Category: Calibration & Air Adjustment

All hort articles on sprayer calibration and air adjustment.

  • Methods for Testing Nozzle Flow Rate

    Methods for Testing Nozzle Flow Rate

    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.

    “Patty” the spray patternator table. Designed and constructed by Mohawk College, Brantford, Ontario.
    Digital manometer on a splitter parallel with the test nozzle.

    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.

    1. Billericay Flowcheck
    2. Delavan Calibration Cup
    3. Graduated Cylinder
    4. Greenleaf Calibration Pitcher
    5. SprayX SprayFlow Turbo
    6. SpotOn SC-1
    7. SpotOn SC-2
    8. SpotOn SC-4
    9. Weighed Output
    10. 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.

  • Gear up – Throttle down

    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 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.
    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.

  • Calibration – “The Fundamental Relationship”

    Calibration – “The Fundamental Relationship”

    The Fundamental Relationship, a concept by Professor D. Ken Giles (Emeritus), UC Davis Biological and Agricultural Engineering Department, is a way of talking about calibration without numbers and formulas. It is valuable for teaching concepts important to calibration. Since it is a relationship, it describes the variables needed and how they relate to each other.

    The Fundamental Relationship:

    Application Rate (gallons/acre) = Flow rate (gallons/minute) ÷ Land rate (acres/minute)

    We see here that land rate is inversely proportional to application rate. Thus, when land rate (either speed or swath width or both) are increased (and no other factors change), application rate is decreased. Likewise, flow rate is directly proportional to application rate. Thus, when flow rate is increased (and no other factors change), application rate is also increased. When flow rate is decreased (and no other factors change), application rate is also decreased.

    The Fundamental Relationship is also a good way to do the math of calibration because nothing needs to be memorized. As long as the units are checked, you can’t go wrong. The Fundamental Relationship works for any sprayer calibration, as long as the units are tracked correctly and the flow rate correlates to the land rate, i.e., the land rate used is the swath that the nozzles (flow rate) are covering.

    So, if the flow rate (GPM) used in the formula is for ½ of an airblast set up, the swath width in the land rate calculation would be ½ of the row width. If, for example, it is for a weed sprayer with 2 nozzles, the swath width would be the width the 2 nozzles are covering. Remember to think about this as what area is being covered by the spray:

    • Flow rate units are straight forward: gallons/minute.
    • Land rate can be a bit tricky because no one thinks in terms of acres covered per minute.
    • Land rate is tractor speed × swath width covered by the nozzles used to calculate flow rate.

    Land rate in the above needs to be calculated in the units “ac/min”. Since there are 43,560 ft2 in an acre, the easiest way to calculate is to use the swath width in feet, and the speed in ft/min. Multiplied, this then will give you land rate in ft2/min, which can then be converted to ac/min.

    Using MPH as Speed

    When you measure speed in the field, those who have a speedometer on their tractor will tell you their speed in MPH. To go from a land rate with speed as MPH to ac/min, the following unit conversion is used when multiplying the speed in MPH times the swath width in feet:

    1 mile/5,280 feet × 43,560 ft2/1 acre × 60 minutes/1 hour = 495
    Land rate (ac/min) = (Speed (mph) × swath width (ft)) ÷ 495

    Note: speed should always be measured and verified. Speedometers are notoriously incorrect!

    Calculating nozzle flow rate (GPM):

    You can also use the Fundamental Relationship to calculate the flow rate needed for a desired spray volume (application rate) when you have a set land rate (speed and swath width). This is necessary to help you choose your nozzles. Tractor speed is first determined by checking the coverage-using water sensitive paper or another coverage indicator like kaolin clay, and the fan (using ribbons in the canopy), to go as fast as safely possible while still getting adequate coverage. Swath width for any given field is set. What is left then is to calculate the GPM needed to achieve that application rate at that speed and swath width. This will allow you to select your nozzles based on individual nozzle GPM for a certain pressure.

    The Fundamental Relationship becomes:

    Flow rate (gallons/min) = Application rate (gallons/acre) × Land rate (acres/min)

    This is the flow rate for the ENTIRE sprayer (both sides, correlating to the swath width):

    GPM = GPA × Land rate

    OR if using MPH for speed:

    GPM = GPA × [(Miles/Hour × swath width (ft)) ÷ 495]

    To get the required GPM for one side of the sprayer, you multiply by ½:

    GPM (one side of sprayer) = GPA × [(Miles/Hour × swath width (ft)) ÷ 495] × 1/2

    GPM (one side of sprayer) = GPA × [(Miles/Hour × swath width (ft)) ÷ 495]

    I’ve seen some folks round up the 990 to 1,000, which makes the above formula easier to remember.

    Why I think the “495 formula” is bad for calibration

    In my experience of teaching calibration math, folks often want to fall back on the formula they have used instead of trying the Fundamental Relationship. The problem I have with the “495 or 990” formulae, is that with using ground speed in MPH, often the step of measuring speed, a critical step for optimizing spray coverage, is eliminated.

    Ground speed is assumed, the speedometer is assumed to be correct, and the entire step of measuring and setting speed is omitted-big mistake! Setting speed using flagging tape in the canopy and looking at the “Fan : Speed : Canopy” interaction is probably the most important step of calibration and optimizing coverage. So, if you must use the “495 formula”, please actually measure your ground speed!

    Measuring speed manually

    Typically, at least 100 feet are marked off to measure actual speed with a stopwatch. If you measure actual tractor travel time for a 100 foot length, you will likely find most common spraying speeds are timed in seconds. These can be converted to minutes, and then used in the formula for speed as ft/min which is then multiplied by the swath (or row) width in feet to obtain ft2/min, which can then be converted to ac/min.

    For example, at 3 MPH, you are travelling:

    3 mph × 5,280 ft/1 mile × 1 hour/60 minutes = 264 ft/min

    If swath width is 6 feet, the land rate (or area the nozzles are covering) is calculated as:

    264 ft/min × 6 ft = 1,584 ft2/min

    In acres covered per minute, we divide by 43,560 ft2/ac to obtain a land rate of 0.036 ac/min. To travel 100 feet at this speed, it takes 0.37 minutes or 22.7 seconds. So, it is not uncommon to time 100-foot tractor runs in 21-23 seconds (which is why you need a good stopwatch). These runs are best done on the type of terrain to be sprayed; and it’s always good to take several times and average.

    Remember that the speed is written as distance travelled/time. Sometimes when measuring speed, I’ve noticed that it will be written as time/distance travelled, which gives the wrong number. Track units!

  • Airblast Nozzles – The Nozzling Process

    Airblast Nozzles – The Nozzling Process

    Establishing an airblast nozzling solution is an involved process. We must first define the working parameters and flush out any special circumstances. Then we use an iterative approach to identify suitable nozzle combinations that require minimal changes to the sprayer.

    This article outlines my process step-by-step and then applies it to a hypothetical orchard scenario. If readers wish to delve deeper into the variables or the reasoning, several links to supporting articles are provided. Be aware that nozzling the sprayer is the penultimate step in establishing optimal sprayer settings. Operators should first adjust air settings, which includes identifying a suitable travel speed. The last step in setting up any sprayer is to verify you are achieving threshold spray coverage.

    Step One: Establish sprayer parameters

    1. Is there more than one sprayer available? In diverse plantings, it may be more efficient to assign a sprayer to blocks that require the same nozzling solution.
    2. How many nozzle positions are there on one side of the sprayer? If the nozzle bodies are roll-over style the operator can alternate between two different nozzles in each position. Some designs have twice as many nozzle bodies as needed. The intent is to assign two unique nozzle solutions in an alternating A-B set-up. This additional capacity gives us some flexibility if needed.
    3. Is this a tower or a low-profile axial sprayer? Generally, we distribute nozzle flow evenly over a tower boom but distribute ½ the flow in the top 1/3 of the boom on a low-profile axial sprayer (depending on canopy shape and density). Air-shear and one-sided sprayers are special cases that are not addressed in this article.
    4. What is the average travel speed, and can the operator easily change it? This process assumes the selected speed achieves a reasonable work rate while optimizing the interaction between sprayer air and the canopy.
    5. What is the average operating pressure, and can the operator easily change it? For sprayers with positive displacement pumps, pressure is easily changed via the regulator. Not so for sprayers with centrifugal pumps. Pressure-based rate controllers empower an operator to dial in their desired volume and are easiest of all .

    Step Two: Establish target parameters

    1. What is the row spacing (or spacings)? Some operations include a variety of canopy morphologies and planting architectures.
    2. What is the target volume (or volumes)? Operators often use a range of volumes to reflect the product being applied and the canopy area-density. This process assumes the volume will provide threshold, uniform coverage without misses or excess.

    Step Three: Are there any environmental, geographical or adjacency concerns?

    Each operation is unique, including conditions that may influence nozzling. For example, open water, sensitive crops, or residential areas adjacent and downwind of the planting may warrant drift-reducing nozzles or require the operator to only spray inward from one side of the sprayer. In another example, dry and windy conditions may require nozzles that produce a coarser spray quality will improve their survivability. Rolling hills and uneven alleys may cause sway that prevents the upper-most nozzles from consistently reaching the target.

    Step Four: Find out why the operator is re-nozzling

    The answer may reveal the operator’s willingness and ability to make changes to sprayer settings. For example, if their objective is to improve the match between sprayer and canopy it implies a willingness to take a more active role in spraying. Conversely, a less experienced operator might be satisfied with a more robust (i.e., wasteful) set up that does not require many changes between blocks.

    Step Five: Determine the highest and lowest boom flow requirements

    The following formulae relate travel speed, row spacing, and the desired volume sprayed per planted area to the output from a single boom. I recommend downloading this Excel-based calculator to make the process easier.

    US Imperial Formula
    Output from single boom (gpm) = [(Sprayer Output (gpa) × Travel Speed (mph)) ÷ 990] × Row Spacing (ft)

    Metric Formula
    Output from single boom (L/min) = [(Sprayer Output (L/ha) × Travel Speed (km/h)) ÷ 1,220] × Row Spacing (m)

    Using the formula with the appropriate units, enter the highest desired volume, the fastest travel speed and the longest row spacing. This will give the highest rate of flow the boom must satisfy.

    Repeat this process using the lowest desired volume, the slowest travel speed and the shortest row spacing. This will give the lowest rate of flow the boom must satisfy.

    The ultimate objective is to select a combination of nozzles that can produce these two flows, distributed sensibly along the boom, with no gaps or excessive flow relative to the target. Ideally, the operator should be able to alternate between these two flows with as few changes as possible.

    Step Six: Satisfy the highest flow

    This step requires a nozzle manufacturer’s catalogue and a calculator (or the downloaded Excel spreadsheet). We must assume the range of available nozzle positions are oriented to span the target canopy with no over- or under-spray.

    Divide the highest flow requirement by the number of available nozzles. Hypothetically, a nozzle size that produces this flow would satisfy the highest flow requirement while providing an even distribution along the boom.

    Using the nozzle manufacturer’s catalog, find the flow table for the nozzle you want. Generally, a molded hollow cone nozzle is the preferred choice (e.g., TeeJet’s TXR ConeJet or Albuz’s ATR). If drift is a concern, there are also air induction (AI) hollow cones available. AI nozzles are most effective in the top two or three nozzle positions where drift potential is highest. However, they may require higher flow than calculated to compensate for a reduced droplet count.

    Find the operating pressure (it may be in either the column or row heading) and find a flow rate in the body of the table that is as close as possible to your calculated ideal. It’s almost never an exact match, so choose the option that is less than the target rate – not higher.

    Imagine placing that nozzle in every available position. Add up all the rates to determine how close you are to the ideal flow. It will likely be less. To compensate, replace the top nozzle on the boom with a higher rate and re-calculate the total flow. Repeat this process, substituting for nozzles with a higher rate, moving top-down along the boom until the flows match.

    You have now satisfied the demand for the highest flow.

    It is important to note that this process assumes the flow distribution along the boom should be relatively even, perhaps skewed towards the top. However, it is sometimes appropriate to distribute the flow differently to reflect each nozzle’s distance-to-target and the density of the corresponding portion of canopy it needs to spray. This tends to be the case when pairing low-profile radial sprayers with large or trellised canopies, and you can read more about that process in this article.

    Step Seven: Satisfy the lowest flow

    This is the art-and-compromise part of the nozzling process.

    Confirm that the range of available nozzle positions still corresponds to the target. Quite often, the lowest flow is intended for smaller canopies. If so, we may no longer have as many nozzle positions to work with.

    Imagine the sprayer is still nozzled for the highest flow per the last step. Leaving the highest effective nozzle on, imagine turning off every second nozzle. Add up the flows and determine how close you are to the lowest rate of flow. It is often still too much. Do not turn off any more nozzles or you may create gaps in the swath.

    Instead, return to the nozzle catalogue and re-calculate the flows for the same nozzles, but using a lower operating pressure. Can you make that work? If not, you may have to go back further in the calculation (Step five) and recalculate the lowest flow required using a faster travel speed. This will reduce the demand for flow.

    If none of those options are viable you will have to consider re-nozzling. Perhaps that’s swapping a few nozzles to lower rates. Hopefully this only requires the operator to flip a roll-over position, but it may mean using a wrench to remove caps and swap nozzles.

    Once you’ve satisfied the lowest flow, the hardest part of the process is complete.

    Step Eight: Satisfy the other permutations

    The last step is no different than what we’ve already done. Go back to Step Five and calculate the flow for each spraying situation. That is, each unique combination of row spacing, travel speed and target volume. Using the nozzles already on the sprayer, adjust the pattern of nozzles in use (and pressure and/or travel speed if required) until each unique flow requirement is satisfied.

    Step Nine: Record the setups, nozzle the sprayer and test the coverage

    Be sure to clearly record the sprayer settings required to achieve each flow. Purchase the nozzles and take the time to test each set up using water sensitive paper to ensure coverage is achieved.

    A working example

    Let’s apply this process in a hypothetical orchard. I’ve included a screenshot of the spreadsheet I use to record the final nozzling solution (below) but feel free to design your own. It includes the nozzling solution for this example.

    Our orchard is a 50 acre operation with both 11 and 15 foot row spacings. They have one tower sprayer with 15 nozzle positions on one side and they are not roll-over bodies. The operator wants to apply a 40 gpa volume (concentrated) and a 100 gpa volume (dilute). Their preferred travel speed is 4.5 mph and preferred operating pressure is 140 psi, but they are willing to change them if required.

    We use the Excel calculator to work out the ideal highest and lowest demands for flow:

    Highest boom flow (gpm) = [(100 gpa × 4.5 mph) ÷ 990] × 15 ft
    Highest boom flow = 6.8 gpm
    We’ll call this “Situation A”

    Lowest boom flow (gpm) = [(40 gpa × 4.5 mph) ÷ 990] × 11 ft
    Lowest boom flow = 2.0 gpm
    We’ll call this “Situation D”

    I usually shut off the lowest nozzle position because it almost never aims at the target. Let’s divide the high flow of 6.8 gpm by 14 available positions to give us an average output of 0.48 gpm per nozzle. This operator wants to use TeeJet TXRs, so using their table (below) we see that at 140 psi the Orange ’02 is too low and the Red ‘028 is too large. If we drop the operating pressure to 120 psi, the Red ‘028 is much closer at 0.465 gpm, so let’s do that.

    A quick check gives us our current boom flow: 14 positions × 0.465 gpm per nozzle is 6.51 gpm of boom flow. We wanted 6.8 gpm, so let’s go up to the Grey ’03 in the top three positions. Now it’s 4 × 0.517 gpm + 10 × 0.465 gpm = 6.72 gpm. That’s close to our ideal 6.8 gpm, so let’s lock that down. If you want to see what this is in gpa, you can plug the value into the Excel calculator to discover it’s 99.6 gpa. Pretty darn close to our target 100 gpa.

    Now using that nozzling arrangement, let’s see if we can satisfy the lowest flow requirement by shutting off every second nozzle position, leaving the highest position on. Doing so reduces us to two Greys and five Reds, totaling 3.36 gpm. That boom flow is much too high compared to the 2.0 gpm we need. However, in our hypothetical orchard, this block has shorter trees so we don’t need the highest nozzle. That drops us to only one Grey and a new total of 2.84 gpm. Good try, but it’s still too much.

    Let’s reduce the operating pressure from 120 psi to 100 psi, which is as low as I like to go. According to TeeJet’s table, the Grey produces 0.473 gpm and the Red produces 0.426 gpm at this pressure. This gives us a new total of 2.60 gpm. Still too high! Well, let’s raise our travel speed from 4.5 mph to 5.0 mph and recalculate the lowest flow for Situation D:

    Lowest boom flow (gpm) = [(40 gpa × 5.0 mph) ÷ 990] × 11 ft
    Lowest boom flow = 2.2 gpm

    This still won’t do it, and driving that fast (even if it’s possible) would change our air settings too drastically. Having exhausted all the easy options we have no choice but to re-nozzle the sprayer for the original lowest flow requirement.

    Returning to the TeeJet table we see the best fit is to spray at 100 psi using one Red TXR80028 and five Orange TXR8002s. It’s a lucky break that our 1.98 gpm has come so close to the 2.0 gpm of flow we wanted.

    Now let’s work out the best arrangement for the other permutations, Situation B and C. We need 5.0 gpm and 2.7 gpm, respectively. For Situation B, let’s use the nozzling solution from Situation A. We see that shutting off four nozzles gets us very close at 4.81 gpm or 97.3 gpa where we wanted 100 gpa. As for Situation C, let’s work from the nozzling for situation D. By adding a few more nozzles from that set, we can manage 2.71 gpm or 40.2 gpa.

    Finally, we record all the settings (refer back to the spreadsheet image). We will need four Grey TXR8003s, ten Red TXR80028s and six Orange TX8002s per side, so 40 nozzles in total (plus a few spares for each rate). We will need to spray at 120 psi for Situation A and be prepared to shut off a few nozzles for Situation B. Situation C will require 100 psi and an entirely different nozzling and we will have to shut a few of them off for Situation D. Not only have we determined a nozzling solution, but we have revealed an efficient order for spraying the blocks that will require as little manual change to the sprayer as possible.

    Summary

    There is no one right answer to the question “which nozzles do I need” but there are certainly wrong answers. Bear this in mind when you buy a sprayer and the dealer offers you a factory-standard nozzle setup. Apply this process to your operation and be sure to use water sensitive paper to confirm the coverage and to make informed changes where required.

  • Centrifugal and Diaphragm Pumps

    Centrifugal and Diaphragm Pumps

    Press Play to hear the audio version of this article

    Adjusting Sprayer Settings

    Operators are encouraged to adjust airblast sprayer settings to conform to the variability in canopy size, density, spacing, and weather conditions. The efficiency and accuracy of the application is improved through the regular and independent adjustment of travel speed, nozzle output, and air settings.

    Airblast design is highly variable.

    Inflexible sprayer design results in a suboptimal match between equipment and crop. For example, sprayers intended to blow across multiple rows in a single pass are promoted for their high productivity, but typically compromise either coverage uniformity or drift control. In another example, low volume mist blowers utilize high speed air to atomize spray and are promoted as a means for saving water and/or pesticide. But, for many such sprayers, moderating air speed to reduce drift potential causes undesired changes to spray quality.

    Even with geared fans, many of Ontario’s airblast sprayers are overpowered for vines, canes, bushberries and high-density orchards. I am uncomfortable with manually obstructing the air intake or adjusting fan blade pitch for safety reasons. Fan gears and travel speed are excellent means for adjusting air energy. Alternately, we have sometimes had success reducing air energy by gearing the tractor up and throttling down (GUTD), but it’s only for very specific situations.

    It has been my experience that centrifugal pumps on axial airblast sprayers can undermine adjustment efforts when spraying small to medium sized canopies (i.e. not tree nut or citrus). In the case of GUTD, slowing the fan reduces pressure at the nozzle. Modest pressure regulation may be possible, but typically the operator must swap to larger nozzles to maintain flow. Hollow cone nozzles are only available in large flow increments (average 0.5 gpm), and stepping-up often results in excessive flow. The operator may be able to increase travel speed to compensate, but this frustrates the original intention by affecting dwell time: air settings must now be reconsidered.

    Within this context, why do some Ontario airblast operators still choose airblast sprayers with centrifugal pumps? Let’s consider Ontario’s Georgian Bay area, which many manufacturers, distributors and mechanics refer to as “the last bastion of the centrifugal pump in Canada”.

    Remember as you read on, Ontario’s airblast crops are predominantly small to moderate sized canopies. Centrifugal pumps are a common and appropriate pump for large canopies like tree nut and citrus.

    Airblast Pumps (in Ontario)

    The Georgian Bay region of Ontario.

    Airblast sprayer design is highly variable, featuring a diversity of pump styles. Piston (or plunger), peristaltic, tractor-hydraulic driven centrifugal pumps are but a few. Historically, piston pumps and centrifugal pumps on John Bean and FMC sprayers were the airblast norm in Canada.

    In the 1950s, Georgian Bay was home to Swanson Sprayers (now part of DW), who manufactured airblast sprayers featuring the Myers centrifugal pump. The sprayer was a good fit for the standard apple orchards found in the region. Huge canopies required high volume applications, and the rough and craggy bark harboured mites that drove the need for drenching sprays. To achieve this, sprayers traveled at 5 km/h (3.1 mph) on 7 m (24 foot) spacing, operating at 10 bar (150 psi) to emit as much as 3,750 L/ha (400 US gal./ac). At the time, a diaphragm pump could not manage this, even traveling at 0.8 km/h (0.5 mph).

    A Swanson Sprayer (This one likely from Georgia, USA).

    By the 1970s Holland’s Kinkelder air-shear sprayer (centrifugal pump) was introduced to Ontario and promoted as a way to use less pesticide. Perhaps ahead of their time, they never really took off because orchards were still too large for their concentrated (i.e. low-volume) applications. By the 1980s a wave of Italian-made sprayers (e.g. the Good-Boy or GB) featuring diaphragm pumps were imported into the Niagara region by distributors such as Rittenhouse.

    Similar to the Kinkelder, this was one of Ontario’s last KWH air shear sprayers. RIP 2018.
    The Italian-made Good-Boy (or GB).

    There were many cases of misuse as unfamiliar operators failed to grease direct-drive diaphragm shafts, ran the throttle beyond 540 rpm or diverted flow intended for agitation to increase flow to the booms. Decreased agitation in relatively large tanks left concentrated spray mix to clog suction filters and destroy the diaphragm pumps. It was an inauspicious start, but the diaphragm pump rallied and today we estimate that 90% of Ontario’s airblast sprayers have diaphragm pumps, while the rest are mostly centrifugal. One Ontario airblast dealer claims to sell 50 diaphragms for every centrifugal, but not in Georgian Bay.

    Is it regional history or a long memory of diaphragm “growing pains” that propagate the demand for centrifugal pumps? Perhaps considerations of maintenance, expense or ease of use play a role. Dealers claim that the centrifugal pump is cheaper, but these savings are offset by custom installation costs. Perhaps weather conditions or the crop morphology make centrifugal a better fit? Let’s consider the relative benefits and limitations of diaphragm and centrifugal pumps.

    Design

    Centrifugal Pumps

    Centrifugal Pump – Exploded View.

    Most centrifugal pumps prime by gravity feed which is why they are located at the bottom of the sprayer. While less common in Ontario, there are self-priming versions that reserve fluid in the case, or employ clever plumbing, permitting a more accessible location on the sprayer.

    Engine-driven centrifugal sprayers are artefacts in Ontario. The more common PTO-driven impeller operates at high speeds, requiring a >1:4 speed step-up mechanism (e.g. gearbox, pulley or hydraulic motor), and unlike diaphragms, they create smooth flow that does not require pulse suppression. While not technically required, most have a relief valve between the pump outlet and nozzle shut off valve to handle changes in pressure.

    Diaphragm Pumps

    Diaphragm Pump – Exploded View.

    Diaphragm pumps are self-priming and readily accessible because the shaft runs through the pump to power the fan at 540 RPM, with no need to step-up. Flow is directly proportional to pump speed which in turn depends on the tractor PTO speed. A pressure regulator is used to control bypass flow, which is convenient for making adjustments in nozzle output.

    Pump Flow and GUTD

    Centrifugal pumps are capable of higher flow at lower nozzle pressure and require more horsepower than diaphragm pumps. Note the large relative difference in flow for a centrifugal pump between the operating pressures of 90 and 100 psi (red curve shaded red) versus that of a diaphragm pump (blue curve shaded blue).

    Relative difference in flow versus PSI at constant RPM for a common Centrifugal (red) and Diaphragm (blue) pump. Shaded pressure represents 90 to 100 psi.

    Centrifugal Pumps

    The flow curve of a centrifugal pump drops off dramatically; pressure (not RPM) dictates flow. If you were to throttle back on a PTO-driven centrifugal pump, reduced flow would reduce the ability to build nozzle pressure. This means fan speed cannot be separated from nozzle pressure, and reducing air speed means re-nozzling.

    Centrifugal flow at different RPM. Shaded pressure represents 90-100 psi.

    While (unfortunately) still rare in Ontario, rate control monitors can be used (regardless of pump type) to calibrate output based on a target rate, speed and material flow using travel speed and flow sensors. Nevertheless, they cannot compensate for the aforementioned pressure loss at the nozzle if a centrifugal pump is throttled down to reduce air speed.

    In any case, throttling back on a centrifugal pump can cause a condition called suction or recirculation cavitation (aka pinging). Tiny high-pressure air bubbles form on the suction side of the impellor, explosively pitting the impellor. The damage is similar to corrosion and it causes vibration that will wear the pump prematurely.

    Any restriction on the inlet side (e.g. clogged suction strainer, collapsed/undersized line) can cause a loss of volume that can damage a centrifugal pump. “Dead-heading” (i.e. closing the outlet) is possible for a short period of time, but it quickly results in heat build-up which can cause damage.

    Diaphragm Pumps

    The flow curve of a diaphragm pump is flatter and more efficient; RPM (not pressure) dictates flow. If you slow the airblast fan by throttling the PTO below 540 rpm, flow decreases moderately, but surplus capacity allows sufficient flow to the nozzles without pressure drop. As long as the tractor does not lug, there is less noise, lower fuel consumption and therefore operator can typically adjust the air without having to change nozzles. Even if the flow changes the pressure regulator on the diaphragm pump can be used to adjust nozzle operating pressure, precluding a change in nozzle size. Convenient.

    Diaphragm flow at different RPM. Shaded pressure represents 90-100 psi.

    Diaphragm pumps are capable of high pressure, but are rarely operated above 150 psi in Ontario. Molded hollow cones (eg. TeeJet’s TXR or Albuz’s ATI) operate well in the lower psi range compared to pressure-loving disc-cores. Therefore, while regulators and springs are sized according to the pump’s maximum settings, they do not reflect the usage pattern. The relatively heavy spring is too stiff to compensate for changes in pressure (e.g. driving on hills or closing one boom) behaving more like a fixed bypass and undermining a calibration. The phenomenon is discussed more detail in this article.

    Maintenance

    Centrifugal Pumps

    A centrifugal pump with self-lubricating bearings and quality seals (e.g. carbide) that is maintained seasonally and operated in the best efficiency point of the curve will run reliably for many years.

    Proponents of the centrifugal pump claim they are low maintenance (compared to the diaphragm pump). This may be anecdotal, because of the pump’s out-of-sight position on the sprayer and their tolerance for neglect. A mistreated centrifugal pump fails by degrees, often forgotten until a seal leaks or a pressure drop is noticed. In the later situation, increased flow from nozzle wear can mask the problem as the sprayer continues to cover the same number of hectares. Often overlooked, worn or misaligned sheaves/belts on a centrifugal sprayer can also cause a loss of flow. Operators might notice a tail breeze that blows spray onto the belts can cause slippage and lower the nozzle pressure.

    Diaphragm Pumps

    Opinion is divided on the longevity and maintenance of diaphragm pumps. Some claim they are reliable and low maintenance as long as regular oil changes occur. Others suggest the complication of connecting rods, o-rings and valves require more upkeep than the simpler centrifugal. Unlike the centrifugal pump which merely loses pressure, failure on a positive displacement pump is complete and requires immediate repair

    Much depends on the diaphragm material and the products being sprayed. For example, corrosive materials (e.g. copper sulfate, urea, etc.) require polymer manifolds to minimize contact with metal. Metal manifolds do not weather well.

    The diaphragm pump can run dry for extended periods. This creates heat but does not often lead to failure. Failures occur from exposure to vacuum, which can happen with dirty suction filters or long and/or improperly sized suction lines, or even lack of oil support on the compression stroke (caused by over-revving).

    While three-cylinder designs may not require pulsation dampening, most require an accumulator to suppress the pulsing created by each stroke. Improper adjustment can lead to “hammering” that cracks mounts and valves, and can exacerbate rub-points on hoses. Diaphragm pumps that use direct drive shafts (i.e. carry the PTO to the fan) are subjected to the thrusting of the drive shaft during turns. It is important to keep them greased.

    Summarily, the longevity and maintenance requirements for either pump design seem about equal. They depend on the products being sprayed, the quality of pump materials, and adherence to the manufacturer’s instructions on correct usage and preventative maintenance.

    Conclusion

    Ontario’s airblast-specific crops have become smaller, closer and denser. High liquid volumes and air speeds are typically not required. Operators are encouraged to use Crop-Adapted Spraying to adjust fan speed and nozzle output to the crop and the weather. In my opinion, the diaphragm pump facilitates this, resulting in lowered input costs, reduced drift and improved coverage uniformity. I recognize that this requires skill and effort on the part of the operator, and setting-and-forgetting a centrifugal pump can be attractive, but it’s unacceptable if it leads to unnecessary environmental impact.

    In the end, the sprayer manufacturer chooses the pump, atomization and air-handling system while considering safety, effectiveness, reliability and price point. The operator must acknowledge the capabilities and limitations of the sprayer design when choosing the best fit for their operation.

    I still don’t know why regions like Georgian Bay seem to prefer one pump over another. Perhaps it’s simply herd mentality. Perhaps they know something I don’t. But consider: an airblast sprayer’s average lifespan is 30 years. That’s a long time to live with a decision.

    Choose wisely.

    Special thanks to the many dealers, manufacturers, engineers, mechanics and end-users that helped to inform this article.