translationally movable element the slot like guide channel has arranged forwardly thereof a perforated plate and a mixing chamber merging thereat also a pulp feed channel having an adjustable lip and merging at the guide channel can possess step shaped widened portions application_number US 18760280 A description describing now the drawings the exemplary embodiment of pulp feed or headbox arrangement illustrated in fig1 and 2 will be seen to comprise a distributor tube or pipe 1 having a conical section or portion 1 39 at which laterally merges a perforated plate 2 containing essentially cylindrical bores or openings 3 viewed in the direction of flow of the stock suspension there is arranged a mixing chamber or compartment 4 after the perforated plate 2 this mixing chamber 4 extends over the entire width of the apparatus the stock suspension or the like arrives from the mixing chamber 4 at a guide channel 5 the principal portion of which essentially extends over the length f as shown in fig2 according to such fig2 there will be further seen that a pulp feed channel 6 merges with the guide channel 5 this pulp feed channel 6 opening at a perforated element here shown in the form of a sieve or screen 7 guided over a perforated sieve cylinder 8 the pulp feed channel 6 is provided with an adjustable lip arrangement 10 11 for adjusting its cross section this lip arrangement or lip means consisting of the adjustable lip elements 10 and 11 these lip elements 10 and 11 are pivotably arranged in known manner about essentially cylindrical portions 12 and 13 and can be adjusted with the aid of the rods.