psi. When agricultural sprayers were all designed for operation at 40 psi and five miles an hour travel speed, selection of nozzle size based on flow rate was sufficient.
Now, agricultural sprayers are operating at a wide range of pressures and speeds. Droplet size can vary considerably as pressure changes due to changes in speed and flow rate. So spray tip manufactures have developed a second colour coding system that detail the droplet size at various pressures. These colour codes are used in spray tip catalogues to assist farmers in selection of a nozzle. A red designation indicates a very fine droplet size, orange — fine, yellow — medium, blue — coarse, green — very coarse, white — extremely coarse.
For example: a violet-coloured 025 Tee Jet TwinJet Twin Flat Spray Tip with an output rating of 0.25 gpm at 40 psi will be applying a coarse spray (blue) at 30 to 60 psi. But the tech sheet for this particular violet nozzle shows at 20 psi the droplet size is larger and is now rated very coarse (green). And applicators using this violet tip at 70 to 90 psi will find the droplet size is now rated as medium (yellow).
Another helpful hint to try and keep all this in mind — spray quality colours were chosen to reflect drift risk. Orange has a higher risk than yellow, and so on.
While having two different colour systems can be confusing, it is also providing farmers with a lot more information to use in selecting the best nozzle to me their needs.