Pump arrangement

A pump arrangement, comprising:

• a pump casing having an interior space;
• a containment can having a central longitudinal axis and being arranged to hermetically seal a chamber in the interior space;
• an impeller shaft;
• an impeller arranged on a impeller end of the impeller shaft;
• an inner rotor arranged within the containment can on an opposite end of the impeller shaft;
• an outer rotor arranged radially outside of the containment can and axially located to interact with the inner rotor,
• a drive motor, and
• a drive shaft arranged to be driven by the drive motor and to be coupled to the outer rotor,
• wherein
• the outer rotor includes a hub and a first carrier element, and a hollow cylindrical section between the hub and the first carrier element,
• the outer rotor is coupled to the drive shaft by a fastening element, and
• the fastening element has
• a first external thread on a first end facing the drive shaft,
• a second external thread on a second end opposite the first end, and
• a spacer section between the first external thread and the second external thread having an outer diameter greater than outer diameters of the first external thread and the second external thread.