WO1999055467A2 - Spraying apparatus and method - Google Patents

Abstract

A modified droplet generator of the kind disclosed in WO97/16257 has a chamber sidewall formed with droplet-generating outlets and the sidewall providing the wall or target at which the change of liquid supply flow direction takes place prior to droplet generation and air-entrainment through the external outlets of the chamber. Liquid supply is through a supply duct (212) extending lengthwise of the chamber and formed with lateral outlets (214) to deliver liquid to the sidewall. As a result, the chamber can be in substantially extended format with a series of external outlets (208) along its length. In one embodiment the droplet generator completely straddles a crop row so as to produce inward spray plumes from all sides and above. A gas supply to the chamber which promotes droplet formation during use is maintained for an interval when spraying ceases so as to inhibit dripping from the outlets by pushing liquid back to tank.

Description

SPRAYING APPARATUS AND METHOD

This invention relates to mobile agricultural or horticultural boom type spraying apparatus generally of the kind as disclosed in our published PCT application PCT/GB96/02664, published as W097/16257 (shortened to WO 257 below), our reference P52821WO. The invention also relates to a method and apparatus for controlling dripping from spray-discharging outlets of agricultural or horticultural spray apparatus after spraying has ceased.

There is disclosed in our prior WO 257 specification spraying apparatus in which (see claim 2 of the claims as published with the International Preliminary Examination report dated 06.02.98), a droplet generator (24, 100) connected to a liquid and air flow supply means and adapted to produce a spray of liquid droplets therefrom; and the droplet generator comprising a chamber external outlet (49) adapted to allow an outward liquid supply through said outlet from an internal wall or target of an air and liquid supply chamber to be entrained in an air flow through said outlet from said air and liquid supply chamber, for droplet formation.

Such an arrangement is particularly advantageous to the extent that, as explained in our WO 257 specification, the apparatus and method enables the production of a jet of droplets in which effectively the liquid medium to be sprayed is diluted with air rather than water, whereby the volume of water required to be carried by the spraying apparatus for a given area of crop treatment is drastically reduced.

Moreover, the nature of the droplet generator is such that the dynamic and size characteristics of the droplets are such that they have the necessary energy and momentum in order to penetrate the crop effectively so as to achieve a thorough coating of external surfaces.

The present invention has for its obπect to provide a development of the method and apparatus disclosed m our prior WO 257 specification m which the same general principles of droplet generation are adopted, but in which an enhanced and improved method is used for enabling the droplet generation method and apparatus to be applied more effectively, and/or m a more versatile fashion to row crops and the like. The invention is not however limited to such applications since the benefits of the extended droplet generator disclosed herein are applicable to other spraying situations than row crops.

According to the invention there is provided a method and apparatus for spraying as defined in the accompanying claims.

In an embodiment of the invention described below there is provided apparatus for distributing droplets of liquid material from a central liquid supply, as defined m claim 2 of the amended claims setforth in the International Preliminary Examination Report dated 06.02.98 of PCT/GB96/02664, which reads :

2. Apparatus (52) for distributing droplets of liquid material from a central liquid supply (68) to a point (66) of liquid application comprising : a) liquid supply means (28) adapted to supply a liquid to be sprayed; b) air flow supply means (28) adapted to supply a flow of air to emerge with a spray of droplets produced by the apparatus; c) a droplet generator (24, 100) connected to said liquid and air flow supply means and adapted to produce a spray of liquid droplets therefrom; and d) said droplet generator comprising a chamber external outlet (49) adapted to allow an outward liquid supply through said outlet from an internal wall or target of an air and liquid supply chamber to be entrained in an air flow through said outlet from said air and liquid supply chamber, for droplet formation; characterised by e) said apparatus being in the form of mobile agricultural or horticultural boom-type spraying apparatus (52) ; and f) said spraying apparatus comprising a mobile spraying boom (54,56) adapted to be caused to pass, for example, lengthwise of multiple crop rows (62,64) while overlying said multiple rows during spraying; and g) said boom carrying multiple droplet generators (24,100) adapted to generate liquid droplets to effect simultaneous crop spraying of said multiple crop rows as said boom overlies said rows; and h) said droplet generators (24,100) being adapted to generate multiple droplet sprays capable of traversing the distance between said multiple droplet generators carried by said boom (54,56) and said crop located below said boom as said boom is caused to travel over said crop, and each droplet generator being capable also of producing its own diverging spray jet (72) adapted to effect spray coverage of its own adjacent portion of said crop so that said crop below said boom is appropriately sprayed. Attention is drawn to the features of paragraph d) of the above claim 2 which provide that a chamber external outlet allows an outward liquid supply through the outlet from an internal wall or target of an air and liquid supply chamber to be entrained in an airflow through the outlet from the air and liquid supply chamber, for droplet formation. In the embodiments of the present application, there is adopted an extended chamber having the format of a tube or duct or conduit in which the external outlets are formed. The tube may for example be in the form of a dropleg with the external outlets provided at intervals along the length of the dropleg. In one embodiment of ^'the invention the dropleg has a format or shape which is generally U- or C- shaped, or otherwise so as to be able to straddle a crop row, with the crop row passing between the ends of the limbs of the dropleg, and the outlets from the chamber being formed so that, in use, the sprays of liquid droplets therefrom travel inwardly and/or downwardly and/or upwardly on two or more sides of the crop so as to effect simultaneous coverage thereof. Thus-far it is clear that the chamber of the droplet generator may have an extended format with outlets provided at intervals along its length, to suit the requirements of the particular application of the droplet generator. We take the opportunity to comment that in our published WO application the droplet generator is in the format of a single relatively short chamber from which outlets open to produce two or more jets on opposite sides of the chamber, such as shown in Fig 7 of the drawings thereof. There is disclosed in claim 25 on page 31 of the published application an arrangement in which the droplet generator comprises at least two chambers disposed in tandem or in-line relationship, with liquid and air supply means extending from one of said chambers to the other. However, this arrangement amounts effectively to a duplication of the individual configuration disclosed in Fig 7 of the application, and therefore does not in itself offer a particularly convenient means for achieving an extended spray format of the kind which is desirable for certain row crops (such as field beans) and other applications, as mentioned above.

Turning now to the internal arrangements in the embodiments whereby the air and liquid supplies are provided to the chamber outlet openings, it is in this area that the principal advance with respect to our above WO 257 specification has been made. In the embodiment's of the WO 257 specification it will be seen that the internal arrangements of the droplet generation chamber are such that in most cases the incoming supply of air and liquid is directed generally axially or lengthwise of the chamber towards a closed end wall thereof. At the end wall the liquid supply intercepts the end wall and then moves generally laterally with respect to its incoming direction and thus undergoes a first approximately right-angled change of direction, followed by a second (generally right angled change of direction at the radially outermost periphery of the chamber end wall, and thus moves (as a liquid film) generally in the opposite axial direction along the chamber side wall(s) towards the chamber external outlets which, in the embodiments, are located at least a short distance axially away from the chamber end wall. Such is the Applicants' understanding of the mechanism in terms of internal flow within the droplet generation chamber of the WO 257 specification, although it will be readily understood that these matters are not particularly easy to study in a manner which will establish the mechanics beyond doubt in the absence of laboratory conditions and facilities for internal inspection, use of dyes etc. Nethertheless, we have now discovered that the generally chamber-like format of the droplet generator, including a chamber end wall is not necessarily an essential part of the droplet generation mechanism, as indeed is foreshadowed by the above-quoted claim 2. With regard to the function of the end wall of the chamber, it is currently thought that this has a function in relation to providing a direction-change function for the liquid flow in the embodiments disclosed in the above WO 257 specification. In otherwords, the end wall causes a change of direction of the generally lengthwise liquid flow (generally axially from the jet at the other end of the chamber) and this is followed by a further change of direction, as mentioned above.

An object of the present invention is to provide means offering a functionality in relation to droplet generation which is comparable with that offered by the method and operation of the WO 257 specification but which offers additional versatility for the system. One example of such versatility is the ability to product droplet generation in a manner such that a crop row is conveniently subjected to a total spraying step or operation so that successive plants in the row receive treatment by droplets not only laterally and from below but on both sides of the row and perhaps also from above. Such a spraying operation can be provide from conventional spraying equipment utilising conventional spraying nozzles arranged in banks or rows on either side of the crop row and likewise above (these being in one arrangement disposed in a generally U-shaped spraying bar configuration) but conventional spray nozzles lead to all the well-known deficiencies of such nozzles in terms of the dynamic and water-consumption parameters of their operation as enumerated in the WO 257 specification. Comparable arrangements of droplet generators in accordance with the illustrated embodiments of the WO 257 specification can likewise be arranged in corresponding banks or rows (and indeed significantly fewer of these generators are needed than in the case of conventional spray nozzles) but a more convenient and effective arrangement is desirable. This represents just one example of the desired enhanced versatility. Others include an ability to modify the construction of the droplet generator itself so that extra numbers of external outlets can be provided conveniently, and/or the mechanical construction of the generator itself is freed from certain design constrains inherent in the illustrated embodiments of the WO 257 specification. An object of the present invention is to provide improvements in relation to one or more of these matters or generally. According to the invention there is provided a method and apparatus as defined in the accompanying claims .

In an embodiment of the invention described below an internal wall or target of the air or liquid supply chamber from which an outward liquid supply is allowed to be entrained in an airflow through the external outlet of the chamber, is provided by a wall of the chamber in which the outlet is formed. The arrangement is such that the flow path of the liquid through the chamber includes at least a change of liquid flow direction prior to intercepting the wall or target, and another change of direction on passing into the outlet from the chamber. By these features there is provided a simplified arrangement in which the droplet generation function of the chamber is enhanced by employing the (for example) side walls of the chamber themselves to intercept the liquid supply and to effect the consequential change of liquid flow direction, whereby the facility becomes available to deliver liquid flow to the side walls of the chamber (for the primary change of flow direction) from lateral outlets in a lengthwise extending liquid delivery conduit .

Also in the embodiment described below the liquid supply means itself comprises structure defining lateral flow-producing means whereby the liquid enters the chamber flowing in a first direction and is then caused by the lateral flow-producing means to flow laterally with respect thereto and thus to intercept the wall or target. Thus, in this embodiment, the example of a lengthwise conduit with lateral outlets or jets constituting the lateral-flow producing means represents just one mode of achieving this effect. It is expected that other hardware may be capable of producing comparable effects, which could be devised by the skilled person. By the use of a liquid supply conduit extending lengthwise of the droplet-generating chamber, the conduit having a plurality of lateral outlets formed therein at intervals lengthwise thereof, and the chamber also having a corresponding plurality of external outlets formed therein at the same or different lengthwise spacings, there results a droplet generator of length which may be chosen according to need. For example, the droplet generator can be of a sufficient length and having sufficient external outlets that it conveniently straddles a crop row on both sides and the top thereof so as to produce simultaneously numerous droplet plumes, or spraying jets which are directed inwards with respect to the croprow from below and laterally and laterally-and- above and above etc. In the embodiments the use of an arrangement in which the target for the inward liquid flow is provided by a sidewall of the chamber, and the liquid supply itself incorporates means providing a primary change in liquid supply flow direction, these features provide in combination the ability to extend the chamber, generally without limit, in terms of its longitudinal extent (as may be needed for providing a wrap-around spraying arrangement as used in the embodiment of Fig 3 for delivering spray to both sides and above a crop row) , and indeed without limitation on the number of droplet-emitting outlets.

The feature of providing a liquid supply arrangement which itself incorporates a change of liquid flow direction enables the droplet generator to have the same liquid and air supply inlet flow arrangements as the short chamber droplet generator of the WO 257 specification in combination with the selective location of the flow direction change at any desired lengthwise location in the chamber whereby multiple liquid feed points to the target wall can be provided with corresponding droplet-emitting non-aligned chamber outlets, whereby a steady state condition may be generated in terms of liquid supply inflow and droplet-format liquid outflow, per unit length of the chamber.

To put it another way, the liquid supply inflow arrangements are such that a convenient and effective system is provided for delivering liquid and air flow supplies to an extended target wall structure at any chosen location lengthwise of the chamber, whereby the corresponding jets or plumes of liquid droplets entrained in the airflow can likewise be produced and directed at any chosen angle, with a degree of versatility not possible in the WO 257 arrangement.

Turning now to the second aspect of the invention relating to the method and apparatus for controlling dripping from said spray-discharging outlets or agricultural or horticultural spray apparatus, this aspect of the invention relates directly technically to the broadest aspect of the preceding embodiments, namely spraying systems in which both a liquid and a gas (usually air) supply are used in order to produced improved characteristics of droplet generation both with respect to droplet size control and with respect to droplet dynamics. The technique also has the advantage that the active ingredient of the spraying medium (which is usually provided in the form of a liquid spraying concentrate) is effectively "diluted" by the air rather than (as in conventional spraying systems) by water or other liquid medium, whereby the size and weight constraints imposed on the system by the need to carry around large volumes of water are greatly reduced. At the same time that the above-mentioned "air dilution" technique enables big advances to be made in terms of vastly reduced volumes of liquid spray medium being needed for application to crops, with correspondingly vastly reduced environmentally-damaging effects on other plants and watercourses, there has developed a corresponding need to reduce other environmental aspects of the use of spraying systems, including reduced dripping from spraying nozzles and other outlets after spraying has ceased. This aspect of the present invention seeks to provide an improved means for inhibiting or eliminating dripping from said spray nozzles and other outlets.

Prior proposals in this regard include:

GB 677,655 (Allman) GB 703,425 (Dorman) WO 96/31118 (Knight)

and all three of the above prior proposals are based upon the concept of using a suction-generating system to, effectively, suck out the liquid spraying medium from the supply lines to the nozzles after spraying has ceased. The two GB specifications show relatively simple systems, but their simplicity arises partly from the fact that they date from the 1950 '2 and do not show the multiplicity of spray outlets/nozzles used in a modern 40 metre boom. The above WO specification, while adopting a technically- related approach to pumping-out the spraying medium, attempts to show the corresponding hydraulic "plumbing" needed for such a system in a modern large agricultural boom-type implement and the resultant complexity is technically and commercially daunting. Accordingly, one important object of the present invention is to provide a method and apparatus for drip control which offers a simpler and less costly approach to drip control, in terms of the extent of equipment needed to be added to the basic equipment which is required for spraying purposes in any case . We have discovered that in the case of spraying systems which utilise both a gas (usually air) and a liquid supply for droplet generation purposes, there can be adopted a simple adaptation of the equipment m order to achieve drip-control. In simple terms, if the air supply is maintained for at least an interval after the supply of liquid spray medium has been interrupted (m order to cease spraying) then the air supply can be used effectively to push-back the liquid supply to the nozzle or outlet through the supply conduit connected to the nozzle or outlet. The liquid medium can thereby be returned to tank, or possible to some other temporary reservoir if such is more convenient.

In the described embodiments of this aspect of the invention the anti-drip function is achieved, m the above manner, with the absolute minimum of additional hardware and control systems since the entire system of liquid and air supply conduits to the nozzles/outlets is present in any case and the principal modification needed is a fairly minor change m the valve arrangement for controlling the liquid supply routes between the pump and reservoir and nozzles/outlets .

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings m which: Fig 1 shows a longitudinal section through an end portion of a droplet generator, the section being taken

Fig 2 shows an end view on the arrow II in Fig 1; Fig 3 shows an elevation v ew of an elongated droplet generator forming an embodiment of the droplet generator of Figs 1 and 2, and

Fig 4 shows in simple block diagram format the pneumatic/hydraulic/power-flow interconnections of the main elements of a spraying system forming a further embodiment of the invention incorporating an anti-drip flow control system.

We refer to our above-discussed and prior published specification W097/16257 and hereby incorporate in the present application the entire text and drawings of that prior application for disclosure purposes.

Specifically, there is disclosed in the WO 257 specification (and the reference numerals in parentheses in this present paragraph refer to reference numerals used in the WO 257 specification, apparatus (52) for distributing droplets of liquid material from a central liquid supply (68) to a point (66) of liquid application comprising: a) Liquid supply means (28) adapted to supply a liquid to be sprayed; b) Air flow supply means (28) adapted to supply a flow of air to emerge with a spray of droplets produced by the apparatus; c) A droplet generator (24, 100) connected to said liquid and air flow supply means and adapted to produce a spray of liquid droplets therefrom; and d) Said droplet generator comprising a chamber external outlet (49) adapted to allow an outward liquid supply through said outlet from an internal wall or target of a air or liquid supply chamber from said air and liquid supply chamber, for droplet generation, characterised by; e) Said apparatus being in the form of mobile agricultural or horticultural boom-type spraying apparatus ( 52 ) ; and f) Said spraying apparatus comprising a mobile spraying boom (54,56) adapted to be caused to pass, 'for example lengthwise of multiple crop rows (62,64) while overlying said multiple rows during spraying; and g) Said boom carrying multiple droplet generators (24,100) adapted to generate liquid droplets to effect simultaneous crop spraying of said multiple crop rows as said boom overlies said rows; and h) said droplet generators (24,100) being adapted to generate multiple droplets sprays capable of traversing the distance between said multiple droplet generators carried by said boom (54,56) and said crop located below said boom, as said boom is caused to travel over said crop, and each droplet generator being capable also of producing it own diverging spray jet (72) adapted to effect spray coverage of its own adjacent portion of said crop so that said crop below said boom is appropriately sprayed.

Turning now to matters disclosed in Figs 1 and 2 of the accompanying drawings, there is shown a droplet generator 200 corresponding to the droplet generators (24,100) of the WO 257 specification and connected to liquid supply means 202 and air flow supply means 204.

Droplet generator 200 comprises a chamber 206 having lengthwise-spaced external outlets 208 adapted to allow an outward liquid supply through the outlets from an internal wall or target 210 of the air and liquid supply chamber 206 and to be entrained in an air flow through the outlet 208 from the chamber for droplet formation.

Looking now at the details of construction of the above-mentioned principal components of droplet generator 200, chamber 206 is in the form of a lengthwise-extending tube or conduit formed for example of a suitable alloy or aluminium material and having a generally circular cross- sectional shape as shown in Fig 2. A circular cross section is not essential and some deviation from this would not necessarily significantly a fect the performance of the device. Likewise, the chamber may be formed of alternative materials, including moulded or otherwise- formed polymeric products. Chamber 206 has a length chosen according to need arising from the required application. Thus, in the case of the embodiment of Fig 3 a length of the order of about 2 meters may be required for certain crops. At the end of chamber 206 remote from the end (the right hand end m Fig 1) at which the liquid supply enters the chamber, the chamber is closed by a end wall (not shown because Fig 1 only shows an end portion of the chamber at its other end) . Thus, chamber 206 is m the form of an elongated generally cylindrical closed tubular structure .

Liquid supply means 202 comprises a conduit 212 mounted within chamber 206 and generally centrally thereof and extending lengthwise thereof at a constant spacing from the walls thereof. To maintain such spacing there may be provided internal support means (not shown) such as webs or stays constructed to minimise interference with the free flow of air and liquid lengthwise or laterally of the chamber and over the internal surfaces of its inner walls.

Conduit 212 has formed therein lateral outlets or lets 214 which constitute lateral flow-producing means to produce a lateral flow of liquid to intercept internal wall 210 of chamber 216. Outlets or ]ets 214 are located at spaced intervals lengthwise of conduit 212 to produce respective laterally-directed liquid flows to intercept wall 210 at corresponding intervals. The outlets 218 in wall 210 are carefully located so as to be in-line with the outlets or nets 214 provided m conduit 212. Airflow supply means 204 is provided to the annular space between the internal wall 210 of chamber 206 and the external surface of conduit 212. The air flow supply is connected thereto from the pump/compressor as described m the WO 257 specification and air travels lengthwise of the annular-format chamber or space 216 and passes out through outlets 218. These latter are constructed substantially as described m the WO 257 specification, but are simply well-defined apertures of generally the same dimensions as described m the WO 257 specification. In use, the liquid and air flow supplying 212 and

214 are connected to their corresponding pressurised sources, and droplet generation commences at the chamber outlets 218 accordingly. Conditions of liquid and air flow supply pressures are substantially as described in the WO 257 specification.

It will be noted m the embodiment of Figs 1 and 2 that by virtue of the non-alignment of the outlets or nets m conduit 212 and the external outlets 218 m chamber 216, there are two changes of direction of the liquid flow within the chamber, namely firstly on intercepting the chamber wall 210 as shown at 218, and secondly on passing out through outlet 208 as shown at 220.

In the embodiment of Fig 3 the chamber 206 is formed into a generally C-shaped structure (with central liquid and air supply) so as generally to enclose and straddle a crop row 222 with spray nets 224. The droplet generator 200 is supported from the sprayer boom (not shown) and thus straddles its crop row, and corresponding droplet generators are provided for each crop row and a complete coverage of crop surfaces can be achieved while the boom moves lengthwise of the rows.

Turning to the embodiment of Fig 4, there is shown apparatus 300 incorporating a method and means 302 for controlling dripping from spray-discharging outlets or nozzles 304, 306, 308 of agricultural or horticultural spray apparatus 310 after spraying has ceased.

In Fig 4, the outlets 304, 306, 308 correspond to the droplet generators 200 of the preceding embodiment and are identified as chambers and N and N-1 and 1 designating three of a long series of such outlets provided on a substantial agricultural boom structure (not shown) forming part of spray apparatus 310.

In this embodiment, the outlet 304, 306, 308 happen to be constructed as described above in terms of the droplet generation technique and in terms of the air and liquid supplies thereto. However, this embodiment of the invention can operate equally effectively in relation to other system for droplet generation incorporating both liquid and air supplies to the droplet-generating outlet or nozzle.

Thus, outlets 304, 306, 308 are connected to a common air supply line 312 which is supplied by compressor 314 driven by the engine or tractor 316 which likewise drives pump 318. Lines 320 and 322 designate diagrammatically the power coupling between the tractor engine and compressor 314 and pump 318 respectively.

The pump 318 draws liquid spray medium from tank 324 via valve 326 and discharges same through liquid supply line 328 coupled to all outlet/chambers 304, 306, 308. A control 330 which is integrated with the spraying control system of tractor 316 is coupled by electrical control lines 332 and 334 to liquid control valve 326 and a pneumatic control value 336 in air supply line 312. In use, apparatus 300 operates as follows. During spraying, pump 318 draws fluid medium from tank 324 through line 325 and valve 326 and delivers same to chambers 304, 306, 308 through fluid line 328. Compressor 314 delivers air to the chambers through pneumatic line 312. When the tractor driver decides to stop spraying, control 330 causes valves 326 to interrupt the supply of liquid spraying medium to line 328 and delivers the output of pump 318 to tank 324. The supply of liquid to chambers 304, 306, 308 ceases.

Control 330 causes valve 336 to continue to deliver air through pneumatic line 312 to chambers 304, 306 and 308 for at least a period of the order of 10 to 30 seconds after values 326 has diverted the outpump of 318 to tank 342. During this period, the pneumatic pressure in chambers 314 and 306 and 308 is maintained and only slightly if at all diminishes as a result of the absence of liquid pressure. This pneumatic pressure is applied to the orifice m each chamber through which the liquid medium enters the chamber and causes the liquid to flow back through the liquid supply line 328 towards valve 326. That valve has been caused by control 330 to permit the liquid to pass through line 325 to line 324. Thus, the maintained pneumatic pressure causes emptying of the liquid supply line 328 to tank.

Claims

1. Apparatus (52) for distributing droplets of liquid material from a central liquid supply (68) to a point (66) of liquid application comprising : a) liquid supply means (28) adapted to supply a liquid to be sprayed; b) air flow supply means (28) adapted to supply a flow of air to emerge with a spray of droplets produced by the apparatus; c) a droplet generator (24,100) connected to said liquid and air flow supply means and adapted to produce a spray of liquid droplets therefrom; and d) said droplet generator comprising a chamber external outlet (49) adapted to allow an outward liquid supply through said outlet from a closed internal wall or target of an air and liquid supply chamber to be entrained m an air flow through said outlet from said air and liquid supply chamber, for droplet formation; e) said apparatus being m the form of mobile agricultural or horticultural boom-type spraying apparatus

(52) ; and f) said spraying apparatus comprising a mobile spraying boom (54,56) adapted to be caused to pass, for example, lengthwise of multiple crop rows (62,64) while overlying said multiple rows during spraying; and g) said boom carrying multiple droplet generators (24,100) adapted to generate liquid droplets to effect simultaneous crop spraying of said multiple crop rows as said boom overlies said rows; and h) said droplet generators (24,100) being adapted to generate multiple droplet sprays capable of traversing the distance between said multiple droplet generators carried by said boom (54,56) and said crop located below said boom as said boom is caused to travel over said crop, and each droplet generator being capable also of producing its own diverging spray j et (72) adapted to effect spray coverage of its own adjacent portion of said crop so that said crop below said boom is appropriately sprayed; characterised by; l) said internal wall or target of said air and liquid supply chamber from which an outward liquid supply is allowed to be entrained m an airflow through said external outlet is provided by a wall of said chamber in which said outlet is formed; and l) the arrangement being such that the flow path of said liquid supply through said chamber includes at least a change of liquid flow direction prior to intercepting said wall or target.

2. Apparatus for distributing droplets of liquid material from a central liquid supply to a point of liquid application comprising a droplet generator connected to liquid and air flow supply means and comprising a chamber having an external outlet, the apparatus being m the form of mobile agricultural and horticultural boom-type spraying apparatus, characterised m that an internal wall or target of the chamber is provided by a wall of the chamber m which the outlet is formed.

3. Apparatus according to claim 1 or claim 2 characterised by said liquid supply means itself comprising structure defining lateral flow-producing means whereby said liquid enters the chamber flowing m a first direction and is then caused by said lateral flow- producing means to flow laterally with respect thereto and to intercept said wall or target.

4. Apparatus according to claim 3 characterised by said liquid supply means comprising a liquid supply conduit having at least one lateral outlet or let constituting said lateral flow-producing means in a sidewall of said conduit.

5. Apparatus according to claim 4 characterised by said conduit extending lengthwise of said chamber and having a plurality of said lateral outlets formed therein at intervals lengthwise thereof and said chamber also having a corresponding plurality of offset external outlets formed therein at the same or different lengthwise spacmgs.

6. A method for distributing droplets of liquid material from a central liquid supply to a point of liquid application comprising providing a droplet generator connected to liquid and air flow supply means and causing an outward liquid flow through an outlet of said chamber from an internal wall or target to be entrained m an air flow through said outlet, the apparatus being in the form of mobile agricultural or horticultural boom-type spraying apparatus, characterised by causing a wall of said chamber in which said outlet is formed to be the internal wall or target from which said liquid supply is entrained in the air flow through said outlet, and causing the flow path of the liquid through the chamber to include at least a change of liquid supply flow direction prior to intercepting said wall or target.

7. A method of controlling dripping from spray- dischargmg outlets of agricultural or horticultural spray apparatus after spraying has ceased, the method comprising: a) providing a plurality of said spray outlets and associated supply means to supply to said outlets an outward flow of a liquid medium to be sprayed from a reservoir thereof, whereby said outlets can effect spraying; b) providing liquid flow control means adapted to control liquid in said supply means so as to be caused to flow away from said outlets when spraying ceases thereby to inhibit dripping from said outlets; c) causing said liquid flow control means to effect said flow control of said liquid away from said outlets when spraying ceases. characterised by; d) providing said supply means for said spray outlets comprising both a liquid supply and a gas supply, and said outlets being adapted to produce a spray of droplets of said liquid utilising said liquid and said gas supply; and e) providing said liquid flow control means comprising said gas supply and causing said gas supply to said outlets to be maintained for at least an interval of time after said liquid supply has been interrupted in order to interrupt spraying whereby said maintained gas supply causes at least partial inward flow of said liquid away from said outlets and thereby inhibits dripping of said liquid from said outlets.

8. A method of controlling dripping from spray- discharging outlets of agricultural or horticultural spray apparatus after spraying has ceased, the method comprising causing a gas supply to spray discharging outlets of said apparatus to be maintained for at least an interval of time after a liquid supply thereto has been interrupted in order to interrupt spraying, whereby said maintained gas supply causes at least partial inward flow of said liquid away from said outlets and thereby inhibits dripping of said liquid from said outlets.

9. A method according to claim 7 characterised by said liquid flow control means comprising controllable valve means and said step of causing said inward flow of said liquid away from said outlets comprising causing said valve to route said liquid to said tank.

10. Apparatus for controlling dripping from spray- dischargmg outlets of agricultural or horticultural spray apparatus after spraying has ceased, the apparatus comprising : a) a plurality of spray outlets and associated supply means to supply to said outlets an outward flow of a liquid medium to be sprayed, from a reservoir thereof, whereby said outlets can effect spraying; b) liquid flow control means adapted to control liquid in said supply means so as to be caused to flow away from said outlets when spraying ceases, thereby to inhibit dripping from said outlets; characterised by: c) said supply means for said spray outlets comprising both a liquid supply and a gas supply, and said outlets being adapted to produce a spray of droplets of said liquid utilising said liquid and said gas supplies; and d) said liquid flow control means comprising said gas supply and said gas supply being adapted to be maintained for at least an interval of time after said liquid supply has been interrupted in order to interrupt spraying, whereby said maintained gas supply causes at least partial inward flow of said liquid away from said outlets and thereby inhibits dripping of said liquid from said outlets.

11. Apparatus for controlling dripping from spray- discharging outlets of agricultural or horticultural spray apparatus characterised by liquid flow control means comprising a gas supply to said outlets which is adapted to be maintained for at least an interval of time after a liquid supply thereto has been interrupted m order to interrupt spraying, whereby said maintained gas supply causes at least partial inward flow of said liquid away from said outlets and thereby inhibits dripping of said liquid from said outlets.

12. Apparatus according to claim 10 characterised by said liquid flow control means comprising controllable valve means and said valve means being adapted to route said liquid to said tank during said inward flow of said liquid away from said outlets.