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Sprayer applicator components

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A range of equipment is used to apply pesticides.  The way in which the equipment is setup and operated determines spray efficiency in terms of pest control and the effect of the application on the environment. The most commonly used method of applying pesticides is in the form of droplets.  

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While sprayers are available in many different configurations they all have the same basic components. These components are a:

  • tank to hold the chemical
  • pump to create pressure
  • control valve to control pressure
  • droplet generator to control the application rate and produce the correct size droplets
  • filtration system to reduce blockages
Tanks

Tanks should be constructed of materials that are:

  • non-corrosive
  • resistant to farm chemicals
  • resistant to sunlight
  • robust and easily repaired

In addition, tanks should have a wide, easy access lid and drain valve.

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Pump

While some controlled droplet applicators use gravity to create the liquid flow a pump is the most widely used method.  A range of different pumps is available depending on the role.

Characteristic Diaphragm  Piston Centrifugal Roller Vane

Pressure (Bar )

40

50

5

20

Maximum Flowrate (L/min )   

360

80

500

125

Relative Durability

High

Low

High

Low

Relative Cost

High

High

Medium

Low

Displacement where used  

Positive

Positive

Not Positive

Semi Positive

Formulation Types

All

Not Wettable Powers

All

Not Wettable Powders

Figure1.  Characteristics of Pumps Suitable for Spraying Systems.
Control Valves

The most important control for any sprayer is a means to turn the sprayer off.  This might be a trigger valve on a knapsack sprayer or an electrically controlled solenoid valve on a boom sprayer.  Other controls normally found are flow controls such as metering orifices found on some controlled droplet application (CDA) sprayers or bypass pressure regulation systems found on boom sprayers and knapsack sprayers.

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For larger sprayers, a pressure gauge and an agitation system is normally incorporated into the control system.  Bypass from the pressure control often provides agitation in the tank.  Pressure regulation for knapsack sprayers is usually done with a spring-loaded valve inside the knapsack tank or with a spray management valve or constant flow valve on the lance.

A pressure gauge or pressure control is required to ensure the equipment is operating correctly.

Filtration system

Most sprayers have a filtration system consisting of a tank filler screen, an in-line filter and a nozzle filter.  Larger sprayers also have a suction filter.  

The nozzle to be used determines the filtration requirements. The smaller the nozzle, the smaller the filter-mesh that is required. The finest filter should not be at the nozzle.

Droplet generation

There are four different types of droplet generation and fluid distribution systems commonly used on sprayers.  These are:

  • Conventional hydraulic
  • CDA boom
  • Air shear boom
  • Air assist which is a combination of air shear and hydraulic
Conventional hydraulic nozzles

Hydraulic pressure is the most common method of applying pesticides.  This system is used on a range of equipment due to its simplicity and flexibility. To produce droplets, liquid is forced under pressure through a small hole, or orifice.  A thin sheet is formed which becomes unstable and disintegrates into spray droplets.  A range of droplet size is produced due to the uncontrolled nature of the disintegration.

The size of droplets produced depends on the pressure, orifice size and orifice design.  Flow rate depends on orifice size and pressure. In general droplet size decreases when:

  • orifice size decreases
  • pressure increases
  • fan angle increases

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The advantages of hydraulic nozzles are that the:
  • components are relatively simple
  • equipment can be tailored to individual situation, i.e. different  row width
  • simple change in operating parameters i.e. nozzle type or pressure can change the set-up for different situations
  • range of droplet sizes gives a "shotgun" approach for different targets and target complexities encountered in most spray situations.
The disadvantages of hydraulic nozzles are that:
  • Some nozzles will wear rapidly, so require regular replacement.
  • The wide spectrum of droplet sizes may result in droplet wastage due to drift of small droplets and run-off of large droplets.
Controlled droplet application (CDA)

Most commercial CDA sprayers use centrifugal energy to produce the droplets.  Liquid is fed to a spinning disc, cage or drum and the centrifugal energy spreads the liquid to the edge where it breaks into ligaments and then droplets.  The system is capable of producing a narrow range of droplet sizes when the flow rate and rotation speed are matched.  If the flow rate is too high for the rotation speed, a wide range of droplet sizes is produced.

Advantages:

  • application volumes can be decreased due to the narrow droplet spectrum
  • increased number of droplets of optimum size.
  • Disadvantages:

  • increased expertise required to set up and operate
  • mechanical failure due to the more complex system  ie due to the hydraulic or electric motors, discs or cages.
  • To decrease the droplet size, the flow rate is decreased or rotation speed increased.

    Air shear

    With air shear, high velocity (>300 kph) air breaks up a stream of liquid into small droplets.  Air shear machines are also called misters.

    Small droplets are produced and the air stream is then used to direct the movement of these droplets.  Misters are used to apply insecticides and fungicides.  Their use to apply herbicides is not recommended.

    With the high air velocity care must be taken when setting up and operating the equipment.  Bounce of the air stream and plant damage can be a problem when plants are small.  For backpack misters, deflectors and diffusers are used to manage the air stream. On boom units, height and spray angle are the only adjustments. Air speed should not be used as an adjustment. To decrease droplet size, the flow rate should be decreased or airspeed increased.

    Air shear and CDA sprayers can apply ultra low volume products

    Air assisted sprayers

    Air assisted sprayers use droplets produced using either hydraulic nozzles or CDA equipment together with an air stream to manage the movement of those droplets.  Air velocity is much lower than in air shear systems (100-170 kph).

    The concept is to replace the air volume in the plant with droplet laden air from the sprayer.  Traditionally, large volumes of slow moving air have been used.  Some of the newer sprayers have been using lower volumes moving faster but with turbulent flow.  Turbulence increases penetration of the canopy and improves coverage underneath the leaf. Air assistance has the potential to reduce drift, increase the canopy penetration and increase the deposit underneath leaf surfaces