A blood washing system (20) having a rotor (22) defining an internal chamber for receiving a multi-component fluid and a skimmer assembly (24) including a moveable buoy (28) having an orifice (32) fluidly connected to an access port for the rotor for selectively withdrawing separated fractions of the multi-component fluid. The multi-component fluid can be fed into the internal chamber before the rotor (22) can be rotated at a first speed to fractionate the multi-component fluid. A brake can be applied to the rotor to slow rotation of the rotor to a slower second speed or stop rotation of the rotor causing the solid and denser fluid fractions to settle on the bottom wall (44) of the rotor (22). The buoy (28) can have a specific gravity corresponding to a selected fraction such that the buoy floats on a surface of the selected fraction, wherein the fractions floating on the selected fraction can be withdrawn through the orifice (32).
