2. Radial thrust on the impeller of a volute casing pump without diffuser

2.1 Understanding phenomena

When a volute casing is correctly sized, the pressure around the impeller is theoretically uniform for the nominal operating point, and the impeller does not support any radial stress. This is no longer the case when the flow rate deviates, plus or minus, from the design flow rate. In this case, distortion of the pressure field results in radial forces on the impeller, the resultant of which can be large, or even very large, and whose evaluation is absolutely essential.

In detuned operation, the pressure at the outer diameter of the impeller becomes a function of the azimuth angle θ, which is positive in the direction of rotation, and whose origin is taken to be the starting point of the volute nozzle. Tests show that the pressure...