FEATURE ARTICLES
The art and science of assessing nozzle wear
Posted: June 9, 2005
• The basics of sprayer calibration
• Field sprayer calibration steps
• More efficient spray application saves money
Deciding if and when to replace worn or faulty nozzles requires judgment. A couple of nozzles, from a new batch of nozzles may be out by five percent of the manufacturers specified flow rate. However, if the overall average from the entire batch is within five percent, those couple of nozzles will not adversely affect overall performance.
Older or used nozzles out by five to 10 percent of manufacturer flow rates should be at least cleaned if they have reduced flow rate, and flagged for replacement if they are worn and have a high flow rate. If the flow rate of several nozzles is out by more than 10 percent, the entire set should be replaced, says Brian Storozynsky, sprayer technology specialist.
Calibration determines the actual output of the nozzles
Replacing only the individual ones that are out by more than 10 percent is an option, but that may cause headaches the following season, he explains. The variation in nozzle flow the next year may be that much greater if the batch of replacement nozzles were, for example, five percent below the nozzle specification at installation. "In testing nozzles over the years, we've found nozzle output varies from batch to batch and year to year," he says.
Even a good set of nozzles will have some variation in spray distribution. When applying 10 gpa, with new nozzles, for example, the actual application across the sprayed swath may range from 7.5 to 12 gpa. "That's 20 percent off from what is displayed by the monitor or nozzle manufacturer's application rate table," says Storozynsky.
Only extended range or wide angled nozzles deliver a narrower application rate range. With sprayers equipped with auto rate controllers, worn nozzles that are out by 10 percent are automatically compensated for as the controller adjusts the flow to maintain the programmed application rate.
Only with careful attention to the pressure, which would fall to around 35 psi, can an operator notice the increase in flow due to worn out nozzles, says Storozynsky.
Operators with sprayers that do not have auto rate controllers can either adjust speed and/or pressure to maintain the manufacturer's rated application rate, or simply just live with the calibrated application rate and mix the chemical accordingly.
To maintain 10 gpa with worn nozzles the producer has the option to reduce sprayer pressure, or travel faster. Instead of 8 km/h the tractor needs to run at 8.8 km/h to maintain the 10 gpa. "The farmer also has to note that worn nozzles adversely affect spray distribution or pattern and result in more spray being delivered below the nozzle," he says.
"With many newer nozzles costing between $7 and $12 each, producers don't want to rush out and spend $500 to $1,000 or more to replace nozzles," he says. "I suggest, if a few are 10 percent out from the manufacturers specified flow, it is an indication the nozzles are getting old and worn. Replacement depends on whether the operator can afford the cost of buying all new nozzles." "If several nozzles fall 10 to 15 percent outside the specified flow rate, it's a good indication the entire set of nozzles should be replaced."
In theory, new nozzles and other new equipment should all perform according to manufacturer specifications, but occasionally they don't. In a set of 36 new nozzles on a 60-foot sprayer, for example, there's a good chance a couple of nozzles will already be out by five percent, says Storozynsky.
And, in fact, it doesn't take much use to cause wear on parts. Researchers in North Dakota say dry flowable pesticides, for example, can wear nozzle tips and cause an increase in application rates after spraying as little as 20 hectares (50 acres). Similarly AgTech Centre found that in using a water dispersible granule (DG) product, there was enough nozzle wear after 40 hours to cause flow rates to be out by at least 10 to 15 percent.
