Self-Priming Centrifugal pump operation under air-water two-phase flow shows a typical mechanical & performance failure such as " Head Drop "，" Increment of Shaft Vibration at the Bearing " and etc. In this study, we tested air-water twophase flow in a centrifugal pump which has a double volute casing construction and unique impeller. Air bubble behavior was visualized to understand the drop in pump characteristics. In addition air-water two-phase flow in the pump was calculated numerically using commercial CFD code CFX-11.0, and calculated results were compared with measured ones. The calculated results agree qualitatively with experimental ones.
