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 21 - 41 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
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Nozzle selection and use: nozzle guidance supported with clear pictograms vital to knapsack users
Application volumes and plant growth
Application volumes may need to be increased when target plant surfaces get more extensive or dense because there is more foliage to cover.
Volumes applied by knaspack sprayers can be increased by:-
- Walking slower: Not easy to keep constant forward speed.
- Increasing sprayer pressure: May cause excessive drift.
- Changing the sprayer nozzle size: Prefered option.
Nozzles on knapsack sprayers; main types in use
Flat fan nozzles: standard and even spray types
These standard types can be used on small multi-nozzle booms whilst even spray designs produce uniform deposits from a single nozzle.
Notes to slide:
The flat fan nozzle has a lens-shaped or elliptical orifice. This produces a narrow lens-shaped pattern, with the highest spray deposit occurring immediately under the nozzle and the amounts of spray lessening towards the edges of the fan. This means the swaths must be overlapped to achieve an even deposit on the target, and hence are usually used in overlapping fashion on a spray boom.
These nozzles are produced in a range of sizes and possible spray angles although the most commonly used spray angles are either 80° or 110°. The larger spray angle (110°) gives a wider swath but generally produces smaller droplets.
Fan nozzles are most suitable for spraying flat surfaces such as soil when applying pre-emergence herbicides, to walls of buildings, for example, when spraying against insect disease vectors or stored product pests.
A special type of flat fan nozzle is known as the 'even spray' nozzle. This is designed to give an even deposit across the swath to eliminate the need for overlapping swaths, and is best suited for a single nozzle on a knapsack lance when band or strip spraying. They are most commonly available only with an 80° spray angle.
Most flat fans are designed to produce a specified throughput and spray angle at a spray pressure of 40 psi or 3 bar. However, also available are low pressure (LP) flat fan nozzles, which give the same flow rates and spray angles but at 15 psi (1 bar). These tend to produce larger droplets and so are better for herbicide spraying to minimise drift.
Hollow Cone Nozzles are typically made from two components
Higher volumes of spray liquid can be atomised into smaller drops - very appropriate for many insecticides and fungicides
Notes to slide:
Cone nozzles are typically made up of two components:
- nozzle tip or orifice disc
- core or swirl plate.
The core has one or more angled holes or slots around it. The angle of these holes causes the liquid to move around the space between the core and the nozzle tip (the swirl chambers) in a swirling or circular motion. This results in a hollow cone-shaped spray pattern.
A wide range of flow rates, spray angles and droplet sizes can be obtained by various combinations of orifice size, number and size of slots or holes in the core, size of swirl chamber and liquid pressure. In general, higher pressures, smaller core slots and larger nozzle tip orifice sizes lead to wider spray angles. A narrow cone and larger droplet sizes are produced by increasing the depth of the swirl chamber, which can be achieved by inserting a washer between the core and orifice disc.
Nozzles consisting of separate components are found commonly - more recent constructions incorporate them into one unit. This nozzles are often colour-coded giving clear information concerning the flow-rate / pressure relation.
Hollow cone nozzles are best suited to spraying crop foliage, because droplets approach the leaves from more directions than in the single plane produced by the flat fan, giving good coverage over the many different target surfaces in a crop. This means they are most commonly used for insecticide and fungicide spraying in crops.
Solid Cone Nozzles: not commonly used on knapsack sprayers
Notes to slide:
If the core or swirl plate also has a central hole in addition to the angled slots, the centre of the cone will be filled with droplets, and therefore this type of nozzle is referred to as a solid cone nozzle. It typically produces smaller spray angles and larger droplets and so is used for spot treatments of herbicides or situations where greater downward penetration of spray is required but tends to be used mainly for tractor boom spraying.
Another type of cone nozzle is occasionally encountered - known as the variable-cone nozzle. With this nozzle, turning the nozzle body adjusts the depth of the swirl chamber and alters the spray angle and droplet size from a narrow jet with large droplets to a wide cone with smaller droplets. This is the nozzle type frequently encountered on sprayers designed for the amateur gardener, but is not recommended for most serious spraying as intermediate nozzle positions are not easily repeated consistently.
Deflector Nozzles: most commonly used on knapsack sprayers especially for herbicides
Note that pressurised spray liquid strikes an angled surface in the nozzle to form the spray sheet that produces the drops and the pattern. Used to apply wider swaths and can be used at low nozzle heights such as under tree/bush canopies.
Notes to slide:
Deflector nozzles are also known as impact, flooding or anvil nozzles. They produce droplets by the impaction of a straight jet of water onto a deflector surface, which produces a wide-angled flat spray pattern. Larger droplets land at the outer edges of the fan, so the pattern is somewhat uneven.
Deflector nozzles used at low pressure are ideally suited for herbicide applications. They are, however, available in a range of flow rates, often colour coded, and the smallest orifice sizes giving flow rates less than 0.6 litres/minute at 15 psi (1 bar) should be avoided since they will produce smaller droplets liable to drift and so are better suited to insecticide or fungicide spraying.
The deflector nozzle sizes which give flow rates in excess of 1.6 litres/minute at a pressure of 15 psi (1 bar) are less suitable for use in knapsack sprayers, since it becomes difficult to maintain an adequate pressure with the higher flow rate nozzles.
Nozzles: Low drift types not yet in much knapsack use but .... could be in the future
Low drift nozzles produce larger droplets and cause less drift
These low drift nozzles are often not available in areas where knapsack sprayers are used, this might change in the future offering a range of different nozzles that would work well with knapsacks.
Drift reducing nozzles: cross sectional drawings
Notes to slide:
- Drift-reducing nozzles generate larger droplets than nozzles of comparable size.
- Generally drift control nozzles fall into three main types:
- Examples from Spraying Systems (ss), Lechler (le), Lurmark (lu) and Hardi (ha) to be used instead of standard nozzle types of the same spray pattern.
- Orifice-design specially made to reduce the portion of drift-prone droplets; Flat fan nozzles: XR (ss), LU (le), VP (lu)
- Pre-orifice types; Flat fan nozzles: DG (ss), AD (le), Lo-drift (lu), LD (ha)
- Air inclusion or venturi types;
Flat fan nozzles: AI (ss), ID and IDK (ss), Drift-BETA (lu), Injet (ha)
Flat fan ‚off-centre‘ nozzles: AIUB (ss), IS (le),
Hollow cone nozzles: ITR (le)
- Further nozzles designed to reduce drift are:
- TF (ss) replaces a conventional deflector nozzle but has a pre-orifice and a turbulence chamber at the exit point to increase droplet size and to give a better spray pattern.
- TT (ss) is like a hybrid between an flat fan and an deflector nozzle and can be used to replace a flat fan nozzle but at a wider range of pressures than the pre-orifice nozzles for examples.
Air inclusion nozzle: detailed cross sectional drawing
These designs have become extensively used on boom sprayers in many countries – especially those where legislation demands that products must not drift onto surface water.
Notes to slide:
There are now a wide range of air inclusion types available which is a more radical change as the resulting large droplets contain small air bubbles which make them less prone to drift than the pre-orifice types but also gives better coverage than similar large droplets as they shatter on impact.
But while e.g. the pre-orifice types are designed to be used at conventional flow rates and pressures, some of the air inclusion/venturi types require higher operational pressures to operate and it is important to check that the sprayer can cope with these higher pressures (typically 60-75 psi). However the higher pressure nozzles do reduce drift to a greater degree than the lower pressure ones. Also the larger droplets of the air inclusion types may be inappropriate for situations where good coverage is needed.
Nozzle selection: adjustable hollow cones
Many knapsacks are supplied with adjustable hollow cone nozzles.
This type of nozzle is not recommended as they are impossible to accurately calibrate, a calibration would be required before each use to ensure the nozzle setting have not been changed. The nozzle setting can change during an application.
These adjustable hollow cone nozzles are often made of brass which is the softest of nozzle materials, meaning that they should be regularly replaced.
If your sprayer comes equipped with one of these nozzles you should change the nozzle.
Filters minimise the risk of partially or totally blocked nozzles and other malfunction of a knapsack sprayer.
Filters should be positioned at key sites; in tank openings, lance and before the nozzle itself.
Filters will protect your nozzles from dirt and grit and give the nozzles a longer life span.
Notes to slide:
A “tuned” cascade of filters helps best.
The basket filter should not be wider than 0.5 mm
The lance filter should not be wider than 0.3 mm
The nozzle filter depends on the size and type of nozzle mounted:
Flat fan nozzles:
sizes …01 to …015 - use mesh filter of size 100 mesh (0.14 mm)
sizes …02 to …08 - use mesh filter of size 50 mesh (0.28 mm)
sizes …09 and bigger - no filter
Hollow cone nozzles - use slotted strainer
Important: The last filter before the nozzle must be somewhat smaller than the orifice. It should be possible to handle filters with gloved hands.
On certain types of sprayer, output pressure can be adjusted to meet the needs of different nozzle designs and sizes.
- Nozzles are designed to work within specific pressure ranges. Ensure that the nozzles chosen are appropriate for the sprayer output pressure. Refer to the manufacturers guidelines.
- If you can change sprayer pressure then the sprayer should be equipped with a pressure gauge to enable reliable calibration. Or fit a constant flow valve.
Note: Increasing or decreasing sprayer pressure will have an effect on sprayer output and also the size of droplets leaving the nozzle.
- The higher the pressure - the smaller the droplets.
Pressure may vary when using a standard lever knapsack
Sprayer output may vary as you pump, reducing the ability to apply an even application rate.
Notes to slide: Pump strokes, intensity and frequency result in fluctuating pressure, flow-rate and less uniform spray pattern.
Nozzle selection and use of constant flow valves
Sprayer pressure can be stabilised and controlled using constant flow
CF valves are available to operate at 1, 1.5, 2 and 3 bar pressures.
- Uniform application
- Less pumping effort whilst spraying
- Can save product
- Increases reliability of product performance
- Reduces spray drift
Constant Flow Valve placement
Located between the pump [or pressurised tank of spray solution] and nozzle.
For the most accurate pressure fit CF valve close to the nozzle.
Caution when removing the trigger assembly as the CF valve will retain pressure in the spray lance.
Notes to slide:
Pressure regulating valves allow spraying at constant flow and serve as well as anti-drip devices.
CFValves from G.A.T.E. (USA)
Material: Delrin (Plastic), weight: 19 grams, ISO 9002 certified
Available in four sizes:
1.0 bar (14.5 psi)
1.5 bar (21.0 psi)
2.0 bar (29.0 psi)
3.0 bar (43.5 psi)
Assembly: Spray lance - Nozzle body – Filter – CFValve – Nozzle
Result: More uniform spray pattern, reduce of waste, reduce of drift potential
Spray drift risks influenced by many factors
Spray drift should be minimized for your safety, the safety of those near you and to lessen damage to adjacent crops, water, the environment.
Many factors influence the risk of spray drift:
- Nozzle: type, size, pressure and drop size [spray quality] produced
- Application Equipment: sprayer pressure, type of sprayer
- Application Skills: calibration, settings, operator accuracy, nozzle height above target
- Meteorological Conditions: wind, temperature, relative humidity
- Structure of the target: distance, especially height, to project spray.
Nozzles are now available that will reduce drift risks by increasing droplet size at the same application volume.
Notes to slide:
Drift control nozzles are becoming increasingly important. They where developed in Europe and the USA based on environmental concerns. In countries where regulations governing spraying in relation to drift risk exist, they offer farmers a cheaper drift control option than low drift sprayers, and can allow spraying in higher wind conditions than might normally be possible, thereby increasing flexibility. Where there are guidelines covering the spraying of pesticides adjacent to water courses with minimum buffer zones required, low drift nozzles allow the user to spray closer to the water bodies than is otherwise permitted, and there is an officially approved star rating system for different manufacturer’s low drift nozzles – the higher the number of stars, the greater is the flexibility to reduce the buffer zone.
Nozzle selection and spray quality
DO NOT clean a nozzle with an abrasive implement
DO NOT clean a nozzle by blowing through it with your mouth
DO NOT use damaged or worn nozzles
DO NOT use fine spray drop sizes on a windy day
- Wear gloves when handling nozzles
- Clean a nozzle with water and a light brush
- Protect nozzles from blockages with use of recomended filters
- Frequently clean nozzles
- Calibrate nozzles and sprayer every season
- Replace the nozzle if damaged
- Follow any product label recommendations
- Change nozzles as necessary depending on the crop, growth stage and product mode of action
- What are the best type of nozzle for applying
- a) herbicides
- b) insecticides and fungicides?
- What are the benefits of using constant flow valves?
- How should you clean a blocked nozzle?
- What is the purpose of the nozzle?
- How can you protect a nozzle from blockage?
- What type of nozzle should not be used and why?
- How frequently do you change nozzles?
- Are different nozzles readily available in your region?
- Have a range of different nozzles available to hand around
- Use water sensitive paper to demonstrate different nozzle spray paterns, this can be done by connecting a nozzle to a small “killer spray“ type bottle fitted with a CF valve.
Constant flow valves