The objective of an agricultural crop spraying machine is to effectively distribute an agro-chemical spray over the largest area of crop in the least amount of time. The conventional design for such a machine is a wheeled base unit, be it trailed or self-propelled, which carries a tank, pump, and controls. The conventional design supplies the agro-chemical to the distribution booms extending from either side of the wheeled base unit, perpendicular to the direction of travel.
Nozzle bodies are placed at regular intervals along the spray boom. This is referred to as a wet boom configuration. The primary role of the nozzle bodies is to provide a sealed connection between the pipe work of the boom supply and the spray tips distributing the agro-chemical. The nozzle bodies also position the spray tips at the correct angle with respect to the direction of travel. Each nozzle body has a turret to which the spray tips are attached to regulate spray pattern and flow rate.
The nozzle body is designed to siphon solution from the pipe or metal tubing from the bottom of the pipe. This orientation causes a situation where air, which is normally present in varying concentration, is pumped into the boom pipe. Air is less dense than the solution being applied and is therefore trapped in the top of the boom pipe above the solution. Air is a compressible gas that accumulates in the top of the boom and builds in pressure. When the sprayer is shut off at the end of a pass on the field or when the operator is finished spraying, the pressure in the boom pipe is still greater than the activation pressure in the diaphragm check valves (e.g., 0.5 bar) due to the air acting as an accumulator. This creates the problem of the nozzle assemblies continuing to dispense solution even after the sprayer valve is shut off. As the nozzle assemblies continue to dispense solution, the air pressure in the boom pipe decreases as the air volume expands. The nozzles will continue to dispense solution until the air pressure in the boom decreases to the point where the pressure in the boom equals the activation pressure of the diaphragm check valve. With the presence of air in the boom pipe, shutoff times can be delayed by up to eight seconds, resulting in a significant amount of solution that is applied when and where it is not intended.