SPRAY NOZZLE ARRANGEMENT

Abstract: An assembly (10) fed by a pressurised pipe (PS) and comprising three identical spray nozzles (N1, N2, N3) is mounted on a spray boom so that N1, N2 and N3 traverse the same area. Using only the supply pressure in the pipe (PS), which pressure may vary (according to the spray delivery requirements of the moment) over the range 1 to 6 bar, nozzles (N1, N2, or N3) are selectively activated to give a spray rate of 0.5 to 2.0 litre/minute, useful in precision farming.

Description: SPRAY NOZZLE ARRANGEMENT This invention relates to a spray nozzle arrangement. For many purposes, especially in agriculture, it is desirable to be able to apply spray of a consistent mean droplet size distribution and fan or cone angle such that the volume distribution pattern below a spray boom is approximately uniform over a range of volumetric spray rates. For agricultural spray nozzles, spray output is classified by the British Crop Protection Council as Fine, Medium or Coarse based on mean droplet size, and chemical manufacturers may specify one of these classifications for applying their product. However, mass produced nozzles generally cannot achieve consistent quality of spray of a given type over a volume flow rate range of more than ±20 or 30% or so. Nozzles exist which are rated over a flow rate range of ±50%, but generally at the extremes of this range the spray quality will deteriorate or the spray output type may change, e.g. from medium to fine as the pressure and flow rate increase. A requirement for a wider range of flow rates with consistent spray type and quality can arise for example in so-called precision farming, that is, applying matter (such as fertilisers or pesticides) to the ground in amounts varying from spot to spot according to the requirements ascertained from a previous mapping of the ground. The mapping and the application of matter can be made to coincide on the ground using global-positioning- satellite techniques. This invention accordingly seeks to provide a spray nozzle arrangement to widen the choice of flow rates available to the user while maintaining reasonable consistency in the physical characteristics (especially droplet size distribution) of the spray, using no other form of control than varying the pressure of the liquid to be sprayed. According to the present invention, there is provided a fluid dispensing arrangement, wherein a fluid under variable supply pressure supplies a plurality of outlet chambers, each outlet chamber dispensing the fluid to an outlet or group of outlets when that chamber reaches a given non-zero pressure, in which arrangement at least one of the outlet chambers, while dispensing the fluid, sends a (preferably hydraulic) signal to at least -1- SUBSTΪTUTE SHEET (RULE 26) one other outlet chamber tending to stop that other outlet chamber from dispensing. In preferred versions, so that all outlet nozzles can be the same, the given pressure for each of at least some of the outlet chambers has the same value in the absence of said signal, and the supply pressure is attenuated to a degree specific to at least some of said outlet chambers. The signal may act to increase the value of the given pressure above which that other outlet chamber dispenses, thereby tending to stop it from dispensing. Preferably, the currently dispensing outlet chamber sends a said signal to all those outlet chambers which dispense at a lower supply pressure. The signal may take the form of a displacement of a pressure-sensing element by the pressure within the currently dispensing outlet chamber. Each outlet chamber may include a valve between it and its outlet or group of outlets, said valves being biassed to close, and preferably the displacement closes the valve of the outlet chamber to which the signal is sent. Preferably, the route of the fluid from the currently dispensing outlet chamber is via the pressure-sensing element. Also according to the invention, a pressure chest assembly comprises an inlet leading to a plurality of outlets, and normally closed passage closure means between the inlet and each outlet, which means open under a different inlet pressure in each case. Each outlet (other than the outlet which opens under the least inlet pressure) is in hydraulic communication with the passage closure means of all the outlets which open at a lesser inlet pressure. Outlet pressure transmitted through said hydraulic communication biasses the closure means to close. Preferably the said hydraulic communication takes the form that the outlet is routed past the respective passage closure means, and preferably the said hydraulic communication acts on a displaceable member of a pressure-sensing element which biasses the closure means to close. Conveniently, the displaceable member is a diaphragm bearing on the closure means. Typically, the closure means is a spring-loaded seal wherein the diaphragm, under hydraulic pressure through the communication, acts in the same sense as the spring. Control of the arrangement will normally be in response to a required spray rate, which may vary from time to time e.g. as the arrangement is moved from place to place in a field, varying according to previously stored information about different places in the field or spontaneously according to the operator's assessment as he drives a spraying machine with a spray boom carrying nozzle arrangements as set forth above across the field. Normally, an acceptable spray quality is maintainable over at least a fourfold change in flow rate, and the four-fold change in flow rate is achievable within a sixfold change in the hydraulic feed pressure. The invention extends to a spray boom or a section of a spray boom, having a plurality of fluid dispensing arrangements as set forth above, with fluid supply lines to the corresponding nozzles in each of the arrangements, which boom or section may be connected to a tank supplying said common feed under a variable hydraulic pressure and having controllers for said hydraulic pressure. The invention will now be described by way of example with reference to the accompanying drawings, in which Figure 1 shows a fluid dispensing arrangement which can be connected or retrofitted to a conventional liquid spray line, Figure 2 shows a four-section spray boom with feed supply lines and pressure- control lines, with a feed tank, pump and controller, the whole being conveyed across a field, Figure 3 shows how the arrangement of Figure 1 is mounted on the boom of Figure 2, Figure 4 shows schematically a four-nozzle arrangement and its supply system, according to the invention, Figure 5 shows schematically an alternative four-nozzle arrangement, also according to the invention, Figure 6 shows in more detail a three-nozzle arrangement, also according to the invention, and Figure 7 shows a curve of nozzle output against supply pressure for the arrangement of Figure 4. In Figure 1, a fluid dispensing arrangement 10 according to the invention is shown schematically, connected to a spray boom, which is viewed in section. Thus, a section 1 of a spray boom with a pressurised pipe 2 of liquid to be sprayed has a conventional nipple or union 3 to which the nozzle arrangement 10 is connected. A number of types of nipple or union, e.g. ones employing a bayonett type fitting, are generally available, and any of these would be appropriate. The arrangement 10 has an array of three conventional flat fan nozzles 11, 12, 13 mounted in line at right angles to the spray boom, in other words one behind the other in the direction of travel, so that each traverses the same track over the ground. Each nozzle 11, 12, 13 is supplied from a manifold box 20, described in more detail later, in relation to Figure 6, which supplies selected nozzles at a desired pressure according simply to the pressure in the pipe 2. A complete spray boom is shown schematically in Figure 2, with four functionally identical sections 1 as shown in Figure 1 , viewed in elevation as if the spray boom were advancing towards the reader. Each of the four sections 1 carries twelve identical nozzle arrangements 10 (shown in full on only the right-most section 1, for simplicity). Each of the arrangements 10 on the section 1 is supplied with pressurised liquid through a respective common pipe 2. Alternatively, the other three boom sections 1 could be fed from a single pipe 2 but, for greater control (better spatial resolution of liquid application rates), each boom section 1 takes a pressurised liquid feed 2 independent of the others, as illustrated, each feed 2 being supplied through a respective pressure regulator 5 independently controlled from a controller C. The pressure regulators 5 are supplied through a common pump P from a tank T. The pressure regulators 5 may be pneumatically, electrically or otherwise actuated. Downstream of the pump P but upstream of the pressure regulators 5, a pressure relief valve is provided with a return flow to the tank T. For greater control still, the regulator 5 and liquid feed pipe 2 need not be common to all twelve arrangements 10 on a section 1 but separate such regulators 5 and pipes 2 may go to each of the twelve arrangements (or subgroups of the twelve) from a central tank T via a common main pump P, which tank, pump and controller are typically mounted on or coupled directly to a tractor hauling the spray boom. It is a matter of assessing the value of a higher spatial resolution in the liquid application against the cost of providing more regulators 5 and a more multi-channel controller C. Depending on the cost of pumps relative to the other components, the common pump P could, if expedient, be replaced by individual smaller pumps each integral with a respective pressure regulator 5. Figure 3 shows in plan view two adjacent arrangements 10 mounted on the section 1 of the spray boom. Flat fan sprays are widely used in agriculture. Their spray footprint is approximately elliptical but highly elongated. Because such sprays would physically interfere with each other if their spray footprints overlapped, they are conventionally mounted angled by some 5° to the boom so as to avoid laterally neighbouring sprays while yet giving, when added to those neighbouring sprays, a constant spray rate at all points underneath the length of the spray boom. Returning to Figure 3, in accordance with the invention, a trio 10 of the nozzles already described 11, 12, 13 are mounted line astern, angled (for the reasons explained) at 5°, or for a greater clearance 10-20°, e.g. 15°, to the vertical plane including the boom. A neighbouring identical trio 10' of nozzles 11 ', 12', 13' is mounted at such a separation as to be capable of achieving the area uniformity of spray already explained, and so on along the boom. The nozzles 11, 12, 13, 11', 12' and 13' (and so on) are supplied from a common hydraulic feed line. In the schematic four-nozzle arrangement of Figure 4, a pressure supply line PS for weedkiller or similar liquid feeds four parallel lines feeding valves VI -V4 respectively. Valve VI is the easiest to open, then V2, then V3, lastly V4. Each valve Vn feeds an identically numbered nozzle Nn, each nozzle Nn being selected to deliver a spray quality which is just acceptable at the opening pressure of its respective valve Vn, and the next-highest-numbered valve, V(n+1), is arranged to open at the pressure corresponding to the upper limit of acceptable spray quality of the nozzle Nn. While liquid is flowing through any one valve Vn to its nozzle Nn, signals are transmitted to each lower-numbered valve VI, ...., V(n-l) to turn off all those lower-numbered valves. In the schematic four-nozzle arrangement of Figure 5, a pressure supply line PS for a liquid plant protection product such as weedkiller feeds four identical valves VI -V4 in series. Valve VI receives the full pressure of the line PS and thus is the first to open. Interposed between the valves VI and V2 is a pressure-reducing valve PR. Further pressure-reducing valves PR are positioned between V2 and V3, and between V3 and V4. Each valve Vn feeds an identically numbered nozzle Nn, each nozzle Nn being selected to deliver a spray quality which is just acceptable at the opening pressure of its respective valve Vn, while the next-highest-numbered valve, V(n+1), is arranged to open at the pressure corresponding to the upper limit of acceptable spray quality of the nozzle Nn. While liquid is flowing through any one valve Vn to its nozzle Nn, signals are transmitted to each lower-numbered valve VI, ...., V(n-l) to turn off all those lower-numbered valves. The pressure-reducing valves act to make valve V(n+1) unable to open while the supply pressure is appropriate for valve Vn. The pressure-reducing valves are of a known design which provides a given resistance to flow whatever the flow rate (within reasonable limits). The pressure drop across, say, PR2 is thus a constant. The presence of the pressure reducing valves mean that identical main valves Vn can be used, but, more importantly, it can ensure that the plot of flow rate against system pressure (Figure 7) is substantially free from steps. If the pressure reducers were not used, it would be necessary to employ values Vn with progressively higher threshold pressures, but this could result in a step increase in flow rate each time the system pressure reached a threshold value for any of the valves Vn. The use of pressure reducers which provide a constant flow resistance irrespective of flow rate means that the Figure 7 plot is substantially linear, which assists the control of the system. Turning to Figure 6, a three-nozzle arrangement is shown in more detail: Figure 6 thus effectively discloses the interior of the manifold box 20 of Figure 1. A pressure supply line PS for liquid product passes first into a valve VI which is normally closed by a spring, but which will open (against the spring) when the supply line pressure reaches a,, in this example 1 bar. When the valve VI opens, the supply line feeds an outlet line 01, which in turn supplies a nozzle Nl . The nozzle Nl displays acceptable spray characteristics over the range 1 bar to 2.4 bar, this being a typical range for a commercially available nozzle. The supply line PS continues through the valve VI (regardless of whether the valve is open or closed), through a pressure reducing valve PR2 and into a valve V2. The valve V2 is normally closed by a spring but, when open, feeds an outlet line 02 which in turn supplies a spray nozzle N2. The outlet line 02 has a feature lacking from 01 ; it passes through a pressure chest assembly PCI associated with the valve VI. The pressure chest assembly PCI is sensitive to a supply pressure in the line of the outlet line 02; such pressure is sensed by a diaphragm which acts, under such pressure, to assist the action of the spring of the valve VI, predisposing the valve VI to close when 02 is under pressure. It will be appreciated that the outlet line 02 need not itself pass through the pressure chest assembly PCI; it would be sufficient if a spur branched off the outlet line 02 and terminated at the diaphragm of the assembly PCI. The supply line PS continues through the valve V2 (regardless of whether the valve is open or closed), through a pressure reducing valve PR2 and into a valve V3. The valve V3 is normally closed by a spring but, when open, feeds an outlet line 03 which in turn supplies a spray nozzle N3. The outlet line 03 passes not only through the pressure chest assembly PC 1 but also through a pressure chest assembly PC2 associated with the valve V2. The pressure chest assembly PC2 is sensitive to a supply pressure in the line of the outlet line 03; such pressure is sensed by a diaphragm which acts, under such pressure, to assist the action of the spring of the valve V2, predisposing the valve V2 to close when 03 is under pressure. Meanwhile, the outlet line 03 has its own diaphragm in the pressure chest assembly PCI ; that diaphragm, under pressure in the line 03, assists the closing action of the spring SI even if the line 02 is unpressurised. That diaphragm should be larger than the diaphragm in 02 since, when called upon, it must resist a greater pressure from PS tending to overcome the spring SI . A certain amount of hysteresis is necessary for good stability of the valves. This is built-in by the valve design and the diaphragm sizes, whereby the pressure-to-open valve VI for example is arranged to exceed the pressure-at-which-it- closes; this prevents "chatter" of the valve. As a general rule, the size of the diaphragm will be a function of the strengths of the springs Sn, the sizes of the valve members in the valves Vn and the resistances offered by the pressure reducing valves PR2, PR3. The outlet line 03 need not itself pass through the pressure chest assemblies PCI or PC2; it would be sufficient if spurs branched off the outlet line 03 and terminated at the diaphragms of those assemblies or a spur passed through one and terminated at the other. However, the advantage of avoiding spurs, i.e. having the pressure chests en route to nozzles, is that the whole arrangement can be more reliably flushed out. The liquid to be sprayed is pressurised in the supply line PS to a pressure appropriate to the desired spraying rate at that moment. Considering the sequence of events as the pressure is increased, let us consider first a low pressure, such as would be applied when the desired spraying rate is less than a spray nozzle can deliver at acceptable spray quality. This low pressure, call it a 0 , is insufficient to overcome the spring pressure of valve VI. It is transmitted (with loss) through the pressure-reducing valve PR2, and is all the more insufficient to overcome the spring pressure of valve V2. It is transmitted through the pressure reducing valve PR3 (with further loss) and is thus even more insufficient to overcome the spring pressure of valve V3. Springs SI, S2 and S3 (of respective valves, VI, V2 and V3) are of equal strength. The nozzles Nl, N2 and N3 have complementary nominal throughput ratings, viz. 0.6, 0.9 and 1.5 litres/minute respectively. At a higher threshold feed-line pressure a,, the valve VI is just pushed open, admitting spray liquid to line 01 feeding spray nozzle Nl . The spring of VI is arranged such that a, is the pressure for minimum spray rate of acceptable quality through Nl. As liquid pressure in the supply line PS continues to rise, the spray rate through the nozzle Nl rises through the range of acceptable spray quality, whose upper limit is at pressure a 2 At this second threshold feed-line pressure a 2 , even after the action of the valve PR2, the spring S2 of valve V2 is overcome. Liquid under (reduced) pressure is therefore admitted to a spray-feed outlet line 02 and thence to a nozzle N2. As will be recalled, the line 02 includes a pressure chest in the assembly PCI bounded in part by a diaphragm tending, under pressure in the chest, to assist the spring SI to close the valve VI. Thus, on firing of the nozzle N2, the pressure in line 02 assists the spring SI to close the valve VI and the nozzle Nl is thereby shut off. As the liquid pressure in the line PS rises further, to a third threshold feed-line pressure a 3 , the flow rate through the nozzle N2 through this range &2 - a gives an acceptable spray quality for this nozzle. As the supply pressure continues to rise above the pressure a ., even after the action of the pressure reducing valve PR3, the spring S3 of valve V3 is overcome. Liquid under (reduced) pressure is therefore admitted to a spray-feed outlet line 03 feeding a nozzle N3. Since the line 03 includes a pressure chest in the assembly PC2 bounded in part by a diaphragm tending, under pressure in the chest, to close the spring S2, then on firing of the nozzle N3, the spring S2 closes the valve V2 and the nozzle N2 is thereby shut off. The line 03 also includes a pressure chest in the assembly PCI bounded in part by a second diaphragm tending to close the spring VI . Thus, when the line 02 loses pressure and ceases to pressurise the diaphragm, the line 03 almost immediately takes over the same function, preventing the nozzle Nl from inadvertently firing. If there were a fourth valve V4, it would be necessary to provide downstream of it a line passing a third diaphragm tending to close the valve VI, a second diaphragm tending to close V2, and a diaphragm to close V3;n valves would require VI to have n-1 diaphragms, and valve Vm would have V(n-m) diaphragms. Figure 7 shows how this arrangement gives a fairly smooth pressure/delivery rate curve, easy to programme into the spray controller. It will also be observed that the successive nozzles have successively higher characteristic delivery-rate/pressure gradients over their operating ranges, whereby a consistently high spray quality over a delivery-rate range of 0.5 to 2.0 1/minute is achievable over the pressure range of 1 to 6 bar. Pressures over 6 bar are inadvisable in normal agricultural conditions because of the risk of failure of pipe unions. The controller C (Figure 1) is preprogrammed with instructions to adjust the hydraulic feed pressure to meet the volumetric delivery rate required at that moment. The controller is "told" what that required rate is either by a human operator assessing the situation as he sees it or by automated real-time sensing, or more usually is "told" with the aid of a map which was prepared earlier of the requirements of a field (e.g. the weed or pest distribution within that field, or the previous harvest yield distribution within that field). Global position satellite technology is used to ascertain where the spray nozzle arrangement is at any moment in that field in relation to the map. The spray nozzle arrangements are mounted on a spray boom hauled up and down the field by a tractor which also conveys a tank T of liquid plant protection product, and a pump P and pressure regulators 5 (controlled by the controller C) to pressurise the liquid feed lines 2 from the tank to the spray boom up to 6 bar.

Claims: CLAIMS 1. A fluid dispensing arrangement, wherein a fluid under variable supply pressure supplies a plurality of outlet chambers, each outlet chamber dispensing the fluid to an outlet or group of outlets when that chamber reaches a given non-zero pressure, in which arrangement at least one of the outlet chambers, while dispensing the fluid, sends a signal to at least one other outlet chamber tending to stop that other outlet chamber from dispensing. 2. An arrangement according to Claim 1, wherein the signal is hydraulic. 3. An arrangement according to Claim 1 or 2, wherein said signal acts to increase the value of the given pressure above which that other outlet chamber dispenses, thereby tending to stop it from dispensing. 4. An arrangement according to any preceding claim, wherein the given pressure for each of at least some of the outlet chambers has the same value in the absence of said signal, and wherein the supply pressure is attenuated to a degree specific to at least some of said outlet chambers. 5. An arrangement according to any preceding claim, wherein the currently dispensing outlet chamber sends a said signal to all those outlet chambers which dispense at a lower supply pressure. 6. An arrangement according to any preceding claim, wherein the signal takes the form of a displacement of a pressure-sensing element by the pressure within the currently dispensing outlet chamber. 7. An arrangement according to any preceding claim, wherein each outlet chamber includes a valve between it and its outlet or group of outlets, said valves being biassed to close. 8. An arrangement according to Claim 7 when dependent on Claim 6, wherein the displacement closes the valve of the outlet chamber to which the signal is sent. 9. An arrangement according to Claim 8, wherein the route of the fluid from the currently dispensing outlet chamber is via the pressure-sensing element. 10. A pressure chest assembly, comprising an inlet leading to a plurality of outlets, and normally closed passage closure means between the inlet and each outlet, which means open under a different inlet pressure in each case, each outlet, other than the outlet which opens under the least inlet pressure, being in hydraulic communication with the passage closure means of all the outlets which open at a lesser inlet pressure, outlet pressure transmitted through said hydraulic communication biassing the closure means to close. 1 1. A pressure chest assembly according to Claim 10, wherein the said hydraulic communication takes the form that the outlet is routed past the respective passage closure means. 12. A pressure chest assembly according to Claim 10 or 11, wherein the said hydraulic communication acts on a displaceable member of a pressure-sensing element which biasses the closure means to close. 13. A pressure chest assembly according to Claim 12, wherein the displaceable member is a diaphragm bearing on the closure means. 14. A pressure chest assembly according to Claim 13, wherein the closure means is a spring-loaded seal and wherein the diaphragm, under hydraulic pressure through the communication, acts in the same sense as the spring. 15. A spray nozzle arrangement for spraying liquid from a variable pressure source, the arrangement comprising: (a) a plurality of sets of nozzles, each set having a different pressure vs. flow rate characteristic; (b) flow diverting means responsive only to the pressure of the said liquid for directing liquid flow from the source to the said nozzle sets; (c) the said diverting means being operable to enable only one nozzle set at any given time, in dependence on the source pressure. 16. An arrangement as claimed in Claim 15, wherein each nozzle set is supplied via at least one valve having a predetermined threshold input pressure at which it will allow liquid to pass to the said nozzle set. 17. An arrangement as claimed in Claim 16, wherein the said threshold input pressure is different for each nozzle set. 18. An arrangement as claimed in Claim 16, when the said threshold pressure is substantially the same for two or more nozzle sets. 19. An arrangement as claimed in Claim 18, wherein the inputs of the valves of the said two or more nozzle sets are connected in series with the interposition of a pressure reducer or reducers. 20. An arrangement as claimed in Claim 19, wherein the said pressure reducer or reducers are of constant resistance design, whereby the resistance to flow offered by the or each reducer is substantially independent of flow rate. 21. A liquid spraying system including a variable pressure source, the system comprising: (a) a plurality of sets of nozzles, each set having a different pressure vs. flow rate characteristic; (b) flow diverting means responsive only to the pressure of the said liquid for directing liquid flow from the source to the said nozzle sets; (c) the said diverting means being operable to enable only one nozzle set at any given time, in dependence on the source pressure. 22. A system as claimed in Claim 19, wherein each nozzle set is supplied via at least one valve having a predetermined threshold input pressure at which it will allow liquid to pass to the said nozzle set. 23. A system as claimed in Claim 22, wherein the said threshold input pressure is different for each nozzle set. 24. An system as claimed in Claim 22, when the said threshold pressure is substantially the same for two or more nozzle sets. 25. An system as claimed in Claim 24, wherein the inputs of the valves of the said two or more nozzle sets are connected in series with the interposition of a pressure reducer or reducers. 26. An system as claimed in Claim 25, wherein the said pressure reducer or reducers are of constant resistance designs, whereby the resistance to flow offered by the or each reducer is substantially independent of flow rate.

Inventors: MILLER PAUL CHARLES HARVEY, PAICE MARK EDWARD RUSSELL, MILLER, PAUL, CHARLES, HARVEY, PAICE, MARK, EDWARD, RUSSELL
Applicants: BTG INT LTD, MILLER PAUL CHARLES HARVEY, PAICE MARK EDWARD RUSSELL, BTG INTERNATIONAL LIMITED, MILLER, PAUL, CHARLES, HARVEY, PAICE, MARK, EDWARD, RUSSELL
Application year: 1998
Main classification: B05B12
IPC codes: B05B1, B05B9, B05B12