A farmer or grower deciding to use a crop protection spray – be it a herbicide, fungicide, insecticide or plant growth regulator – should be aiming to use the recommended dose rate safely and effectively, by ensuring that as much as possible reaches the specific target, and that as little as possible misses or fails to impact upon the target or drifts to where it may be a hazard. He will also want to carry out the operation speedily and economically, which will generally mean using the lowest spray volume and the highest forward speed compatible with efficient application.
The types of nozzles, their positioning, the pressure and the forward speeds at which they are operated are prime factors which, in combination produce the spray quality which determines whether or not such objectives can be met.
A basic outline of the different types of available nozzles will be presented in this section. For further and more complete nozzle information refer to a Spraying Systems catalog, Delavan catalog or The Broyhill Company Sprayer Parts & Specialty Catalog (nozzles & Tips section).
The success of your spraying operation depends to a large extent on the nozzles. They must be selected and assembled properly to apply the pesticide where it is intended and in a uniform manner. Although the same sprayer may be used, a different set of nozzles is sometimes required for different jobs.
Conventional nozzles produce what are essentially straight stream, cone or fan spray discharges. A plain orifice nozzle will produce a relatively solid stream useful for gun spraying to reach the upper branches of trees or for pressure cleaning. A plain orifice with a core, or whirl plate, behind it to im part a rotary motion to the discharge, creates a conical pattern made up of many droplets. This type is useful for creating an overall wetting action which spreads the spray into a wide but thin fan shape. The breakup, or atomization, is rather similar to the cone type but usually with coarser droplets. This nozzle is commonly used on a boom for flat surfaces and low field crops.
Droplet size from cone and flat fan nozzles is most strongly affected by orihce ske, the core in cone nozies and operating pressure. The smaller the orifice and the higher the pressure, the smaller the droplets produced. The argument continues over the merits of large, medium and small droplets. Many variable factors affect the effectiveness of a given droplet size, and all nozzles produce a relatively broad spectrum of skes, so the arguments may be somewhat academic. Experience is the best guide to nozzle selection for a given application.
Nozzles must be selected to fit a given application based on operating conditions and equipment. Usually the swath covered is determined by the effective reach of the sprayer. The amount of spray for a given area should be worked out with the help of the extension agent or spray consultant. The pump capacity and general conditions affect the speed at which the area can be covered. Nozzle size and operating pressure affect the nozzle discharge. All these factors must be considered and balanced to arrive at an effective spraying operation.
Regardless of the kinds of nozzle tips, they are the most neglected and abused part of the sprayer, yet these tips are the most important parts con cerning the even distribution of chemicals. Since clogging can occur when using spray nozzles, it is necessary that the tips and strainers be cleaned after each application and tested before using again. When using spray tips, be sure to control all of the factors in the spraying application (speed, spray ing pressure, spray height, etc.) in order to place the proper amount of chemicals in the right areas.
Replace all worn tips and those with streaked uneven pattems. Rinse and clean all the equipment including the nozzle tips. Be careful not to use a metal probe in the orifice. Wash the tips thoroughly with water or a cleaning solution. If the orifice remains clogged, clean it with a fine bristled brush or toothpick being careful not to damage the orifice. Water rinse and dry the tips before storing.
Flooding Nozzles: the flooding nozzle produces a wide, flat spray pat tern when the liquid atomizes as it leaves the edge of the nozzle. The wide spray angle (110 to 130 ) allows wider nozzle spacings and lower boom heights in broadcast applications. Both the wider spacings, which allow a larger orifice, and the round shape of the orifice make the nozzle less susceptible to clogging. Typical operating pressure is 10 to 25 psi.
Wide-Angle Full-Cone Nozzles: the wide-angle full-cone nozzle pro duces large droplets that are distributed uniformly in a full-cone pattern. The uniform spray pattem is maintained over a pressure range of 10 to 40 psi. You can use the wide, 120 spray angle on up to 40″ spacings, as with flooding nozzle. This nozzle is well suited for soil-applied and systemic herbicides.
Hollow-Cone Nozzles: a hollow-cone nozzle produces a spray pattern with the liquid concentrated on the outside of a conical pattern. The typical spray distribution is saddle-shaped with less liquid in the center of the distribution, tapering off rapidly at the edges. For this reason, the hollow cone nozzle is not well-suited for broadcast applications because proper overlap is difficult to achieve. You generally would use hollow-cone nozzles to apply insecticides, fungicides or growth regulators where penetration and coverage is critical. Spray drift can be high because of the many small droplets produced at the typical operating pressure of 40 psi and above.
Boomless Nozzles: in some areas the terrain or obstructions make it difficult or impossible to operate a boom sprayer. Typically you would use the boomless or cluster nozzle in these situations. This compact nozzle assembly mounts at the rear of the sprayer and can deliver a spray swath 30 to 60 ft. wide, depending on pressure and capacity. The nozzle assembly, consisting of up to five separate nozzles, produces a wide flat spray pattern. Spray distribution is not as uniform as with a boom sprayer; however, double-overlapping swaths can compensate for this to some degree. Keep in mind that this doubles the application rate and increases spraying time.
It is important to select nozzles made of the type of material that will resist wear and corrosion when used as recommended. Nozzle material is discussed under (1) materials for nozzle bodies and caps and (2) materials for nozzle tips.
- MATERIALS FOR NOZZLE BODIES AND CAPS. The materials most often used for the nozzle body and cap are as follows:
- Stainless Steel. Recommended for use with all spray materials and fertilizer.
- Nylon. Resist corrosion and abrasion. Swells when exposed to some solvents.
- Aluminum. Subject to corrosion. Has short thread life.
- Brass. Not resistant to abrasive materials such as wettable powders.
- MATERIALS FOR NOZZLE TIPS. Materials commonly used for the nozzle tip are as follows:
- Hardened Stainless Steel. Most wear-resistant of any of the readily available metals.
- Stainless Steel. Excellent wear resistance with either corrosive or abrasive materials.
- Nylon. Resists corrosion and abrasion. Swells when exposed to some solvents.
- Brass. Wears quickly when used to apply abrasive materials such as wettable powders.
- Ceramic or Porcelain. Highly resistant to abrasion and corrosion.
- Kematal. Excellent chemical and wear resistance to abrasive chemicals. Approximately 11% longer life than stainless steel.