5
Calibration
Nozzle Selection and Calibration Checking
Chemical application rates and hence nozzle
selections will vary greatly depending on the
crop type, and the stage of crop development.
Information on application rates should be
available from your chemical supplier.
Nozzle selection can be made by following the
four simple steps shown below. The final step,
checking calibration after nozzle selection, is
essential for spraying efficiency by ensuring a
known amount of spray is applied per hectare.
STEP 1
Operating Factors
First establish the following factors.
a)
Application rate (l/ha)
in litres per hectare.
b)
Travel speed (km/hr)
The speed indicated by
your tractor can be checked by timing the
sprayer over a measured distance. The timing
should be done in seconds over 100 metres with
the PTO engaged and water in the tank to
simulate real spraying conditions. In hilly terrain
the sprayer should be timed driving up and down
the hill and the two times averaged. The speed
can be calculated according to the following
formula.
c)
Row width (m)
The distance between rows
measured in metres. For single side spraying
use half the row width.
d)
Spray pressure (Bar)
A pressure of between
10 and 20 Bar is usually selected.
STEP 2
Total Output Required
Calculate the total spray output required in litres
per minute (l/min) using the following formula.
Check that the calculated output does not
exceed the rated capacity of the pump. If it does,
reduce the travel speed or the application rate.
STEP 3
Nozzle Selection
Decide on the number of nozzles to be used in
total. Note, that if not all nozzles are used, the
number of nozzles will be the number of those
“on” only.
Nozzle Output (l/min) =
Add up the flow rates of the individual jets to
check that the total output matches the
calculated value. Small variations can be
corrected by increasing pressure to increase
output or reducing pressure to reduce output.
STEP 4
Calibration Checking
After installing the selected jets, test the sprayer
with water to confirm the application rate. Fill the
tank to the brim or a specific mark then run the
sprayer for a measured time at operating
pressure and with the nozzles spraying. A run
time of two minutes should be sufficient.
Measure the volume of water, in litres, required
to refill the sprayer to the brim or the specific
mark chosen then divide this volume by the time
of the run.
Verify that the measured output matches the
total output value calculated at Step 2.
Speed (km/hr)
=
360
Time in Seconds for 100m
Total Output (l/min
)
=
Application rate (l/ha) x Speed (km/hr) x Row width (m)
600
Output (l/min) = Volume to refill (litres)
Time (min)
Used
Nozzles
of
No.
Total
Output
Total
