Spray application manual
31 January 2025
Module 16: Overview of the spraying systems available
16.4 Multi-step booms
Published 24 January 2025 | Last updated 20 January 2025
Multi-step booms are fitted with more than one nozzle per nozzle outlet, with a rate controller that can be programmed to switch between the nozzles as the spraying speed changes. This effectively increases the range of spraying speeds available, or the range of application volumes that can be obtained without having to change the nozzles on the boom.
Single line multi step system the ARAG Selectron
10 January 2025The ARAG Seletron 4 nozzle system, single line, multi-step. Another video from GRDC's Spray Application GROWNOTES™ series.
Graham Betts: What I want to talk through today is the ARAG Seletron four-fold.
Why you would look at this system is to improve your speed range, because a standard hydraulic nozzle only has a 4–6 k speed range, so that wouldn't suit a lot of people. The other thing is that it's a real pain in the backside changing nozzles a lot, so this gives the operator a lot more flexibility to change the water rights without having to change their nozzles.
When you start spraying the O1 nozzle comes on first and at a certain speed and whatever program setting in the controller, the O15 nozzle will come on and the O1 nozzle will go. When you get up to a certain speed and setting the O2 nozzle comes on and the O15 will turn off. When you get up to a higher speed again, the O25 nozzle will come on and your O2 nozzle will turn off.
This combination can go up to an O7 nozzle so you have a lot of flexibility in speed and in water rate, and a lot more control over droplet size because we're not pushing these outside their limits. How this works is electronically – the little electric solenoid in there, this is very positive in its turning on and turning off and you can have a lot of back pressure in the sprayline flushing back to boom and the nozzle won't open up because it's closed with an electric solenoid.
Another good thing about these models is they turn off per nozzle, so in this boom here there are 66 nozzles and it turns off per nozzle, so you've got 66 boom sections. Another big reason why you'd go this is when you're starting off and you haven't got this system you can over-apply your chemical far too much which can cause issues in the soil, and the other thing is if you've got every nozzle as a boom section, there's no underlap and overlap.
Two-tier or two-step dual booms
One of the original application systems developed to increase the speed range (and range of application volumes) of the boom sprayer was the use of two boom lines and a dual boom controller.
Typically these systems would operate the first boom line up to a nominated speed (or equivalent pressure or total flow rate through the boom) and then it would turn on the second line as well, so that both are operating. This is called a two-step or two-tier system, switching from one boom to both booms.
Two-step dual booms were introduced when extended range (XR) flat-fan nozzles were commonplace. XR nozzles are generally designed to operate from 1 bar to 4 bar, which is the increase in pressure required to double the flow rate (e.g. 4 x pressure = 2 x flow rate). With two-step dual booms, both spray lines are usually fitted with nozzles that have the same orifice size. When the pressure in the first boom line hits 4 bar, the second boom also switches on, and the pressure in both spray lines initially drops back to 1 bar, then increases as speed increases.
This system would allow the operator to effectively double the speed range that would have been achievable with a standard boom fitted with a single spray line. However XR nozzles cannot achieve a coarse spray quality in the orifice sizes that are commonly used on this system.
The ability to produce a coarse spray quality from smaller orifice sizes typically requires the use of pre-orifice or air-induction nozzles, which generally have a minimum operating pressure of 2 bar.
Nozzle selection for a coarse (or larger) spray quality on the two-step system is more difficult because of the 4-fold increase in pressure required to double the flow rate. When using air-induction nozzles, often a larger orifice size (e.g. 025 or lilac) nozzle is fitted to the first line and smaller orifice size (e.g. 015 or green) nozzle fitted to the second line. This way the pressure does not drop too much for the nozzles to function when the second line engages.
Three-tier or three-step dual booms
The early versions of this system also utilised two spray lines, the major modification when compared to the two-step systems is in the automatic rate controller functions of the sprayer.
As the name suggests, this system changes in three steps: from the first boom, then to the second boom (on its own), then it switches both booms on. The transitions are determined by the operator who selects the speeds, pressure or flow rates that determine the changes from one boom to the next, for them to both operating together.
This system provides an even greater speed range than the two-step systems, with almost three times the operating speed range of a standard single-line sprayer.
Three-step systems are also much better suited to the use of pre-orifice and air- induction nozzles.
When using air-induction nozzles, typically the first boom is usually fitted with smaller orifice size nozzles than the second boom. For example, it is common to have 015 nozzles (green) fitted to the first boom, and 02 (yellow) fitted to the second boom. Together, they produce the equivalent flow rate of an 035 sized orifice, but with the spray quality of the 015 and 02 nozzles.
Spray systems 3 step dual boom
10 January 2025Three step dual boom spray system. Another video from GRDC's Spray Application GROWNOTES™ series.
Bill Gordon: Ok we're looking at a multi-step, multi-tier boom here, sometimes known as a jewel boom and basically this system operates like having two or three single booms to change between each other. You'll notice in the foreground here there's 2 nozzle bodies, and the way this system operators is it'll run the first novel typically a smaller one after a certain speed and then it will change to the second nozzle, and then when you get up to a particular speed it will operate both.
The advantage of this particular system is it'll actually allow you to have a much greater speed range than a standard boom which would have just single nozzles on it. Typically one of these nozzles by itself on a boom would only give you 5 to 8 km/h, with this you can get up to maybe 10 to 15 depending on the voluem you're choosing. For guys in sandhills or undulating countries or lots of areas where they slow down that can be really good. Now these two particular novels, the one in front and one at the rear are low-pressure air inductions, which means they have a minimum pressure requirement probably about 2 bar or 13 psi in the old speak, so we need to be able to ensure that we have enough pressure running in these particular nozzles to get them to operate quickly.
That presents a bit of a challenge for the guys that operate them because one you gotta work out when to switch them or you determine the transition between this one to this one, but also when you're operating in your comfortable speed and operating volume you want to make sure when they are running together the pressure is not too low and you need to select nozzle types that don't get to coarse or the droplet size too large for what you're trying to do down here, so this particular system is very versatile but it requires the operator think just a little bit more about the speed and volume they're setting at and make sure that the pressure on these is not running too low, particularly that 2 to 3 bar, ideally you'd run these particular nozzles at 3 to 4 bar somewhere around there.
Variations of three-tier or three-step systems on a single spray line
A variation of the three-step system uses a single spray line fitted with narrower nozzle spacings (such as 0.25-metre spacing instead of 0.50m spacing), combined with on/off switching at the nozzle (rather than the whole boom section) using either air shut-off valves or electric shut-off valves.
A Goldacres® three-step system
With the three-step on a single line system, the odd nozzles (e.g. the first, third, fifth, etc.) will act as the first boom, and the even nozzles (second, fourth, sixth, etc) will act as the second boom (or vice versa), which then turns a single spray line into the equivalent of a three-tier or three-step dual boom system capable of running the equivalent of first boom, then the second, then both.
Alternatively, the nozzles can be aligned one behind the other on a single line, operating as a three-step system.
Strengths of a three-step system
Provides a large range of spraying speeds available to the operator.
May reduce the need for nozzle changes when a change in application volume is required.
Possible limitations of a three-step system
There are speed and volume combinations where the pressure at the nozzle can be too low to operate many air-induction nozzles effectively.
Changing spray quality may require the transitions between nozzles to be reprogrammed, or the operator to change one or more sets of nozzles.
For the versions using narrower nozzle spacing (alternating between odd and even nozzles), the plumbing of the nozzle bodies on the single spray line must be carefully considered, particularly on the boom ends. The sprayed width of each ‘boom’ could differ when operating at higher and lower speeds (e.g. odd line versus even line, or single line versus full boom), which may affect the overlap of the spray patterns at the boom ends.
Operating at spraying speeds where a transition between nozzles is programmed to occur can cause the system to attempt to alternate between boom lines, causing pressure and spray-quality variations.
Multi-step systems
There are several multi-step systems commercially available, where up to four nozzle sizes are fitted into the nozzle body at each nozzle outlet on the boom.
The sprayer’s rate control system can be programmed to transition between individual nozzles, or to operate any combination of the four at the same time to match the application volume, spraying speed and desired spray quality.
Switching between nozzles can be controlled by using either air valves or electric nozzle shut-off valves, which are also a very useful feature when using boom recirculation and auto section control to prevent pressure spikes in the line when sections shut off.
HARDI-TWIN-FORCE-boom-air-assisted spraying
20 January 2025HARDI TWIN is the most effective boom on the market. Her are only a few of the benefits when spraying with the TWIN air assisted spraying system: -5...
There is no speaking in this video.
A Goldacres® quad nozzle body
Depending on the plumbing arrangement and the valve types used on the nozzle bodies, some systems may also offer the ability to have single nozzle section control.
An Arag® Selectron multi-step system with 4 nozzles per outlet
Strengths of multi-step booms
They provide the largest increase the effective speed range, helping to prevent overdosing or nozzles collapsing when the sprayer slows down.
They greatly increase the range of application volumes of any spraying system.
By combining two or more nozzles, it can avoid the need for changing nozzles when changing spray jobs.
Possible limitations of multi-step booms
Spray quality of each nozzle will change with pressure in response to changes in spraying speed.
Selecting for a particular spray quality may require careful nozzle selection, or an adjustment to the speed, volume or pressure at which the nozzles are programmed to transition from one orifice size to another orifice size.
Find out more
For more information on multi-step systems, see Module 17: Pulse width modulation systems.