How to Use a Knapsack Sprayer

It is important to calibrate sprayers so that the correct dose of chemical is applied. The factors that affect the application rate are: 

·         Spraying pressure

·         Size of the nozzle or nozzles

·         Travel speed of the applicator

·         Height of the nozzle above the target 

Information about correct pressures and nozzles for different types of applications should be contained in the instruction manual that comes with the spray unit.   

Calibrating a knapsack sprayer 

To calibrate a knapsack sprayer you need to determine: 

·         The walking speed of the operator

·         Spray pattern width

·         Nozzle output


Walking speed (km/hr) – calculated by dividing 360 by the time it takes in seconds for the operator to spray over a distance of 100 metres i.e. If the time required is 95 seconds the calculation is 360/95 = 3.79 km/h


Spray pattern width – check this by spraying on concrete or in an area where the pattern in noticeable, and take a measurement.


Nozzle output – calculate by spraying water into a measuring jug for one (1) minute.




For the purposes of this example assume the following:


·         Walking speed = 3.79 km/hour

·         Spray pattern width = 1.5 m

·         Nozzle output = 2 litres/min


Volume (litres/hectare) = 600 X nozzle output (litres/min)

Spray width (m) x speed (km/h)


Volume = 600 x 2 litres/min   = 211 litres/hectare

1.5 m x 3.79 km/h