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Portable spraying equipment

Visit our new site Pesticidewise.com for more help on choosing a knapsack sprayer, the different types of knapsack sprayer and how they work.


A wide range of portable sprayers to meet many contrasting needs

Portable sprayers may be:

  • carried on the back and pumped manually; or have a
  • motor that pressurises the spray liquid and may also force air to carry the spray. Others use
  • rotary atomisers to form spray drops to typically apply very low volumes; Portable sprayers also include those that are moved
  • on wheels as in wheel barrow sprayers whose pumps supply spray solution to single or multiple hoses having on/off valves.

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Notes to slide: There are many different types of portable application equipment. The range reaches from very small, single hand operated sprayers ones to wheeled units equipped with a tank too large to be carried by a person.  Different types of portable application equipment are:

  •  piston or diaphragm pump [Lower left]; others use
  •  compressed air to pressurise the spray liquid [Lower centre]; or
  • a motor that pressurises the spray liquid and may also force
    air to carry the sprayed drops [Lower right]. Others use
  • rotary atomisers to form spray drops to typically apply very
    low volumes [Top right] ; Portable sprayers also include those that are
  • on wheels as in wheel barrow sprayers whose pumps supply spray
    solution to nozzles through single or multiple hoses having on/off valves [Top left]

No application equipment is able to be used universally suiting every & all application purpose. Therefore, different systems are produced. Carefully choosing the type of sprayer matching the intended use and goal is essential for the successful use of crop protection products. 

Examples of types of portable spraying equipment used

 Hand-sprayer/Dusters (top right); typical use

  • Spot treatment,
  • Individual plants,
  • Stores.

 CDA-Sprayers [rotary atomisers] (not shown); typical use

  • Areas with limited available water.

Lever-operated and motorised Knapsack sprayer  (lower left); typical use

  • Small fields;
  • Individual plants;
  • Areas accessible by foot only;
  • Inter-row teratments.

Compression type (lower centre): typical use

  • Very small areas;
  • Individual plants;
  • Areas accessible by foot only and conditions where lever-operated is not practical;
  • Public health operations;
  • Stores

Motorized Mistblower (lower right); typical use

  • Tree & Bush crops;
  • Spray-target can not be reached without air-stream;
  • Multi-row spraying;
  • Dusting

Operator controlled wheeled sprayer with lance (top left); typical use

  • Midsize area especially those intensively cropped:
  • Fields, tree and bush crops, vegetables, flowers, greenhouse

Fogger (thermal or cold) (not shown); typical use

  • Treatment of store/warehouses;
  • Public health operations (Vector control);
  • Flying insects

General Considerations

  1. Select the best, most appropriate equipment for the job.
  2. Always repair leaks prior to application.
  3. Practice good hygiene when using spraying equipment.
  4. Lever operated knapsacks are the most commonly used sprayers for small areas and for inter-row applications.
  5. FAO specifications identify preferred design features of sprayers including knapsacks.
  6. Motor driven pressurised sprayers are more frequently used in tall crops and areas such as tea plantations where spray needs to be projected some distances.

Why and where hand held equipment is used

 Why?

  1. Cost of larger equipment restricting purchase
  2. Convenience and simplicity of use
  3. Size of farm not demanding larger sprayer

Where?

  1. Small fields
  2. Inter-row or spot treatments
  3. Areas where it is hard to access with larger machinery
  4. Localised weed control around the farm

FAO specifications help ensure better sprayers and use

There are FAO guidelines that cover the specifications of hand held spraying equipment. The following slides contain some of the key recommendations but for the complete list of recommendations please use the  FAO site.

FAO sprayer guidelines: the tank and lance

Tank

  • Durable and resistant to impacts and UV-ray exposure
  • Smooth surface not entrapping liquids
  • Without sharp corners that are difficult to rinse clean
  • At least 5 litres capacity for knapsack sprayers
  • Graduation scale showing volume of spray solution contained
  • Withstand a drop of 1 meter without leaking

Lance

  • At least 50 cm long, from nozzle to trigger
  • Allowing free movement, adequate hose length
  • Positive on/off valve (trigger), lockable OFF-position

FAO sprayer guidelines: hoses and straps

Hoses

  • Non-flattening when bent unsupported through 180° radius of 5 cm
  • Connections able to be adjusted with gloved hands, eg wing nuts
  • Connections must not leak after being re-used

Straps

  • Non-absorbent material
  • At least 5 cm wide
  • Quick release catches (easily operable when sprayer is full)
  • Resistant to UV-light and approved chemicals
  • Waist strap

FAO sprayer guidelines: tank lid, weight, parts and manual

Tank lid

  • Large opening (to allow a fill rate of 1.6 litre / minute)
  • Strainer placed deep in the tank opening
  • Must seal well (Lever and Motor knapsacks: ventilated with valve)
  • Convex shape to ensure no liquid build up on lid
  • Tank lid and strainer operable with gloved hands

Weight

  • Sprayer weight must not exceed 25 kg when fully loaded

Spare parts

  • Supply and make available a spares kit of components most likely to wear out first. Spare parts sheets available and easily identified.

Instruction manual

  • All sprayers must be supplied with an adequate instruction manual

Sprayer maintenance

Maintain your spraying equipment to a high standard (its rated specifications) following recommendations in the sprayer manual.

  • Always wash all equipment after use.
  • Repair any leaks immediately.
  • Replace worn parts.
  • Keep spraying equipment safe, away from children, food stuff and animals.
  • Regularly calibrate sprayer output and keep all spraying records.

Notes to slide: The basic features of lever operated knapsack sprayers are a spray tank of 10-25 litre capacity usually with a basket filter and wide neck for easy filling and cleaning, a lever-operated pump and pressure chamber, and a hose and lance with a trigger-operated valve.

Lever Operated Knapsack Sprayer

The world’s most used type of sprayer.

  • Often locally manufactured.
  • New International Standards now specify their requirements and state performance limits with which they must comply.
  • Leakage, endurance, stability and much more included for the safety of both the operator and the environment.

Check their compliance with this scheme before purchase.

Notes to slide: As a type of application equipment, the lever operated knapsack-sprayer represents a standard used by millions of farmers all over the world (for example the Philippines have a demand for 100’000 units per year).
Typical use: Field, bush and tree crops
Product categories for lever-operated knapsack sprayers include herbicides, fungicides and insecticides.

Areas of use: Small areas of field and bush-type crops
 
Products applied: Herbicides, Fungicides and Insecticides

Water spray volume rates used:  

  • Field crops 100 – 500 l/ha  
  • Bush  crops e.g. vines: 600 – 1600 l/ha

Advantages

Disadvantages

+  Optimised tank capacity

-   Constant pumping needed during application

+  Simple to use and maintain  

-   Big influence of operators skills on results

 See also Efficient knapsack use training module.

Notes to slide: The work capacity reached depends on factors like crop, topography, spray volume etc. Factors not to underestimate include weather conditions (e.g. temperature), how comfortable a sprayer is to carry and of course the human factor including physical strength as well as skills and training.

Many designs are available and made in many contrasting materials.

Types may vary by:

  • Metal or rigid plastic tank
  • Under-arm levered pump operation
  • Over-arm levered pump operation
  • Externally mounted pump
  • Internally mounted pump
  • Type of pump using piston or diaphragm mechanisms
  • Location of pressure chamber

Note: some features will be combined

Notes to slide:

There are, however, many variations on these basic features, for example the lever might be underarm or over arm action. The pumps are of two basic designs, the diaphragm pump and the piston pump, and it is important to distinguish between the two, since each type is more suited to certain uses.

Mechanical agitation of the spray liquid in the tank is available with some models equipped with piston pump. When using diaphragm pump type sprayers, or any sprayer without agitation device, it is important to remember that there is no means of mixing the spray liquid in the tank during spraying. Therefore when using formulations that might be prone to settling in the tank, such as wettable powders, it is advisable to stop spraying at intervals and stir the contents with a clean stick.

Info: How the two types of pumps affect their field of use :
Diaphragm pump type lever-operated knapsack sprayers: These are good, durable sprayers ideally suited for herbicide application. If a range of spray operations is envisaged, then a diaphragm-type sprayer can be used either for herbicides or insecticides/fungicides, particularly if fitted with a variable pressure control valve. However, if high flow rates are required, for example when fitting a multi-nozzle boom to the sprayer, the pressure output may be insufficient without excessive pumping speeds which are difficult to maintain over long periods.

Piston pump type lever-operated knapsack sprayers: The higher pressure capabilities of this type of sprayer make it most suitable for insecticide and fungicide applications, or situations where a high spray liquid throughput is required. These sprayers rely for their efficiency on the seal between the piston and the cylinder, and this is subject to a high degree of wear, thus making this type of sprayer less durable than the diaphragm pump type over long periods of use, and requiring higher levels of maintenance.

Lever operated knapsack sprayer: cross sectional drawings showing operation of diaphragm pump

Lever operated knapsack sprayer: corss sectional drawings showing operation of diaphragm pump (32 KB JPEG)
Lever operated knapsack sprayer: corss sectional drawings showing operation of diaphragm pump (32 KB JPEG)

Notes to slide:

Working principle of a sprayer with diaphragm pump:
Diaphragm pumps consist of a flexible diaphragm made of synthetic rubber connected to the pump handle by a crankshaft mechanism, a rigid diaphragm chamber and either flat or ball-type inlet and outlet valves. The outlet valve is connected to a pressure chamber, which in many diaphragm pump sprayers has a variable pressure setting valve. These pumps typically operate between pressures of 1 and 3 bar (15-44 psi) and are, therefore, particularly suitable for herbicide application where large droplets are required to minimise spray-drift.
The operation of the sprayer is as follows:

  1. As the pump lever moves upwards the diaphragm is pulled downwards, thereby increasing the volume of the diaphragm chamber and reducing the internal pressure. 
  2. This low pressure causes liquid to flow from the tank to the diaphragm chamber through the inlet valve.
  3. On the downstroke of the pump lever, the diaphragm moves upwards compressing the liquid in the diaphragm chamber causing the inlet valve to close and the outlet valve to open.
  4. Liquid is forced into the pressure chamber, compressing the air present in the chamber.
  5. This cycle is repeated with the lance trigger valve closed until sufficient pressure is generated in the pressure chamber. In sprayers with a pressure relief valve set to a given pressure, this is achieved when the pressure relief valve opens circulating excess liquid back to the tank.
  6. The trigger valve is then opened and the air pressure in the pressure chamber causes the liquid to flow to the nozzle. 
  7. The operating pressure in the pressure chamber is maintained by regular lever strokes of about 30 per minute or approximately one every two paces.

Lever operated knapsack sprayer: cross sectional drawings showing operation of an over-arm lever sprayer with piston pump

Lever operated knapsack sprayer: cross sectional drawing showing operation of an over-arm lever sprayer with piston pump. (27 KB JPEG)
Lever operated knapsack sprayer: cross sectional drawing showing operation of an over-arm lever sprayer with piston pump.

Working principle of a sprayer with piston pump:
A piston or plunger-type pump consists of a piston attached to the pump lever allowing reciprocation, a piston cylinder, either ball or flat inlet and outlet valves and a pressure chamber. There is a seal between the piston and the cylinder wall. In many types the pressure chamber is integral with the piston - i.e. the whole pressure chamber moves up and down with its lower end acting as the piston.
It is a much more efficient pump than the diaphragm pump and can generate pressures up to 5 bar (70 psi). This makes this type of sprayer more suitable for applying insecticides and fungicides where smaller droplets are required; less pumping effort is required to maintain a pressure of say 3 bar, compared with the diaphragm type. The principles of the pump operation are similar to diaphragm pumps, as follows:

  1. On the upward stroke the piston moves upward, lowering the pressure in the cylinder and drawing liquid from the tank to the cylinder through the inlet valve .
  2.  As the piston moves downward, the inlet valve is closed by the pressure increase in the cylinder, the outlet valve opens and liquid is forced through it into the pressure chamber. The increase in air pressure in the pressure chamber means that the spray liquid will be forced out of the nozzle once the trigger valve is opened.

The precise design of piston pump sprayers varies considerably, e.g. some have externally mounted pumps. The pump cylinder may sometimes be fitted with a pressure relief valve to prevent over-pressurisation but this usually does not have the variable setting capability of those often found on diaphragm pump pressure chambers, although in some types the spring can be replaced with others of various tensions to give some pressure variability.

Some piston pump sprayers have a mechanical agitator in the spray tank, in the form of a paddle attached to the piston.

Lever operated knapsack sprayer: cross sectional drawings showing operation of internally mounted piston pump

Lever operated knapsack sprayer: cross sectional drawinds showing operation of internally mounted piston pump. (28 KB JPEG)
Lever operated knapsack sprayer: cross sectional drawinds showing operation of internally mounted piston pump.

Lever operated knapsack sprayer: cross sectional drawings showing operation of externally mounted piston pump

Lever operated knapsack sprayer: cross sectional drawings showing operation of externally mounted piston pump (41 KB JPEG)
Lever operated knapsack sprayer: cross sectional drawings showing operation of externally mounted piston pump
Cutaway of externally mounted piston pump (19 KB JPEG)
Cutaway of externally mounted piston pump

Lever operated knapsack sprayer: cross sectional drawings showing operation of externally mounted piston pump with pressure chamber above

 

Lever operated knapsack sprayer: cross sectional drawings showing operation of externally mounted piston pump with pressure chamber above (27KB JPEG)
Lever operated knapsack sprayer: cross sectional drawings showing operation of externally mounted piston pump with pressure chamber above
Cutaway of externally mounted piston pump with pressure chamber above (18 KB JPEG)
Cutaway of externally mounted piston pump with pressure chamber above

Lever operated knapsack sprayer: cross sectional drawings of Chinese made sprayer showing operation of externally mounted piston pump with pressure chamber above

Lever operated knapsack sprayer: cross sectional drawings of Chinese made sprayer showing operation of externally mounted piston pump with pressure chamber above (30 KB JPEG)
Lever operated knapsack sprayer: cross sectional drawings of Chinese made sprayer showing operation of externally mounted piston pump with pressure chamber above

Pressure control flow vlaves

Spraying pressure will vary between pump actions. These pressure changes will influence the applied volume, dose and nozzle swath width so pressure changes must be avoided.
Note: A pressure change from  5 bar to 2 bar will reduce nozzle output by 58 %.

Sprayer pressure variation may be overcome with use of a pressure control valve fitted behind the sprayer nozzle.

Pressure control valves are available to control pressure at 1, 1.5, 2 and 3 bar.

 


Portable spraying equipment slides 1 - 21 | slides 22 to end | Flash movie


 
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