In this study, effects of flow behavior in a non-traditional centrifugal pump, whose diffuser was subjected to different radial gaps, were investigated numerically using multi-purpose FLUENT code. Flow was assumed to be three dimensional, viscous and incompressible. k-epsilon RNG with standard near-wall functions was used. Centrifugal pump had a five backward curved-bladed impeller running at 890 rpm and a nine vaned diffuser. Investigations for three different radial gaps (10%, 15%, 20%) have been carried out for 15 different volume flow rates. For present pump, 20% radial gap is found most suitable for pressure fluctuations.