The Sand Classifier with Longitudinal Hopper make a selection of the grit for the principle of gravity and thanks to the whirling motion create by blower, moving the particles, separates the grit from the organic material that due to major specif weight respect to the water decants on the bottom of the hopper, where there is a bottom screw that carries the grit in a collection tank; also bring in suspension oil and grease. An inclinated, called extractor, pick up the grit and bring it out of the machine. The grease removal system is make of a series of plate moved by chain that scrapes the water and bring the grease in a collection hopper.

The water rich of organic material exit to the machine for overflow from an appropriate discharge.