7 it separates into stratified layers of the individual components or phases the staggered flow passages 30 inhibit flow from the drum inlet 20 directly to the first and third phase outlets 22 26 inhibiting the flow increases the residence time of the mixture in the drum 7 so that the oil and water of the original mixture are substantially separated upon arrival at the first and third phase outlets 22 26 an interface between the water and oil is therefore formed the radial position of the interface can for example be controlled by varying flow rates through the first and third phase outlets 22 26 although it will be appreciated that alternative methods are possible the water flows over the outer periphery of the weir plate 29 towards the third phase outlet 26 the position of the interface is controlled so that it remains radially outward of the first phase outlet 22 and radially inward of the outer periphery of the weir plate 29 this ensures that the separated oil is prevented from exiting through the third phase outlet 26 and instead flows along the passage defined by the annular plate 31 towards the first phase outlet 22 an emulsion or rag layer forms at the interface of the oil and water and or the interface of the water and solids the centrifugal forces cause the solid particulates to u201c settle u201d.