The container with a filter medium separated into upper and lower chambers constitutes a simple filter. The suspension was added to the upper chamber, under pressure through the filter media into the lower chamber to become filtrate, the solid particles are trapped in the filter medium surface to form a residue (or cake). Filtration process residues accumulated in the filter medium surface layer gradually thickened liquid through the filter cake layer resistance will be increased, the filtration rate decreases. When the filter chamber filled with residue or filtration rate is too small, stop filtering, removing residue, the filter media regeneration to complete a filtration cycle. Layer and the liquid residue through the filter medium must overcome the resistance, so both sides of the filter medium must have a pressure difference, which is the driving force to achieve filtering. Increasing the pressure difference can accelerate the filtration, but the compressive deformation of the particles in a large pressure difference is easy to plug the filter media pore filtration but slow down. The suspension was filtered residue layer has filtration, depth filtration and sieving in three ways. ① residue level filtering: to the initial filtration filter media as retaining a large solid particles, small particles with filtrate passes through the filter media. After the formation of the initial layer of residue, filter residue layer plays a major role, then large and small particles are trapped, such as frame filter filtration. ② depth filtration: filter medium thick suspension containing solid particles less, and the particles are smaller than filter media channels. Filtration, adsorption particles from entering after being in the tunnel, such as porous plastic tube filter, sand filter filtration. ③ sieve: rejection filter solid particles are larger than the pores of the filter medium, the filter medium is not inside the adsorption of solid particles, such as drum filter screen filtered sewage coarse impurities. In the actual filtering process, three ways are often simultaneously or one after another.
