Abstract：To clearly and intuitively study the self-priming characteristics of a self-priming pump under different impeller diameters, a visualization test bench was built based on the visualization technology. The self-priming time of five self-priming pumps with different impeller outer diameters and the transient changes of gas-liquid flow state in each region of the self-priming pump were recorded and compared by using high-speed camera, and the self-priming characteristics of the self-priming centri-fugal pump were experimentally studied. The results show that the visualization experiments can accurately capture the gas-liquid two-phase flow in the pump, and the flow state is transient and clear. It can clearly reveal the influence of different impeller outer diameters on the gas-liquid two-phase flow state at each stage of the self-priming pump during the self-priming process. The change in the outer diameter of the impeller affects the gap between its outlet and the baffle, thereby causing changes in the gas-liquid mixing state inside the pump and the characteristics of bubbles in the mixed fluid. Within a certain range(D2/160 is 0.963-1.000), the outer diameter of the impeller is directly proportional to the self-priming performance of the self-priming pump. As the outer diameter of the impeller increases, the gas-liquid mixing efficiency inside the pump increases, the self-priming time decreases, and the self-priming performance improves. On the contrary, the smaller the outer diameter, the worse the self-priming performance of the pump. When the outer diameter of the impeller decreases to a certain extent(D2/160 is less than 0.963), the gas-liquid mixing process stops and the self-priming pump cannot perform self-priming.
