A washer for washing and dewatering cellulose pulp is disclosed, comprising a rotary drum with a plurality of external compartments on the drum defined by axial compartment walls distributed along the circumference of the drum, a stationary cylindrical casing enclosing the drum, defining a ring-shaped space between the casing and the drum, and longitudinal seals in the axial direction of the drum diving the ring-shaped space into a forming zone for forming the pulp, at least one washing zone for washing the pulp at an overpressure, and a discharge zone, and where the longitudinal axial seals are attached to positioning cylinders for adjusting the radial position of the seals, and the longitudinal seal has an articulated connection with the positioning cylinders to make possible oblique positioning of the seal.