Abstract: A low contaminant level is maintained in a high flow rate paper machine coating fluid circulation system by shunting a significant minority portion of the total flow through a full flow, atmospherically open, self-cleaning screen having a fine mesh screen cloth. Accept flow from the open screen is directed to the flow inlet of an entrained air purging apparatus for dispersing consolidated particulates of excessive size. Flow from the particulate disbursing apparatus is thereafter pumped through an enclosed pressure screen of moderate screen mesh.