Abstract: In a decanter centrifuge, which comprises an outer drum (1) and an inner drum (5) concentric therewith, the two drums being rotatable at different speeds around a common center axis, the inner drum (5) carries several blades (6, 7) arranged to convey axially in the outer drum (1) sludge having settled on the inside of the drum. The blades (6, 7) are placed in parallel blade rows, each of which extends in a certain pitch along a first helical line (9, 10) around at least part of the center-axis. Each one of the blades extends along a second helical line (29c), which has a pitch opposite the pitch of the first helical line (9, 10). The distance between the rows of blades is substantially larger than the distance between two adjacent blades in one and the same row. Possibly, the inner drum may be provided with only a single row of blades.

Abstract: A decanter centrifuge comprises a drum (1) with a conveyor (2) containing an inlet (4). The liquid to be separated flows in a jet centrally into the inlet (4) towards an end wall (11 ), at which the liquid is radially distributed and flows axially onwards towards the second end wall (13) through an area of the inlet (4) free of members imparting an angular velocity to the liquid. The inlet (4) is provided with inlet apertures (6) positioned on a radius larger than the radius to the overflow edge (9) at the liquid discharge. The design of the inlet (4) implies that the free liquid surface in the inlet during operation is drawn far towards the axis of the drum, thereby causing excess energy supplied to the liquid during acceleration to the angular velocity of the conveyor (2) to be dissipated in the comparatively thick liquid layer before the liquid discharges into the separation space (7) through the inlet apertures (6).