The basics of sprayer calibration

Posted: June 9, 2005

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Good economics and reduced environmental risk drive the need to calibrate sprayers.

Whether using new or older equipment, a field sprayer should be calibrated prior to each spraying season for each nozzle size used to ensure it's delivering pesticide at the targeted rate.

The procedure takes time, but it can be worthwhile use to reduce pesticide waste, ensure proper pesticide rates and reduce downtime, says Brian Storozynsky, a sprayer technology specialist with Alberta's AgTech Centre in Lethbridge.

"There's nothing worse than coming up a few acres short after filling up for an 80 acre field," he says. "Having to reload for those few acres is as time consuming as filling for the whole 80 acres and can be frustrating when adverse weather conditions are on the horizon."

Two basic systems

Depending on the age or type of field sprayer equipment, farmers may simply rely on a pressure gauge to tell them how the sprayer is operating, or the unit could be equipped with the newer electronic monitor or controller. The auto rate controller mounted inside the cab of the sprayer or tractor, provides a constant display of sprayer operations such as nozzle flow rate, application rate, tractor speed and spray pressure.

It's good technology, but a monitor and controller may not always tell the full story, says Storozynsky. "These monitors function only as accurately as they are programmed," he adds. "The key is to understand, program and calibrate the monitoring accessories for accurate application rates."

"The monitor will display application rate and the controller is programmed to adjust sprayer flow rate to maintain a constant application rate," he explains. "But, to maintain that flow rate, the controller may reduce spray pressure and in doing so, may affect the spray pattern and coverage. Even though the monitor says one thing that may not be what's actually happening. This system should be checked in detail at least once a year, preferably before the spraying season starts. A quick check on accuracy can be done several times throughout the spraying season. During tank and line rinses, the sprayer should be placed on test speed and monitor outputs checked."

In his 25 years of using and monitoring spraying equipment, Storozynsky also advises producers not to assume all new equipment operates at manufacturer specifications. "We've tested brand new nozzles that are out by five percent or more," he says. "It's not a huge issue if it is only one or two nozzles, but if the whole set is out by five percent, that can be cause for concern."

On all systems

The purpose of calibration is to ensure the pesticide is being applied at the proper rate. Therefore, nozzle pressure, sprayer speed, nozzle flow rate and application rate must be in sync and match the nozzle manufacturer's application rate tables. With a yellow nozzle, for example, a producer may be targeting a 10 gallon per acre (gpa) application rate, a .757 litres per minute (L/min) average nozzle flow rate, at 40 pounds per square inch (psi) pressure, at a travel speed of five miles per hour (mph).

"If that's the target application rate, then you have to make sure the equipment is delivering that," says Storozynsky.

Producers should check the following key operations as part of the annual calibration process:

• The flow rate of the nozzle - usually measured in litres/minute. The flow should be within 10 percent of the nozzle manufacturer's rated flow. The total flow from all the nozzles should match the output of the flow rate sensor (meter).
• The accuracy of the pressure gauge or transducer on the sprayer. (Note: there are two types of auto rate controllers - pressure and flow based. The pressure-based type, in particular, should always be checked against a spare pressure gauge used only for calibration).
• The travel speed of the tractor or self-propelled unit.

These key operations are included in the sprayer application rate formulas and nozzle manufacturers application rate tables.

Nozzle output basics

The following table shows flow and application rates for five of the most common color coded nozzles, all operated at 5 miles (8 km) and 10 miles (16 km) per hour and 40 psi. The orange nozzle, for example, has a U.S. rating of .1 gallon/minute, which translates into .379 litres/minute. It will apply five gallons per acre or 56 litres/hectare at 5 mph. And in a combination of metric and Imperial measures, that's the same as 22 litres/acre at 5 mph and 11 litres/ac at 10 mph travel speed.

Nozzle	U.S. Nozzle rating	L/minute	Gallons per acre 5 mph	Litres per hectare 8 km/h	L/ac 5 mph	L/ac 10 mph
Orange (01)	.1 US gpm	.379	5	56	22	11
Yellow (02)	.2 US gpm	.757	10	112	45	22
Blue (03)	.3 US gpm	1.136	15	168	67	34
Red (04)	.4 US gpm	1.514	20	224	90	45
Brown (05)	.5 US gpm	1.893	25	279	112	56

Next: The art and science of assessing nozzle wear