The present invention relates to an agricultural sprayer for spraying a carrier liquid, such as water, mixed with at least one active ingredient and including a container for the carrier liquid, at least one container for an active ingredient, such as a fertilizer, an insect or disease controlling ingredient or a weed killing ingredient, in concentrated form, a mixing chamber for mixing the carrier liquid for feeding the active ingredient to the mixing chamber and for deeding the carrier liquid to the mixing chamber, a boom structure having at least one nozzle connected with the mixing chamber for spraying the active ingredient mixed with the carrier liquid, and means for generating and discharging a flow of gas under pressure, preferably air.
Such agricultural sprayers are generally known from the disclosure of EP 86 031, for example, and are used as a modern alternative to conventional agricultural sprayers where the active ingredient is mixed with the carrier liquid prior to the sprayer being advanced over the field.
The use of this new type of agricultural sprayer often involves, however, a significant loss of expensive active ingredient when the lines that connect the active ingredient containers with the nozzles, are emptied after the termination of the spraying operation for allowing subsequent spraying of a different active ingredient. This problem is particularly pronounced where the mixing-chamber, in which the active ingredient is mixed with the carrier liquid, is arranged at a relatively great distance from the active ingredient container. The active ingredient emptied from the lines is at times merely led to the sewer, leading to severe environmental problems.
The invention provides simple means whereby the above loss of active ingredient may be prevented, allowing ia. reduction of the costs involved in the spraying operation.
In accordance with the invention connecting means is provided that allow gas flow communication between the means for generating and discharging a flow of gas under pressure and the active ingredient container, the connecting means being located such that discharged gas under pressure sets up a flow of active ingredient which has not been mixed with the carrier liquid and which is present in the line connecting the mixing chamber with the active ingredient container, in a direction from the mixing chamber toward the active ingredient container.
The connecting means may include a valve, such as a one-way valve. The use of a suitable valve arranged at the mixing chamber may permit a sealing-off or the mixing chamber when pressurized gas is discharged and active ingredient is led back to the container. The pressurized gas may also be used for simultaneous or subsequent discharge of any liquid present in the mixing chamber through the nozzles.
The means for generating and discharging a flow of gas under pressure may preferably be a compressed air container or, alternatively, an air blower, whereby the invention may be implemented to particular advantage in connection with so-called air-assisted agricultural sprayers (see, for example, EP 734 203), where the air-flow from the blower may thus be utilized for the mentioned purpose after the termination of the spraying operation.
The lines for feeding the active ingredient to the mixing chamber may also be connected with a container for a cleaning or rinsing liquid, such as the container for carrier liquid, to allow flushing thereof after the active ingredient has been driven back to the active ingredient container.
Further, the mixing chamber may be positioned close to the nozzles on the boom structure, so that a prescribed change of the metered amount of active ingredient per unit of time and thereby of the concentration of active ingredient in the mixture is registered in the spray discharged from the nozzles immediately after the change has been made. The invention provides quite special advantages in this case, since a degree of freedom is achieved as regards the positioning of the active ingredient containers, without involving an unnecessary loss of active ingredient after the termination of a spraying operation. It will be appreciated that in this situation the active ingredient containers may be positioned close to the carrier liquid container, thereby allowing the operator-operated parts of the agricultural sprayer to be gathered at one place.
Means may also be provided for equalising the pressure in the container for active ingredient. The provision of such means is, however, no prerequisite for the proper operation of the invention, particularly when collapsible containers for the active ingredient are used.
Alternatively, the means may be adapted to generate a negative pressure in the container for active ingredient, thereby drawing back active agent present in the hose leading to the mixing chamber. In this case, too, means for providing a pressure equalisation may be provided.
It will be appreciated that the invention may find application in connection with agricultural sprayers having one or more containers for different active ingredients, including e.g. where each of these are connected with the same or different mixing chambers by means of hoses, which may thereby be emptied after the termination of a spraying operation. Such an agricultural sprayer may e.g. conceivably be used for spraying during the same operation of an area where e.g. a fungicide is needed in one area, while an insecticide is needed in an adjoining area.