WO2000072975A1 - Atomiser - Google Patents

Abstract

An atomiser including a cylindrical screen (16) fitted edgewise in grooves within opposed end cap (17) and air deflector (15), wherein the end cap (17) and air deflector (15) are secured together with bolts (20, 21). The screen (16) mesh size is one of the factors controlling droplet size. Another controlling factor is the size of the air deflector (15); its diameter is greater than the screen (16) which leads to generally larger droplet sizes. The atomiser also includes a secondary cut-off valve (47) within a nose cone (31). The atomiser is connected to a combined check valve and variable restrictor unit with an aerodynamically compact body, the shape of the body minimising undesired airflow turbulence that may lead to spray drift.

Description

ATOMISER FIELD OF THE INVENTION

This invention relates to an atomiser for atomising liquids for agricultural spraying purposes.

BACKGROUND OF THE INVENTION

There are known spray arrangements utilising an atomiser head rotated by passing air flow to atomise liquids. Typically and in simple terms these comprise an atomiser assembly that rotates at high speed, a number of blades which under the influence of quickly moving air flow effect spinning of the atomiser head, a central stationary liquid outlet which introduces liquid into the atomiser assembly, and a perforated cylindrical screened cage through which the liquid passes. The centrifugal force experienced by the liquid and the cage, effect formation of very small liquid droplets or, in other words, atomise the liquid. The speeds at which the atomiser assembly rotates will often exceed 4000 m with 6000 φm being typical but greater speeds are not unknown. At these rotational speeds the centrifugal forces experienced by spinning components can be very great.

These factors have led in the past to the cage comprising a perforated cylindrical screen wall with two end plates one at either end. The wall generally is a fine gauge wire gauze made from a strip of gauze rolled into a cylinder with the ends soldered together. This provides a lightweight construction for the wall which is structurally weak and very readily compressed or otherwise deformed by hand. The end plates are soldered to respective ends of the wall which provide structural rigidity and integrity. The end plates also typically have mounting components such as threaded inserts for mounting the cage to the body of the atomiser head.

This construction provides a cage that can withstand the forces experienced by the cage whilst spinning at operating speeds. However, the manufacture of such a cage is complex and expensive. Great care is required to ensure the cage is balanced about its cylindrical axis since any imbalance may set up unacceptable vibrations and possibly lead to failure of the cage or atomiser head.

A terrestrial vehicle spray machine will typically have four or more atomiser heads and use a large fan and ducting arrangement to supply air at high speed to flow past the atomiser head to effect rotation of the atomiser assembly and also to carry the atomised liquid away from the machine. An airborne spray machine, such as is commonly known as a crop duster, makes use of air flowing past the atomiser head to effect the rotation thereof and will typically include ten to twenty atomiser heads.

In practice a cage has a relatively short working life due to failure of the wall. Such failure occurs due to a number of factors including physical damage due to sticks and stones striking the cage, and the corrosive or abrasive or both effects of the liquids being sprayed through the material of the cage.

The number of atomiser heads in a typical spray machine and the frequent need to replace cages leads to considerable maintenance costs for the operator of such a spray machine. Further, the manufacture of the cages leads in part to a considerable cost, either reflected as a cost to the purchaser or a reduction in profit to the manufacturer.

It is a proposed object of this invention to provide an atomiser head, an atomiser assembly or a kit to obviate or minimise at least one of the aforementioned problems, or at least provide the public with a useful choice.

SUMMARY OF THE INVENTION The invention may be said to reside, not necessarily in the broadest or only form, in an atomiser assembly including: an air deflector; an end cap spaced from and facing the air deflector; a tubular perforated screen edgewisely disposed between the air deflector on one side and the end cap on the other side; and, fastening means between the end cap and air deflector adapted to compressively hold therebetween the screen; and, the air deflector and the end cap each respectively having screen edge locating means adapted to respectively locate an edge of the screen and resist relative movement thereof under the influence of centrifugal force experienced at atomiser assembly rotational operating speeds.

It will be appreciated that the screen itself may be independent from the end cap and air deflector and replaces the cage of previous designs described under the heading BACKGROUND OF THE INVENTION above. When not installed the screen is quite readily deformed by hand. It may have a quite small cost of manufacture. When a screen needs to be replaced the fastening means are undone, the end cap removed, the screen replaced by a relatively cheap new screen, the end cap reinstalled, and the fastening means done up.

In one form the screen is retained at each end by the screen edge locating means bearing against the radial outer surface of the screen proximal the respective end edge. This may take the form of a groove within which the end edge is received.

Alternatively, the screen edge locating means may be an annular projection within which the screen edge fits. The annular projection may be continuous, or alternatively discontinuous but in use locates the screen and resists relative radial movement thereof. The groove may be annular and of slightly greater diameter than the diameter of the screen, of width to accept the edge of the screen and of depth to allow firm location of the edge of the screen within the groove. Further the groove may be continuous. A continuous groove does not require the edge of the screen to be cut to allow for interlocking with a discontinuous groove. The screen may have an edgewise thickness of approximately 1 mm, with the groove depth of 1 to 2 mm deep, and the groove width of approximately 1.5 mm. It has been found that these groove dimensions permit quite simple assembly whilst providing a snug fit for the screen. The screen is readily deformable and may have some eccentricity. For the just mentioned conditions the screen may be manipulated and inserted into the groove which holds the screen against substantial radial movement.

In one form both the air deflector and the end cap have a respective groove which is recessed within the face thereof. This has been found to provide an easily manufactured form.

Further, the width of the groove may be selected to permit a snug fit of the screen therein. A snug fit is preferred since it locates the screen and holds the screen in place during installation which is therefore made easier. A looser fit can be used but requires care in placement of the screen during installation.

The screen may be made from stainless steel gauze. The gauze may be of 8 to 20 mesh. The wire thickness is typically about 0.3 to 1 mm.

In one form, the end cap or air deflector or both, are manufactured of a plastics material. This plastics material may be a plastic commonly known under the trade name DELRIN (trade mark of Du Pont, a UN. stabilised acetal resin, of grade known at least in Australia as Black Acetyl) but other suitable materials may be used including fibre glass. Alternatively, the end cap or air deflector or both are manufactured of aluminium but other suitable materials such as monel metal and stainless steel may be used.

In one form, the screen is cylindrical, the fastening means are elongate, and the end cap and air deflector are circular in shape normal to an axis of rotation of the atomiser assembly.

According to one form the screen may be manufactured from a sheet of gauze, with two opposed edges of the sheet being soldered together, and a row of solder to balance the screen being placed opposite the soldered edges. Alternatively the screen may be manufactured from a sheet of gauze, with two opposed edges of the sheet being spot welded together.

In one form the diameter of the air deflector is greater than the diameter of the screen by at least 5 mm and has a flared portion adapted to deflect air flow away from the screen. This has been found to lead to the production of a larger droplet size which is often desirable to minimise excessive spray drift caused by the production of very fine droplets. Generally, it is believed preferable to reduce turbulent air flow past the screen and so the flaring may be gradual rather than abrupt but even some quite abrupt flaring has been found to lead to increased droplet size. The flaring of the air deflector in one form is concave whereas in another form is convex. The convex flaring is more streamline. Previously known atomisers, of the type discussed under the heading

BACKGROUND OF THE INVENTION above, the cage was of the same diameter or greater than the atomiser frame from which the blades project. It has been found that even a concave flaring of 10 mm radius between the atomiser body and directly transverse thereto has an advantageous effect. It is however preferable to use a less abrupt flaring.

According to another form, the diameter of the end cap is greater than the diameter of the screen and has a flared portion adapted to deflect air flow away from the screen. This has been found to improve dispersion of the atomised liquid away from the atomiser assembly.

In one form the elongate fastening means is small in diameter compared with the diameter of the screen. It has been found that relatively thin obstructions within the screen do not have too great an effect on the a-omisation of the liquid. Where the screen diameter is 73 mm an elongate fastening rod with a diameter of 3 mm has not been found to significantly effect the uniform atomisation of the liquid. The elongate fastener means may be a plurality of bolts and associated nuts or threaded holes.

In one form the atomiser assembly has an axial shaft in communication with a source of liquid to be atomised and sprayed. The liquid is supplied under pressure from the source and liquid flow is controlled by a primary valve remote from the atomiser assembly.

The invention may be said to reside, again not necessarily in the broadest or only form, in an atomiser head including an atomiser assembly substantially as herein described axially mounted to an atomiser frame, and a plurality of blades adapted to effect rotation of the atomiser frame around the axis of the atomiser frame due to air flow past the blades.

In one form the atomiser head includes a secondary cut-off valve adapted to cut off liquid flow when the pressure of the liquid is less than a predetermined pressure which may be 4 PSI (27 kPa). This valve can reduce draining of pipes supplying the atomiser head with liquid to be sprayed and may lead to a faster response in turning on or off the liquid being atomised by the atomiser head.

The blades may be spaced around and project radially from the atomiser frame, and the pitch of the blades being adjustable and thereby adapted to permit the speed of rotation of the atomiser assembly to be set for a specific speed of air flow. By adjusting the length and pitch of the blades, an atomiser head may be used in different machines such as in a terrestrial machine or an airborne machine. Further, as speed of rotation of the atomiser assembly is a factor in determining liquid droplet size, then adjusting the blades in a certain spray arrangement allows control of the droplet size and may permit the same sprayer to spray liquids that otherwise would have quite different droplet size. As previously mentioned, droplet size is an important factor in spray drift.

According to one form, the air deflector is integral with an atomiser body portion of the atomiser frame. In another form the air deflector is separate from and secured to the atomiser body of the atomiser frame. It will be appreciated that the invention may reside in an atomiser assembly or an atomiser head including such an atomiser assembly. Whilst it is generally preferred to make the air deflector as merely part of the atomiser body it has been found that a separate removable air deflector may be fitted to the atomiser body of previously manufactured atomiser bodies allowing the invention to be retrofitted thereto. The invention may be said to reside, again not necessarily in the broadest or only form, in kit including an atomiser or an atomiser assembly as herein described. In one form the kit also includes a mounting block and a combined check valve and variable restrictor unit. The combined check valve and variable restrictor unit may in one form mount onto the atomiser head and have an aerodynamic shape so as to minimise turbulence of the air passing the assembly due to the combined check valve and variable restrictor unit.

According to one form the check valve turns off fluid flow therethrough at a fluid pressure of 8 PSI (55 kPa) and the variable restrictor unit controls the fluid flow therethrough at a fluid pressure of 30 PSI (206.25 kPa) in the range of 0 - 30 litres/minute.

It will be appreciated that the atomiser head produces droplets in a range of diameter sizes. The range has a probability distribution with the likelihood of smaller or larger droplets outside the range being low. Droplets of less than about 60 μm in diameter are generally undesirable due to the increased risk of spray drift whilst droplets of greater than about 50 μm in diameter are generally undesirable due to not effectively distributing sprayed liquid upon plant foliage. Generally it is desirable that the diameter of 90% of the droplets lie within the range of 140 - 180 μm vineyards; 200 - 450 μm cotton; 250 - 750 μm general crops. Factors effecting droplet formation include spray liquid characteristics, rotational speed of an atomiser head, screen gauze mesh size, and, as found by the inventor, air flow proximal the screen.

BRIEF DESCRIPTION OF THE DRAWINGS

To assist in the understanding of the invention preferred embodiments will now be described with reference to the accompanying drawings: Figure 1 is a sketch of a side view of an atomiser head;

Figure 2 is a sketch of the cross sectional view along AA' in Figure 3 of the air deflector;

Figure 3 is a sketch of a face of the air deflector;

Figure 4 is a sketch of the cross sectional view along BB' in Figure 4 of the end cap;

Figure 5 is a sketch of a face of the end cap; Figure 6 is a sketch of the atomiser head looking in the direction of air flow;

Figure 7 is a sketch of a second embodiment of an atomiser head;

Figure 8 is a sketch of a longitudinal cross sectional view of the atomiser head illustrated in figure 7;

Figure 9 is a sketch of a cross sectional view along AA in Figure 10;

Figure 10 is a sketch of a side view of a secondary cut off valve;

Figure 11 is a sketch of an end view of the secondary cut off valve;

Figure 12 is a sketch of a perspective view of the secondary cut off valve; Figure 13 is a sketch of an end view of a valve plunger;

Figure 14 is a sketch of a cross sectional view along AA of Figure 13;

Figure 15 is a sketch of a perspective view of a spring retainer;

Figure 16 is a sketch of an end view of the spring retainer;

Figure 17 is a sketch of a side view of the spring retainer; Figure 18 is a sketch of a further perspective view of the spring retainer;

Figure 19 is a sketch of a perspective view of a combined check valve and variable restrictor unit;

Figure 20 is a sketch of a cross sectional view of the combined check valve and variable restrictor unit illustrate in Figure 19 along its elongate axis;

Figure 21 is a sketch of a face of the end cap according to a further embodiment;

Figure 22 is a sketch of the cross sectional view along CC in Figure 23 of further form of an air deflector; Figure 23 is a sketch of a face of the air deflector; and,

Figure 24 is a sketch of a perspective view of combined check valve and variable restrictor unit mounted to the atomiser. DETAILED DESCRIPTION OF THE INVENTION

It will be appreciated that the figures are not engineering design drawings but only sketches for the puφose of assisting in explanation of the invention. Accordingly, features, perspective, proportions or the like may be inaccurate, and features may have been omitted.

Referring to the Figures 1 to 6 inclusive, a first preferred embodiment will now be described.

The atomiser head (1) comprises two main parts, an atomiser assembly (A) and an atomiser frame (B). The atomiser frame includes an atomiser body, an atomiser mount and blades; hereinafter described in more detail. The atomiser assembly includes an end cap, an air deflector and a screen; hereinafter described in more detail.

This form is suited for terrestrial vehicle spray arrangements but may also be used in aerial spray arrangements with incidental modifications. It has a circular air deflector (2) which is made of DELRIN (trade mark of Du Pont, a UN. stabilised acetal resin, of grade known at least in Australia as Yellow Acetal, and also available Hoechst- Celanese under the trade mark CELCOΝ) and secured by three small bolts (two marked as 3 and 4) to an atomiser body (5) of the atomiser head which is made of aluminium. The atomiser body may be of a pre-existing atomiser head to which the invention is being retrofitted or it may be a new manufacture. In another form the air deflector would be an integrally made part of the atomiser body.

The atomiser body is about 100 mm in diameter and has four blades (6, 7, 8 and 9) which are adjustable in pitch. The blades effect rotation of the atomiser frame and atomiser assembly when in an air flow and by being adjustable in pitch the speed of rotation for a given velocity of air flow may be adjusted. Each blade is about 70 mm long and 70 mm wide and made of DELRLΝ (trade mark of Du Pont, a UN. stabilised acetal resin, of grade known at least in Australia as Yellow Acetal, and also available Hoechst-Celanese under the trade mark CELCOΝ). To mount the atomiser head there is an atomiser mount being a DELRIN (trade mark of Du Pont, a UN. stabilised acetal resin, of grade known at least in Australia as Black Acetal, and also available Hoechst-Celanese under the trade mark CELCOΝ) plate (10), a washer (11), nut (12) and 12 mm threaded portion (13). The threaded portion is inserted through a suitable hole of a supporting mounting block (not shown) and the washer and nut fastened tight. The threaded portion is also used to attach a liquid supply and is a hollow shaft which communicates with liquid outlet (14). The atomiser frame and atomiser assembly rotate about the liquid outlet and the threaded portion, and are mounted by bearings to the shaft.

The air deflector has a flared portion (15) which deflects air away from the screen (16 shown in partly removed fashion to reveal inner parts). This together with the increased diameter of the air deflector compared with the screen is believed to create a region of low pressure proximal the screen which leads to the formation of larger droplet size than otherwise would occur at any particular speed of rotation. Irrespective of the actual cause it has been noted that the arrangement tends to lead to droplets of larger size. The screen is a stainless steel wire gauze of 14 mesh and 0.4 wire thickness. It is a cylinder 78 mm long and 73 mm in diameter. It is edgewisely disposed between the air deflector on one side and a circular end cap (17) on the other side. The end cap is also made of DELRIN (trade mark of Du Pont, a UN. stabilised acetal resin, of grade known at least in Australia as Black Acetal, and also available Hoechst-Celanese under the trade mark CELCOΝ), is spaced from the deflection cap and faces (18 and 19), face each other. The screen has a soldered join at the ends of the strip of gauze from which it is made and a balancing line of solder opposite.

It will be appreciated that for other applications the gauze size may be altered. The gauze size is one factor that helps determine average droplet size and size distribution. For differing applications gauze sizes of 8 to 20 mesh has been found useful.

To compressively hold the screen between the end cap and air deflector there are three 3 mm stainless steel counter sunk bolts (two shown as 20 and 21). The heads of the bolts reside within counter sunk spaces (one shown as 22) provided in face (23) of the air deflector. The bolts pass through three holes (two marked as 24 and 25) and are secured with nylon insert nuts (two marked as 26 and 27).

The air deflector also has holes (two shown as 28 and 29) for passage of bolts (3 and 4).

In face (18) of the air deflector there is a recessed annular groove (98) approximately 2 mm deep, 1.5 mm wide and 73 mm diameter. There is a corresponding and similar groove in face (19) of the end cap. These grooves accept respective edges of the screen with a snug fit. The width of the grooves allows for some eccentricity in the diameter yet the hold is snug enough to retain the screen during installation. The air deflector also has a central aperture (30) to provide clearance for the outlet and a nose cone (31 shown in partly removed fashion to reveal an inner part). The nose cone is cylindrical and foranious. The end cap has an annular ridge (32) and hole (33) for mounting a distributor (34). The distributor comprises three mitred stainless steel legs (two shown as 35 and 36), each side of a leg being about 5 mm wide and one side is tangential to the rotation, between circular brass plates (one shown as 37). One of the brass plates fits into the space provided by ridge (32) and has a central threaded insert for bolt (38) to secure the distributor to the end cap.

To further assist with deflection of air and hence dispersion of liquid, the end cap has an chamfered face (39).

The outlet (14) has two orifices for liquid emission, one each side. The liquid flows out of these and is dispersed along the length of the nose cone by the rotating distributor. The apertures in the nose cone cause the liquid to be distributed over the screen in smaller droplets which are further reduced in size by the screen. The low pressure proximal the screen mentioned in association with the air deflector is believed to allow larger droplets to form than would occur if the diameter of the screen was as large or larger than the atomiser body. It is believed that in the latter case, the air flow rushing past the screen can lead to some very fine droplets being created which can be suspended in the air and drift considerable distances leading to unintentional spray damage.

An atomiser assembly has been field tested and found to work well at 6000 φm without any sign of deformation or likely failure of the screen. The simplified construction and much cheaper manufacturing costs allow a screen to be replaced more often and more cheaply. The gauze size of the screen is a factor in determining average droplet size and size distribution. By changing the screen the atomiser assembly may be adjusted for different spray applications.

A second preferred embodiment will now be described with reference to Figures 7 to 18 inclusive.

The second preferred embodiment is similar to the first embodiment. It also is an atomiser head (40) comprises two main parts, an atomiser assembly (A) and an atomiser frame (B). It has an atomiser body with an integral circular air deflector (41) which is made of aluminium and secured by a compressive threaded means to an atomiser mount (42) of the atomiser head which is made of aluminium. It will be appreciated that whilst the air deflector is physically integral with the atomiser body it is conceptually part of the atomiser assembly. There is also a mounting bracket (43) partly shown which is attached to the atomiser mount and allows mounting of the atomiser head to a structure such as an aircraft wing or boom.

There are four blades (one shown as 44) made of DELRIN (trade mark of Du Pont, a UN. stabilised acetal resin, of grade known at least in Australia as Yellow Acetal, and also available Hoechst-Celanese under the trade mark CELCOΝ) which are radially equally spaced about the atomiser head and effect rotation of the atomiser assembly relative to the mounting bracket due to the influence of air flow past the blades. The blades are secured by screws (not shown) between the air deflector and an aluminium clamp ring (45).

The compressive threaded means consists of a hollow main shaft (46) which has threaded ends. At one threaded end proximal the atomiser assembly there is a brass secondary valve body (47) which is screw threaded onto the shaft. At the other end there is a stainless steel locking nut (48) and washers (49) which bear against the atomiser mount. The atomiser mount in turn bears against washers (50), deflector cap (51), stainless steel compression bush (52), first bearing (53), spacer (54), second bearing (55) and the secondary valve body. It will be appreciated tightening the locking nut causes the atomiser mount, the secondary valve body and the components therebetween to experience compressive securing force. The clamp ring rotates upon the first bearing whilst the atomiser body rotates upon the second bearing. Between the second bearing, the air deflector and the secondary valve body is a brass V ring housing (56) and a V ring seal (57) which is made of VITOΝ (trade mark of Du Pont), a fluoroelastomer.

The compressive threaded means allows primary disassembly to substantially occur with the untightening of the locking nut. This permits easy access to the screws securing the clamp ring and the atomiser body together which by removal of the screws allows access to the blades. This arrangement permits blades to be replaced without requiring disassembly of the atomiser assembly.

The threaded shaft distal the atomiser assembly has a hollow threaded brass hose tail (58). To the hose tail is secured a hose for conducting liquid to the atomiser. The hollow hose tail, the shaft and the secondary valve body allow liquid to be supplied under pressure to a secondary cut off valve located within the secondary valve body projecting from the atomiser body and within the atomiser assembly. The secondary cut off valve comprises the secondary valve body, a chamfered sealing face (59) portion of and within the secondary valve body, a stainless steel plunger (60) biased by a spring (61) against the sealing face, and a brass spring retainer (62). The plunger has a hollowed end (63) into which one end of the spring fits. The other end of the spring is registered around a central projection (64) of the retainer so that between the plunger and the retainer the spring is retained. The plunger is free to move to and from the sealing face within the secondary valve body and subject to its constraints against the bias of the spring. When the plunger compresses the spring, radial apertures (one shown as 65) within the secondary valve body are in communication with the shaft and liquid therefrom may pass out of the apertures. The retainer is threaded and screws into an internally threaded end of the secondary valve body.

The spring is selected so that when the retainer is securely located within the end of the secondary valve body, a fluid pressure within the shaft of approximately 3 PSI (22 kPa) is required to open the secondary cut off valve. In typical arrangements the liquid from the source is pressurised using a pump to a pressure of typically 30 PSI (207 kPa).

A primary valve controls liquid flow between a reservoir and hoses leading to atomiser heads. Typically, there is a pump connected to the reservoir which is connected to wing mounted booms. Off the booms may be mounted the atomiser heads with liquid being communicated thereto via respective hoses. In each respective hose are typically in-line check valves operating at approximately 8 PSI (55 kPa) and a variable restrictor unit valve which is used to set the spray rate, by setting a flow rate for a given fluid pressure. The primary valve is typically distal the atomiser heads and some liquid may be contained within the hoses and shafts of the atomiser assemblies downstream the check valve. Without the secondary cut off valve the fluid within these hoses and shafts is largely drained to effect full cessation of spraying and similarly must be supplied before full commencement of spraying. With the secondary cut off valve the hoses remain filled with liquid and so response to the primary valve is quicker.

Whilst the mentioned pressure range has been found useful with conventional spray equipment to which the subject atomiser heads are connected, it will be appreciated that other spray arrangements may require a different operating pressure than that given. The preferred operating pressure of the secondary cut off valve is a matter of choice dependant upon the application. The air deflector has an external surface (66) which provides a convex flaring rather than a concave flaring as in the first embodiment. This seems to result in less turbulent air flow over the atomiser assembly. It has been noted that less spray drift seems to occur with this arrangement. The screen in this second embodiment is manufactured as for the first embodiment excepting that its ends are not soldered together or that a countering and balancing longitudinal line of solder is not applied. Rather the ends of the mesh or gauze used to manufacture the cage are spot welded. A cylindrical former is used around which the mesh is wrapped. The former acts as an electrode, contains a longitudinal electrode or has a longitudinal slot for acceptance of an electrode. A matching elongate electrode is brought to bear on the outer surface of the mesh over the other electrode and the spot welding is performed.

The atomiser assembly, except for the mentioned differences due to the secondary cut off valve, is as described for the first embodiment. Referring to figures 19 and 20 a combined check valve and variable restrictor unit will now be described which may be used with the atomiser head of the second embodiment.

The combined check valve and variable restrictor unit (67) has an aerodynamic shape. It axial mounts to the threaded shaft distal the atomiser head. It has a threaded swivel hose connection (68) to which a hose from a boom can be connected for supply of liquid to be sprayed. The swivel hose connection is made of brass and has two thread portions of different size. A first (69) is for hose connection. A second (70) is for a retaining nut (71). A faced portion (72) is provided to allow for use of two spanners to effect tightening of the retaining nut without swivelling of the swivel hose connection. The swivel hose connection has a cylindrical shank (73) with an O ring seal (74) and an expanded end (75). It is inserted into an axial bore within the body section of the swivel hose connection (76) and retained in place by installation of the retaining nut. The O ring seal allows relative rotational movement of the swivel hose connection within the body section. The body section has a threaded portion (77) by which it is connected to the check valve body (78).

The check valve is of similar construction to the secondary cut-off valve previously described. Within the check valve body is an axial bore (79) with a chamfered radial face (80). A spring biased plunger (81) retained with the check valve body mates with the chamfered face. In its open position, as illustrated, the spring (82) is compressed and the plunger is away from the chamfered face so allowing fluid flow through radial apertures (one shown as 83) into an annular chamber (84). The spring is selected to close off the check valve when the supply fluid pressure drops below approximately 8 PSI (55 kPa). The check valve body is fully screwed into part (85). To the part is screwed the fore section (86) of the variable restrictor unit. This has the annular chamber and clearance for the check valve body. It also has two radially spaced axial bores (one shown as 87) which lead to a chamfered valve face (88).

The rear section (89) of the variable restrictor unit is screwed into the fore section and sealed therewith by an O ring seal (90). It also has a matching chamfered valve face (91) which closes off the axial bores when the rear section is fully screwed into the fore section. There is provided an axial threaded bore (92) in the rear section communicating with the chamfered valve face by which the variable restrictor unit may be screwed unto the shaft of the atomiser head. By adjusting the screwed in extent of the fore and rear sections of the gap between the two sections is adjusted and hence control of fluid flow therethrough is achieved.

It will be appreciated that the main portion of the combined check valve and variable restrictor unit, between the swivel hose connection (68) and the rear section (89) of the variable restrictor unit, may be rotated with respect to those parts. The outer surfaces of the fore and rear sections of the variable restrictor unit have markings (93) allowing for the selection of a fluid flow.

Prior known arrangements had separate in-line check valve and variable restrictor units within the hose connection between boom and atomiser. These are relatively large and are believed to create turbulent air flow past the atomiser. This turbulence is believed to be a causal factor in spray drift.

Figure 21 is essentially the same as figure 5 excepting that the annular ridge (32) thereof has been replaced by a series of spaced annular sections (94) that serve the same function.

Figures 22 and 23 are essentially the same as figures 2 and 3 respectively. The difference between the two forms is the use of a plurality of annular sections (95) in stead of the annular groove for retention of the edge of the screen. These two forms serve the same function. Figure 24 illustrates the combined check valve and variable restrictor unit (96) mounted to an atomiser head (97).

In another form, the nose cone projecting from and secured to the atomiser body, alternatively integral with the atomiser body, extends to the end cap. Within the end of the nose cone are thread apertures to receive bolts which secure the end cap thereto.

It will be appreciated that this disclosure is not intended to limit the invention to preferred embodiments or details thereof. A skilled addressee will readily conceive differing embodiments exhibiting the invention and these would fall within the spirit of the invention disclosed herein.

Claims

1. An atomiser assembly including: an air deflector; an end cap spaced from and facing the air deflector; a tubular perforated screen edgewisely disposed between the air deflector on one side and the end cap on the other side; and, fastening means between the end cap and air deflector adapted to compressively hold therebetween the screen; and, the air deflector and the end cap each respectively having screen edge locating means adapted to respectively locate an edge of the screen and resist relative movement thereof under the influence of centrifugal force experienced at atomiser assembly rotational operating speeds.

2. An atomiser assembly as in claim 1 wherein the screen is retained at each end by the screen edge locating means bearing against the outer surface of the screen proximal the respective end edge.

3. An atomiser assembly as in claim 2 wherein the screen edge locating means includes a groove within which the end edge is received.

4. An atomiser assembly as in claim 3 wherein the groove is annular and of slightly greater diameter than the diameter of the screen, width to accept the edge of the screen and depth to allow firm location of the edge of the screen within the groove.

5. An atomiser assembly as in either claim 3 or 4 wherein the groove is continuous.

6. An atomiser assembly as in either claim 3 or 4 wherein the groove is discontinuous but in use locates the screen and resists relative radial movement thereof.

7. An atomiser assembly as in any one of claims 3 to 6 inclusive wherein the width of the groove is selected to permit a snug fit of the screen therein.

8. An atomiser assembly as in any one of claims 3 to 7 inclusive wherein the screen has an edgewise thickness of approximately 1 mm, the groove depth is 1 to 2 mm deep, and the groove width is 1.5 mm.

9. An atomiser assembly as in any one of claims 3 to 8 inclusive wherein the groove is recessed within the face of the respective deflector or end cap.

10. An atomiser assembly according to any one of the preceding claims wherein the screen may be made from stainless steel gauze.

11. An atomiser assembly according to any one of the preceding claims wherein the gauze is of 8 to 20 mesh.

12. An atomiser assembly according to any one of the preceding claims wherein the wire thickness is typically about 0.3 to 1 mm.

13. An atomiser assembly according to any one of the preceding claims wherein the end cap or air deflector or both are manufactured of aluminium, monel metal or stainless steel.

14. An atomiser assembly according to any one of claims 1 to 12 inclusive wherein the end cap or air deflector or both, are manufactured of a plastics material.

15. An atomiser assembly according to claim 14 wherein the plastics material is acetal resin or fibre glass.

16. An atomiser assembly according to any one of the preceding claims wherein the screen is cylindrical, the fastening means are elongate, and the end cap and air deflector are circular in shape normal to an axis of rotation of the atomiser assembly.

17. An atomiser assembly according to claim 16 wherein the screen is manufactured from a sheet of gauze, two opposed edges of the sheet being soldered together, and a row of solder to balance the screen being placed opposite the soldered edges.

18. An atomiser assembly according to claim 16 wherein the screen is manufactured from a sheet of gauze, two opposed edges of the sheet being spot welded together.

19. An atomiser assembly as in claim 16 wherein the diameter of the air deflector is greater than the diameter of the screen and has a flared portion adapted to deflect air flow away from the screen.

20. An atomiser assembly as in claim 19 wherein the air deflector is flared is concavely.

21. An atomiser assembly as in claim 19 wherein the air deflector flared is convexly.

22. An atomiser assembly according to any one of claims 16 to 21 inclusive wherein the diameter of the end cap is greater than the diameter of the screen and has a flared portion adapted to deflect air flow away from the screen.

23. An atomiser assembly according to any one of the preceding claims adapted for aerial use.

24. An atomiser assembly according to any one of claims 1 to 22 inclusive adapted for terrestrial use.

25. An atomiser including an atomiser assembly according to any one of claims 1 to 24 inclusive axially mounted to an atomiser body, and a plurality of blades adapted to effect rotation of the atomiser body around the axis of the atomiser body due to air flow past the blades.

26. An atomiser claim 25 including a secondary cut-off valve adapted to cut off fluid flow when the pressure of the fluid is less than a predetermined pressure.

27. An atomiser as in claim 26 wherein the predetermined pressure is 3 PSI (22 kPa).

28. An atomiser as in either claims 26 or 27 wherein the secondary cut-off valve is within a nose cone which projects within the screen.

29. An atomiser as in any one of claims 25 to 28 inclusive wherein the blades are spaced around and project radially from the atomiser body, and the pitch of the blades being adjustable and thereby adapted to permit the speed of rotation of the atomiser assembly to be set for a specific speed of air flow. .

30. An atomiser according to any one of claims 25 to 29 wherein the air deflector is integral with and part of the atomiser body.

31. An atomiser according to any one of claims 25 to 29 inclusive wherein the air deflector is separate from and secured to the atomiser body.

32. A kit including an atomiser according to any one of claims 28 to 31 inclusive and a mounting bracket for mounting the atomiser assembly to a support.

33. A kit including an atomiser assembly according to any one of claims 1 to 24 inclusive and a mounting bracket for mounting the atomiser assembly to a support.

34. A kit as in either claim 32 or 33 including a combined check valve and variable restrictor unit.

35. A kit as in claim 34 wherein the combined check valve and variable restrictor unit mounts onto the atomiser assembly.

36. A kit as in claim 35 wherein the combined check valve and variable restrictor unit has an aerodynamic shape so as to minimise turbulence of the air passing the assembly due to the combined check valve and variable restrictor unit.

37. A kit as in any one of claims 34 to 36 inclusive wherein the check valve turns off fluid flow therethrough at a fluid pressure of 8 PSI (55 kPa).

38. A kit as in any one of claims 34 to 37 inclusive wherein the variable restrictor unit controls the fluid flow therethrough at a fluid pressure of 30 PSI (206.25 kPa) in the range of 0 - 30 litres/minute.