Abstract: A centrifugal blood separator for separating whole blood into at least two blood fractions such as a plasma fraction and a blood cell fraction is disclosed. The blood separator has a centrifuge vessel with a separation chamber having at least two sections with different diametric sizes. The large diameter section collects the heavier blood cell fraction during centrifugation. The smaller diameter section collects the lighter plasma fraction. Fluid communication subassemblies preferably have a feed conduit, a product or an outflow conduit and a vent which are mounted in a non-rotatable part and positioned in an extending or extendible manner into the separation chamber to allow blood fractions to be removed while the centrifuge vessel is rotating or after rotation has stopped depending upon specifics of the particular embodiment.