An apparatus for separating at least two discrete volumes of blood into at least a first component and a second component, said apparatus comprising: a centrifuge rotor adapted to rotate about a rotation axis, at least one separation cell, adapted to receive a separation bag of a set of tube-connected bags (14, 44, 16, 38), said set comprising at least said separation bag containing a volume of blood, and at least one component bag (14, 44, 16, 38), a cavity adapted to receive at least said component bag (14, 44, 16, 38), a plurality of valves (128, 130, 132) mounted on the centrifuge rotor, the valves (128, 130, 132) being adapted to control fluid flow between parts of the set of tube-connected bags (14, 44, 16, 38), each of said valves (128, 130, 132) comprising: a spring-loaded valve section comprising: a jaw mounted on a shaft, and a spring adapted to move said jaw into a closed position for radio frequency welding of a tube, characterised in that the apparatus also comprises: a stepper motor section comprising a stepper motor adapted to push against said shaft to move said jaw into an open position, the apparatus being arranged such that said stepper motor section is mechanically and electrically disconnected from said valve section whenever said jaw is in a closed position during radio frequency welding that seals a tube, and said apparatus further comprising: a controller electrically connected to said stepper motor section. a centrifuge rotor adapted to rotate about a rotation axis, at least one separation cell, adapted to receive a separation bag of a set of tube-connected bags (14, 44, 16, 38), said set comprising at least said separation bag containing a volume of blood, and at least one component bag (14, 44, 16, 38), a cavity adapted to receive at least said component bag (14, 44, 16, 38), a plurality of valves (128, 130, 132) mounted on the centrifuge rotor, the valves (128, 130, 132) being adapted to control fluid flow between parts of the set of tube-connected bags (14, 44, 16, 38), each of said valves (128, 130, 132) comprising: a spring-loaded valve section comprising: a jaw mounted on a shaft, and a spring adapted to move said jaw into a closed position for radio frequency welding of a tube, characterised in that the apparatus also comprises: a stepper motor section comprising a stepper motor adapted to push against said shaft to move said jaw into an open position, the apparatus being arranged such that said stepper motor section is mechanically and electrically disconnected from said valve section whenever said jaw is in a closed position during radio frequency welding that seals a tube, and said apparatus further comprising: a spring-loaded valve section comprising: a jaw mounted on a shaft, and a spring adapted to move said jaw into a closed position for radio frequency welding of a tube, a jaw mounted on a shaft, and a spring adapted to move said jaw into a closed position for radio frequency welding of a tube, characterised in that the apparatus also comprises: a stepper motor section comprising a stepper motor adapted to push against said shaft to move said jaw into an open position, the apparatus being arranged such that said stepper motor section is mechanically and electrically disconnected from said valve section whenever said jaw is in a closed position during radio frequency welding that seals a tube, and said apparatus further comprising: a stepper motor section comprising a stepper motor adapted to push against said shaft to move said jaw into an open position, the apparatus being arranged such that said stepper motor section is mechanically and electrically disconnected from said valve section whenever said jaw is in a closed position during radio frequency welding that seals a tube, and said apparatus further comprising: a controller electrically connected to said stepper motor section.