Cleaning an airblast sprayer

Next to sprayer math, cleaning the sprayer is one of the more distasteful aspects of airblast spraying. It’s time-consuming, you never really know when you’re finished, and sprayer manufacturers and pesticide labels offer only limited guidance.

Clean sprayer rinsate looks and smells exactly like contaminated sprayer rinsate.

When airblast sprayers are not cleaned as often or as thoroughly as they should be, it creates problems:

  • Unnecessary operator and environmental exposure.
  • Residue in (or on) the equipment can damage sprayer components.
  • Residue can cause physical or chemical incompatibility issues with future spray mixes.
  • Carry-over can deposit damaging or unlabelled residues on crops.
Keeping the sprayer clean, inside and out, as part of the spray day. K. Bell is pictured giving his FMC a bath. This picture was staged – he normally wears PPE and so should you.
Keeping the airblast sprayer clean, inside and out, as part of the spray day. Ken Bell is pictured giving his FMC a bath. This picture was staged – he normally wears PPE and so should you.

Dr. Tom Wolf (Agrimetrix Research and Training), defines cleaning as two processes. Rinsing is the dilution of any remaining spray solution. Cleaning is rinsing with additional steps to decontaminate sprayer components (e.g. filters, nozzles).

Rinsing

1. Rinse ASAP

Don’t let residue sit in (or on) the sprayer, even if you plan to use the same product the next day. Multiple studies have shown that products adsorb onto, and absorb into, plastic and rubber parts. They form hard-to-clean residues when left to dry.

Think about cleaning oatmeal or egg yolk off dishes – it’s far easier if you clean them before they dry. Rinse right away, while the sprayer is still wet.

2. Minimize the volume remaining in the sprayer

Experience, sprayer math, and familiarity with airblast sprayer design helps minimize the volume remaining in the sprayer. Rate controllers and volume-monitoring systems (e.g. Ontario’s Accu-Volume) provide real-time feedback so the operator can speed up or slow down to empty in the right place. Minimizing any remaining volume makes rinsing far more effective.

Even an “empty” sprayer can still retain several litres of standing volume in the sump and lines. Operators should know this volume. Never Drive-and-Drain to empty standing volume onto the ground.

Standing volume from the booms allowed to drain to a holding tank via the bottom nozzles.

3. Dilute the remnant: The Triple Rinse

Rinsing the system multiple times with low volumes (aka The Triple Rinse) is more effective at reducing pesticide concentration than a single, high-volume rinse. See for yourself using this clever dilution calculator.

Once the sprayer is “empty”, use clean water to fill the tank to 10% of its capacity (or add 10 parts water to one part standing volume) for the first rinse. The use of such low volumes may not be possible with centrifugal systems where the tank must be filled above the top of the pump for priming. Know your sprayer design.

Agitate and circulate it through the entire sprayer for a few minutes. Spray out the rinsate and repeat the process two more times. Where do you perform this? Where does the rinsate go? Read on.

A wooden sprayer tank. You know that had to be tough to clean thoroughly.
A wooden sprayer tank. You know that had to be tough to clean.

Where does the rinse water come from?

Nowadays, all airblast sprayers should include an onboard tank-rinse system consisting of a clean water tank and tank-rinse nozzles inside the tank. They may even include a pressure wand to rinse the exterior.

Sadly, most airblast sprayers do not have these features. But, aftermarket rinse kits are available. If you are considering installing a rinse system, check out the continuous rinse system.

Left- Product-pump-powered water tank, Right- external-pump-powered water tanks. Images from Paolo Balsari’s (DiSAFA) “Sprayer Cleaning: Importance and Phases” at AAB Sprayer Cleaning Workshop, Oberbozen, Italy. October 2019.
The Hol features a separate 150 L tank to supply clean water to its automatic tank rinse system.
The Hol features a separate 150 L tank to supply clean water to its automatic tank rinse system.

Alternately, the clean water for this process can be carried on a support vehicle or sourced from holding tanks strategically-located near the planting.

Where to rinse

Precautions must be taken to ensure rinsing is performed away from wells or open water. It is best to perform the triple rinse in the crop that was just sprayed. The dilute rinsate can be flushed through the lines and sprayed out through the nozzles onto the crop. You can choose to overspray treated areas again at a lower dose (label permitting), or use a hedgerow or target row that has been set aside for this purpose.

As regulatory agencies concerned with environmental contamination re-evaluate chemistries critical to horticulture, it becomes even more important for airblast operators to manage rinsate responsibly.

While it is best to rinse the sprayer exterior in the planting as well, most return to the farm. Too often, the entire rinsing procedure takes place on-farm, on crushed gravel. This creates point-source contamination: a leading source of off-target pesticide movement. Washings should be secured (e.g. on an inflatable or permanent loading/mixing pad.

Cleaning an airblast sprayer on an inflatable pad. Images from Victoria Nelissen’s (pcfruit, Belgium) “On-farm systems to avoid point pollution” at AAB Sprayer Cleaning Workshop, Oberbozen, Italy. October 2019.

In Europe, operators are encouraged to collect contaminated rinsate for safe disposal. There are four systems in use:

  • Bioremediation – Employs a bio-active matrix (E.g. Biobed).
  • Evaporation / Dehydration – Residue following evaporation is collected and disposed of (E.g. Heliosec).
  • Physico-chemical – A combination of filtration and active carbon.
  • Photocatalytic – Photo degradation (E.g. Phytocat).

Cleaning

A complete cleaning is required prior to long-term storage, or when residues from previous applications are known to cause physical or chemical antagonism with scheduled applications. Perform the following steps after a complete triple rinse:

One. Remove the suction and in-line screens. Remove nozzle strainers and nozzle tips. These will be inspected and cleaned shortly.

Two. Fill the tank about 1/2 full of water and add an appropriate tank cleaning adjuvant. For example, ammonia at 3%/100L water will raise the pH and helps remove those products whose solubility benefits from this. A detergent at 1.0 kg /150 L water will remove the oily layer formed by EC formulations. Commercial cleaners like All Clear or Cleanout conveniently combine these properties in one jug. Be aware that adding a surfactant or a commercial cleaner can generate a lot of foam, so have de-foamer handy.

Ammonia cleaner products do not “neutralize” pesticides; they raise the pH, improving the solubility of some products. Do not use chlorine bleach! It is not as effective a cleaner as ammonia and can form chlorine gas when mixed with ammonia-containing liquids.

Three. Collect a bucket-full of cleaner solution from the tank. Using a brush, clean the suction and in-line screens, and the nozzle strainers and tips.

Four. Meanwhile, agitate and circulate it the cleaner solution through the entire sprayer for five to 10 minutes. Open and close any lines or valves during this process to ensure everything is exposed to the rinse.

Five. You might spray a small volume through the booms, but drain the vast majority through the plumbing system. Collect some for cleaning the exterior of the sprayer.

Six. Clean the exterior of the sprayer. High pressure washers and scrubbing with a push broom works well. Studies in Europe have shown the vast majority of residue is found on the sprayer head (i.e. fan outlet and boom area).

Pressure washers are handy tools on a farm, and they’re fun to use, too. However, they can cause a great deal of damage if they are used to wash delicate things like engine parts, electronics housings, or sealed bearings. Use caution!
Pressure washers are handy tools on a farm, and they’re fun to use, too. However, they can cause a great deal of damage if they are used to wash delicate things like engine parts, electronics housings, or sealed bearings. Use caution when power washing an airblast sprayer.
Relative external contamination on a low profile axial airblast sprayer. Image from Paolo Balsari’s (DiSAFA) “Sprayer Cleaning: Importance and Phases” at AAB Sprayer Cleaning Workshop, Oberbozen, Italy. October 2019.

Seven. Rinse it all off. Replace all parts unless preparing for long-term storage.

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