GB2227399A - Spraying using high pressure air. - Google Patents

Abstract

A method of spraying agricultural material from a sprayboom including : providing high pressure low volume air (86,87) emerging along the span of the boom (80), causing or permitting said emerging air (86,87) to entrain ambient air to produce a multiplied volume of air flowing from said boom (80) along the length thereof, providing a source of material (83) to be sprayed from said boom (80), directing material from said source (83) in the direction of said flow of the multiplied volume of air to be entrained therein for spraying from said sprayboom (80) along its length as a spray of liquid droplets.

Description

SPRAYING This invention relates to the spraying of agricultural liquids, which include insecticides, herbicides, fungicides and other materials of agricultural use.

The techniques for spraying of liquids for agricultural purposes have recently been subject to much investigation and regulation. The need to avoid "drift" of spray, which can harm adjacent plants, animals and people, to provide accurate control and placing of dosage, for correct action with minimal expense of material, and to achieve efficient use of the equipment, in terms of area covered and labour required, all affect the techniques employed or proposed.

Electrostatic spraying can improve the proportion of spray which actually reaches a plant, more precise control of droplet size, particularly smaller sizes of droplet, can permit the use of smaller amounts of active material for the same degree of control. However smaller droplets can not always penetrate the crop.

Spraying machinery is subject to various constraints. The machine, be it a tractor with boom attachment or a purpose-built machine, can not be too heavy to avoid damage to the ground. The amount of liquid carried in a given machine welght controls the area that can be covered before refilling, which can involve a lengthy journey and time not used for spraying. The spray boom should have as wide a span as possible to maximize area covered per traverse, subject to the nature of the ground, and foldable for transport by road between areas to be sprayed. The power demand for spraying should be as small as possible to reduce demands for fuel and avoid large engines or auxiliary power sources.

Given these various controls and constraints there is a strong demand for spraying techniques of improved efficiency which avoid the shortcomings of present techniques.

It is an object of the present invention to provide spraying techniques which have improved efficiency of deposit of material and minimise non-target contamination.

According to the invention there is provided a method of spraying agricultural material from a sprayboom including providing high pressure low volume air emerging along the span of the boom, causing or permitting said emerging air to entrain ambient air to produce a multiplied volume of air flowing from said boom along the length thereof, providing a source of material to be sprayed from said boom, causing or permitting material from said source to be entrained in said flow of a multiplied volume of air for spraying from said sprayboom along its length as a spray of liquid droplets.

The air emerging along the boom may be from a linear "air mover". The air emerging along the boom may exhibit the Coanda effect to direct its flow. The multiplied volume of air may form the spray from the source.

The material to be sprayed may be an agricultural liquid.

The spray of liquid droplets may be formed as a fan by an hydraulic nozzle positioned just above the emerging air.

According to the invention there is provided a boom having a spanwise duct to carry pressurized air to escape through spanwise elongate nozzles at the entrance to a passage forming an ejector to entrain atmospheric air at the top of the passage to flow through the passage and having means to spray droplets for entrainment in said entrained air flow so that mixed streams form a high volume air stream directed downwards over the whole span of the boom.

The passage may be first convergent and divergent downstream. The spray droplets may be sprayed into said passage for entrainment therein in said airflow.

There may be more than one passage. The or each passage may be convergent-divergent. The arrangement may have the general form of an ejector to which spray is added. The elongate nozzles may be formed by a linear "air-mover".

The arrangement may include active boom height control, using response to the effect of crop arranged to reflect air directed from the boom to indicate the closeness of the crop and maintain the boom in a required position over the crops or ground. A height sensor may be fitted to each end of the boom and can be coupled to a valve regulating an air pressure flow at that end of the boom, so as to control the boom attitude with varying ground conditions.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a cross section of the spray boom: the section plane being vertical and parallel to the direction of travel, Figure 2 is a side section of the complete spraying machine mounted on an agricultural tractor, Figure 3 is a rear elevation of the centre section of the spraying machine, Figures 4 and 5 show an arrangement employing a separate ejector duct for each spray nozzle.Figure 4 is a cross section of one such duct and Figure 5 is a rear elevation of part of the spray boom showing the arrangement of the ejector ducts and nozzles, Figure 6 shows an embodiment of the invention where the spray nozzles are placed outside the ejector but aligned so that the spray droplets impinge on, and are entrained by, the airstream from the ejector, Figure 7 shows an embodiment of the invention where two ejectors are used, arranged one behind the other with the spray nozzles between them, Figure 8 shows a schematic end view, partly sectioned, of a sprayboom forming an embodiment of the invention, and Figure 9 shows a cross-section of another form of air jet source Referring to Figure 1, the spanwise duct 1 has on its lower surface a row of closely spaced nozzles 2. These nozzles may be individual circular holes or longer slots with structural webs between them.In either case they will be shaped so as to provide a high velocity vertical airstream over the whole span of the boom. Below the duct 1 are positioned two spanwise bodies 3 and 4 which are shaped so that their inner surfaces form a convergent-divergent passage from top to bottom of the boom over its whole span. The bodies 3 and 4 can conveniently form the load bearing structure of the boom and may be made using appropriate lightweight constructlons such as foam-filled, fibre reinforced plastic.

The shape of the bodies 3 and 4 and their relationship to each other and the duct 1 are optimized so to provide an efficient linear ejector. Joining panels generally in the plane of the section will be necessary at intervals along the boom to provide structural rigidity and to maintain the spacial relationship of the parts but without obstructing airflow.

The ejector functions in the manner of known ejectors or jet pumps in that the high pressure air stream from the nozzles 2 passing into the converging-diverging passage between 3 and 4 entrains additional air through the gaps at 5 and 6 resulting in a high-volume low-pressure downward air stream at the exit from ejector 7.

The atomizers for the spray chemical can conveniently be positioned at or close to the exit from the ejector and as shown in Fig 1 at 8. They are fed from a manifold pipe 9 which is shown outside the body 4, but which could be incorporated within it.

The atomizers may be of the conventional hydraulic type, or of the spinning-disc type for control of droplet size, or of the electrostatic type or of the air shear type, in which type there is interaction between liquid and air flow to produce spray.

These techniques may be combined to produce electrostatically charged droplets formed by either an hydraulic or a spinning-disc atomizer. Should spinning-disc atomizers be used they can conveniently be driven by turbines operating in the airstream from the ejector.

Figure 2 shows the spray boom mounted with its tank, pump etc. on a tractor to form a complete spraying vehicle.

Alternatively it can be mounted on a purpose-built spraying vehicle or other specialised prime-mover, or on a trailer to be towed by a prime-mover. In this view the boom is shown in cross-section at 10 with a centrifugal compressor 11 mounted above it to provide the high-pressure air supply. The compressor may alternatively be of the positive displacement type using vanes or lobes, or may be a turbo-compressor driven by the exhaust of the engine of the prime-mover. If a mechanically driven compressor is used it may be driven from the p.t.o. of the tractor.

Figure 2 shows a typical arrangement where the p.t.o. drives a shaft 12 mounted in bearings 13 via a universally jointed shaft 14. The shaft 12 is coupled to the compressor by a belt 15 running on a large driving pulley 16 and a small driven pulley 17. Depending on the characteristics of the compressor, additional gearing may be required to obtain the correct rotational speed. Alternatively the compressor may be driven by a separate engine if insufficient power is available from the prime-mover.

Speed-related spray metering may be provided, for example by a pump for the spray chemical driven from the shaft 12 or by a land wheel where appropriate.

Figure 3 shows a rear view of the boom, mounted on a vehicle. The spray liquid is contained in a tank 23. The centre section of the boom 18 is connected to the vehicle by known means, not shown, to eliminate oscillation and maintain its position parallel to the ground. It may also be adjustable for height. The outer sections of the boom are connected by hinges at 19 and 20. Additional hinges will be required in the outer sections to enable the complete boom to be folded to a convenient size for passage along public roads. The compressor 11 is connected to the boom by flexible connections at 21 and 22. At the boom hinge points flexible connectors are provided to join the sections of high-pressure air duct; alternatively 'plug-in' joints of the cone and socket type may be used.

Figure 4 shows an arrangement in which each chemical spray nozzle 24 has its own separate ejector duct 25, with one or more primary nozzles 26 fed by high-pressure air. The ejector ducts may be circular in plan when used with chemical spray nozzles giving a circular spray pattern, or may be elongated to an oval or rectangular section when used with chemical spray nozzles with an elongated distribution pattern. The ejector duct may conveniently be made as a plastic injection moulding incorporating a means for fixing it to the spray boom 27, a mounting for the primary air nozzle 28 and for the chemical spray nozzle 29, which may incorporate the nozzle feed pipe.

Figure 5 shows a rear view of the spray boom 30 mounted on a vehicle. In this arrangement the boom serves only as a structural member to carry the ejectors and chemical spray nozzles. It is connected to the vehicle by known means and has hinges to fold it for transport.

Attached to the boom are the ejector ducts 25, each carrying a chemical spray nozzle 24 and a primary air nozzle 26. It will be apparent that the arrangement just described produces a substantially spanwise air and spray flow.

The chemical spray nozzles are fed by a manifold pipe 31 and the primary air nozzles by a manifold pipe 32. The high pressure air supply is provided by a compressor 11 as described above.

Figure 6 shows a further alternative embodiment of the invention. A linear ejector extending spanwise along the whole width of the boom provides a high-volume low-pressure downward air stream as described above. An array of atomizers for the spray chemical 31 are positioned outside the ejector and carried by a manifold pipe 32 which feeds the spray chemical to the atomizers. Each atomizer is aligned so that the chemical droplets impinge upon the airstream from the ejector along a line shown in the diagram by point 33 and are then entrained by the airstream and carried on to the crop.

This arrangement is most beneficial where atomizers producing a diverging fan-shaped spray are used. Point 33, where the chemical droplets are entrained by the air stream, can then be chosen such that each fan-shaped spray intersects that from the adjacent atomizer on each side at that point. In this way an even spread of droplets across the whole span of the boom will be applled to the crop. However tn general it is believed to be more effective not to supply direct spray obliquely into the entrained air stream as some spray can be blown away.

Figure 7 shows a further alternative embodiment of the invention. Two spanwise linear ejectors 34 and 35 are arranged one behind the other, so as to provide two separate downward airstreams at 36 and 37. An array of atomizers for the spray chemical 38, mounted on and fed by a manifold pipe 39, are positioned between the two ejectors.

This arrangement provides two 'curtains' of air; one in front of and one behind the spray atomizers. These air curtains will move the foliage of the crop so as to maximise spray penetration and will isolate the atomizers from horizontal air movement due to wind or forward speed. By this means the problem of spray drift can be reduced.

The agricultural spray boom of Figure 8 is formed of a skeletal framework, 80, which supports two parallel continuous spanwise extending sources 81, 82 of air-jets. At intervals along the boomspan are spray nozzles 83 supported by the framework above and between the air-jet sources so that the spray liquid emerges from the nozzles just above the alr-jets.

In a specific form the air eft sources are the so-called linear or strip "air-movers" supplied by HMC-Brauer Limited as type SE in various lengths typically 300 and 600 millimetres as SE300 and SE600 respectively. In this specific form the spray nozzles are LURMARK (RTM) type 80 01 flat fan hydraulic nozzles.

The spray fan is arranged to be parallel with the span of the boom and the nozzles are spaced at about 500 millimetres apart.

Fans of 800 and 1100 angle are suitable but the boom may have to be used at different heights above crop to be sprayed when the angle is changed. Other nozzles may be used including air-assisted nozzles, for example the so-called twin fluid type, one of which is the AIRTEC (RTM) supplied by Cleanacres Machinery Ltd.

The exact construction used is not critical provided the boom is mechanically sound. As will be understood from the following the framework 80 should not obstruct the ingress of air from above the boom and the exit of air and spray below the boom. The boom can be used in conventional manner and fitted with appropriate attitude controls.

The air jet sources are supplied with air under pressure as indicated at 86 and 87. The hydraulic nozzles 83 are supplied with spray liquid as indicated at 88.

Skirts 891 and 892 may be fitted to extend down from the boom. These may be curved, as shown, or flat. The depth and spacing of these skirts depends on the use to be made of the boom. One skirt, or none, may be used.

In a specific form of the boom the air-movers 81, 82 are about 70 millimetres apart while the skirts are about 80 to 100 millimetres apart and about 70 to 100 millimetres deep. The nozzles are placed so that the spraysheet, before break up into spray, extends to below the outlet of the air mover. Typically the nozzle exit is about five millimetres above the air-mover outlet.

The air-movers make use of the well known Coanda effect. The air-movers have a very narrow lengthwise gap 90 from which air emerges and remains "attached" to the body of the air-mover bending around the body downwards, in the figure, while entraining a much larger volume of air drawn into the top of the boom to flow in the same direction. Typically up to ten times the mass of air emerging from the air mover is entrained by the jet. The spray of liquid from the nozzle is also entrained in the air flow to be carried by the air flow down to the crop. The spray of liquid from the nozzle can also entrain air to augment the air flow.

In the specific arrangement just described the air supply to the air-movers is at a pressure of about one-third bar, i.e.

between five and seven pounds per square inch while the spray liquid is supplied to the spray nozzles at about three bar. The gap 90 is adjustable to produce the Coanda effect at the given supply pressure although care is needed to avoid leaks from the air movers. With the given supplies the velocity of the air emerging between skirts 891 and 892 is about three to four metres per second and is fairly uniform along the length of the boom, apart from some fall-off at the ends.

The availability of a compressed-air supply makes possible the use of such air in the control of the height or attitude of the boom. For example the action of the crop canopy in reflecting or obstructing an air stream can be sensed and used to control the boom, while a quite small amount of air emerging in controlled manner at the end of a boom could provide rapid trimming of boom attitude.

Figure 9 shows another form of source of an air jet which can be arranged spanwise of the boom.

A tube 98 has a continuous or occasionally interrupted lengthwise slot 91. Over this slot are strips 92, 93 arranged to define a slit 94 through which air supplied under pressure to tube 98 can emerge as a jet in the form of a sheet. The strips 92, 93 are attached to tube 98 in any convenient way. If required one or both can be adjustable, using means not shown, to determine the slit size. In a very simple form the strips are of metal welded to the slotted metal tube 98 each with a continuous weld to make a seal and occasional welds to bridge the slit to give some rigidity. The slit can be set by a jig for this arrangement.

In a sprayboom one or two such tubes are arranged spanwise to produce downwardly directed air sheets, either directly or by Coanda effect, and entrain spray as described above. It may be possible to use the tube as part of the structure if it is metal. In another form it may be possible to extrude a light tube from plastic complete with the defined.slit.

It will be clear to those skilled in the art that various constructional arrangements including those described above, can be used as appropriate for spray arrangements embodying the invention.

Tests in which actual plants and simulated plants have been sprayed show an acceptably uniform deposit. A particularly important aspect of the spray action from the technique described is the improved penetration of dense canopies of broad and narrow leaved crops, especially the latter. The technique can also provide an adequate deposit on the underside of the leaves of broad-leaved plants when the sprayboom is used with the nozzles about 400 millimetres above the upper surface of the target crop, for 1100 nozzles. The boom can be moved at high speeds, towards the accepted maximum of about 6 metres/second (20 kph). The spray, being entrained in a well-directed air stream or curtain, Is contained and made resistant to drift, such as is caused by the wind.The skirts are believed to further significantly improve the resistance of the spray to drift caused by the wind.

In some cases it may be useful that the crop can be opened by the action of the entrained air and the boom can then be operated close to the top of the crop, further improving resistance to wind caused drift of spray. The velocity of the air emerging from the boom, from the skirts if fitted, may need to be adjusted for example to suit different crop canoples. To achieve this the air supply pressure and/or the gap 90 can be adjusted.

The techniques described permit small volumes of high pressure air to entrain much larger volumes of air which also includes spray droplets to produce efficient and effective spraying at much less air consumption than present proposals which use large volumes of low pressure alr. The spray droplets can be produced at a size which will produce the required deposit because the entraining air flow assists and directs the droplets, which in the absence of air flow would have to be sized with regard to the trajectory to reach the target crop. If smaller droplets can be used a much larger area can be sprayed from a given volume of spray liquid, improving the amount of useful travel of the sprayer.

Claims (17)

1. A method of spraying agricultural material from a sprayboom including: providing high pressure low volume air emerging along the span of the boom, causing or permitting said emerging air to entrain ambient air to produce a multiplied volume of air flowing from said boom along the length thereof, providing a source of material to be sprayed from said boom, causing or permitting material from said source to be entrained in said flow of a multiplied volume of air for spraying from said sprayboom along its length as a spray of liquid droplets.

2. A method according to Claim 1 including causing the air emerging along the boom to be from a linear "air mover".

3. A method according to Claim 1 including causing the air emerging along the boom to exhibit the Coanda effect to direct its flow.

4. A method according to Claim 1 in which the multiplied volume of air forms spray from said source.

5. A method according to Claim 1 including providing material to be sprayed as an agricultural liquid.

6. A method according to Claim 1 including causing the spray of liquid droplets to be formed from liquid from a hydraulic nozzle positioned above the emerging air as a lengthwise fan below the emerging air.

7. A spray boom having a spanwise duct to carry pressurized air to escape through spanwise elongate nozzles at the entrance to a passage forming an ejector to entrain atmospheric air at the top of the passage to flow through the passage and having means to spray droplets for entrainment in said entrained air flow so that mixed streams form a high volume air stream directed downwards over the whole span of the boom.

8. A sprayboom according to Claim 7 in which the passage is first convergent and divergent downstream.

9. A sprayboom according to Claim 8 in which said spray droplets are sprayed into said passage for entrainment therein in said airflow.

10. A sprayboom according to Claim 7 including more than one passage.

11. A sprayboom according to Claim 10 in which the or each passage is convergent-divergent.

12. A sprayboom according to Claim 7 in which the elongate nozzles are formed by a linear "air-mover".

13. A sprayboom for agricultural liquids having the general form of an ejector to which spray is added.

14. An arrangement for a sprayboom according to any one of Claims 7 to 13 and including active boom height control, using response to the effect of crop arranged to reflect air directed from the boom to indicate the closeness of the crop and maintain the boom in a required position over the crops or ground.

15. A sprayboom arrangement according to Claim 14 including a height sensor fitted to each end of the boom and coupled to a valve regulating an air pressure flow at that end of the boom, so as to control the boom attitude with varying ground conditions.

16. A method of spraying agricultural material from a sprayboom substantially as herein described with reference to the accompanying drawings.

17. An agricultural sprayboom substantially as herein described with reference to the accompanying drawings.