Agitation

Agricultural products are formulated to be as emulsifiable as possible, but many do not mix well in water. They contain elements that do not dissolve (e.g. wettable powders), or they may be petroleum distillates (e.g. emulsifiable concentrates). Other products are heavier than water and form precipitates (e.g. fertilizers and powdered metals like copper). Consequently, good agitation is very important.

Effective agitation requires water to “sweep” the bottom of the tank so that any precipitated material is picked up and re-mixed. Turbulence is often not enough. If there is too little agitation, the pesticide will be applied unevenly and not always at the required rate. If there is too much agitation, the pesticide may foam (which can be controlled using anti-foamers) or cause an invert emulsion (a gel). There are two common types of airblast sprayer agitation: Mechanical and Hydraulic.

Mechanical Agitation

Mechanical Agitation is produced by paddles that are attached to a shaft mounted near the bottom of the spray tank. While relatively effective, this system cannot always sweep the very bottom of the tank, so there is always some material that precipitates out of reach. Are your nozzles and screens plugging frequently, and is there “sludge” left at the bottom of the tank after spraying? You have an agitation issue.

Note the two paddles set at 90° to one another on the mechanical agitation shaft in this very cool “cutaway” Turbomist sprayer.

Note the two paddles set at 90° to one another on the mechanical agitation shaft in this very cool “cutaway” Turbomist sprayer.

Hydraulic Agitation

Hydraulic Agitation is accomplished by returning a portion of the pump output to the tank. Cylindrical and oval tanks are the ideal configuration for the sparging (i.e. rinsing) type of hydraulic return agitation system. This system consists of a tube located longitudinally along the wall of the tank, with volume booster nozzles aimed at the centreline so they sweep across the bottom. Volume booster nozzles take a small amount of water pumped into their venturi chamber and create a vacuum that draws three to four times that volume from the surrounding water and expels it out the end. For hydraulic agitation to the effective, the agitator nozzle(s) should be fed by a dedicated line from the pressure side of the pump (not the pressure regulator). They should have a valve to throttle the flow or completely shut it off to prevent foaming.

A mixing nozzle in the basket of a Hol sprayer.

A mixing nozzle in the basket of a Hol sprayer.

With enough pump capacity, a hydraulic return in the tank basket is a great way to agitate as you mix. A return in an old FMC.

With enough pump capacity, a hydraulic return in the tank basket is a great way to agitate as you mix. A return in an old FMC.