Rotary pump assemblies are known, wherein the runner of the pump is mounted on the end of the motor shaft. These pump assemblies have the disadvantage, that motors with a special shaft must be used, and that the motor bearings must be implemented in a strengthened manner for receiving the pump forces.
There are also known rotary pump assemblies, where the pump shaft implemented as a hollow shaft is mounted on the normally short stub shaft of the motor and is supported by the same, without requiring any additional bearing (U.S. Pat. No. 2,291,346). This implementation has also the disadvantage, however, that the bearings of the motor must be implemented in a strengthened manner for receiving the pump forces. Such special implementations of drive motors are expensive and make procurement of spare parts more difficult.
In the new development it has therefore been decided to free the motor shaft from the forces of the pump completely, by the pump shaft being completely supported, which always is the case in pumps of the type which are not coupled to a motor to form an assembly. It is known, for example (German printed application No. 1,653,721) to completely support the motor-facing end of the pump shaft, which is formed as a hollow shaft and mounted on the motor shaft in the intermediate housing, by means of two grooved ball bearings. This has the disadvantage, however, that a high manufacturing precision is necessary, so that the bearings in the intermediate housing and in the motor are precisely aligned. In lieu thereof, it is also possible to select a yieldable coupling, equalizing alignment errors between the pump shaft and the motor shaft, which, however, results in additional expense. In order to equalize alignment errors and to nevertheless obtain an essentially rigid connection between the pump shaft and the motor shaft it is also known (French Patent 1,391,431) to implement the intermediate housing without any devices for centering with respect to the motor housing, the intermediate housing containing the complete bearing support of the pump shaft, and to only then connect these parts rigidly to one another, if the bearing supports have taken on an aligned position during assembly. It has been shown, however, that the required precision of assembly or mounting is not obtainable under practical circumstances and also would be too costly.