For those on the fly, hit play to hear a shortened, narrated version.
I have far too many photos and videos of airblast sprayers blowing straight up through treetops, or downwind through the last row, during spring applications. I chose not to include any in this article to avoid people recognizing the operations. If you haven’t seen anyone doing it, maybe it’s you!
I recognize that it can be a tricky balance to adjust a sprayer for spring applications. It’s counterintuitive, but a bare tree can be difficult to spray. Young and/or bare trees represent small targets which have a very low catch efficiency, so a lot of spray will miss. Switching nozzles to adjust rates doesn’t help much in this regard – it’s far better to adjust travel speed and air settings, and we’ll get to that in a moment.
That lack of foliage also means wind moves through the orchard unabated, so the sprayer may have to blow a little harder into the wind to compensate. In the case of a low-profile axial sprayer, which blows laterally and upward, that means creating greater risk for blowing too high, and blowing through downwind rows.
That off-target deposition represents a huge loss of materials and potential for drift incidents. To add insult to injury, many of those early season applications often have oil components, which require a drench (higher volume) and are more easily seen by bystanders (opaque droplets). All in all, it’s a bad time of year for crop protection PR. Learn more about drift and drift prevention here: BeDriftAware.
Air Adjustments
So, let’s start with air. Air carries spray droplets, so perform a ribbon test to ensure the air outlets are oriented correctly. This is achieved by adjusting deflectors (e.g. low-profile axial), the air outlets on a tower, or the entire head on a wrap-around design with individual fan/nozzle combinations.
Spray height should always exceed the canopy height by a small degree. This compensates for the increase in wind speed with elevation, the potential loss of spray height with faster travel speeds, and uneven alleys that cause the sprayer to rock, which changes the spray angle.
It is less critical that spray align with the lower portion of the canopy. As air energy wanes, or as droplets begin to lose momentum, finer droplets will slowly fall, depositing on random surfaces. Coarser droplets will quickly fall towards the bottom of the canopy, settling primarily on upward-facing surfaces. This secondary deposition can also occur from the cumulative impact of blow-through from upwind rows.
Nozzle Adjustments
Now pay particular attention to which nozzles are on or off. Park the sprayer in an alley. Stand behind the sprayer and extrapolate a direct line from each nozzle to target canopy. Nozzles that point at the canopy should be left on. Nozzles that point above or below can be blocked, or turned off, via valves or rotating roll-overs.
Some roll-over nozzle bodies can be swiveled up or down 15 degrees to fine tune the spray angle. An alternative would be to permanently rotate the nozzle body fitting in the boom line. When aiming nozzles using a roll-over nozzle body, be careful not to swivel them too far or the valve will partially close and compromise the spray pattern.
When extrapolating, remember that the centre of a nozzle only indicates the centre of the spray pattern. Cone and fan angles can span 60 to 110 degrees, depending on the influence of air. Therefore, even though the centre of the lower-most nozzle intersects the bottom of the target canopy, you may still be able to turn it off because the nozzle above has that portion covered.
Travel Speed, Wind, and Coverage Assessment
Now let’s consider travel speed. If the wind is blowing hard through the orchard, you can increase the air speed or slow down the sprayer to focus longer. However, in both cases, you run the risk of overblowing the downwind rows by a considerable margin. Easily three rows in a high-density orchard.
This downwind coverage is cumulative, so when you assess your coverage (preferably using water sensitive paper), don’t do so until you’ve made a few upwind passes. So much of that spray ends up on the orchard floor, and still more evaporates or blows up, but some of it will hit and it adds up.
Downwind Boundary
Finally, pay attention to where you are in the block. It may be necessary to turn off the downwind bank of nozzles on the final downwind three (or more) rows. That means you’ll be performing the dreaded alternate row (one-sided) application, and I’ll be the first to say that’s not ideal. However, in this case, the spray will blow back and help cover the unsprayed side. Again, use water sensitive paper to confirm the job you’re doing.
Final Thoughts
And, of course, seriously consider when it’s time to wait for better conditions. No one likes to do that, especially when rain is imminent and the ground stays soft, but the alternative is a lot of waste and a poor application. If this always seems to be the fight you’re having, maybe it’s time to consider the return on investment of a tower sprayer, or a shrouded sprayer. Towers improve matters since they more easily reach the treetop without having to blow as hard, and without angling air upward. Shrouded recycling-style sprayers (if they fit the architecture) help even more.
Plan to do all of this (especially the capital investment number crunching) before the season starts and be prepared to change sprayer settings on the fly, as required. Don’t be the subject of my next spring drift photo.
Did you come here looking for advice on which sprayer is best for your small operation? Are you looking to ditch the backpack mist blower? Do you want to avoid repeatedly mounting and dismounting a 3-pt hitch sprayer from your only tractor? Are you concerned you’ll have to sell an organ to be able to afford one? We hear you, and we’ll try to help. Let’s set the stage with a few facts.
Airblast sprayers stay in service for a long time; more than twenty five years is not unheard of. The majority of them are the generalist, PTO-driven low profile radial design with capacities ranging 150 to 1,200 gallons. Typical fan diameters are around 30″ and can produce >40,000 m3/h of air, making them a good fit for most pomme, citrus and tender fruit canopies. These sprayers come with a horsepower price tag of perhaps 45 hp or more. Many of these sprayers eventually enter the used sprayer market, making them an affordable option for small acreage specialty operations. But, affordability should not be the sole motivation when choosing a sprayer.
Ontario, c.1980 and probably still out there spraying somewhere!
The key to optimizing sprayer performance is to match the air settings to the the canopy you’re trying to spray. You can start reading about the process here. In the case of small and medium-sized canopies like vine, cane and bush crops, the fleet of gently-used sprayers we just described tend to produce too much air. There are options to improve the fit, like driving faster to reduce dwell time, or perhaps the operator can employ the Gear-up Throttle-down method. But, the best plan is to employ a smaller sprayer, which produces a more appropriate air volume, has a smaller profile, delivers better fuel efficiency and won’t break the bank.
So, where are these sprayers? Unfortunately there aren’t many, and options are especially limited if you don’t own a tractor to power them.
The budget-conscious grower may be tempted to buy a sprayer that does not have air-assist. We do not recommend this. Air is a critical component for spraying canopies consistently and efficiently. Caveat Emptor!
We encountered a good solution in June, 2014, when we were invited to Durocher Farm in New Hampshire to see their new airblast sprayer. In years previous, spotted-wing drosophila (SWD) was a significant pest in this two acre, high bush blueberry planting. They claimed that since buying their new sprayer they no longer had any trouble with SWD. That’s quite an endorsement!
The Carrarospray ATVM (200 L option pictured)
I’m not sure what I expected, but I was captivated by this miniature orchard sprayer. The toy-like size carried a zero-intimidation factor and I immediately wanted to start using it. Italian-made, Carrarospray’s hobby line is designed to be pulled behind vehicles without PTO. The ATVM is available in capacities from 120-400 L. The one I saw had a 400 L capacity, adjustable air deflectors, a fan speed gear box, and it was powered by a quiet and efficient pull-start Briggs & Stratton four-stroke engine. It even had a trash guard, a kick-stand and a clean water tank for hand washing. That’s a lot of features.
Thanks to Kitt Plummer (Durocher Farm), Penn State, Univ. New Hampshire and Chazzbo Media for filming these 2014 videos:
The sprayer was pulled (in this case) by a mower, so the grower not only sprayed, but mowed his alleys at the same time. It fit beautifully between the bushes, so the potential for physical damage to the berries was minimized. The air speed and volume was enough to displace the air in the blueberry canopy and replace it with spray-laden air with minimal blow-through. Combined with an appropriate spray volume and distribution over the boom, we found that the coverage it provided was excellent.
Coverage from the top-centre of the bush.
Since seeing this sprayer, we have had reports that importing it to Canada has proved challenging. But there are alternatives. A few companies here in North America offer economy-sized airblast models that are ATV trailed, or skid-mounted, or attached to a small tractor via a three point hitch. PBM’s Lil Squirt is a simple and versatile option. Available primarily in the western US from California through to Washington.
PBM’s trailed Lil Squirt (Image from their website)
Another option is the mounted, PTO-driven mistblower line from Big John Manufacturing in Nebraska.
BJ 3PT mistblower from Big John Manufacturing (Image from their website)
Or MM Sprayer‘s ATV sprayers, which come PTO or Engine-driven. The LG400 has a 106 gallon tank and a 20″ fan. I’d like to see deflectors, but you could easily add them. Here’s a 2024 pdf on features.
Picture of the LG400 engine-driven model from www.mmsprayers.usa
Or Wisconsin’s Contree Sprayer and Equipment. They carry the “Terminator” line. Skid mounted, one-sided air shear units with capacities from 15 to 100 gallons, this company offers a range of possibilities both PTO and gas-driven. Well worth a look.
The “Terminator” skid-mounted mist blower from Contree Sprayer and Equipment (Image from their website)
Then there’s the A1 Mist sprayer series, also out of Nebraska. They carry the Terminator line as well as an interesting two-sided volute option that employs conventional nozzles and allows one pass down an alley rather than two. This is a big productivity booster:
A1’s two-way volute header. (Image from website)A1’s PTO-driven 60 gallon, skid-mounted “Terminator”. (Image from website).
Then there are larger, PTO-driven, three-point hitch options. In fact, there are many options for this manner of sprayer, but they tend to be out of the price range for small operations, and they do require a tractor. That isn’t a deal-breaker, though, as they can sometimes be found used. Pictured below is British Columbia’s Major 193 (Slimline Manufacturing) and a Brazilian-made option (Jacto) distributed out of Quebec.
Slimline Manufacturing (aka Turbomist) makes the Major 19P 3-pt hitch tower sprayer (PTO-driven)Jacto’s Arbus 200 3-pt hitch airblast sprayer (PTO-driven)
When considering your options, give serious thought to your work rate, refill time and other factors that go into developing a robust spraying strategy. What’s a spraying strategy? That’s a farm’s overall management and operational plan for achieving safe, effective and efficient spray coverage. You can read more in chapter 8 of Airblast101, which you can download for free, here. And, just to play Devil’s Advocate, go small but not so small that the sprayer is underpowered.
We staged this video in 2011 (spraying only water, so don’t mind the lack of PPE) to show how a sprayer can be too small for an operation. This 3-pt hitch GB cannot overcome the cross wind and the spray barely reaches the apple trees. Reducing travel speed and increasing pressure won’t cut it, either.
Of course, other possibilities are emerging for crop protection in small acreage perennial crops. Multirotor drones are capable of delivering air-assisted spray from above the canopy. While it’s still a drift-prone and inconsistent means for broadcast spraying, it might lend itself to perennial row crops. Equipment design is evolving quickly and global research is underway to establish best practices. As regulators and agrichemical companies focus more on this method we may see drones as a cheap alternative to a tractor/airblast sprayer, with no compaction, no mechanical damage to fruit/berries, and no potential for splashing infection throughout an operations.
DJI’s Agras T30
Even further into the future, small autonomous sprayers may be viable, too. Very much in their early days there is great potential. One example is the XAG Revospray Ground 2 with it’s 150L capacity or the R150 with it’s 100 L capacity.
The R150 – Image from https://hse-uav.com/. Modular system and ~32K USD (as of 2023)… if you can find one.
It’s early days, but there are researchers looking at the spray pattern from these units. The image below may not be a fair indication because the nozzle used may not have produced as wide a swath as possible. Thanks to Dr. M. Reinke for the image.
A test pass using food grade dye. You can see the waveform created by the two spray heads as they move up and down during travel.
And recently, small autonomous platforms have become more common. Perhaps there’s an opportunity to place a gas powered sprayer on these platforms, or use them to pull a hitch-style sprayer. One such possibility is created by the Burro, shown below at the Ontario Fruit and Vegetable Convention in 2024.
An “Alternate Row Middle (ARM)” traffic pattern is where the sprayer passes down every second row. The intent is to improve work rate by cutting the driving time in half. The operator hopes to provide suitable coverage on both the sprayer-facing half of the canopy, and that half of the canopy facing the next alley. In our experience, this depends on sprayer design, and only works in very small/young plantings (or only for the first few applications of the season). Even then, the side facing the sprayer tends to get saturated in an effort to ensure a threshold dose reaches the far side. We’ve already captured the pros and cons of ARM in this article, and (spoiler alert) unless you’re using a wrap-around style design, it’s generally not the best approach for protecting an orchard, bush, cane or vine crop.
So why on Earth would we be testing it here?
We were contacted by an orchardist who planted a test block of Gala (est. spring, 2017) in an unusual way. He called it “V-Trellis Vertical Axis Cross”. Basically, he created an orchard architecture that only allowed equipment (e.g. platforms, sprayers) to pass down every second row. He figured it would save 35% of his labour costs. In the photo and illustration below, you can see the posts lean over the drivable alleys, creating a “V” shape.
So, given that he couldn’t fit a sprayer down every row, we had no choice but to try to optimize sprayer settings for ARM applications. Note the six numbers in circles in the above illustration. They indicate where we would eventually place water-sensitive papers to diagnose spray coverage.
Here are the settings the orchardist was using before we made any adjustments:
Turbomist sprayer with 11 foot high tower
Bottom-most nozzle was on and every second nozzle position skipped for a total of 5 nozzles active per side
Nozzles were TeeJet ceramic disc-core. Top to bottom: D3-DC45, D3-DC45, D3-DC45, D3-DC45, D3-DC25
7 km/h (4.35 mph) travel speed per a speedometer app on a smartphone
Tractor engine speed was 2,150 rpm (PTO was ~ 540 rpm)
Fan set in low gear
Pressure was 190 psi
Ambient wind gusting to 8 km/h, temperature of 30°C, RH ~65%.
And here is a video of what the sprayer was doing before we changed any settings. This is a single upwind pass, and as you can see, the spray blew through at least five downwind rows. Obviously, this was far too much air and spray volume.
When we diagnose coverage in an every-row situation, we drive the alleys on each side of the target row (i.e. two passes). But, when diagnosing ARM spraying, we want to account for every drop of cumulative coverage from spraying upwind rows. So, we have to do three passes, as shown in the illustration below. In this top-down diagram, the sprayer travels the red line.
In order to establish a baseline, we diagnosed coverage for the original settings using water-sensitive papers in the six positions indicated above. We folded them in half, so a sensitive side faced each alley. We sprayed water and later digitized the cards to determine the percent coverage on the papers. Remember, if 80% of the cards receive at least 10-15% surface coverage and a deposit density of 85 drops per cm2, it’s typically sufficient.
Here are our results, with percent area-covered indicated in each position, as well as a representative scan of one of the papers. There’s no need to provide deposit density, which after about 30% surface coverage cannot be reliably determined.
So, if the video doesn’t convince, then the papers certainly do: This was way too much air and spray mix.
Next, we performed a series of air adjustments using ribbons (detailed here and here) which led us to reduce engine speed from 2,150 rpm to 1,300 using the Gear-Up, Throttle-Down method. Then we used the OrchardMax calculator to establish an ideal spray volume and guide us to which nozzle rates we should use:
Bottom-most nozzle was on and every second nozzle position skipped for a total of 5 nozzles active per side
Top nozzle was TeeJet AITX8002, followed by TeeJet TXR80015, TXR80036, TXR80015, TXR80015
7 km/h (4.35 mph) travel speed per a speedometer app on a smartphone
Tractor engine speed was 1,300 rpm (PTO was ~ 300 rpm)
Fan set in low gear
Pressure was 100 psi
Ambient wind gusting to 4 km/h, temperature of 26.5°C, RH ~70%.
The following video shows the coverage from a single pass (to be clear, no extra upwind pass). We eventually did three passes to capture the cumulative coverage, just like with the first sprayer settings. This video simply serves to show how in ARM applications, the sprayer-facing side always looks much better than the side facing away. Also note how much quieter the sprayer is, as well as the reduced blow-through.
And here is the resultant, cumulative coverage from three passes. Once again, deposit density isn’t required as it exceeded our threshold in each position.
In the end analysis, we saved the grower ~30% of their spray mix, greatly reduced noise and spray drift, and still achieved suitable coverage in the target canopy. So, does this mean ARM applications are redeemed? We refer you, kind reader, to our introduction where we said ARM can work in young plantings and early season applications.
Note that the upwind side of the canopy received less coverage than the downwind side. As this new planting grows and fills, it’s going to be increasingly difficult to achieve sufficient coverage. Changes to the sprayer settings may be able to account for the imbalance, but they will also make the applications less efficient (i.e. more spray mix, more drift and coverage will still not be uniform). It remains to be seen if the spray inefficiency inherent to this orchard architecture is worth the estimated 35% savings in labour costs.
“Precision agriculture” is many things to many people. In the context of spraying, let’s define it as “detecting and responding to variability”. One example of precision ag is the use of crop-sensing optics to efficiently and accurately direct spray application. This is nothing new to field sprayer operators, but did you know that before Ken Giles published the first paper on pulse-width modulating nozzles in 1989, airblast sprayers already had crop-sensing technology?
In the 1970s, Bert Roper noted the wastefulness inherent to citrus spraying. Losses to the ground of 30-50% and off-target drift of 10-20% of applied volume were (and still are) not uncommon for airblast sprayers. So, using Polaroid’s autofocus technology, and enlisting the help of a few engineers, they developed an ultrasonic sensor system that enabled a computer to “see” the target tree and engage nozzles accordingly. He and son Charlie built prototypes in their kitchen before proving it in their family groves, spraying 10 gal/ac instead of the usual 250 gallons. The first Tree-See system was sold to Cola-Cola in 1984.
Figure 1 Tree-See on a Swanson sprayer (www.treesee.com)
This technology is still used today; Sensors detect specific zones on the canopy and actuate boom sections, or individual nozzles, to only spray the target zone. But optics and machine learning are evolving. Now they can modulate flow from individual nozzles in response to changes in canopy density. To be clear, that’s not just “on/off”, but variable flow.
Eventually, these systems will be able to identify and respond to specific pests (or pest damage) and adjust plant growth modifier rates based on canopy density or bloom counts. The possibilities are amazing. As an aside, interested readers can learn more about airblast sensors in this excellent article from Oregon State University which one of the authors later summarized for us here.
Figure 2 LiDAR and control interface for a Smart Apply system fitted to a Turbomist sprayer
However, as operators embrace this technology, they should be aware of the current limitations. Canopy-sensing optics are great at managing waste (their primary selling point seems to be pesticide savings), but this depends on crop morphology and planting architecture. It makes sense to not spray what isn’t there, but the gaps may not be as big as you think.
Non-continuous canopies require the spray to lead and lag to some extent before and after passing the target to ensure sufficient coverage. Given the difficulty inherent to spraying to the tops of tall canopies, some specialists believe the top nozzles should never disengage. And, in the case of uniform canopies that form continuous hedge-like rows, the potential savings is greatly reduced.
Further, all of these systems assume that application efficiency is primarily dependent on matching liquid flow rates to the profile (or perhaps density) of the target canopy. I don’t believe that’s true. At least, not entirely true. The impact of air settings on coverage efficiency and efficacy seems to have been marginalized.
For example, these sprayers do not account for the spray’s ability to span the distance from nozzle to target (i.e., transfer efficiency). That depends on the droplet size, sprayer air settings and the environmental conditions – none of which are monitored by sprayer optics. They also cannot “know” if the spray gets intercepted by the target (i.e., catch efficiency) or if it deposits a biologically-active residue on the target surface (i.e., retention). Droplets must be retained by the target surface and not bounce or run off.
What this means is that these sprayers, like any sprayer, can only promise “coverage potential”. Operators are still required to perform the following tasks:
Optimize air direction and air energy in relation to canopy size, travel speed and environmental conditions.
Use water-sensitive paper, or some other means of quantifying coverage, to ensure your target receives threshold coverage.
Monitor and adjust practices throughout the season in response to changing conditions.
HOL’s Intelligent Spray Application (I.S.A.) system employing Weed-It sensors.
So what’s missing? How do we progress beyond what is arguably a sophisticated rate-controller?
In my opinion, I believe the pitcher needs a catcher – a closed-loop feedback system. Optics would identify the target, nozzle flow would respond, and then a digital spray sensor in the target canopy would detect and report coverage back to the sprayer so machine learning could make iterative adjustments in real-time.
Spray-sensors are not a new idea, as wetness-detection systems have been used in forestry since the 70s. But, a sensor that can discern spray coverage would yield far more detail, and once again it seems Ken Giles is a pioneer in this concept. Such a sensor, integrated with sprayer optics and machine learning, could summarily account for all the unknowns that interfere with spray from the moment it’s released to the point that it (hopefully) lands. That’s some serious crop-adapted spraying.
And yes, it would be fantastic if there were some manner of anemometer tied to a baffle or louvers in the spray head. Air energy could be balanced between up- and down-wind sides, and further adjusted to compensate for the distance to the canopy… but I’m dreaming in technicolour, now.
Until then, sprayer eyes can only blindly dictate the release of spray into the airstream based on an assumed coverage constant (e.g., 1.2 oz./ft3). It remains for the sprayer operator to act as the brain, optimizing sprayer settings, quantifying coverage, and making changes to reflect conditions.
Learn more about how to optimize the fit between your airblast sprayer and your target by downloading a free copy of our Airblast 101 textbook.
Calibration should be a regular practice for every operation that uses a sprayer. Part of that process is confirming that each nozzle is operating within the manufacturer’s specifications. This is a must for researchers that adhere to Good Laboratory Practices and for custom operators that sell their services. But we didn’t just fall off the turnip truck… we know nobody else does it. In fact, we’re surprised when we hear an operator HAS checked their nozzle flow.
And we get it. It can be awkward and time consuming. A field sprayer with 72 nozzle bodies and three nozzles in each position has a whopping 216 nozzles. A tower-style or wrap-around airblast sprayer has fewer nozzles, but the operator needs a ladder to reach them all and they don’t point straight down, so a tube must be used to guide the spray into a collection vessel.
And when pressed, any operator that does not regularly check their nozzles counters by saying “my tank empties in the same place every time, so why check them?” Even if the sprayer does start to go further on a tank, the operator can speed up or adjust the rate controller to drop the pressure a little.
Fair enough. This isn’t a hill we choose to die on.
But we will say that nozzles worn by even a few percent don’t only cause a change in flow rate, but may indicate a deteriorating spray quality and spray geometry. And, when one (or a few) nozzles are worn and others are not, it’s the same as when a single nozzle is plugged – the operator won’t be able to tell from the cab because the rate controller tends to mask the problem. And, if using PWM to apply a simultaneously reduced broadcast rate, perhaps the issue is amplified? All of this impacts coverage uniformity.
We’ll get off our soapbox now.
Over the years we’ve encountered many methods for determining a nozzle’s flow rate. We wanted to try each of them and characterize their accuracy, precision, time required, and ease of use. This is not a ranking where we wanted to find “The Best” method. The best method depends on your situation. If you’re a researcher, then accuracy and precision may trump time and expense. If you’re a custom applicator, then perhaps time is the critical factor. And if it’s your own operation, perhaps expense matters most. It’s up to you.
Method
The following tests were performed on a spray patternator table. A single nozzle was operated by a ShurFlo 2088-594-154 positive displacement pump. Pressure was set using a bypass regulator and an analog pressure gauge, confirmed by a SprayX digital manometer positioned under the nozzle body via a splitter. Room temperature water was used.
We tested ten nozzle flow rate measurement systems. There are others out there, but we limited the selection to farmer-oriented systems and not those used in mandatory government inspections.
Billericay Flowcheck
Delavan Calibration Cup
Graduated Cylinder
Greenleaf Calibration Pitcher
SprayX SprayFlow Turbo
SpotOn SC-1
SpotOn SC-2
SpotOn SC-4
Weighed Output
Lurmark McKenzie Calibrator
Three samples were taken from a new TeeJet XR8004 at ~40 psi and three samples taken from a new TeeJet AIXR11004 at ~70 psi. An exception was made for the Billericay Flowcheck which specified 43.5 psi (3 bar) for all sampling. All systems were emptied or dried as much as their design permitted between samples.
All data was converted to gallons per minute and the flow measured was compared to the calculated flow for the nozzle and pressure used. For example, if the manometer read 38 psi for the 8004, then the formula 0.4 x (38 psi ÷ 40) 0.5 gives us a calculated flow of 0.39 gpm. If the method reported 0.41 gpm, then it would be off by +5.1%.
Results
Consider the accuracy and the precision of each system when you review the results. Remember that precision means you get the same result with very little variation while accuracy means that on average you get the correct result. And, for context, remember that most recommend changing a nozzle when it is 10% more than the ideal flow rate. We prefer 5%, and if three or more nozzles are off spec, replace them all as a batch because they’re likely all very close. Compared to most spraying costs, a set of nozzles is not worth quibbling about. Some operators just change them annually and don’t bother with testing at all.
Billericay Flowcheck: This is a passive measurement system. You must select the nozzle size on the bottom of the collector and suspend the unit from the nozzle body. It’s designed for a horizontal boom and you’d have trouble using it with any other sprayer. You also have to set the pressure to exactly 43.5 psi (3 bar). While fairly accurate, it spanned about +/-2.5% off ideal. You have to read from the right scale, which in this case was red and rather difficult to read because of the low contrast. It took about two minutes to reach equilibrium for each reading and a lot of liquid is lost during the process.
We attempted to keep the unit plumb so the meniscus and scale aligned correctly. We found it difficult to read the ’04 scale because of low contrast. Pictured is 1.53 lpm.
Delavan Calibration Cup: This small, one-handed plastic cup had a scale printed on the outside. We were limited to a 15 second collection because of how quickly it filled. Some spray was lost to mist and bounce and we used the “Fluid Oz” scale to get the highest resolution from the measurement. It took less than a minute to collect and read from the cup, but had the lowest precision and accuracy.
Graduated Cylinder: There was little or no mist or bounce from escaping spray during collection. Our 1,000 ml graduated cylinder took 30 seconds at 40 psi and 20 seconds at 70 psi to fill making it roughly one minute per reading. A few light taps removed bubbles and once the liquid settled we could read the level. This must be performed on a level surface (in our case we used the digital level app on our iPhone). This was a very precise method, varying by less than 2%, but it wasn’t very accurate. We may have introduced error when reading the meniscus (always read from the centre) or perhaps the plastic distorted over time and affected accuracy. It may be difficult for most people to get a high quality, scientific-grade graduated cylinder.
Greenleaf Calibration Pitcher: The pitcher had multiple scales but once again we used fluid ounces because it had the highest resolution. With the highest capacity, we were able to collect for an entire minute. Despite holding the vessel at different angles and distances, we lost a lot of spray to mist and bounce and the nozzle body was beaded with water at the end of each trial. After tapping the vessel to remove bubbles and reading on a level surface, it took about 1.5 minutes per sample and averaged an average 3% more than the calculated ideal flow rate.
Innoquest Spot On Digital Calibrator: We’ll discuss all three Spot Ons together. The Spot Ons were a game-changer in North America when they first came out. You can read a peer-reviewed article about the SC-1 by Dr. Bob Wolf et al. published in 2015 in the Journal of Pesticide Safety here. The SC-2 is a new version of the SC-1 with added digital features that allow the user to calculate gallons per acre and it indicates tip wear based on the 10% industry standard . The most important improvements were a reduced sensitivity to foam and a thicker foam diffuser to reduce the chance of errors. The SC-4 works exactly like the SC-1, but has a larger capacity intended for high flow rate nozzles (e.g. hollow cones on an airblast sprayer). In each case, the Spot On will report in several units, and must be held steady under the nozzle flow (i.e. not moved during reading). The SC-1 and 2 took less than 12 seconds for each reading and the SC-4 took closer to 30. The SC-1 and SC-2 were relatively precise but read consistently higher than the calculated flow rate. This may be an artefact given that the units only read to 2 decimal places and this may have exaggerated any error. The SC-4 was the least accurate and precise of the three. The Spot Ons were the fastest and easiest to read of the methods used.
Weighed Output: This method is based on the fact that 1 ml of water weighs one gram. Spray was collected for 30 seconds and weighed on a new, $25 CAD digital kitchen scale, which was tared (i.e. the weight of the vessel subtracted from the overall weight). While subject to errors from manual timing, it has the merit of removing the challenge of reading a meniscus and it’s relatively inexpensive. This method was precise and relatively accurate compared to the other methods used. It took about a minute per sample.
SprayX SprayFlow Turbo: This was the most sophisticated method we used. The kit comes with a digital manometer, a flowmeter and a digital scale. It works though a smartphone app (screenshot below). You first have to set up a virtual sprayer, informing the app how many sections and nozzles will be tested. Then you must calibrate the flow sensor by taking three measurements versus a weighed output to eliminate possible variations caused by the nozzle, pressure, temperature, and the density of the liquid. The app walks the user through each step. This method took the most time to set up (easily 10 minutes). However, once it was set up, each nozzle could be tested in less than 30 seconds apiece. This method was the most accurate and precise, but the price may place it out of reach for the typical user.
Screenshot from the SprayX SprayFlow app.
Lurmark McKenzie Calibrator: This method is not reported in the box-and-whisker plot because there were significant problems that prevented accurate readings. It was difficult to get a seal over the nozzle and the floater ball would either stick or fluctuate. After several attempts, this method was abandoned.
Conclusion
In order to test if a process, or a thing, is occurring or produced within acceptable limits, we need a detection system with a high enough resolution. In manufacturing (e.g. factory production) this is an essential requirement in quality assurance. Let’s consider a +10% deviation from the nozzle’s ideal flow rate to be our indication that a nozzle needs to be replaced. We need a measurement system with an appropriate scale and one with sufficient precision to ensure we don’t get a false reading. Based on our data, I would suggest all systems reviewed, save the measurement cup, are viable. Even if we elect to use a more stringent rejection threshold of 5%, some systems are more precise than others (i.e. less variability), but all but the cup should still be sufficient.
What’s the penalty for not testing, assuming we’re not talking about significantly deviant nozzles? Let’s say, for example, we are not using a rate controller and we are applying 20 US gpa at 12 mph using 72 nozzles on 20″ centres. Our boom would have to spray 58.2 gpm, which means each nozzle would have to emit 0.81 gpm. If those nozzles sprayed 5% more than intended, we’d be spraying 21 gpa instead of 20 gpa. That means for a 1,200 gallon sprayer, you’d do 57 acres instead of 60. We would have the same result if we dropped from 12 mph to 11.45 mph, which is about 5% slower. Maybe that’s a big deal for your operation, or maybe not. For most, 5% is well within the typical error inherent to spraying. Then again, perhaps it’s more important to know that each nozzle is performing in a manner similar to its neighbours to ensure the highest degree of coverage uniformity.
Ultimately, it is important to ensure you’re as efficient as possible, and that means understanding what your nozzles are doing so you can decide if-and-when it’s time to replace them. Pick whichever method makes it easiest for you to justify testing your nozzles and do it at least once a year when you take your sprayer out of long term storage.
Thanks to all the companies that donated or loaned their calibrators to make this article possible.
