Method for mixing dilution liquid into a stock flow in a paper or board machine to control basis weight using coarse and fine controls

Not applicable. A method and an apparatus for mixing dilution liquid into a stock flow in a paper or board machine. Dilution is carried out in at least two stages using in the first dilution stage (I) valves (V, V, V. . . ) fitted with a larger mutual spacing at different points of width across a headbox and passing the dilution water through the valves to desired points of width of the headbox according to the requirement of control of the basis weight of paper or board. In the second dilution stage (II), dilution water is passed into connection with the stock flow coming from the first dilution stage (I), said dilution water being controlled by means of valves (V′, V′ . . . ), which valves (V′, V′ . . . ) have been fitted with a denser spacing than the valves (V, V, V. . . ) of the first dilution stage (I).