Abstract: The flow ratio of a paper machine headbox is adjusted by arranging such a by-pass out from the slice chamber that the flow conditions, such as the speeds and turbulences in all parts of the headbox remain unchanged regardless of the adjustment. The adjustment is carried out by opening the slice chamber wall or by using a separate discharging device positioned inside the slice chamber.

Abstract: The invention relates to a headbox of a paper or board making machine, particularly a hydraulic headbox, which has an inlet header section (1) with a manifold tube section (2) and an equalizing chamber (3) in the stock suspension flow route, a turbulence generator section (4) following the equalizing chamber (3), after which a tapered slice section (8) is located, through which the stock suspension is discharged onto the wire. The headbox also has an attenuation chamber (6) for pressure variations, which defines one or several air spaces (7) under the flow channel of the stock suspension, the spaces being connected with the flow channel by way of a connecting channel (5). The air space or spaces (7) are preferably confined by subjacent frame structures including a bottom wall (16) and vertical walls (18) and walls (19) defining the flow channel from below.