Thickening: When the shaft is driven by the screw, moving rings around the shaft move up and down relatively. Most water is pressed out from the thickening zone and fall down to the filtrate tank for gravity. Dewatering: The thickened sludge moves forward continuously from the thickening zone towards the dewatering zone. With the pitch of the screw shaft thread getting narrower and narrower, the pressure in the filter chamber increases higher and higher. In addition to the pressure generated by the back-pressure plate, the sludge is greatly pressed and dryer sludge cakes produce. Self-cleaning: The moving rings rotates continuously up and down under the pushing of the running screw shaft while the gaps between the fixed rings and moving rings are cleaned to prevent from clogging that happens frequently for traditional dewatering equipment.