Some sprayers are equipped with flow proportioning devices which are designed to compensate for slight changes in forward speed while still maintaining a constant application rate. When using these sprayers, make sure you know the limits of this compensation mechanism. Drive wheel slippage will reduce the accuracy of speed measurement with a tractor tachometer. This becomes a very important consideration with hilly fields or fields of varying soil texture. Mechanical or electronic speedometers controlled by a ground-driven wheel will increase the accuracy of speed measurement.
Low pressures tend to result in fewer small droplets.
It is important to be able to maintain a constant pressure at the tip. Variations in pressure result in increases and decreases in spray angle and flow rate and therefore, uneven herbicide application. The angle of the spray pattern determines the distance the tip must be held from the target. For preemergence or soil-incorporated herbicides, the target is the soil surface, while with postemergence broadcast spraying, the target is the top of the weeds or crop, whichever is taller. The wider angle can give better penetration into a canopy or around crop residue on the soil surface.