18 u2032 that interconnects two diverging limiting surfaces that constitutes a first distribution chamber 8 u2032 the second distribution gap 14 u2033 is arranged from the first circular arc shaped edge 18 u2032 forward to a second circular arc shaped edge 18 u2033 that interconnects two diverging limiting surfaces that constitutes a second distribution chamber 8 u2033 the third distribution gap 14 u2032 u2033 is arranged from the second circular arc shaped edge 18 u2033 forward to an edge 18 u2032 u2033 extending essentially linearly in the transverse direction that interconnects two substantially diverging limiting surfaces that constitutes a third distribution chamber 8 u2032 u2033 the edge extending in the transverse direction constitutes the passage to the outlet gap 20 sections of the side edges 12 u2033 of the gaps 14 u2032 14 u2033 14 u2032 u2033 and 20 are angled in the broken points p at the second distribution gap 14 u2033 and at the third distribution gap 14 u2032 u2033 the second distribution gap 14 u2033 preferably has a lower column depth than the first distribution gap 14 u2032 the third distribution gap 14 u2032 u2033 preferably has an equal column depth as the first distribution gap 14 u2032 the outlet gap 20 has preferably a larger column depth than the third distribution gap 14 u2033 with reference now to.