Semi-continuous, small volume centrifugal blood separator and method of using therefor

The field of this invention is small volume centrifugal blood separators used to produce one or more fractions from whole blood, the fractions of whole blood being used for purposes such as analysis of the blood fraction or fractions for health diagnostics and other purposes. 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.