Spray Equipment and Calibration (continued)

AE-73 (Revised), September 2004

Strainers

Aplugged nozzle is one of the most frustrating problems that applicators experience with sprayers. Properly selected and positioned strainers and screens will do much to prevent nozzle plugging and reduce nozzle wear.

Three types of strainers are commonly used on agricultural sprayers: tank-filler strainers, line strainers, and nozzle screens. Strainer numbers (e.g. 20-mesh, 50-mesh, or 100-mesh) indicate the number of openings per inch. Strainers with high numbers have smaller openings than strainers with low numbers.

Coarse basket strainers set in the tank-filler opening prevent debris from entering the tank as it is being filled. A 16- or 20-mesh tank-filler strainer will also restrain lumps of wettable powder until they are broken up, helping to give uniform mixing in the tank.

The line strainer is the most critical strainer of the sprayer (Figure 10). It usually has a screen size of 16 to 80 mesh, and it can be positioned between the tank and the pump, between the pump and the pressure regulator, or close to the boom, depending upon the type of pump used. Roller and other positive displacement pumps should have a line strainer (40- or 50-mesh) located ahead of the pump to remove material that would damage the pump. In contrast, the inlet of a centrifugal pump must not be restricted. A line strainer (usually 50-mesh) should be located on the pressure side of the pump to protect the spray and agitation nozzles. Be sure to clean this screen regularly.

Figure 10. Line filter. (9KB b&w illustration)

Self-cleaning line strainers are available for sprayers. However, these units require additional pump flow capacity to continually flush a portion of the fluid over the screen and carry trapped material back to the spray tank. Figure 11 shows a cut away of a self-cleaning strainer.

Figure 11. Self-cleaning line strainer. (9KB b&w illustration)

Nozzles are the third place screens are located. Small-capacity nozzles must have screens to prevent plugging. Typically 50- to 100-mesh screens are used (Figure 12). There is little benefit in using a screen size smaller than the nozzle orifice itself. In general, 80- to 100-mesh strainers are recommended for most nozzles with flow rates below 0.2 GPM, and 50-mesh strainers for nozzles with flow rates between 0.2 and 1 GPM. The pesticide being used or nozzle manufacturer may dictate the strainer size; e.g. a 50-mesh or larger screen is used with wettable powders. With a flow rate above 1 GPM, a nozzle strainer is not usually necessary if a good line strainer is used. Nozzle strainers are sometimes used with liquids containing suspended solids.

Figure 12. Nozzle strainer and screen. (16KB b&w illustration)

Sprayer Distribution System

The sprayer will not function properly without proper hoses and controls to connect the tank, pump and nozzles as they are the key components of the spraying system.

Select hoses and fittings to handle the chemicals at the selected operating pressure and quantity. Peak pressures higher than average operating pressures are often encountered. These peak pressures usually occur as the spray boom is shut off. Choose components on the basis of composition, construction, and size.

Hose must be flexible, durable, and resistant to sunlight, oil, chemicals, and general abuse such as twisting and vibration. Two widely used materials that are chemically resistant are ethylene vinyl acetate (EVA) and ethylene propylene dione monomer (EPDM).

Suction hoses should be air-tight, non- collapsible, as short as possible, and as large as the pump intake. A collapsed suction hose can restrict flow and ���starve��� a pump, causing decreased flow and damage to the pump. If you cannot maintain spray pressure, check the suction line to be sure that it is not restricting flow.

Other lines, especially those between the pressure gauge and the nozzles, should be as straight as possible, with a minimum of restric-tions and fittings. The proper size of these varies with the size and capacity of the sprayer. A high but not excessive fluid velocity should be maintained throughout the system. Lines that are too large reduce the fluid velocity so much that some pesticides, such as dry flowables or wettable powders, may settle out, clog the system, and reduce the amount of pesticide being applied. If the lines are too small, an excessive pressure drop will occur. A flow velocity of 5 to 6 feet per second is recommended. Suggested hose sizes for various pump flow rates are listed in Table 1. Some chemicals will react with plastic materials. Check sprayer and chemical manufacturers literature for compatibility.

Table 1. Guide for determining hose size.
Pump Output (gals/min.)	Suction Hose	Discharge Hose
	(inside diameter in inches)
Under 12 GPM	3/4	5/8
12�����25 GPM	1	3/4
25���50 GPM	1-1/4	1
50���100 GPM	1-1/2	1-1/4

Boom stability is important in achieving uniform spray application. The boom should be relatively rigid in all directions. Swinging back and forth or up and down is not desirable. Gauge wheels mounted near the end of the boom will maintain uniform boom heights. The boom height should be adjustable from 1 to 4 feet above the target.

Nozzles

Functions

The nozzle is a critical part of any sprayer. Nozzles perform three functions:

1. Regulate flow
2. Atomize the mixture into droplets
3. Disperse the spray in a desirable pattern.

Nozzles are generally best suited for certain purposes and less desirable for others. In general, herbicides are most effective when applied as droplets of approximately 250 microns, fungicides are most effective at 100 to 150 microns, and insecticides at about 100 microns.

The chart in Table 2 compares various nozzles, their droplet sizes and their effectiveness for broadcast spraying. Table 3 compares nozzle characteristics for banding or directed spraying.

Table 2. Nozzle guide for broadcast spraying. (38KB b&w table with illustrations)

Table 3. Nozzle guide for band and directed spraying. (26KB b&w table with illustrations)

Nozzles determine the rate of pesticide distribution at a particular pressure, forward speed, and nozzle spacing. Drift can be minimized by selecting nozzles that produce the largest droplet size while providing adequate coverage at the intended application rate and pressure.

Nozzles are made from several types of materials. The most common are brass, plastic, nylon, stainless steel, hardened stainless steel, and ceramic. Brass nozzles are the least expensive but are soft and wear rapidly. Nylon nozzles resist corrosion, but some chemicals cause thermoplastic to swell. Nozzles made from harder metals usually cost more but will usually wear longer. The durability of various nozzle materials compared to brass is shown in Figure 13. Nozzles wear with use and flow rate. It is important to check and replace worn nozzles regularly, because worn nozzles may increase pesticide application cost and cause crop injury, illegal rates or residue. For example, a 10 percent increase in flow rate may not be readily noticeable; however, spraying 150 acres with a pesticide that costs $10 per acre at the increased rate would cost an extra $1 per acre or $150 more for the field.

Figure 13. Wear rates of various nozzle materials. (8BK b&w graph)

Each nozzle on a sprayer should apply the same amount of pesticide. If one nozzle applies more or less than adjoining nozzles, streaking may occur. Nozzle flow rates need to be monitored by regularly collecting the flow from each nozzle under operating conditions and compare the output. If the discharge from a nozzle varies more than 10 PERCENT above or below the average of all the nozzles, replace it.

Do not mix nozzles of different materials, types, discharge angles, or gallon capacity on the same sprayer. Any mixing of nozzles will produce uneven spray patterns.

Care must be used when cleaning clogged spray nozzles. The nozzle should be removed from the nozzle body and cleaned with a soft bristled nozzle cleaning brush. Blowing the dirt out with compressed air is also an excellent method. Do not use a small wire or jackknife tip to clean the nozzle orifice as it is easily damaged.

Flow Rate

Nozzle flow rate is a function of the orifice size and pressure. Manufacturers��� catalogues list nozzle flow rates at various pressures and discharge rates per acre at various ground speeds. In general, as pressure goes up flow rate increases, but not in a one-to-one ratio. To double the flow rate, you must increase the pressure four times. Many spray control systems use this principle to control output. They increase pressure to maintain correct application rates with an increase in speed. Use caution in speed changes as the spray system pressures may need to operate above recommended nozzle operating ranges, producing excessive driftable fines.

Drop Size

Once the spray material leaves the nozzle orifice, only droplet size, number and the velocity of drops can be measured. Droplet size is measured in microns. A micron is one millionth of a meter, or 1 inch contains 25,400 microns. To give this some perspective, consider that a human hair is approximately 56 microns in diameter.

All hydraulic nozzles produce a range of droplet sizes ��� some large droplets to many small drops. The size is expressed as volume median diameter (VMD). In other words, 50 percent of the volume is composed of droplets smaller than the VMD and 50 percent of the volume is in larger droplets. The VMD should not be confused with the NMD (number median diameter), which is usually a smaller number. The NMD is the median size that divides the spectrum of droplets into an equal number of smaller and larger drops. The design of the nozzle affects the droplet size and is a useful feature for certain applications. Large droplets are less prone to drift, but small droplets may be more desirable for better coverage. Pressure affects droplet size ��� higher pressures produce smaller droplets.

The size of the spray droplet can have a direct influence on the efficacy of the chemical applied, so selecting the proper nozzle type to control spray droplet size is an important management decision. When the average droplet diameter is reduced to half its original size, eight times as many droplets can be produced from the same flow. A nozzle that produces small droplets can theoretically cover a greater area with a given flow. This works down to a particular drop size. Extremely small drops may not deposit on the target, as evaporation is reducing their size during travel to the target and air currents in the drop pathway may interrupt the drop movement and carry the drop off-target. Environmental conditions of relative humidity and air currents (wind) can have a major affect on drop deposit on the target when small drops are used to apply pesticides.

Water-sensitive paper can be used to assess droplet size and density. Experience has shown that for low volume sprays with medium size droplets, insecticides should have a density of not less than 20 to 30 droplets/cm2, herbicides 20 to 40 droplets/cm2, and fungicides 50 to 70 droplets/cm2. Drop number and size can be estimated with a hand lens.

Nozzle Check Valves

Some nozzle strainers are equipped with check valves that produce quick shutoff and prevent dripping at the nozzle during turns or transport. Diaphragm check valves (Figure 14) are best at stopping nozzle drip. Ball check valves are more susceptible to corrosion than diaphragm check valves and are not as trouble free. Check valves cause a pressure drop of 5 to 10 psi, depending on the spring pressure in the valve. Check valves allow the nozzles to be changed without material leaking from the boom.

Figure 14. Diaphragm check valve. (11KB b&w illustration)

Nozzle Spray Patterns

Every spray pattern has two basic characteristics: the spray angle and the shape of the pattern. Most agricultural nozzles have an angle from 65 to 120 degrees. Narrow angles produce a more penetrating spray; wide-angle nozzles can be mounted closer to the target, spaced farther apart on the boom, or provide overlapping coverage (Figure 15).

Figure 15. Basic nozzle spray angles and patterns. (10KB b&w illustration)

Though there are a multitude of spray nozzles, there are only three basic spray patterns: the flat fan, the hollow cone and the full cone. Each of these has specific characteristics and applications.

Flat-Fan Spray Nozzles

Flat-fan nozzles are widely used for broad- cast spraying of herbicides and some insecticides. They produce a tapered-edge, flat-fan spray pattern. Less material is applied along the edges of the spray pattern, so the patterns of adjoining nozzles must be overlapped to give uniform coverage over the length of the boom. For maximum uniformity, overlap should be about 30 to 50 percent of the nozzle spacing (Figure 16) at the target level. Normal operating pressure is variable depending on the nozzle used.

Figure 16. Proper overlap with a flat-fan type nozzle on a 20-inch nozzle spacing. (5KB b&w illustration)

Lower pressures produce larger droplets, which reduces drift potential, while higher pressures produce small drops for maximum plant coverage, but small drops are more susceptible to drift. Newer extended range nozzles are available that will operate over a range of 15 to 60 psi without causing a significant effect on the width of the spray pattern. These nozzles produce the same flow rate and spray pattern as a regular flat-fan nozzle at the same pressure. Lower operating pressure produces larger droplets and reduces the drift potential while the higher pressures produce fine drops with higher drift potential. Extended range nozzles operate over a wider pressure range and work well with automatic spray controls.

Flat-fan nozzles are available in several spray discharge angles. The most commonly used nozzles are listed in Table 4. Proper spray boom height depends on nozzle discharge angle and is measured from the target to the nozzle. For postemergence pesticides, the target is the growing crop and not the soil surface (Figure 17).

Figure 17. Spray height ��� nozzle tip to target ��� flat fan. (10KB b&w illustration)

Table 4. Minimum suggested spray heights.
Spray Angle	Nozzle Height
	20��� Spacing	30��� Spacing	40��� Spacing
65��	22���24���	33���35���	NR*
80��	17���19���	26���28���	NR*
110��	12���14���	16���18���	NR*
120��	14���18���**	14���**	14���18���**
*Not recommended **Nozzle angled 35�������45�� to vertical

Another flat-fan nozzle designed as a drift reducing nozzle was recently introduced by several manufacturers. This nozzle has a chamber ahead of the final orifice that is effective in reducing the number of fine droplets dispersed that are susceptible to drift. It contains an internal chamber that reduces the operating pressure at the outer orifice, reducing the fines produced.

A recent nozzle introduction is calledthe Turbo Teejet flat-fan nozzle from Spraying Systems Co. It contains a pre-orifice design that creates a large drift-resistant drop over a wide pressure operating range of 15-90 PSI that will reduce the driftable fires. This nozzle is designed to fit nozzle caps that hold standard flat fan nozzles.

���Even��� Flat Fan Spray Nozzles

���Even��� flat-fan nozzles apply a uniform coverage across the entire width of the spray pattern (Figure 18). They should be used for banding pesticides over the row and should be operated between 30 and 40 PSI. This nozzle should not be used for broadcast applications. The width of the band is dependent upon the nozzle height above target and spray pressure as shown in Table 5.

Figure 18. Discharge pattern of an ���Even��� spray nozzle. (4KB b&w illustration)

Table 5. Height for banding with even flat fan nozzles.
Band Width	Approximate Spray Height
	40�� Series	80�� Series	95�� Series
8���	11���	5���	4���
10���	14���	6���	5���
12���	16���	7���	6���
15���	20���	9���	8���

Flooding Fan Nozzle

Flood fan nozzles produce a wide-angle, flat-spray pattern and are used for applying herbicides and mixtures of herbicides and liquid fertilizers. The nozzle spacing for applying herbicides should be 60 inches or less. These nozzles are most effective in reducing drift when they are operated within a pressure range of 10 to 25 PSI. The width of the spray pattern of flood nozzles is changed more by pressure changes than occurs with flat-fan nozzles. Also, the distribution pattern is not as uniform as that of the regular flat-fan nozzle. The best distribution is achieved when the nozzle is mounted at a height and angle to obtain at least 100 percent overlap (double coverage). When set for 100 percent overlap, a change in nozzle pressure distorts the spray pattern.

A new nozzle called the ���turbo floodjet��� from Spraying Systems Company produces larger drops and a more uniform spray pattern than a standard flood tip. It is designed to reduce drift and provides uniform deposition with 30 to 50 percent overlap instead of 100 percent required by standard flood nozzles. The turbo flood nozzle is designed for use with soil incorporated herbicides and liquid fertilizer and should be operated at pressures ranging from 10-20 PSI.

Flood nozzles can be mounted so they spray straight down, straight back, or at any angle in between (Figure 19). Studies indicate the most uniform pattern is obtained when the spray is directed straight back, but this will produce the greatest chance for drift of the small droplets. Directing the spray straight down will minimize the drift potential but produces the most irregular spray pattern. The best com-promise position is to set the nozzle at a 45 degree angle with the sprayed surface. Care should be taken so incorporation equipment does not intercept or interfere with the spray discharge pattern.

Figure 19. Various positions for mounting flood nozzles. (14KB b&w illustration)

Hollow Cone Nozzles

Hollow cone nozzles are generally used to apply insecticides or fungicides to field crops where complete coverage of the leaf surface is important. The hollow cone pattern is used for applications where a fine spray pattern is needed for thorough coverage. These nozzles usually operate in the pressure range of 40 to 100 PSI or more depending on the nozzle being used and the pesticide applied. Spray drift is higher with hollow cone nozzles than with other nozzles as small droplets are produced.

A hollow cone nozzle produces a spray pattern with more of the liquid concentrated at the outer edge of the pattern (Figure 15) and less in the center. Any nozzle producing a cone pattern, including the whirl-chamber type, will not provide uniform distribution for broadcast applications when directed straight down at the sprayed surface. They must be angled 30 to 45 degrees from the vertical.

Hollow cone nozzles used on high pressure sprayers for applying fungicides can be aimed straight down when they are spaced 10 to 12 inches apart. This produces extremely fine drops which move enough to compensate for the non-uniformity of the pattern.

���Raindrop��� nozzles from Delavan have been designed to produce large drops in a hollow cone pattern at pressures of 20 to 60 PSI. They are designed to reduce spray drift and are recommended for broadcast applications when tilted 45 degrees or more from the vertical.

Full Cone Nozzles

The full cone nozzle produces a swirl and a counter swirl inside the nozzle that results in a full cone pattern. Full cone nozzles produce large, evenly distributed drops and high flow rates. A wide full cone tip maintains its spray pattern over a range of pressures and flow rates. It is a low-drift nozzle and is often used to apply soil incorporated herbicides.

Nozzle Adjustment Problems

For broadcast application, flat-fan nozzles should be properly spaced and adjusted on the sprayer. For good spray coverage, nozzle discharge angle, nozzle distance from the sprayed surface and nozzle spacing on the boom must all be considered. Refer to table 4 for proper nozzle adjustments. Figure 20 shows some of the spray patterns that may result from common boom adjustment problems.

Figure 20. Some common errors in nozzle and boom adjustment. (24KB b&w illustration)

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AE-73 (Revised), September 2004