Explanation using the example of PP/PE separation in PET bottle recycling: The pre-shredded material is fed into the separation tank via 2 screws below the water surfaces. As PET is heavier than water, it sinks to the discharge unit for the sediment and is conveyed out of the machine by a screw or scraper chain conveyor. PP and PE, on the other hand, rise to the surface of the water and are conveyed to the floating material discharge by various paddle drums connected in series and pressed under water several times in order to separate any PET that may still be adhering. A Frictionwasher is usually installed downstream of a separation tank, as this can separate large quantities of liquid from the material.