Rotating stall phenomenon limits the operation range of turbomachines, therefore it is important to understand the crucial parameters of this phenomenon. In the present study, the diffuser rotating stall in a three-stage centrifugal pump was experimentally studied. Examined main parameter was an axial offset of rotor against the stationary part, which might be unavoidable due to accumulation of geometrical tolerances and assembling errors. The effect of leakage flow rate at the balance drum section employed as a thrust balancing device, which increases the thru-flow rate at the first and second stage diffusers, was also studied. The effect of rotor axial offset was clearly observed and, with the rotor axial offset to the suction side, the rotating stall appeared only at the third stage diffuser. By setting the balance flow rate set to zero, the onset range of rotating stall became wider in the first and second stage diffusers, which was well explained by the decrease of the thru-flow rate.
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