EFFECTS OF ENTRAINED AIR ON THE PERFORMANCE OF CENTRIFUGAL PUMPS - 2. EFFECTS OF NUMBER OF BLADES.

Abstract

To investigate the effects of the number of impeller blades on the pump performance under air admitting conditions, tests were carried out for semi-open impellers having three, five and seven blades, respectively. The flow patterns in the impellers were also observed. When the number of impeller blades is sufficient, namely, five or seven, the flow pattern in the impeller is not altered substantially by air admission, and the performance of the pumps is decreased in a similar tendency. An impeller with three blades, however, shows an abnormal tendency in a small air range q//s/Q less than equivalent to 0. 03, namely the head developed is increased by the admitted air, when phi //0 greater than 0. 03. The admitted air improves considerably the unevenness of flow pattern due to the unreasonable form of the impeller passages, and causes an increase of the impeller work and the pump head. When the air quantity is increased further, all of the pump performances fall rapidly and the pumps lose their prime. With knowledge of the test data under a pure water running, an assessment of the pump performance under the air admitting conditions is made.