The working principle of the second-hand box type filter press is composed of a plate filter plate and a hollow filter frame. The filter cloth is fixed on the plate and frame, which is the main form of the early filter press. The main advantage of the box type filter press is that it is convenient to change the filter cloth, but the disadvantages are low efficiency, poor filtering effect and easy damage of the filter plate; the filter chamber of the box type filter press is composed of two adjacent concave filter plates The working principle of the second-hand box type plate and frame filter is that the filter chamber is composed of filter plates arranged (the two sides of the filter plate are concave, and each two pieces of filter plates are combined into a box shaped filter chamber). The principle diagram is as follows: the surface of the filter plate has pockmarks and boss to support the filter cloth. There are through holes in the center and corner of the filter plate. After assembly, a complete channel can be formed to pass in the suspension, washing water and extract filtrate. There are handles on both sides of the filter plate to support on the beam, and the filter plate is pressed by the pressing device. The filter cloth between the filter plates plays a sealing role. Under the pressure of the conveying pump, the material liquid to be filtered is sent to each filter chamber, and the solid and liquid are separated through the filter medium (select the appropriate filter cloth according to different industries). The filter residue is formed on the filter cloth until the filter chamber is filled to form a filter cake. The filtrate passes through the filter cloth and flows along the filter plate groove to the lower outlet channel, and is discharged centrally. After filtration, the filter residue can be washed with washing water. After washing, sometimes compressed air is introduced to remove the remaining washing liquid. After filtration, open the filter press to remove the filter cake (the filter cake is stored between two adjacent filter plates), clean the filter cloth, and press the plate filter again to start the next working cycle.