backpack sprayer troubleshooting and how to guide
Tips & Tricks

Common Backpack Sprayer Problems and How to Fix Them

Backpack sprayers are a gardener’s best friend not only do they make watering your garden a breeze, they also make it easy to apply herbicides with ease and efficiently. This is why being able to fix your backpack sprayer should it malfunction is a priority.

Keep reading to learn how to troubleshoot any issues you may experience when using your backpack sprayer and learn how to use it more efficiently.

Why is my backpack sprayer not building pressure?

Below are some reasons why your sprayer is not building pressure;

Clogged Filter

Most sprayers have a filter system inside of the tank that filters out the product to be sprayed of any solid particles.

This can help stop the hose, trigger wand, and pump system from getting clogged. If you are experiencing lost or low pressure on your sprayer, check to see if the filter in the backpack is clogged.

Solution: Some clogs can be fixed as easily as spraying water into the empty backpack to flush out the filter. Rinse out the tank a few times and see if that fixes the problem.

If the filter is still clogged after rinsing the backpack, the filter will need to be removed and cleaned more thoroughly, or possibly replaced.

All filters will need to be replaced eventually. It is not uncommon for larger sprayers, such as backpack models, to have several filters within the system.

There is likely one in the tank, one at the connection of the hose and wand, and one at the nozzle.

Broken Impeller or Impeller Coupling

If your sprayer is outputting with low pressure, there may be an issue with the pump impeller or the impeller coupling. The impeller creates pressure within the pump by spinning and forcing water to flow through it.

A worn or broken impeller will not be able to properly pressurize the pump and will not output water at high pressure, if at all. The impeller coupling connects the impeller to the source of water or product that is to be sprayed.

This coupling has a seal that, if lost, will compromise the pump’s ability to pressurize and pump water. If you are experiencing low-pressure output from your sprayer and have ruled out any other parts as the cause, the impeller coupling may have lost its seal, or the impeller itself may be damaged, clogged, or broken.

Solution: In some cases, the pump may be disassembled and cleaned to fix the problem. If you are opening the pump, make sure to replace any seals or gaskets when reassembling to ensure that a tight seal is kept.

Refer to your user manual for further instructions on how to care for your pump and how to deal with any issues related to it.

Broken Clutch

If your sprayer is not outputting with the same pressure that it normally does, it is possible that there is an issue with the clutch. The clutch drives the pump which moves the liquid through the unit.

The clutch allows the engine to idle without causing the pump to constantly output. When the clutch is engaged, it should force the pump to start working.

If the clutch is out of alignment or broken, the pump may not function or may pump with significantly less pressure than usual. This is an indication that the clutch is not fully engaging with the pump system.

If you believe this is the cause of low pressure, you can disassemble the machine to expose the clutch and ensure it is working properly.

Solution: The clutches attachment to the pump system need to be aligned perfectly in order for the unit to run properly. Refer to your user manual for further instructions on how to access or repair a clutch that is not working properly.

Clogged Nozzle

If you are experiencing a loss in pressure, check the nozzle tip for any clogs or blockages. If any solid matter is allowed to enter the pump system (sand or dirt, for example), it can build up at certain points and cause a reduction or complete loss in spraying pressure.

If your nozzle is clogged, remove it from the trigger wand try to clean it out, and remove any solids in the lines that may be causing the block.

If the nozzle tip is damaged or clogged to the point where it cannot be cleaned, it should be replaced altogether.

Back sprayer leaking from the bottom

Damaged Gaskets

If your sprayer is leaking water it is likely that there is a broken seal or gasket near the source of the leak. As water passes from the tank, through the pump, and into the wand, it passes through a series of connections that are all sealed by gaskets or o-rings.

These gaskets and o-rings can wear over time, causing them to crack and leak.

If your sprayer is leaking, disassemble the sprayer at the source of the leak and inspect the seal inside of the assembly.

If the seal is broken or is showing any signs of wear, it should be replaced. Refer to your user manual for the proper part numbers when replacing seals and gaskets.

Cracked Wand Hose

If your sprayer is leaking directly from the wand hose, the hose itself may have become cracked, which has caused the seal of the hose to become compromised. These hoses do wear over time and are especially likely to leak at points that are stretched or bent frequently.

A broken or leaking hose can be easily replaced. Refer to your user manual for specific instructions on how to remove the old hose and reinstall a new one, and also for the proper replacement part number if a new hose is required.

Trigger Wand

The trigger wand contains a valve inside of it to cut off the flow of water or chemicals being sprayed. This valve can wear or break from regular use, causing it to leak. It is also common for this part to crack if the pressure washer is not properly winterized.

Water expands when it freezes into ice. If the trigger wand has water left in it in the winter the internal valve or piping will likely crack when the water freezes.

If you have a leak coming from the trigger gun itself (as opposed to the wand hose, or the point at which these two components connect), it is likely that the seal inside of the trigger wand has worn and is no longer making a tight seal.

Depending on the build of your specific trigger wand, you may be able to open the wand and replace any broken seals or repair any minor damage.

Refer to your user manual for more specific instructions on how to address leaks from the trigger wand. In some cases, the entire trigger wand will likely need to be replaced entirely.

Backpack sprayer not pumping

Below are some reasons why your backpack sprayer is not pumping;

Loose hose

One of the common causes is not having the hose installed properly. Remove the hose from the tank. Most sprayers have a hose barb (2 plastic, white tabs) located at the end of the hose under the hose nut.

Reinsert the dip tube into the tank making sure to align the hose barb with the cutouts (see picture below). Push the tabs down into the notches until they cannot go any further.

Then hand tighten the hose nut onto the tank – being careful not to cross-thread or overtighten. If your sprayer does not have a hose barb, you can just reinsert the dip tube into the tank and hand tighten the hose nut as described previously.

 Damaged pump gasket

Depressurize the sprayer and remove the pump from the tank. The pump gasket is located at the top of the pump right above the threads. Remove the dirt or debris from the gasket and pump threads by wiping with a clean cloth.

Then lubricate the gasket with a light oil (i.e., 3-IN-ONE® Multi-Purpose Oil) to keep the gasket from drying out. Replace the pump in the tank and hand tighten until it is snug. Do not overtighten as it can cause damage to the gasket.

NOTE: If you notice the gasket is chipped, torn, swollen, or misshaped, it will need to be replaced.

Damaged pump check valve.

With the pump removed, locate the check valve at the bottom of the pump. Make sure there is no dirt or debris underneath the check valve.

It can be easily removed, washed, and put back into place. If you notice it is damaged or worn, it will need to be replaced.

Damaged pump piston o-ring.

You will need to remove the pump from the tank to do this. Then separate the pump piston from the pump barrel. First, pull the pump handle up until it cannot go any further.

Then use a flat screwdriver to push the tabs in on both sides of the pump cylinder and pry up.

At the end of the plastic piston/rod, there will be a black o-ring. Periodically this o-ring needs to be lubricated with a heavy coating of petroleum jelly to ensure a nice tight seal in the pump barrel – delivering as much air as possible per stroke

Signs that your backpack sprayer is clogged

Your backpack sprayer is clogged if;

  • There is no liquid output
  • The sprayer is difficult to pump

How do you unclog a backpack sprayer?

Pump sprayers use a telescopic plunger to draw a solution, such as an herbicide or pesticide, out of the reservoir.

After the solution leaves the reservoir, the plunger pushes it through the hose, into the spray gun, and out the nozzle.

Pump sprayers require cleaning in between uses to flush out chemicals that may dry up and clog the inner workings of the sprayer. To unclog the sprayer;

  • Remove all chemicals from the pump sprayer.
  • Empty the chemicals from the pump sprayer by either using them up or disposing of them according to manufacturer’s recommendations.
  • Soak the nozzle of the pump sprayer in a small bowl of warm water and a squirt of dish soap.
  • Allow the nozzle to soak for approximately 10 minutes.
  • Rinse the nozzle with warm water and dry it with a paper towel.
  • Pump sprayers use a telescopic plunger to draw a solution, such as an herbicide or pesticide, out of the reservoir.
  • Empty the chemicals from the pump sprayer by either using them up or disposing of them according to manufacturer’s recommendations.
  • Pour warm water into the reservoir of the pump sprayer along with a few squirts of dish soap. If you do not have dish soap, any mild detergent will suffice. Soak for approximately 10 minutes.
  • Reattach the nozzle to the pump sprayer.
  • Pump the soapy water through the sprayer several times to rinse out the hose, sprayer gun and the sprayer nozzle.
  • Pour the soapy water out of the pump sprayer, and fill the reservoir with warm, clear water.
  • Pump the clear water through the hose, sprayer gun and nozzle to remove any soapy residue.
  • Allow the pump sprayer to air dry.
  • Pour warm water into the reservoir of the pump sprayer along with a few squirts of dish soap.
  • Pour the soapy water out of the pump sprayer, and fill the reservoir with warm, clear water.

Note: If you have used an herbicide or pesticide in the sprayer, clean the sprayer with ammonia instead of dish soap;

  • Pour the ammonia into the reservoir at a ratio of 1 quart of ammonia for every 25 gallons of water.
  • Allow the ammonia solution to sit in the reservoir for 15 minutes and then pump it through the hose, sprayer gun and nozzle until the reservoir is completely empty.
  • Allow the pump sprayer to air dry.
  • Check the information booklet that came with your particular pump sprayer to see if the pump mechanism requires yearly maintenance.
  • Some manufacturers recommend taking the mechanism apart to clean and oil it once a year.

How to prevent your backpack sprayer from clogging

Don’t Mix Chemicals

Certain chemicals cannot be used at the same time or back to back without thoroughly cleaning the tank and lines. When certain chemicals come in contact with each other they may clump.

Pro tip: Liquid fertilizer and some weed killers are ok and can be applied at the same time… some will make a huge mess. Speak to your local Ag extension agent about this.

Clean your sprayer

This is the most important tip that anyone will suggest. Keeping your sprayer clean will always eliminate problems like chemical clogging. If you are finished spraying, wash your tank out. To learn how to properly clean the tank on your sprayer, watch this video.

Agitate or mix your chemical

If it rains and you have to let your herbicide sit in your sprayer for a couple of days, take the time to agitate the liquid in your tank each morning – even if you’re not spraying.

Pro tip: Watch out for product settling out. Be especially careful if one or more products were in a dry form before they entered the tank.

Clean your nozzles

Herbicides will often clog up your spray tips first as these are at the end of your spraying system.

Pro tip: If your sprayer has a valve between the tank and boom, shut it off when it sits.

Use clean water

Clean water free of insects or debris will eliminate a lot of clogging. Always use clean water when you are mixing with herbicide.

Hard well water and water with foreign minerals can react badly with both Round-up and 2-4-D.

“If you leave any mix in the sprayer overnight, it starts to get white looking clots and they clog up the spray nozzle and strainer. The longer I leave any residue, the worse the clotting gets. I have to mix and immediately spray. I would suggest you not mix too vigorously before spraying, also check with the local Ag extension agent as to problems with your water type and the chemical you are using.” – Sprayer User

Sprayer User

Check your filters

It’s important to check your filters after each day to ensure no objects or clogs of herbicide are trapped.

Pro tip: If clogged, you can quickly clean sprayer filters in a bucket with recommended cleaning agent.

Store in the Correct Place

Park your sprayer out of direct sunlight. If you are in below freezing temperatures, this will also negatively affect the herbicide.

Note: Although these tips will help eliminate clogging in your herbicide sprayer, you may still have problems if you leave chemicals in your sprayer for more than a week.

How to clean a backpack sprayer

Cleaning your sprayer is a major part of keeping your sprayer working for years and needs to be done more than once or twice a year.  Regular cleaning is critical for sprayer longevity.  It’s easy to overlook, and many people do.

If you find yourself searching for the answer to “why is my backpack sprayer not holding” pressure or something similar, you might find that regular cleaning and maintenance can help prevent those issues.

Note:  Leaving chemicals such as pesticides inside a backpack sprayer for a long time will cause the seals to swell, crack, and deteriorate. This leads to an array of issues such as poor pressurization, leaks.

You should also clean your sprayer between uses.

Cleaning sprayers between using a herbicide and fertilizer is critical, and failure to clean the tank properly can harm your lawn.

Routine cleaning can save you precious time on repairs and cut down on hours of lost time and business, and it can prevent you from spraying residual chemicals where you shouldn’t apply them.

Cleaning is inexpensive and quick, and all you need is Dawn dish soap and water to flush the system.

Steps to clean your sprayer;

Triple rinsing is the best and most common way to clean your sprayer effectively. The triple rinse process is what it sounds like: you rinse the sprayer three times. Here is the process of triple rinsing

  • Fill the tank with water, shake it, and dump it to remove any excess product in the tank.
  • Next, fill the tank with soap and water, shake the tank again, and spray the soapy solution to flush the entire pump system.
  • Finally, fill the tank with clean water, shake the tank, and spray clean water to flush the pump system one final time.

What products do I need?

You can opt for a tank sprayer cleaner, but a mix of about 6-8 drops of dish soap with water is all you need to thoroughly clean your sprayer.

When you flush your sprayer regularly, you remove the chemical build-up from the pump assembly. We already know what happens if you allow residue to sit in the sprayer: a broken backpack sprayer.

Follow the steps below to clean your backpack sprayer;

Tools You Will Need:

  • 6mm Allen wrench


  • Empty out any liquid remaining in the tank.
  • Fill up the tank with clean water.
  • Examine the wand tip for sediment build up and clean out as needed.
  • Flush out water through the hose and handle press.
  • Flush out the remainder of the water with the wand attached.

For a thorough cleaning;

  • Detach the hose from the pump.
  • Use a 6mm Allen wrench to loosen the bolts on the brass pump.
  • Loosen the brass tubes on the pump.
  • Turn the engine ON.
  • Fill tank with clean water and flush through until all sediment is cleansed.
  • Screw the bolts back in to secure the pump in place.
  • Reattach the hose to the pump once pump is clean.

How to prime a Milwaukee backpack sprayer

Follow these steps when priming your pump;

  • Fill the tank at least three-quarters (¾) full with water
  • Make sure the pump cylinder is completely submerged
  • Let the water sit in the tank for a few hours (2-3 hours)
  • Once the unit has sat for that amount of time, turn the switch to the “On” position
  • “l” indicates the on position
  • “0” indicates the off position
  • With the switch turned on, place a rubber band around the trigger of the shut off assembly to hold the trigger open (as if spraying)
  • Let the unit run for 12-15 minutes
  • A strong stream should be released at the 12-15-minute mark
  • The unit is now cleaned and primed and ready for use

NOTE: The spray may not come out right away as the pump may run but it may not build pressure. This is acceptable and part of the priming steps.

How to adjust a backpack sprayer nozzle for different spray patterns

Spray nozzles are an important part of reducing spray drift. Choosing the correct nozzle for the job and taking proper care of them is an essential part of spraying safety.

Nozzles regulate the spray flow, droplet size, and spray pattern. Proper selection and operation of spray nozzles are important steps in precise application. Choosing the correct nozzle is critical for safe spray application.

By using the proper nozzle for the job, less spray will drift to unintended areas. Such as other crops, backyards, or animal pastures.

Flow regulation

Flow regulation affects the application rate. Nozzle opening size and spray pressure are key features affecting the flow rate through nozzles. These factors can be varied by selecting a different nozzle size or adjusting the pressure.

Droplet size varies due to pressure, climatic conditions (such as: temperature, humidity, wind speed, and direction), and nozzle size. The size may be affected by the spray angle and the spray pattern shape (nozzle design).

In a conventional system, droplet size can be decreased by increasing the pressure at the nozzle. Droplet size can also be decreased by increasing the spray angle of the tip.

The weather has a strong influence on spray drift. Both wind direction and velocity can cause spray to drift away from its intended target.

The larger the droplet, the faster it falls toward its target, and the less likely it is to drift. However, high winds can cause large droplets to drift off target.

Nozzle Spray Patterns

There are three basic types of nozzle spray patterns: flat-spray, hollow-cone, and full-cone patterns. The characteristics of each spray pattern favor certain chemical applications.

Flat-spray nozzles

They spray droplets from a flat-spray tip, forming a fan-shaped pattern as they leave the nozzle opening. The edges of the pattern have a lower spray volume, so patterns of adjacent nozzles must overlap to obtain uniform coverage along with the spray boom.

Wider-angle nozzles produce smaller droplets, but they can be spaced farther apart on the spray boom or operated closer to the target. Narrow-angle spray tips produce a more penetrating spray and are less likely to become clogged.

Flat-spray tip characteristics make them ideal for broadcast applications of herbicides when uniformity is critical.

Wide-angle full-cone nozzles

These produce large droplets that are distributed uniformly in a full-cone pattern. The uniform spray pattern is maintained over a pressure range of 10 to 40 psi. the droplets are larger than with other tip styles of equal capacity at similar pressures.

They are best used for soil-applied and systemic herbicides. Maximum drift control at pressures of 15 to 20 psi is achieved.

Hollow-cone nozzles

They produce a spray pattern with the liquid concentrated on the outside of a conical pattern. The typical spray distribution is saddle-shaped with less liquid in the center of the distribution, tapering off rapidly at the edges.

It is not well-suited for broadcast applications because the proper overlap is difficult to achieve. They generally produce the smallest droplets.

They are best used for applying insecticides, fungicides, or growth regulators where penetration and coverage are critical.

Their spray drift can be high because of the many small droplets produced at the normal operating pressure of 40 psi and above.

Adjusting Pressure

On some models of backpack sprayers, you will be able to adjust the level of pressure. If you adjust it to a higher pressure, you will have smaller drops of spray, but you may be able to apply to a larger area at once time.

Spraying Tips to Reduce Drift

  • Follow label recommendations to avoid drift with highly volatile pesticides.
  • Use nozzles that produce coarser droplets when applying pesticides on targets that do not require small, uniformly distributed droplets.
  • Keep spray volume up, and use nozzles with larger orifices.
  • Use nozzles with narrower spray-fan angles.
  • Avoid spraying on extremely hot and dry days.
  • Do not spray when wind speeds are higher than 5 miles per hour.
  • Avoid spraying near sensitive crops that are downwind. Leave a buffer strip of 50 to 100 feet, and spray the strip later when the wind shifts.

Why is my battery powered backpack sprayer not working?

This could be a result of motor problems or component problems. If your battery-powered sprayer is not working, do the following first before starting to replace parts.

Checking the Wire Connections

  • Make sure the tank is empty and not pressurized
  • Loosen the bolt in the front of the sprayer
  • Slowly pull down the switch housing
  • When the wires are visible, make sure they are connected near the pump and at the switch
  • Once verified the wires are properly connected, reattach the housing to the tank in the same manner the housing was removed

Cleaning Your Filters

There are two (2) filters that need to be cleaned regularly. The first filter is located in the body of the shutoff assembly. The shutoff assembly is the handle with the red grip and trigger that is squeezed to create the spray. The second filter is in the tank, next to the pump.

  • Shut Off Assembly Filter
  • Unthread the shut off assembly from the hose
  • In the body of the handle is a white filter
  • Remove the filter and soak in warm soapy water to clean any debris or chemical residue
  • Once cleaned, this filter reattaches the handle to the hose

In-Tank Filter

  • Looking inside the tank from above, there is a black stick with a finger hole
  • Pull this stick straight up
  • Soak the filter in warm soapy water to clean up any debris or chemical residue
  • Once cleaned, slide the filter back into place alongside of the pump

If You Don’t Hear the Motor Running

If you’ve followed the instructions above and the motor of your still isn’t running, try these steps;

  • Confirm that the trigger lock is disengaged.
  • Double-check the battery tab has been removed.

If you still don’t hear the motor running, it may be time to change out the batteries. Unscrew the battery compartment on the base of the wand and replace the AA batteries.

If You Hear the Motor Running, but It’s Not Spraying

If the motor is running, but you’re unable to spray, follow these steps to get back into action.

  • Check the cap.

Make sure the knob is turned to “ON.

  • Check the nozzle setting.

Confirm the nozzle is rotated to a spray pattern.

  • Re-prime the sprayer.

Re-prime the sprayer by engaging the trigger for up to 30 seconds, until it begins to spray.

  • Check the nozzle for clogs.

If the sprayer tip is clogged, don’t use soap or other cleaning agents to clean it. If necessary, clean the outer sprayer surface only with a damp towel. Never submerge the wand handle in water.

Cleaning Nozzles

  • Use water that looks clean enough to drink when cleaning the sprayer. Foreign materials found in the water can wear out nozzles.
  • Observe the output pattern of nozzles periodically. Streaks in the pattern indicate that foreign materials are inside the nozzles.
  • Remove and clean nozzles, using a soft brush for the tip and screen and strong detergent solution or kerosene.
  • Cleaning with a pin, a knife or any other metallic object can completely change the spray pattern capacity of the tip.
  • Use a wooden toothpick to unclog nozzle tips.

Note: If you’re still having problems, don’t hesitate to reach out to the Manufacturer’s Consumer Services team.

How to calibrate a backpack sprayer

There are four times when a sprayer must be recalibrated. The calibrated output of the sprayer will remain constant as long as ground speed, spray pressure, number of nozzles, and nozzle orifice are unchanged. Whenever any of these are changed, the sprayer must be recalibrated.

Ground Speed. The speed at which the sprayer travels over the ground will significantly affect sprayer output. Faster speeds produce lower output per surface area, while slower speeds increase output. However, adjusting ground speed is not the best way to adjust sprayer output.

Speed should be dictated by the evenness of the terrain, obstacles, condition of the equipment, etc. The primary consideration of ground speed is safety. The speed should be set to complete the operation as quickly as possible without risk to people or property.

Spray Pressure

Several considerations affect spray pressure decisions. Some product labels require pesticides to be applied within a specified pressure range.

A number of products are low-pressure, low-volume pesticides applied under very low pressure. Applicators must also always be aware of drift potential from their operations.

High pressures present greater risks from drift, so adjusting spray pressure to change sprayer output is usually not a good choice.

Also, unless a significant change of 10 or more pounds per square inch (psi) can be accomplished, adjusting spray pressure will produce only minor changes in output.

Number of Nozzles

Nozzle number is determined by sprayer design. For sprayers that are equipped with directional boom control valves for partial boom applications, each arrangement of boom selection should be calibrated independently.

In most cases, the number of nozzles will remain constant unless the sprayer is rebuilt or retrofitted.

Nozzle Orifice

The nozzle opening or orifice directly affects output and is the most practical way to adjust sprayer output. Several brands of nozzles are available with similar spray patterns (flat fan, cone, etc.) and with various orifice sizes for adjusting output.

Getting Started

Basic tools needed to calibrate a sprayer:

  • Personal protective equipment: gloves, goggles, rubber boots, etc.
  • Measuring tape 50 foot or greater
  • Measuring beaker in fluid ounce graduations
  • Stopwatch or watch with a second hand
  • Calculator

These figures will be needed to make calibration calculations:

  • 43,560 square feet (ft2) per acre
  • 128 fluid ounces (fl oz) per gallon

Calibration Procedure 1

Sprayer calibration is accomplished by determining the effective spray width, using a test area to test the sprayer’s output and time needed to cover the test area, and summing these values to determine the sprayer output per acre.

Step 1: Determine effective spray width (ESW) for broadcast applications. (ESW = nozzle spacing × number of nozzles)

Example: 20-inch spacing × 8 nozzles = 160 inches

160 inches / 12 inches = 13.3 feet ESW

Step 2: Measure and mark off a test area with a length of between 50 and 100 feet; any convenient length, such as a fence line or driveway, will work. The width of the test area will be the ESW as determined in Step 1. After measuring and marking off the test area, determine the square footage of the area. (Square feet of test area (TA) = length of TA × ESW)

Example: 50-foot TA × 13.3 feet = 665 ft2 per TA

Step 3: Determine number of TAs per acre. (TAs per acre = ft2 per acre / ft2 per TA)

Example: 43,560 ft2 / 665 ft2 = 65.5 TAs per acre

Note: Lawn and garden pesticide rates are often given per 1,000 ft2. To determine the number of TAs in 1,000 ft2, simply replace 43,560 with 1,000 in Step 3.

Step 4: Determine the time required to cover the TA. Use water only in the tank during this calibration.

Operate the sprayer with speed and pressure at field operating conditions.

Achieve operating speed before entering the TA course.

Mark start and finish time from the same point on the machinery (e.g., driver’s seat).

Take an average of three timed trials for shorter TA lengths.

Record the average or most accurate time required to cover the TA.

Step 5: Determine the sprayer output for the TA. Use water only in the tank during this calibration.

Set parking brake or otherwise secure the machinery.

Operate the sprayer at field operating pressure.

Collect spray output from one nozzle for the same period of time required to cover TA (determined in Step 4). (Total sprayer output per TA = fl oz per nozzle × total number of nozzles)

Example: 6 fl oz per nozzle × 8 nozzles = 48 fl oz per TA

Note: While performing Step 5, it is a good time to compare nozzle wear by testing all nozzles. Nozzle output should be within ±5% of each other. Replace worn nozzles with those that have equal flow rates.

Step 6: Determine the sprayer output per acre. Sprayer output per acre = fl oz per TA × TAs per acre

Example: 48 fl oz per TA × 65.5 TAs per acre =3,144 fl oz per acre

Conversion to gallons per acre: fl oz per acre / fl oz per gallon

Example: 3,144 fl oz per acre / 128 fl oz per gallon =24.5 gallons per acre

There are at least two techniques for using a backpack sprayer when spraying an area or plot. You can hold the nozzle tip steady at a suitable height above the target surface, usually within a range of 14-18 inches. 

Or, you may choose to swing the wand back and forth in a pendulum motion as you walk. With either technique, make certain that you achieve uniform coverage of the treatment site. Use the same pressure, speed, and technique for the application as was done in calibration.

Calibration for treating small land areas

If you are applying pesticide to an area measured in square feet, calibrate the sprayer by staking out a 1,000-square-foot test plot (for example, 20 feet × 50 feet) on a surface similar to the treatment site.

Step 1. Fill the sprayer tank half full with water (no pesticide)

Step 2. Record the number of seconds it takes to spray the test plot evenly while walking at a comfortable, steady pace. (It is a good idea to spray the test plot two or three times and figure the average time.)

Step 3. Stand still and spray into a container for the average time found in Step 2.

The number of ounces collected equals the amount of spray delivered to 1,000 square feet.

With this number, you can calculate the amount of pesticide and water needed to treat the target area.


Apply herbicide to a lawn 40 feet × 65 feet

Area to be treated: 40 ft. × 65 ft. = 2,600 sq. ft.

Test-plot time to cover 1,000 sq. ft. = 80 seconds

Amount of water collected in 80 seconds: 57 oz.

Sprayer output: 57 oz. per 1,000 sq. ft.

1.   To determine the total spray mixture needed, set up the following ratio and cross multiply:

X = 148.2 oz. (round off to 148).

2.   To determine the amount of herbicide needed, set up the following ratio and cross multiply:

X= 5.2 oz. of herbicide

3.   To treat the target area, a little more than 5 oz. of herbicide should be added to 143 oz. of water (148 – 5). Because there are 128 ounces in 1 gallon, this will mean adding 5 ounces of herbicide to 1.1 gal. of water (143/128 = 1.1 gallons of water).

Calibration for treating small trees, shrubs, and ornamentals

In this situation, you will find out how much water is needed to treat an average plant. If the label says “spray to wet”, spray as if you were painting the plant with spray paint. Try to avoid over-application and minimize dripping of the pesticide off the plant.

Add water (no pesticide) to the tank and pressurize it. Then record the number of seconds it takes to spray a representative plant thoroughly. Now spray water into a container for that length of time. Use this number to calculate the amount of water and product needed.


Apply insecticide to 18 azaleas in a plant bed.

Labeled rate = 3 ounces of insecticide per gallon of water.

Number of plants to treat = 18

Seconds to spray one average plant = 12.

Amount of water collected in 12 seconds = 10 oz.

1.   To determine the total spray mixture needed, multiply the total number of plants to treat by the amount of water collected to treat one plant.

18 × 10 oz. = 180 oz.

2.   To determine the amount of insecticide needed, multiply the labeled rate by the total spray mixture.

3.   Add a little more than 4 oz. of insecticide to 176 oz. of water (180 – 4) to treat 18 azaleas.

Calibration for treating rows of plants

Use the method described in the Ounces-to-Gallons unit of this Web site. Use row width to determine the distance to travel, and record the time it takes to spray (water only) both sides of the row if sprayed in two passes.

In a container marked in ounces, collect the output from the nozzle for the time it took to cover the 1/128th of an acre calibration course. The number of ounces collected equals the application rate in gallons per acre.

How do I attach the straps on a Greenwood 4-gallon backpack sprayer?

The shoulder straps usually come already attached to your backpack sprayer, and the bottom one can be attached without too much fuss. If the sprayer does not have the shoulder straps attached or if you need to replace them;

  • Lift the frame up slightly and place the metal from on the buckle and push down slowly and firmly until the buckle snaps into place.
  • To attach your belt straps, hook the ends to the metal frame where it sticks out and bends by the plastic.
  • If your backpack sprayer came with pre-attached upper straps, slide the lower waist belt through the loops of the upper strap and attach the buckle.

How to disassemble a Solo backpack sprayer

Follow the step to disassemble the following parts of the Solo sprayer when fixing it.

How to disassemble the piston pump;

  • Using a 13mm socket wrench remove the handle bolts, and set aside. Lay unit on its back with pump assembly facing you.
  • Loosen hose clamp. Pull off sprayer hose. Caution: There may be liquid inside the hose and pressure cylinder even when the tank is empty. Wear protective gloves.
  • Next, remove the nut and bolt from protective cap, and remove cap.
  • Rotate the pump shaft to access the two lever bolts in the center.
  • Using a 6mm allen head wrench, remove them.
  • Pull the piston out of the piston cylinder.
  • To remove the piston cylinder assembly, turn the cylinder counter clockwise when viewing from the bottom. Caution: The piston cylinder has sharp edges.
  • Check the outside of the piston and inside of the cylinder for scratches. If the piston or cylinder are scratched, replace with part# 0610409-K (piston) or part# 4073190 (cylinder).
  • To replace the Viton® collar, push it off the top of the piston with your thumb. Install the new collar on the piston onto the form fitted sides.
  • Remove the valve plate and O-rings from the outside of the piston cylinder. Install the new valve plate and the two O-rings making sure the O-rings seat in the grooves.
  • Finally, inside the piston cylinder you will find a second valve plate. Using needle nose pliers, pull out the red or orange pin and remove the valve plate.

How to disassemble the plastic adjustable nozzle;

  • Unscrew the nozzle cap from the nozzle body. This is best accomplished while the retaining nut is fastened tightly to the elbow.
  • Next, unscrew the retaining nut.
  • Push the nozzle body out of the retaining nut.
  • The filter with gasket will come out with the body.

Note: for further instructions refer to your user manual

Why is my Solo backpack sprayer not working?

Check for an airlock in the line & pump.

Air can get locked in between the tank and the trigger, but there is an easy fix for this. Simply turn the pump on and hold the trigger at a level lower than the tank, squeeze and hold.

What this will accomplish is the sprayer will force the air down and out of the wand. This will cause the pump to change noise once the pump is then primed and will become silent once your sprayer has built pressure back up and is ready to go.

Check for filter blockages inside the tank.

If our first step hasn’t worked, the next thing we need to try is to check our filter inside the tank for any blockages. Firstly, remove the lid of the sprayer and then the filter basket. Looking in the tank, you will notice a suction line coming from the bottom of the tank.

At the bottom of this suction line is a small, easily-accessible white strainer. Simply remove this strainer, check for blockages and give it a clean. While you are inside the tank, also ensure to check the top of the suction line and ensure that the small clamp located there is tight.

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Ensure all clamps are tightened.

Thirdly, if our first steps have provided no solution, the next step is to ensure all clamps are tightened within the housing of the sprayer pump. Located on the sides of the sprayer are 4 x screws, holding the pump housing together with the sprayer’s tank.

Let’s remove these screws and pull the pumps housing away from the tank, exposing the battery-powered pump.

Upon doing this, you will notice a hose connecting the tank to the pump. Simply ensure that the clamps at either end of this hose and connected and tightened. This will ensure that no air will enter the pump, causing a loss of functionality.

Solo Backpack Sprayer Troubleshooting Guide

Difficulty in moving pump leverDirty bushingRemove pump lever, clean & grease bushings
Dirty cylinder walls (425)Remove piston, clean/replace piston & collar
Collar swollen from long term exposure (425)Replace collar and maintain according to instructions
Lack of lubrication (425)Lubricate Viton collar
Insufficient resistance during repeated pumping and no pressureDamaged/dirty valve platesClean or replace valve plates or cylinder
Damaged O-ring at valve seatReplace O-ring
Collar or piston (425) wornReplace collar or piston
Seal in pressure regulator is leakingCheck seal and valve seat
High resistance after just a few pumping strokes, pressure lasts only brieflyLittle or no air cushion in pressure cylinderRemove PVC hose, drain pressure cylinder, Reconnect hose. Preventive measure – release pressure after each use
During spraying, upward pumping becomes more & more difficult and tank walls may indent upwardsWrong formula tank cap (no vent hole)Replace with vented cap
Vent hole cloggedClean vent hole.
Lower valve plate sticksReplace valve plate
Intake channels cloggedClean channels & tank
When handle is pulled up it wants to move itself forcibly back downInlet screen at base of pressure cylinder cloggedClean intake screen with a small brush and detergent
Leaks inside cylinder (425)Damaged/dirty collar or pistonClean or replace collar and possibly cylinder if worn
Leaks outside cylinder (425)Damaged O-ring on cylinder

Damaged O-ring on pressure cylinder
Replace O-ring

Replace O-ring
Leaks from diaphragm pump  (474, 475, 476, 485)Damaged diaphragm

Damaged O-ring on diaphragm housing

Damaged O-ring on pressure cylinder
Replace diaphragm

Replace O-ring

Replace O-ring
Leaks from end of spray wandWorn or damaged shut-off valveInspect and rebuild shut-off valve
Note: Always wear rubber gloves, safety goggles and appropriate protective clothing when repairing a sprayer. Work in well ventilated area. Prior to repair, flush unit with water by filling, then spraying the water into an appropriate container or area. Ensure that all pressure is released by locking the shut-off valve in the open position. Once a repair is completed, fill the unit with clean water, pressurize, and check for leaks. If the sprayer leaks, Do Not Use. Repair leaks and recheck.

How to make a backpack sprayer spray further?

To increase the spray distance of your backpack sprayer, do the things listed below;

Change the spray attachment to a slide pump sprayer

A slide pump sprayer works by using a two-handed, telescopic plunger action that draws the spray material from an open container and discharges it through an adjustable nozzle.

The pump has continuous or intermittent action which will help the sprayer to build pressure up to 150 psi and allow you to reach targets over 30 feet away. Additionally, the nozzle adjusts allowing you to have spray patterns up to 25’ or 30’.

Use an adjustable nozzle

This type of nozzle will allow you to switch between fine and coarse mist that can reach further depending on the density of the liquid being dispensed.

Note: Calibrating the sprayer will also help to make it spray further. You can use either of the calibration techniques discussed above to adjust the calibration.