Simple Cylindrical Hydrocyclone can be considered as conventional hydrocyclone with an included cone angle of 180 degree.
The circulating bed classifier is typical, there is a natural circulation near the outlet which improves the sharpness of classification. They can be used for separation by particle size, particle shape or particle density.
In a cylindrical hydrocyclone the feed enters an upper chamber before entering the main cylinder through tangential slots. The underflow can be discharged continuously but because these cyclones are generally used with dilute feeds, the solids are normally discharged intermittently from a grit box.
A place near the bottom deflects the liquid upwards towards the overflow. This design is claimed to give little erosion.