Abstract: Method and arrangement for separating impurities from the machine circulation of a processing agent of a processing station used in processing paper or board, in which method the processing agent is led from a reservoir (1) to the processing station (2), where it is spread on the surface of the web being processed, and the excess processing agent led to the processing station (2) agent is led back to the reservoir (1). The flow of processing agent coming from the processing station (2) is led to at least one pressure sieve (6), which is located below the level of the processing station (2), in such a way that the feed pressure of the processing agent is created on the basis of the difference in height between the station (2) and the pressure sieve (6).

Abstract: Method and arrangement for separating impurities from the machine circulation of a processing agent of a processing station used in processing paper or board, in which method the processing agent is led from a reservoir (1) to the processing station (2), where it is spread on the surface of the web being processed, and the excess processing agent led to the processing station (2) agent is led back to the reservoir (1). The flow of processing agent coming from the processing station (2) is led to at least one pressure sieve (6), which is located below the level of the processing station (2), in such a way that the feed pressure of the processing agent is created on the basis of the difference in height between the station (2) and the pressure sieve (6).

Abstract: A treating agent is fed to an application apparatus (40) used for applying coating color or surface size directly or indirectly to a paper or board web. Part of the treating agent fed to the application apparatus (40) is returned via a bypass line (24) to the treating agent feed system and part of it is passed into an application chamber in the application apparatus (40), from which application chamber substantially all treating agent fed into it is applied to a moving web or to a transfer surface. The flow of a treating agent (Q) to the application apparatus (40) is measured, and the feeding of the treating agent is controlled on the basis of the measured flow (Q) and of a predetermined set value (Q0), which set value has been selected according to the desired amount of treating agent to be applied to the moving web or transfer surface.