A device (10, 310) for separating and isolating components of a biological fluid with centrifugation, said device comprising: an enclosure (48, 334) comprising an interior circumferential surface (24, 324) defining a chamber (26, 326) for containing a biological fluid having multiple components; a float (130, 340) slideably disposed within said enclosure (48, 334) and partitioning said enclosure into a lower volume zone (260, 336) and an upper volume zone (262, 338); said float (130, 340) comprising an interior isolation chamber (208, 378) defining an intermediate volume zone,; a first valve means for opening and closing communication of biological fluid from said upper volume zone (262, 338) to said interior isolation chamber (208, 378) within said float; characterised in that said device includes a second valve means for opening and closing communication of biological fluid from said interior isolation chamber (208, 378) within said float (130, 340) to said lower volume zone (260, 336)of said enclosure, said float (130, 340) comprising an exterior circumferential surface (142, 352) circumferentially spaced from said interior circumferential surface (24, 324) of said enclosure for defining a circumferential gap (148, 356) therebetween, and wherein said first valve means and said second valve means are adapted to control under centrifugation at least one closed loop circulation of biological fluid into said interior isolation chamber (208, 378) from said upper volume zone (262, 338), out of said interior isolation chamber (208,378) into said lower volume zone (260, 336), out of said lower volume zone (260, 336) and through said circumferential gap (148, 356) to said upper volume zone (262, 338), and back into said interior isolation chamber (208, 378)as a function of a first pressure differential of biological fluid on said first valve means and as a function of a second pressure differential of biological fluid on said second valve means for isolating at least one target component of the multiple component biological fluid within said interior isolation chamber (208, 378) of said float (130, 340). an enclosure (48, 334) comprising an interior circumferential surface (24, 324) defining a chamber (26, 326) for containing a biological fluid having multiple components; a float (130, 340) slideably disposed within said enclosure (48, 334) and partitioning said enclosure into a lower volume zone (260, 336) and an upper volume zone (262, 338); said float (130, 340) comprising an interior isolation chamber (208, 378) defining an intermediate volume zone,; a first valve means for opening and closing communication of biological fluid from said upper volume zone (262, 338) to said interior isolation chamber (208, 378) within said float; characterised in that said device includes a second valve means for opening and closing communication of biological fluid from said interior isolation chamber (208, 378) within said float (130, 340) to said lower volume zone (260, 336)of said enclosure, said float (130, 340) comprising an exterior circumferential surface (142, 352) circumferentially spaced from said interior circumferential surface (24, 324) of said enclosure for defining a circumferential gap (148, 356) therebetween, and wherein said first valve means and said second valve means are adapted to control under centrifugation at least one closed loop circulation of biological fluid into said interior isolation chamber (208, 378) from said upper volume zone (262, 338), out of said interior isolation chamber (208,378) into said lower volume zone (260, 336), out of said lower volume zone (260, 336) and through said circumferential gap (148, 356) to said upper volume zone (262, 338), and back into said interior isolation chamber (208, 378)as a function of a first pressure differential of biological fluid on said first valve means and as a function of a second pressure differential of biological fluid on said second valve means for isolating at least one target component of the multiple component biological fluid within said interior isolation chamber (208, 378) of said float (130, 340).