Designing a truly effective spray nozzle is a challenge the sprayer industry has grappled with for generations. For despite larger tanks, clever recirculation layouts and automated rate systems, it is still the small plastic nozzle that ultimately determines the end result.

The aim, as ever, is to improve product efficacy, reduce the volume of active ingredient required and cut the volume of water required to apply it.

In recent years there has been some success in achieving these objectives. The days of 25-litre chemical drums and application rates of 220 litres/ha are now a thing of the past for most pesticide applications.

The end of the splash-it-all-over era was only possible when manufacturers developed nozzles that ensured the chemical arrived at its chosen target. This was particularly important for fungicides that were required to cover plant leaves and stems.

Producing a truly effective spray nozzle has been exercising the minds of manufacturers for years

However increasing the coverage while keeping volumes low means using spray droplets that are as small as possible. Small droplets are vulnerable to drift, though, which not only takes the chemical away from the target but also creates a risk to the environment.

Nozzle designers have been trying to solve this conundrum for years, and the best they have achieved with conventional nozzles is still a compromise – a system which limits the number of very fine droplets produced and, at the other end of the scale, also limits the very large droplets.

But then came the bubble jet nozzle which, through the inclusion of air, created large droplets filled with air bubbles that “exploded” on contact with the target to produce a similar coverage to finer sprays.

A Bubble Jet in action and (inset) an example of the droplet produced which is large
and contains air bubbles which produce fine droplets on impact with the plant

Designed by Billericay Farm Services (BFS), the technology has had a marked influence on the spraying scene. Fluid enters the top of the nozzle and passes through a tapered section which accelerates the flow as it passes two slots.

This causes a venturi effect which draws air in through the slots, which then combines with the fluid to create an air/fluid mixture. As the mixture flows through the mixing chamber it is compressed, before being sprayed out through a fan nozzle.

The air induction system devised by BFS has proved to be a solution to the large droplets/small droplets conundrum and trials are said to show that application rates as low as 50 litres/ha when applying fungicides are possible.

Other air induction nozzles have been developed by rival manufacturers. The Guardian Air nozzle uses the same droplet technology as the Syngenta Amistar 025 nozzle, which was co-developed by Hypro and Syngenta using data produced by Silsoe Research Institute.

The inclined angle of the spray produced by the new Guardian air induction nozzles
is claimed to result in a more even covering of the plant.

It works in a similar way to the bubble jet, with air drawn in via a venturi to mix with the liquid to produce droplets containing bubbles. Hypro says the Guardian nozzles produce more droplets per litre than any traditional air induction nozzle and that the droplet structure makes them stick to the target once they land.

This is achieved by reverse-angling the nozzles, which cancels out the effect of the forward speed of the sprayer so that droplets are falling vertically and distributed evenly over their target.

The Guardian Air nozzles are available in seven sizes – from 015 through to 05. The larger sizes mean, claims Hypro, that work rates can be increased without adversely affecting spray quality.

For example, the 025 nozzle applies 100 litres/ha at 12kph and 3bar pressure and the 035 will put the same volume on at 16kph – if the terrain allows such speeds.

The nozzles have all been designed to apply 100 litres/ha but, should conditions deteriorate and drift become a problem, pressure can be reduced to produce larger droplets. Hypro points out that the 110deg spray pattern is sustained down to pressures as low as one bar.