is at the outlet 12 of the pulp distribution device 10 u2014 i e the actual segment is constantly changing when the first permeable surface 21 is moving in general the result is better the closer the throttle 31 is positioned to the outlet 12 of the pulp distribution device 10 due to the risk of plugging before the throttle 31 if the distance between the throttle 31 and the outlet 12 is too big but the invention will work at least in the distance of 0 0 5 m from the outlet 12 of the pulp distribution device 10 in the embodiment where the second permeable surface 14 u2032 is considered to be a segment of the first permeable surface 21 there should of course be a balance between having a sufficiently large dewatering segment 14 u2032 and having the throttle 31 sufficiently close to the outlet 12 of the pulp distribution device 10 the throttle gap width wt may be fixed and the throttle 31 simply formed as an edge wedge knife or similar 30 in the transportation chamber wall 22 it is however preferable that the throttle gap width wt is adjustable and even more preferable that the throttle gap width wt is adjustable during operation a simple solution for the adjustment could be to choose an appropriate number of shims to set the position of said edge.