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Choose The Right Nozzle For Spraying

The most important factor in reducing drift is the size of the droplets produced by the nozzle.

Choosing the correct nozzles for field sprayers is important because nozzles determine the uniformity of application, coverage on the target surface and amount of potential drift, and influence the amount of spray applied.

Most pesticide applicators likely depend on nozzle manufacturers and retailers to recommend the right nozzle but there are some guidelines to follow to help sort out the variety of nozzles available from different manufacturers. Start by reading the pesticide label because it lists the recommended product and carrier rates per acre. The label also may specify recommended droplet size, nozzle type, spacing, overlap pattern, nozzle height above the crop canopy and information on spray drift management.

“The label generally specifies gallons per acre, but nozzles are rated in gallons per minute,” says John Nowatzki, North Dakota State University agricultural machine systems specialist. “Manufacturers’ nozzle selection guides include charts indicating the expected rate per acre with varying operating pressure, nozzle spacing and ground speed. The nozzle opening size and spray pressure affect the flow rate.”

After determining the nozzle size, choose the desired nozzle material. Nozzles are made from brass, plastic, nylon, stainless steel and ceramic. Brass nozzles are the least expensive but are soft and wear rapidly. Nylon and plastic nozzles resist corrosion, but some chemicals can cause these materials to swell. Stainless steel and ceramic nozzles are harder and usually last longer.

Most field sprayers use nozzles that produce a flat-fan spray pattern. Flat-fan nozzles spray a single-dimension, fan-shaped pattern that applies a uniform coverage across the top of the target. The edges of the pattern have a lower spray volume than the center, so adjacent nozzles must overlap application areas to provide uniform coverage. Flat-fan nozzles are generally available with spray-fan angles of 80 or 110 degrees. Flat-fan nozzles are used for most broadcast herbicide and insecticide spraying if complete foliar penetration and coverage are not required.

Variations of flat-fan nozzles include extended-range flat-fan, low-pressure flat-fan, even flat-fan and flooding flat-fan nozzles.

Try to choose nozzles that minimize drift potential. Spray drift potential is determined by droplet size, which is determined by the type and opening size of the nozzle, sprayer operating pressure, boom height and atmospheric conditions.

“The most important factor in reducing drift is the size of the droplets produced by the nozzle,” Nowatzki says. “The American Society of Agricultural and Biological Engineers developed standard droplet size classification categories that range from very fine to extremely coarse.”

In addition to selecting a spray pattern, there are several types of nozzles to choose from, such as standard flat-fan and variations of flat-fan, pre-orifice, turbulence chamber, venturi, blended- pulse and flexible-orifice nozzles.

Standard flat-fan nozzles are available in various orifice sizes that operate in pressure ranges from 15 to 60 pounds per square inch. Choosing nozzles with larger orifices and operating at lower pressures will reduce drift potential because of the larger droplets produced, but the target coverage will be reduced.

Pre-orifice nozzles add an inlet orifice at the top of the nozzle, allowing liquid to enter the nozzle body reducing the liquid pressure before leaving the nozzle though the exit orifice at the bottom. Reducing the internal pressure increases droplet size.

Turbulence-chamber nozzles add an inlet orifice at the top of the nozzle, allowing liquid to enter a chamber inside the nozzle body that reduces the liquid velocity and pressure before leaving the nozzle through the exit orifice at the bottom. Reducing the velocity and pressure increases the application droplet size.

The air-induction or venturi-type nozzles incorporate a venturi to introduce air into the nozzle chamber. Initial studies indicate air-induction or venturi-type nozzles reduce drift potential when compared with regular flat-fan nozzles.

Variable-rate nozzles are capable of controlling flow rate and maintaining a spray pattern and droplet size over an extended range of flow rates. Flow rates can be varied with different operating pressures.

Pulsing-solenoid nozzles are designed to provide independent control over nozzle pressure and flow rate. Systems are available that may be operated manually or used in conjunction with a rate controller that allows a constant application rate and droplet size over varying travel speeds.

Finally, after determining the required flow rate and considering spray pattern, nozzle type, construction material and drift potential, consult the nozzle manufacturers’ catalogs for specific nozzle information.

Pesticide applicators can use the NDSU spray nozzle comparison Web site at http://www.ageng.ndsu.nodak.edu/spraynozzles/ to compare drift, percent of coverage and droplet size of common pesticide application nozzles.

A NDSU Extension Service publication on choosing drift-reducing nozzles is available on the Web at http://www.ag.ndsu.edu/pubs/ageng/machine/fs919.pdf.

For more information, contact John Nowatzki at 701.231.8213 or john.nowatzki@ndsu.edu

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