The objective of cyclone pressure control is to have a consistent pressure at or near the manufacturer’s recommendations for classification efficiency for a variety of feed flows and densities. A relatively constant cyclone feed pressure is maintained by adjustment of the number of cyclones turned on in the cluster. The cluster is assumed to have of the order of 10 to 15 cyclones. Because of the quantisation effect of selecting a whole number of cyclones in service, it is impossible to keep the pressure completely constant. However, variation in pressure does not greatly affect cyclone d50c, so the small variations in pressure that remain have no significant affect on cut size or ball mill circuit control.