Abstract: A hydrocyclone device having complementary upper vortex finder and lower cone units each made of hard polyurethane together with a resilient, flexible, replaceable, polyurethane liner having a positive sealing flange associated therewith. The sealing flange of the liner complements with and engages with complementary sealing surfaces on the vortex finder and the lower cone unit when they are joined together by respective threaded portions. Thus, only three elements make up the basic hydrocyclone device with greatly improved resistance to leakage thereof. An outlet opening at the bottom end of the lower cone unit can also be provided with an adjusting unit and a wear insert therewith.