Sand and gravel filters are one of the most common and effective filtration devices used both at home and abroad to remove organic impurities from water. They are typically applied in industries such as industrial water treatment, water filtration for agricultural irrigation, and physical filtration for urban water use. The filtering medium of the sand and gravel filter is quartz sand filter material. When the raw water passes through the quartz sand filter material, impurities in the water are intercepted, thus achieving the purpose of filtration for the effluent.

During normal operation, the water to be filtered passes through the inlet and reaches the medium layer. At this time, most pollutants are retained on the upper surface of the medium, while fine dirt and other floating organic matter are retained inside the medium layer to ensure that the production system is not disturbed by pollutants and can work well.

After operation, when the impurities and various suspended solids in the water reach a certain amount, this filtration system can detect the pressure difference between the inlet and outlet in real time through the pressure difference control device. When the pressure difference reaches the set value, the electric control PLC will send a signal to the three-way hydraulic control valve in the control system. The three-way hydraulic control valve will automatically control the corresponding three-way valve of the filtration unit through the waterway. Let it close the inlet channel while opening the sewage channel.

At this time, due to the relatively low pressure in the sewage channel, water from other filter units will enter through the outlet of this filter unit under the action of water pressure and continuously flush the medium layer of this filter unit, thereby achieving the effect of cleaning the medium. The flushed sewage, under the action of water pressure, enters the sewage pipe through the sewage outlet of this filter unit, completing one sewage discharge process.