Under certain pressure, water enters into the rotational flow dirt separator through the inlet tangentially and generates intense rotary motion. Due to different densities, under the joint action of centrifugal force, centripetal force, and liquid drag force, the lower density water will move upward and flow out of the separator through the outlet, and the higher density sand grains will be discharged through the drain outlet at the bottom of the equipment. Individual micro grains will be filtered out by the secondary filtering apparatus. Thus, sand removal is achieved Our rotational flow dirt separator has an additional filtering unit (filtration precision is selectable), compared with rotational flow dirt separators in present market. It is space-saving, with high sand removal efficiency, low escape rate of individual micro grains, and stable operation. Based on the advanced mechanism and structure, our rotational flow dirt separator has a cut diameter (grain diameter when pollutant removal efficiency is 50%) of 0.07mm, when grain diameter is 0.3mm, its pollutant removal efficiency may reach as high as 98%. Besides, the equipment is convenient to clean during operation.