These are the ranges that do something to the liquid rather than simply move it. A submersible aerator puts oxygen into waste water; a mixer keeps a tank homogeneous; a magnetic agitator stirs a sealed vessel without a shaft penetrating the wall; a high shear emulsifier forces two immiscible phases into a stable dispersion.

The magnetic agitator is worth singling out because it solves a specific problem. Any stirrer with a shaft through the tank wall has a seal there, and that seal is both a contamination route and a leak path. A magnetically coupled agitator drives the impeller through the wall, so there is no penetration and nothing to seal.

High shear emulsifiers and defoamers tend to arrive as a pair in process lines, because the energy that creates an emulsion also entrains air, and the foam that results has to be dealt with somewhere downstream. Specifying the emulsifier without thinking about the foam is a common way to build a process that works in a beaker and not in a tank.

All of these are sized against the vessel rather than against a flow rate, which is why the tank volume and geometry matter more than a duty point when specifying them.