A pump set (7) for use with a pumping apparatus (1) having a rotor (37) with a plurality of rollers (43) mounted on the rotor (37) rotatable about an axis of rotation, the pump set (7) comprising: a cassette body (5) comprising a flexible stator member (113) with a fixed portion secured to the cassette body (5), a second portion opposite the fixed portion, a reaction surface and a second surface opposite the reaction surface, the reaction surface defined between the fixed portion and the second portion, the flexible stator member (113) being at least partially free to float in a stator opening (115)； and a deformable tube (45) secured to the cassette body (5), at least a portion of the tube (45) is disposed against the reaction surface, wherein the flexible stator member (113) has a constant thickness extending along the entire length of the flexible stator member (113).
