Tag: airblast

Adjusting Orchard Airblast Sprayers for Spring
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.
March 31, 2025
Airblast Spring Start-up and Winterizing
Any description of airblast sprayer start-up must, contextually, make assumptions on how it was winterized for long-term storage. This cyclic relationship is why I use a chicken-and-egg title slide when giving this presentation.
Answer: It was the rooster.
The inability to describe one process without the other is further complicated by the possibility that the sprayer is brand new and was therefore never winterized. So, what follows is an attempt at a logical sequence of pre-season maintenance activities to restore a winterized sprayer, or initiate a new sprayer.
New Equipment
If this is a new sprayer, you have an opportunity to perform some preventative maintenance.
Loosen, lubricate and re-tighten clamps. Always back gears off before tightening to avoid stretching them. (Image from Purdue Extension publication PPP-121: Preparing Spray Equipment for Winter Storage and Spring Startup)
Use double clamps on pressurized lines for added safety. Wider clamps are better and T-bolt clamps are better than worm-gear.
Put thread release on bolts and re-tighten with a torque wrench (not an impact tool). Use a paint pen to mark nut, washer and bolt for future visual checks. This is called a “Witness Mark”.
Protect hoses and wires at rub points. Follow hoses and with a paint pen, number the hose-ends and connections for future reference.
Using a new tractor? You may have to re-calibrate to account for different gear ratios. When hitching a new sprayer, note that the distance from the ball on the drawbar hitch to the tip of the PTO should be ~14″. Don’t exceed maximum working angles for PTO shafts (usually <25 degrees). If your tractor or implement manufacturer says differently, go with that. And get it in writing.
Winterizing (Long-term storage)
If you are preparing the sprayer for long-term storage, follow the normal rinsing process, but don’t reinstall strainers and nozzles.
Look in the nozzle bodies for debris. Discard worn or broken nozzles.
Soak, scrub, rinse and store nozzles and nozzle strainers. You may replace them once the sprayer is clean, but I prefer to store them separately since they have to come back off during start-up.
With the agitation on, circulate undiluted plumbing antifreeze (the sprayer already has 5-10 L (1.25-2.5 gallons) of water in the system from the decontamination process) for five minutes and drain it through the plumbing system (not the booms).
Disconnect hoses where they attach to the booms and drain as much liquid from the sprayer as possible. (Image from Munckhof Sprayers). Take the time to examine any hose fittings.
Clean the sprayer (Triple rinse with a detergent) and scrub the exterior. Do not use pressure washers on bearings, fittings, pumps or any lubricated or moving parts.
Examine fan blades for cracks, build-up or nicks that can cause imbalance. Replace (not just repair) punctured entrance grills.
Don’t ignore tank damage. Poly tanks are prone to sun damage and cracks. Never climb into a tank to repair it. Quite often, replacement is the best option.
Clean and inspect wheel assemblies. It’s best to do this during winterization to prevent bearing corrosion as the sprayer sits all winter.
Remove any rust and repaint (or just touch up). Paint not only looks good, it protects.
The excellent YouTube channel Ask Tractor Mike proposed storing the PTO shaft indoors in two pieces, and to cut away a portion of the interior guard to facilitate reassembly later on. Also, use a paint pen to mark the splines on the shaft for easier hook-up (see inset top-right of image).
RV antifreeze is a 50% solution of antifreeze and water with a rust inhibitor. It should not cause phytotoxicity if sprayed or dumped, but be sure to dispose of it away from water sources during start-up. Turn the pump manually to get antifreeze throughout the system. Close the nozzle bodies, loosely fit the tank lid and store indoors. (Image from Purdue Extension publication PPP-121: Preparing Spray Equipment for Winter Storage and Spring Startup).
Spring Start-up
Most operators are guilty of neglecting their airblast sprayers and babying their tractors. Sprayers are precision tools that must be kept in good operating order to prevent costly breakdowns, improve their performance, and increase their lifespan.
Your car is serviced based on distance travelled. Your sprayer should receive regular maintenance based on working hours, per the manufacturer’s recommendations. Daily sprayer inspections are part of regular maintenance since the operator will (hopefully) find small problems before they become big problems.
Never assume your sprayers is ready to go right out of long-term storage. Parts seize, scale breaks away from surfaces, and small beasties sometimes choose to eat, or make their homes in, cozy sprayers.
When planning spring start-up, never assume the winterized sprayer is ready for immediate hook-up. Expect a minimum half day per sprayer.
Attempting to loosen or shift something that hasn’t moved in several months is risky. Pressure gauges snap off, fittings crack, welds break. Expect the unexpected and either have spare parts on hand, or a plan to get them quickly.
Parts are most likely to seize during the first spray. Bearings and PTO universal joints, especially.
Start-up is a good time to lubricate parts. Grease the guard ring bearing every 100 hours, the universal joint cross every 25 hours and the shaft and shear bolt regularly.
Insects, birds and rodents eat, or make homes in, sprayers. Professional rodent bait/traps, steel wool and peppermint oil/gel are possible solutions.
Check belt tension, alignment and wear. (Image from Purdue Extension publication PPP-121: Preparing Spray Equipment for Winter Storage and Spring Startup).
Pump specific maintenance is beyond the scope of this article. Hypro recommends changing oil after 40 hours of break-in operation and every 500 hours after that. The diaphragms should be replaced every 1,000 hours. Generally speaking, EPDM (black) diaphragms are a better choice for airblast sprayers, while the Desmopan (amber) diaphragms are really for lawn care sprayers.
Pump maintenance is beyond this article, but change the oil every 500 hr or 3 months. Use a paint pen to write on the pump what type of oil it requires, and then date the filters. Note the “winterized” sticker.
At minimum, check the tire pressure. Hard tires drive faster, but leave compacted ruts. Soft tires drive slower, but disperse weight better. Airblast sprayer wheel assemblies should be cleaned and inspected as part of regular annual maintenance. Wheel bearing maintenance before long-term storage may prevent water from corroding the bearings.
Ensure tire pressure matches the ideal stamped on the tire. Or, if using less pressure to avoid spring soil compaction, ensure both tires have the same pressure.
The relief valve on your sprayer should always be in the bypass position during start-up. If your gauge spikes then the gauge may always read high afterwards and should be replaced.
A reminder to always set the relief valve to the bypass position when starting up the sprayer. This is one reason why pressure gauges spike and can eventually fail.
Replacing leaking, opaque or inaccurate gauges improves sprayer performance. Be sure to use the oil-filled variety of gauge to eliminate a bouncing needle. You can also get suppressors that fit between the gauge and sprayer to prevent pulsing. Consult the article on testing airblast pressure gauge reliability.
Use a wrench to turn gauges at the nut. Don’t twist them by hand holding the face. Ensure they are not opaque, leaking, plugged or resting above the zero pin.
Many spray materials do not mix well and one of the common causes of uneven application is poor agitation. If you find deposits at the sump in the bottom of the sprayer after an application, your agitation is insufficient. For mechanical agitators, check for propeller wear and ensure paddles are secure on the agitator shaft. Learn more about agitation here.
If the agitator shaft is leaking a little, tighten the packing. The packing gland is a common source of leaks. Keep it properly greased. If a leak occurs you can usually repair it by tightening the bolts on the packing gland by ½ a turn, but if that doesn’t work you may have to remove and repack (or replace) it.
On sprayers with mechanical agitators, look for prop wear and loose or damaged paddles. Fill the sprayer with water and looks for tank leaks. Tighten the bolts 1/2 turn if the packing gland on the agitator shaft is leaking. You may have to remove and repack the gland if the leak persists.
Look for signs of hose wear and examine the sprayer for leaks while under pressure. Be careful when pressurizing the sprayer for the first time in the spring; this is when lines are likely to come loose or burst. (Image from Purdue Extension publication PPP-121: Preparing Spray Equipment for Winter Storage and Spring Startup).
Minerals chelate (i.e. scale) more readily on stainless steel than plastic tanks. In either case, the first tank of water and leftover antifreeze should be sprayed from the nozzle bodies with no line or nozzle strainers, and no nozzles. Replace them once the tank is sprayed out.
The last step is calibrating the sprayer, and that process really depends on your definition. If the preceding steps conflict with those of the manufacturer’s, always follow the manufacturer’s. Do this for reasons of safety and to preserve any warranty.
Thanks to Fred Whitford (Purdue University), Gail Amos and Mark Ledebuhr (Application Insight LLC) for reviewing the content of this article and for their helpful edits.
March 29, 2025
Airblast Sprayers for Small Operations
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.
The Burro autonomous platform.
Are you aware of a sprayer that’s not in this article? Let us know! Good luck and make sure you have only slightly more “sprayer” than you need.
February 14, 2023
Optics on Airblast Sprayers – What They Can’t See
“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.
September 2, 2022
Gear up – Throttle down
In 1977, David Shelton and Kenneth Von Bargen (University of Nebraska) published an article called “10-1977 CC279 Gear Up – Throttle Down”. It described the merits of reducing tractor rpm’s for trailed implements that didn’t need 540 rpm to operate. In 2001 (republished in 2009), Robert Grisso (Extension Engineer with Virginia Cooperative Extension) described the same fuel-saving practice. Again, it was noted that many PTO-driven farm implements don’t need full tractor power, so why waste the fuel? He tested shifting to a higher tractor gear and slowing engine speed to maintain the desired ground speed. 700 diesel tractors were tested, and as long as the equipment could operate at a lower PTO speed and the tractor itself didn’t lug (i.e. overload), as much as 40% of the diesel was saved.
How this applies to Airblast
For airblast operators with PTO-driven sprayers and positive-displacement pumps, this has potential for reducing air energy. Gearing up and throttling down (GUTD) sees the operator reducing the PTO speed from 540 rpm to somewhere between 350-375 rpms, which not only saves fuel but more importantly slows the fan speed. This may be an option when air energy from the sprayer, even at higher travel speeds and a low fan gear, still overblows the target canopy.
Some airblast sprayers, like this one, feature fan blades with manually-adjustable pitch to increase or lower air volume and speed. It’s often a pain to try to adjust them, and most operators only try it once.
A good time to try this out is early in the spraying season when (most) canopies are dormant and at their most sparse. For example, when applying dormant sprays in apple orchards, look to see if the wood on the sprayer-side gets wet, but does not creep around the sides. This suggests that the air, and much of it’s droplet payload, are being deflected. When the air speed is slowed, it will become more diffuse and turbulent on target surfaces, and this turbulence helps more droplets deposit in a panoramic fashion within (not past) the target canopy. Look to see if the wood is wet >50% around the circumference of the branches. You’ll get the rest when you spray form the other side.
Limitations
GUTD is not always appropriate. It requires airblast sprayers with PTO-driven positive displacement pumps (e.g. diaphragm). Airblast sprayers with centrifugal pumps would experience a drop in operating pressure and would have to be re-nozzled. Further, the pump must have sufficient surplus capacity to maintain pressure at low rpms.
GUTD is not intended for air-shear sprayers that employ twin-fluid nozzles because dropping air speed below a certain threshold may compromise spray quality; the air needs to be fast enough to create and direct spray droplets
The tractor must have sufficient horsepower (more than 25% in excess of minimally-required capacity) to permit the reduction in engine torque. This is especially important if the operator is on hilly terrain. If the tractor begins to lug (e.g. black smoke, sluggish response, strange sounds) you’ll be in trouble.
Observations
We first experimented with GUTD in 2013. We noticed how much quieter the sprayer was, and the fuel consumption was certainly reduced. One grower-cooperator switched to a GUTD spray strategy mid-way through their dormant oil application in pears. We saw the trees immediately began to drip. Panoramic coverage was improved significantly; once the operator passed down the other side of the target, capillary action and surface tension helped to give near-complete coverage.
However, in one instance, the operator was already applying a low spray volume per hectare using air induction nozzles and their lowest fan gear. By further slowing fan speed using GUTD, coverage at the top of his cherry trees was compromised.
In short, GUTD can work under the right circumstances. If you want to try it, use water-sensitive paper to establish a base-line with your current practice, and then evaluate coverage after you change your sprayer settings.
May 18, 2022