Author: Jason Deveau

  • Selecting a Sprayer Pump

    Selecting a Sprayer Pump

    When I had to replace a pump on a small scale sprayer, I had a lot of questions about how they worked, their capacities, hose sizes, mounting solutions and fittings. I turned to the Pentair Hypro Shurflo catalog and found a very helpful guide on pages 2 – 10. This article summarizes the steps recommended in the catalog.

    Select Pump Style

    Sprayer pumps can be divided into two categories: Positive Displacement Pumps and Non-Positive Displacement Pumps.

    Positive Displacement Pumps

    These include Roller, Diaphragm and Piston pumps. They are self-priming and traditionally operate at high pressures. Flow from these pumps is directly proportional to the pump speed, which is why they require a relief valve and bypass line between the pump outlet and the nozzle shut-off valve.

    • Roller pumps : This is the most popular pump with farmers world-wide. The seal and roller materials should be selected based on their compatibilities with the pesticides.
    • Diaphragm pumps : These compact pumps are popular for use with abrasive and corrosive pesticides. Their oil-filled piston chambers protect the pump materials.
    • Piston pumps : Similar to car engines, these pumps are relatively low-flow and high-pressure and suited for use with handguns sprayers. The piston cup materials should be selected based on their compatibilities with the pesticides.

    Non-Positive Displacement Pumps

    These include Turbine (or Transfer) and Centrifugal pumps. They must be primed and traditionally operate at low to medium pressures, although there are models available that can go up to 190 psi. Flow from these durable pumps comes from a rotating impeller that feeds liquid through the lines instead of pumping “per stroke”. Therefore, if the outlet is closed for brief periods, the impeller spins harmlessly, so a relief valve is not needed.

    Determine PTO Pump Drive

    When selecting a pump, you must specify the shaft rotation. Hypro suggests two steps for determining the required rotation:

    1. Eyes on the End: Face the rotating Power Take-Off (PTO) and determine if it is spinning clockwise (CW) or counter-clockwise (CCW).
    2. Opposites Attract: The pump must rotate opposite to the PTO. For example, if the PTO rotates CW, then the pump must rotate CCW and vice versa.

    You should also be aware of your tractors’ horse power, and in order to determine the size of pump shaft, you should know the spline dimensions (e.g. 1-3/8″ (6 spline) pto shaft or 1-3/8″ 21-spline pto shaft).

    Determine Pressure and Flow Requirements

    In order to size the pump, you have to know the sprayer settings, such as intended application rate, average ground speed, agitation requirements, etc. Most can be calculated form the following formulae (provided in US and Metric units):

    Calculating Agitation Requirements

    • Liquids :

    Tank Volume (US gal.) × 0.05 = Agitation Requirement (gpm)
    Tank Volume (L) × 0.05 = Agitation Requirement (L/min.)

    • Wettable Powders and Flowables

    Tank Volume (US gal.) × 0.125 = Agitation Requirement (gpm)
    Tank Volume (L) × 0.125 = Agitation Requirement (L/min.)

    If the sprayer has a hydraulic agitation system equipped with a jet, it multiplies the agitation output without the need for additional flow. For example, it might have a 1 gpm input flow and boost it to a 10 gpm output. This savings should be accounted for:

    Agitation Requirement (gpm) × (Input ÷ Output) = Total Agitation (gpm)
    Agitation Requirement (L/min.) × (Input ÷ Output) = Total Agitation (L/min.)

    Therefore, if you calculate a 60 gpm requirement for agitation, and have a jet that boosts the output 3:1:

    60 gpm x (1 / 3) = 20 (gpm)

    Calculating Nozzle Requirements

    Once the agitation requirements are accounted for, you have to account for nozzles. The calculations are a little different for each sprayer, but they amount to the same thing – Total flow in US Gallons per minute or Litres per minute. Here is the calculation for a boom sprayer. For an airblast sprayer, assuming you are spraying every row, substitute “Row Spacing” for “Boom width”.

    Total Flow Requirement (gpm) = [Output (gpa) x Ground Speed (mph) × Boom width (ft)] ÷ 495

    Total Flow Requirement (L/min.) = [Output (L/ha) x Ground Speed (km/h) × Boom width (m)] ÷ 600

    When the flow requirement for agitation and the flow requirement for the nozzles have been calculated, they are added together. It is important not to under-size the pump, so always factor in an extra 20% to compensate for changes in performance (such as pump wear and slower ground speeds) and restrictions in the plumbing systems that can cause pressure drops between the pump and nozzles, as follows:

    (Agitation Requirement + Nozzle Requirement) × 1.2 = Total Flow Requirement

    Finally, be sure to account for any other flow requirements, such as tank rinsing nozzles and hose length/diameter (which causes pressure drops), and have some idea how you want to place the pump relative to the tractor and sprayer. If you prepare all this information, you can quickly and easily discuss your options with the retailer and select the pump that best suits your needs.

    For more information on various types of pumps, check out this article by Dr. Bob Wolf:

  • Pressure Spikes and Relief Valves on Air-Assist Sprayers

    Pressure Spikes and Relief Valves on Air-Assist Sprayers

    A properly-sized pump should produce more flow than is needed and work in conjunction with the atomizers to regulate that flow. Typical to high pressure pumps, a piston relief valve (aka regulator) should maintain the desired system pressure through the normal speed range of the sprayer, regardless of the number of booms (or boom-sections) that are on or off. This is achieved by balancing the sprayer pressure against the relief valve spring, which must move freely across a range of flows.

    But what does it mean when the pressure gauge briefly spikes off-scale when boom are turned on or off? This is bad for the gauge and will eventually cause it to fail. Quite often, pressure spikes are an indication of one of two things:

    • A dirty or stuck valve
    • An inappropriate spring size
    A pressure gauge spiking beyond its range.
    A pressure gauge spiking beyond its range.

    Relief valve maintenance

    Sometimes, pressure spikes indicate a need for valve cleaning and maintenance.

    • The regulator spring cavity may be packed with dirt, which limits valve travel. Clean the housing and spring, and then lubricate and adjust.
    • The regulator may be partially seized or sticky. If the regulator piston and cylinder bores are caked with spray they will ‘hold’ the valve until the pressure/spring balance overcomes the friction.
    • Sometimes valve, and/or the valve guide pin are seized. Disassemble them, clean all sliding surfaces, then lubricate and adjust.
    • Valve/seat wear may have created a leak. You may have already tightened the spring to compensate, but this loads the spring past the pressure balance point you want to spray at. This means that when the booms are shut off, the pressure increases until it reaches the ‘new’ spring balance point. Repair (or replace) the regulator, then lubricate and adjust. Be aware that any leak (external or internal) can contribute to this condition and tightening the spring isn’t the solution.
    • The spring may be damaged (e.g. bent, corroded, etc.). Replace the spring, lubricate and adjust.

    Note: Be sure to read the operator’s manual before you do anything. You should understand your sprayer’s design before you perform any maintenance, adjustments or calibration.

    Spring size

    Sometimes, the relief valve may be mechanically sound, but the spring may not be sized to match a reduced operating pressure. Relief valve springs match the maximum pressure range of the pump. Sprayers operated at lower pressure may be unable to compress the spring. This is common when people switch from disc-core nozzles operated at higher pressure to molded nozzles operated at lower pressure.

    This would manifest when one boom is shut off for single-boom operation; there may not be enough pressure to open the bypass. As a result, flow increases over the remaining boom.

    Recognizing this problem, some operators have teed-in a second relief valve capable of finer adjustments at lower pressures. Make sure you know what you’re doing if you’re considering this option.

    Technically, a spring can either be too weak, or too heavy:

    • The spring may be too weak for the pressure being used (i.e. any adjustment bottoms out). In order to obtain sufficient pressure the operator tightens the spring until it is virtually collapsed, essentially creating a fixed orifice. When the booms are closed the ‘fixed orifice’ doesn’t compensate and pressure rises to force the increased flow through that small orifice.
    • If the spring is too heavy for the pressure being used (any adjustment barely touches the spring when pump is turned off). In this case, the pressure being used will not deflect the spring, so the operator closes the regulator until the ‘fixed orifice’ creates sufficient restriction to flow to achieve the desired pressure. When the booms are closed the ‘fixed orifice’ doesn’t compensate and pressure rises to force the increased flow through, or until the spring begins to deflect.
    • In either situation the spring must be sized so it is in the centre-third of its flex range (i.e. rest state > fully collapsed) at the desired pressure. You can buy springs from the sprayer dealer or hardware supply. Try to maintain original length and diameter of the coil, while varying the diameter of the wire.

    Engineering

    In some cases, it is not a matter of valve maintenance, or spring size, but poor engineering. Consider the following:

    • The valve supply and return may be too small for the pump flow. Consult hose and fitting catalogs for flow capacities and lengths. Re-size the hoses and fittings appropriately, and then adjust the regulator.
    • There may be kinks or sharp bends in in the supply and return lines. Re-route the hoses and/or fittings to avoid kinks and sharp bends, and then adjust the regulator.
    • The relief valve may be too small for the pump flow. Consult a regulator catalog for flow capacities and replace the regulator with an appropriate size. Calibrate the regulator spring and adjust.
    • Relief valves have a ‘cracking’ pressure (that’s when the valve just starts to open). Well-designed regulators have small pressure changes from ‘cracking’ to full flow. That information is in their catalogs. Poorly designed regulators have large pressure changes between these two ratings and these regulators should be avoided.
    • The pump may be too big for system. This often happens when sprayers are upgraded and pumps are replaced. Consult the catalogs and reduce pump size or speed, or increase the sizes of the hoses, fittings and regulator.
    • There may be a hydraulic agitator jet on the regulator ‘tank’ line. An agitator jet applies considerable back pressure to a system, and when booms are closed the increased flow causes more than a linear increase in pressure.
    • Broadly, the sprayer system as a whole may be poorly engineered. Inspect and draw a flow path of the sprayer system. Examine where everything is going (or not going). Is it possible someone made changes that the manufacturer did not intend? Consult the manufacturer if you are uncertain. Sometimes, it will have to be re-engineered, which may require expert consultation.

    Note: Your pressure gauge can tell you a lot more than your operating pressure – it can indicate a problem with your regulator, pump, lines or overall sprayer engineering. Don’t ignore it – address it.

    Thanks to Murray Thiessen, Consulting Agricultural Mechanic, for his contribution to this article.

  • Sprayer Wheel Maintenance

    Sprayer Wheel Maintenance

    This article was co-written with Murray Thiessen, Consulting Agricultural Mechanic.

    Sprayer wheel assemblies should be cleaned and inspected as part of regular annual maintenance. Wheel bearing maintenance before long-term storage may prevent water from corroding the bearings. The exploded diagram details the parts found in a typical trailed air-assist sprayer wheel assembly.

    Exploded diagram of typical airblast sprayer wheel assembly.
    Exploded diagram of typical airblast sprayer wheel assembly.

    The following procedure was performed on a 2012 Durand-Wayland sprayer by Mr. Murray Thiessen, Consulting Agricultural Mechanic and renowned “Sprayer Whisperer”. The steps are applicable to most sprayer makes and models. The entire process should take approximately half-an-hour per wheel.

    Step 1

    Empty the sprayer and park it in a well-lit, level spot. Un-hitch the tractor and raise one side of the sprayer using a bottle or floor jack to clear the wheel. Secure the sprayer with a jack stand.

    Raise with one jack, secure with another.
    Raise with one jack, secure with another.

    Step 2

    Remove the lug nuts and take the wheel off the hub. Do not remove the wheel and hub together because it is heavy and you might bang the delicate seal on the spindle. Check the wheel rim for signs of corrosion or distortion (often caused by either loose or over-tightened lug nuts). Check the tread for wear or cuts and check the tire pressure.

    Remove the lug nuts and take the wheel off the hub.
    Remove the lug nuts and take the wheel off the hub.

    Step 3

    Remove the hub cap and pull out the cotter pin. Then remove the nut and washer that hold the hub on the spindle. Put all the small parts in a plastic container with some de-greaser (e.g. Varsol) to clean the parts and keep them from getting lost.

    Remove the nut and washer that hold the hub on the spindle.
    Remove the nut and washer that hold the hub on the spindle.

    Step 4

    Knock out the seal and hub bearing and put them in the plastic container. Unless it is damaged, there should be no need to remove the bearing cup (or race) from the hub. The seal is designed to keep dirt out of the assembly, not to keep grease from escaping. Be sure to note which way it is facing. The seal is often ruined during disassembly; have a replacement on hand.

    Knock out the seal and hub bearing.
    Knock out the seal and hub bearing.

    Step 5

    Clean the old grease out of the hub. This hub has too much and it has filled much of the air space (or cavity) within the hub. That air space is provided so grease is not forced out as the hub heats up, and so dirt is not pulled in as the hub cools. Note the colour of the grease – if it is black and stains your hands, it has burned because too much grease has caused overheating. Look for evidence of dirt or water in the bearing, which indicates seal failure.

    Clean the old grease out of the hub.
    Clean the old grease out of the hub.

    Step 6

    Wipe dirt from the spindle. Never pressure-wash wheels when they are on the spindles because the spray drives dirt and water past the seal and into the hub. Inspect the sealing surface of the spindle for damage or wear.

    Wipe dirt from the spindle.
    Wipe dirt from the spindle.

    Step 7

    Clean the seal thoroughly. Seals are easily damaged and may need replacement.

    Clean the seal thoroughly.
    Clean the seal thoroughly.

    Step 8

    Clean the hub bearing. Compressed air is a good way to get all the old grease out, but do not spin the bearing with the air.

    Clean the hub bearing.
    Clean the hub bearing.

    Step 9

    Look for scratching, pitting or blue metal (indicating heat). This scorch mark indicates the bearing was moving on the spindle, and the friction created heat. Agricultural wheel bearings do not fit tight to the spindles. If there is too much clearance, the bearing race will turn on the spindle where it is not supposed to.

    Look for scratching, pitting or blue metal (indicating heat).
    Look for scratching, pitting or blue metal (indicating heat).

    Step 10

    Repack the bearings, reassemble the hub and re-grease the hub. Bearings should only be ~40% full. Too much grease creates heat and does not let the bearing roll properly. Too little increases friction. No matter which grease you choose to use, never combine greases; they may not be chemically compatible.

    Re-pack and reassemble.
    Re-pack and reassemble.

    Step 11

    Mount the hub tightly on the spindle. Replace the washer, cotter pin, nut and cap. There is no need to bend the arms of a cotter pin all the way back – it weakens the metal. Just bend one arm to 90° and cut off the excess. Use anti-seize on the wheel pilot to make the rim easier to remove next time.

    Mount the hub tightly on the spindle.
    Mount the hub tightly on the spindle.
    Some airblast sprayers (such as this Durand-Wayland) have wheel assemblies that can be rotated to four different positions in the chassis. This will raise or lower the sprayer to better align it with the tractor hitch and PTO shaft.
    Some airblast sprayers (such as this Durand-Wayland) have wheel assemblies that can be rotated to four different positions in the chassis. This will raise or lower the sprayer to better align it with the tractor hitch and PTO shaft.

    Step 12

    Replace the wheel and rim. Do not grease the lug nuts or they might loosen. Over- or under-torqueing lug nuts can cause damage. Look in the manual for your correct torque and consider using a torque wrench. Tighten the nuts in a star-shaped pattern – not sequentially.

    Replace the wheel and rim.
    Replace the wheel and rim.
  • Airblast Nozzles – On or Off?

    Airblast Nozzles – On or Off?

    Spray that is not directed at the target is wasted spray. Many pesticide labels specifically require the operator to restrict spray to the target canopy. Spray that escapes above the canopy is a significant source of off-target drift. Foliar applications that extend below the canopy are not efficacious and represent waste and lost productivity.

    A spring application or oil and chloropyfiros. Estimate of 50% waste (in red).

    Air carries spray droplets, so the first step in any adjustment should be to perform a ribbon test to ensure the air outlets are oriented correctly. This is achieved by adjusting deflectors (e.g. low profile axial), the air outlets on a tower, or the entire head on a wrap-around design with individual fan/nozzle combinations.

    Spray height should always exceed the canopy height by a small degree. This compensates for the increase in wind speed with elevation, the potential loss of spray height with faster travel speeds, and uneven alleys that cause the sprayer to rock, which changes the spray angle.

    Spray angles change as a sprayer rocks on uneven alleys. It is more important that spray is directed at the top of a canopy than at the bottom.

    It is less critical that spray align with the lower portion of the canopy. As air energy wanes, or as droplets begin to lose momentum, finer droplets will slowly fall, depositing on random surfaces. Coarser droplets will quickly fall towards the bottom of the canopy, settling primarily on upward-facing surfaces. This secondary deposition can also occur from the cumulative impact of blow-through from upwind rows.

    Once the air is aligned, park the sprayer in an alley. Stand behind the sprayer and extrapolate a direct line from each nozzle to target canopy. Nozzles that point at the canopy should be left on. Nozzles that point above or below can be blocked, or turned off via valves or rotating roll-overs. Some roll-over nozzle bodies can be swiveled up or down 15 degrees to fine tune the spray angle. An alternative would be to permanently rotate the nozzle body fitting in the boom line. When aiming nozzles using a roll-over nozzle body, be careful not to swivel them too far or the valve will partially close and compromise the spray pattern.

    Use a ladder when adjusting nozzles on a tower sprayer. Some sprayer chassis and tanks are designed to accept a climber, but even so they can be slippery. Please be careful.

    When extrapolating, remember that the centre of a nozzle only indicates the centre of the spray pattern. Cone and fan angles can span 60 to 110 degrees, depending on the influence of air. Therefore, even though the centre of the lower-most nozzle intersects the bottom of the target canopy, you may still be able to turn it off because the nozzle above has that portion covered.

    Adjust spray distribution across the boom at the beginning and roughly mid-way through the spray season to ensure the sprayer will uniformly cover the target with the optimal volume. These adjustments should account for both canopy growth and fruit set.

    For example, as the season progresses in an orchard, fruit may cause limbs to hang lower and warrant a new spray distribution. Turning on the bottom nozzle position will help, but it doesn’t account any increase in density throughout the canopy. You may need more volume distributed across the entire boom. Another example: as grape bunches begin to close, sprayer operators may direct fungicides exclusively at the fruit zone and not the entire canopy.

    Remember to always check coverage using water sensitive paper. It’s not worth saving a bit of spray if you’re missing a bit of your target.

  • For Sale: Gently Used 1950s Boom Sprayer

    For Sale: Gently Used 1950s Boom Sprayer

    This article isn’t about best practices, or social contracts, or innovative new technologies. It’s just a fascinating bit of history. If it has any moral at all, perhaps it’s to remember where we came from. I wonder where we’ll be tomorrow?

    Let’s be clear – the practices described in this article are anachronistic and while I shouldn’t judge from my 2020 high-horse, they’re flat-out terrible. Don’t see them through nostalgic eyes. Instead, be thankful that sprayers and practices have evolved.

    Here’s the background. A colleague of mine, a grower and well-respected pesticide safety / sprayer expert, recently held a farm auction in Innerkip, Ontario. He sent me a photo of his family sprayer, used in Oxford county in the 50s and 60s. I fell in love with it.

    It was used to control broad leaf weeds in cereal crops. He recollected that thistle was a particularly painful issue. Especially when you had to grab hold of the grain sheaves and stook them. I confess I had to look up the term “stook“. They also sprayed a few cereal acres for neighbours, but never too far from home.

    A 1950s barrel sprayer. The frame would be attached to the front of a Massey Harris 44, suspending the 21 foot wet aluminum booms. The drum was supported on the tractor tongue. When you shut down, you picked up the booms and hung them on the fenders. The booms then leaked all over until they were empty.
    Fortunately, there was clear guidance for the operator. The speed and rate was written on the distribution head. Still somewhat legible.
    A rod would extend from distribution head to the tractor, supported on the steering column. The driver could select the boom: left, right, both or off. The distribution/filter head/pressure gauge (shown here) was supported on front of tractor. On the up side, there was no need for the driver to do a shoulder check. Here the distribution selector is set to ‘off’. The filter, shown here as well, was a metal screen wrapped in a cotton cloth (typically a flour bag).
    This is the line from the pressure side of the pump, entering the distribution unit. The butterfly screws made a tight connection… using canning jar rings as gaskets!
    Both the cotton bag on the filter and the pressure line were sealed with canning jar rings.
    When the broadcast work was done, they would set up a hand boom and spray the fence posts. Bare hands were the order of the day.
    Spraying the fence posts was a two-person job, with a driver in the tractor and a kid aiming the boom. Here’s a close-up of a flat fan nozzle on the hand boom.
    Here is the supply drum with opening for suction hose and screen. It served double-duty as pesticide tank and seat for the person holding the hand boom. Pesticide swished out onto the person sitting on the drum. Getting their butt wet as a matter of course. The drum was filled with a 1/2 inch hose right from the well.

    When the long season was through, it was over-wintered (with whatever spray liquid remained) in the cellar.

    We’ve come a long way.