A wall means intended for apparatus for separation of a liquid-containing portion from a liquid-containing particle material which is fed through the apparatus in a predetermined direction (A). The wall means comprises a plurality of bar profiles defining continuous slots between them to allow through the liquid-containing portion. According to the invention each bar profile has on its inner side facing the liquid-containing particle material a ridge portion extending between the ends of the bar profile and being provided with two continuous guide surfaces which, as seen in a cross section of the rod profile, are inclined in relation to the drainage direction (B) of the liquid-containing portion through the adjacent slot. Furthermore, the inclined guide surfaces in their longitudinal direction are disposed to coincide with the predetermined direction of feed (A) of the liquid-containing particle material in order to influence the liquid-containing particle material to maintain this direction of feed (A).