Spray application manual
31 January 2025
Module 16: Overview of the spraying systems available
16.1 Introduction
Published 24 January 2025 | Last updated 20 January 2025
There are several spraying systems available, either as options on new sprayers or as retrofits to existing sprayers.
When trying to decide between the various options, the key question the operator must ask themselves is what they require the sprayer to be able to do. Often this process starts with identifying if a standard spraying system will limit your ability to operate the machine in the most efficient manner possible for your enterprise.
Possible limitations of the ‘standard’ spray system
Using a ‘standard’ single spray line fitted with an automatic rate controller where the flow rate (litres per hectare) is controlled by manipulating the pressure can have two possible limitations:
the speed range that can be achieved from a single set of hydraulic nozzles (usually limited to about 5 to 8 kilometres per hour) before the nozzles may no longer perform correctly. This is particularly noticeable when slowing the spraying speeds. The resulting reduction in pressure at the nozzle may cause the fan pattern to collapse, or, where a minimum setting is engaged in the rate controller, overdosing can occur; and
the change in spray quality (droplet size) that occurs with most hydraulic nozzles when the rate controller adjusts pressure to match the travel speed (to maintain the sprayer output).
Often the speed range and spray quality can be managed when the average spraying speed of the sprayer is relatively low (16km/h or less) and by using large enough headlands.
However, in situations where the average spraying speed is higher (usually above 20km/h) and the paddock contains contour banks or washouts, trees or obstacles, raised beds, or is set up for furrow irrigation with narrow tail drains, it may not be possible to maintain a narrow range of spraying speeds or to use larger headlands.
Spray systems single line
10 January 2025Single line spray systems. Another video from GRDC's Spray Application GROWNOTES™ series.
Bill Gordon: When considering what sort of sprayer you actually need, if we start with the baseline or basic entry-level—a single spray line on the standard trailing rig—we can then talk about its functions and build on those when we look at other systems.
So as a starting point, we're considering the boom. This one is a 36-metre boom, and the tank size relates to the number of hectares per hour and the machine's capacity, which is a really important consideration. I'll be looking at boom stability, but also plumbing. The number of sections that this sprayer is plumbed into is really important, particularly if you're going to use auto-section control. The more sections you have, the more even the job will be, and the more chemical you’ll save in turns.
The other functions on this sprayer we should be really interested in include the tank capacity—this one has quite a large tank, 6,500 litres—so you're looking at how many hectares per load you can get out of it. If you look at your comfortable travel speeds, you can calculate hectares per hour.
Apart from tank capacity and boom width, I’m also interested in some of the control functions. This particular sprayer has proportional valves on the back, meaning I can tune the pressure in each section and return the excess to the tank. It’s a really nice feature, but not available on all sprayers. Again, it’s worth looking at what systems are available to make your machine run really well.
When we're looking at a single spray line like this—so we’re talking about just one line with standard hydraulic nozzles—whether I’m running air inductions, low-drift nozzles, or even extended-range fans in a larger size, all these nozzles will have a certain operating range in terms of pressure. That range really limits us to about a five- to eight-kilometre speed range in the paddock.
So, when you look at your farming operation, ask yourself very carefully: how big is my real speed range? Look at your maximum speed, your comfortable averages, and how much you slow down for obstacles like washouts, contour banks, or even going up and down hills. If you have a bigger speed range than that, with a single line, you’ll tend to under- or overdose, which will cost you money. In that case, it might be worth looking at a different type of spray system.
Spraying systems that can increase the practical speed range in the paddock
Spraying systems that can assist the operator to manage larger variations in the range of spraying speeds in the paddock include:
pulse width modulation (e.g. Case AIM Command®, Capstan SharpShooter®, Raven Hawkeye®, JohnDeere ExactApply®, Agrifac StrictSprayPlus and TeeJet DynaJet®);
VariTarget® nozzles;
some twin fluid systems (where air is injected into the nozzle using a compressor); and
multi-step systems (such as dual booms, two or three-step systems on a single line, or multiple step using up to four nozzle sizes at each nozzle position).
Of these systems, pulse width modulation is the only one that will maintain the pressure in the spray line and can therefore maintain spray quality as the spraying speed changes.
Some twin fluid systems may be able to maintain spray quality over a smaller range of spraying speeds. With the other systems, spray quality will vary according to the actual spraying speed and application volume selected (due to changes in pressure).