The continuous thickener consists of a cylindrical tank. Pulp is fed into the centre of the tank via a feed-well placed up to 1 m below the surface of the suspension, in order to cause as little disturbance as possible. The clarified liquid overflows a peripheral launder, while the solids which settle over the entire bottom of the tank are withdrawn as a thickened pulp from an outlet at the centre. Within the tank are one or more rotating radial arms, from each of which are suspended a series of blades, shaped so as to rake the settled solids towards the central outlet. On most modern thickeners these arms rise automatically if the torque exceeds a certain value, thus preventing damage due to overloading. The blades also assist the compaction of the settled particles and produce a thicker underflow than can be achieved by simple settling. The solids in the thickener move continuously downwards, and then inwards towards the thickened underflow outlet, while the liquid moves upwards and radially outwards. In general, there is no region of constant composition in the thickener. Thus solids and liquid getting separated effectively from the suspension fed into the tank.