The Dewatering Grid is an oblong framework of angular metal plates that lock sludge set up because it rises on the floor. Only when sludge has thickened enough to rise higher than the very best edge of the grid can or not it's skimmed and pushed to the float hopper. http://airflotationunits33209.bloguetechno.com/Top-Air-Flotation-Units-Secrets-17627282