Patent Publication Number: US-2013233940-A1

Title: Spraying Assembly, and Sprayer Equipped with at least one such Assembly

Description:
The present invention relates to a spraying assembly, and a sprayer equipped with at least one such assembly. 
     BACKGROUND 
     A traditional agricultural sprayer, for example a tractor, includes a ramp equipped with a plurality of spray nozzles connected to ducts in which a liquid product to be sprayed on the plants to be treated circulates. The plants to be treated may be of any type, and the term “agricultural” is to be understood here in the broad sense, in particular including arboricultural crops. 
     In the case of a direct injection spraying system, an active liquid or powdery material is incorporated or mixed into the liquid to be sprayed (in general clean water) upstream of the ramp, over the course of the spraying, as considered in WO-A-90/11010, where a ball-shaped check valve is installed at the outlet of a dosing pump relatively remote from the nozzles it supplies. 
     Such a system has a certain number of drawbacks. 
     When the sprayer slows down, the flow rate of the injection of active substance into the liquid to be sprayed decreases. 
     However, in particular in the case of a very long ramp, the liquid with a smaller dose of active substance takes some time to reach the nozzles, and during that time the plants are overdosed with active substance. The ramp causes inertia in the dosing of the mixture of active substance and liquid to be sprayed. 
     Conversely, when the sprayer accelerates, the injection flow rate of active substance into the liquid to be sprayed increases. 
     The liquid with a higher dose of the active substance takes some time to reach the nozzles, and during that time, the plants are underdosed with active substance. 
     Furthermore, during the modification of the speed of the sprayer, these overdosing or underdosing phenomena overlap, which accumulates, amplifying them and their respective negative effects described above. 
     It has also been possible to observe that the overdosing or underdosing phenomena were irregular and asynchronous, depending on the distance of each nozzle relative to the point of the incorporation of the active substance into the liquid to be sprayed, in particular in the case of very long ramps. 
     Furthermore, when the spraying is restarted by a ramp segment comprising several nozzles after a temporary interruption in that spraying, the liquid that initially flows in the duct results from dosing done before that interruption. However, such dosing generally does not correspond to the required dosing after that restart, since the speed of the sprayer changes relatively often. 
     WO-A-2005/048704 describes a spraying assembly comprising a nozzle for projecting a liquid to be sprayed and active substance pumps that are located directly upstream of the nozzle, to introduce the active substance into a mixing area with the liquid to be sprayed. 
     However, the pumping chamber of each active substance pump is in permanent fluid communication with said mixing zone. Yet although the volume of that pumping chamber is substantially smaller than the volume of the ramp, it also causes a certain volume inertia in the dosing of the mixture to be produced, which prevents the spraying assembly from making quick, or even instantaneous, variations in the concentration of said mixture and leads to overdoses. 
     SUMMARY OF THE INVENTION 
     An objection of the present invention aims to resolve these drawbacks by proposing a spraying assembly and a sprayer that are very reactive and reliable, and relatively easy to adjust remotely, potentially electronically. 
     To that end, the present invention provides a spraying assembly comprising at least one nozzle for liquid that is to be sprayed, and at least one active substance injector into the liquid that is to be sprayed, the injector being situated directly upstream from at least one nozzle and supplied with liquid to be sprayed by means of a pump or a pressurized reservoir, with interposition of an obturator on a conduit connecting the pump or the pressurized reservoir to the injector. This assembly additionally comprises, for each injector, an outlet valve designed to close the or each outlet orifice. 
     Within the meaning of the present invention, the injector is situated directly upstream from the or each nozzle, i.e., the flow path of the active substance between the outlet of the injector and the nozzle has a length of only several centimeters. 
     Owing to these features, the assembly according to the invention makes it possible to incorporate the active substance into the liquid to be sprayed at the last minute, i.e. just upstream from a nozzle or a group of nozzles, and therefore just before the actual spraying of that liquid. 
     It is therefore possible to adjust the dosing of active substance in the liquid to be sprayed instantaneously, and consequently to avoid the overdoses or underdoses observed in the prior art. 
     According to other advantageous, but optional, features of the spraying assembly according to the invention, any one of the following features may be considered alone or according to any technically allowable combination:
         the or each outlet valve is a needle adapted to come alongside a seat formed at the outlet orifice;   the or each nozzle and the or each injector are mounted on the same body or two adjacent bodies, a mixture of the liquid to be sprayed with the active substance occurring through turbulence in the or each body;   this assembly comprises a plurality of injectors situated directly upstream from the or each nozzle;   this assembly comprises means for remotely controlling each injector and/or each outlet valve, and the or each injector and/or the or each outlet valve can be actuated remotely;   the or each injector is chosen from the group comprising a valve or pump of the ceramic, electromagnetic, piezoelectric or peristaltic type;   the assembly comprises means for injecting air into each injector.       

     The present invention also provides a sprayer equipped with at least one assembly according to the present invention, comprising at least one primary conduit designed to supply the or each nozzle with liquid to be sprayed, and at least one secondary conduit designed to supply the or each injector with active substance. 
     According to other advantageous, but optional, features of the sprayer according to the invention, any one of the following features may considered alone or according to any technically allowable combination:
         the sprayer comprises a plurality of secondary conduits respectively supplying each injector;   the sprayer comprises means for keeping the pressure of the liquid to be sprayed constant directly upstream of the or each nozzle;   the sprayer comprises means for regulating the flow rate of active substance in the or each body;   the sprayer comprises regulating means adapted to regulate the flow rate of active substance in each injector as a function of the displacement speed of the sprayer and/or the state of the plant surface to be treated, for example depending on whether the plants to be sprayed are healthy or in poor health;   each means for maintaining the pressure of the liquid to be sprayed and each means for regulating the flow rate can be actuated individually and independently;   the or each injector comprises a pump or a piezoelectric, electromagnetic or peristaltic valve, and the control means are adapted to vary the operating speed of the pump or the valve so as to drive the flow rate thereof; and   at least one of the secondary conduits is adapted to convey a first type of active substance, for example an herbicide (potentially selective, and therefore dangerous for other crops), and at least one other of the secondary conduits is adapted to convey a second type of active substance, for example an insecticide, a fungicide, or a wetting agent;   the or each primary conduit includes at least one valve to control the circulation of liquid to be sprayed and the or each secondary conduit includes at least one obturator to control the circulation of active substance, the or each valve and the or each obturator being able to be actuated remotely.       

     The present invention also provides a method for cleaning a spraying assembly in which means are provided for injecting air into each injector through its outlet orifice. This method comprises steps consisting of injecting a quantity of air into each injector, countercurrent from the direction of flow of the liquid to be sprayed in that injector, and pushing part of the liquid to be sprayed that is present in that injector and in its supply means back toward a storage reservoir for the product to be sprayed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be well understood, and advantages thereof will also emerge, in light of the following description, provided solely as a non-limiting example, in reference to the appended drawings, in which: 
         FIG. 1  is a diagram of the spraying assembly according to a first embodiment of the invention; and 
         FIG. 2  is a diagram similar to  FIG. 1  of a spraying assembly according to a second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a nozzle  1  mounted on a body  3  connected to a primary vat  5  by means of a shared conduit  78  and a primary conduit  7 . The inlet of the shared conduit  78  is connected on the primary vat  5 . The primary conduit  7  emerges in the body  3 . 
     The term “connect” relates to a fluid communication, which means a conduit allowing the fluid to circulate between two components of a spraying assembly, for example between the primary vat  5  and the body  3 . Such a conduit may be embodied by a flexible hose, a rigid tube, or any other known equivalent means. 
     Alternatively, the or each nozzle  1  and the or each injector  21   a  to  21   d  may be mounted on two adjacent bodies  3 , i.e. close to one another. 
     The or each body  3  is adapted to produce a mixture of the liquid to be sprayed with the active substance. To that end, the or each body  3  may be equipped with a static mixer, baffles and/or propellers, etc. A valve  203  is arranged on the primary conduit  7  so as, if necessary, to prevent said mixture from returning into the primary conduit  7 . Alternatively, the valve  203  may be replaced by a check valve. 
     The body  3  is in turn mounted on a spraying ramp structure  9 . 
     The primary vat  5  and the ramp  9  are mounted on the chassis  11  of an agricultural sprayer, such as a tractor or trailer. 
     A primary pump  13  is arranged on the shared conduit  78  between the primary vat  5  and the body  3 . The conduit  78  is said to be shared because it emerges, by means of a T coupling  210 , on the one hand on the primary conduit  7  and on the other hand on a return conduit  8  designed to allow the liquid to be sprayed to circulate up to the primary vat  5 . 
     The first spraying assembly includes a valve  207  and a valve  208  respectively arranged on the primary conduit  7  and on the return conduit  8  to control the circulation of liquid to be sprayed therein. 
     The valves  203 ,  207  and  208  are driven into the open position or closed position by suitable electrical means. 
     When the valve  207  is open, the liquid to be sprayed circulates in the primary conduit  7 . When the valve  207  is closed, the liquid to be sprayed does not circulate in the primary conduit  7 . 
     Likewise, when the valve  208  is open, the liquid to be sprayed circulates in the return conduit  8 . When the valve  208  is closed, the liquid to be sprayed does not circulate in the return conduit  8 , but flows in the primary conduit  7  if the valve  207  is open. 
     This spraying assembly can thus operate through recirculation, in particular to keep the liquid in motion even after having temporarily, partially or completely, interrupted the spraying thereof. 
     Several injectors  21   a ,  21   b ,  21   c  and  21   d , four in the illustrated example, are mounted on the body  3  and each respectively connected to a secondary vat  25   a ,  25   b ,  25   c  and  25   d  by secondary conduits  27   a ,  27   b ,  27   c  and  27   d.    
     Respective pumps  33   a ,  33   b ,  33   c  and  33   d  are located on the secondary conduits  27   a  to  27   d.    
     The injectors  21   a  to  21   d  may be valves or may be ceramic or electromagnetic or piezoelectric pumps. Each of the injectors  21   a  to  21   d  can be actuated remotely, i.e., it may be controlled by suitable and remote electrical means. 
     Each injector  21   a ,  21   b ,  21   c  and  21   d  also includes a respective obturator or check valve  24   a ,  24   b ,  24   c  and  24   d , in which a corresponding secondary conduit  23   a ,  23   b ,  23   c  and  23   d  is arranged so as to cut the supply. 
     Furthermore, the spraying assembly comprises outlet valves that are respectively arranged close to and downstream from each injector  21   a  to  21   d  so as to close off the outlet orifice  26   a  to  26   d  thereof. Each outlet valve is made up of a needle  22   a  to  22   d  with a conical, flat, or piston shape, adapted to come alongside a seat or bore with a complementary shape that is formed at the corresponding outlet orifice  26   a  to  26   d.    
     Each needle  22   a  to  22   d  serves to allow or stop the fluid communication between the specific volume of the injector  21   a  to  21   d  able to contain active substance and the nozzle  1  or, more specifically, the body  3 . 
       FIG. 1  shows a single body  3  supporting a single nozzle  1  and four injectors  21   a  to  21   d , but the ramp  9  may be provided with a plurality of bodies  3  each supporting one or more nozzles  1  and one or more injectors  21 . 
     Each of the bodies  3  is in fluid communication with the primary conduit  7 , and each of the injectors  21  is in fluid communication with a secondary conduit  23  concerning it. 
     Means for creating turbulence are provided in the body  3 . They favor mixing by turbulence between the liquid to be sprayed and the active substance leaving an injector  21 . 
     Typically, the bodies  3  may be distributed at regular or irregular intervals as needed, for example every 50 cm on the ramp  9 . 
     Alternatively, the bodies  3  may be mounted on independent segments of the ramp  9 . A “segment” is a group of standard nozzles  1  that are successively arranged along the ramp  9  or juxtaposed on an independent branch, and whereof the nozzles can be controlled and operate simultaneously, when they are not controlled individually. 
     In a first embodiment, the secondary pumps  33  are typically adapted to generate a liquid pressure in the secondary conduits  23   a  to  23   d  that is higher than that prevailing in the primary conduit  7  and the body  3 . This pressure may for example be approximately 10 bars. 
     In a second embodiment, there are no more pumps  33  and the cans  25  are kept at a slight overpressure, of several decibars, relative to the spraying pressure generated by the primary pump  13 . This may for example be obtained using pneumatic or hydraulic pressure exchangers, with pistons or membranes but with different sections, situated between the circuits  7  and  23 . 
     In order to control the size and spectrum of the sprayed crops, the agricultural sprayer also comprises means for keeping the pressure of the liquid to be sprayed constant directly upstream from each nozzle  1 . Such means may for example be made up of valve or membrane regulators or other known equivalent means. The terms “upstream” and “downstream” refer to the flow direction of the considered fluid, i.e., the liquid to be sprayed, the active substance, or the mixture thereof. 
     The agricultural sprayer also comprises means for example, a regulator or valve, for regulating the flow rate of active substance in each secondary conduit  23   a  to  23   d . The supply of each injector  21   a  to  21   d  with active substance therefore depends on these regulating means or regulators. 
     Such means for regulating the flow rate of the active substance, as well as the obturators  24   a  to  24   d  (in all or nothing mode), or the injectors  21  (in discrete variation mode, by electrical pulses) controlling the supply of liquid to be sprayed, may be controlled as a function of data supplied by a global positioning system (of the GPS type) or an onboard camera on the ramp or the agricultural vehicle coupled to an image processing system. 
     Such an image processing system makes it possible to detect adventives to be destroyed or to use the color of the plant to evaluate its needs with respect to the active substance for growth, such as fertilizers or growth regulators. 
     Furthermore, the active substance circuits may have structures and/or arrangements that differ as a function of the type of active substance they are respectively designed to convey. 
     Thus, each secondary vat  25   a  to  25   d  can be adapted to receive a predetermined type of active substance and each secondary conduit  23   a  to  23   d  may be adapted to convey the corresponding type of active substance. 
     For example, the secondary duct  23   a  may be reserved to convey only selective herbicides (dangerous for other crops), while the secondary conduit  23   d  may rather be adapted to convey fungicides or insecticides (the residues of which are not harmful for other crops). 
     Such means may be adapted to regulate the flow rate of active substance in proportion to the speed of travel of the sprayer and/or the plant surface to be treated. The plant surface to be treated may be evaluated using an onboard camera on the ramp or the agricultural vehicle coupled to an image processing system. 
     In the case where each injector  21   a  to  21   d  comprises a valve or an electromagnetic or piezoelectric pump, said regulating means are formed by an electronic circuit adapted to vary the vibrational frequency of each injector  21   a  to  21   d . The operating mode and the advantages of the present invention result directly from the preceding description. 
     A liquid to be sprayed is placed in the primary vat  5 . This may be either clean water, or a mixture of clean water and a phytosanitary product, or potentially a liquid fertilizer, which must be sprayed in pure state and at a large volume per hectare. 
     During operation, the primary pump  13  sends the liquid to be sprayed into all of the bodies  3  distributed on the ramp  9 , thereby allowing that liquid to be sprayed by the nozzles. 
     The pump  13  may be of the displacement, constant pressure or constant flow rate type. It may have pistons, membranes, a centrifuge, or other means. 
     With the injector devices  21 , which directly regulate the quantity of active substance per hectare, the pump  13  is kept at a constant pressure. This pressure is selected, in association with the type of nozzles installed, to generate drops with a predetermined size and spectrum, not modified by the speed of travel or the quantity of active substance introduced by the injectors  21 . 
     Exceptionally, when it is preferable to use the sprayer traditionally, without using the injectors  21 / 221 , the pump  13  may then be interfaced with a braking system of the DPA (output proportional to forward speed) type, which makes it possible to adapt the liquid flow rate in the primary conduit  7  as a function of the forward speed of the sprayer. 
     Mixtures containing active substances designed to be incorporated into the liquid to be sprayed are placed in the secondary vats  25   a  to  25   d.    
     This incorporation is done by acting on the secondary pumps  33   a  to  33   d , selectively or simultaneously. This incorporation may also be done by placing the vats  25   a  to  25   d  under air pressure, or under hydrostatic pressure using pressure exchangers, as mentioned above, inasmuch as pumps  33   a  to  33   d  are not used, but the injectors  21 / 221  are rather used directly, which then act as simple dosers. 
     In so doing, the injectors  21   a  to  21   d  inject the concerned mixtures of active substances into the body  3 , i.e. just upstream from the nozzle  1 . 
     These active substances are therefore incorporated into the liquid coming from the primary vat  5  immediately before spraying, and therefore sprayed on the plants to be treated taking the forward travel speed of the sprayer into account, which prevents overdoses and underdoses. 
       FIG. 2  shows a second spraying assembly as an alternative to the first spraying assembly illustrated in  FIG. 1 . In  FIG. 2 , the components of the second spraying assembly that have a structure and function identical to the components of the first spraying assembly bear the same numerical references and operate comparably, with the exception of the differences indicated below. 
     Each indicator  221   a  to  221   d  of this embodiment comprises a piston  223   a  and  223   d , controlled by a piezoelectric component  229   a  to  229   d  arranged inside the body of the injector, which is only partially shown in  FIG. 2 . This makes it possible to form, within each injector, a piezoelectric micro-pump capable of delivering a predetermined quantity of liquid to the nozzle  1 , proportional to its vibrational frequency. In practice, each piston  223   a  and  223   d  can be made up of one or more surfaces of the piezoelectric component, since the vibrations of such a component cause alternating translations of its surfaces. 
     Alternatively, the pistons  223   a  to  223   d  are replaced by membranes controlled by an electromagnetic device. Membrane pumps are then used. 
     Alternatively, a magnetic or ceramic micro-pump or a peristaltic micro-pump may be used in each injector  221   a  to  221   d.    
     Depending on the type of pump used in the injectors, and its withdrawal power, it is possible to do without the pumps  33   a  to  33   d , which are therefore optional, for example by placing the reservoirs  25   a  to  25   d  under a slight overpressure of several decibars with respect to the conduits  7  and  8 , as considered above with a pressure exchanger. 
     Outlet valves made up of needles  222   a  to  222   d  are respectively arranged near and downstream from each corresponding injector  221   a  to  221   d , so as to close off the outlet orifice  226   a  to  226   d . Each needle  222   a  to  222   d  has a globally conical shape to come alongside a seat with a complementary shape that is formed at the corresponding outlet orifice  226   a  to  226   d.    
     Each needle  222   a  to  222   d  serves to allow or stop the fluid communication between the injector  221   a  to  221   d  and the nozzle  1 . 
     The respective needles  222   a  to  222   d  of the injectors  221   a  to  221   d  are mounted in opposite directions relative to the needles  22   a  to  22   d  of the injectors  21   a  to  21   d . The needles  222   a  to  222   d  act as discharge valves, while the needles  22   a  to  22   d  of the injectors  21   a  to  21   d  act as opening valves of the respective chamber  21   a  to  21   d  with respect to the body  3 . The needles  22   a  to  22   d  and  222   a  to  222   d  also perform a check function in the upstream direction. 
     Each injector  221   a  to  221   d  also includes a valve, such as the obturator  224   a , arranged on the corresponding secondary conduit  23   a  to  23   d , so as to cut the supply. Such an obturator may also operate in suction. It advantageously forms a check valve. 
     During operation, when the piston  223   a  has withdrawn to suction the active substance in the injector  221   a , the obturator  224   a  opens automatically. Then, when the piston  223   a  moves forward within the injector  221   a , toward the needle  222   a , the obturator  224   a  closes automatically. 
     When the active substance pressure in the injector  221   a  exceeds the force due to the stiffness of a spraying  225   a  returning the needle  222   a  to the closed position, the latter part opens and the active substance is discharged outside the injector  221   a  into the body  3  and toward the nozzle  1 , without rising in the primary conduit  7  toward the primary vat  5 , due to the presence of the check valve  203 . 
     The injectors  221   a  to  221   d  have the same structure and operate in the same way as the injector  221   a  described above. 
     Since the valve  207  and each pump can be actuated remotely, it is possible only to control the circulation of active substance and/or drive the spraying of liquid in the presence of plants to be treated. 
     The agricultural sprayer is triggered by signals detecting plants to be treated, which determine the spraying phases and/or active substance injection phases. Such signals may for example be generated by an image processing system processing images acquired by an onboard camera on the ramp or the agricultural vehicle. In this way, the spraying may be activated, nozzle by nozzle, only in the presence of plants to be treated, by actuating the valves  203 ,  207  and  224  and/or the injectors  21   a  to  21   d  or  221   a  to  221   d.    
     Likewise, the injection of active substance from each of the nozzles may be activated, deactivated, or dosed differently, depending on the state of the crop to be treated, for example by infrared imaging, or by the GPS position characterizing the shape and borders of the field, or a surface that has already been treated, or the proximity of a sensitive area to be respected. For example, in particular when a weedkiller is applied, the injection of active substance may depend on whether the plants to be treated are healthy or in poor health, which may be detected by infrared imaging. The control means, for example, a controller, therefore make it possible, using the injectors, to regulate the flow rate of active substance as a function of the state of the plant surface to be treated. Alternatively or additionally, these control means make it possible to regulate the flow rate of active substance as a function of the speed of movement of the sprayer, i.e. the speed of forward movement of a tractor supporting or pulling it. 
     Irrespective of the embodiment, the spraying assembly can thus operate by recirculation, in particular to keep the liquid in motion, even after its spraying has been partially or completely temporarily interrupted. 
     In all of the embodiments, in particular those illustrated, the spraying assembly according to the invention makes it possible to incorporate the active substance(s) into the liquid to be sprayed “at the last minute,” i.e., just before actual spraying of that liquid. 
     It is therefore possible to adapt the dosing of active substance of the liquid to be sprayed instantaneously by controlling, in a suitable manner, i.e. complete, partial or proportional, the injectors  21   a  to  21   d  or  221   a  to  221   d , and consequently to avoid the overdoses or underdoses observed in the assemblies of the prior art. 
     In fact, the specific volume of each active substance injector  21   a  to  21   d  or  221   a  to  221   d  is not in permanent fluid communication with the mixing area of the body  3 . Consequently, an injector  21 / 221 , which is physically on the borderline and very close to the mixing chamber  3 , which must be very small and turbulent to ensure good homogenization, does not cause inertia in the dosing of the mixture, which allows each nozzle  1  to make quick, even instantaneous, variations in the concentration of that mixture. 
     It is possible for the injectors  21   a  to  21   d  or  221   a  to  221   d  and/or the secondary pumps  33   a  to  33   d  also to be interfaced with any DPA regulating system of the pump  13 , so as also to adapt the quantity of active substance incorporated into the liquid to be sprayed to the speed of movement of the sprayer. 
     The secondary vats  25   a  to  25   d  may either contain different mixtures or identical mixtures. In the latter case, it is possible to have a wider variation range for the quantity of a given active substance incorporated into the liquid to be sprayed. 
     This in fact makes it possible to adapt the quantity of active substance injected into the body  32  at an extended speed variation range of the sprayer for example situated between 3 and 30 km/h. 
     This may in particular be useful when the active substance(s) to be incorporated into the liquid to be sprayed in the body  3  are incompatible with the phytosanitary product conveyed by that liquid, by means of the pump  13  and the conduit  7 , or when said active substance(s) must be incorporated into the liquid to be sprayed at a very small dose and/or only at certain moments. 
     Another advantage of the spraying assembly according to the invention lies in the fact that once the size of the drops of liquid to be sprayed by the nozzle  1  is chosen, in particular by acting on the liquid pressure in the primary conduit  7  and the type of nozzle, the incorporation of active substances using injectors  21  or  221 , at the nozzle  1  or various segments of the ramp  9 , has practically no effect on the size of those drops. 
     In fact, an assembly according to the invention, including used without DPA or pressure variation of the pump  13 , implements means, for example, a regulator or valve, for maintaining the pressure of the liquid to be sprayed, which makes it possible to keep the size of the projected drops substantially constant. It is therefore possible to control this drop size, and consequently to optimize the adaptation of spraying to each category of plants. 
     Furthermore, such an assembly implements means making it possible to regulate the active substance flow rate, and therefore its concentration in the liquid to be sprayed, in proportion to the speed of forward movement of the ramp  9 , without, however, altering the flow rate of that carrier liquid itself. 
     Aside from the size of the drops, which in this case is constant, the user can thus vary, as desired and potentially manually, the concentration of active substance, in a particularly precise and localized manner. 
     Furthermore, each pressure maintenance means and each means for regulating the flow rate can be actuated individually and independently, which allows “unitary” control of each injector and each nozzle independently of one another, which guarantees that the sprayer can be used flexibly and with a wide spectrum as to the plants to be treated. 
     According to one aspect of the invention which is optional and which is shown only in  FIG. 1 , the nozzle  1  comprises a ramp  400  for injecting air in countercurrent in the injectors  21   a  to  21   d . More specifically, an air injector  401   a  belonging to the ramp  400  emerges in the injector  21   a  and is oriented toward the conduit  23   a . Corresponding injectors belonging to the ramp  400  emerge in the other injectors. The ramp  400  is connected to a compressed air source S through a control valve  402 . 
     Thus, at the end of a half-day or a full day of spraying, it is possible for the user to inject, in the injectors  21   a  to  21   d , and countercurrent with respect to the normal direction of circulation of the liquid to be sprayed, a sufficient quantity of air to clean said injectors and push the products to be sprayed effectively toward the reservoirs  25   a  to  25   d , through the conduits  23   a  to  23   d , the obturators  24   a  to  24   d , the pumps  33   a  to  33   d  and the conduits  27   a  to  27   d . Thus, the products present in the injectors  21   a  to  21   d  and in their respective supply means may be recovered at the end of a spraying period. This operation also makes it possible to decrease the quantity of water or liquid product necessary to clean the injectors  21   a  to  21   d  and their means for supplying products to be sprayed at the end of a spraying operation. 
     A similar construction, with means for injecting air in countercurrent, may be adopted with the spraying assembly and the sprayer of  FIG. 2 . 
     Of course, the present invention is in no way limited to the example described above, which has been provided as an illustration and non-limitingly.