With increasing oversight of field applications by regulators, your company needs to be keeping pace with the nozzle industry, there are new nozzle designs being marketed that might make sense to be mounted on your spray booms.
There have been some important developments in nozzles for effective pesticide application while reducing the potential for drift. Paul Sumner, engineer with the University of Georgia Cooperative Extension Service, notes that in general this “has been accomplished by using nozzles/atomizers and air-assist technology.”
Sumner says, “Nozzles producing spray droplets of 300 microns or larger is necessary for reducing drift.”
As each nozzle company tries to keep pace with their competitors, each one has introduced their version of a “low-drift” nozzle. “These nozzles are designed to create larger droplets at the same flow rate and operating pressure than comparable standard flat-fan nozzles. This has been accomplished by adding a pre-orifice to the nozzle tip assembly just ahead of the conventional discharge orifice. These nozzles will produce an average droplet size of 300 to 400 microns” according to Sumner.
The air-assist nozzles accomplish producing a larger droplet and fewer fine droplets in another way. Sumner explains, “As with other low-drift nozzles, air-assisted nozzles contain a pressure reduction chamber with a narrow port used to draw air into this pressure chamber. As the liquid passes through the orifice plate, as a result of the pressure drop created by this venturi, air is sucked into the nozzle body. In the mixing chamber, air and spray solutions are blended much like a water aspirator. As the liquid is discharged from the nozzle tip, droplets filled with air are produced. Upon leaving the nozzle orifice, the air included in the nozzle expands, which makes the size of droplets somewhat larger and causes an increase in velocity of droplets.
“In addition to the large droplets having a higher velocity, the nozzles further improve the chances the droplet will reach the target before becoming subject to drift. Another benefit of this nozzle is that the large droplets shatter and splatter on contact, causing the small air-filled drops to spread out on the target for better coverage. These nozzles will produce an average droplet size of 400 to 600 microns. Total volume applied with these type of nozzles should be rates above 15 gallons per acre.”
The first step in sprayer calibration is to determine the correct nozzle type and size for flow rate, and naturally the sprayer has to be re-calibrated every time the nozzle type and size is changed.
As for the basics, it is simple to remember that flat-fan nozzles are used for broadcast spraying of most herbicides and some insecticides where a medium droplet size is needed. You might think of them being used for banding herbicides.
Flood type or full cone nozzles are used for pre-plant herbicides in most cases. They produce large droplets and are often spaced wider apart.
Hollow cone nozzles produce the small droplets and are used for insecticide applications and contact herbicide applications in most cases. The small droplets are needed to penetrate or engulf the canopy with the pesticide, and these droplets are the most subject to drift.