Pump Sleeves help direct water flow to properly cool motors. Submersible pump motors require water flow over them to dissipate heat. In open water, such as a lake or cistern or in large diameter wells, heat dissipation becomes a problem since water is likely to flow directly into the intake of the pump, instead of flowing over the motor. In these situations, a pump sleeve or shroud is required.
Pump sleeves are also required if the well is top feeding (water flows in from above), or if the pump is placed below screens or perforations, and sand is able to fall into the pump inlet. As a side note: pump sleeves, flow sleeve, flow inducer sleeve, and pump shroud all mean the same thing!