Nozzles and Calibration

Notes on Choice of Nozzles and Calibration of Knapsack Sprayers to Apply Roundup 

In order to achieve the best results with Roundup ProBio/Roundup ProVantage it must be applied at the correct rate.

Firstly, suitable nozzles should be selected; secondly the equipment must be properly calibrated before use and; thirdly, maintenance of the sprayer in good working order will allow accurate application every time.

Users are advised to attend a suitable course organised through the National Proficiency Test Council, leading to PA 6 certification in Hand operated spraying.


New international standards (ISO / DIS 10625) for nozzles colours were introduced in 1998 to try and minimise the confusion caused by different manufacturers using different colours for the same output nozzle. This may well cause more confusion for some time as both sets of colours remain available until old stocks are exhausted. Colour and tip code reference denote orifice size and thus flow rate. The lower the number, the smaller the flow rate per minute.

New ISO Colours

01 = Orange 05 = Brown
015 = Green 06 = Grey
02 = Yellow 08 = White
03 = Blue 10 = Light Blue
04 = Red    

Use the standard nozzle code defined by the British Crop Protection Council to choose suitable nozzles. It is expressed as follows:-

Nozzle TypeSpray AngleNozzle OutputRate PressureSpray Quality
F = Flat Fan In degrees, not always included for HC and D types Litres/min @ rated pressure 3 bar (40 psi) is standard and 1 bar (15 psi) for D and FLP nozzle types Very Fine
HC = Hollow Cone Fine
D = Deflector Medium
FE = Even Fan Coarse
FLP = Low Pressure Fan Very Coarse

Roundup Pro Biactive and Roundup ProBiactive 450 both specify D or FE / 0.23 - 0.92 / 1  Medium or Coarse.

Nozzle Choice

A medium to coarse spray is needed to avoid damaging drift, to achieve this a pressure of 1 bar is optimum. Hollow cones are designed to give fine drops at 3 bars and are thus best suited to insecticide and fungicide application.

Standard flat fan nozzles work at 3 bar pressure and low-pressure flat fan nozzles, though they are rated 1 bar are usually designed to work on boom sprayers with an overlap of 50% and so are unsuitable for single nozzle knapsack application.

An even spray fan is designed to give even coverage from a single nozzle but most are rated at 3 bars and so not optimum for Roundup Pro Biactive. Spraying Systems Co. produce the DG Teejet® Even spray tip, (DG =Drift Guard.) This nozzle works down to 1.5 bars by virtue of a pre-orifice chamber, which produces larger droplets. It gives 80l/ha output when used at 50cm above the target (Nozzle Code, DG95015EVS). This narrows down the choice from the huge range to just the two types:

Low pressure, Even, flat fans like the green DG and the deflector tips available under a number of names but all referring to the same thing:

Anvil/ Deflector / Deflector Tip / Floodjet / Polijet

Spray fan

These consist of a circular orifice, through which the liquid jet passes to impinge on a deflecting surface, resulting in a wide-angle fan spray with a narrow rectangular spray pattern. They are rated at 1 bar and produce a relatively even distribution.

For variable width spraying the range of Anvil / Deflector /Polijets often supplied with knapsack sprayers enable alteration of swath widths without changing nozzle height.   There are usually four nozzles designed to work at a height 50cm above the target at 200 l/ha

2m swath width
1.5m swath width
1m swath width
0.5m swath width

There is no advantage in applying Roundup Pro Biactive in any more than 250 l/ha and indeed results are actually improved from lower volumes. Since knapsack applications involve the operator carrying the necessary water on his back there is little justification for choosing any other than the VLV, (Very low volume), type of  deflector nozzle.

These use reduced volumes, e.g. the Cooper Pegler orange DT 0.5 gives an application rate as low as 35 litres/ha and the Sprays international  orange DEF-01 as low as 27 litres per hectare. Choose a VLV Deflector nozzle with ISO colour Orange, green, yellow, blue or red.

Swath widths vary with these low volume nozzles but are usually are at least 1 metre at 50cm above the ground. To reduce the swath width it is necessary to drop the height of the nozzle, for example the CP orange DT 0.5 nozzle height drops to 23cm from the normal 50cm to achieve a 0.5m width when the output would be 80 l/ha. (See detailed section on nozzle height). Always refer to the manufacturer’s literature for details of specific nozzles.

  • Never clean nozzles with a sharp object, use a soft brush or airline
  • Always replace nozzles at least once a year or at the first sign of wear


Knapsack sprayers vary in the degree of pressure adjustment available. Generally there is a pressure relief valve either inside or outside the top of the tank. This prevents the chamber pressure building up excessively, but does not provide an accurate or constant pressure. Roundup Pro Biactive should be sprayed at Low pressure where the choice is high or low and between 1 and 2.5 bars where nozzle pressure gauges are fitted.

It is possible to dampen out the variation in pressure caused by hand pumping with a Fluid Control Valve incorporated into the lance. For a modest extra cost Sprays International supply a CFV (Constant flow valve) with fittings to suit most knapsacks which can be pre-set at 1.5, 2 or 3 bars.

There are Spray Management Valves (SMV) included with Cooper Peglar Series 2000 sprayers which perform the same function. Monsanto would recommend this type of valve as they mean much higher accuracy, no wasted chemical and reduced risk of driftable droplets produced by over pressurising.


Nozzle Calibration

The ultimate application rate is a function of nozzle output, walking speed and swath width. Good calibration is essential for efficient use of Roundup Pro Biactive/Roundup ProBiactive 450. Download our Knapsack Calibration Procedure Sheet for more information.

Many people underestimate the importance of nozzle height in accurate application. Most are designed to work at 50cm above the target, but the swath width is dependent on this height and halving it will also halve the swath width and double the application rate.

Nozzle Widths & Heights

To illustrate this let us assume a correct nozzle is chosen, e.g. CP Orange VLV DT0.5 and a walking speed of 1 metre per second at 1 bar pressure. Using the calibration equation in the Knapsack Calibration Procedure Sheet and Cooper Peglar nozzle output tables, when the nozzle height above the target is 50cm the swath width is 110cm and therefore achieves a rate of 35 l/ha. If the nozzle height was reduced down to 35cm the swath is only 77cm wide and the rate per hectare rises to 50 l/ha. This is a 43 % increase in application rate! 

A very simple way to keep the nozzle height correct whilst working is to attach piece of light-weight chain of the required length to the end of the hand lance and keep its end just at target height.