Tag: pump

Centrifugal and Diaphragm Pumps
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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.
November 8, 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

Pumps for Applying Crop Protection Products

The pump is the heart of the sprayer and a key component for producing the flow of spray material and sprayer output. Because various spraying situations require different pressures and flow rates, using the correct sprayer pump is essential to achieving desired results. In addition to sprayer considerations, a pump must also be durable enough to withstand harsh chemicals that may cause excessive wear. Even though pumps with added chemical corrosion protection are more expensive, they are a popular choice because of their durability.

Roller, centrifugal, diaphragm, and piston pumps are commonly used to apply crop protection products. Centrifugal and roller pumps are typically used for low-pressure sprayers, and diaphragm and piston pumps are more popular when high-pressure sprayers are needed (i.e., vegetables, orchards, etc.). Less common pump types include squeeze, gear, and turbine.

Pumps are typically either ground driven or powered by main or auxiliary engines, power takeoff (PTO) shafts, or hydraulic pumps. The choice of pump depends on the material to be pumped and the capacity or volume needed. However, no particular type of pump is ideal for all purposes.

Sprayer pumps can be divided into two general categories: positive displacement and non-positive displacement. Positive displacement pumps (roller, diaphragm, and piston) maintain a flow output directly proportional to the pump speed. These pumps require a pressure-relief valve and a bypass line for proper performance. Non-positive displacement pumps do not have a proportional output flow to pump speed and do not require a relief valve and bypass line. The centrifugal pump is an example of a non-positive displacement pump style. A summary of common pump types and characteristics is found in the following Table (contributions from ACE Pumps Corporation, Hypro Pumps Inc., and CDS-John Blue Company).

Characteristic	Roller	Centrifugal	Diaphragm	Piston	Ground Driven Piston
Cost	Low	High	Medium	High	High
Displacement	Positive, self priming; Requires relief valve	Non-positive, needs priming; Relief valve not req’d	Positive, self-priming; Requires relief valve	Positive, self-priming; Requires relief valve	Positive, self-priming; Relief valve not reg’d. Runs off drive wheel and can be lifted on hydraulic-controlled applicators, or can be purchased with clutches to to disengage pump when flow is not desired.
Drive Mechanism	PTO, gas engines, electric motors	PTO, hydraulic drives, gas engines, electric motors	PTO, hydraulic drives, gas engines	PTO, gas engines, electric motors	Primarily ground-driven. Although less common, can be used with hydraulic drives, electric motors or gas engines.
Adaptability	Compact and versatile	Good for abrasive materials; Handles suspensions and slurries well.	Compact for amount of flow and pressure developed.	Wide range of spraying applications; Dependable	Wide range of spraying applications from clear liquids to suspensions. Very accurate regardless of ground speed or back pressure. Very dependable.
Durability	Parts to wear; replace	Very durable, not much wear	No corrosion of internal parts	Parts to wear; replace	Very durable. With basic care and maintenance, pumps can easily be in service 30 years or more.
Serviceability	Easy to work on, repair	Basic maintenance extends life	Low maintenance	Potential for high maintenance	Low maintenance
Pressure Range	up to 300 psi	up to 180 psi	up to 725 psi	up to 400 psi	up to 120 psi
Output Volume	2 to 74 gpm; high volumes for size; proportional to pump speed.	up to 190 gpm; High volumes for size and weight; Proportional to pump speed.	3.5 to 66 gpm; Proportional to pump speed.	up to 10 gpm; Proportional to pump speed, independent pressure.	0.5 gpm to 68.4 gpm.
Revolutions per minute	540, 1000	Requires speed-up mechanism. Very efficient at higher speeds; up to 6,000 rpm.	540	540	Ground-driven. Maximum 450 rpm.
Notes	Best choice by farmers.	If hydraulic-driven, no PTO required. Popular in commercial ag. applications. Running pump dry i s a problem.	Good for higher pressure requirements. Popular for horticultural applications. Pump can run dry.	Similar to an engine; Low capacity.	No gpa flow variation due to pressure or ground speed changes. No concern of electric failures on controllers or radar systems. Dependable accuracy.

Pump Efficiency

Regardless of the type of pump, the necessary flow rate must be provided at the desired pressure. Enough spray liquid should be pumped to supply the gallons per minute (gpm) required by the nozzles and the tank agitator, with a reserve capacity of 10 to 20 percent to allow for flow loss as the pump becomes worn. Unfortunately, pumps lose efficiency for a number of reasons, such as drive friction or leakage.

When estimating the pump horsepower needed for an application, efficiency (Eff) of 40 to 60 percent should be assumed. The horsepower (HP) required to drive the pump can be estimated by using the following formula:

HP = (gpm × psi) / (*1,714 × Eff)
*Constant derived when converting gallons, minutes, pounds, and inches to horsepower.

Example: How much horsepower is required to run a pump if the maximum output is 50 gpm at 40 pounds per square inch (psi)? Assume a pump efficiency of 40 percent.

HP = (50 gpm × 40 psi) / (1,714 × 0.40 Eff)
HP = 2.92

Because of inefficiencies of the drive units, electric motors should be approximately one third larger than the calculated horsepower. Gasoline engines should be one half to two thirds larger than the pump horsepower required. Ground-driven pumps that vary flow rates as ground speed changes are accurate and dependable; they are often used when applying high volumes of materials such as fertilizer.

Many pumps are PTO driven, but most modern spray pumps are hydraulic driven because of mounting versatility, ease of maintenance, and customization for individual sprayers. Charts are available to match pumps to various tractor hydraulic systems. You can access these charts by following the links to the following major pump manufacturers:

Hypro Pumps – www.hypropumps.com
ACE Pump Corporation – www.acepumps.com
CDS-John Blue Company – www.cds-johnblue.com
Hardi – North America – www.hardi-us.com
Delavan Ag Spray – www.delavanagspray.com
Watson-Marlow – www.watson-marlow.com

Pump Capacity

Proper pump size is an important consideration when selecting a sprayer pump. Requirements for nozzle capacity, hydraulic agitation, and overcoming the efficiency loss noted previously are essential points to consider. Nozzle capacity is determined by multiplying the number of nozzles on the boom times the output (gpm) of each nozzle for a specific application. Be sure to give consideration to the range of spray pressures that will be used for the given application. Agitation requirements typically account for another 5 percent of the sprayer tank capacity. Efficiency losses due to friction and pump wear may account for an additional 10 to 20 percent increase in the required flow rate. Spray pump manufacturers provide useful Web page worksheets to help determine pump sizes based on typical field application scenarios.

Manufacturers also make product guides available to help match sprayer pumps and hydraulic motors to the tractor’s hydraulic system (Table 2). A simple pump selection worksheet is provided at the end of this article.

No matter what type pump is used, it must be plumbed to route liquid from the pump to the spray boom with a minimum amount of restriction, a necessity for achieving the pump’s maximum rated capacity. The hoses should be the same size as the pump’s suction and discharge ports. Other recommendations include installing a pressure gauge and valve on the pressure side of the pump to measure the shut-off pressure and using a minimum number of elbows, fittings, and valves to reduce pressure losses.

Following these guidelines is necessary for delivering the highest pressures to the boom.

Pump Rotation

Pump rotation is critical for PTO and belt and- pulley driven pumps. The direction of rotation is always determined when facing the pump and drive shaft, and pumps are available in both clockwise and counter-clockwise rotation. Thus, when direct coupling shafts, the opposite rotation pump should always match the shaft. When mounting a pump with belts and pulleys, either pump rotation can be used to match the drive shaft rotation and the desired direction of the pump. Gasoline engine and electric motor shafts rotate in a counter-clockwise direction, and a tractor PTO shaft rotates in a clockwise direction.

Pump Types

Roller pumps are popular for small sprayers because of their low initial cost, compact size, ease of repair, and efficient operation at PTO speeds of 540 and 1000 revolutions per minute (rpm). Roller pumps are self-priming, positive displacement pumps, and a variety of models is available. Maximum outputs range from 2 to 75 gpm, and pressures range up to 300 psi.

Figure 1 - Roller Pump — Figure 1 – Roller Pump

Roller pumps are usually constructed with cast iron or corrosion resistant housings (non-symmetrical in shape), rotors, four to eight rollers (either nylon, Teflon, or rubber), and seals (Viton, rubber, or leather). The type of material selected depends on the chemical being pumped. A typical roller pump is shown in Figure 1.

Nylon or Teflon rollers are the most resistant to agricultural chemicals and are recommended for multipurpose sprayers. Rubber rollers are preferred when the pump is used only for water solutions and wettable powder slurries at pressures less than 100 psi. Because sand and scale are abrasive to the rollers, the solution being pumped must not contain these materials. Polypropylene rollers wear better than either nylon or rubber rollers when applying weak solutions or solutions with little or no lubricating qualities.

Some operators have experienced problems with excessive wear of the rollers, especially when using wettable powders. Other operators have achieved long pump life by allowing the pump to run continuously when spraying with wettable powders, and by properly maintaining and storing the pump, including keeping abrasive materials out of the sprayer. Specific seal, roller, and casting materials can be selected for compatibility with certain herbicides, insecticides, fungicides, and fertilizers Consideration should also be given to the adjuvants used in the spray solution.

Centrifugal pumps are the most popular type of low-pressure sprayer. They are durable, simply constructed, and can readily handle wettable powders and abrasive materials. Because of the high output of centrifugal pumps (70 to 190 gpm), the spray solution can be agitated sufficiently even in large tanks at pressures up to 180 psi. The initial cost of a centrifugal pump is somewhat higher than that of a roller pump, but its long life and low maintenance make it an economical choice. Pump housings of cast iron, stainless steel, and polypropylene are advantageous because they withstand strong chemicals. Stainless steel pumps are ideal for use with glyphosate or other acid applications. Polypropylene pumps are lightweight and provide excellent resistance to corrosive chemicals. Figure 2 shows a typical centrifugal pump.

Because centrifugal pumps are not self-priming, they should be mounted below the supply tank to aid in priming. In addition, a small vent tube should be installed from the top of the pump housing to the supply tank. This positive vent line allows the pump to prime itself by “bleeding off” trapped air upon starting and when the pump is not operating.

The inlet of a centrifugal pump should never be restricted. A partially clogged suction strainer, collapsed suction line, or a suction line with insufficient capacity causes a loss of pressure control and possible damage to the pump. Centrifugal pumps can handle small pieces of foreign material without damage, so a suction strainer is not always required. If a suction strainer is used, however, it must be capable of handling the large capacities of the pump with a minimal drop in pressure across the strainer, and it must be cleaned frequently. Typical centrifugal pump plumbing would place the strainer on the pressure side of the pump.

Centrifugal pumps for low-pressure sprayers can generate pressures of up to 70 psi when the impellers are running between 3,000 and 4,500 rpm. The output volume drops off rapidly when the outlet pressure exceeds 30 to 40 psi. The decrease in volume is an advantage because the nozzle pressure is able to be controlled without a relief valve. See Figure 3 for a typical centrifugal pump performance curve. The pump performance curve describes the relationship between flow rate and pressure for the actual pump.

Figure 2 - Centrifugal Pump — Figure 3 – Centrifugal Pump Performance Graph

The need to operate at high impeller speeds requires a type of step-up speed mechanism when operating centrifugal pumps from PTO shafts. The simplest and least expensive of these mechanisms is a belt and sheave assembly. Other step-up mechanisms have planetary gears that are completely enclosed and mounted directly on the PTO shaft.

Another method of driving a centrifugal pump is with a close coupled, high speed hydraulic motor. Using the tractor hydraulic system to drive the pump keeps the tractor PTO shaft free for other uses. It is essential to consult manufacturer pump selection guides to match the proper pump to your tractor. Pumps can also be driven by direct-coupled gasoline engines when other drive mechanisms cannot be used.

Airplane pumps may be wind-driven, directly powered from the aircraft engine, or powered by an electric or hydraulic motor. The pump may also power the tank agitation system. For fixed-wing aircraft, the most common type of pump is a wind-driven centrifugal pump mounted under the aircraft (Figure 4). The propeller slipstream drives a fan mounted on the front of the pump. Some fan-driven pumps have variable pitch blades that allow for changing pump speed, and thus output. The centrifugal pumps commonly used on aircraft produce high volumes (up to 200 gpm) at typically low pressure, usually ranging between 10 and 100 psi. These pumps usually require operating speeds from 1,000 to 5,000 rpm.

Figure 4 - Airplane Pump — Figure 4 – Airplane Pump

Diaphragm pumps are popular when higher pressures are needed for applying foliar herbicides, insecticides, and fungicides. Models are available that provide maximum outputs ranging from 3.5 to 60 gpm and maximum pressures ranging from 200 to 700 psi. These pumps are extremely durable because all moving parts are sealed in an oil bath and spray solutions. Diaphragm pumps are self-priming and considered positive displacement pumps. Figure 5 shows a typical diaphragm pump. Smaller electric diaphragm pumps (Figure 6) are available for use by homeowners, ranchers, and hobbyists to apply pest control products. A good example is a spray system mounted on an ATV for spraying pastures and rights-of-way.

Figure 5 - Diaphragm Pump — Figure 5 – Diaphragm Pump

Piston pumps are positive displacement pumps that are favored by many users for their priming ease, higher pressure capability, and constant volume spraying. Piston pumps are often used to apply crop protection products and fertilizers in combination with a ground drive so that flow rate stays proportional to ground speed and application rates remain constant. A pressure relief valve is required, though. Figure 7 is an example of a piston pump used to accurately meter liquid fertilizers.

Figure 7 - Piston Pump — Figure 7 – Piston Pump

Turbine pumps are also available for low‑pressure sprayers. A turbine pump consists of a rotating turbine within an enclosed housing. These pumps are similar to centrifugal pumps, except they provide higher flow capacity and pressures of up to 70 psi when mounted directly on a 1,000 rpm PTO shaft, eliminating the need for step‑up mechanisms. Because of the close tolerances between the turbine blades and the casing, turbine pumps are better adapted for clean fluids of low viscosity but may have difficulty with wettable powders and suspensions. Figure 8 shows a typical turbine pump.

Figure 8 - Turbine Pump — Figure 8 – Turbine Pump

Gear pumps are positive displacement pumps capable of providing a smooth, low-volume, continuous flow of material. Gear pumps are typically two gears meshing together revolving in opposite directions within a casing. Abrasive materials such as wettable powders rapidly wear the gears and pump housing. Figure 9 shows a typical gear pump.

Figure 9 - Gear Pump — Figure 9 – Gear Pump

Squeeze pumps are low-pressure, positive displacement pumps with output proportional to speed. Pump flow is created when liquid is trapped by squeezing the hose between a roller and casing. Pump flow is determined by the size and number of hoses. This pump is ideally suited for metering small quantities of fertilizers or pesticides and would be practical for injection-type pumping systems. Figure 10 shows a typical squeeze pump.

Figure 10 - Squeeze Pump — Figure 10 – Squeeze Pump

Pump Maintenance

Proper pump maintenance is critical for maximum pump life. Regular cleaning is essential to removing all chemical residues and preventing wear to the pump from corrosive solutions. Do not allow spray solutions to remain in the sprayer for extended periods of time. Using lightweight antifreeze or a motor oil as the final spray solution after cleaning can preserve the pump during a period of non-use.

Pump Selection Worksheet

Acknowledgements

Excerpts for this article were adapted with permission from University of Illinois Circular 1192 developed by Loren Bode and Jack Butler (May 1981), Extension Agricultural Engineer and Professor of Agricultural Engineering, Univerity of Illinois at Urbana-Champaign. Contributions for this article were also received from ACE Pumps Corporation; Hypro Pumps Inc.,; and CDS-John Blue Company.

For more information on pump selection, check out this article.

January 10, 2021

What do European Sprayers Bring to the North American Market?
For many years, European agricultural machinery was considered too small to be relevant for North American conditions. That started to change when Claas and New Holland began introducing large harvesting equipment 20 yrs ago. Larger tractors from the likes of Fendt, and seeding and tillage equipment (e.g. Horsch) followed soon after. Now, European sprayers are knocking on our doors. What do they bring to the party?
Overall capacity
The typical large self-propelled European sprayer of 2020 has all the capacity of the largest North American models, and sometimes more. Boom widths of 36 m (120 ft) are common, and wider booms extending to 40 and even 50 m (~131 and 164 ft) are available. Tank sizes of 5,000 and 6,000 L (~1,300 and 1,600 US gal) are not uncommon, and 8,000 to 12,000 L (~2,000 to 3,000 US gallons) are featured on some. On those specs alone, they qualify.
European sprayers can be significantly larger than their North American counterparts (Dammann DT 3500 H S4).
Dimensions
The first thing people notice about European sprayers is their more compact design. In order to comply with the 3 m maximum transport width allowed by law, everything is narrower. That doesn’t prevent the wheel track from widening in the field, of course, where stability is needed or where tramlines need to be matched.
More efficient use of space in a European sprayer allows a smaller sprayer footprint with equal capacity (Amazone Pantera).
The more compact design does come at a cost. There’s no room for large ladders with handrails to enter the cab, and catwalks are usually gone, too. Access to service points can be more cramped. But the upside is that most of these sprayers are lighter than their North American siblings, with dry weights between 9,000 to 12,000 kg (20 – 25,000 lbs) not uncommon even for the larger capacities.
Compact, efficient designs featured in Bateman sprayer, one of UK’s top makes.
Frame and Cab
Less space has provided some frame innovations. A central channel frame is sometimes featured, creating room for a sophisticated swingarm suspension, or a walking beam. The cabs typically sit in front of the chassis, with a centrally mounted engine. This offers superior visibility, although it does take some getting used to. Overall, the cabs on these more compact sprayers are every bit as spacious and comfortable as North American types, with better rearward views possible due to the narrow chassis.
Wishbone swingarm from central tube frame in Fendt Rogator.
Monitor systems vary, but due to the majority of sprayers being made by smaller firms, third-party controllers will be more likely. Ag Leader, Topcon, and others can be seen in place of the proprietary systems of the larger manufacturers.
There are no shortcuts with European cabs.
Tank design
Again, the compact real-estate requires some unique solutions. The barrel-shaped tank resting on a cradle that we’re used to in North America is replaced by a more complex-shaped tank that needs to utilize every possible available space. Although this is done with steel on many units, molded plastic is once again more common. Access to the tank lid is also more difficult due to the general absence of walking platforms. However, attention is paid to sump design and minimizing the remaining volume, making cleaning easier.
Less room on narrow frames requires more complex tank shapes. Will cleanout be as effective?
Booms
European sprayers have well-engineered booms with better height control and contour-following capabilities than North American units. Usually triple-fold, they are compact and many offer Norac (Topcon) height sensors. Steel remains the most common material, with aluminum deployed as necessary on outer sections. Wet booms have 25 mm outside diameters and as such are slightly smaller than North American types. However, flow and pressure drop are measured to ensure a quality distribution. If these systems are used at faster travel speeds, flow limitations may become an issue and that will require closer evaluation.
Large tanks and wide booms are commonplace in Europe (Sands sprayer)
Plumbing
An aspect where the European sprayers excel is plumbing design. Most have recirculating booms; some offer continuous rinsing. Both designs minimize waste generation and simplify rinsing and cleaning, saving time. More sophisticated tank level gauge systems that offer cab readouts, better resolution at low volumes and less dependence on having the sprayer resting on a level surface, can also be seen.
Recirculating booms are common on European sprayers (Bateman sprayers).
Pumps tend to be diaphragm, with only a few brands offering centrifugal types. The reasons are both technical and traditional. On the one hand, diaphragm pumps can run dry, don’t need to be primed and can be located beside the tank, for example, and can push air into a boom. On the other, they are bulkier and more expensive, noisier, need a pulsation damper and require maintenance. Some manufacturers, notably the Fendt Challenger and the Chafer, ship with centrifugal pumps. These are now equipped with wet seals, and the Challenger has employed an auto-prime system that prevents air-locks.
Diaphragm pump on Amazone Pantera (top of picture)
Flow Control
Whereas all North American manufacturers offer a pulse-width-modulation (PWM) option which now comprises an estimated 30% of new sales, the European sprayers are only beginning to consider this flow management approach. The majority still offer multiple nozzle bodies that permit automatic switching between various sized nozzles to achieve extended travel speed ranges or changes in spray quality. One of the reasons for the delayed adoption of PWM is the European regulatory system, which have yet to approve some aspects of the PWM system. Low-drift performance, for which most air-induction nozzles have been approved, must still be validated for nozzles that must be used with PWM (recall that air-induced nozzles are not generally recommended for PWM).
Multiple nozzle bodies are favoured over PWM in Europe, but PWM is gaining acceptance.
Many UK sprayers also use an interesting means of managing bypass, via a so-called Ramsay Valve. This type of valve uses an air-filled diaphragm to divert flow, and air-pressure change is used to alter the bypass. Such a system was an answer to early butterfly valves which had slow, uneven response, but is bulkier than the modern mechanical bypass valves now available, and may require maintenance.
Drivetrain
Like North American sprayers, wheels are driven by hydraulic motors. Hybrid Continuously Variable Transmission (CVT) systems are also available, and these offer superior torque characteristics at slower speeds. Engines are like those offered in North America, supplied by major manufacturers such as John Deere, Deutz, Fiat, etc. We are seeing smaller engines on European sprayers owing to the slower travel speeds. Slower speeds don’t just save cost, weight, and fuel consumption, they also provide the advantage of better boom height control and lower spray drift, as long as productivity can be maintained.
Wheels
European sprayers generally use the same wheel sizes as North America, with 46” wheels being common. A unique feature of UK sprayers is their use of 28 to 38” wheels. Although native ground clearance is sacrificed, it is enough for most crops except for corn, for which many sprayers require a lift kit anyway. These smaller wheels allow booms and other components to be cradled lower, improving the centre of gravity and safety.
Wheel sizes vary, but are sometimes significantly smaller, particularly in the UK.
Summary
There is very active competition between European sprayer brands. Many dozens of manufacturers are in the market, and customers have high expectations. Although some of the features on European sprayers will appear strange at first sight, they should be evaluated purely on performance criteria, not aesthetics. Does the sprayer improve efficiency by reducing downtime? Does it make drift control easier? Does it waste less product that one would otherwise dump on the ground? Is it more fuel efficient? In this regard, customers will benefit from the competition introduced by other sprayer brands. A rising tide lifts all boats.
January 15, 2020
The Agitation over Agitation
Sprayers101 recently received a couple of seemingly unrelated questions about airblast sprayers:
What are the advantages and disadvantages of mechanical versus hydraulic agitation? Why would someone want a stainless tank versus the cheaper poly or fiberglass options?
Recognizing that each manufacturer has their own reasons for the features and materials used in their sprayers, we posed these questions to Mr. Kim Blagborne (formerly of Slimline Manufacturing). The following article was written from Kim’s response, and it turns out these two questions are very much related. Kim writes:
This is a great debate among customers and manufacturers, and it’s difficult to stay neutral. Let’s consider the following:
Hydraulic Agitation
The flow required for hydraulic agitation requires about 30% of the pumps total capacity. This is very important because many sprayers cannot achieve, or maintain, this minimum requirement whilst spraying. This may be why it’s rare for a sales person to demonstrate agitation while the sprayer is spraying; quite often, the agitation slows or even stops. And, of course, because everyone gets wet.
Let’s say an airblast sprayer has a pump with a manufacturer-listed capacity of 26 gallons per minute (gpm) (Click to download the spec sheet for the pump). The figure in that output chart is determined on a bench at 540 rpm and at 50 psi. However, when an operator uses that pump in the field, they run it at ~150 psi, and that brings the pump capacity down a bit to 25.5 gpm.
Now we build in the line pressure drop associated with the sprayer’s plumbing. Effectively, another 8-10% of the pump’s output is lost to plumbing (a figure easily measured by collecting the total output capacity of the pump). Let’s say we are now down to a practical capacity of 23 gpm.
If the operator’s crops are on 14 foot rows, it would be reasonable to spray 200 gpa at a travel speed of 3 mph at 150 psi. With both booms spraying that’s a required flow of 16.8 gpm.
Remember, our hypothetical 26 gpm pump can only provide 23 gpm in the field. When we subtract the 16.8 gpm required for spraying, we’re left with 6.3 gpm excess capacity for agitation. But, we said we needed 30% of the pump’s 26 gpm capacity, and that comes out to 7.8 gpm. We’re short by 1.5 gpm, or stated differently, we’re about 20% short of what we need.
Why don’t we see that deficit? Because the flow to the booms is prioritized, and therefore the sprayer output matches the calibration, so everything seems OK. But no one sees the reduced return flow through the regulator, and certainly no one peeks into the tank while spraying to see that the hydraulic agitation is greatly reduced.
And so, while everything looked great during loading, the spray mix (especially SC and WDG formulations) may not stay suspended correctly during spraying. In extreme cases, that could lead to burning a crop (high concentration) at the start of a spray job, and reduced efficacy (low concentration) at the end. We’re quick to blame the chemical, but no one ever thinks to question hydraulic agitation.
Let’s consider it from another angle: TeeJet suggests a model number 62905c-5 jet agitator for a sprayer with a 250 US gallon tank. To correctly agitate the contents of this tank, we will need 30 psi and 7.6 gpm (see the chart below).
Unfortunately, there is no simple way for an operator to measure the agitation pressure or the flow, so it goes unchecked. The only way to determine if the flow demand is satisfied is to apply the generic rule of 30% of pump capacity and make an estimate. That’s pretty loose math since we’ve already established that the listed capacity may not reflect reality.
Still another angle: Many operators now employ the Gear Up, Throttle Down (GUTD) approach to match their sprayer air settings to the crop canopy. However, when we reduce PTO input speed we also reduce pump capacity. Remember our piston diaphragm pump with the 26 gpm capacity at 540 rpm? We still need 16.8 gpm to spray, but reducing the rpm’s by 100, per GUTD, drops our pump output to only 23.16 gpm.
23.16 minus 16.8 equals 6.36, and we needed 7.8 gpm to maintain sufficient hydraulic agitation. Oops.
Mechanical Agitation and Tank Material
There are definite advantages to mechanical agitation. It is not affected by the PTO speed because it is already excessive at 540 rpm. This means there is no pump capacity issue and it allows the operator to take advantage of GUTD.
There are also a few disadvantages. Unlike a hydraulic system, mechanical agitation requires maintenance, such as regular (daily?) greasing. The packing where the the system inserts into the spray tank also requires occasional inspection and adjustment to prevent leaks.
And of course there’s sticker shock. Many European manufacturers offer hydraulic agitation because it is ~$500.00 CAD less expensive. Further, mechanical agitation creates vibrational stress on tanks walls, which fiberglass or plastic tanks can’t handle for long. The solution is stainless tanks, which is a more expensive material. Further, stainless cannot be moulded around pumps and rotating parts, so more steel is required, adding to expense and weight.
In my opinion, there is sufficient benefit to stainless to easily recover the investment. Beyond permitting mechanical agitation, there’s durability. We have stainless tanks built in 1948 that are still operating today, and we’ve never found a plastic or fiberglass tank that can claim that. There’s also sprayer sanitation. It has long been know that stainless cleans more easily and more reliably that plastic or fiberglass, especially as the tanks begin to age.
Closing
The decision to buy a sprayer with hydraulic agitation or mechanical agitation lies, ultimately, with the consumer. But be sure to look past the price tag, and under the hood. Ensure that you have sufficient agitation to properly suspend your tank mix, and give you the flexibility to Gear Up and Throttle Down to improve your spray coverage and efficacy.
October 10, 2017