filter (filter) is an indispensable device on the transmission medium pipeline, usually installed in the pressure reducing valve, pressure relief valve, fixed water level valve, square filter other equipment import end equipment. The filter has a certain specification of the filter cartridge, its impurities are blocked, when the need to clean, as long as the detachable filter cartridge is taken out, after processing can be reloaded, therefore, the use and maintenance is very convenient. The working principle of the filter is: the water to be treated by the filter enters the body from the inlet, and the impurities in the water are deposited on the stainless steel filter screen, resulting in pressure difference. The change of inlet and outlet pressure is monitored by the differential pressure switch. When the differential pressure reaches the set value, the electric control device will give the hydraulic control valve and drive the motor signal. After the equipment is installed, the technical personnel will conduct debugging, set the filtration time and cleaning conversion time, and the water to be treated will enter the body through the inlet, and the filter will start to work normally. When the preset cleaning time is reached, the electric control device will give signals to the hydraulic control valve and the driving motor to trigger the following actions: The motor drives the brush to rotate to clean the filter element, and the control valve is opened to discharge the water. The whole cleaning process only lasts for tens of seconds. When the cleaning is finished, the control valve is closed, the motor stops rotating, and the system returns to its initial state and begins to enter the next filtering process. The shell of the filter is mainly composed of coarse filter screen, fine filter screen, suction pipe, stainless steel brush or stainless steel nozzle, sealing ring, anti-corrosion coating, rotating shaft and so on. A simple filter is made by dividing the container into upper and lower cavities with filter media. The suspension is added to the upper chamber and enters the lower chamber as filtrate through the filter medium under the action of pressure. The solid particles are trapped on the surface of the filter medium to form filter slag (or filter cake). During the filtration process, the filter slag layer on the surface of the filter medium gradually thickens, and the resistance of liquid through the filter slag layer increases, and the filtration speed decreases. When the filter chamber is full of filter slag or the filtration speed is too small, stop the filtration, remove the filter slag, so that the filter medium regeneration, to complete a filtration cycle. Liquid through the filter slag layer and filter medium must overcome resistance, so there must be a pressure difference between the two sides of the filter medium, which is the driving force to achieve filtration. The filtration can be accelerated by increasing the pressure difference, but the deformed particles after compression are easy to block the pores of the filtration medium when the pressure difference is large, and the filtration is slowed down. There are three ways of suspension filtration: filter slag layer filtration, deep filtration and sieve filtration. (1) Filter slag layer filtration: at the initial stage of filtration, the filter medium can only intercept large solid particles, and the small particles pass through the filter medium with the filtrate. After the formation of the initial filter slag layer, the filter slag layer plays a major role in the filtration, at which time both large and small particles are intercepted, such as the filter of a plate and frame filter press. (2) Deep filtration: the filter medium is thicker, the suspension contains less solid particles, and the particles are smaller than the passage of the filter medium. During filtration, particles enter and are adsorbed in the pore, such as the filtration of porous plastic pipe filters and sand filters. (3) Screening: the solid particles intercepted by filtration are larger than the pores of the filter medium, and the solid particles are not adsorbed inside the filter medium, such as the rotary filter screen to filter the coarse impurities in the sewage. In the actual filtering process, the three methods often appear simultaneously or successively.