Pump arrangements for pumping fluid

A pump comprising:

• a housing and
• a rotor rotatably accommodated in the housing and having a longitudinal axis of rotation;
• the housing comprising:
• a resilient seal member,
• an inlet and
• an outlet for fluid;
• the rotor comprising first and second surface areas;
• the rotor and housing cooperatively configured such that the second surface area is radially recessed from the first surface area, a second surface and an interior surface of the housing defining a chamber,
• the first surface area having a sealing engagement against the interior surface to contain the fluid within the chamber;
• the seal member is located azimuthally between the outlet and the inlet;
• the seal member sized and shaped to engage the first and second surface areas as the rotor rotates about the longitudinal axis of rotation to prevent the passage of fluid from the outlet to the inlet;
• wherein an unattached edge of the seal member defines an aperture with the housing.