Visit our new site Pesticidewise.com for more help on spraying pesticides with a knapsack sprayer including:
- Choosing a nozzle type
- Choosing the right nozzle for your spraying task
- Calibrating your knapsack sprayer
- Managing pressure
Nozzle selection and their optimised use
N.B. This is a text only version of slides 1 - 20 of the training module "Nozzle selection and their optimised use" which is also available to download as a PowerPoint presentation or view as a Flash Movie
Nozzles have three main functions:
- Nozzles regulate spray liquid emission rates
- Nozzles break the liquid into droplets
- Nozzles ensure the spray is distributed as intended
These three nozzle functions are each critical to the safe, effective use of pesticides
- Regulating spray liquid emission at the nozzle - helps control the volume and dose applied.
- Droplets carry the product to the target surface - the size of these droplets and their numbers will affect product performance as well risks of drift or run-off.
- Effective distribution of droplets by the nozzle over the intended area and/or target surface avoids product waste through less ‘point to point’ variability.
Best product performance can only be gained if:
- The choice of nozzle, their condition and correct use is suitable for the intended spray application.
- Nozzles must be in perfect working order. A defective nozzle may cause higher costs - through non-optimal product use - than that spent for its replacement.
Note: Although each nozzle design has some flexibility in use and is designed to work at a range of pressures, the required flow rates and pressures must be safely achieved and used with the intended spraying equipment.
Introducing the ranges
Introducing nozzle colours
Nozzles of the same colour will have the same flow rate whilst at the same pressure, irrespective of nozzle design. These colours are defined by International Standard and have been agreed by all major nozzle manufacturers.
Note: Each flow rate category has a defined rate of emission
Understanding nozzle codes
Codes can be used in catalogues and on the nozzle itself to identify the nozzle type, spray angle and size. Note: These codes may vary between manufacturers.
The BCPC introduced a ‘generic’ system to be used as a nozzle code to encourage greater use on product labels. The code uses letters and numbers such as FF/110/03 to indicate that this specific design is a flat fan nozzle, with a 110 spray angle and an ’03’ capacity.
Notes to slides:
Nozzles should be labelled providing useful and important information to the user. Different nozzle producers use their own system, but labelling should indicate:
- Flow rate (at standardised pressure)
- Spray angle (at standardised pressure)
Additionally information may include the nozzle type, material etc.
Flow rate data are of great use for checking on a nozzle's condition. A worn out nozzle would deliver higher flow rates than indicated when operated at the standardised pressure. Also a mounted pressure gauges can be checked using brand new nozzles of a producer of repute.
Concerning the spray volume it is recommended to carry out a proper calibration. Of course, the flow rate figure allows to calculate the spray volume as well.
Unfortunately not all nozzles are labelled. In this case calibration and a check on the spray pattern is highly indicated.
Nozzle manufacturing material and wear
Nozzles that are readily eroded and/or corroded in use – may not emit the intended rate of spray liquid, may produce non optimal spray patterns and drop sizes. Nozzle manufacturers minimise these effects but the range of materials used in their manufacture still have a differing wear resistance.
Relative wear resistance of nozzles is dependant on the products sprayed, the purity of water used [such as lack of sand] and the material of which the nozzle is made.
Wear scales used are typically multiples of that measured with brass; the most readily worn material in common use.
Materials most often used for nozzle manufacture are brass, stainless steel, various plastics and ceramics.
- Brass - fairly cheap to produce and resistant to many chemicals. However, particulate materials such as wettable powders easily abrade brass.
- Stainless steel - excellent resistance to both abrasion and corrosion, but more expensive to produce than brass.
- Ceramics - very resistant to abrasion and corrosion but expensive, and prone to damage (chipping) when dropped.
- Plastics - nylon resists corrosion and abrasion but may swell when exposed to certain solvents. Nylon has the advantage that it is cheap to produce. Some of the newer plastics such as Kematal®* offer excellent resistance to abrasion and corrosion, are unaffected by most chemical solvents and are relatively cheap to produce. Plastic nozzles also allow for colour coding for easy identification. (*Lurmark Ltd., Longstanton, Cambridgeshire.)
Most manufacturers now produce nozzles with the outer part made from a plastic which is cheap and can be colour coded, and a small insert including the orifice, made from a more resistant but more expensive material such as stainless steel or ceramic.
Nozzle selection: spray volume rates
Water volume rates are usually stated on product labels to ensure adequate coverage of target surfaces.
Too low a volume rate:
- Poor coverage
- Poor penetration
Too high volume rate:
- Product run off from the target
- Over dilution of product and surfactants
More time taken to spray the crop
Note: Label stated volumes may be shown as a range to enable adequate drop movement/placement through the canopies of developing crops; the greater the density of the crop canopy the larger the volume and vice versa.
Nozzle height [distance to target surface] may influence the applied volume rate, quality of distribution and swath width.
Different nozzle designs, as well as nozzle size, produce different drop sizes and therefore different drop dispersion patterns.
The effect of these different dispersion patterns on product performance is dependent on that product's “mode of action” - how it works. Product labels may state a required drop size [spray quality] and/or the preferred nozzle type and/or pressure. Water Sensitive Paper is a most useful tool to check on a nozzles spray pattern.
Water Sensitive Paper (WSP) shows size and numbers of drops likely to impact on target sites
Optimum coverage can be checked in the field with Water Sensitive Papers
See also the section 'Spray Distribution' for more details about using water sensitive papers.
Nozzle selection and maintenance can have a major impact on the quality of your application and the efficacy of the products applied.
Nozzle selection and spray pressure will have an impact on potential environmental and personal contamination through either run off and/or drift.
Nozzle selection and spray quality [drop size]
More droplets from the same volume of water are produced if drop size is decreased.
Which drop size is best may be dependent on the product used, the drift risk or be a compromise.
Drop Size and some 'rules of thumb'
Ideally, the droplets produced by nozzles should be in the range from 150 to 700 µm. Drops smaller than this range are likely to drift and affect operator safety whilst, droplets too large, reduces their available number - and may not be retained - by the target surface due to the higher energy of large droplets on impaction.
More droplets available = more coverage on the target.
Rule of thumb:
Systemic acting products:
20 – 30 drops/cm2
Contact acting insecticides/fungicides:
50 – 70 drops/cm2
30 – 40 drops/cm2
General rule in the field for any product: Aim for an average 20 drops/cm2
Notes to slide: All important for the success of an application is the amount of droplets reaching the target and forming a deposit there.
Droplet sizes below 150 µm are likely to be lost as drift while large drops may bounce off the target.
The proportion of droplets below 150 µm should therefore be small e.g. less than 5% of the spray volume.