Nozzle technology holds the key to sprayer performance
Published 24/06/2015 | 02:30
They may not sound exciting but it's the developments in nozzles over the last two decades that hold some of the greatest potential for farmers to improve the performance of their sprayers, according to Teagasc machinery specialist, Dermot Forristal.
While the basic sprayer function has not changed in recent years, and GPS technology has the potential to make spraying more efficient, it's nozzle design that holds the most promise for farmers looking for cost-effective ways to get the most out of their sprayer.
The sprayer nozzle tip is the most important component of the sprayer because it determines the rate of product application, how evenly it is applied, and the droplet size distribution that is produced.
This affects how much of the product hits the target plant, and how much is prone to drift. The latter is a big issue, since it can result in uneven spray application on the crop, damage to adjacent crops and habitats if it hits water courses or other sensitive areas.
The biggest determinant of drift is the size of droplets produced by the nozzle, wind conditions at the time of spraying and the height of the sprayer boom.
In the past, nozzle size and pressure were the main focus for reducing drift. Larger nozzles operated at lower pressures are capable of producing reasonably large droplets that were less prone to drift.
The 'brown' 05 standard nozzle at three bar working pressure produces medium-sized droplets, but requires a quite high application rate of 200-250l/ha. With growers trying to reduce spray volumes to 100-150l/ha, the focus has shifted to nozzles that can give low drift even at these lower application rates.
Pre-orifice Low Drifts
The first generation of low-drift nozzles were pre-orifice nozzle types, which had a restriction in the nozzle body that effectively reduced the pressure at the spraying tip in a controlled way that could not be achieved by simply reducing the line pressure.
These nozzles gave a significant reduction in drift with a 'blue' 03 nozzle capable of producing a medium droplet at three bar, or larger at two bar pressure, even at outputs as low as 100l/ha. It's Achilles heel however is its tendency to block.
Air Induction nozzles
The current generation of low-drift nozzles are all air-induction nozzles where a venturi in the nozzle body allows air to be mixed with the liquid, producing larger air-filled droplets that are less prone to drift, while still providing reasonable coverage on the plant.
A typical 'blue' 03 nozzle in an air induction design generates a very large droplet at three bar pressure, and bigger again at two bar pressure. These give significant drift reduction capacity, allowing driftless spray patterns to be achieved at application rates from as little as 50l/ha.
While this type of nozzle now dominates the low-drift market, there are significant differences between individual air-induction nozzle types both within a manufacturers range and between manufacturers.
While the droplet sizes of the most commonly used air-induction nozzles is frequently below what is recommended by spray manufacturers, the performance is actually quite good.
In reality, the benefits of being able to optimise the timing of a spray outweighs any drop in performance due to the larger droplets.
If small plant areas are the target, it may be wise to avoid the very coarsest air induction nozzles. In particular avoid using very low water volumes with air induction nozzles on grass weeds or contact products. For example, avoid using less than 80l/ha with air induction nozzles, or less than 100l/ha if applying reduced rates of product with air induction nozzles.
Remember though, all low drift types can be prone to blockage so good sprayer filtration is particularly important.