When the pressure difference between the inside and outside of the filter screen reaches a predetermined value ( 0.05 MPa), the differential pressure switch transmits a signal to the control box, the control box opens the drain valve and at the same time starts the motor to drive the wire brush, turning the wire brush to brush off the dirt and impurities inside the filter element, and under the pressure of the water, the sediment is discharged through the drain valve with flotsam.