Airblast sprayer

Technical presentation

A tractor-mounted sprayer uses the lift of an air stream to spray the spray liquid in fine drops onto the vegetation.

The droplet is transported by a large air current created by a fan, traditionally helical (on most machines). The volumes of air moved vary from 20,000 to 80,000 m3/hour and air speeds from 50 to 200 km/h.
These machines are designed to treat large volumes of foliage. The large volume of air generated ensures thorough mixing of the foliage and good penetration of the product inside, as well as good coverage of the vegetation.

Pulvérisateur jet porté face par face - IFV Davy

Face-to-face airblast sprayer

The liquid circuit of an airblast sprayer is comparable in every way to that of a jet sprayer. However, the booms are located where the air blown by the fan exits to charge it with droplets.

Why air-blast?
Because the droplets produced by pressurising the liquid or centrifuging it are picked up as they leave the nozzle by a large volume of air, which carries them towards the target and penetrates the vegetation. A fan can also be used to agitate the vegetation, helping to improve penetration.

Descente de pulvérisateur à jet porté - Belly

Descent - Belly

PreciJet - Tecnoma

The different types of mounted sprayer

Airblast sprayer with axial-flow fan

Airblast sprayer with axial flow fan

These are called axial flow fans because the air passes through the turbine parallel to the turbine's axis of rotation.

These devices are often mistakenly referred to as aeroconvection devices. This term refers to a particular type of air-blast device consisting of a high turbine combined with deflectors that direct the air towards the ground, which acts as a reflector, so that the air loaded with droplets is treated from the bottom upwards, hence the term convection associated with aeroconvection.

Airblast sprayer with tangential flow fan

Pulvérisateur jet porté à flux tangentiel

Airblast sprayer with tangential flow fan

These sprayers use fans consisting of a cylinder with a large number of small fins on its periphery (with the profile of an aircraft wing).

The special feature of this system is that it generates a very homogenous volume of air over the entire height of the vegetation to be treated, into which the droplets produced by the nozzles are integrated.

Airblast sprayers with centrifugal nozzles

Characterised by the production of highly homogenous droplets, this type of spraying uses centrifugal force to break up the stream of liquid into droplets. The droplet is formed by the rotation of a small-diameter disc, or bowl, with a crenellated periphery. On some machines, the element that forms the droplet can have other shapes, such as a screened cylinder (often used for aerial spraying).
Nozzles are usually driven by a hydraulic motor, which also drives the fan to transport the drops. Sometimes, electrical energy (or more rarely pneumatic energy) can replace hydraulic energy.

In centrifugal spraying, the finer the drop, the better:

The flow rate of the equipment is low
The speed of rotation of the nozzle is high
The diameter of the element that forms the drop is large.

The VMD (Mean Volumetric Diameter) is often between 100 and 200 microns.
The CH (Coefficient of Homogeneity) is generally between 1.2 and 1.6.

Airblast sprayers based on pneumatic equipment

These sprayers are very similar in configuration to pneumatic sprayers, using a centrifugal fan. The difference lies in the diffuser, where the droplets are produced by a turbulence or slot nozzle.
Although they are very similar to pneumatic sprayers, they are air-jet sprayers, since the droplets are formed by pressurising the liquid and transporting it by air. It should be noted that the conversion of some pneumatic equipment to air-assisted spraying is not without its problems (lack of pump pressure, high and unnecessary pressure losses in the nozzles).

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