A cassette is disclosed that comprises an interface element having a first position and a second position, the interface element configured to be driven from the first position to the second position and back to the first position by unidirectional rotary motion of a driving element, and a first and a second pumping chamber each having a volume and each coupled to the interface element such that the volume of the first pumping chamber is increasing while the volume of the second pumping chamber is decreasing as the interface element moves from the first position to the second position and the volume of the first pumping chamber is decreasing while the volume of the second pumping chamber is increasing as the interface element moves from the second position to the first position.
