FEATURE ARTICLES
Variable rate nozzles may offer good coverage and minimize drift
After years of trying to find the perfect balance, a Lethbridge, Alberta researcher says variable rate nozzles such as the VariTarget system may adequately tackle both coverage and drift at a variety of speeds
Posted: January 27, 2009
Although more work needs to be done to know for sure, preliminary tests reveal variable rate technology may hold the key to the long-running challenge of minimizing airborne chemical spray drift while achieving adequate spray coverage, says a project manager with the AgTech Centre in Lethbridge, Alberta.
Brian Storozynsky is a researcher with three decades of experience in testing spray nozzle technology. Over that time, he has seen a number of technologies come along to tackle the problem of spray drift only to pose new challenges to producers. As a result, he admits he is slow to be impressed by new product claims.
However, going by the preliminary data from an ongoing series of research projects on drift from variable rate nozzles, he wonders if variable rate nozzle technology may hold the solution to the drift-coverage dilemma and certain other nozzle-related challenges crop sprayers experience.
"Going by what we've seen from the research to this point, VariTarget nozzles, which we've chosen as an example of the latest in variable rate technology, appear to offer better coverage at a greater variety of speeds than many conventional and venturi nozzles on the market right now. At the same time, their capacity for spray drift is comparable to or better than many of the best drift-reducing nozzles available today," says Storozynsky.
"In many ways, depending on what further studies reveal, it could turn out to be the only nozzle producers need, which could in turn mean less down time spent changing nozzles."
How they compare
Perhaps the key differentiating factor of variable rate nozzles, which use solenoids or spring-loaded valves to control flow, is their compatibility with auto rate controllers, says Storozynsky. "In my opinion, VariTarget nozzles are probably the first nozzles to come along that are truly compatible with rate controllers because they're built to respond to them," he says.
"If an operator was to program a rate controller to apply 10 gpa at 10 mph using a conventional nozzle, they could only travel between 7.5 mph and 12.5 mph without compromising coverage or droplet size. With variable rate nozzles, however, operators can open up their speed options. With a VariTarget variable rate nozzle, for example, the operator can travel between 3.5 mph and 20 mph while maintaining a certain level of consistency in coverage and droplet size, meaning better uniformity."
What was tested
Since variable rate nozzles came on the market a few years ago, one of the most frequent questions Storozynsky has received from producers is how they compare to air induction, or venturi, nozzles, a popular nozzle type which produces larger spray droplets which minimize drift. At the same time, however, venturis can compromise coverage because of their coarser droplets.
The AgTech Centre is in the early stages of testing selected variable rate nozzles in order to gather drift data that can be compared to existing data on several venturi nozzles currently on the market. For the purposes of the research, VariTarget variable rate nozzles were chosen as an example of the latest in variable rate technology.
There are four different sizes of VariTarget nozzles: green (very coarse droplets), blue (coarse droplets), yellow (medium droplets) and orange (fine droplets). Based on the research numbers to date, an operator can reduce drift by about 50 percent by going from a yellow VariTarget to a blue and by about 20 percent by going from a blue to a green.
Three of the four VariTarget nozzle caps were tested under a water volume of 7.5 gal/ac and a spraying speed of 15 mph, which is comparable to using single red 04 or twinned yellow 02 nozzles. Not surprisingly, the green VariTargets, with their very coarse droplets, had the best results with about 50 droplets per square centimetre counted downwind in a 15 mph wind. "This was comparable to the TurboDrop XL TwinFan, a medium pressure venturi, which counted 45 droplets per square centimetre under the same conditions," says Storozynsky.
The blue VariTarget, at about 60 droplets per square centimetre, was more comparable to a single red 04 Air Bubble Jet, a low pressure venturi which also counted 60 droplets per square centimetre. VariTarget yellow caps, meanwhile, measured about 130 droplets. "This makes them most comparable to the Turbo TeeJet single red 11004, one of the oldest pre-orifice low drift nozzles currently on the market, which resulted in about 135 droplets," he says. "For comparison, 135 droplets/cm2 in wind tunnel drift tests translates to about eight percent drift in field conditions."
More information available
Although variable rate nozzles look promising to producers looking to reduce drift and increase spray coverage, there is still more research to be done, says Storozynsky. For more information, contact Storozynsky at the AgTech Centre at (403) 329-1212. Results of AgTech's machinery evaluations, applied and scientific research, and information on its development of innovative agricultural technologies are available to producers to help them make management decisions.
Author: Jeff Melchior
Sponsored by: AgTech Centre
