The filter medium is used to separate the container into upper and lower cavities to form a simple filter. The suspension is added to the upper cavity and passes through the filter medium into the lower cavity under pressure. The solid particles are trapped on the surface of the filter medium to form a filter residue (or filter cake). During the filtration process, the filter residue layer on the surface area of the filter medium is gradually thickened, and the resistance of the liquid to pass through the filter residue layer is increased, and the filtration speed is reduced. When the filter room is full of filter residue or the filtration speed is too small, stop filtering, remove the filter residue, and regenerate the filter medium to complete a filtration cycle. The liquid passing through the filter residue layer and the filter medium must overcome the resistance, so there must be a pressure difference on both sides of the filter medium, which is the driving force to achieve filtration.