The capacity of dense medium cyclones is often restricted by the solids-carrying capacity of the underflow, referred to as spigot capacity. Cyclone manufacturers normally recommend the spigot capacity for a cyclone of a particular size; however, it is not clear how these capacities are determined and whether they can be increased. In the literature, spigot capacity has previously been associated with roping flow at the underflow, although this notion has neither been clearly proven nor disproved. Furthermore, the effect of overloading the spigot on the operation of a dense medium cyclone has not been adequately studied. In this study, test-work on a 165 mm diameter dense medium cyclone was performed to investigate its spigot overloading behaviour. This work established clearly that spigot capacity was reached at the onset of roping flow, and that there was a critical underflow ore concentration at which roping/spigot overloading occurred. This ore concentration was shown to be a useful tool in anticipating and avoiding spigot overloading. Spigot capacities obtained in this study were higher than those specified in the DSM handbook, indicating that dense medium cyclone could possibly be operated at higher spigot capacities. However, separation efficiencies were not monitored during this investigation.
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