| | The big developments in sprayers and how they led to today’s high- tech design
As recently as 1975, controlling spray variables was essentially a manual task. "This was fairly simple because tractor speed was limited to a fairly constant 5 miles per hour (mph)," says Storozynsky. Recommended spraying pressure was 40 psi, and the key to avoiding drift was to avoid spraying in winds above 6 mph and using 10 gallons per acre (gpa) nozzles (e. g. 8002 nozzles). Around 1980, that put drift loss below three percent, a fairly reasonable margin of loss for the time. For today’s farmers using conventional nozzles, this advice still applies.
The demand for more flexible spray systems emerged when advances in machinery allowed farmers to vary tractor speed, says Storozynsky.
Auto-rate controllers reduced error, enhanced flexibility
Auto- rate controllers, introduced about 20 years ago, took a lot of the guesswork out of spraying and allowed greater flexibility for farmers, says Storozynsky. An auto-rate control feature monitors and measures water flow and tractor speed to automatically keep the application rate constant.
"This technology reduced the chance of error. Farmers no longer had to sit on a tractor or a self propelled sprayer and adjust pressure - with auto-rate control, it was done automatically. Basically, if you wanted to apply 5 gpa, you entered the number, and it automatically delivered that for you, no matter what the speed.
"Some small farmers still do without auto rate controls because they really don’t need it," he says. "For the farmers still going 5 mph, their speed doesn’t change all that much when they’re spraying. With high clearance rigs and truck mounts going anywhere from 10 to 20 mph, their speed is always changing. When they’re going that fast, they can’t really control the pressure anymore. For them, auto-rate control reduces a lot of error."
However, despite its dramatic benefits for the industry, autorate control created another problem-- inadequate coverage.
Wide-angle nozzles provide better coverage (1985)
Wide-angle nozzles, introduced in 1985, allowed producers to keep the coverage uniform across the length of the boom no matter what the speed, especially with the extended range 110 degree nozzles, Storozynsky says. "With auto rate controllers, the older tips didn’t have enough angle to cover between the nozzles. With the 65 and 80 degree tips, when you slowed down and your pressure went from 40 to 20 psi, there was inadequate coverage and misses in the field. As spray angles widened, coverage improved, making the automatic rate controller more suitable."
"With wide-angle nozzles, farmers with modern rigs with auto rate control can slow down and speed up as much as they want, because the nozzles are designed for coverage from 15 to 100 psi," he says.
Although increased nozzle angle allowed greater coverage at slow speeds, it created yet another challenge - increased drift, often as high as 15 percent. Also during this time, there was a trend towards using smaller droplets as air-assisted sprayers, rotary nozzles and electrostatic sprays were introduced. Manufacturers of these spraying systems claimed smaller droplets were more effective because of better coverage and under- leaf coverage.
"All of a sudden we were drifting five times more than we were five years before," says Storozynsky. "Since then, we’ve been trying to get our drift levels back down to three percent, to what they were in 1980. And it’s taken industry 20 years to do that, starting with shrouds, then low drift and finally venturi nozzles."
Shrouds introduced to control drift (1988-1995)
To address drift, some manufacturers introduced a shroud device to cover the nozzle and its spray. From the nozzle tip to ground level, a plastic shield fitted in the front or the rear of the sprayer, prevented the spray from drifting.
"Shrouds were really popular from about 1988-1995," says Storozynsky. "The problem was, most farmers found them a nuisance. Farmers couldn’t see the spray, so they didn’t know If the nozzles were plugging. They also had to wash the shroud when switching chemicals. Chemicals clinging to the shroud could damage the next crop, and a lot of farmers didn’t like that."
Addressing drift
"At the AgTech Centre, ever since we started testing nozzles using a wind tunnel, we’ve seen a dramatic improvement in sprayer tips," says Storozynsky. "From our wind tunnel studies of the past 10 years, we found that, no matter what type of nozzles we test, or their size or pressure, the material that drifts is always the same size in terms of the droplets that float in the air. Those droplets are almost always less than 150 microns in diameter."
"After this information was released, the nozzle manufacturers set out to get rid of the 150 micron droplets. And that’s what’s happened with the low-drift nozzles and the venturi nozzles - they eliminated droplets less than 150 microns, which is why we get less drift now."
The venturi nozzle works by passing spray solution through a tapered passage in the nozzle. As the passage diameter decreases, the spray is accelerated. At the tapered passage outlet, this acceleration creates a natural vacuum causing air to be sucked from outside the nozzle tip through one or two holes. The spray solution and air are mixed in the chamber before exiting the nozzle tip. The compression in the mixing chamber causes air bubbles to be formed inside the liquid spray droplets.
This nozzle design produces larger spray droplets, which has a positive effect on spray drift, and a reduced number of droplets per plant with little compromise in application uniformity or chemical efficacy. As an added advantage for farmers, the venturi nozzle tip fits into existing nozzle caps, says Storozynsky.
Venturi nozzles have rapidly become popular with producers because drift levels are reduced down to 3 percent, back to what they were 20 years ago, says Storozynsky. "Some venturi nozzles are more effective than a shroud, in terms of reducing drift, and now you don’t have a shroud to wash when you’re switching crops and chemicals. With the sprayer visible again, farmers can see the spray again, which they seem to like, to detect which nozzles are plugging."
"At AgTech Centre, we have divided all of the venturi nozzles into two categories: high pressure venturis, and low pressure venturis," Storozynsky says. Low pressure venturis can be used the same way as conventional tips with the average spraying pressure set at 40 psi. Storozynsky recommends low- pressure venturis for farmers who have always used conventional tips and want assurance of efficacy. Low pressure venturi nozzles can also be used on high clearance sprayers, even though high pressure venturis are often the better option.
"We’re recommending the high pressure venturis for the high clearance sprayers - those big 200 hp machines. High pressure venturis reduce drift up to 90 percent, depending on nozzle type, size and pressure. High pressure venturis should be operated above 70 to 80 psi to get adequate coverage in small and grassy-type weeds." Until all the results are in, high pressures are recommended for all venturi nozzles with some chemicals used to control weeds at the cotyledon stage.
Producers should remember to carefully calculate their application rates when using pressures other than 40 psi with venturi nozzles, Storozynsky cautions. "Twenty years ago, everybody sprayed at 40 psi, in part to reduce drift. Now, with venturi nozzles, we are spraying from 40 to 120 psi. With venturis, high pressure now does not necessarily mean more drift, which was the case with conventional and extended range nozzles." |
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