Enviromist - manufacturers of specialist spraying equipment

Controlled Droplet Application (CDA)

Advantages of Controlled Droplet Application (CDA) Spraying Technology

The importance and significance of Controlled Droplet Application (CDA) spraying technology is often not widely understood by those who have always used conventional nozzles. Major points for consideration are:

Hydraulic nozzles force liquid under pressure through a small orifice to create unstable sheets of liquid, which break up (shatter) into a range of droplet sizes.
With the CDA system, liquid enters at the centre of a spinning disc and is propelled outwards by centrifugal force towards teeth on the outer edge of the spinning disc rotary atomiser to give optimally sized, evenly distributed spray droplets for maximum spray efficiency.
The aim of CDA spraying technology is to produce all chemical solution into a uniform droplet size that can be defined as “optimum” for the target.
CDA spraying technology has the advantage that by altering the rotational speed of the disc and/or feed rate of liquid, the narrow spectrum of droplet size can be altered to suit differing applications.

The principle of droplet size is important for the optimum application of chemicals such as pesticides. Lack of control of droplet size may seem of slight significance until the following aspects are considered:

If a droplet diameter is doubled, the volume is increased 8 times.
A tenfold diameter increase contains 1,000 times the volume (and chemical).

As an example with contact insecticides, if the chemical contained in a 20um droplet is sufficient to kill one insect, a 400um droplet of the same concentration (that can only contact a single insect) contains 8,000 times the volume and consequently sufficient chemical to kill 8,000 insects. Should you need further convincing, the formula to calculate the volume of a sphere (droplet) is 4/3 πr³.

Another aspect to be considered when using hydraulic nozzles is the amount of spray solution that actually remains on the target plants. Research has indicated that conventional nozzle spraying often results in the spray solution being dispersed as follows:

1/3 being lost to the atmosphere.
- Droplets less than 30um diameter make up the majority of this category and are lost either through drift or evaporation.
1/3 goes into the soil.
- Droplet diameters greater than 350um are in this category, particularly if they merge while on a leaf and roll off.
- The direct action of the hydraulic nozzle creates sufficient velocity for droplets to:
- Bounce off leaves
- Directly target the soil.
1/3 on to the target plants.

Contrary to the losses indicated for the hydraulic nozzle systems, the narrow spectrum mist of uniform, optimally sized droplets contained within the shroud when using Enviromist covered CDA spraying equipment offers the following advantages:

Almost no loss to the atmosphere.
- This is due to the combination of very few fine droplets being produced along with the added protection of the shroud.
Minimal run-off from plant surfaces.
- Again the narrow spectrum of droplet sizes virtually eliminates the production of larger droplets that are likely to cause this problem. Optimally sized droplets have a much better chance of remaining on the plant surface.
Greatly reduced direct targeting of the soil.
- The horizontal centrifugal action does not directly propel the droplets downwards. Consequently the droplets fall via gravity, and do not achieve the same downward velocity as those produced by a hydraulic nozzle.

All factors combined result in less wastage, with a greater amount of spray being available to settle on the target leaves.

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