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:
Eyes on the End: Face the rotating Power Take-Off (PTO) and determine if it is spinning clockwise (CW) or counter-clockwise (CCW).
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:
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:
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:
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.
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:
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
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.
Centrifugal Pump – Exploded View.
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 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
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
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
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
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
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
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.
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.
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.
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.
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.
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.
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.
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.
Step 7
Clean the seal thoroughly. Seals are easily damaged and may need replacement.
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.
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).
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.
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.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.
