In the case of a canned pump a bar-shaped permanent magnet 6 is provided in a shaft extension 5 which projects into a cap 7 which is arranged on the housing cover 3 of the pump housing. The magnet is aligned in the axis of the shaft extension 5 at its free end. Opposite this a correspondingly aligned Hall probe 9 is arranged on the outside of the end of the cap 7. This probe is connected, intrinsically safe, to a device for recording its signal. A variation of the axial position of the shaft extension 5 or of the pump shaft can thereby be observed by way of the recording device as a magnetic field change by the Hall probe 9. <IMAGE>
