Sprayer math can be intimidating, but the effort gives solid value. When combined with a calibrated sprayer you reap the following benefits:
Determine how much spray mix is required to apply the intended rate.
Estimate how much crop protection product must be ordered for the season.
Populate spray records which allow you to review practices, respond to enquiries and satisfy traceability requirements.
There are many ways to perform sprayer math, and you need only look to local pesticide safety courses, industrial catalogues, and extension resource centres for examples. If you’re already comfortable with your current method, don’t mix and match with others. Sprayer math is a series of related calculations that employ constants to keep the units straight. It’s all or none.
Walkthrough
Let’s start with the classic, US Imperial formula for calculating the sprayer output. We’ll weave in Metric, later. This base formula can be adjusted to allow you to solve for any factor, as long as you’re only missing one piece of information. Turns out your high school teacher was right – you DO need algebra.
GPM = [GPA x MPH x W] ÷ 5,940
In this case, you can determine an output rate (GPM – gallons per minute). You’ll need to know your target volume (GPA – gallons per acre), your average travel speed (MPH – miles per hour) and your nozzle spacing (W – which is width in inches). The number “5,940” is a constant that handles all the unit conversions. If you divide the GPM by the number of nozzles on your sprayer (assuming they are all the same rate), you can hone in on the ideal nozzle size.
But, as we noted earlier, you can do a lot more with sprayer math than just pick the ideal nozzle size. The rest of this article includes examples of both Metric and US Imperial formulae, but watch out for unit conversions. If at any time you don’t see the units you’re looking for, you can consult our unit conversion tool.
Grab your calculator – it’s math time!
Don’t be intimidated. With a little practice, sprayer math gets easier and it’s always worthwhile. The real trick is navigating unit conversions.
Step 1 – How large is the area you need to spray?
Multiply the length of the area you plan to spray times the width. If you are using metres, then divide the product by 10,000, which is the number of m2 in a hectare (ha). For feet and acres, divide by 43,560 which is the number of ft2 in an acre (ac):
Step 2 – How much product is needed to spray the area?
Consult the rate(s) shown on the label. In Canada, rates are often based on planted area (E.g. hectares). In Australia and New Zealand, they may be based on row length (not covered in this article). If you measure your area in acres, you’ll have to convert the rate by multiplying by a constant: 0.4.
Now multiply the area you want to spray (step 1) by the rate (step 2).
Step 3 – How far can you go on a full tank?
You know your sprayer output (determined through calibration) so you divide that into your tank size. Watch your units:
Step 4 – How much pesticide per tank?
Multiply the area that can be sprayed per tank (Step 3) by the pesticide rate (Step 2). Again, watch your units:
Step 5 – How much area is left to spray?
Just subtract what you’ve already sprayed from the total area.
Step 6 – How much pesticide in the last, partially-full tank?
Multiply the area you have left to spray (Step 5) by the pesticide rate (Step 2). Yes, watch your units:
Step 7 – How much spray mix will I need for the partial tank to finish spraying the total area?
Multiply the area you have left to spray (Step 5) by the sprayer output (determined through calibration). Guess what? Watch your units:
Sample problems
Time to test your knowledge. Let’s suppose you want to apply a product rate of 3 L/ha to your blueberries. You calibrate your sprayer and determine your output to be 50 L/ha. Your tank holds 400 L of spray mix. Your planting is 500 m long and 200 m wide.
Q1 – How large is the area you need to spray?
Q2 – How much product is needed to spray the area?
Q3- How much area can be sprayed on one tank?
Q4 – How much product should be added to a full tank?
Q5 – After the tank is empty, how much area is left to spray?
Q6 – How much product to add to the last, partially full tank?
Q7 – How much spray mix will be needed to finish spraying?
Tank mix calculator
You might feel we buried the lead by adding this calculator to the end of the article. It’s important for a sprayer operator to understand the math required to interpret labels and calculate tank mixes, so hopefully you read and understood the process before you got here. And now that you have, this is a very helpful tool. Try it online, or download a standalone version.
Notable exceptions
Certain situations aren’t covered in this article. If you are spraying a greenhouse, the math is different. If you are performing a banded application, the math is different. And, if you’re an airblast operator trying to reconcile why a pesticide label uses planted area rather than canopy volume for its rates, you’re in for some additional reading.
Crop spraying is one of the most important and highly skilled jobs undertaken on any arable farm, but it is facing increased public scrutiny. This is why it is vital that the kit you use as a means to apply pesticide to crops is in prime working order and is set up correctly to deliver the product safely and accurately to its target. Optimum sprayer set up will help to maximize the efficacy of applied products, reduce spray drift and keep machinery in good condition.
For this best practice guide to sprayer set up, Farmers Weekly teamed up with former Farm Sprayer Operator of the Year Iain Robertson. Mr. Robertson is assistant arable farm manager at David Foot Ltd, a 2,200ha mixed farm south of Dorchester in Dorset, growing wheat, barley, beans, oilseed rape and maize as forage for the farm’s three dairy herds. The machine used for this guide is a Bateman RB26 self-propelled sprayer and while most of these checks and tests are universally applicable to all sprayers, it is also important to refer to the handbook of the manufacturer of your specific machine.
Watch the video tutorial with Mr. Robertson and then see the step-by-step guide below for more detail.
Pre Start Checks
Before firing up the engine, the first thing to do is your pre-start checks – that means checking your machine’s vital fluids like fuel, hydraulic oil, hydrostatic oil, engine oil and coolant levels. If yours is a self-propelled sprayer, chances are you’ll need to get up on to the back of the machine to check some of these.
“While I’m up on the back of the sprayer I also have a quick look in the top of the tank to make sure that it is nice and clean and the tank rinse nozzles have worked properly – cleanliness is next to godliness,” says Mr. Robertson. Next, move on to the tires. Use a pressure gauge to check all tires are at the correct pressure and refer to the manufacturer’s guidelines. If you’ve got a trailed sprayer, don’t forget to check the tractor tire pressures as well.
Aim for tires to be run at the lowest pressure recommended for the load to be carried. This will help with boom height and stability and also helps tires act like a shock absorber to ride out bumps. If using a trailed sprayer, use a spirit level to ensure that the drawbar is level. Mr. Robertson says he tries to work around the machine in a methodical, clockwise manner to ensure that he doesn’t miss anything.
Coming to the pumps, check that they have got enough oil, check that any tool boxes have enough spare parts and any equipment needed and make sure you are carrying a spill kit with absorbent granules and a spade in case the worst happens and there is a spillage. Make sure all parts are lubricated daily and that any grease nipples are cleaned before and after use to avoid them collecting dirt and blocking.
Check all hydraulic hoses, spray lines and air lines for any signs of wear that could result in problems while operating.
It’s best to run the sprayer at a minimum of 5 bar to check for leaks. Also check the spray tank is fixed down securely, all straps and bolts are tight.
Boom checks
Once opened out, check the boom has good movement in the x- and y-axis. All machines are different so check with your manufacturer as to how the boom is set up. Mr Robertson’s Bateman has tie rods and stock bots that can be adjusted to set the boom up to ride well.
Check the tie rod nearest the back of the machine is slightly loose when moving and that the front rod is tight. Next, check for up and down movement by gently pushing the boom down by about 50cm and letting go. The boom should return to the central position without too much bouncing around.
“We want a little bit of movement but not excessive so that you can ride over the bumps as you go along without over- and under-dosing the crop,” says Mr. Robertson. Boom height is one of the most critical factors when spraying and the ideal height is 50cm above the crop. One of the easiest ways to work this out is by using a cable tie that is cut off at the correct length to use a visual aid from the sprayer cab.
Don’t forget to measure from the tip of the nozzle to the crop, not the spray line.
Good sprayer cleanliness is important, so make sure the system is rinsed through at the end of each day with clean water to make sure there’s no residue left in the boom. If your machine’s boom doesn’t have recirculation, remember to take the end caps off occasionally and flush out the whole boom.
Nozzle checks
Check that the nozzles are aligned both vertically and horizontally, according to the NSTS guidelines. Loosen clamps to adjust any nozzles that need realignment.
Check the nozzle output at least twice a year by running the sprayer with clean water at 3 bar pressure. Time the output of each nozzle for 30 seconds. If nozzles have been used previously, it’s best to check their output against that of a new pair. Mr Robertson advises using a measuring cylinder rather than a jug to measure the flow rate as a jug is less accurate “because you get a bigger variation over the wider surface area”.
With an 03 nozzle running for one minute at 3 bar pressure, the output should be 1.2 litres/minute as a rule of thumb but refer to the nozzle manufacturer’s output chart for the expected flow rate. “An easy way to remember this is: at 3 bar your nozzle size multiplied by four will give you your target litres/minute output. It works for all nozzle sizes.” If the output varies more than 4% of the average, or if the spray pattern visually doesn’t look correct, you need to change the nozzle set.
After checking the output, cross-reference this figure with the rate controller – you may need to adjust the flow figures to ensure that the two correlate. If a nozzle becomes blocked while spraying, Mr. Robertson says he will swap it for a new one and then clean it later using a toothbrush or airline. Never blow through a nozzle with your mouth.
Nozzle choice
The choice of nozzle is highly dependent on the sort of job you’re doing. “Timing is crucial but using the right nozzle at the right time will make the job so much easier, cut drift and mean that you’re getting more of the product where you want it to go. If you aim at it you will hit it,” says Mr. Robertson.
His nozzle of choice is an 03 size and he prefers to use the Defy 3D nozzle alternated forwards and backwards across the boom for pre-emergence work and T0 applications as well as the T3 ear spray. “In less than optimum conditions I may prefer to use the Amistar/Guardian Air, a fine induction nozzle. I would use this at T1 and T2 and also in sub-optimum conditions.” This nozzle has a 3-star Local Environmental Risk Assessment for Pesticides (LERAP) rating and is 75% drift reducing.
A water volume of 100 litres/ha is a good rate for spring fungicide application. It provides enough coverage for good disease control and allows maximum efficiency from the sprayer.
Forward speed
The third and final part of reducing spray drift is forward speed. Depending on nozzle size and water volume, aim to travel at 12kph.
Mr Robertson says he finds that this speed gives a good overall output and means you don’t get shadowing or turbulence behind the machine.
Tips and tricks
One of the biggest risk of contamination is at fill up. “A fantastic, cheap trick that I learned through Farm Sprayer Operator of the Year is to take a 200 litre plastic drum and cut it in half to create two drip trays to catch any spillages under the induction hopper and the tank overfill.” This eliminates point source contamination, he says.
“Finally, there’s a plethora of information out there on the internet, loads of good apps to download. The technology is there to help us do the best job possible and make our job as safe as possible.”
A Veteran Applicator’s Questions about Pesticide Handling
Time and again, after years of working with dozens of different chemicals, I would wonder to myself “How dangerous is this chemical?”, “Is glyphosate as safe as they say it is?”, “How do I find out what type of safety gear I need while handling this chemical?”
Beyond the agrichemical dealer, ag. consultants, and university or government ag. extension specialists, a quick internet search reveals many sources of pesticide information. Collectively they identify the active ingredient(s) in formulated products, they detail which pests are best controlled by the pesticide, and they provide instruction for application. But it’s more difficult to find consistent, practical information about safe pesticide handling. Sometimes it’s excessive to the point of being impractical (try finding actual “chemical proof” gloves), and sometimes it’s minimal and vague – it depends where you look. No matter the level of precaution, pesticide safety is time consuming and involves some fussing, but it is the hallmark of responsible pesticide use. Just as we ensure that we are applying “safe rates” when spraying chemicals, we must also ensure we are respecting our own well-being while handling chemicals.
In Canada, the Pesticide Regulatory Directorate (PRD) is charged with protecting human health and safety by monitoring pesticides that are sold in this country. According to the Federal Pest Control Products Act all pesticides sold in Canada must be registered with the PRD. There’s a very nice overview of how that process works here. It is during this registration process that pesticide handling precautions are identified for the label. Further classification may take place under provincial acts.
All pesticides are designed to disrupt, repel, control or kill living organisms, but when it comes to safe handling, insecticides receive the most attention. This is because herbicides and fungicides target biochemical pathways that only exist in plants or fungi. However, most pesticides can be hazardous if they are not handled correctly. The handling precautions that appear on the label are based on five factors.
Five factors that affect handling precautions:
1. Pesticide Family
This factor is the broadest way to categorize potential risk to the handler. Generally, herbicides and fungicides are considered safer than insecticides, but there are notable exceptions. Do not rely solely on the pesticide family when making decisions on pesticide handling.
2. Pesticide Mode of Action
The mode of action gives further detail into how a pesticide should be handled. Modes of action that inhibit biochemical pathways that exist in the target pest, but not in mammals (people, in particular), have lower acute toxicities. Examples include herbicides that inhibit enzymes involved in amino acid synthesis or in photosynthesis – these enzymes do not exist in mammals. However, once again, there are always exceptions. Do not rely solely on mode of action when making decisions on pesticide handling.
3. Pesticide Formulation & Route of Entry
Pesticide formulation affects how a product can potentially be absorbed into the body. Emulsifiable Concentrates (ECs), for example, have higher rates of absorption than solutions or dry products. When it comes to the route of entry, dermal contact is considered safer than inhalation or ingestion. However, not all parts of your skin are created equal, and the point of dermal contact on the body matters a great deal.
4. Pesticide Toxicity
Taken collectively, the first three factors form the overall toxicity of the pesticide. The level of toxicity cannot be predicted – it has to be tested. The LD50 (defined below) values that are reported for a pesticide come from standardized experiments such as animal feeding. Although the chosen species (usually white rats for mammalian endpoints) are known to be similar to humans in their response, there is still the possibility of error. Nevertheless, toxicity forms an important basis for establishing handling precautions.
5. Operator Exposure
People handle toxic substances every day. Household bleach, for example is surprisingly toxic, and yet it can be readily found on kitchen shelves in many homes. The risk of being harmed by a toxic product can only be determined by the likelihood of exposure. While it is possible someone might accidentally consume a hazardous dose of bleach, it’s improbable. Exposure does not just refer to a single exposure to a substance – repeated exposures to small doses of a toxic substance can have a cumulative effect. The goal when handling any pesticide is to minimize exposure, but it becomes even more critical when that pesticide is highly toxic. Together, exposure and toxicity form the basis for risk.
Risk = Hazard x Exposure
Studies have shown that exposure is greatest for handlers of agricultural pesticides during the mixing and loading phase of spraying. During this phase, the risk to the handler may be increased due to:
physical stress
the denial of risk
a negative opinion of personal protective equipment (PPE)
The main method of pesticide exposure is dermal, and many of the surfaces on a piece of equipment are already contaminated.
Health effects of pesticides: Acute and Chronic
Acute: short term
High exposure, resulting in immediate reaction due to a high dosage of pesticide exposure. The severity depends on the toxicity of the molecule and entry into the body (dermal, oral, eyes, etc.). The most common acute reaction is skin irritation, although in certain cases respiratory, digestive, and neurological systems may be affected. Organophosphate (e.g. Lorsban, Malathion) and carbamate (e.g. Sevin, Lannate) insecticides inhibit the cholinesterase enzyme, which is found in humans and affects nerve function. Frequent users of these insecticides undergo regular blood tests to ensure their levels are normal.
Chronic: long term
Chronic affects are more prolonged as they are usually due to lower doses of pesticide exposure over a longer period of time. Although some rare cancers and disruption of the reproductive system have shown to be related to this type of exposure, when the general population and farming population have been compared in studies, the farming population has shown an under-representation in the majority of cancers. In the cases were reproductive malfunctions were observed, a different cause of the malfunction, such as genetic offset, was most often observed in these situations. However, cancer types such as skin cancer and brain cancer were overrepresented in the farming community. A study in France has shown that the onset of neurological disorders in Agriculture communities shows a strong connection between Parkinson’s disease and exposure to pesticides.
Label Information
The majority of information needed to safely handle pesticides is found on the label. Pesticide labels are legal documents, meaning they can be enforced by the federal government. The problem is that most sprayer operators rarely look at the label as they are not very reader friendly and easy to skim through. Most pesticide boxes even have the recommended rate, or acres/case on the side of the box now, so there is even less reason to look at the label.
LD50– the dose of pesticide in mg per kg of the test animals body weight that is lethal to 50 percent of the group of test animals. For example, if the pesticide has an acute oral LD50 value of 1000 mg/kg, and the test animals each weigh 1 kg, then 50 percent of the animals would die if they each ate 1000 mg of pesticide at once. A 100 kg animal would need to ingest 100,000 mg (100 g) of the pesticide for the same effect. LD50 is often expressed by the route of entry – dermal, inhalation, acute oral (ingestion) are the main examples.
Degree of Risk and Hazard Symbols
Two Factors that Determine the Appropriate Level of PPE
The Hazard Rating (above) incorporates the minimum protection generally required for a substance with the rating.
The Label Recommendations will usually give the additional specific protective clothing and equipment needs for an applicator.
Degree of Exposure
This increases as the length of each pesticide application increases. As the number of pesticide applications increases, the time between exposures decreases. If an operator becomes exposed to spray, dust or fumes the degree of exposure increases. Essentially, more protective wear is needed as the degree of exposure becomes greater.
Knowledge
This encompasses all of the above information. In order for a pesticide applicator to avoid injury or the chances of adverse effects on the body, a pesticide applicator must be knowledgeable about pesticides. It can be overwhelming for an applicator to sort through all of the information on the label or on-line regarding pesticides. So much so, that most often applicators avoid the information altogether. Ongoing training and learning will ensure that they are effective in their work. Many aspects of pest control change continuously, as new studies are conducted on the effects of pesticide exposure.
A Safety Data Sheet (SDS) is available for each pesticides registered, and these are usually linked on manufacturers’ websites. It can be eye-opening what types of toxicity tests are done, and what the results are.
Denial that pesticides can potentially cause harm is also a major flaw in the behaviour of applicators. Maintaining a safe work environment and practicing personal safety will reduce the chances of an applicator experiencing serious injury throughout their farming career.
Unknowns
There is very little certainty in toxicology. For one, most testing is done using acute oral and dermal dosing. Basically, toxicologists expose test animals to the neat active ingredient and watch what happens. There is a lot of missing information – what about formulant like solvents, and surfactants? What about synergies in tank mixes? Some, but not all of these, undergo testing. We also have much less information on chronic (long-term) effects, and can only simulate these in quasi long-range tests. In addition, toxicological methodologies and statistical approaches can vary, and we should not be surprised that some reports disagree, and that there are outright conflicts between toxicologists and epidemiologists (scientists that study patterns of health in populations). Regulators are aware of these shortcomings and often use safety factors to account for them. But those of us that use these products regularly, the message is simple: be cautious, and protect yourself.
Avoid Cross-Contamination
Disposable nitrile gloves are the product of choice for handling pesticides. But one of the most common problems with the use of gloves is cross-contamination. You’re handling product with your gloves on, touching containers, hoses, valves, and couplers. When you’re done, you climb back into the cab where you take off your gloves. Later, someone climbs up into the cab to talk to you, using the railing and operating the door handle without gloves. Guess what’s on their hands? Even later, you put away the hose without gloves and return to the sprayer. Now it’s on the steering wheel and all the levers. There are a few solutions:
Double-glove so you can take the dirty outside glove off and still be protected.
Wipe down surfaces that you might touch with gloved or bare hands daily.
If using non-disposable gloves, avoid lined gloves and rinse the insides out daily.
Learn More
If you would like to learn more about pesticide safety, or to obtain pesticide application training, the Pesticide Applicator License can be obtained from the Ministry of Agriculture. This course offers in depth, valuable safety information for applicators, as well as general knowledge for pesticide applicators. The Pesticide Regulatory Directorate provides workers, employers, and the general public with a wide range of pesticide information. The PRD can be contacted from anywhere in Canada toll free at: 1-800-267-6315
Download this Quick Reference Guide for commonly used herbicides. Print, laminate and post it at the fill station or pesticide storage area for easy reference. Also, grab a copy of Health Canada’s “Stay Safe when using Pesticides” factsheet.
The level of filtration required for any given spray operation depends on the materials sprayed and the nuisance factor: That is, the balance between lost productivity from plugged nozzles and the effort required to address them during rinsing.
There are opportunities to install strainers at the tank opening (usually a basket), the suction-side of the pump, each section line, and behind the nozzles. While we’ve yet to see an operation that uses all four (speciality or field operations), the suction strainer and line strainers are required bare-minimum.
This infographic explains how strainers are classified. Be aware that older strainers may use a different colour code (e.g. 50 mesh used to be red – now it’s blue).
To convert these ratings to actual size exclusion, we look at the Mesh Width (mm). An 80 mesh (yellow) leaves a distance of 0.18 to 0.23 mm between the wires. We can convert Mesh Width from mm to microns by multiplying it by 1,000, giving us 180 – 230 microns.
Each level of filtration should get progressively finer, ending with the nozzle strainers being slightly finer than the nozzle orifice. Nozzle catalogues will often advise you on which strainer is appropriate for the nozzle you are using.
When we ask why operators don’t use nozzle strainers, the response is either “Because they plug” or “It’s one more thing to clean”. Well, if your nozzle strainers are plugging, it’s likely because you have an agitation (see here) or mixing issue (see hereand here) further up the line. They can handle a lot before the spray pattern begins to suffer … but yes, you do have to clean them regularly so they can continue their good work.
Running water through any strainer often fails to remove plugs and debris, which are a source of contamination that can wreak havoc later on. They have to be removed and physically scrubbed during rinsing. We ran a demo to show why this irritating process is still a must-do (here).
If you use an airblast sprayer, you should use slotted (not mesh, which plug too easily) nozzle strainers. Beyond the obvious benefit of preventing plugged nozzles, the strainer shoulder plays a role in keeping the nozzle snug in the nozzle body. Without it, you may need additional gaskets to prevent leaks. Be aware that some nozzle strainer designs can plug a nozzle body. Learn more here.
If you use a field sprayer with clean carrier water, liquid formulations and large nozzles, you may never need nozzle strainers. But, if you’re using a lot of dry formulations, if your agitation is under-powered, or if your fill water is less than pristine (we’ve seen frogs in sprayer tanks) then you might consider them… even if they are a nuisance to clean.
“I’m an organic apple grower with constant nozzle-clogging problems. These problems occur when we use wettable powders such as micronized sulfur and Surround WP. We always premix before adding to the tank through its strainer. Our airblast sprayers have towers and employ mechanical agitation. The nozzle/filter combo is TeeJet TXR8001K Ceramic Conejet Visiflow Hollow Cone spray tips with TeeJet 4514NY10 50-mesh nylon slotted strainers. The nozzle strainers rarely make it through a full tank without having problems. Do I need to add an additional level of filtration or is there something that I’m missing?”
A clogged slotted strainer inside the nozzle body. Note that the inners of the check valve seem clear (a good thing).A clogged slotted strainer.
You can almost feel the frustration. When I receive grower enquiries, I first turn to the library of articles on Sprayers101 as well as the Airblast101 textbook. I was surprised to discover that we didn’t have anything that addressed this issue directly. So, I checked through university extension and industrial resources. Ultimately I couldn’t find what I was looking for, so let’s correct this oversight.
Possible causes
There may not be a single reason for why nozzles plug. It might be a combination of the following factors:
1. Product choice
While any tank mix can create clogs if they prove to be physically incompatible, there are two formulations that have a reputation for clogging nozzles.
Wettable powder (WP) formulations such as micronized sulfur and diatomaceous earth are notorious for clogging nozzles. WPs consist of a finely ground solid active ingredient often combined with wetting and bulking agents to help hold them in a dilute suspension. They tend to be dry products rather than liquids.
In a similar vein, suspension concentrate (SC) formulations also consist of a finely ground solid active ingredient, but this time they are suspended in a liquid and kept dispersed in the sprayer tank by wetting agents, dispersants, and thickeners. These formulations are known as “flowables” or “suspensions”.
By the way, for those thinking he should change products, he already uses Kumulus DF (or Microthiol Disperss), which are reputedly the least troublesome formulations… and smell better than other sulfurs.
2. Mixing practices
Pre-slurries are sometimes prescribed for SCs. I personally feel that pre-slurries create exposure risks and more things to clean, but this opinion is moot in the case of WPs: Micronized sulfur and diatomaceous earth are not soluble. They’re particles that are held in suspension by fluid flow or agitation, so there’s no point in a pre-slurry.
For those readers that cook, consider the corn starch metaphor. You’re making a sauce, and you choose to thicken it with a pre-slurry of corn starch and water. The particles disperse, but do not dissolve, so if you fail to use it immediately they settle to the bottom of the container. They must be forcibly scraped up and resuspended.
3. Agitation
Best practice is to fill the tank at least ½ full of water and engage agitation before you add anything. To extend the cooking metaphor, you want a simmer but not a rolling boil. Once filled, never stop agitating or WPs and SCs will settle and may not resuspend uniformly, if at all.
Your sprayer design may affect matters. Some hydraulic agitation systems flag if they have undersized pumps. If your pump is busy sending flow to the nozzles, it may not have sufficient capacity to run the agitation. When your sprayer is “empty”, is there a thick accumulation at the bottom? You may have insufficient hydraulic agitation. Mechanical (paddle) agitation does not suffer this issue because it is direct-driven off the PTO. Read more here.
4. Clean-out practices
Perhaps plugs are occurring because of the previous tank, not the current tank. WPs can leave a buildup of settled pesticide in the tank, suction strainer and nozzle strainers. If you aren’t diligent about rinsing at the end of each day, products will settle and harden. Micro sulfur particles, for example, are less than 10 µm in diameter and harden into a flakey shell that can break loose and cause plugs.
5. Flow restriction
Several things can restrict flow. Elbows, bends and fittings can increase friction, reducing flow. The greater the distance a fluid needs to travel, the more flow is reduced. The greater the head (a pump’s head is the maximum height that the pump can achieve pumping against gravity), the more flow is reduced. There is an excellent description of this relationship here.
So, if an operator is using nozzles with a particularly small orifice, plus nozzle strainers, on a vertical boom, liquid flow will be reduced. This allows particles to fall out of suspension and settle, forming further restriction to flow and eventually, plugs.
Possible solutions
Now, armed with these potential causes, let’s return to the grower. After some back-and-forth, he clarified that the clogs were a problem, but restricted flow was worse. An operator will stop to clean or replace a plugged nozzle, but may not notice reduced flow. This has the potential to affect several rows as well as leave unsprayed product in the tank.
My first proposal was to increase nozzle size. An ’01 tip is very, very small and even with slotted strainers (as opposed to mesh), that’s a lot of restriction. I suggested recalibrating for larger tip orifices. This is a rather involved process, but options included using every second nozzle (as long as there were no gaps in coverage), and/or dropping pressure, and/or increasing travel speed (as long as the spray still reached the tree top and canopy centre). I shared this Excel outputcalculator to help with the process.
Failing that, we discussed a plumbing project. Section 5.2.1 of Airblast101 describes a way to create a self-cleaning line filter that replaces nozzle strainers. That means instead of climbing a ladder to pull tips off a tower to reach the strainers, all filtration is conveniently located at ground level for easier (and more frequent) cleaning.
The outcome
The grower felt the numbers worked best running orange 02 TXR’s in every second position. He ordered new 50 mesh slotted nozzle strainers. His new operating parameters would be 5 nozzles/side, at 8.2 bar (120 psi) and 5.1 km/h (3.2 mph) for a total 51.5 L/ha (55 gpa). He noted some incompatibility issues running Braglia nozzle bodies (spec on his Rears sprayer), TeeJet TXR’s, TeeJet slotted strainers and TeeJet CP20230 caps. That was an important observation, and you can learn more about it here.
We felt good about this, but while there was an improvement, it didn’t solve the problem. There was still strainer clogging after the first tankload. So, he added inline filters and removed the tip strainers. The result:
“Yesterday I sprayed over 350 pounds (over 1,000 gal) of Surround WP and had no issues. I’m really excited about this new setup – it looks very promising. I’ve attached more pics if you’re interested (I don’t spend a lot of time scrubbing sprayers until after Surround season). Thanks again for all your help in this matter. – Joe Fahey, Peck & Bushel Fruit Company”
A 50 mesh inline filter assembly with a 1/4 turn ball valve for quick flushes.New filter plumbed and secured. Note the anti-rub wrap on the line – always a good idea.The new loadout. 02’s in every second position, with no tip strainers, and a new inline filter on each side of the sprayer.
Fantastic. Thanks to Joe for letting me share this story. Hopefully his experience will help you diagnose and solve any flow or nozzle plugging issues in your own operation.
Happy Spraying.
Epilogue
This article elicited some interesting comments. I’ll share two:
One grower proposed switching from a low profile axial sprayer to an air-shear system (there are a few examples here). In this case, the grower had a European make with hydraulic agitation. The grower re-plumbed theirs by installing a bigger pump and swapping the sparge system with a 3/4″ pipe oriented toward the bottom to sweep it out. When mixing, the agitation valve is left wide open. He says he doesn’t even bother with a tank basket; he dumps the Surround (as much as 2 x 50 pound bags in 1,000 litres) and has no plugging issues.
Another grower with considerable boom-sprayer experience was genuinely surprised this was even an issue. Self-cleaning filters have been commercially available for more than 30 years and most boom sprayers have them. This is a comment on the stagnation of the North American low-profile radial airblast design. Perhaps the long life of these sprayers (sometimes 40 years of service) makes iterative change slow, or perhaps most operators aren’t aware of new features, or perhaps change is a risky proposition in such high-value crops. This is a shame given that the first optic sensors were installed on airblast, not broad acre field sprayers. That comes as a surprise to many. But it seems to have been the exception and not the rule.
