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Proper calibration is one of the most important parts of spraying. Properly calibrated sprayers
will save you both time and money.
How to determine the gallons per minute (per nozzle).
GPM=GPA x MPH x W
5940
GPM—Gallons Per Minute
GPA—Gallons Per Acre
MPH—Miles Per Hour
W—Nozzle spacing (in boom spraying)
This formula is useful to determine which tip to use on your boom, especially when your nozzle
spacing is different from the standard 20 or 40” nozzle spacing on Certified
TM
Sprayers. For
example: You know you want to travel 3 MPH (5 km/h), and apply the chemical at a rate of 20GPA.
The nozzle spacing’s are 33” (84 cm) on centre. By using the formula you will determine how many
gallons per minute (GPM) per tip will be required to give you the correct application.
Example: 20 GPA x 3 MPH = 60 x 33” (nozzle spacing) = 1980 divided by 5940 + .333 GPM
You have now determined that you need a tip with GPM of .333. Find the type of tip you want to
use. For example, an 80 degree flat fan spray tip and then determine what pressure you plan to
spray at. Let’s say 30 PSI. How do you check this calibration? By using this formula.
GPA = 5940 x GPM (Per Nozzle)
MPH x W
Multiply 5940 x .333 GPM + 1783.8. Multiply 3 MPH x 33 (nozzle spacing) = 99.
Divide 1783.8 by 99 = 18.06 gallons per acre.
By simply adjusting your pressure or your tractor speed, you will obtain the 20 GPA rate.
The second formula is used to determine whether an old tip (one on which you cannot identify
the number) is still spraying the right amount of chemicals. You can determine how many GPM
a tip is spraying, with the use of a catch jar and stop watch. Hold the jar under the tip so you
catch the total spray for one minute. The amount in the jar indicates the GPM.
Calibrate your sprayer carefully. If your tips are worn, replace them. New tips are a fraction of
the cost of using either too much or too little chemicals. Also, you can use these formulas to help
determine if the intended pump has the volume capacity to meet your spraying needs.
Spr
ayer Cal
ibr
ation
