A pump including a stator (8), a rotor (6) comprising an axial extension (14,16) slidably and rotatably mounted at least partially in a rotor chamber (10) of the stator, and at least first and second valves between an inlet and the rotor chamber, respectively between the rotor chamber and an outlet (12), that open and close as a function of at least the angular displacement of the rotor. The pump comprises interacting cam elements (42,44) on the rotor and stator and biasing means acting on the rotor for applying a force on the rotor in the axial direction of the stator cam element.
