Note: Descriptions are shown in the official language in which they were submitted.
CA 02235946 1998-04-23
W O 97/16257 PCT/GB96/02664
AGRICULTURAL AND OTHER SPRAYING SYSTEMS
This invention relates to a method and apparatus
applicable to agricultural and horticultural and other
spraying systems. The invention is particularly
applicable to such spraying systems as disclosed in
our prior patents and patent applications relating to
boom-type sprayers having droplegs carrying spray
nozzles. However, the invention is more widely
applicable than to dropleg-type sprayers and is
applicable to conventional spray-from-above sprayers
likewise, and to lance and other hand-held sprayers
for certain applications. An additional application
of the invention is in harvesting machines such as
potato harvesters for spray-treatment of the harvested
crop and in related applications such as the spray-
treatment of potatoes coming into or coming out of
store. Additional applications are likely to arise in
which a facility to provide a low dosage rate of
treatment material in a spraying operation is
advantageous. Further applications include de-icing
treatment of aircraft with de-icing fluid and
industrial uses including industrial spray-treatment
processes. It is entirely possible that the invention
may be applicable to the spraying of liquids which
have a significantly higher viscosity than ~ater and
the like.
A problem which arises generally in relation to
sprayers concerns effective penetration of the crop or
other material to be sprayed, by the spray of droplets
produced by the sprayer. Conventionally, various
forms of spray nozzle are utilised in which a spray of
droplets is produced solely by virtue of the energy
derived from the supply of liquid under pressure.
However, such conventional arrangements do not
achieve the level of crop penetration which can be
CA 0223~946 1998-04-23
W O 97/16257 PCT/GB96/02664
desired.
Various attempts have been made to improve crop
penetration including the use of air flow producing
means in association with conventional spray nozzles.
However, such an arrangement has been found to be
bulky and relatively ineffective.
Attempts have also been made to utilise the
effect of electrostatic charges to cause the sprayed
droplets to be attracted to the crop material and
deposited thereon. These also have been found to be
relatively ineffective and have not been widely used.
The use of droplegs to permit crops to be sprayed
from a low location generally below the canopy of
leaves in the case of crops such as potatoes has been
found to improve very substantially the ability to
cover the under surfaces of plants, as compared with
conventional spraying arrangements in which the
droplets are discharged onto the canopy of leaves
from above.
A further prior proposal known to the Applicants
utilises an air supply in association with a liquid
supply. However, the liquid supply is directed via a
restrictor onto a baffle plate where primary
atomisation occurs before the liquid is mixed with the
compressed air. The compressed air then forces the
thus-produced droplets through a circular passage onto
an inner face of a flood jet. There, secondary
atomisation takes place, prior to the spray emerging
in a flat fan-shaped pattern. This dual stage
atomisation process leads, so it is claimed, to the
production of relatively large droplets in which air
bubbles are trapped and which, by virtue of their
size, are less subject to unwanted spray drift. It
has been established that the droplets size thus
produced is notably ineffective in effecting crop
coverage. In practice, what is particularly wanted is
CA 0223~946 1998-04-23
W o 97/16257 PCT/GB96/02664
the production of a droplet size similar to that which
is produced in atmospheric conditions such as a misty
morning in a damp climate overnight whereby the
droplets which condense on surfaces such as the
external surface of a standing car are of such a size
that they have little tendency to roll over the
surface, and they therefore stay where they are
deposited. In combination with this objective, there
is the corresponding need to be able to produce such
droplets travelling at a sufficiently high velocity in
order to penetrate the crop sufficiently.
Further prior proposals are disclosed in GB
952,457 and GB 1,378,190 and US 4,465,832 and US
4,179,068. These proposals involve systems for .the
admixture of liquid and air for liquid entrainment
and/or droplet formation. The most pertinent of these
with respect to the present invention is the latter US
'068 specification (assigned to NRDC) which discloses
a liquid spray device in which liquid enters a swirl
chamber in a generally radially inwardly-directed
manner for subsequent onward movement through the open
end of the swirl chamber under the action of a gas
flow delivered at that open end for subsequent
discharge from a spaced opening-see Fig 2. We have
established that a system in which both the airflow
and the liquid flow do not proceed via an air-and-
liquid supply chamber having a closed end wall or
target and one or more associated outlets in the
manner of the embodiments of the present invention,
cannot achieve the beneficial results of the present
invention and the system of this prior disclosure
operates in a significantly different manner involving
~ generally axial droplet flow (with respect to the
liquid supply direction), as compared with the
generally radially or outwardly directed flow of the
system of the present invention (or up to 45 degrees
CA 0223~946 1998-04-23
on each side thereof~. Moreover, the system of this
prior US '068 specification operates on the effective
principle of the maintenance of droplet size at
differing air supply pressures, whereas described
embodiments of the present invention operate in a
manner such that the droplet size changes with changes
in sys~em pressure.
There are disclosed in US patents 4,828,182 and
4,899,937 (assigned to Spraying Systems Co) spray
nozzle assemblies which have been marketed for use in
agricultural spraying situations. The US '182
specification discloses a spray nozzle assembly that
finds particular utility in humidification and
- evaporative cooling applications in which it is
desirable that a spray be discharged in a wide and
relatively flat spray pattern, which is there
contrasted with many prior air assisted nozzles which
discharge with a relatively tight round spray pattern.
The system disclosed facilitates pre-atomization
of liquids by means of an insert member which includes
an elongated impingement element having a transversely
extending circular hole which is struck by the
pressurised liquid, to break up same. A pressurised
stream of air is admitted to the device and a side
surface area defines an imp-ingement surface which
deflects and breaks up the airstream and considerable
turbulence for pre-atomizing the liquid stream is
created, and as a result of the airstream being
injected transversely into the longitudinally flowing
liquid stream, there is produced a liquid flow in the
downstream direction towards an outlet nozzle, in the
form of finely divided pre-atomized particles. This
preliminarily atomized liquid flow stream is then
directed axially through a discharge orifice at the
open end of the device and an external deflector
flange which is transversely oriented to the line of
~MEN~~tl~ S~EET
lP~~~P
CA 0223~946 1998-04-23
travel of the liquid, directs same through a final
discharge orifice where the pre-atomized droplets are
broken into extremely fine liquid particles which are
then deflected into a flat, wide spray pattern in a
manner which maximises their exposure to the ambient
air. A cup-shaped recess is believed to produce
pressure waves or acoustic energy which assists in the
liquid breakdown. The nozzle assembly has particular
utility in humidification and evaporative cooling
applications.
The US '937 patent discloses the use of the same
nozzle assembly in a manner in which it can be easily
removed from the nozzle body to enable the nozzle to
be used as an hydraulic nozzle.
Accordingly, it can be seen that these prior US
patents contain no disclosure whatever relevant to the
concept of providing a chamber to which liquid and air
supplies are provided, the liquid supply being in
unatomised form, and the chamber having a wall o~
closed end towards which said air and liquid supplies
are directed, and from whic~ chamber the liquid and
air supplies are discharged outwardly with respect to
the closed end of the chamber through an outlet formed
in a chamber side wall and in the form of an air flow
with entrained liquid droplets.
There is disclosed in US 51 29 5~3 (Bailey) an
atomizer for discharging a jet of one fluid in another
fluid. The atomizer comprises an atomizer head
disposed generally in-line with the incoming water
supply direction and the head is formed wit:h at least
one nozzle hole for discharging the jet through the
head and generally forwardly and outwardly. The
nozzle hole is profiled to reduce deposition on the
atomizer when used for spraying into dust--laden flue
gas. The nozzle profile is adapted to reduce
turbulence. The general direction of water and air
AAAEN~ SHE~T
- IPE~P
_
, CA 0223~946 1998-04-23
-
flow through the atomizer is actually lengthwise of
the atomizer and onwards through the open atomizer
head with the addition of a slightly outward component
S of movement resulting from the nozzle holes' slightly
inclined attitude.
There is disclosed in US 3,096,023 (Thomas) a
system for distribu,ting lubricant or oil to chains,
gears and other machine parts. The system may be
readily used with nearly all types of oils regardless
of viscosities and changing temperature and humidity.
The system provides a plurality of spaced outlets for
application to the machine part which is to receive
the lubricant. No data is provided regarding
pressures needed to produce the requisite ~lows. Jet
units apply a jet directly onto the bearings to be
lubricated, or they may be provided with tube or hose
connections to convey such jet to a bearing unit-and
thus the jet is as narrow as such tube or hose. In
the embodiments other than those of Figs 4 and 7 the
material flow is axial throughout the jet units
whereby these themselves,,are incapable of operating in
accordance with the principles of the present
invention, while that of Fig 4 shows a super~icial
Z5 resemblance to the latter but is used in a system
whereby it produces narrowly-aimed jets O e lubricant
or coolant to be pin pointed on defined areas of the
chains, gears or other machine parts. In the case
where coolant is applied, the objective is to apply a
concentrated jet of sufficient liquid volume to
produce the requisite coolant effect. This is an
inversion of the requirements of the present invention
which, in a boom-type spraying machine, seeks to apply
a uniform liquid coating of droplets, as disclosed
herein, utilising the absolute minimum of liquid per
AMEN~ tE~T
Ip~A~Cp
CA 0223~946 1998-04-23
5B
unit area, ~hile applying such coating uniformly to
crop areas which can be measured in terms of hectares
per unit time, instead of square centimetres per unit
time.
Accordingly, there is a considerable need at
least in relation to agricultural and horticultural
boom type sprayers, for improvements in relation to
droplet generation as discussed above, having regard
to crop penetration, particle size, and minimisation
of water carrying requirements, and an object of the
present invention is to provide a method and apparatus
offering improvements in relation to one or more of
these matters, or generally.
According to the invention there is provided a
method and apparatus apPlicable to spraying as defined
in the accompanying claims.
In an embodiment, a droplet generator is provided
AMEt~ 1E~
_ _ _
CA 0223~946 1998-04-23
W O 97/16257 PCT/GB96/02664
comprising an air-and-liquid supply chamber to which
both a liquid supply and an air flow supply are
connected for supply of air and liquid towards an
internal wall or target formed by a closed end of the
chamber. The droplet generator further comprises
structure defining an edge or boundary of an external
outlet from the chamber and the liquid supply means is
adapted to supply the liquid to the outlet through the
chamber via the closed end of the chamber.
In the embodiment, the air flow supply means and
the liquid supply means are adapted in relation to the
chamber to supply air and liquid towards the closed
chamber end for production of the spray of droplets
from the chamber outlet by entrainment of the liquid
in the air flow. These features produce several
significant benefits. These include a particularly
useful mode of droplet formation whereby the droplet
size is well adapted to enable the air flow to entrain
and carry the droplets into the crop. Thus, firstly
the arrangement is capable of producing a suitable or
optimum droplet size which is consistent with very low
liquid volume requirements while achieving
satisfactory or better crop penetration. Moreover,
the mode of droplet generation is particularly adapted
to enable the droplets to be effectively carried by
the air flow in a required direction into the crop,
for example from a dropleg.
Accordingly, by providing the general arrangement
of air flow and liquid supply means to supply air and
liquid towards a wall or generally closed chamber end,
and for corresponding outward flow through an outlet
with entrainment of liquid in the air flow, the
advantage is provided that the flow of air and
entrained droplets has the required physical and
dynamic characteristics and can be directed in any
required direction. Additionally, in a given set of
-
CA 0223~946 1998-04-23
W O 97/16257 PCT/GB96/02664
apparatus, considerable flexibility exists in
designing the direction and width of the spray output.
For example, if it is required to generate a
relatively wide and fan-shaped output of spray in a
given direc~ion then the apparatus is provided with a
series of suitably spaced orifices with suitable
directions corresponding to the requisite fan-shaped
output. The fact that, for example, six orifices are
provided instead of one does not, of itself, increase
the liquid volume requirements of the spray head in
which the orifices are required. Whereas provision of
a corresponding number of conventional spray nozzles
would produce a corresponding requirement for six
times as much liquid flow to the apparatus as compared
with a single nozzle apparatus, this does not apply in
the case of the embodiments described below. For a
multi-orifice spray head, the same volume of liquid to
be sprayed may be supplied and all that is needed in
order to produce the required spray pattern is the
maintenance to all the orifices of the modest air
pressure required for the liquid entrainment and
droplet formation steps. In other words, more
orifices can be provided at the same volume of liquid
supply merely by increasing the air supply.
To put it another way, the embodimerlts of the
present invention enable liquid volume supply to be
reduced, at will, to levels very substantially below
those required for conventional spray nozzles,
provided that the air supply is always sufficient for
the required entrainment and droplet formation steps.
Also in the embodiments, the one or more orifices
is or are formed in a chamber or gallery to which the
liquid is supplied in the form of an unatomised jet
directed at a closed end of the chamber which has an
associated outlet through which the liquid and air
flows supplied to the chamber proceed. It is not
CA 0223~946 1998-04-23
W O 97/16257 PCT/GB96/0266
known whether some or all of the droplet formation
occurs at the closed wall of the chamber, or later in
the flow path of the materials through the chamber.
Possibly, a surface layer of liquid is produced in the
chamber which proceeds to the outlet opening and is
formed into droplets at that region.
The relative disposition as between the closed
end or wall of the chamber towards which the liquid
supply is directed, and the location of the one or
more outlet openings is of some importance. Broadly,
the outlet opening is located relative to that wall of
the chamber so that the direction of material flow
from the location of impact of the unatomised jet of
li~uid towards the outlet is generally outwardly of
the chamber. In the embodiment, both the air and
liquid supply paths to the chamber are generally
axially thereof and lengthwise of the chamber towards
its opposite closed end, but it may not be necessary
for the air supply direction to be exactly axial.
Moreover, the location of the one or more outlets
relative to the chamber may be but need not be
strictly at the outer periphery of the wall or target
at which the liquid supply is directed. Thus, in the
Fig 2 embodiment, the outlets are somewhat axially (of
the chamber) offset from that wall, and the
arrangement is such that the outlet(s) is or are
located so as to enable a smooth and effective flow of
materials from the chamber end wall outwardly
thereof.
Likewise in the embodiments, the jet or flow of
liquid supplied to the chamber is disposed generally
symmetrically with respect to two or more orifices
formed in the chamber so that each orifice receives a
generally equal supply of liquid to its entrainment
edge or boundary.
Also in the embodiments, provision is made not
-
CA 0223~946 1998-04-23
W O 97/16257 PCT/GB96/02664
only for a generally central and thus even supply of
liquid to the chamber in which the entrainment
orifices are provided, but also of a relatively even
or uniform distribution of air to that chamber and
thus to the orifices. For this purpose, there are
provided axially-directed air flow ducts or drillings
in the conduit leading to the air-and-liquid supply
chamber, these ducts or drillings being uniformly
distributed around a jet or liquid supply member in
the conduit.
Other notable features of the embodiment include
the function of the air-supply arrangements to act as
a venturi or pump with respect to the liquid supply.
The surface of the wall or target towards which
the jet or flow of liquid is supplied to the air-and-
liquid supply chamber may be constructed to promote
uniform distribution of liquid to the entrainment edge
or boundary of the associated orifice or outlet. For
example, the surface may have a convex and outwardly
broadening form having its apex directed at the source
of the jet or flow of liquid, and the form of the
convex structure being such as to promote the
production of a uniform outward liquid flow to the one
or more orifices provided in the chamber A flat
surface may alternatively be provided as shown in Fig
7. It is also envisaged that a concave surface (as
shown in Fig 2) produces useful results. It has been
found that in the absence of a uniform liquid supply
to two or more spaced orifices in the chamber, there
can be a gravitational effect on the distribution of
liquid to those orifices whereby non uniformity of
spray production can result.
It will be understood that the invention utilises
an approach to droplet formation having some technical
common ground with carburettor technology. The air
supply provides power in the spray plume to penetrate
CA 0223~946 1998-04-23
W O 97/16257 PCT/GB96/02664
the crop. Droplet formation may occur, as mentioned
above, either at the chamber wall which intercepts the
liquid supply and/or in the region of the edge or
boundary defining the outlet orifice or orifices of
the chamber. It has been observed in tests that the
plume of spray produced by the apparatus of the
invention includes an inner portion, which may for
example be of length about 10 to 20 centimeters, and
in this portion of the plume the air and entrained
liquid is relatively significantly less visible than
in the outer portion of the plume where it assumes the
characteristic mist or fog-like form. It is not known
what effect gives rise to this change in appearance,
which is uncharacteristic of conventional spray
nozzles.
An important aspect of the embodiments described
below is the relatively low power consumption of the
air supply system. Whereas currently available so-
called airbag sprayers usually require a power input
of the order of 80 kilowatts to the fan, the air
supply system of the embodiments described below
requires only about 10 to 15 kilowatts for a 12 metre
spray boom.
It is to be understood that the orifice or outlet
from which the droplets are discharged may be modified
in shape with respect to the round profile disclosed
below. Among the principal advantages of the
described embodiment are the simple construction of
the droplet generator and the low tendency for
orifice blockage, the highly directional droplet
propagation, and the low liquid volumes involved.
Moreover, very little lateral dispersal of the
droplets occurs away from the main jet thereof, as
compared with prior proposals, such as those discussed
above, which tend to produce a fogging effect.
By reducing liquid volume requirements, the
CA 0223~946 1998-04-23
W O 97/16257 PCT/GB96/02664
embodiments substantially reduce the usual sprayer
down time which is about 40 per cent of working time
which is devoted to refilling the tank. Therefore,
approaching 40 per cent more work can be produced. A
further factor is that the orifices or outlets from
which the droplets emerge no longer need to be at the
relatively very small sizes required by liquid spray
systems. Thus, orifices of the order of 1 millimetre
diameter can be utilised compared with 0.3 millimetres
for prior liquid systems. This reduces the occurrence
of blockages.
It has been found in practice that the
embodiments of the invention are extremely tolerant of
changes in the pressure of the liquid supply. Thus,
for example, it has been found that the li~uid supply
pressure can be reduced to a level which is even below
that of the air flow supply pressure. Indeed it is
apparently the case that the embodiments of the
invention do not require a liquid supply in the form
of a jet of liquid which must intercept, for example,
an end wall of the air-and-liquid supply chamber so as
to produce a dynamic effect. On the contrary, it
appears to be sufficient for the purposes of the
invention that merely a sufficient supply of liquid is
provided so that the droplet entrainment process can
proceed without any shortfall in the supply of liquid
therefor. Accordingly, it is thought likely that in
view of this fact the droplet formation and
entrainment process may well occur largely in the
region of the outlet opening from the chamber, rather
than within the chamber as such, although the
mechanism might differ somewhat according to the
nature and dynamic characteristics of the liquid
supp ly .
In this regard, test work shows that modification
of the form of the closed chamber end wall in the
CA 02235946 1998-04-23
W O 97/16257 PCT/GB96/02664
embodiment, against which the jet of liquid is
projected, does not significantly affect the
performance of the apparatus and this also appears to
support the likelihood that the droplet entrainment
process does not significantly occur within the
chamber as such.
Further with regard to the mechanism of the
droplet entrainment process, it appears to be an
important aspect of the process that the liquid/air
flow undergoes a change of direction immediately
before or during the droplet entrainment process.
Thus, it is clear that the process does not occur
effectively in an entrainment chamber in which direct
onward axial flow through an outlet orifice is
permitted in-line with the general direction of
material flow through the chamber, as might be
expected from the teaching of the above-discussed
prior US patents. The mechanism of this effect is
presently unknown. It is also noted that there is
apparently what may be termed a venturi or siphon
effect in the region of the chamber outlet opening or
openings, produced by the airflow and serving to
deliver liquid to the edge or boundary of the outlet
opening. There is also a similar effect where the air
and liquid supplies enter the chamber, the outer air
flow producing a venturi effect on the inner liquid
flow whereby the required liquid pressure in the
liquid supply is reduced.
An important practical aspect of the invention
relates to the several inter-related magnitude
parameters of the main components of the liquid and
air supply system. These parameters include the size
of the outlet openings or orifices in the air and
liquid supply chamber, the air supply pressure, the
liquid supply pressure, and the output of the air
compressor which supplies air to the system etc.
CA 0223~946 1998-04-23
Considering first the size of the outlet openings
in the air and liquid supply chamber, these may be in
the range Qf O. 5 to 2.0 millimetres in diameter, or
openings of a similar area in non-circular shapes. It
is found that sizes of less ~han 0.5 millimetres lead
to a significantly reduced throw or travel of the
plume of droplets produced by the apparatus. A
preferred range of diameters (or sizes for other
opening shapes) is from 1.3 to 1.8 millimetres and
preferably 1.6 to 1.7 millimetres. These latter
larger sizes provide the significant advantage of
avoiding the frequent nozzle blockages which are a
feature of conventional spraying systems. It is found
that droplet size is not greatly affected by outlet
opening size, but as such size increases, crop
penetration increases due to increased velocity of the
droplets caused by higher volume throughput as flow
resistance reduces.
So far as air supply pressure is concerned, this
relates directly to the capacity of the compressor
provided to deliver the air supply. While of course
an agricultural tractor usually has ample reserves of
power to drive a compressor of very substantial
proportions, the cost implications of large
compressors render them unattractive and it has been
found that air supply pressures in the range of up to
0.6 bar and 0.6 to l.o bar (above atmospheric
pressure), and preferably between 0.7 and 0.9 bar, are
convenient utilising a compressor capable of supplying
an output of approximately 142 to 566 litres (5 to 20
cubic feet) of air (measured at such pressure) per
spraying head or dropleg, per minute. Usually, an
output in the range of 2~3 to 425 litres (10 to 15
cubic feet) per dropleg per minute will be suitable.
~ 35 It is found that the use of pressures above these
quoted ranges leads to the production of droplets
P~M5~NE~ SHEEl~
I P~At~P
CA 0223~946 1998-04-23
W O 97/16257 PCT/GB96/02664
envisaged, namely to be propelled towards and to
adhere to or coat crop and other surfaces exposed to
them. Thus, droplets preferably in the range of 80 to
120 or up to 150 microns in maximum dimension are
found to be suitable for these purposes. Larger
droplets are used for spraying crops from above (not
using droplegs) to reduce spray drift caused by wind.
Droplets significantly below 80 microns are found to
be too small to adhere effectively to sprayed
surfaces.
So far as the pressure of the liquid supply is
concerned, the principal requirement is a sufficient
supply of liquid to the chamber outlet orifice,
without the use of a directly-transmitted jet passing
through the centre of the orifice. However, pressures
of 0.6 bar (above atmospheric pressure) upwards have
been found to be suitable in the described embodiments
and pressures of 2.5 and up to 6 bar have been tested
and found to produce acceptable results in which the
air supply is still able to proceed through the
orifice or orifices satisfactorily. It appears that
the air supply effectively serves to maintain the
central opening or void in each orifice during
operation, while droplet entrainment occurs, probably
at the edge or boundary of the orifice.
One aspect of the versatility of the system
becomes apparent from the use of varying liquid supply
pressures. It is found that, while satisfactory
droplet production occurs at the higher liquid supply
pressures mentioned above, the use of these higher
pressures produces significantly greater dosage rates,
such as 60 litres or even up to 300 litres of liquid
per hectare sprayed. Accordingly, it can be seen that
this aspect of the invention permits a method of
spraying to be adopted in which the dosage rate is
varied according to the local requirements of the crop
,
CA 0223~946 1998-04-23
W ~ 97J16257 PCT/~5GI'~664
or other material being sprayed. By use of a variable
output liquid supply system, the dosage rate can be
significantly varied. Conventional spraying systems
are not susceptible to such significant variation in
dosage rate merely by changing the liquid supply
pressure. It appears that this versatility arises
from the use in the present invention of significantly
larger outlet orifices than in conventional liquid
only spray ~ystems in which the limited outlet size
itself prevents significant variation in liquid supply
rate, whereas the central air-filled orifices of the
present invention can readily accommodate such
varlation .
It will be apparent from the above that the
invention, and notably the embodiments of it described
below, provides its own distinct approach to the
generation of spray droplets suitable to meet the
requirements of agricultural and horticultural
spraying requirements, and indeed related requirements
outside that field. Prior proposals have, in general
terms, been based upon the approach of providing
droplet generation systems in which, usually, there is
provided a step of preliminary atomisation internally
of the droplet generating apparatus, this involving
inevitably a corresponding step of liquid-and-air
interaction, which is then followed by emergence
through a nozzle and lateral deflection using a target
or anvil to achieve a further degree of atomisation
and droplet generation.
The contrasting approach of the present invention
is based upon the use of an internal target or wall
within an empty or open chamber to which the air and
liquid supplies are delivered. A change of direction
of the liquid flow is effected accordingly towards an
outlet or orifice which is not directly in-line with
the liquid flow through the chamber. The liquid and
CA 0223~946 1998-04-23
W O 97/16257 PCT/GB96/02664
air flows through the outlet or orifice produce a
spray of air-entrained droplets which, at air
pressures which are readily determinable, produce
droplet sizes suitable for effective coating of plant
and other surfaces. There are no internal or external
structures to interfere with the through-flow of
liquid and air through the orifices. Moreover,it is
found that by appropriate choice of outlet opening
sizes and dispositions, there can be achieved a
direction and degree of crop or other penetration by
the spray according to requirements.
The mechanism for droplet generation is not
easily determinable without the use of sophisticated
equipment. However, it is apparent from the
differences in structure of the droplet generator as
between the invention and the prior art that there is
a difference of mechanism amounting in simple terms to
the use in the present invention of a target or wall
followed by an unrestricted outlet orifice, whereas
the prior art, generally speaking, uses the inverse
arrangement.
Summarising, it is believed that the present
invention represents somewhat of a reversal of
existing technology in the area of air-facilitation of
droplet generation for agricultural and horticultural
and related applications, which can benefit from the
enhanced generation of the droplets of a size which
promotes uniform coating of a substrate utilising
minimum volumes of a liquid vehicle for the purpose of
diluting an active surface treatment medium. The
technique utilises air as a means for replacing the
diluting liquid vehicle. The technique is independent
to a significant extent of the pressure of the liquid
supply. As regards air supply pressure, this is
chosen in accordance with the required range of
droplet sizes. The range and degree of penetration
_
CA 0223~946 1998-04-23
WO 97/16257 PCT/GB96/02664
provided by the plume or jet of spray droplets is
determined to a large extent by the size of the outlet
openings from the air and liquid supply chamber in
combination with the corresponding required volume of
air flow at the chosen air supply pressure (the latter
being in accordance with droplet size requirements).
And, these technical features and advantages are
provided by the relatively simple combination of
features to be found in the air-and-liquid supply
lo chambers shown in the described embodiments, most
notably the provision of a wall or target in the open-
centre chamber to which the liquid ~low is supplied
and which enables, with a change of flow direction,
the liquid to reach the requisite number of outlets or
orifices in combination with the required air flow
through those orifices whereby droplet entrainment
occurs in accordance with matters described above.
The liquid flow to and through the orifice is
generally outwardly of the target or wall and indeed
of the chamber, though by no means necessarily in a
truly radial direction.
An embodiment of the invention will now be
described by way of example with reference to the
accompanying drawings in which :
Fig l shows an axial section through a jet and
tube assembly;
Fig 2 shows a corresponding longitudinal section
through a complementary entrainment chamber adapted to
be mounted on the jet and tube assembly;
Fig 3 is an end elevation view of the jet and
tube assembly as viewed in the direction III in Fig l;
and
Figs 4, 5 and 6 are taken from the present
applicants' corresponding published prior
International applications including inter alia
PCT/GB92/01356 showing tractor-drawn spraying
.
CA 0223~946 l998-04-23
W O 97/16257 PCT/GB96/02664
18
apparatus of the dropleg kind and to which the present
invention is applicable;
Fig 4 shows a plan view of tractor drawn spraying
apparatus incorporating a compressor for supply of air
to individual droplegs;
Fig 5 shows, on a larger scale, a corresponding
plan view of an individual dropleg passing between two
crop rows and with a direction of a plume or spray of
droplets indicated;
Fig 6 shows an end elevation view of a spray boom
of the spraying apparatus of Fig 4 showing the boom
itself and an associated dropleg; and
Fig 7 shows, on a larger scale, a droplet
generation or entrainment chamber representing a
second embodiment of same and incorporating angularly
inclined outlet openings to produce simultaneous jets
or plumes of spray droplets in the indicated inclined
directions.
As shown in Fig 1, a liquid and air supply and
connection assembly 10 comprises a machined connection
and supply jet member 12 which is a friction fit
within the end of a tube member 14.
Tube 14 forms the lower end portion of a dropleg
of a dropleg-type sprayer as described in one or more
of my prior patents, for example EP 0 600 919 B and EP
0 539 360 B, and as more fully described below with
reference to Figs 4, 5 and 6 hereof.
Jet member 12 is a tight friction fit in tube 14
and has a projecting portion 16 formed with an
external screw thread 18 to co-operate with a
corresponding internal screw thread 20 provided on the
internal surface of a collar portion 22 of an
entrainment or chamber member 24 - see Fig 2.
Jet or connection member 12 is formed with a
pattern of six axial bores 26 extending lengthwise
thereof to deliver air from the pressurised internal
CA 0223~946 l998-04-23
W 097/16257 PCT/GB96/02664
volume of dropleg tube 14 to a chamber 28 defined
within entrainment or chamber member 24.
Jet or connection member 12 also serves to
provide an unatomised jet or flow of liquid into
chamber 28, for the purpose to be described.
Accordingly the connection member 12 is also provided
with a hose sleeve 30 at its inner end, a lengthwise
bore 32 leading therefrom, and a jet or supply member
34 to produce an unatomised jet or supply of spray
liquid. Jet 34 has its own axial bore 36 w~ich opens
into bore 32 and receives liquid therefrom. The
lengthwise bore 36 of jet 34 is simply a uniform-
section endwise bore with no provision for the
generation of droplets in the manner of a spray
nozzle.
Thus, summarising the structure and function of
jet or connection member 12, it serves to receive
spray liquid from a hose which extends lengthwise of
the dropleg tube or shank 14 within that tube, and
receives also supplies of air pumped lengthwise of
that tube in the annular space between the hose and
the tube's inner surface. The spray liquid is
delivered from jet 34 as a thin uniform stream or
supply of liquid. The air is delivered generally
uniformly around the periphery of jet member 12 by
virtue of the six streams of air produced by bores 26.
These flows of liquid and air are delivered to chamber
28 of the entrainment or liquid and air supply chamber
member 24.
Turning now to more details of the structure of
entrainment or chamber member 24, the principal
structural features are its internal form and the
provision of orifices or outlets 38 leading outwardly
from chamber 28 for the delivery of air and spray
liquid from chamber 28. That chamber, 28, is of
cylindrical form, comprising an axial bore 40. In
CA 0223~946 1998-04-23
W O 97/16257 PCT/GB96/02664
this embodiment it is formed with a conical-form end
wall 42 with a fairly large cone angle and having an
apex 44 at which the jet of liquid from jet 34 is
delivered in use.
The orifices 38 are disposed in two groups of
three orifices or outlets, making six in all, these
groups of three being spaced within the group and
between the groups so as to produce two laterally-and-
upwardly directed plumes of spray in use from the
dropleg tube 14 upwardly and laterally outwardly into
the crop in directions in accordance with the teaching
contained in my above-mentioned prior patents.
Figs 4, 5 and 6 show tractor-drawn spraying
apparatus of the kind suitable for incorporation of
droplet generation apparatus in accordance with the
above-described embodiment of the invention.
Thus, in Fig 4, a tractor 50 has mounted on the
hitch links thereof boom type spraying apparatus 52
comprising spraying booms 54, 56 having associated
droplegs 58, as described in our prior published PCT
applications.
Each dropleg 58 comprises a downwardly-projecting
dropleg shank portion 60 (corresponding to shank 14 in
Fig 1) which enters between crop rows 62, 64 and
carries a droplet generator 66 for crop spraying
purposes.
Each dropleg 58 has its own droplet generator
indicated in Fig 5 at 66, and this is provided with
air and liquid supplies delivering liquid (to be
sprayed) and air supplies from the liquid tank 68 and
a compressor 70 shown in Fig 4. The droplet generator
66 produces twin spray jets or plumes 72 (see Fig 5)
directed generally forwardly and upwardly and
laterally with respect to the direction F of forward
travel of the tractor and the droplegs, and
symmetrically with respect to the crop rows. Droplet
CA 0223~946 1998-04-23
WO 97/16257 PCT/GB96/02664
generator 66 corresponds to the entire apparatus of
Figs 1, 2 and 3 described above. Such a pl~me 72 is
produced at each side of the dropleg to pro~ride spray
treatment of each of the crop rows 62, 64. In Fig 5,
the dropleg 58 shown is constructed as described in
our above--mentioned prior PCT applications, whereas in
Fig 6 the dropleg 58 is adapted for the purpose of the
present invention to receive both the air and the
liquid supplies for transmission of these within the
dropleg tube lengthwise thereof to the droplet
generator 66 at the lower end thereof, the supplies
being delivered thereto as described abo~e and as
illustrated in Fig 1.
In use, liquid and air supplies are delivered to
the upper end of each dropleg 58 and thus to its jet
or connection member 12 as mentioned above and chamber
28 is pressurised by the air while receiving a jet or
supply of liquid on the chamber end wall or target 42
at the apex 44 of the conical form of that end wall.
This jet or supply is believed to produce at least a
partial film of liquid on the inner surface of the
chamber end wall 42 which flows outwardly towards
orifices or outlets 38 and passes, likewise as a film,
outwardly and lengthwise of the orifice bo3ces 46 to
their end edges 48. A degree of droplet formation may
occur at the end wall or target 42 of chamber 24.
It is not known exactly what happens at the outer
ends of the bores 40, notably at the edges or
boundaries of the outlets 49 thereof, except that the
result is as described earlier in this application and
droplets are formed either in the region of the
outlets 49 and/or earlier at the chamber end wall 42,
or at a later stage when the air/liquid stream has
been sufficiently decelerated by the ambient air.
In the embodiment of Fig 6, the droplet generator
66 of the droplegs 58 of Fig 6 is, instead of the
CA 0223~946 1998-04-23
In the embodiment of Fig 6, the droplet generator
66 of the droplegs 58 of Fig 6 is, instead of the
assembly 10, 24 of Figs 1, 2 and 3, constructed as
follows. The droplet generator 100 of Fig 7 comprises
a air and liquid supply chamber 102 to which are
provided air 104 and liquid 106 supplies, these being
provided in the same relative spacial dispositions as
in the previous embodiment, for delivery towards the
chamber end wall or target 108, which is planar.
The chamber outlets 110 are disposed in two
groups comprising generally forwardly-directed outlets
112 and generally rearwardly-directed outlets 114,
with respect to the direction F of normal forward
motion of the sprayer.
As Fig 7 clearly shows, the entrances 116 to the
oulets are disposed so that liquid passing to the
bores 118 of the outlets from the end wa]l 108 must
change in direction before entering the bores.
Moreover, the entrances 116 are offset from the end
wall 108 by a distance d in the axial or liquid flow
direction of chamber 102.
This embodiment of the invention is able to
discharge spray droplets simultaneousl~ in the two
indicated directions which is of benefit for certain
agricultural operations.
Broadly speaking, in at least some embodiments of
the invention the use of the flow of air to cause
movement of the spray of liquid droplets has the
effect of replacing the water or similar diluent
vehicle conventionally used for spraying purposes,
whereby it becomes possible to spray treat
agricultural or horticultural or industrial or other
objects with a liquid treatment medium without the
need for the use of any liquid as a diluent or carrier
medium, or at least to reduce the effective volume of
such a liquid vehicle by a factor of 10 or more.
AMEN~ E~
IP~At~P
-
CA 0223~946 1998-04-23
W O 97/16257 PCT/GB96/02664
sprayed is chosen in accordance with the desired size
of the droplet to be generated. In an envisaged
embodiment, the liquid vehicle for the treatment
material may be non-aqueous, for example the liquid
vehicle may be an oil-based liquid comprising an
aromatic hydrocarbon. It is envisaged that the liquid
vehicle which forms part of the liquid to be sprayed
will be chosen in accordance not only with the nature
of the active chemical ingredient involved, but also
in relation to the surface tension and other
characteristics of the liquid to be sprayed, these
being chosen in order to achieve a desired degree of
adhesion to plant surfaces, or related requirements.
An example of a related requirement may be the
requirement ~or the sprayed material to be rain-
resistant.
Accordingly, in accordance with this embodiment
of the invention it can be seen that the invention
offers the additional advantage of permitting non-
aqueous based liquid vehicles to be offered forspraying purposes whereas such a basis for spraying
operation has hitherto been considered commercially
unacceptable in view of the relatively high cost of
the liquid vehicle due to its volumetric requirements
as determined by prior art spraying apparatus.
A further aspect of the present invention
relates to tl~e relative importance of providing an
ability to inject or otherwise deliver the liquid to
be sprayed to the delivery system close to the
spraying nozzles on the boom. In this way, the
lengths of spraying lines in which relatively
concentrated chemicals are transmitted are reduced.
This leads to significant advantages in terms of
ability to switch from one spraying medium to another
at relatively short notice.
Amongst other modifications which could be made
_
CA 0223~946 1998-04-23
W O 97/16257 PCT/GB96/02664
24
in the above embodiments while remaining within the
scope of the invention are the following. Firstly,
the actual cross sectional shape and dimensions of the
air and liquid supply chamber may be varied. A non
cylindrical chamber may be used and its axial length
in the liquid flow direction may be varied, as
indicated by comparison of Figs 2 and 7. Routine test
work by a competent technical person in the field will
reveal the applicable limits. Likewise, variations in
lo the dispositions of the outlets relative to the
chamber end wall can be accommodated and provided.
The wall or target towards which the liquid supply
flows can itself be modified considerably in terms of
its profile being planar, generally convex or
generally concave. Indeed, the target may be provided
as an internal construction in the chamber providing
for suitable liquid flow outwards to the chamber
outlets. Routine test work will reveal the
modifications which may be made in this regard.
It is envisaged that satisfactory results may be
obtainable where the air inlet to the chamber is
located, for example, at the opposite end from the
liquid inlet, or indeed in a side wall of the chamber.
Tests have been made of a liquid and air delivery
system to the chamber permitting, effectively, a
gravity feed to the chamber end wall or target, and
thus without the controlled metering of liquid supply
to that structure. This arrangement could be adopted
where attitude changes are not of significance, but
generally it is desirable to provide metering means
for delivering an even supply of liquid to the chamber
end wall or target. Such may be achieved in a variety
of ways additional to the jet or flow indicated in the
described embodiments, including the use of several
such jets or flows within the chamber. It will be
understood from the foregoing description that the
CA 02235946 1998-04-23
W O 97/16257 PCT/GB96/0~664
chamber end wall or target provides a function of a
distribution baffle or member serving to supply an
appropriate flow of liquid to the chamber outlets for
droplet entrainment.
-
