The types of filtration can be classified as follows: • Normal flow filtration: the suspension to be filtered passes through the filter perpendicular to the filtering surface. • Cross flow filtration: the suspension to be filtered passes through the filter parallel to the filtering surface. • Cake filtration: the suspension to be filtered passes through a “cake” made up of the solid to be separated which accumulates on the filtering surface. In this case the “cake” is supported by a metal grid with pores with the largest diameter of the particles to be filtered. • Deep bed filtration: the solid to be separated is retained inside the filter media (an example could be the sand filter) and usually, when it is saturated, the filter media is completely changed.
To increase the filtration speed, a greater pressure difference can be used between upstream and downstream of the filter. In these cases the fluid upstream is often pressurized with pumps. In this case batch or depression filtration will be needed so it will be possible to work without any stops.