28
Notes on Use of Mistblowers
Comparison of principles of backack mistblowers and
backpack high-pressure sprayers
The methods of operation of low-volume mistblowers and
high-pressure sprayers are fundamentally different.
In the case of the
high-pressure sprayer
the carrier liquid
in the solution serves as the transport medium for the
active ingredient. The solution is applied at a comparative-
ly high pressure produced by a high-pressure pump and a
small-bore nozzle. The size of the droplets formed in this
process is generally in the order of 300 to 400 um. Owing
to the resultant small number of droplets, which have to
wet the same crop area as in low-volume mistblowing, the
active ingredients can only be applied in highly diluted
form with a lot of carrier liquid.
The only way to produce smaller droplets is to consider-
ably increase pump pressure and use much higher driving
power - both these factors increase the complexity of the
unit. The energy required to accelerate water is relatively
high. For this reason the efficiency of high-pressure spray
ers is generally low. The units themselves are quite heavy
and have a short range of only 30 to 50 cm (measured
from the nozzle).
In the
mistblower,
air is used as an additional transport
medium for the active ingredient. An engine-powered fan
produces a powerful, concentrated airstream to which the
solution (active ingredient in carrier liquid) is added via a
metering system. The solution is atomized into very fine
droplets and discharged at high velocity by the airstream.
Depending on the design of the atomizer, it is possible to
produce droplets with a size of approx. 50 to 250 pm. The
large number of fine droplets and the airstream's excellent
penetration of the crop ensure high efficiency. This means
that the quantity of carrier liquid (normally water) can be
reduced, i. e. a higher concentration of active ingredient
can be used in the solution.
Considerably less energy is required to accelerate air.
Therefore, low-volume mistblowers, are more efficient
(long range with relatively low driving power and low
weight) and can cover a larger area per unit time.
Advantages of low-volume mistblowers over high-pressure
sprayers:
•
High efficiency as a result of large area coverage per unit
time.
•
Less physical effort - high-performance mistblowers are
relatively compact and lightweight.
•
High wetting capacity as a result of high kinetic energy of
droplets.
•
Very fine and uniform distribution of active ingredient for
better biological effectiveness.
•
Active ingredient is saved by reducing losses due to
solution dripping from crop.
•
Better adhesive properties and resistance to rain.
•
No growth inhibition caused by clogging the foliage.
