During the hydraulic clamping of the filter press, high-pressure oil is supplied by the hydraulic station, filling the element cavity composed of the cylinder and piston. When the pressure exceeds the frictional resistance of the clamping plate, the clamping plate slowly presses the filter plate. When the clamping force reaches the pressure set by the overflow valve (indicated by the pressure gauge needle), the filter plate, filter frame (plate-frame type), or filter plate (housing type) is clamped. The overflow valve starts to unload. At this point, the motor power is cut off, and the clamping action is complete. During the return, the directional valve reverses direction, and the pressure oil enters the rod-end cavity of the cylinder. When the oil pressure can overcome the frictional resistance of the clamping plate, the clamping plate begins to retract.

When the hydraulic pressure of the filter press is set to automatic pressure maintenance, the clamping force is controlled by an electrical contact pressure gauge. The upper and lower limit pointers of the pressure gauge are set to the values required by the process. When the clamping force reaches the upper limit of the pressure gauge, the power is cut off and the oil pump stops supplying power. Due to internal and external leaks that may occur in the oil circuit system, the clamping force may decrease. When it reaches the lower limit pointer of the pressure gauge, the power is reconnected and the oil pump starts supplying oil. When the pressure reaches the upper limit again, the power is cut off and the oil pump stops supplying oil. This cycle ensures that the clamping force is maintained during the filtration process.

Filtering Methods: The filtration of filtrate can be divided into open flow and hidden flow. In open flow filtration, each filter plate has a water nozzle installed on the lower outlet hole, and the filtrate flows directly out of the nozzle. In hidden flow filtration, each filter plate is equipped with an outlet channel hole at the bottom, and the outlet holes of several filter plates are connected to form an outlet channel, which is discharged through a pipeline connected to the outlet hole below the stopper plate.

Washing Methods: When filter cakes require washing, there are sometimes single-direction and double-direction washes, as well as submersible single-direction and double-direction washes. In a single-direction open flow wash, the washing fluid enters through the inlet holes of the stop plate, sequentially passing through the filter cloth and cake, and exiting through the solid filter plate. At this point, the outlet nozzles of the perforated plate are closed, while those of the solid plate are open. A double-direction open flow wash involves the washing fluid entering from the two side inlets above the stop plate for two consecutive washes, starting from one side and then the other, with the outlet and inlet aligned diagonally, hence also known as cross-directional double-direction wash. For submersible single-direction wash, the washing fluid enters through the inlet holes of the stop plate and passes through the perforated plate, the filter cloth, and the cake before exiting through the solid filter plate. In a submersible double-direction wash, the washing fluid enters from the two side inlets above the stop plate for two consecutive washes, starting from one side and then the other, with the outlet aligned diagonally, hence also known as cross-directional submersible double-direction wash.