Abstract: A settling unit for separating a liquid and the particles. Such as sand, suspended therein, comprises a basin with an inlet for the liquid mixture containing the particles, and an overflow for discharging the liquid after at least some of the particles have been removed therefrom through settling. With a view to increasing the efficiency, a plate separator is provided at the position of the overflow, which plate separator has a liquid outlet which is connected to the overflow and an outlet for settled particles which is connected to the basin. The gaps defined between the plates can be shut off at their underside by a non-return valve which can be moved into an open position under the influence of the weight of the separated particles.