13
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. Lower spray
pressures will produce larger droplets which are
generally less effective than the smaller droplets
produced at higher pressures.
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. For single nozzle holders the number of
nozzles will be 10. 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
