Abstract：The present study shows the internal flow fields of a rotational flow self-priming pump under three test conditions by using the two-dimensional particle image velocimetry measurements and the three-dimensional Navier-Stokes code CFX. The velocity fields of the special volute are analyzed in detail. The detailed flow analysis shows that the special volute contributes to the self-priming characteristic. The diversion wall and the outlet of the impeller constitute a ″nozzle″ and ″diffuser″ which promote the formation of gas-liquid mixture and the bubble flow. The streamwise vorticity and the ma-ximum swirl velocity as well as the uniformity of the flow are increased through the ″nozzle″. An exchange of momentum occurs between the liquid and gas in passage 1. The gas is compressed and dispersed into bubbles of different sizes and water is dispersed into droplets, and the gas-liquid mixture is formed. The gas is further compressed through the ″diffuser″. Large bubbles break up into countless tiny bubbles, while droplets are aggregated into liquid, forming bubble flow. Two swirls of different sizes and directions are formed in the gas-liquid separation chamber, which make the gas and liquid separated due to the centrifugal force. The gas flows to the center and exits from the outlet pipe. The separated liquid moves downward and comes into collision with the boss structure. The collision makes the gas bubbles entrained with the liquid separated again. The liquid flows back and once again participates in the above processes until all the air has been evacuated from the suction line.
