Abstract: The invention relates to a continuous-working process and apparatus for replacing the liquid in a liquid suspension of a fibrous material with another liquid by forming of this material a bed on a moving filter surface and by displacing the liquid present in this bed with the other liquid. The bed of material is formed on a cylindrical filter surface installed in a vertical orientation below the liquid surface in a container and conveys it continuously forward filtration and several successive liquid displacements effected by maintaining a hydrostatic pressure difference across the formed bed, which is conveyed continuously horizontally forward, and through it there flow liquids horizontally during the filtration and liquid displacement.