A pump comprising a housing comprising a rotor chamber, inlet and outlet channels opening into the rotor chamber, and inlet and outlet seals mounted on a surface of the chamber, and a rotor rotatably and axially slidably received in the chamber and comprising a first axial extension comprising a liquid supply channel and a second axial extension comprising a liquid supply channel, the first and second axial extensions having different diameters. The inlet and outlet seals engage a surface of the rotor, whereby the liquid supply channel of each axial extension in conjunction with a corresponding seal forms a valve that opens and closes as a function of the angular and axial displacement of the rotor. At least one of the inlet and outlet channels opens transversely into the rotor chamber and at least one of the inlet and outlet seals forms a closed circuit circumscribing said at least one of the inlet and outlet channels.
