Page 10
Nozzle Selection and Calibration
Nozzle Selection and Calibration Checking
Chemical application rates and hence nozzle
selections will vary greatly depending on the crop
type, stage of crop development and the regional
area. Information on application rates should be
available from your chemical supplier or State
Department of Agriculture.
Nozzle selection can be made by following the four
simple steps shown below. The fourth step,
checking the calibration after nozzle selection,
improves 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)
Speed (km/hr)
The travel 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.
Speed (km/hr)= 360
Time in seconds for 100
c)
Row width (m)
The distance between rows measured in metres.
d)
Spray pressure (Bar)
A spray pressure of
between 20 and 30 bar is usually selected. Lower
spray pressures will produce larger droplets which
are generally less effective than 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.
Total output (l/min) =
Application rate (l/ha) x Speed (km/hr) x Row width (m)
600
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
a) Nozzle sets to suit a variety of applications can
be selected directly from the Jet/Swirl Plate
Combination charts on the following pages.
b) For other applications or those not requiring all
jets to be used, such as vineyards, the correct
nozzles can be selected by calculating the nozzle
requirements for one side of the sprayer then
copying the selected nozzles on the other side of
the sprayer.
Decide on the number of nozzles to be used on
one side and the percentage of spray required from
each (the total should be 100%).
To obtain the individual nozzle flow rates, halve the
total output calculated at Step 2, to obtain the total
output for one side, and multiply it by the
percentage output required from each nozzle.
Use the Nozzle Output Chart on the following page
to select the nozzle and swirl plate combination
which will give the required nozzle output at the
spraying pressure you have chosen.
Output per side (l/min) = Total output (l/min)
2
Nozzle output (l/min) =
Nozzle percentage (%) x Output per side (l/min)
100
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 be sufficient
.
operating pressure and with nozzles spraying. A
run time of 2 minutes should
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
test run, in minutes.
Output (l/min) = Volume to refill (litres)
Time (min)
Verify that the measured output matches the value
calculated at Step 2. For small variations increase
the spraying pressure to increase the output or
reduce the pressure to reduce output.
A nozzle selection example and worksheets to
record calibration results are shown on page 14.
