A hydrocyclone which includes a main body having a chamber therein, the chamber including an inlet section, and a separating section, the separating section having an inner side wall which tapers inwardly away from the inlet section, the hydrocyclone further including a feed inlet feeding a particle bearing slurry mixture into the inlet section of the chamber, an overflow outlet at one end of the chamber adjacent the inlet section thereof, and an underflow outlet at the other end of the chamber remote from the inlet section of the chamber. The hydrocyclone further includes an overflow outlet control chamber adjacent the inlet section of the chamber of the hydrocyclone and in communication therewith via the overflow outlet, the overflow outlet control chamber including a tangentially located discharge outlet and a centrally located air core stabilising orifice which is remote from the overflow outlet.