When the water flows through the filter, impurities will gradually accumulates in the surface of its screen, results in the water pressure difference between the water inlet pipe and outlet pipe. When the differential pressure reaches a preset value 0.05MP, backwashing starts work. Sucking scanner driven by motor, and do spiral motion around the screen, on the scanner suction by sucking impurity particle movement, through the sewage discharge valve, but does not contact the screen, the cleaning process for 30-60 seconds. According to the requirement of the water quality, suction type (500-30 micron) a variety of filtering accuracy.