Drum and ejection control arrangements for centrifugal separators and separation methods employing multiple pistons to control separate intermittent ejection of heavy and intermediate material

A drum and ejection control assembly for a centrifugal separator, the drum and ejection control assembly including:

• (a) a drum assembly defining a separator rotational axis and including a separator volume in fluid communication with a feed inlet to the separator volume, the drum assembly including a number of drum ejection passages spaced apart at different angular orientations about the separator rotational axis, each respective drum ejection passage extending from a respective drum ejection passage inlet to a respective drum ejection passage outlet;
• (b) a first piston mounted on the drum assembly for movement along a first piston range of movement between a first piston open position and a first piston closed position, wherein in the first piston open position the first piston leaves each drum ejection passage open for ejection of material from the separator volume to an area outside the separator volume and wherein in the first piston closed position the first piston blocks each drum ejection passage;
• (c) a number of intermediate ejection paths spaced apart at different angular orientations about the separator rotational axis, each respective intermediate ejection path extending from a respective intermediate ejection path inlet to a respective intermediate ejection path outlet, each respective intermediate ejection path inlet being located at a position which is radially inward of a maximum diameter of the separator volume;
• and
• (d) a second piston mounted on the drum assembly for movement along a second piston range of movement between a second piston open position and a second piston closed position, wherein in the second piston open position each intermediate ejection path is open for fluid communication from the separator volume to the area outside the separator volume and wherein in the second piston closed position each intermediate ejection path is closed to fluid communication from the separator volume to the area outside the separator volume.