The overall performance of a vane-island type diffuser of a centrifugal pump model was obtained by means of directional probe traverses. These measurements were performed in an air model of a real hydraulic pump for five volume flow rates. Directional probe traverses are performed with a classical three-hole probe to cover most of the complete inlet section of the diffuser from hub to shroud and from pressure to suction side. Some assistance from already existing URANS calculation, including leakage effects, is used to evaluate the numerical approach capability and to correctly define the initial conditions that come from the impeller outlet section to evaluate pressure recovery and the measured total pressure loss levels inside this particular vane diffuser geometry. Detailed analysis of the flow structure at the inlet section of the vane island diffuser is presented to focus on local pressure loss during the vaneless gap after the impeller and incidence angle distributions along hub to shroud direction. Previous 2C-2D particle image velocimetry measurement results are also given to compare probe measurements between the inlet throats and outlet of vane island diffuser at mid-span
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