Hydrocyclones are used in various duties in mineral processing plants as well as in oil, recycling or chemical industries. Due to its broad areas of application, different designs are established to meet particular requirements. In this thesis the focus is on two special types of hydrocyclones named water-only cyclone (WOC) and flat bottom cyclone. These types are characterized by their wide cone angle. Tests were made in the hydrocyclone lab of FLSmidth Krebs in Tucson, Arizona, with the WOC, the flat bottom and a standard hydrocyclone. The separation performance of each test is presented by use of a partition curve. Design and operational parameters were changed for each device and as a consequence thereof the separation performance observed and compared. The parameters examined were the vortex finder diameter, the vortex finder length, the type of apex installation, the apex diameter and the pressure drop. Additionally, the Krebs prognosis model was applied on the standard hydrocyclone to compare the prognosticated cut size at partition number 50% with the measured one.