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| G'day RexxT,
What brand of sprayer/PWM system are you using? Some will have different capabilities, so you might as well opt to maximize whatever you have the sprayer you have. (e.g. JD ExactApply has the ability to do dual nozzle, which works really well for 15-20+ rates, so might as well use it).
As a starter, I have made a few videos to walk through the nozzle selection process with PWM. Again, it is for Wilger nozzles, but much of the same applies for non-Wilger tips. (https://www.wilger.net/pwm_walkthrough/) The rule of thumb of 'use double the size nozzle' isn't a good rule of thumb, especially if you are only running ~8mph or so. I also made a bit of a cheat-sheet for Wilger tips, more suited to growers in Western Canada in this example, but it'd still have some good points to get the jist of the benefits of PWM sprayers and how to make the most of them.
So that you don't confuse yourself trying to take all the nozzle selection stuff at once, break it into two steps:
1. Size the nozzle - Make sure your nozzle size is appropriate FIRST before looking at any spray quality/coverage/etc. This means you are only looking at your pressure, speed range (you get a speed range now compared to a SET speed/pressure since you have PWM), as well as duty cycle. I'd advise you look at charts that are designed for PWM systems as they take the duty cycle into account a bit more as well as the pressure drop through the solenoid. The pressure drop through the solenoid for higher flow rates (like 15+ gpa) can be pretty extreme, so if you aren't looking at a PWM spray nozzle chart, then you might find yourself short of flow out of the nozzle to get the speed/rate you wanted.
Generally for duty cycle, aim for like 60-80% duty cycle or somewhere around there. If you are too close to 100%, it will impact your turn compensation to work (as once your nozzle hits 100% duty cycle, it will start under-rating if you go faster). If you are too low, like lower than 50% or below, then it'll increase the risk of checker-boarding or physical skips in coverage, which we want to avoid.
So, between 60-80% gives you a healthy room on the UP-side (remember your outter wing will be swinging up to speeds of like 20mph if you are turning at 8mph), as well as the ability to slow down if you need to as well.
Since you are travelling relatively slow at 8mph, you could probably keep it around the 60% so that you can get a full turn-comp speed range.
2. Pick the nozzle series based on spray quality/droplet size/advanced metrics like drift control/coverage.
AFTER you have a nozzle size hammered down, then you can start looking at the spray quality that you need to match. Filter out the ones that don't match what your chemical label requirements are (e.g. guessing your pre-emerge chem might dictate you need a nozzle producing a VC or coarser spray perhaps).
Wilger nozzle charts have extra info as far as a % of driftable fines and % of volume being made of small enough droplets for coverage, but each manufacturer is a little different.
So, for your setup:
15GPA @ 8 MPH, on 20" spacing (assuming 20" spacing, but correct me if I am wrong):
You'd be looking at a 110-06 sized nozzle for sure.
If you are using it for pre-emerge work, you might try find a nozzle that makes like a VC or XC spray (or coarser if you are in drift sensitive areas when doing pre-emerge) at lower pressure around like 35-40PSI. Then to give you the flexibility to improve coverage if you needed to if you were doing burndown as a separate application, you can use the same nozzle at a higher pressure (as you can select your pressure with PWM systems) and get that little bit more coverage that'll help burndown compared to soil-applied pre work. If both are mixed, then you could go for a middleground.
As far as the duty cycle and size for a 110-06 (I attached a chart as an example, this chart would be universal for any 110-06 nozzle):
At 40PSI, your duty cycle is 71%, perfect.
At 60PSI, your duty cycle is 58%, so no issues there.
Now that size is figured, I'd be looking at something similar to a Wilger MR110-06 for an example if you were chasing a bit more coverage. There are finer series, but I feel like unless you were in less of a drift sensitive area, they might start to get a bit finer for drift, even though coverage would be a large step better.
Alternatively, a DR110-06 would also reduce drift by about half (the driftable fines % in the chart is the column that is marked %<141µ), but you'll notice the coverage go down about ~15% as well (the coverage factor is the column marked %<600µ).
Anyways, you can compare other brands of nozzles to the same sort of charts as well, I just wanted to give you an example of where I might be looking without getting more information for you as far as the chem being sprayed or drift sensitivity in your fields/area.
For your 20GPA rate, the same steps would apply. Since you are going a bit slower, the nice thing is you aren't stepping too crazy large into the large nozzle side of things, so for your Liberty, you can at least still do a good job with a single nozzle. Often for folks that are pushing more like 15-16MPH, they get forced to use nozzle sizes that start garden hosing the spray in despite picking the finest nozzles in that flow/size.
Technically you could do 20GPA work with your 110-06, BUT, since Liberty needs a lot of coverage, so using the same nozzle for PRE work as Liberty is probably not a good idea as you'll be leaving a ton of coverage on the table.
Technically an MR110-06 could do it, but you'd be spraying at 60PSI all the time though (as you are getting about 10PSI pressure drop even at your speed).
For size, the 110-08 has a solid duty cycle of like 60-80% duty cycle from 35-60PSI, which works well for size.
So, if you were looking at a 20GPA nozzle, I'd be looking for something like an SR110-08, which is a size larger than the 110-06, but a series finer on the sliding scale of droplet size/series.
Alternatively, if you were running this on a JD ExactApply system, you could do something like using the MR110-06 for burn-down, and then have like a finer 110-02 on the second nozzle position that sprays at the same time. The flow would be of a 110-08 (-06 + -02), but it'd have a lot more finer droplets that'll help your liberty coverage.
Anyways, hopefully some of that info is helpful to start off. Otherwise, maybe chime in with your brand of sprayer, chem being sprayed for your pre/burndown, and give me an idea of whether you generally have to watch yourself much for drift or if most of the area is planted similarly to yours or less sensitive.
-Lucas
 (20GPA_SR110-08 (full).png)
 (MR110-06_15GPA (full).png)
Attachments
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 20GPA_SR110-08 (full).png (59KB - 4 downloads)
MR110-06_15GPA (full).png (58KB - 4 downloads)
CheatSheet_2page_updated20250312.pdf (1711KB - 2 downloads)
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Best tips for PMS (pulse) sprayer?
