Match inflow meters to the rate controller

Once the rate controller has been calibrated and fine-tuned, use it as the calibration standard for the inflow meter.

Step 1: Record the tag figure or calibration number of the inflow meter.

Step 2: Drain the spray tank until empty.

Step 3: Pump 1000 litres of water into the spray tank though the inflow meter. If using a petrol-driven pump, mark the location of the accelerator on the pump motor. Record the volume per minute from the inflow meter – this enables you to check the consistency of supply over time.

Step 4: In the tractor, clear the total litres sprayed in the rate controller. Operate the sprayer at the operating pressure according to your spray plan until the sprayer is empty. Record the total volume pumped out from the rate controller.

Step 5: Calculate a new constant for the inflow meter.

Using a calculator:

New PPU = Old PPU x inflow meter (total litres) ÷ rate controller (total litres)

Worked example:

Inflow meter tag indicates the PPU is 650 Our inflow meter reads 1000 litres

The accurate rate controller pumped out 990 litres

New PPU (inflow) =

Old PPU x Inflow meter total litres ÷ rate controller total litres

= 650 x 1000 ÷ 990

= 656.56 as the new PPU constant for the inflow meter

Step 6: Make a final check.

Drain the sprayer again. For this final check, put 20 litres in the spray tank to prevent the sprayer sucking air. Use the inflow meter to add 1000 litres. Use the same RPM as before. Check that the volume per minute is the same as in Step 2.

Clear the rate controller total volume. Operate the spray unit at the operating pressure as per your spray plan until 1000 litres has been applied. Drain the sprayer and 20 litres should be recovered.