Zion Enviro - Multi–Grade Sand Filters

The term "multi -grade,” refers to a type of filter bed which is graded by size of sand. Coarse less dense particles are at the top of the filter bed, and fine, denser particles are at the bottom. Down flow filtration allows deep, uniform penetration by particulate matter and permits high filtration rates and long service runs. Because small particles at the bottom are also more dense (less space between particles), they remain at the bottom. Even after high-rate backwashing, the layers remain in their proper location in the mixed media filter bed.