Very high pressure differences with compact design can be achieved with this set in which the stages are arranged on both sides of the canned motor. The total quantity pumped flows through the canned motor and at the same time carries away the motor heat losses. Since, as a result, no heated part of the delivery flows back to the suction side considerably more stable NPSH values are produced in the part load range. Aggregates of Tandem design can therefore be used for considerably smaller pumping capacities, than pumps of single-stage design.