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Airblast Sprayer Calibrator

Sprayer calibration should be done at least once per season, but preferably every time there is a significant difference in the desired spray volume (gal/acre). For example, early-season applications cover a small canopy and therefore require a lower spray volume for thorough coverage compared to later applications to a full canopy. This worksheet is intended to take you stepwise through the calibration process.

1. Determine tractor speed.

In a pre-set gear, note the throttle settings. Fill the spray tank half full with water for a speed test. Insert numbers into the equation below and calculate the result. For the test run:

Establish a preferred operating speed.

Measure the length in feet of a row in your berry field.

Determine the time required to travel the row at the preferred speed.

Tractor speed:

(Row length in ft is (A) X 60 sec./min) ÷ =

2. Check spray pressure and spray pattern.

Take these steps to check spray pressure and pattern.

  1. Fill the tank with water.
  2. Engage the fan, turn on the manifold, and make a test run in your berry field at your preferred operating speed.
  3. Before you move forward, observe the spray pattern and turn off nozzles that do not spray the plant canopy.
    • Record the pressure gauge reading while spraying.
    • Visually check the accuracy of your spray pattern and the completeness of your spray coverage by putting water-sensitive paper in the canopy.
      • Poor or excessive coverage requires adjustment of either tractor speed, spray pressure, or nozzle size.
  4. If speed or pressure is subsequently adjusted, record the new figures in the appropriate blanks on this page.

3. Determine required total nozzle output in gal/min (GPM).

Fill in the following known quantities, insert into the equation below, and calculate the result.Preferred tractor speed from above:

See pesticide label for instructions for use. Consider differences in canopy size through the season.

Measure the distance between rows:

total required nozzle output in GPM:

X X Distance in feet is (F) ÷ 43,560 ft2/acre =

4. Check nozzle size.

Do you currently have the correct size nozzles in your sprayer? Enter ouput in the spaces below. Enter a zero for nozzles turned off for the upcoming application.

Determine the expected output of each nozzle at your selected spray pressure (D) from the manufacturer’s catalog.

Left side Right side

total expected nozzle output in GPM:

+ Right total in GPM =

Compare the total expected output with the total required output.

If the difference between expected and required output exceeds 10 percent, replace with appropriate disc-core nozzle combinations that will provide the required output at your operating pressure. Keep in mind that all nozzles do not need to have equal output. You may want to have higher output nozzles pointing at the fruit zone. Remember that total expected output still must equal total required output, so use lower output nozzles elsewhere on the boom. Repeat this procedure for nozzles on the other side of the sprayer.

5. Is your sprayer delivering the desired spray volume?

With the correct discs and cores determined and installed, do the following;

  1. Fill the spray tank with water.
  2. Park the sprayer on level ground and mark the water level on the spray tank’s sight gauge.
  3. Using your preferred tractor speed with the airblast fan engaged and both sides spraying, make a trial application run down your test row.
  4. Return to the same place and position where you marked the sprayer water level.
  5. Using a calibrated 5-gallon container, measure the amount of water required to refill the tank to your mark on the sight gauge.
  6. Record as test gallons applied.

Fill in the following known quantities and calculate the result.

43,560 ft2 X ÷ X =

6. Compare your actual and desired spray volume.

Compare known quantities:

Desired application rate in gal/acre is (E)

If the difference is within 10%, the sprayer is properly calibrated.

  • If actual spray volume exceeds desired spray volume by more than 10%, nozzles may be worn and need replacement.
    • Change disc and core accordingly for each nozzle and repeat step 5.
  • If actual spray volume is less than desired spray volume, double check calculations.
    • Repeat steps 4, 5, and 6, and replace discs and cores if necessary.

7. Prepare the spray mixture.

Use known quanities and calculate for the end result:

Quantity per acre from the label, in lb, oz, or gal is (L)

total volume in gallons:

÷ =

X =