Tag: airblast

Optimizing Sprayer Air Settings – Part 2
This is part two of a two part article on how to optimize the match between the sprayer air and the target canopy. You can find the first part here. For a more fulsome description of the process, consult chapters 3, 9, 10, and 11 of Airblast101.
A close up of an airblast gear box. There are usually two options – high or low.
Evaluating air energy – Ribbon test part 2
Air behaviour can change radically between stationary operation and driving. We learned in part one of this article that slower travel speeds increase the throw and the spray height. The simplest way to monitor where air is going is for a partner to watch the leaves in the target canopy. Leaves that are ruffling indicate that air is reaching them.
A more informative method, and one that works during dormancy, requires a length of flagging tape tied to the end of a long stick. The partner (wearing eye and ear protection) can move the ribbon around in the air wash, extending it into areas of interest. The ribbon’s behaviour will indicate gaps, the air angle and relative air energy. The ribbon can be interpreted using the following figure.
Work with the sprayer oriented to blow into any crosswind. Extend the ribbon into the sprayer air while the sprayer is stationary, or preferably, while driving. The ribbon’s behaviour will show what you couldn’t otherwise see. Here are a few possible outcomes: A. The angle and air energy are appropriate while the sprayer is stationary. B. The air energy is not sufficient to reach the tree top when the sprayer is driving. C. Obstructions or deflector misalignment can create gaps. D. Air is angled too low for the target canopy.
Evaluating canopy penetration – Ribbon test part 3
This final diagnostic accounts for the influence of any intervening canopy (or canopies for multiple-row strategies). It confirms that the air energy has the potential to carry droplets the full extent of the swath. Evaluating one side will give you a lot of insight but if you have the time it’s better to do both sides. Since most sprayers have at least some imbalance in air handling, the results may surprise you.
1. Choose a canopy that is upwind and on the lift side of the sprayer (if applicable).
2. Move the sprayer a distance into the row to allow it to reach target speed and to avoid wind effects on the periphery.
3. Attach 25 cm (10 in.) lengths of flagging tape on the far side of the target canopy. Do this at the top, middle and bottom of the canopy. In tall canopies this might require a ladder, telescoping pole, or sections of galvanized pipe to raise the ribbons.
4. With deflectors/spray outlets adjusted and the desired fan gear (or fan speed) selected, start the air without spraying and bring the sprayer up to the target travel speed. A partner wearing eye and ear protection will stand in the next alley and observe the ribbons as the sprayer passes (preferably recording a video for the operator).
Three ribbons are positioned on the far side of the upwind target canopy. In this case, an every-row traffic pattern is depicted. The observer watches or records the ribbons as the sprayer drives past with the air on (not the spray). For an every-row traffic pattern, the air energy is too high if the ribbon strains at 90⁰. It is ideal for the ribbon to briefly flutter (0⁰-60⁰). If the ribbon does not move (0⁰), the air energy may still be sufficient as long as it penetrates to the centre of the canopy. This is often the case with particularly dense/wide trees like nuts and citrus.
Tying ribbons on the up-wind side in an apple orchard just past green-tip. The red vest has lots of pockets to hold supplies and sprayer operators can see it clearly for safety. The Hawaiian shirt is because it was a Friday.
Repeat this process this for EACH significantly different crop sprayed with the sprayer. As with air direction settings, multiple set-ups might be needed to reflect each block, or you might choose to group of similarly-sized blocks and calibrate air to the worst case scenario. Record the set-up for each sprayer/block combination and keep a copy in the tractor cab(s).
Interpreting the ribbon tests
Interpreting the ribbons is not always straightforward. When they don’t behave as anticipated they may be indicating one or more of the following problems:
1. The air angle is incorrect.
2. The air energy is too low.
3. The air energy is too high.
There might be a single cause or several contributing factors. As you diagnose and attempt to correct these problems be aware that addressing one may create others. If the problem cannot be corrected, the sprayer configuration (or design) may be inappropriate for the canopy or the environmental conditions.
Ribbons that don’t point from the sprayer to the canopy may indicate a misalignment of spray outlets or deflectors. The bottom of the air should align with the bottom of the target. More critically, the top of the air should slightly overshoot the top of the target. We want to avoid spray drift, but we must account for wind speed increasing with height and vertical booms that rock on uneven alleys. If the spray does not slightly overshoot the top of the target, it may miss it entirely.
Adjusting horizontal alignment, when possible, can significantly impact sprayer performance. It can be tricky to optimize the angle because it represents the sum of several complicated interactions. Air outlets on wrap-around sprayers may be positioned too close to the target canopy to permit a ribbon test. However, you can still use the ribbon-on-a-stick technique to visualize how the air is behaving. Consider the following when positioning air outlets on either side of a canopy:
Unresponsive ribbons are often observed during a ribbon test. Depending on where the ribbon is located, this may or may not indicate a problem. Ideally, the top ribbon should always move in response to sprayer air. In larger canopies, this location represents the greatest distance sprayer air must travel and the highest wind speed it will encounter. The middle and bottom ribbons may or may not move in response to sprayer air. This is common in larger, denser canopies. To confirm this, an observer would have to stand at the trunk and watch the leaves rather than the ribbons.
Shingling and canopy distortion
When possible, do not position laminar air outlets in direct opposition. The convergence creates a high pressure zone that reduces spray penetration. Laminar flows will deflect unpredictably around this pressurized area and carry droplets back out of the canopy. Unless the canopy is narrow and sparse, turbulent air handling systems do not typically create this problem. In both cases, canopy penetration is improved when fans are staggered and/or are angled slightly forward or backward.
When too much air is vectored directly at the canopy face, it may close and compress that canopy rather than penetrate it. This is more likely when air is high energy, has a narrow air wash or is more laminar in nature. When leaves shingle, the overlap blocks spray and creates resistance to sprayer air. Air will then take the path of least resistance and either deflect around the canopy or channel through any openings. Shingling can be corrected by angling air outlets slightly forward or backward. A little goes a long way as small changes can have big effects.
Dr. Bernard Panneton (formally with the Horticultural R&D Centre, Agriculture and Agri-Food Canada) performed a series of experiments exploring the relationship between potato canopies and wind and his observations extend to all broad leaf crops. Bernard showed that as wind speed increased, the percent of leaf surface area exposed to spray also increased, but only to a point. If the wind got too fast, the percent of leaf surface exposed to spray dropped significantly: ~20% less!
His interpretation was that low to moderate air speeds just ruffled the leaves, exposing their broad surfaces to spray more consistently. When air speed became excessive, leaves and twigs aligned with the wind, exposing only their thin edge to spray. The take home lesson is that spray will be more likely to impinge on all target surfaces when air speed and volume are calibrated correctly.
Bernard summed this article up succinctly: “More air is not better!”
Potato canopy distortion in an air tunnel. Research by Dr. B. Panneton.
Video summary
We’ll finish the article with a light-hearted video describing how the process works. It doesn’t explore the second ribbon test, but that’s more of a concern with distant targets or alternate row spraying strategies where the sprayer must penetrate one or more canopies in a single pass.
January 25, 2021
Optimizing Sprayer Air Settings – Part 1
This is part one of a two part article on how to optimize the match between the sprayer air and the target canopy. For a more fulsome description of the process, consult chapters 3, 9, 10, and 11 of Airblast101.
Why is air so important?
Air handling is the most important and least understood mechanical system on a sprayer. Most air-assisted sprayers for three-dimensional perennial crops produce droplets that are Medium or smaller according to the ASABE S572.3 droplet size classification standard. These small droplets have very little mass relative to their surface area, so they don’t have much kinetic energy. Without air to impart speed and direction, most droplets would never go where we want them to. In addition, air opens and moves a canopy, exposing otherwise hidden surfaces to the droplets it’s carrying.
Imagine throwing a feather. Now imagine throwing it as hard as you can. It may travel a little farther, but not much relative to the extra effort. Even then, an errant gust of wind might change its direction entirely. Similarly, we cannot rely on hydraulic pressure to propel small droplets. This is the primary reason for the “air” in air-assist spraying.
Air-assist spraying attempts to replace the empty air within a canopy with droplet-laden air (and then get it to stay there). If we don’t have enough air energy, we won’t displace enough empty air and the throw will fall short. Likewise, if we have too much air energy, the throw will extend beyond the the target, wasting spray and likely compromising coverage. Ultimately, we want the air to expend all its energy, spreading, stalling and depositing droplets inside the target canopy.
Travel speed
Travel speed can have a significant impact on work rate. However, the effect of travel speed on air behaviour (and ultimately coverage) should be the sprayer operator’s primary concern. There will always be a trade-off between travel speed, coverage and work rate. Travel speed is the first and easiest adjustment to throw, spray height and canopy penetration. Just as travel speed modifies the liquid rate per row, it also modifies air energy per row.
Environmental and canopy conditions
Whenever calibrating or adjusting a sprayer, it is critical to do so in the crop, in environmental conditions you would typically spray in. You would not expect a sprayer to achieve the same results in high winds in a dormant vineyard as it would in calm conditions in a mature citrus orchard.
I recommend using a handheld weather meter because local weather reports often don’t match the conditions in the planting. For temperature and relative humidity, take readings in the shade. For wind conditions, face into the prevailing wind and hold the meter as high as you can. Wind speed increases with height and we want to evaluate the most challenging part of the target – the top third of the canopy.
Evaluating vertical air angles – Ribbon test part 1
The air angle (or direction relative to the target) is the first concern. Research has shown that low profile radial airblast sprayers without effective straightening vanes or deflectors make the air go up on one side and down on the other. In extreme situations, this might compromise the spray job (e.g. miss the lower portion of the target on one side of the sprayer) or it might simply waste spray and stir up debris. Here’s how you can see if this is happening on your sprayer:
1. Park the sprayer in an alley between the rows.
2. Affix 25 cm (10 in.) lengths of tape along the air outlets. Tie them to nozzle bodies or use duct tape to position them so that they stand out in the sprayer-generated air.
3. Bring the fan(s) up to the desired speed but do not spray. Stand back behind the sprayer and use the ribbons to extrapolate the air angle relative to the target canopy. Look for asymmetries and wasted air (i.e. angled above the canopy or into the ground.)
The ribbons on the LPR sprayer in this photo are twice as long as they should be, but fortunately it was a calm day. Note the angles of the lower ribbons compared to the “ideal” broken white lines. The asymmetry corresponds to the misaligned bottom right deflector. Observe the ribbons while adjusting deflector positions. Any ribbons above the upper broken white lines indicate wasted air energy (and likely spray). Large upper deflectors, positioned horizontally, would reclaim wasted air and focus it into the crop.
By observing the ribbons, you can extrapolate where deflectors or fan heads should be aimed. Air should be adjusted to slightly over- and under-shoot the target canopy. For ducted outlets, such as low profile Turbomist sprayers, the air outlet is not a uniform width – it’s widest about half-way down. Using ribbons to extrapolate air direction, aim the widest part of the outlet at the densest part of the canopy. This automatically repositions the booms as well, facilitating the next calibration step where we turn off nozzles that will significantly over- or under-shoot the target. This is discussed in another article.
Using a piece of scrap wood with a ribbon on the end to demonstrate how deflectors would channel air on an Economist airblast sprayer. Once convinced, this grower fabricated and installed deflectors and has been very pleased with their performance.
When repositioning the air outlets on a Turbomist with no towers, aim the widest part of the outlet towards the densest part of the canopy, then turn off unneeded nozzles. Lubricate the nuts and bolts that hold the outlet bands tight.
Video Extras
These videos are a bit long-in-the-tooth now, but the concepts are still sound. If you hear anything in the videos that contradicts what’s written in the article, go with the article. Live and learn. Thanks to Penn State, the University of New Hampshire and Chazzbo Media for producing these 2014 videos.
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This article will conclude in the second half:
Optimizing Sprayer Air Settings – Part 2
January 25, 2021
Homemade Air-Assist Tower Retrofit
It was Saturday morning in April, 2016 when I received an email from Steven Bierlink, an orchardist in Washington State. He was curious about the impact of air induction nozzles on lime-sulphur applications (intended to thin apple blossoms). Work-life balance notwithstanding, I happily grabbed a hot cup of coffee and we got on the phone. It was a great conversation.
The top two nozzles are capped in this orchard (targeting 10′ and below). It’s very evident that the top two nozzles are not in use.
It turned out Steve, like many growers, also had a knack for metal working. Displeased with his Rears sprayer’s performance, he told me he’d replaced his classic radial air outlet and curved boom with a ducted tower assembly, very much like the H.S.S. sprayer had just been introduced to North America.
I asked if he would share his story and a few photos of how he did it and he didn’t disappoint! What follows is a photo journal of how he designed and built his new sprayer. He wrote:
“Sorry it’s taken me so long to get back to you. Spring is like a tornado and there’s just no time to get things done! Here’s a quick/not so quick rundown of the process:“
1 – I started by cutting the horizontal supports that attach the fan box to the front deflector wall. I plugged all the old holes with nuts and bolts to keep the air going where I wanted it.
Fan box cut away from deflector wall. Holes filled with bolts.
2- I then got a 10″ wide sheet of 16 ga cold-rolled steel from a local HVAC guy. I marked out where I wanted to attach it, drilled and tapped the holes, and attached using only stainless hardware. I marked out for a total of 8 holes per side evenly spaced, and drilled them out with a 4” hole saw. I then cut 3″ long sections of 4″ diameter thin-wall pipe (about 0.125” thick) and welded them flush with the inside.
Welded pipe outlets for air.
3 – I had several conversations with the local HVAC guy about turning vanes, nozzles, cubic feet/min. and wind speeds. The reason I decided to use hose after all these conversations is because there are no 90° angle turns. Those turns during testing severely decreased wind speeds because of the turbulence it caused. The hose is standard 4″ suction hose for woodworking chip/dust collection. Together, we came up with a 1.5” x 8” outlet to use. The numbers written on the outlet are average wind speed with 10 feet of hose attached at the desired tractor rpm’s.
Commercial woodshop hose and air outlets.
4 – Initially I was set on having the same distance of hose for each outlet, like headers for an internal combustion engine. I let that go since volume matters so much more in this situation and there is no “real” back pressure pressure to be concerned about. This was the initial drawing:
Early sketch of equal hose lengths and positions.
5 – My measured dimensions showed the rectangular tower frame would fit through my tightest V-trellis, but only if I drove 0.5 mph and who is going to do that!? So, I needed to rethink it, break it down, and redo it. I decided on a partial, center-mast design.
Original tower frame would not clear the V-trellis. A center-mast solved the issue.
The top of the mast can be removed and the hoses disconnected and just left to hang. This allows me to hit 12′ tall V-trellis easily, as well as 14′ vertical trees all the way to the top.
6 – After putting everything together I realized the air volume wasn’t always balanced across the each outlet. This was because the bend in the hose was too sharp and too close to the outlet. This REALLY MATTERS because if the air volume is too “heavy” on one side of the outlet, it doesn’t capture and carry the spray consistently. I corrected it by attaching support rods to increase distance between bends and outlets to about 18”.
Gradual angles on hose prevented uneven air from the outlets.
7 – On the painted, final design, you might notice lowest nozzle is angled. This is because I’ve noticed that foliar applications don’t often hit the lowest branches. I angled one outlet upwards to correct this. I notice in your article on the H.S.S. sprayer that the Woolly Apple Aphid nozzle does the same thing. I feel like I need to meet these people; we have incredibly similar ideas!
Lowest nozzle and air outlet angled up to better hit lowest branches.
8 – I used TeeJet’s ¼ turn AIC air-induction flat fan nozzles. They’re molded into the cap, so they are always oriented the right way. I set the nozzle bodies outside the air outlets to reduce turbulence in the airflow. It also makes servicing cleaner and easier. I also ended up adding some shielding around the lower nozzles just in case someone loses focus and runs into something.
Shields prevent physical impacts to AIC (air induction) nozzles. Coverage map was created for 55 gpa in a 6’x14′ vertical planting.
Close up of nozzle location versus air outlet.
I asked Steve to stay in touch and let me know how his spraying season goes with the new sprayer. I’ll add to this article as he checks in and lets us know how the sprayer holds up and what changes, if any, he wants to make in the future.
July 2016 Update
As promised, I checked in with Steve to see how the sprayer was holding up. Here’s what he had to say:
“It’s awesome. Works fantastic. Very effective in windy weather without having to worry about drift. Also, it works perfectly for sunburn protectants because of how directed the application can be. It has held up well considering how many acres its gone through this year.”
Of course, there are always a few hiccups. I’ll interject here to suggest that what Steve is about to note about thinning is not a reflection of his design. I believe many orchardists experience the same difficulties with their conventional towers, too. Steve continued:
“A few downsides I’ve noticed throughout the season: For blossom thinning (lime sulfur), gallonage is critical to get the stamen of the flower burned sufficiently to prevent fertilization. Even when spraying ~100 gallons per acre with this sprayer, it wasn’t enough to effectively blossom-thin the fruit. Part of this may be because I’m now distributing the spray evenly through the entire canopy, rather than spraying up through the canopy below. Another downside is the droplets’ tendency to accumulate in the lower portions of the tree (since every droplet doesn’t hit foliage), and over-apply in those areas. My Sevin/NAA application this year definitely prove this theory as my lower branches were over-thinned.”
So, what’s the final word on this cool sprayer mod?
“Overall, it’s great, and with a few tweaks this winter will be even better.“
January 18, 2021
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:
January 15, 2021
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.
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.
January 13, 2021