Works from the raw water inlet pipe into the filter, the filter layer filter from top to bottom, the connecting pipe water from the storage tank is injected into the village, after the tank is full, the water passes through the outlet pipe into the clean water tank, filter layer continuous retention of suspended solids, resulting in increasing resistance to the filter layer, which has prompted the rising water level in the siphon. When the water level reaches the siphon tube when the auxiliary port, the water from the pipe fall through the exhaust pipe in order to take away the downcomer siphon air, when the vacuum reaches a certain value, then the siphon effect. Then the water in the pipe from the bottom up through the filter layer of filter backwash. When the flush tank below the surface down to siphon tube, air enters the siphon, siphon effect damage.