A system is provided for controlling fluid flow in a flow circuit of the type including at least two flexible containers (16, 18, 20, 22) which are fluidly connected by a conduit (24a-24c). The system includes a pressure chamber (14) having an interior (32) which receives one of the containers of the flow circuit. The pressure chamber has at least one port (34a-34c) which communicates between the interior of the pressure chamber and the outside environment and receives at least a portion of the conduit of the flow circuit. The pressure chamber also includes a pressure/vacuum source (48) for increasing the pressure in the interior of the pressure chamber above atmospheric pressure and decreasing the pressure in the interior of the pressure chamber below atmospheric pressure. The pressure chamber may include other elements, such as interface detectors (40), clamping devices (42), sealing devices (44), and access devices (46) for automatically processing fluid, such as separated blood.
