A continuous digester comprises a wash zone having a plurality of individual wash screens disposed about an inner wall of the digester for the withdrawal of co-current downflow liquor from the wash zone. A conduit is connected in fluid communication between each of the wash screens and a collector for co-current downflow liquor withdrawn from the wash zone of the digester. A valve is interposed along the length of the conduit leading from each of the wash screens. The valve is operable between open and closed positions in response to a signal received from a temperature sensor associated with the conduit leading from each of the wash screens. The signal represent changes in temperature of a corresponding co-current down flow liquor through a corresponding conduit wherein a corresponding valve permits adjustment of a corresponding flow rate of liquor through said corresponding conduit to a flow rate that is substantially equal to each of the other flow rates of co-current downflow liquor through each of the other conduits.