Maintaining Uniform Application For Sprayers

Proper sprayer operation involves calibrating equipment often and documenting it each time.

By John Fulton
Extension Specialist, Biosystems Engineering
Auburn University

Screen Shot 2014-12-04 at 1.40.58 PMSprayer technology has rapidly advanced in recent years with new rate control systems along with technologies such as guidance and automatic section control. While these modern technologies can provide substantial benefits for farmers and/or sprayer operators, they do require proper setup, operation, calibration and maintenance.

The primary considerations include selecting the proper nozzles for a specific application, flow meter calibration and checking nozzle uniformity. These are critical to maximizing the benefits of technologies while also maintaining the necessary spray efficacy of products.

Check Flow Meter Rate
During recent on-farm visits, we found sprayers that were operating outside of 10 percent from the target application rate because of an incorrect flow meter calibration number being set in the controller. The flow-meter calibration number is something that needs to be routinely checked by the operator, especially when changing products.

The easiest method of checking is to place a known volume in the tank, spray this volume, and then check and see if the controller indicates the same amount of volume has been applied. If the applied amount is not within a few percent, then the flow meter needs to be re-calibrated. Sprayer and rate control manufacturers have good, detailed calibration procedures to ensure one establishes the correct calibration number.

Other procedures exist but consult your operator’s manual. If you find that this number is inconsistent during your check for a particular product solution, then call your dealer or manufacturer. Incorrect flow meter calibration can lead to additional problems.

Pressure Affects Droplet Size
Another area of concern is that most rate controllers are flow-based systems, meaning they control flow but not necessarily pressure. This type of control system needs to be well understood by operators, since pressure in these flow-based systems can vary during field operations.

Screen Shot 2014-12-04 at 1.41.26 PMIn one example, we found that the pressure ranged from five pounds per square inch to 65 pounds per square inch during application in three fields. We had pressure spikes to more than 100 pounds per square inch at times. While this pressure fluctuation may not impact some applications, it can for applications where droplet size is critical for product efficacy as in fungicide application.

Pressure variations can also impact the risk of drift since these high pressure spikes normally occur when entering and exiting headlands. Along with sprayer operation, nozzle selection is important to ensure the product is applied correctly.

Other Considerations
These are just a few comments about proper sprayer operation. Be sure to review and follow the calibration procedures by sprayer and technology manufacturers. Don’t base this year’s setup on last year’s.

Make sure you are selecting the proper nozzles for the application at hand and expected sprayer operation in the field (e.g. ground speed). Ensure that a pressure sensor is easily visible to the operator so they can keep an eye on it while spraying. This feedback can be important so the operator can maintain the desired pressure range for a nozzle/setup combination. PG

For more information or links on this subject, visit the precision ag Web site at

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