The magnetically suspended impeller centrifugal blood pump (MSCBP) has shown its superiority as compared to other artificial hearts. However, it is still plagued by hemolysis and thrombus formation in the clearance gap between the impeller shroud surface and the pump casing. In an early study, a 5 : 1 scaled up model was built in order to measure the radial and tangential velocities at the gap under the operating condition of a flow coefficient (Phi) of 0.04 using a hot wire anemometer. In this study, velocity profiles were obtained at two critical flow coefficients, Phi = 0.078 (fully opened condition) and 0 (fully closed condition), to further the understanding of the flow field in the pump. Similar to the operating condition, the vector plot of the resultant velocity under these two flow coefficients showed that there were no vortices in the gap and a washout mechanism presented at the region around the starting of the splitter plate of the double volute. It was found that the washout mechanism was more obvious in the fully closed condition than in the fully opened condition. This has suggested that with real life operation, the pump could occasionally be operated at a relatively lower flow rate (e.g., under the resting condition of the patient) to obtain a good washout in the gap and thus reduce thrombus formation at the pump casing.