In cases where heavies are a very small part of the whole liquid, it is sometimes advantageous to accumulate them in the bottom of the hydrocyclone for batchwise removal.
A hydrocyclone is most likely to be the right choice for processes where lights are the greater part of the mixture and where the heavies settle fairly easily.
Generally, hydrocyclones are used in continuous flow systems so that the instantaneous liquid inflow to the hydrocyclone is equal to the total instantaneous outflow of lights plus heavies.