A pump includes a housing having an inlet and an outlet configured to convey fluid, an impeller configured to convey the fluid from the inlet to the outlet, the impeller being arranged on a rotatable shaft, and a balance drum configured to relieve axial thrust. The balance drum includes a rotor rotationally fixedly connected to the shaft, the rotor having a high and low pressure sides, a stator stationary with respect to the housing, a relief passage extending between the rotor and the stator from the high pressure side up to the low pressure side of the rotor, a return passage connecting the low pressure side of the rotor to the inlet. An intermediate passage opens into the relief passage between the high pressure side and the low pressure side of the rotor. A blocking member is configured to influence the flow through the intermediate passage.