Patent ID: 7887872

Claim:
A method for separating impurities from a machine circulation, of a flow of processing agent mixture used in a processing station to coat a paper or board web, the method comprising the steps of: pumping the flow of the processing agent from a reservoir at a first level through a gap-drum pressure sieve and removing impurities from the processing agent in the gap-drum pressure sieve and hence to the processing station at a second level; spreading at least a portion of the flow of processing agent on a surface of the paper or board web, coating the web and producing an excess flow of processing agent which leaves the processing station by a return pipe; leading at least part of the excess flow of processing agent to pass through at least one perforated drum pressure sieve using a perforated plate as a separating element located at a third level between the first level, and the second level of the processing station at a feed pressure created at least in-part by a difference in height between the processing station and the perforated drum pressure sieve; and leading a flow from the at least one perforated drum pressure sieve of at least part of the excess flow of processing agent back to the reservoir.