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Pesticide Safety Education Program (PSEP)
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Sprayer Nozzles

Sprayer Nozzles

Prepared by Donald R. Daum
Thomas F. Reed
The Pennsylvania State University

The nozzle tip is a critical component of sprayer apparatus. Although a relatively inexpensive part of the total system, it must not be neglected. The nozzle regulates the flow rate, atomizes (breaks up) the mixture into droplets, and disperses the droplets in a specific pattern. The proper tip nozzle must be selected for the desired job. No single nozzle can meet all the spraying needs.

Size of Nozzle Tips

Nozzle size depends largely on the desired application rate. Nozzle tips provide a wide range of rates depending on the orifice size, the pressure and ground speed, as well as the nozzle spacing on boom sprayers. Check the chemical label for the recommended spray rate. Manufacturers' catalogs list nozzle flow rates at various pressures and ground speeds. Once you determine the recommended rate and pressure, select the proper size and nozzle. Remember, a nozzle rated at a specific gallonage per acre will apply that rate only under standard conditions such as 4 miles per hour (speed) and 30 psi (pressure). The spray rate increases with higher pressure or slower ground speed and by using closer nozzle spacing on boom sprayers. Changing these variables in the opposite direction will decrease the spray rate.

Effect of Nozzles on Atomization

Liquid breakup results from the collapse of unstable fluid sheets, jets and ligaments or from the tearing action of air. These actions produce drop- lets with a wide size variation. However, the average size can be controlled and, in many cases, is related to the spray pattern. Increasing the pressure produces finer atomization (smaller droplets), thus increasing the risks of drift. Conversely, larger droplets and less drift may be expected as the nozzle orifice increases.

Types of Nozzles and Their Uses Flat Fan Nozzles

The spray droplets form a fan as they leave the nozzle. It is well suited for most herbicides and some insecticides where the foliage pene- tration is not essential. The fans are commonly available in 65-, 73-, and 80-degree spray angles. A wide-angle nozzle can be operated closer to the ground to minimize drift. The edges of the flat fan pattern have lower spray volumes, so the nozzle heights must be adjusted to overlap on each side of the spray pattern. For example, proper overlap is 40-50% of nozzle spacing from an adjacent nozzle. Therefore on 20 inch nozzle spacing the proper overlap would be 8-10 inches. This will insure uniform coverage. Typical operating pressure is 20-40 psi. Also available are low pressure flat fan nozzles (10-25 psi). Lower operating pressures and larger orifices on these nozzles reduce clogging and provide larger spray droplets which reduce drift. Flat fans are recommended for boom sprayers. Nozzles on a boom should always be the same type and size to ensure even distribution.

     Spray                       Nozzle Height
     Angle                       Above Target*
     65 degrees                  21-23 inches
     73 degrees                  20-22 inches
     80 degrees                  17-19 inches
     * At standard rating of 30 psi and 20 inch row spacing.


Even Flat Fan Nozzle

The 'even' spray nozzle is similar to a regular flat fan nozzle but applies materials uniformly across the entire pattern. They are used for banding chemicals over row crops. 'Even' nozzles are available with 80- or 95- degree spray angles. Typical working pressure is 20-40 psi. The width of the band can be adjusted by raising or lowering the nozzle. This nozzle should not be used on a boom for broadcast spraying.

Flooding Fan Nozzle

The flooding fan nozzle produces a wide, flat spray pattern. The wide spray angle (110 to 130 degrees) allows wider nozzle spacing and lower boom heights on boom sprayers. Flooding nozzles work well for applying herbicides and chemical-fertilizer mixtures. One exception is contact herbicides applied at low gallonage. The nozzles are also used for applying post- emergence chemicals to the row middles of maturing crops. The large orifice produces large droplets and makes the flooding nozzles resistant to drift and clogging. Optimum broadcast coverage is achieved by overlapping spray patterns 100% to obtain double coverage. Pressures of 10-30 psi are commonly used.

Cone Nozzles

A hollow cone nozzle produces a spray pattern with the liquid concen- trated on the outside of a conical pattern. The solid cone nozzle distributes the droplets over the entire circle. Cone nozzles are used mainly to apply insecticides, fungicides, or growth regulators where penetration and complete coverage of foliage is needed. Working pressures range from 50-400 psi. Spray drift is high due to the small, light-weight droplets produced. Use of these nozzles should be restricted to areas where some drifting is not hazardous. Hollow cones are ideal for low-volume applications, and solid cones are used to apply high volumes. A new type of low-drift, hollow cone is available for applying herbicides. The nozzle has a standard core with a disc inside a specially designed cap. The cap removes many of the small spray droplets which cause drift. Operating pressure is 20-60 psi.

Air-Shear Nozzles

Some air-blast sprayers use the high-speed air discharge to breakup the spray liquid into droplets rather than orifice nozzles and pressure. This method is limited to sprayers with high velocity air streams. Depending on nozzle configuration and injection angle, air speeds of 170 to 400 miles per hour are required. Discharging the spray directly into the airstream against the air flow produces the smallest droplets; at 90 degrees to the air- stream, intermediate breakup; with the air flow, you obtain least breakup and the largest droplets.

The air-shear nozzles operate at low pressures, often in the 15-35 psi range. This results in low wear rates for both nozzles and the pump. Also, air-shear nozzles have large openings which minimize plugging.

Since air-shear nozzles are limited to air-blast sprayers, they are used only to apply insecticides, fungicides, and growth regulatores.

Nozzle Tip Materials

Brass, nylon, aluminum, stainless steel, hardened stainless steel, and tungsten carbide are used for nozzle tips. Brass and aluminum tips are the cheapest, but the metal is soft and the tips wear quickly with abrasive mixtures. The aluminum tips are for applying liquid fertilizers since liquid nitrogen corrodes brass. Nylon nozzles are available at about the same price as brass or aluminum nozzles and have better wearing characteristics. Tips made from stainless steel and hardened stainless steel cost more but wear much longer. They resist abrasion and corrosion and are recommended when applying wettable powders. Tungsten carbide is very long-wearing and extremely corrosion resistant. Nozzle tips made from hard metals cost more initially but, in the long run, pay for themselves because of long-lasting properties.

Screens for Nozzles

To prevent plugging and excessive wear of the nozzles, screens should always be used to remove large particles from the spray mixture, except when spraying very large volumes. At low rates, use 100-mesh screens. When using higher rates or applying wettable powders, use 50-mesh size. Check the manu- facturer's recommendations for the specific nozzle. Some screens have a ball check valve to prevent drip. These are useful if you stop in the field, since excessive applications may leave residues which damage the following crop.

Replacing Your Tips

Worn nozzles increase application rates and change distribution patterns causing poor pest control, crop damage, residue problems, and increased costs. Check your boom sprayer to see that each tip is delivering an identical volume of spray in a smooth pattern with no heavy streams or blank areas. Should a nozzle become clogged, it is best to blow out the dirt with compressed air or use a soft bristled brush. Never use a wire or nail as the orifice can be damaged easily. Remember, improperly functioning or worn nozzles are costly.

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