CIRCULATION PUMPS
Circulation pumps can be used for agitation and mixing, typically by laying the discharge
pipe of the recirculation system along the bottom of the tank in the same fashion as an air
agitation pipe, perforating it with holes on periodic centers, and pumping the recirculating
solution through it. -The majority of the pump's energy is lost to turbulence right at the
pipe/solution interface, so this approach has not been very popular.
The recent development of engineered eductor systems, however, is rapidly changing this
situation. In this approach, an eductor is mounted at each of the discharge holes to improve
the mixing efficiency greatly. The pump propels the primary solution through a nozzle, but the
nozzle is mounted inside a venturi bell, which induces a large secondary stream to flow
laminarly through the bell as well. The result is efficient mixing.
Eductor systems can often deliver benefits similar to air agitation systems, while not
drawing in dirty shop air, nor aerating or oxidizing the solution.
Pumps are also commonly employed with other aims in mind, and in meeting their
primary objectives, they may serve to mix and agitate the solution. For example, circulation
pumps that are installed to skim away floating grease on cleaning tanks will deliver solution
agitation as a side benefit (see Fig. 8).
On systems employing circulation pumps, care should be exercised in limiting the
amount of process solution that is at risk of being lost to drain in the event of a malfunction
or improper valve setting. Also, caution should be used to ensure that safety is not
compromised; the pump shown in Fig. 8 must be low pressure and the holes in the skimmer
pipe must be large lest partial blockage raise the possibility of squirting alkaline cleaning
solution at an operator.