Abstract: The paper-making stock is fed continuously to a tank with two chambers separated by a partition having an opening for passage of stock from the first to the second chamber, evacuation means being provided for maintaining equally low gas pressures in the two chambers. A stock consumer is connected to a stock outlet of the first chamber, and stock from an outlet of the second chamber is returned to the tank via a recycle line. Means for sensing the stock level in the first chamber are provided to control valve means in the recycle line, whereby said stock level is maintained constant.