Patent Publication Number: US-6338444-B1

Title: Spray nozzle

Description:
RELATED APPLICATIONS 
     This is a continuation of International Application PCT/GB98/02974, with an international filing date of Oct. 5, 1998 which claims priority from GB 9721297.1 and has a priority date of Oct. 7, 1997. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a spray nozzle. 
     BACKGROUND OF THE INVENTION 
     Various forms of agricultural spray nozzles are known. In each, a liquid such as a fertiliser or pesticide is supplied to the spray nozzle. The spray nozzle breaks up the liquid into droplets on exiting through an outlet provided in the spray nozzle tip. The spray nozzles may produce various different spray patterns, such as a flat spray pattern, a “solid” cone of drops, a “hollow” cone of drops, etc. 
     Various spray nozzles have been produced which attempt to provide a better dispersion of the liquid being sprayed in order to reduce the amount of liquid used per unit area of crop in order both to keep down costs and also to minimise any adverse effect on the environment. 
     In the spray nozzle marketed by the present applicant as “TurboDrop,” a flow of liquid through the spray nozzle passes through a venturi restriction which causes air to be entrained with the liquid flow, the air being drawn in through an air inlet in the side of the spray nozzle assembly. The liquid and entrained air pass into a relatively long mixing chamber. The liquid and air mix and air-filled droplets form when the mixed liquid and air pass out through the spray tip in a selected spray pattern. The air-filled droplets tend to drift much less than droplets produced by conventional spray apparatus and provide excellent coverage of an area. 
     A similar device is disclosed in GB-A-2256817 in which liquid passes into a convergent inlet end of a venturi in the spray nozzle, there being a gas inlet to that convergent inlet end of the venturi. The venturi itself is relatively long and passes to a so-called mixing chamber though it is understood that mixing will take place in the venturi as well as in the mixing chamber itself. 
     In each of these prior art spray nozzles, each of which relies on the venturi effect, the venturi or mixing chamber has to be relatively long in order to ensure that sufficient mixing of the liquid with the entrained air is achieved to allow turbulence to be created so as to provide air-filled liquid droplets. The venturi/mixing chamber also has to be long in order to prevent liquid passing straight out of the nozzle; in other words, there must be sufficient time for mixing to occur before liquid exits the spray nozzle. This means that these prior art spray nozzles as a whole are long. 
     The length of the prior art spray nozzles is a problem in the field because the spray nozzles are mounted on booms that are either carried by or towed by a tractor, for example. Such booms are usually folded for storage or and for transit between spraying areas. The long prior art spray nozzles are easily knocked off when the booms are folded. 
     Moreover, it is usually recommended to use a liquid supply pressure of typically 7 bar (approximately 700 kPa) for some of the prior art spray nozzles. Such high pressures (compared to a typical value of 3 bar (approximately 300 kPa) for conventional spray nozzles) require expensive powerful pumps. Such high pressures can also cause damage to the spray components that incorporate the spray nozzle assembly. Moreover, the long mixing chambers/venturi make these prior art spray nozzles difficult to clean. This is compounded by the fact that, in practice, such spray nozzles will typically be covered in mud as a result of having been carried behind a tractor. 
     Another type of prior art spray nozzle is a so-called twin fluid nozzle. A liquid is forced into a mixing and atomising chamber in the spray nozzle and typically strikes a plate provided within the chamber. Pressurised air is forced into the chamber to carry the liquid out of the chamber outlet to a spray nozzle outlet where the liquid atomises and droplets issue as a spray. It should be noted that the air is forced into the chamber in a twin fluid nozzle rather than being drawn in by movement of liquid through the chamber as in a venturi nozzle. Examples of twin fluid nozzles are disclosed in EP-A-0225193, GB-A-2157591, WO-A-96/20790 and U.S. Pat. No. 4,828,182. 
     SUMMARY OF THE INVENTION 
     According to a preferred embodiment of the present invention, the present spray nozzle comprises a pre-chamber and a mixing region, a first inlet defining a first fluid flow path for admittance of a first fluid to the pre-chamber, a second inlet defining a second fluid flow path that is crossed by the first fluid flow path for admittance of a second fluid to the pre-chamber, a wall between the pre-chamber and the mixing region and having an aperture therethrough coaxial with the first fluid flow path, and an outlet from the mixing region through which fluid can pass from the mixing region out of the spray nozzle. The outlet does not lie on either the first or second fluid flow paths, such that in use a first fluid entering through the first inlet mixes with a second fluid entering through the second inlet in the mixing region before the mixed first and second fluids passing out through the outlet. 
     The aperture in the wall between the pre-chamber and the mixing region allows fluid to pass from the pre-chamber to the mixing region, while the wall itself tends to prevent fluid in the mixing region passing back to and out of the second inlet. In the preferred embodiment, the wall defines the pre-chamber positioned upstream of the mixing region and into which the first and second inlets open. In a venturi nozzle where air is drawn in as the second fluid through the second inlet, the size of the aperture in the wall can be adjustable to allow some degree of control over the amount of air that is drawn in through the second inlet. The pre-chamber helps to keep down the overall length of the nozzle by promoting more efficient mixing of the first and second fluids. 
     A first end of the second inlet is preferably open to atmosphere and a second end of the second inlet preferably opens to a position adjacent the first fluid flow path, whereby passage of a first fluid through the first inlet causes air to be drawn in through the second inlet. 
     Alternatively, there may be means for connecting the second inlet to a supply of pressurised air. 
     The spray nozzle may have a wall opposite the first inlet and transverse to the first fluid flow path, with the wall having an aperture defining the outlet that is offset from the first fluid flow path. The aperture of the wall between the pre-chamber and the mixing region preferably has a cross-sectional area that is greater than the cross-sectional area of the first inlet. 
     The first inlet preferably includes two first inlet apertures. In this embodiment, the wall between the pre-chamber and the mixing region preferably has two apertures therethrough, which are respectively coaxial with the two first inlet apertures. The use of two inlet apertures helps to ensure that the pattern of fluid exiting the outlet in use is symmetrical, ensuring more uniform coverage during spraying. The inlet apertures are preferably symmetrically spaced either side of a central longitudinal axis of the spray nozzle. 
     The second fluid flow path is preferably perpendicular to the first fluid flow path. The second inlet preferably comprises two second inlet apertures. 
     The outlet may lie on a central longitudinal axis of the spray nozzle. 
     The spray nozzle is preferably provided in two parts, the first part having the first and second inlets, the second part having the outlet. The use of two parts means that the size of the outlet can be altered easily by using a different outlet part having a different size outlet. The use of two parts also facilitates cleaning of the nozzle. 
     According to a second aspect of the present invention, there is provided a method of spraying using a spray nozzle having a pre-chamber and a mixing region, a first inlet defining a liquid flow path for admittance of a liquid to the pre-chamber, a second inlet defining an air flow path that is crossed by the liquid flow path for admittance of air to the pre-chamber, a wall between the pre-chamber and the mixing region and having an aperture therethrough coaxial with the liquid flow path, and an outlet from the mixing region, through which mixed liquid and air can pass from the mixing region out of the spray nozzle. Again, the outlet preferably does not lie on the liquid and air flow paths. The method comprises the steps of passing a liquid through the liquid inlet, mixing said liquid with air entering through the second inlet in the mixing region, and passing mixed liquid and air out through the outlet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which: 
     FIGS. 1A to  1 E are respectively a view from an inlet end, a first side view, a first longitudinal cross-sectional view, a view from the outlet end of an inlet part, and a second side view of a first example of a spray nozzle according to the present invention; 
     FIGS. 2A to  2 E are respectively a view from an outlet end, a first side view, a longitudinal cross-sectional view, a view from an inlet end, and a second side view of an outlet part of the first example of the spray nozzle; 
     FIGS. 3A to  3 E are respectively a view from an outlet end, a first longitudinal cross-sectional view, a first side view, a second side view, and a second cross-sectional view of the first example of the assembled spray nozzle; 
     FIGS. 4A and 4B are perspective views of the assembled spray nozzle and the disassembled spray nozzle of the first example respectively; and 
     FIGS. 5A and 5B are perspective views of a disassembled spray nozzle and an assembled spray nozzle of an alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     In FIGS. 1A to  1 E, there are shown various views of an inlet part  10  of a first example of a spray nozzle  1  according to a preferred embodiment of the present invention. In FIGS. 2A to  2 E, there are shown various views of an outlet part  30  of the spray nozzle  1 . The assembled inlet and outlet parts  10  and  30  are shown in FIGS. 3A to  3 E and  4 A. 
     Referring initially to FIGS. 1A to  1 E, the inlet part  10  generally has a circular cross-sectional shape having reduced stepped outer diameters as shown particularly clearly in the side views FIGS. 1B,  1 C and  1 E. FIG. 1C is a cross-section on lines I—I of FIG.  1 A. 
     The base portion  11  of the inlet part  10  has the greatest external diameter and has two apertures or through holes  12  therethrough, which define first inlets for a first fluid. The through holes or first fluid inlets  12  pass through the base portion II in a direction parallel to the central longitudinal axis X—X of the inlet part  10 . The first fluid inlets  12  are symmetrically placed either side of the central longitudinal axis X—X of the inlet part  10  and so are positioned at an equal spacing on opposite sides of the central longitudinal axis X—X. The first fluid inlets  12  define flow paths A for the first fluid in a direction parallel to the central longitudinal axis X—X of the inlet part  10 . 
     A second or intermediate portion  13  of reduced external diameter is adjacent the base portion  10 . Opposite sections of the wall defining the second or intermediate portion  13  are relieved or absent so as to provide opposed second inlets  14  for a second fluid to enter through the second fluid inlets  14  into the hollow centre  16  of the inlet part  10  in a direction B transverse to the first fluid flow paths A. As can be seen from the drawings, the second fluid inlets  14  open onto the first fluid flow paths A and are thus crossed by flow of the first fluid through the first fluid inlets  12 . The second fluid inlets  14  are at a position which is rotated through 90° around the longitudinal axis X—X relative to the first fluid inlets  12 . In the embodiment shown, the second fluid inlets  14  are open to atmosphere. 
     The intermediate portion  13  of the inlet part  10  leads onto a final portion  15  of reduced external diameter. This final portion  15  defines therein a hollow cylindrical volume  16  which will be discussed further below. The end portion  15  of the inlet part  10  has a first external annular bead  17  and a second external annular bead  18 . 
     In this example, the intermediate portion  13  of the inlet part  10  has four locating wedge-shape recesses  19  facing in a direction parallel to the longitudinal axis X—X on the stepped surface  20  which connects the intermediate portion  13  externally to the final portion  15 . 
     Within the inlet part  10 , at a position just downstream of the second fluid inlets  14  and corresponding to the junction between the intermediate portion  13  and final portion  15  of the inlet part  10 , is an intermediate wall  21 . This intermediate wall  21  has two circular apertures  22  which are coaxial with and of slightly larger diameter than the first fluid inlets  12 . 
     Referring now to FIGS. 2A-E, The outlet part  30  of the spray nozzle  1  has a first circular wall  31  which defines a mixing chamber  32  in the form of a cylindrical central volume  32 . The circular wall  31  is sized to fit over the narrow portion  15  of the inlet part  10  and has an internal annular recess  33 . The outlet part  30  has wedge-shape teeth  34  which correspond to and are received in the wedge-shape recesses  19  of the inlet part  10  to fix the relative orientation of the two parts  10 , 30  in the assembled spray nozzle  1 . 
     As can be seen particularly clearly in FIG. 2C, which is a cross-sectional view on II—II of FIG. 2A, and in FIGS. 3B and 3E, which are cross-sectional views on IV—IV and III—III of FIG. 3A respectively, the central volume  32  of the outlet part  30  terminates in a wall  35 , which is opposite the first fluid inlets  12  in the assembled spray nozzle  1 . A through hole  36  is provided centrally of the wall  35  and provides an outlet from the central volume  32 . The longitudinal extent of the outlet  36  is defined by a short cylindrical wall  37  running parallel to the central longitudinal axis of the spray nozzle  1 . The short wall  37  has a wedge-shape recess  38  which flares outwardly away from the outlet  36  to define a fan spray tip as is well known in the art of spray nozzles. It will be appreciated that the portion of the wall  37  surrounding the outlet  36  can be provided with different shapes in order to provide spray patterns of different shapes, such as cones for example. 
     In use, the spray nozzle  1  is formed by assembling the inlet and outlet parts  10 , 30  with the wall of the final portion  15  of the inlet part  10  being received in the central volume  32  of the outlet part  30 . The second bead  18  snaps into the annular recess  33  and the first bead  17  provides a seal for the junction of the inlet and outlet parts  10 , 30 . The intermediate wall  21  of the inlet part  10  defines a pre-chamber  39  (FIG. 3B) upstream of the mixing chamber  32 . The assembled spray nozzle  1  can then be fitted to an agricultural boom by means of a conventional spray cap (not shown) for example. 
     A first fluid, which may be a liquid such as a solution of a pesticide or fertiliser for example, is supplied under pressure to the first fluid inlets  12  so that the first fluid flows in the direction indicated by arrows A. The flow of the first fluid transversely past the laterally disposed second fluid inlets  14  draws air in through the second fluid inlets  14  into the pre-chamber  39  and the air is entrained with the first fluid. On passing through the apertures  22  of the intermediate wall  21  into the mixing chamber  32  provided by the volume  32  defined in the outlet part  30 , the first fluid strikes the opposed wall  35  of the inlet part  30 . It will be appreciated that because the first fluid inlets  12  are offset relative to the outlet  36 , there is very little tendency for the first fluid to pass straight out of the outlet  36 . The intermediate wall  21  tends to prevent the fluid in the mixing chamber  32  passing back to and out of the second fluid inlets  14 . 
     After striking the wall  35  opposite the first fluid inlets  12 , the first fluid having entrained air atomises to produce air-filled droplets on being forced out of the mixing chamber  32  by the action of further incoming first fluid entering the mixing chamber  32  through the first fluid inlets  12  and apertures  22  of the intermediate wall  21 . It will be appreciated that this is achieved without requiring a long mixing chamber, in contrast to the prior art spray nozzles of this type. The effective mixing chamber of the present invention is provided by the relatively short volume  32  of the second part  30 . 
     A second example of a spray nozzle  1  in accordance with the present invention is shown in FIGS. 5A and 5B. The second example is similar to the first example described above and those parts which are the same have the same reference numerals and will not be further described. 
     The second example of the spray nozzle  1  differs in the way relative orientation of the two parts  10 , 30  is achieved. In the second example of the spray nozzle  1 , the wedge-shape recesses  19  and wedge-shape teeth  34  of the first example are replaced by a pair of opposed lugs  40  on the second part  30  which project rearwards of the second part to engage with corresponding opposed recesses  41  provided in the stepped surface  20  which connects the intermediate portion  13  externally to the final portion  15  of the first part  10 . 
     It has been found that the spray nozzle of the present invention can operate at a pressure of only 3 bar (approximately 300 kPa) which is much less than the 7 bar (approximately 700 kPa) required of some prior art spray nozzles of this type as discussed above. A pressure of 3 bar (approximately 300 kPa) is more typical of the pressures used in conventional spraying equipment and therefore the spray nozzle  1  of the present invention is much more convenient for the user. The spray components which incorporate the spray nozzle  1  are much less likely to suffer damage, for example to seals, due to the supply pressure of the first fluid. 
     It has also been found that the manufacturing tolerances required of the spray nozzle  1  of the present invention are much less stringent than those similar spray nozzles of the prior art. For example, in the “TurboDrop” spray nozzle mentioned above, it is necessary to balance carefully the inlet orifice size compared to the outlet orifice size to within very fine tolerances in order to prevent flooding and liquid outflow through the air inlet. In the present invention, the requirements on manufacturing are much less stringent. The present invention allows the outlet orifice size to be varied relatively freely, which allows much greater freedom in manufacture which in turn enables the ultimate droplet size to be varied simply by providing different outlet parts  30  having different sizes for the outlet  36 . Different droplet sizes have different dispersion characteristics and therefore the present invention allows the user to obtain the required dispersion characteristic more easily. In some circumstances, a small droplet size is preferred whereas in other circumstances a larger droplet size is preferred. At present, the reason for the less stringent requirements on manufacturing tolerances is not clear but it is believed to be related to the non-alignment of the inlets and outlets in the spray nozzle  1  of the present invention. 
     Moreover, the size of the apertures  22  of the intermediate wall  21  can be adjusted to provide some degree of control over the amount of air which is drawn in through the second fluid inlets  14 . 
     The inlet and outlet parts  10 , 30  can be made of any suitable materials, including plastics such as acetal. 
     An embodiment of the present invention has been described with particular reference to the examples illustrated. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the appended claims. For example, more than two first fluid inlets may be provided, there preferably being a corresponding number of apertures in the intermediate wall. More than two second fluid inlets may be provided.