Southeastern U.S. Vegetable Crop Handbook - 2023 - 121

4. The discharge rate, gallons per minute (GPM), required
for the nozzles must be calculated in order to choose the
right nozzle size. Discharge rate depends on the application
rate; ground speed; and nozzle spacing, spray width,
or spray swath.
For applications using nozzle spacing or nozzle spray width
(inches), use Equation 2.
Equation 2. Discharge Rate =
Application Rate x Ground Speed x Nozzle Spray Width
5,940
For applications using the spray swath (feet):
Equation 3. Discharge Rate =
Application Rate x Ground Speed x Spray Swath
495
5. Choose an appropriate nozzle or nozzles from the manufacturer's
charts and install them on the sprayer. Check
each nozzle to be sure it is clean and that the proper
strainer is installed with it.
6. Fill the tank half full of water and adjust the nozzle pressure
to the recommended setting. Measure the discharge
rate for the nozzle. This can be done by using a flow meter
or by using a collection cup and stopwatch. The flow
meter should read in gallons per minute (GPM). If you
are using the collection cup and stopwatch method, the
following equation is helpful to convert ounces collected
and collection time, in seconds, into gallons per minute.
Equation 4. Discharge Rate =
Ounces Collected x 60
Collection Time x 128
7. Whenever possible, calibrate with water instead of spray
solution. Do not calibrate with spray solution unless
required by the chemical label. Follow all recommendations
on the label. If the spray solution has a density
different than water, the rate can be corrected using the
procedure shown in Calibration Variables.
8. On boom sprayers or sprayers with multiple nozzles, average
the discharge rates of all the nozzles on the sprayer.
Reject any nozzle that has a bad pattern or that has a discharge
rate 10 percent more or less than the overall average.
Install a new nozzle to replace the rejected one and
measure its output. Calculate a new average and recheck
the nozzles compared to the new average. Again, reject
any nozzle that is 10 percent more or less than the average
or has a bad pattern. When finished, select a nozzle
that is closest to the average to use later as your " quick
check " nozzle.
On backpack sprayers or sprayers with a single nozzle,
compare the discharge rate of the nozzle on the sprayer to the
manufacturer's tables for that nozzle size. Reject any nozzle that
has a bad pattern or that has a discharge rate 10 percent more or
less than the advertised rate. Install a new nozzle to replace the
rejected one and measure its output.
2023 Vegetable Crop Handbook for Southeastern United States
Once the sprayer has been properly prepared for calibration,
select a calibration method. When calibrating a sprayer, changes
are often necessary to achieve the application rates needed.
The sprayer operator needs to understand the changes that can
be made to the adjust rate and the limits of each adjustment. The
adjustments and the recommended approach are:
* Pressure: if the error in application rate is less than 10 percent,
adjust the pressure.
* Ground speed: if the error is greater than 10 percent but
less than 25 percent, change the ground speed of the
sprayer.
* Nozzle size: if the error is greater than 25 percent, change
nozzle size. The goal is to have application rate errors less
than 5 percent.
Calibration Methods
There are four methods commonly used to calibrate a sprayer:
The basic, nozzle, and 128th
acre methods are " time-based
methods " which require using a stopwatch or watch with a
second hand to ensure accuracy. The area method is based on
spraying a test course measured in the field. Each method offers
certain advantages. Some are easier to use with certain types of
sprayers. For example, the basic and area methods can be used
with any type of sprayer. The 128th
acre and nozzle methods
work well for boom and backpack sprayers. Choose a method
you are comfortable with and use it whenever calibration is required.
BASIC
METHOD
1. Accurate ground speed is very important to good calibration
with the basic method. For tractor-mounted sprayers,
set the tractor for the desired ground speed and run
the course at least twice. For backpack sprayers, walk the
course and measure the time required. Walk across the
course at least twice. Average the times required for the
course distance and determine ground speed from Equation
1.
2. Calculate the application rate based on the average discharge
rate measured for the nozzles, the ground speed
over the test course, and the nozzle spacing, nozzle spray
width, or spray swath on the sprayer.
When using nozzle spacing or nozzle spray width measured in
inches, use the following equation:
Equation 5. Application Rate =
5,940 x Discharge Rate
Ground Speed x Nozzle Spray Width
For spray swath applications measured in feet:
Equation 6. Application Rate =
495 x Discharge Rate
Ground Speed x Spray Swath
3. Compare the application rate calculated to the rate required.
If the rates are not the same, choose the appropriate
adjustment and reset the sprayer.
4. Recheck the system if necessary. Once you have the accuracy
you want, calibration is complete.
121
Southeastern U.S. Vegetable Crop Handbook - 2023

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