Pump suction performance was improved by injecting the leakage flow from a radial labyrinth seal to the impeller cavitation generating area as reported in the previous paper. In this paper, it was tested that several specific speed pumps labyrinth seals (Radial labyrinth type) have not only a high sealing performance, but also improve suction performance due to the radial labyrinth seals injection. This study was carried out by CFD and experiments. It was confirmed that radial labyrinth seals have the effect of increasing pump efficiencies, even when the specific speed is changed.