Hoshizaki prefilters are designed to increase the life of Hoshizaki pre-coat water filters in areas with an unusual amount of dirt in the water. With a 10 micron (nominal) rating, the economical Everpure prefilter traps much of the dirt which contributes to scale buildup in ice makers, and clogs the delicate orifices of other water-using equipment.
When you install an Hoshizaki prefilter, the pre-coat filters can concentrate on what they do best: remove particles 1/2 micron and larger in size.
Spec Sheet (PDF)