Air blast sprayer nozzles

Air blast sprayer nozzles DEFAULT

Orchard Sprayers

Orchard Sprayers

Paul E. Sumner, Extension Engineer

Air Delivery Sprayers

Air delivery or air blast sprayers are used to apply pesticides, plant growth regulators and foliar nutrients to orchard trees. They apply these materials as liquids carried in large volumes of air. Air blast sprayers have adjustments in the fluid and air delivery systems that permit tailoring applications to fit a wide range of orchard conditions.

The efficiency and cost effectiveness of orchard pest management programs are influenced by the skills of managers and sprayer operators who evaluate orchard conditions and alter machine settings and operating techniques to optimize performance of sprayers. A combination of operational skill, equipment performance, timing and chemical selection is necessary for optimal results.

Selecting a Sprayer

A sprayer must be adequate for the worst of orchard conditions; one that is adequate only under favorable conditions is a liability under adverse conditions. Sprayers should at least meet the demands of spraying large, thick trees under the poorest conditions allowable for spraying. Consider reliability, maintenance history and the ability to cover the projected acreage in selecting spray equipment.

Horsepower requirement is a very important consideration because fans must move a considerable weight of air and materials. Manufacturers provide recommended horsepower range, but reliability and equipment longevity are often enhanced by selecting from the upper range of suggested horsepower.

A good practice is to observe sprayers operating in orchards where tree size, row spacing, weather, speed, application volume, and so on, are challenging and examine the coverage. Request dealer demonstrations and ask for names and locations of customers who are operating models of interest. Consult university personnel, pesticide industry representatives, and growers or custom applicators that operate sprayers. When observing a demonstration, try to relate demonstration conditions and operating techniques such as speed, pressure, nozzle output volume, etc., to the more challenging conditions you anticipate.

Figure 1. Basic components of an air blast sprayer.Figure 1.Basic components of an air blast sprayer.

All sprayers have components that are necessary for good operation. The following are a few suggestions for these components.

Tanks for sprayers should be corrosion-resistant and designed for ease in filling and adding pesticides, and for rapid, complete drainage to facilitate cleaning. Agitation should be sufficient to keep all materials uniformly distributed throughout the tank. Wettable powder pesticide formulations require vigorous agitation. Paddle or propeller type mechanical agitators and hydraulic jet agitators are common. Regardless of design, thorough agitation is required, both when trees are being sprayed and when spray nozzles are shut off. Pesticides settling in tank mixtures may cause spray equipment problems and reduce pesticide effectiveness.

Pumps for orchard sprayers are usually piston or centrifugal units. Centrifugal pumps move a high volume of liquid at low to medium pressure. Piston pumps are usually selected for high pressure applications.

Pressure Regulators are variable orifice devices that are opened or closed to change system pressure. With air blast sprayers, pressure regulators are primarily used to divert varying amounts of the pump output back to the tank. They are often referred to as pressure relief valves or unloading valves. Actual spray output is seldom governed by pressure regulators on air blast sprayers. Spray pressure is sometimes regulated by varying pump speed, and it can also be regulated by varying engine RPM. Accordingly, it is very important to maintain consistent engine speed so the RPMs of the sprayer PTO remain in the range needed.

Pressure Gauges are monitors of spray system operation. Experienced operators will quickly observe spray system malfunctions that visibly reduce spray output and pattern. Malfunctions that cause 10 to 20 percent changes in spray output, however, may easily go unnoticed. Pres-sure gauges indicate spray manifold pressure. Because a sprayer is set up to operate within a specified pressure range, the pressure gauge should alert the operator when a malfunction has changed manifold pressure. Malfunctions can arise from restricted or clogged strainers (particularly line strainers), restricted or leaking lines, changes in pump output, pressure regulator malfunctions, and so on.

Control Valves may simply be off/on valves but, most often, they provide manifold selection options. Valves may be manually operated or operated by electric solenoids. Mount valve controls within easy reach of the operator.

Manifolds deliver spray to nozzles and typically allow selective nozzle placement to achieve the desired spray pattern.

Spray Nozzles meter spray liquid and atomize the spray (influencing droplet size and the number of droplets obtained from a given volume of liquid). Nozzle type and location also influence spray pattern. Nozzles usually have several components including a body, cap, strainer, disc and core (orifice and whirl plate). The disc and core, or tip, are quite susceptible to wear. Wear resistant and chemical corrosion resistant materials such as hardened stainless steel, tungsten carbide or ceramic material, are usually selected. Even so, check nozzle output periodically and make adjustments for nozzle wear, as even a small amount of wear can significantly increase flow. For example, the flow rate of a D6 disc is increased 36 percent with only 0.005 of an inch of wear.

Fans, both axial and centrifugal, are used on air blast sprayers. The airstream’s major function is moving spray into trees and enhancing the uniformity of pesticide deposit on fruit, foliage and wood. Air movement also displaces leaves and branches, which aids spray penetration and increases the exposure of surfaces to spray. The air stream assures spray droplet velocity, which increases impingement (sticking) of very small spray droplets to the target. The air stream conveys the spray into the tree canopy and helps atomize the spray. Some systems depend on the air stream for atomization, although most sprayers depend primarily on nozzles. The effect of the air stream on spray droplet size is proportional to the relative velocity difference between the liquid spray and the air stream. The greater the velocity difference, the greater the atomization. If the nozzle injects spray into the air stream moving in the same direction as the air, the spray droplet break-up caused by the air forces will be minimal. Injecting spray directly into (against) the air stream produces the maximum degree of atomization.

Air stream characteristics that influence coverage include air volume (CFM: cubic feet per minute) and velocity (FPM: feet per minute). These parameters are influenced by fan type and speed, size, volute design, and so on. As these and previous comments indicate, a number of factors, most being interactive rather than independent, are involved in air delivery sprayer performance. Performance data concerning many of these factors for specific sprayers are not generally available.

Sprayer Setup

Setup of an air blast sprayer includes selection and placement of nozzles, orienting air director vanes and other air control devices, and setting pressure, throttle and engine speed.

Figure 2. Recommended proportioning of spray volume.Figure 2.Recommended proportioning of spray volume.

Nozzle arrangement and air guide or director vane settings should place most of the spray in the top half of trees, where most of the foliage and fruit are located. Air blast sprayers are typically set up to apply ⅔ to ¾ of the spray to the top half of trees, and ⅓ to ¼ to the bottom half (Figure 2). This targeted spraying is accomplished by placing more or larger nozzles on manifolds in the area that supplies spray to the upper half of trees and setting the air directors on the fan outlet to direct the air stream accordingly. Consider tree growth and target pest habits in determining the setup for specific applications.

Nozzle selection decisions influence the gallons of spray per acre that will be applied and sprayer speed. Orchard spray volumes vary from 30 to 150 gallons per acre (GPA). Table 1 contains a recommended application rate based on tree size. Sprayer speeds range from one to three miles per hour, most commonly 1.5 to 2.0 miles per hour (MPH). Better coverage is obtained at the lower speeds and at wind speeds below 5 miles per hour.

Table 1. Recommended total spray volume of application for pecan.
Tree Height
Total Volume
(gallons per Acre)
Up to 2525
25 to 5050 to 90
50 and up100 to 150

Other items that must be determined are spray system pressure (PSI), the number of nozzles on the sprayer, and the tree row spacing. Manufacturers usually recommend operation within a specified pressure range, normally 60 to 260 PSI for sprayers with conventional hydraulic nozzles. Many manufacturers also provide nozzle setup suggestions.

Sprayer setup decisions are made using information from pesticide labels, operator manuals, extension recommendations, anticipated orchard conditions, and experience. Factors can be listed as known and unknown.

Known will include:

  • GPA (gallons per acre) desired
  • PSI (pounds per square inch) pressure desired
  • MPH (miles per hour) desired
  • Number of nozzles on sprayer
  • Tree row spacing
  • Spraying one or both sides of the sprayer

The information that needs to be determined and set for the machine can be listed as unknowns:

  • GPM (gallons per minute) output needed
  • Nozzles (sizes and placement)

Gallons per minute output for a sprayer traveling between each row and spraying from both sides can be calculated with the following equation:
GPM = (GPA x MPH x Row Spacing(ft)) ÷ 495(spraying both sides)

Gallons per minute output for a sprayer traveling between each row and spraying from one side only and both sides of the tree can be calculated with the following equation:

GPM = (GPA x MPH x Row Spacing(ft)) ÷ 990(spraying one side)

Nozzle sizes can be selected from the manufacturer’s catalogues using the calculated GPM, the selected pressure (PSI), and number of nozzle positions on the sprayer. Arrange nozzles so that ⅔ to ¾ of the spray will be applied to the top half of trees, with the residual applied to the bottom half. Calculating the average nozzle output will help in making nozzle selections from the manufacturer’s tables.



  • GPA = 100
  • PSI = 150 at the manifold
  • MPH = 1.5 (selected travel speed)
  • Number of nozzles = 16
  • Tree row spacing = 60 feet
  • Spraying out one side of sprayer on both sides of tree


  • Gallons per minute output needed

GPM = (GPA x MPH x Row Spacing(ft)) ÷ 990(spraying one side)

GPM = 100 x 1.5 x 60 ÷ 990(spraying one side) = 9

  • Nozzles (sizes and placement).

There are 16 on each side. Select 16 nozzles that have a combined output of 9 GPM/side. Arrange nozzles to provide the desired volume in the top half of trees for one side, and then select nozzles for bottom half.

Determine the average nozzle output as a starting point for making nozzle selections from the manufacturer’s tables. This can be calculated as follows:

9 GPM ÷ 16 Nozzles = 0.56 GPM Nozzle

To place ¾ of the spray volume in the top half of trees, the nozzles placed on the top half of each manifold will need a combined output between ¾ x 9 GPM = 6.75 GPM.

Use the manufacturer’s table to find 16 nozzles having a combined capacity of approximately 9 GPM that can be mounted on the sprayer manifold, with between 6 and 6.75 GPM applied to the top half of trees.

Most spray nozzle manufacturers publish tables showing the GPM capacity of various nozzle sizes for various pressures. Table 2 is part of a manufacturer’s nozzle capacity table.

Table 2. Nozzle Capacity Data (Spraying Systems, Inc.)
Disc and Core NozzlesLiquid Pressure
in P.S.I.
in G.P.M.
per Nozzle
Disc and Core NozzlesLiquid Pressure
in P.S.I.
Capacity in
G.P.M. per

Two or more nozzle sizes are normally required to produce the desired spray volume and pattern. A variety of nozzle arrangements can be used to achieve the volume and spray distribution needed. A good selection would be as follows (Figure 3).

Figure 3. Nozzle placement for proportioning spray material on each manifold.Figure 3.Nozzle placement for proportioning spray material on each manifold.

Top Tree Half
Tip SizeNumber Nozzles
on Boom
Top Half Total6.73

6.73 GPM/side or 75 percent

Bottom Tree Half
Tip SizeNumber Nozzles
on Boom
Bottom Half Total2.22

2.22 GPM or 25 percent

Air Blast Sprayer Calibration

Calibration is the process of measuring and adjusting the gallons per acre of spray actually applied. Sprayers need to be calibrated to meet the coverage needs of the orchards to be sprayed and to facilitate precise dosing of each material. A sprayer should be set up to apply a gallon per acre rate at a desired speed and pressure. In-orchard calibration frequently indicates a need for adjustments to achieve the target gallons per acre.

Speed of travel of a sprayer is a vital factor in obtaining the number of gallons of spray per acre desired. Change in gallons per acre (GPA) applied is inversely proportional to the change in speed. If speed is doubled, the gallons per acre will be halved, so if nozzles have been installed and pressure set to provide a gallon per acre rate at a certain speed, the sprayer should apply the GPA rate at that speed.

To determine the travel speed, measure a known distance. Use fence posts or flags to identify this distance. A distance more than 200 feet and a tank at least half full are recommended. Travel the distance determined at your normal spraying speed and record the elapsed time in seconds. Repeat this step and take the average of the two measurements. Use the following equation to determine the travel speed in miles per hour:

Travel Speed(MPH) = (Distance(feet) x 0.68) ÷ Time(seconds)

(0.68 is a constant to convert feet/second to miles/hour)

Check Gallons per Minute Output

The gallons per minute output required for a sprayer traveling along both sides of each row spraying from one side for a desired gallon per acre rate can be calculated with the following equation:

GPM(req) = (GPA x MPH x Row Spacing(ft)) ÷ 990(spraying one side)

(If one pass is made between rows spraying from both sides of the sprayer, use 495 as constant.)

GPA = Gallons Per Acre
MPH = Miles Per Hour

To check actual output:

  1. Fill sprayer with water. Note the level of fill. If a material with considerably different flow characteristics than water is to be sprayed, fill the sprayer with this material.
  2. Operate the sprayer at the pressure that will be used during application for a measured length of time. A time period of several minutes will increase accuracy over a time period of 1 minute.
  3. Measure the gallons of liquid required to refill sprayer to the same level it was prior to the timed spray trial with the sprayer in the same position as when it was filled initially. The actual GPM can be calculated as follows:
    GPM(actual) = Gallons to refill sprayer ÷ Minutes of spray time
  4. Calculate the GPA being applied by the sprayer.
    GPA = (GPM(actual) x 990 (spraying from one side)} ÷ MPH x Row Spacing(ft)

If the actual GPA is slightly different from the required GPA, the actual GPA can be increased or decreased by increasing or decreasing spray pressure on sprayer models that have provisions for adjusting pressure. Only small output changes should be made by adjusting pressure. Make major changes in output by changing nozzles.


Cromwell, R. R. 1975. Citrus growers’ guide to air spraying. Florida Cooperative Extension Service Circular 351. p. 31.

Weed Control Sprayers

Orchard herbicide sprayers must be able to efficiently place herbicides on the orchard floor with minimal risk to the trees. Successful orchard herbicide application requires: (1) appropriate herbicide selection, (2) proper timing of applications, and (3) correctly adjusted, calibrated and operated spray equipment. Boom sprayers are the predominant orchard herbicide sprayers. They operate at low spray pressure and volume. Sprayers can be mounted on or pulled behind a tractor. Figure 4 depicts a well-conceived sprayer design.


Tanks of corrosion-resistant metals and plastic-lined and fiberglass tanks are available in a variety of sizes. Sprayer tanks should have a large filling hole to facilitate easy filling, inspection and cleaning of the tank. A strainer to filter out debris, which is easily introduced during loading, is also needed. Tanks should also have drains for fast, complete drainage without exposing workers to herbicide.

Provide strainers in the locations shown in Figure 4. In-line strainers can be provided as optional equipment. Strainers are especially important where wettable powders are used. In-line and nozzle strainers are generally 50- to 100-mesh screens.

Figure 4. Components of a properly designed weed control sprayer.Figure 4.Components of a properly designed weed control sprayer.

Agitators provide the turbulence needed to keep herbicides properly mixed. Herbicides are formulated as liquid concentrates, emulsions, soluble powders, wettable powders and dry flowables. These materials are mixed with water before they are applied. Liquid concentrates, emulsions and soluble powders require little agitation to maintain a good sprayable solution. The bypass hose usually does not furnish enough agitation. Wettable powders require vigorous agitation because they readily settle out. Use jet agitators, sometimes referred to as hydraulic boosters, to maintain proper agitation.

Pumps of four designs (roller, centrifugal, piston and diaphragm) are common on herbicide prayers. Consider three factors in selecting the pump for herbicide sprayers: capacity, pressure and resistance to corrosion and wear. Each pump design offers advantages and disadvantages.

Pump capacity should be sufficient to readily supply the boom output, provide agitation and offset pump wear. If hydraulic, or jet, agitation is used, allow at least 5-7 gpm equivalent mixing action for each 100 gallons of tank capacity. Suitable agitation can also be obtained by pumping 2 gpm per 100 gallons of tank capacity through a siphon, or venturi, agitator that increases the flow through the agitator 2.5 times. Of course, mechanical agitation does not require any pump capacity. Finally, add 20 to 25 percent to spraying and agitation requirements to compensate for loss of power from pump wear.

The pressure control system of a sprayer includes a pressure regulator, pressure gauge and cutoff valve. These components should be within reach of the driver. The pressure regulator regulates the pressure to the nozzles and relieves excess pressures so some of the liquid can return to the tank through the bypass hose. For low-pressure sprayers, a pressure gauge with a 0 to 100 psi range is desirable. A quick-acting cutoff valve handy to the driver is also needed on a sprayer. Often, valves are provided so that each side and the center sections of the boom can be cut off independently.

Boom sprayers get their name from the booms or long spray-bearing arms that extend laterally to cover a particular swath as the sprayer passes over the field. Booms may be “wet” or “dry.” Wet booms use the material of the boom as the conduit for the spray liquid. Pipes or rigid tubes through which the material can pass are used. Dry booms have a rigid boom constructed of angle iron, channel iron or pipes to which hoses and fittings carrying the spray liquid are attached. The spray material passes through the hoses and not the boom itself. Dry boom sprayers are more common. Flexible nozzle spacing, ease of repairs, and cost favor dry booms.

Nozzles meter flow, atomize the liquid in a targeted range of droplet sizes, and disperse the droplets in a specific pattern for proper impact with plants or soil. Nozzles are available in brass, stainless steel, polymer, ceramic and hardened stainless steel. Brass and polymer nozzles are popular, primarily due to low cost. Stainless steel and hardened stainless steel nozzles last three to 15 times longer than brass, but they cost about three to five times more than brass. Ceramic nozzles last about 100 times longer than brass.

Figure 5. Flat-fan nozzles angled to 5 degrees from the boom.Figure 5.Flat-fan nozzles angled to 5 degrees from the boom.

The type of nozzle used for applying herbicides is one that develops a large droplet and has no drift. The nozzles used for broadcast applications include the regular flat fan, extended range flat fan, drift reduction flat fan, turbo flat fan, twin flat fan, and air induction nozzles. Operating pressures should be 20 to 30 psi. Pressure more than 40 psi can create significant drift. Air induction nozzles and drift reduction nozzles should be operated at 30 psi and above. These nozzles will achieve uniform application of the chemical if they are uniformly spaced along the boom. Flat fan nozzles should be overlap 50 to 60 percent. Table 3 suggest boom heights for flat fan nozzles with different angles. Also, the orientation of each flat fan along the boom should place with an angle of 5 degrees from the center line of the boom (Figure 5).

Table 3. Suggested Minimum Spray Nozzle Height (Flat Fan).
Spray Tip AngleNozzle Height (Inches)1
20" Spacing30" Spacing
1 Nozzle height should be adjusted such that spray pattern overlaps 50-60 percent.

Calibration of Boom Sprayers

Calibration of sprayer equipment is very important. Calibrate sprayers often to guard against using excessive amounts due to nozzle wear, speed changes, and etc. Inaccurate calibration can cost money and may cause crop damage. Safety and economics dictate calibrating with water alone. Be careful while working with sprayers and pesticides in the field. Always carry a plastic jug of clean water on the tractor in case of pesticide contamination.

Orchard herbicide applications are broadcast. Broadcast applications spray 100 percent of area under the boom. In orchards, herbicide strip applications normally spray the orchard floor beneath the trees’ drip line. To determine the sprayed acreage (herbicide strips), divide the herbicide strip width by the tree row width, then multiply by the total acres of trees. This will yield the number of acres to purchase chemical for.


The procedure below is based on spraying 1/128 of an acre per nozzle or row spacing and collecting the spray that would be released during the time it takes to spray the area. Because there are 128 ounces of liquid in 1 gallon, this convenient relationship results in ounces of liquid collected being directly equal to the application rate in gallons per acre.

Calibrate with clean water when applying toxic pesticides mixed with large volumes of water. Check uniformity of nozzle output across the boom. Collect from each for a known time period. Each nozzle should be within 10 percent of the average output. Replace with new nozzles if necessary. When applying materials that are appreciably different from water in weight or flow characteristics, such as fertilizer solutions, calibrate with the material to be applied. Exercise extreme care and use protective equipment when active ingredient is involved.

Step 1. From Table 4, determine the distance to drive in the field (two or more runs suggested). For broadcast spraying, measure the distance between nozzles.

Step 2. Measure the time (seconds) to drive the required distance, with all equipment attached and operating. Make note of throttle setting and gear!

Step 3. With sprayer sitting still and operating at same throttle setting or engine RPM as used in Step 2, adjust pressure to the desired setting. Machine must be operated at same pressure used for calibration.

Step 4. Collect spray from one nozzle for the number of seconds required to travel the calibration distance.

Step 5. Measure the amount of liquid collected in fluid ounces. The number of ounces collected is the gallons per acre rate on the coverage basis indicated. For example, if you collect 18 ounces, the sprayer will apply 18 gallons per acre. Adjust applicator speed, pressure, nozzle size, etc., to obtain recommended rate. If speed is adjusted, start at Step 2 and recalibrate. If pressure or nozzles are changed, start at Step 3 and re-calibrate.

Step 6. To determine amount of pesticide to put into a sprayer tank, divide the total number of gallons of mixture to be made (tank capacity for a full tank) by the spray output in gallons per acre(Step 5) and use recommended amount of pesticide for this number of acres.

Step 7. Sprayers should be frequently checked for proper calibration.

Sprayer calibration sheets and wallet size cards are available from your local county extension office.

Table 4. Calibration distances with corresponding widths.
Nozzle Spacing
Calibration Distance
To determine distance for spacing or band width not listed, divide the spacing or band width expressed in feet into 340.3. Example: For a 13" band, the calibration distance would be 340 divided by 13/12 = 314.1.

Status and Revision History
Published on Mar 30, 2006
Published on Feb 23, 2009
Published on May 14, 2009
Published with Full Review on Feb 09, 2012


Airblast Sprayer Calibration

Dr. Douglas G. Pfeiffer, 205C Price Hall; e-mail

I. General

A. How the sprayer works: Airblast sprayers operate by using a relatively low pressure pump to deliver the spray mixture into an airstream. This airstream is produced by a large fan and serves to carry the spray to the target. Advantages of this technology are that spray is delivered rapidly, and the entire air volume of the orchard may be treated with a pesticide-laden mist. One of the main disadvantages is the problem of drift; much of the mist is dispersed into the air either before hitting the target, or entirely missing the target. There is research and development underway on ways to reduce such drift, such as the tunnel sprayer at West Virginia University, as well as "smart sprayer" technology, where sensors determine missing trees, etc. and interrupt spray delivery accordingly.

B. Nozzles: Nozzles are of several types; the most common type has several parts through which the mix passes. As the spray passes from the supply line, it passes through a filter. This is to remove debris and other particulate matter before entering the nozzle. The next part is the swirl plate (or simply swirl). This plate has two or three beveled holes of variable size. As the pressurized liquid is forced through these beveled openings, the plate turns, breaking the spray into droplets, the size of which varies with the pressure and the swirl size. The spray then passes through the outer disc. The disc also has a hole of variable size. The entire assembly is held in place by a flange. These parts are shown here, with the inner parts on the right, and outward parts to the left.

The combination of disc and swirl sizes is critical to determining the output of the sprayer. Different combinations produce droplets of varying size. Small droplets have greater surface area and evaporation may be a problem. Therefore such combinations are not used on tall trees, or in upper parts of the spray pattern, because droplets may never contact the target surface. Large droplets carry farther. Treating upper parts of the tree is generally more difficult than treating the lower parts, especially in older, larger trees. The following illustration carries two lessons: (1) ensure that calibration will allow treatment of upper parts of the canopy, and (2) do not put phytotoxic materials in an airblast sprayer tank!

Nozzle parts are produced of several materials. The least expensive is brass; brass fittings are often supplied with the sprayer. These fittings are relatively soft and wear out the fastest. Other, harder materials include ceramic and carbide steel. Although these are more expensive, they are more economical because of increased durability.

C. Dilute sprays versus concentrate, low-volume sprays: Sprays are often applied at a recommended gallons per acre, read from the pesticide label. This is often referred to as dilute spraying. In order to reduce spray time, fuel, and water use, the recommended amount of pesticide is often applied in a reduced volume of water. This is referred to as concentrate or low-volume spraying. A spray may be described using multiplication factor of the mix used, e.g. a 3X spray. There are some advantages associated with concentrate spraying (mentioned above); there are disadvantages as well, that increase in severity with the degree of concentration. Droplet size tends to become smaller with highly concentrated sprays, so evaporation rate increases. Any other error factor (such as wind speed, etc) may become more important.

II. Sprayer selection

The first calculation that must be made is involved in sprayer selection: How large a sprayer is needed. The air capacity needed depends upon the tree volume to be sprayed. The tree volume is estimated by the equation:

tree volume (ft3) = pi r2 h,

where r is the radius of the tree and h is tree height. For example, for trees 12 ft in diameter and 15 feet tall, the tree volume will be (3.14)(6 ft)2(15 ft) = 1,696 ft3.

The air capacity may now be calculated, using the formula:

air capacity (ft3/min) = [speed (ft/min)/tree spacing (ft)] X tree volume (ft3) X 2 sides)

The speed is usually described in MPH; 1 MPH is equivalent to 88 ft/min. If the above trees are planted to a 25 by 25 foot spacing, and the sprayer will be driven at a speed of 2.5 MPH, then the air capacity will be:

air capacity (ft3/min) = [(2.5 X 88 ft/min)/25 ft] X 1,696 ft3) X 2 = 29,850 ft3/min

III. Calibration

Determining Gallons/Acre (GPA): Calibration is the adjusting of sprayer output to a desired level. The first step is determining the desired output, or gallons per acre (GPA). An old standard was 400 gallons per acre. This is rarely used now, except for fully dilute sprays on large trees, including dormant sprays. A more usual approach is to determine desired output based on tree row volume (TRV). A discussion of the relative efficacy of TRV spraying is available from West Virginia. A graph is published in the Virginia-West Virginia-Maryland Spray Bulletin for Commercial Tree Fruit Growers (Va. Coop. Ext. Pub. 456-419) that simplifies this task (click on the PDF for "growth regulators"). The following information is required to use the graph:

(a) Distance between rows,
(b) Tree height X width (ft2)

After these values are found on the axes of the graph, the desired value for gallons per acre are read. Furthermore, since less spray mix is wasted by runoff from the sprayed foliage, a reduced amount of pesticide per acre may be used, also determined from the graph. In our example orchard, the distance between rows is 24 ft. Tree size is 12 ft X 15 ft - 180 ft2. A dilute spray for this block would require 230 GPA.

New Jersey has posted information on tree row volume as well. New Zealand is also using the tree row volume method.

Determining Gallons/Minute (GPM): Once desired GPA is known, the output rate, or gallons per minute (GPM), must be calculated. The equation for this is:

GPM = (GPA X MPH X tree spacing X 2 sides) / 1000

In our example orchard, with a tree spacing of 16 ft within a row, and assuming a sprayer speed of 2 mph, this equates to:

GPM = (230 X 2 X 16 X 2 sides) / 1000 = 14.72 GPM

(Note the effect of travel speed - New Jersey Link)

An airblast sprayer has two manifolds, one on each side. Divide the calculated figure by 2 to determine to allocation of nozzle combinations on a manifold. (GPM per side = 7.36)

With the distributional pattern of output of 50% in the top third, 35% in the middle third and 15% in the bottom third, the following outputs should be allowed in the respective thirds: 3.68, 2.58, and 1.10. Some discretion may be required, depending on the number of nozzles on the manifold, and output values for specific disc/swirl combinations.

The following are output values (GPM) for a selection of nozzle settings at 200 psi:

.................................Disc size......................

Swirl size

For the 8 nozzles on the manifold, a suitable distribution would be:


The calculated output was 7.36 GPM, comparable with the 7.32 GPM obtained.

Checking the calibration: The calibration should be checked both immediately following renozzling the sprayer, as well as periodically during the season. Immediately after adjusting, put a measured volume of water in the sprayer and determine the time trequired to spray out the water. Compare this with your calculated gallons per minute value.

Spray a known area of orchard (with known trees per acre calculated from tree spacing). How much water was required to spray this area?

To enable checking the calibration during the season, note where the sprayer runs out in the first spray after calibrating the sprayer. Mark this area. As the season progresses, note how soon the sprayer runs out. When the sprayer runs out significantly earlier than when freshly calibrated (about 10%?), it is time to recalibrate. The nozzles have become worn and output has consequently increased.

See also the New England recommendations for sprayer calibration, with comments on concentrate sprays, adjuvants, and alternate row sprays, and Penn State and New Jersey comments. 

Updated 11 October 2002
  1. Soompi chinese drama
  2. Snowmobile trailer grip
  3. Microsoft tag generator
  4. Suzuki ninja

Airblast operators should know how to read a nozzle table. They are found on dealer and manufacturer websites as well as in their catalogs. Table layout varies with brand, but they all relate a nozzle’s flow rate to operating pressure. The better tables also provide the spray angle and the median droplet size (i.e. spray quality).

Operators need this information to complete calibration calculations (aka sprayer math) and when deciding how to distribute nozzle rates, angles and spray quality along a boom relative to the target canopy.

This article focusses on hollow and full cone nozzles, which are commonly found on airblast sprayers. For more information on flat fan nozzle tables (e.g. for banded under-canopy or, vertical booms or broadcast applications from horizontal booms), refer to this article.

Reading the table

Let’s use the table below to determine a nozzle’s flow rate for a given pressure. First, find the nozzle colour in the top row. Second, find the operating pressure in the left-most column. Finally, the flow rate is indicated in the cell at the intersection between the row and column. For example, a red ATR hollow cone nozzle operated at 9 bar will emit a flow rate of 1.83 L/min.

Perhaps you want to determine which nozzle will give a specific flow rate. Find the rate in the body of the table and trace the column and row to determine which nozzle/pressure combination will achieve it. For example, if we want a flow rate of ~1.00 L/min, we can use a Yellow at 10 bar or an Orange at 5 bar. Yellow is the better choice since the Orange would have to be operated at the bottom of its pressure range (more on that later).

Do not to confuse TeeJet’s ISO-standardized TXA or TXB nozzles with TXVK or Conejet nozzles. They may be the same colour, but their outputs are very different.

Higher flow rates or full cone patterns can be achieved using combination disc and core (or disc and whirl) nozzles. Depending on the manufacturer, the disc plate is defined by it’s diameter in 64th’s of an inch. The core or whirl plate might be described by the number of holes (e.g. 2-hole, 3-hole, etc.), or some other manufacturer-specific nomenclature (e.g. 45’s, 25’s etc.).

Using the table below, we see that a D2 disc and a DC35 core will emit 0.34 gpm at 80 psi. By continuing along the row, we see that the spray angle for this combination will be 47 degrees at that pressure.

This nozzle Table for TeeJet disc & cores is fairly typical of any manufacturer’s nozzle table. Find the disc & core combination in the two left-hand columns, and follow the row until it intersects your operating pressure to determine the rate in US gallons per minute. Or, if you know your ideal rate already, you can find the best disc & core combination for a given pressure to achieve that rate.

Pressure problems

Do not choose a nozzle at the extreme of their flow or pressure range. A trailed PTO sprayer will experience pressure changes from driving on hills, or rate controllers will create pressure changes in response to changes in travel speed. In either situation, coverage will be compromised if the nozzle is pushed outside its optimal range.

Use pressure to achieve small changes in flow, but for more extreme changes, switch nozzles. Remember, it takes 4x the pressure to get 2x the flow. Stated differently, it takes 1/4 the pressure to get 1/2 the flow.

You may not find a nozzle/pressure combination that emits the rate you are looking for. When your desired rate or pressure falls between the figures listed in the table, you can take the average. When nozzling an entire boom with different nozzle rates, get each position as close as you can to achieve the overall boom rate for a given pressure. It’s always a compromise – don’t stress over it.

The author looking up nozzle rates during a spring calibration. The operator was running at 190 psi, but the catalogue only listed 180 psi and 200 psi. When span is only 20 psi, it’s fairly safe to approximate the output. When the table only lists in 50 psi increments, it is more difficult to determine the rate without testing the output. This issue usually occurs at pressures above 200 psi, and that’s very high for most horticultural operations. Consider using a lower operating pressure, if possible.

Different nozzles, same rate

Different disc core combinations, or molded nozzles at different pressures, can produce similar flow rates. However, their spray quality and spray cone angles can be very different (see last three columns in the TeeJet table above).

The angle of the spray cone can have a big impact on spray coverage. When the target is far away from the corresponding nozzle (e.g. the tops of nut trees), or the canopy is very, very dense (e.g. citrus canopies), consider tight-angled full cones under high pressure. This is inefficient and can give variable coverage, but it is sometimes the only option in extreme situations.

Two hollow cone nozzles on top and five full cone nozzles below. Note the lack of spray overlap with the full cones for the first few meters. This would be a concern if the target were closer to the sprayer, such as grape or berry. Also note that the top two nozzles should not be on; their spray will likely not reach the intended target.

When the target is very close to the sprayer, full cones do not overlap and create undesirable striping or banded coverage. Creating a full, overlapping spray swath that spans the entire canopy is a function of nozzle spacing, distance-to-target, and sprayer air-settings. It can also be affected by humidity, wind speed and wind direction at the time of spraying.

Confirm your settings by parking the sprayer in the alley between crops. With the air on, spray clean water while a partner stands a safe distance behind the sprayer to look for gaps in the swath. The partner will see things the operator’s shoulder check will not reveal.

Shoulder checks may not show you what’s really happening. Have someone stand behind the sprayer while spraying clean water to see the nozzle spray overlaps sufficiently to span the entire canopy.
Shoulder checks may not show you what’s really happening. Have someone stand behind the sprayer while spraying clean water to see the nozzle spray overlaps sufficiently to span the entire canopy.

Nozzle tables can be wrong

Sometimes nozzles do not perform per the nozzle table. We have discovered errors in published tables, worldwide. Here are the big three:

  • Conversion errors. Manufacturers publish catalogs in Metric and in US Imperial, but we have found many errors in the conversions.
  • Spray angle errors. When nozzles are operated at the extremes of their pressure ranges, spray angles deviate from those listed in the tables.
  • Flow rate errors. When tables are not updated to reflect changes in nozzle design, or the manufacturing process, actual flow rates deviate from those listed in the tables.

Perhaps it’s not the table, but the nozzle itself. Most nozzle manufacturers accept a flow variability up to +/- 2.5% for new nozzles, but we have seen higher. It depends how they are made (machined, stamped, printed) and the material they are made of.

Validate flow rate and pattern

When errors are discovered and reported, the manufacturers can be slow to issue corrections and the errors will persist in old tables. Yes, even apps (which are often based on tables) can be wrong. So, predicted flow rates can prove unreliable. This is why it is important to double check by observing nozzle overlap and validating flow rate when you replace nozzles – even when they are brand new.

Thanks to Dr. David Manktelow (Applied Research and Technologies, Ltd., NZ) for input into this article.

Low Volume Air Blast Sprayer for Citrus Growers


Blast sprayer nozzles air


Low Volume Air Blast Sprayer for Citrus Growers


You will also be interested:


1039 1040 1041 1042 1043