Adjusting the airblast air direction
This is part one of a two part article on how to adjust the air direction, and air speed/volume. If you’ve purchased a new airblast sprayer, you’re spraying a crop you’re not familiar with, or you are ready to reconsider your traditional practices, this is the article for you! When performed correctly, these adjustments are a qualitative form of calibration that will help you optimize the fit between your sprayer settings and the target you wish to spray. This amounts to better coverage and less waste.
It is important to emphasize that any adjustments are only as good as conditions during the adjustment. In other words, don’t adjustments made in low wind, high humidity and moderate temperatures to give the same coverage in high winds, low relative humidity and high temperatures. Droplets get blown off course and evaporate rapidly. Only make adjustments to the sprayer in weather conditions you would normally spray in.
I recommend using a handheld weather meter to monitor the conditions. Record those conditions along with your calibration notes (because really, sprayer adjustments are part of calibration). Local weather reports often don’t match the conditions in the planting. Hold the weather meter as high as you can – preferably readings should be taken at the top of a spray swath. Reading wind, for example at the orchard floor results in wind speeds approximately ½ that at the top of the orchard.
The weather conditions during spraying will affect everything, so only make sprayer adjustments in conditions you would spray in, or your settings may no longer be appropriate.
The air stream created by the sprayer fan (or turbine) carries the spray solution into the target (e.g. tree, bush, shrub, vine, etc.) and distributes it throughout the plant canopy. To reach all target surfaces, and the achieve adequate spray coverage, all of the air in the plant canopy must be replaced by spray-laden air.
The air direction is important. Research has shown that radial fans without effective straightening vanes or deflectors make the air go up on one side and down on the other. In extreme situations, this might compromise the spray job (e.g. miss the lower portion of the target on one side of the sprayer) or it might simply waste spray and stir up leaf litter and dust. Here’s how you can see if this is happening on your sprayer:
- Park the sprayer in the alley between the rows – preferably with no cross wind.
- Tie 25 cm lengths of ribbon (not flagging tape) to the upper, middle and lowest nozzle bodies and attach lengths to the deflectors (if present) using duct tape.
- Turn on the air, but beware of the fan intake – if the ribbons are too long they won’t stand straight out and may get sucked into the intake.
By observing the ribbons, you can extrapolate where the deflectors should be aimed. Adjust the deflectors to just over- and under-shoot the target canopy. Deflectors should not be optional on fan-equipped radial airblast sprayers – they should be standard equipment. Not only do they compress the spray-laden air into a tight stream that more easily reaches and penetrates canopies, but they can also prevent leaf litter and dirt from being stirred up. This helps to keep the fan blades and grill clean and reduces the potential for “sandblasting” on grape and berry crops.
For suspended airblast fans, such as over-the-row systems, the ribbons can still be used to adjust deflectors when present. Perhaps more importantly, be sure the air outlets do not point directly at one another (imagine looking down over the crop – they should not be at right angles to the row). Research in Quebec and experience in Ontario have shown that crop penetration will improve by orienting the outlets in any manner other than in direct opposition (e.g. one forward, one back or both forward, etc.).
For Turbomist sprayers without towers, upper and lower deflectors are not an option. Instead, the sprayers are designed to channel air using adjustable outlets. Note that the air outlet is not a uniform width – it’s widest about half-way down. Using ribbons to extrapolate air direction, aim the widest part of the outlet at the densest part of the canopy. This automatically repositions the booms as well, facilitating the next calibration step where we turn off nozzles that will significantly over- or under-shoot the target. This is discussed in another article.
This process should be performed for EACH significantly different crop or block sprayed with the sprayer. Some operators dedicate sprayers to certain blocks to minimize the number of adjustments required. This may necessitate re-ordering the sequence in which blocks were traditionally sprayed. If that’s not possible, multiple set-ups might be needed to reflect block diversity. This can be minimized by grouping similarly-sized blocks together and calibrating to the worst-case scenario (i.e. the target with the greatest area-density). Smaller blocks may be slightly over-sprayed, but it’s still an improvement in efficiency. Record the set-up for each sprayer/block combination and keep a copy in the tractor cab(s).
Be sure to read the next installment:
Adjusting airblast sprayer air settings: Part two –Air speed / volume.
The right size sprayer for the job – thanks to Penn State, Univ. New Hampshire and Chazzbo Media (2014).
Calibrating the air on an airblast sprayer – thanks to Penn State, Univ. New Hampshire and Chazzbo Media (2014)