Tag: plot

  • Calibrating a Plot Sprayer for Airblast Crops

    Calibrating a Plot Sprayer for Airblast Crops

    The calibration of handheld plot sprayers is an important part of agricultural research, and this article already covers all the bases… as long as you are spraying broadacre or row crops. But what happens when you are trying to emulate an airblast sprayer and treating a tree, bush, cane or vine?

    The key difference is that spraying a two dimensional area requires the operator to pass the boom over the target at a uniform height and pace to achieve consistent coverage. But, a three-dimensional target requires the operator to circle the target, or spray from both sides, until it has received the required dose (or volume).

    In order to scale down a typical airblast carrier volume for small plot work, we need to know three things:

    1. The area you wish to treat (e.g. bush, grape panel, tree, etc.), including it’s share of the alley (in m2).
    2. The emission rate from the calibrated plot sprayer (in US gal./min.)
    3. The airblast carrier volume you wish to scale down (e.g. L/ha).

    The illustration below shows two options for calculating the treated area. Option A requires you to measure from the outermost edges of the canopy (imagine if the canopy was wet and dripping – the dripline is that outermost point). It is less consistent than the preferred Option B, where the area is determined from row centres and planting distance.

    Two options for scaling down an airblast carrier volume for small plot work. Both produce the same treated area, but Option B is the preferred method.
    Use the average planting distance and row spacing in metres. For a panel of grapes, use the centre of each panel as the planting distance.

    If you are using a CO2 powered hand wand (preferred over a manual pump) with one or more hydraulic nozzles, then you can calibrate it using the methods in this article. There are battery-powered options from Jacto and Petra Tools, the latter offering a battery powered ULV system as well. Makita also has a battery entry (image below). However, if you are using a backpack mistblower, which better approximates an airblast sprayer compared to a hydraulic hand boom (see this article), it requires a different approach. Plus, you get to look like a Ghostbuster, which is a win in my book.

    PM001GL201 – 40V max XGT Brushless Cordless 15L Backpack Mist Blower (8.0Ah x2 Kit)

    Follow along in the following images as we explore how to calibrate a backpack step by step:

    When transporting a mistblower, use a loop of nylon cord to secure the boom in an upright position.
    For calibration, fill the completely empty sprayer with a known volume of water. If the boom is gravity-fed, be sure the feed valve is closed so the water doesn’t run out of the boom.
    With the sprayer on the ground, brace it with your foot. Step on the metal frame, not the motor housing or tank. Follow the operating instructions to pull start the motor.
    Being cautious of the hot exhaust, set the sprayer on a tailgate, or other elevated surface to facilitate strapping it on.

    Be aware that most mistblowers use gravity to feed the spray mix from the tank to the boom. A pressure pump kit is recommended for applications where the spray tube is held upward more than 30 degrees to maintain a consistent discharge rate. A hip belt is also recommended to reduce fatigue. Examples are shown below are for Stihl-brand sprayers. Some may or may not require the pump (e.g. Tomahawk) but they are primarily intended for mosquito control and in that case a consistent rate over a vertical plane may not be as important.

    If your sprayer does not have a pump kit, pointing the boom upward will cause spray to slow or even stop. This greatly diminishes your ability to reach high targets and achieve consistent coverage. In this case, attach the deflector (which comes with the sprayer) before proceeding with the calibration.

    Deflectors angle the spray upwards without having to lift the boom. This is easier on your shoulder and keeps the rate consistent.

    Set the flow rate to the preferred setting (usually a dial at the end of the boom), and using a stopwatch, time how long it takes to spray the entire volume. Be sure to move the boom exactly as you would when spraying the target, either side-to-side or up-and-down, to capture possible rate changes from the gravity feed. Convert the output to US gal./min.

    When timing output, move the boom as you would when spraying the target.

    Alternately, some people will stand on a bathroom scale with the backpack full. Then get off and spray for a period of time. Then get back on the scale. One millilitre of water weighs one gram, so you can calculate the flow from the weight difference.

    Now you know the area and the emission rate. You should have a target carrier volume in mind (e.g. L/ha). Using the following example, let’s determine how long you need to spray the target:

    A sample calibration.

    In this example, an ideal airblast Carrier Volume [C] for the orchard is 400 L/ha. We want to scale this down to determine the Volume for Treated Area [V]. First, divide [C] by 100 to convert it to 40 mL/m2. Then, because in Canada our nozzles are in US units, we do an ugly conversion: Since 1 mL = 0.000264 US gallons, [C] becomes 0.0106 US gal./m2.

    The Treated Area [A] measures 3.5 m by 2 m = 7 m2.

    The Emission Rate [R] is the rate the plot sprayer sprays. While we prefer using a mistblower, many still use a hand wand with no air assist. In this case let’s suppose we are using a hand wand with two 8002 flat fan nozzles operating at 40 psi. According to our calibration, we confirm it sprays 0.4 US gal./min.

    • [C](US gal./m2) × [A](m2) = [V] (US gal.)
    • 0.0106 US gal./m2 × 7 m2 = 0.074 US gal.

    We know we want to spray the target with 0.074 US gal., and we also know [R] which says our boom emits 0.4 US gal./min. We convert this to seconds by dividing by 60, so [R] = 0.0067 US gal./sec. From this we can calculate how long [T] we must spray the target.

    • [V](US gal.) / [R](US gal./sec.) = [T](seconds).
    • 0.074 US gal. / 0.0067 US gal./sec. = approximately 11.0 seconds.

    So, we know that to spray the target with an equivalent 400 L/ha, we must achieve consistent coverage from all sides by spraying it for a total of 11 seconds. Pro tip: Always mix a little more spray volume than you will need to account for priming.

    This is only one way to calibrate a backpack sprayer for spot spraying. If it’s isn’t quite what you need, check out these resources:

    1. Calibrating a Knapsack Sprayer (www.weedfree.co.uk – 2008)
    2. Don’t Overlook Backpack Sprayers (John Grande, Rutgers)
    3. Hand Sprayer Calibration Steps Worksheet (Bob Wolf, Kansas State University – 2010)
    4. Sprayer Calibration Using the 1/128th Method for Motorized Backpack Mist Sprayer Systems (Jensen Uyeda et al., University of Hawai’i – 2015)
    Pro Tip: To maintain a consistent boom height without a wheel, coil a measured length of wire from a plot marker flag to guide you.

  • Calibrating a Plot Sprayer

    Calibrating a Plot Sprayer

    It’s the rite of passage of many agricultural summer students across the world: applying experimental treatments to field plots using a research sprayer. The results of these experiments may be the basis of new product use registrations, or provide clues into future scientific studies. Needless to say, the application method needs to be bullet proof to ensure the results are reliable. Here are a few guidelines, starting with some tips:

    Pro Tips:

    1. When assembling a hand-held boom, ensure the threads are properly sealed using Teflon tape. More or less tape can be used to create a snug fit at the right part of the thread rotation.

    2. Choose nozzle bodies with diaphragm shutoff valves. These valves stop flow below 10 psi and prevent dripping of the nozzles after shutoff, without pressure drop during operation.

    3. Avoid the use of older style “check-valve strainers”. Although these also prevent drips, they create a pressure loss of about 5 psi which creates uncertainty around the actual spray pressure.

    4. Install a trusted pressure gauge on the handle of the sprayer in clear view for the operator. This provides important information. Don’t believe the gauge on the regulator. Ours, for example, is stuck at 30 psi.

    5. For hand-held booms, rotate the booms so that the nozzles point down, for each application. Different size people or height of crops will change this angle and make accuracy more difficult.

    6. Set the boom height so that you achieve 100% pattern overlap. This means that a nozzle’s pattern width should be twice the boom’s nozzle spacing. Boom height will be close to 50 to 55 cm above target, depending on fan. Too low, and the pattern may cause striping. Your supervisor will see that all year long and think of you.

    7. You can test the spray pattern by applying water to a concrete pad. At the right boom height, the entire boom width should dry at a similar rate.

    8. Install a visual guide for boom height. For example, place a wire flag at the end of the plot, at the correct height. This will provide a handy reference of boom height as your arms get weary. Or hang a wire, zip tie, or chain from a spot that doesn’t interfere with your spray pattern (thanks ACC).

    9. Minimize weight by using smaller bottles of CO2. We use 20 oz paintball bottles, they are much lighter, last long enough, and can be legally refilled with liquid CO2 or topped up with gas from a nurse tank in the field.

    10. Spray out leftover mix in a designated part of the plot area. Do not pour any mix on the ground. Please. Consider a biobed on your research farm.

    11. When completing a treatment, spray the boom completely empty so air comes out of each nozzle. This provides certainty that the next liquid at the nozzles is from the next bottle, be it water or another treatment.

    12. When spraying dose responses of the same product, always start with the lowest dose. Again, spray out in a designated place until the boom produces air, no need to flush.

    13. Construct a boom hanger from electric fence posts and coat hangers. Nozzles face down and can be serviced. The boom should never lie on the ground.

    14. Use nozzle screens to prevent time delays due to plugging. Usually 50 (blue) or 80 (yellow) mesh is sufficient. Any finer mesh may interfere with some dry formulations. Note: Beware old screens – ISO mesh colours have changed. Learn more here.

    15. It’s very useful to apply research sprays with low-drift nozzles. Air-induction tips are most effective. These reduce drift, and are also closer to the commercial spray quality used by producers.

    16. 01 size (orange) air-induced nozzles are available from Albuz (AVI Twin and AVI), Arag (CFA, CFAU, AFC), Billericay (Air Bubble Jet), Greenleaf (AirMix and TurboDrop XL), Lechler (ID3 and IDK). No other major manufacturer produces this small size of tips in air-induction.

    17. 015 size tips (green) and larger are produced by the above, as well as Albuz (CVI Twin and CVI), Hypro (GuardianAIR or ULD) and TeeJet (AIXR, AI, and TTI), within both manufacturers listed in order of increasing coarseness.

    18. Always carry several other nozzles of the same size and type already on the boom. Should a nozzle plug, replace it, don’t clean it. Clean it later.

    19. If a nozzle plugs and there is no extra nozzle, use compressed air to clean it. Compressed air electronics cleaners are available in most electronic stores.

    20. If a plugged nozzle can’t be cleaned, simply place it at the end of the boom and continue. Plot ratings and yields are usually taken from the centre. Remind your supervisor of this.


    21. Always de-pressurize a sprayer before disconnecting any liquid hoses. You can’t rely on check valves. If two people work together, make sure you practice and communicate this with each other.

    Calibration:

    1. Assemble the sprayer and run water through it to ensure it’s free from silt or residue. Repair leaks.

    2. Install nozzles and ensure none are plugged and the pattern looks good.

    3. While spraying water, set pressure to what you intend to spray with. (Note: boom pressure will be lower than regulator (attached to CO2 canister) by a few psi, hence the separate pressure gauge on the boom. Also note that the set pressure will always be higher when the system is at rest.)

    4. Obtain four containers of similar size that can hold about 500 mL, and place on ground at nozzle spacing. Using stopwatch, emit spray directly into all four for a set time, say 30 s.

    5. Expected spray volume at 40 psi: 01 tip, 380 mL/min; 015 tip, 570 mL/min; 02 tip, 760 mL/min. In other words, from a 2 L bottle you’ll not get much more than 30 s spray time from 4 tips.

    6. Measure collected volume from four tips using the same graduated cylinder.

    7. Repeat, for total of three times.

    8. Average three reps for each nozzle and convert to mL/min. Make sure all nozzles are within 5% of the average flow. Replace those that aren’t or place worst offender on outside edge of boom.

    9. Advance to “Calculations”, but be prepared to conduct another calibration

    Now for the fun part.

    Calculations

    There are three options for applying the correct amount. We’ll be using metric in these examples:

    1. Use the average nozzle flow from the calibration (mL/min) and the target application volume (L/ha) to calculate the necessary walking speed (km/h);

      or
    2. Use the flow from the calibration and a set walking speed to arrive at an application volume;

      or
    3. Use a set walking speed and a set application volume to calculate a required calibrated flow.

    Option 1:

    Walking Speed = (60*flow)/(Volume*nozzle spacing)

    If your nozzle flow was 330 mL/min and you wanted to apply 100 L/ha using a sprayer with 50 cm nozzle spacing, your required walking speed is 60*330/100/50 = 3.96 km/h

    Option 2:

    Application Volume = (60*flow)/(Speed*spacing)

    If your nozzle flow was 330 mL/min and you wanted to walk 5 km/h using a sprayer with 50 cm nozzle spacing, your application volume is 60*330/5/50 = 79 L/ha

    Option 3:

    Required flow = (Speed *Volume*spacing)/60

    If your speed is 5 km/h and you wanted to apply 100 L/ha using a sprayer with 50 cm nozzle spacing, your required flow is 5*100*50/60 = 417 mL/min

    If you selected Option 3, you now need to return to your sprayer and find a nozzle, or a pressure, that delivers an average of 417 mL/min. You can use math to get into the ballpark with the nozzle you already have:

    New Pressure = (required flow/calibrated flow)2*calibrated pressure

    If your required flow is 417 mL/min and the calibrated flow is 330 mL/min, and you calibrated at 30 psi, then you should be close to your required flow at (417/330)2*30 = 48 psi

    Now, return to your sprayer, set the pressure to 48 psi, and confirm this estimate.

    We use Option 3 when comparing nozzles of the same size but from different manufacturers. It’s not uncommon for these to have slightly different outputs. Rather than adjusting our walking speed slightly, which is very difficult to do accurately, we change pressure slightly so all nozzles produce the same flow. This is also useful when comparing water volumes by switching to a larger nozzle.

    Travel Speed:

    The last step is to confirm travel speed. Say you want to walk at 5 km/h. The best way to calibrate walking speed is to measure a known distance (m) in the field you’ll spray. Wearing the gear and carrying the sprayer you will use to spray, walk this distance. Use a wire flag to mark the start and end points; when the boom hits the flags, start and stop the timer. Repeat until comfortable.

    Time needed to walk distance:

    Time (s) = Distance *3.6/required speed

    Say your walking distance is 10 m, and you need to walk 5 km/h.

    10*3.6/5 = 7.2 s

    A simple spreadsheet that can be used for the calculations can be found here.

    Congratulations! You’re done. Happy spraying! Remember to not worry too much about a 5% deviation from your expected application. That’s definitely an acceptable error, as long as you don’t allow too many of those to add up.

    Low Volume Research (Aerial)

    Some product uses are by air, and the label volumes for those are often 30 to 50 L/ha. Registrants need to provide efficacy data at those volumes. Ground application can be accepted as a surrogate for aerial as long as the volumes are correct.

    Since the spray nozzles aren’t typically available below the 01 (orange) size and if they are, they usually plug so easily and make such a fine spray that they’re frustrating to use. The alternative, to travel faster, is also problematic on research plots.

    We recommend that Turbo TeeJet nozzles be used for this purpose. They produce such a wide fan angle that a 100 cm spacing is justifiable. Simply cap off every second nozzle body. Booms need to be elevated to ensure overlap, for uniformity. The value of the small nozzles and wider spacings is the low total application volume that is now possible.

    The TT tips can also be used at fairly low spray pressures (say 20 psi) further reducing their output.

    Spray Quality of TeeJet Turbo TeeJet (ASABE S572.1). This tip is available in smaller sizes and, due to its wide fan angle, can be used at 40″ (100 cm) spacing, therefoe applying low water volumes.

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  • Venting Liquid-Filled Pressure Gauges

    Venting Liquid-Filled Pressure Gauges

    Liquid-Filled or Dry?

    Small-plot agricultural sprayers should have a pressure gauge on the wand or boom to ensure accurate application rates. Most are added after-market and the operator has the choice of buying liquid-filled or dry gauges.

    Glycerine- or silicone-filled gauges are preferred because they dampen pressure spikes, pulsation and mechanical vibration. Compared to dry gauges, they are available in higher ranges and are less prone to moisture problems (which cause corrosion, accuracy and visibility issues).

    We use 100 psi (~7 bar) liquid-filled gauges for our handheld sprayers. Only recently did we acknowledge the sticker affixed to the glass advising the user to cut the nipple off the rubber plug located at the top. Preferring to avoid messy leaks, we have always left it intact.

    We wondered what impact, if any, this was having…

    What are Vents?

    Expensive gauges have mechanical vents that can be opened prior to use and closed to retain liquid when stored. More commonly, there is a rubber plug with a protrusion (referred to as a nipple).

    Why Vent?

    Mechanical, liquid-filled gauges are sealed to keep the liquid in. When there are temperature fluctuations, the liquid expands or contracts and creates “case pressure”. This exerts a force that interferes with the pressure reading.

    According to Marshall Instruments, case pressure can offset the accuracy by approximately 1 psi (0.07 bar) for every 35˚F (20˚C) temperature change, but is only noticeable when measuring lower pressures (0-15 psi or 0-1 bar). Nevertheless, they advise all gauges should be vented prior to use.

    The plug can be removed to allow the user to refill the gauge, maintaining an air space of about ½” at the top of the window. If the nipple is cut off, the gauge is permanently vented and will leak if the gauge is not kept vertical.

    Testing

    We performed an experiment to see if typical working temperatures had a practical impact on the accuracy of an unvented gauge. We suspended an unvented, liquid-filled gauge upright in a water bath at approximately 15˚C, 30˚C or 45˚C (59˚F, 83˚F or 113˚F) until it equilibrated. The high temperature may seem unreasonable, but gauges left in trucks on summer days get far hotter.

    The gauge was quickly removed and placed in a manometer (Ametek T-975) where it was subjected to pressures of 15, 30 and 45 psi (1 bar, 2 bar and 3.1 bar) and readings recorded. This was repeated five times. We then vented the gauge and repeated the process.

    Results

    At first, there appeared to be very little difference in average accuracy of vented and unvented gauges. Accuracy refers to the closeness of a measured value to a standard or known value. Perhaps there was some small increase in the pressure reported by an unvented gauge, but very little practical difference.

    However, when we look at variability we get a different picture. Variability is a measure of precision, which refers to the closeness of measurements to one another. The graphs show that an unvented gauge has greater variability (less precision) at lower temperatures and lower pressures.

    A good way to think of accuracy and precision is using the classic archery bulls-eye metaphor. The unvented pressure gauge is best represented by the third image, where it is accurate (on average) but not precise (variable).

    Real-World Example

    What does this mean in practice? Consider someone spraying a small plot using a TeeJet XR8002 nozzle on a CO2-powered hand boom at 30 psi. The difference in output between 30 psi and 40 psi is about 0.003 gpm / psi.

    An unvented pressure gauge used on a hot day may read 1.5 psi lower, causing you to overcompensate and raise the pressure 1.5 psi higher than intended. That would result in 0.0045 gpm (0.5%) more applied. Compensating for an unvented gauge on a colder day might be closer to 0.009 gpm (1%) more applied.

    Assuming a walking speed of 3.1 mph (5 km/h) and a swath of 20” (50 cm), the nozzle should emit about16.3 gpa at 30 psi. Unvented in the heat, that’s 16.7 gpa. At 33 psi, that’s 17.15 gpa. That’s almost 1 gpa more than intended. Potentially, the lack of precision could make a significant difference.

    Conclusion

    • Liquid-filled gauges are preferred over dry gauges.
    • To ensure precision, the gauge should be vented prior to use.
    • Permanent venting on a hand-held sprayer causes leaks, which is a nuisance, so we suggest simply lifting the edge of the plug with a screwdriver or fingernail to vent the gauge prior to each use.

    This work was performed by OMAFRA summer student, Aidan Morgan.

  • Plot Sprayer Calibration Worksheet

    Plot Sprayer Calibration Worksheet

    Need a worksheet for calibrating a plot sprayer? Well, we just so happen to have one here:

    Plot Sprayer Calibration (May 15, 2018)