the fibers from the dirt particles but also for the purpose that after the separation the fibers are not moved out of the current the fringe layer must not be 34 disturbed 34 and the removal of the waste must be dynamically decoupled the laminations 8 2 of the paddle wheel 8 are shown in two parts in fig3 the outer part can be rubber flexible plastic or similar material with which the gap between the laminations and the wall of the trough can be sealed a certain quantity of infiltrated air will always escape from the pressure head chamber 30 during the discharge operation and cause pressure fluctuations the dynamics of which must be damped the permanently continuing renewal of the filter layer from waste material serves this purpose the trough is closed above on a transition between the pressure head chamber 30 defining a first pressure zone and a discharge chamber 30 1 for this purpose suitable sealing means such as flexible flaps 7 1 7 2 are fitted which are pressed against the walls of the trough through the pressure head pressure variations are unavoidable in the lower discharge chamber 30 1 as in a suction chamber 30 2 defining.