A pump system having a pump module (10) comprising a stator housing (28) with a chamber (30), a rotor (32) rotatably and axially slidably received in the chamber and comprising a first axial extension (46) with a liquid supply channel (50) and a second axial extension with a liquid supply channel (52), the first and second axial extensions having different diameters, and first and second sealing rings (54, 56), mounted around the first and second axial extensions.