15
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 30 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, or
alternatively use the Spraying Output Chart on the
following page.
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
For chemical applications the jet and swirl plate
combination for each individual nozzle can be
selected by calculating the requirements for one
side of the sprayer, as follows, then copying the
pattern on the other side.
Decide on the number of nozzles to be used on
one side and the percentage of spray required
from each nozzle (the total should be 100%).
Calculate the individual nozzle flow rates by
halving the total output from Step 2, to obtain the
output for one side, then multiply this by the
percentage output required from each nozzle
Use the Single Nozzle Output Chart on page 17
to select the jet and swirl plate combination which
is the closest match to the required nozzle output
at the chosen pressure.
Add up the flow rates of the individual jets to
check that the total output per side 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.
Speed (km/hr) =
360
Time in Seconds for 100m
Total output (l/min)
2
Output per side (l/min) =
Nozzle output (l/min
) =
Nozzle percentage (%) x Output per side (l/min)
100
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)
