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How filters work


2022-04-29 14:34

When the filter is working, the water to be filtered enters from the water inlet, flows through the filter screen, and enters the pipeline required by the user through the outlet for process circulation, and the particulate impurities in the water are trapped inside the filter screen. With such a continuous cycle, more and more particles are trapped, and the filtration speed becomes slower and slower, while the imported sewage continues to enter, and the filter holes will become smaller and smaller, thus generating pressure between the inlet and outlet. When the magnitude difference reaches the set value, the differential pressure transmitter transmits the electrical signal to the controller, and the control system starts the drive motor to drive the shaft to rotate through the transmission component, and the sewage outlet is opened at the same time, and the sewage is discharged from the sewage outlet. After cleaning, the differential pressure drops to the minimum value, the system returns to the initial filtering state, and the system operates normally. The filter consists of a shell, a multi-element filter element, a backwashing mechanism, and a differential pressure controller. The diaphragm in the shell divides its inner cavity into upper and lower cavities, and the upper cavity is equipped with multiple filter elements, which fully enriches the filtering space and significantly reduces the volume of the filter. The lower cavity is equipped with backwashing sucker. When working, the turbid liquid enters the lower cavity of the filter through the inlet, and enters the inner cavity of the filter element through the baffle hole. The impurities larger than the gap of the filter element are retained, and the clean liquid passes through the gap to the upper cavity, and finally is sent out from the outlet. The filter adopts a high-strength wedge-shaped filter screen, which automatically cleans the filter element through differential pressure control and timing control. When the impurities in the filter accumulate on the surface of the filter element, the pressure difference between the inlet and outlet increases to the set value, or when the timer reaches the preset time, the electric control box sends a signal to drive the backwashing mechanism. When the mouth of the backwash suction cup and the inlet of the filter element are directly opposite, the drain valve is opened, and the system is depressurized and drained, and a negative pressure area with a relative pressure lower than the water pressure outside the filter element appears on the inside of the suction cup and the filter element, forcing part of the net circulating water to flow from the outside of the filter element. Flow into the inner side of the filter element, and the impurity particles adsorbed on the inner wall of the filter element flow into the pan along with the water and are discharged from the drain valve. The specially designed filter screen produces a jet effect inside the filter element, and any impurities will be washed away from the smooth inner wall. When the pressure difference between the inlet and outlet of the filter returns to normal or the timer set time expires, the material flows continuously during the whole process, and the water consumption for backwashing is small, realizing continuous and automatic production. Filters are widely used in metallurgy, chemical industry, petroleum, papermaking, medicine, food, mining, electric power, and urban water supply. Such as industrial wastewater, filtration of circulating water, regeneration of emulsion, filtration and treatment of waste oil, continuous casting water system, blast furnace water system in metallurgical industry, high-pressure water descaling system for hot rolling. It is an advanced, efficient and easy-to-operate automatic filter device.
The water to be treated by the filter enters the body from the water inlet, and the impurities in the water are deposited on the stainless steel filter screen, thereby generating a pressure difference. The pressure difference between the inlet and outlet is monitored by the pressure difference switch. When the pressure difference reaches the set value, the electric controller sends the hydraulic control valve to drive the motor signal. After the equipment is installed, the technicians will debug, set the filtration time and cleaning conversion time, the water to be treated enters the body from the water inlet, and the filter starts to work normally. When the preset cleaning time is reached, the electric controller will supply the hydraulic control valve. , Drive the motor signal to trigger the following actions: the motor drives the brush to rotate, cleans the filter element, and at the same time the control valve opens for sewage discharge. The entire cleaning process only lasts for tens of seconds. When the cleaning is over, the control valve is closed and the motor stops rotating. The system returns to its original state and begins to enter the next filtering process. The inside of the filter shell is mainly composed of coarse filter screen, fine filter screen, suction pipe, stainless steel brush or stainless steel suction nozzle, sealing ring, anti-corrosion coating, rotating shaft, etc.
A simple filter is formed by dividing the container into upper and lower chambers with filter media. The suspension is added to the upper chamber, and enters the lower chamber through the filter medium under pressure to become filtrate, and 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 existing on the surface of the filter medium gradually thickens, the resistance of the liquid passing through the filter residue layer increases, and the filtration speed decreases. When the filter chamber is full of filter residues or the filtration speed is too low, the filtration is stopped, the filter residues are removed, and the filter medium is regenerated 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 realize the filtration. Increasing the pressure difference can speed up the filtration, but the deformed particles are easy to block the pores of the filter medium when the pressure difference is large, and the filtration is slowed down.
There are three ways to filter the suspension: filter residue layer filtration, depth filtration and sieve filtration.
①Filter residue layer filtration: In the initial stage of filtration, the filter medium can only retain large solid particles, and the small particles pass through the filter medium with the filtrate. After the initial filter residue layer is formed, the filter residue layer plays a major role in filtration. At this time, both large and small particles are trapped, such as the filtration of plate and frame filter presses.
②Deep filtration: The filter medium is thicker, and the suspension contains less solid particles, and the particles are smaller than the pores of the filter medium. During filtration, the particles are adsorbed in the pores after entering, such as the filtration of porous plastic tube filters and sand filters.
③Screening: The solid particles retained 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 drum filter screen to filter out coarse impurities in the sewage. In the actual filtering process, the three ways often appear simultaneously or sequentially.

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