Sprayer calibration saves money and environment

WOODSTOCK, Ont. — Most sprayers vary five to 15 percent from nozzle to nozzle.

“The whole unit might be pretty close to spot on (for rates of application), but from nozzle to nozzle or side to side, it could be out quite a lot, and most are,” said Helmut Spieser, an engineer with the Ontario agriculture department.

He said he has seen first-hand the evidence of sprayer variability and the research that backs it up.

He said farm sprayers, whether they are small, medium or large, are not the precision instruments the industry thinks.

Jason Deveau, a pesticide application specialist with the department, said research has shown that sprayers misapply millions of dollars in product, wasting chemical and hurting crops and yield.

“U.S. farmers’ sprayers have been shown to be out of calibration in a substantial way. Two-thirds of machines are accurate to plus or minus five percent. One-third are out of whack by more 10 percent,” he said during Canada’s Outdoor Farm Show in Woodstock in mid-September.

“Rate controllers don’t calibrate machines. You can have the best in precision agriculture tools, but they don’t have control of each nozzle. Only people can calibrate a machine.”

Rate controllers balance the flow of material through the sections of a boom, but that region of the machine can be significantly out of calibration within each section because of the variability of the nozzles.

“What is acceptable variation? We recently had a farmer bring in a new set of nozzles. They were packed in sixes, in a plastic case. He said there was a problem. We tested 17 percent over,” said Deveau.

“Dealers don’t like to hear that sort of thing. They will push back. They will tell you, you are wrong. They might even say worse than that. You can ask them to test for themselves.… A few dealers have set up testing units in their shops to examine the flow of nozzles before they are sold.”

Spieser said the only way to be certain whether a sprayer is properly calibrated is to test nozzle by nozzle.

“Testing takes as little as 20 minutes. And you only need to do it once a year, unless you make changes or are spraying a lot of abrasive stuff.”

It might take as long as 90 minutes to test all 72 points on larger sprayers, with a nozzle every 20 inches.

Adding micro nutrients or spraying with water that contains a lot of tiny fine particles can rapidly wear nozzles.

Deveau said some air-blast spray systems that put out high flows of material at 200 pounds per inch can wear through a couple of sets of brass nozzles in a season.

Poly wears the fastest, with higher priced ceramics lasting longer.

“They all wear,” he said.

“You don’t buy a few sets of different (rates) and think you’ll be keeping them for the whole time you own that sprayer and have them perform properly.”

Spieser said calibrating a set of nozzles or replacing a few will pay for itself the first day in increased yields.

“A new set will pay for themselves in saved spray and proper application in the first season, and likely a lot sooner than that,” he said. “Not to mention, the environmental issues with proper application.”

Producers can check each nozzle for errors by using graduated cylinders or other accurate measuring devices. They can also run the sprayer for a specific time.

The sprayer’s controller should be matched to a known, measured distance on the farm. Many producers maintain a set of marked posts that they can quickly use to ensure that the machine remains properly set. This is critical for machines using Hall sensors on driveline shafts or radar units for speed and distance monitoring.

It is less variable for GPS units, but these should also be verified on occasion.

Once distance and speed are known to be accurate, producers should establish a target rate based on which nozzles they selected and the pressure that is applied by the pump and controller system. Manufacturers’ performance charts will indicate the gallons or litres per minute that are the standard for a specific nozzle at a specific pressure.

Multiply U.S. gallons per acre by miles per hour and by the sprayer’s width between nozzles in inches.

In metric, it should be litres per acre multiplied by kilometres per hour multiplied by width in centimetres. Divide by 5,940 for the imperial version and by 60,000 for metric.

This will provide a gallons per minute or litres per minute result.

Standing still should yield a result that is similar to the rated amount for the nozzle after setting the sprayer to produce the target pressure and capturing the outflow from the nozzles.

For example, a nozzle rated at 0.4 gallons or 1.5 litres per minute at 40 lb. per square inch should generate that result when nozzles that are spaced at 20 inches on a boom travelling at 12 m.p.h. and applying 10 gallons per acre do this for one minute.

Test each nozzle using water and note the rate. A nozzle should be replaced if it doesn’t match its rated capacity by plus or minus five percent.

An automated spray controller can manage the application rates if all the nozzles are out by similar amounts so that that there aren’t drastic variations across the booms. However, nozzle performance might be compromised.

There are automated methods of calibrating. Wilger’s quick calibrator sells for $399, while the SpotOn units from Innoquest that are popular with researchers and machinery engineers sell for $150.

Deveau said even the automated systems aren’t fool proof and must be used in the same way each time to be reliable.

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