An apparatus for separating at least two discrete volumes of a composite liquid into components, comprising a valve design that facilitates loading and unloading of sets of blood bags. The valves comprise a jaw mounted on a shaft, the jaw being adapted to apply radio frequency energy to seal a tube, a stepper motor section, and at least two position sensors. The valve sections are mounted on an upper plate, and the stepper motor sections are mounted on a lower plate. A main radio frequency coil is selectively electrically coupled to each of the valves through a multiplexing switch.