Duplex filters does not all adopt high-quality SUS304. The rust steel is made, it is that two round cylinders make up, 0.4um, of polishing of surface of inside, appearance, equipped with the man-ometer, air bleed-ing valve on the top, is suitable for removing the purification of different invisible solid impurity of naked eye in the liquid, such as fresh milk, candyliquid, beverage, oral liquid, etc. Two filters are used alternatively, can exchange the filter screen in case of shutting down, suitable for producing in succession for a long time.