Innovazionenelle irroratrici abarra
L’evoluzione di questemacchine riguarda soprattutto la componenti-
stica,mentreè rimastasostanzialmente immutata lastrutturadi ba-
se: un telaio,unserbatoio,uncircuito idraulicoper lacircolazionedel-
lamiscela fitoiatricadal serbatoioal sistemadi distribuzionecostitui-
todagli ugelli collocati suunabarraorizzontale.
Oggi l’aspettodell’uniformitàdi distribuzione,garantitadall’ausiliodei
computer di bordoedei sistemi di assistenzasatellitareallaguida,è
addirittura passato in secondo piano rispetto all’attenzione verso la
sicurezzadell’ambienteedell’uomo. Caratteristichequali il dosaggio
automaticodellamiscela, il lavaggiodell’impianto idraulicoedellema-
ni dell’operatore, la possibilità di riempire il serbatoio senza che l’o-
peratore venga a contatto con il prodotto sono caratteristiche larga-
mentediffuse tra le irroratrici nuove immessesulmercato.
L’elemento caratterizzante delle irroratrici per le colture erbacee è la
barra, lacui larghezzadi lavoropuòarrivarea48metri,manel nostro
Paese in genere ci si orienta sumodelli larghi al massimo24metri.
Essa è caratterizzata da leggerezza e nel contempo rigidità in posi-
zione di lavoro, nonché dalla stabilità longitudinale e trasversale ne-
cessaria per garantire l’uniformità, contrastando le oscillazioni oriz-
zontali e verticali che inevitabilmente vengono trasmesse alla strut-
tura durante il lavoro, determinando irregolarità di distribuzione e fe-
nomeni di deriva. Di importanza fondamentale sono ovviamente gli
ugelli, oggi quasi sempre di tipo antideriva ad inclusione d’aria, che
garantisconounapolverizzazionepressochéesenteda gocce fini. La
formadel gettoa ventaglio consentediminimizzare l’effettodelle va-
riazioni di altezzadovutealle inevitabili oscillazioni,soprattuttonel ca-
so di barremolto larghe,mantenendo quindi un diagramma di distri-
buzioneuniforme. Infine,nellebarredotatedimanicad’aria, l’azione
dellacorrentedeterminamaggiorecopertura,migliorepenetrazionee
la possibilità di trattare anche in presenza di vento di moderata in-
tensità, riducendo i fenomeni di deriva, soprattutto in abbinamento
con i sempre opportuni ugelli a inclusione d’aria. Va però sottolinea-
to che non sempre azionare il ventilatore è la sceltamigliore: infatti,
su terrenonudoe inassenzadi vento, la turbolenza creatadal getto
to make calibration as precise as possible in terms of the
crop to be sprayed and the spray mixture to be applied. A
choice has to bemade on some fundamental operating pa-
rameters suchas volumeper surfaceunit, typically litresper
hectare, and the right degreeof pulverisation toavoid, as far
as possible, the formation of an excessive share of fine
droplets (indicatively, diameter less than 100micron) since
they hang in the air and aremore easily blown beyond the
target areaby thewind. For air aidedandpneumaticmodels,
precise calibration is also needed on the quantity of air the
blower produces and the direction of the air flows.
Innovation in Spray Booms
The basic structure has changed little since spraying booms
were first introduced inFranceand theUS in the late1800s,
but various componentshavebeen improved, from the frame
and tank tohydrauliccircuits for the circulationof plant treat-
ment mixtures from the tank to the nozzles.
While achieving uniform distribution is still an aim aided by
on-board computers and GPS navigation systems, it is seen
as less important these days than safety for the operators
and theenvironment.Recent sprayermodels include features
suchas automatic dosagemeasurement,washing of thehy-
draulicsand theoperator’shandsof theoftenharmful spray,
andautomatic fillingof the spray tankwithout any human in-
tervention.
Sprayboomsare themain featureof sprayersused for herba-
ceous crops. Booms can stretch along a front aswide as 48
meters (about 158 feet), although in somewhere like Italy
where fields are smaller, themaximum is about 24meters.
A spray boom has to be both light and rigid when extended
in the working position. To ensure spraying uniformity and
drift control, there should also be stability along and across
the boom, damping out vibrations transmitted along the de-
vicewhen at work.
The shape of thenozzles is also crucial. They almost always
use a system called air inclusion to exclude as far as possi-
ble the creation of fine droplets. They will also create a fan-
shaped spray designed tominimise the effect of variations
inheight due to vibration,especiallywith very longbooms for
which vibration canmore easily translate into falling unifor-
mity.
Some booms have air sleeves,which ensure that the airflow
achieves greater cover, improved penetration, and a chance
to spray even when the wind is moderately strong. Sleeves
and air-inclusion nozzles together can help a lot with drift.
It shouldbe clear,however, that it isnot always thebest idea
touse the sprayer’s fan to createairflow through the sleeves.
Even if there is no wind, spraying fields without plant cover
canbeproblematic.A jet of air creates turbulence,which can
leave spray dropletshanging in theair for longer and lead to
an increase in drift. In this case, the best bet is air-inclusion
nozzles, which guarantee an excellent job in still conditions.
Another big disadvantage for air sleeve sprayers is the high
cost and weight, and the fan uses a lot of power meaning
that a powerful tractor is needed to power it, even for trac-
tor-mountedmodels.
SprayingTree Crops,Vines
Themain factor in successful spraying in orchards and vine-
yards is how the airmoves through the vegetation.Themost
recentmodels take this intoaccount by focussingon fan fea-
tures and how the air carrying the spray is distributed.
Theairflow’smagnitude canbeadjusted,andair jets can tar-
get theairflowaccording to theprofileof the vegetation.When
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