To explore the feasibility of establishing pump performance in air, two different designs were tested over the same range of shaft speed and flow rate in both water and air. The larger unit of 3000-gpm capacity was of unshrouded design, whereas the smaller, 195-gpm capacity pump was fabricated with a full tip shroud on the impeller. Although similar trends in performance were observed for each pump tested in air and water, some dissimilarities were observed. In particular, the head rise characteristic curves for both pumps were noticeably higher in air than in water. This is contrary to trends predicted by Reynolds number effects and is apparently due to significant difference in the impeller tip leakage flows when pumping liquid or gas.

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