To facilitate the fixing of instruments to the rotating impeller or bringing stationary instruments close up to it, the impeller was allowed to discharge freely into the atmosphere without a volute casing. Throttling and flow measurement was carried out on the suction side of the impeller. While this provided a convenient means of taking measurements it was found that the entry and exit vane angles of that impeller were such that, when generating a reasonable head, server “shock” must have taken place at the entry. This might not have greatly affected the overall performance because of the large radius ratio (D2/D1=2.72), but uniform and steady velocity distributions could not be expected in the impeller passages.
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