A new four-channel screen changer with the patented ability to backflush or change screens in only one channel at a time keeps the pressure interruption minimal because the active filtration area never drops below 75% of the maximum. Kreyenborg in Germany (U.S. office in Lawrence, Ga.) developed the K-SWE-4K/75 device with two parallel pistons and two screen cavities per piston. Only one screen cavity is removed from the process stream at a time. Sized for outputs from 200 to 15,000 lb/hr, the unit is mounted on a wheeled frame and is installed before or after a melt pump. A production-scale lab line is available for testing. Special designs for PMMA and PC are also available.