The hydraulic spray nozzle, used to atomise liquid to enable target coverage, has been with us since the late 19th century. Many might correctly argue that it has not changed much since then, but it has gone through a series of metamorphoses. We have seen a range of changes that took us from the simple cone, to precision cone nozzles, and on to fans.

Increased sophistication arrived when we moved to twin fluid nozzles, which were promoted initially on the Cleanacres Airtec system. Then there was a move to non-pressurised twin fluid nozzles, which we now know as air induction nozzles.

The ability to reduce spray drift has become an increasingly important issue

These brought additional flexibility, in that they were better able to control droplet size distribution, to reduce spray drift at given output and pressure levels.

The ability to reduce spray drift has become an increasingly important issue, as all agrochemicals now have an imposed buffer zone for watercourses. For most products, this is either 1m or 5m but some require a waterway buffer of up to 20m. However, specific nozzles, which have the ability to decrease drift by either 50%, 75% or 90% compared with standard flat fan nozzles, can be used under the STRIPE scheme to decrease the buffer requirement. This can be further reduced if the rate used is lower than the recommended rate.

Conventional nozzle

For conventional nozzles with a fixed orifice size, output is a factor of the pressure in the liquid and the forward speed. Without automated control systems, increasing speed reduces rate and vice versa. Similarly, increasing spray pressure increases output where forward speed is maintained. Where automated output controls are fitted, the control system increases pressure to compensate for faster forward speed and vice versa.

The most sophisticated systems enable individual nozzle control rather than section on or off

Many tillage farmers now have this type of integrated technology on their sprayers. We have also seen significant uptake of precision farming GPS control systems, thanks to support from TAMS. This technology enables the automated switching on and off of the sprayer boom and boom sections to help minimise overlaps on headlands.

The most sophisticated systems enable individual nozzle control rather than section on or off. This brings a new level of application accuracy, giving individual nozzles the ability to turn off to avoid overlap. However, this technology cannot compensate for the relative speeds of the inside and outside of a boom turning at a bend or corner in a tramline. But the most recent nozzle technology advances further increase application capabilities.

The pulsing nozzle

Pulse Width Modulation, or PWM, operates a system of very rapid opening and closing of each nozzle, somewhere around 10 times per second. This is electronically controlled and uses conventional boom plumbing on a single boom line. So, a specific individual nozzle can have a variable rate on the move, without alteration of pressure or forward speed. The same system can also be used to adjust for changing forward speed or pressure. If 10 times per second is the full rate, then five pulses per second is about half the application rate, with minimal detectable changes in pressure or nozzle function.

PWM is electronically controlled and the system can easily be used to reduce the rate through a single nozzle. It can be used to respond to a signal or instruction to reduce application rate at different places in a field.

The system can switch between nozzles to put out more or less liquid

While the maximum output of a single nozzle is set by the size of its orifice and recommended pressure range, the electronic systems used for PWM can equally cope with more than one nozzle at the same outlet. Indeed, some of the commercially available systems now have up to four different nozzles at each outlet, all of which can be at a different capacity to provide a huge spray rate range.

The system can switch between nozzles to put out more or less liquid and can use two, three or four nozzles at the same time to get a big output. It can also switch off nozzles individually to apply no spray.

In summary

This technology adds huge flexibility to the standard hydraulic spray nozzle. It adds to the accuracy of desired output and facilitates GPS to minimise overlaps.

While the system adds to the cost of a sprayer, it is precision farming technology and is therefore eligible for support within TAMS.