Studies on the Improvement of High-Specific-Speed Pump Performance at Low Flow Rates

概要

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To improve the performance of high specific speed pumps at low flow rates, we developed new type propeller pumps which have a part of narrow passage in front of the impeller blades. Some improved characteristics shown by applying this method to pumps of n_8=1550 (rpm, m^3/min, m) are as follows : (1) The shut-off brake horsepower ratio υ_<rel>was reduced (υ_<rel><1.2). (2) Unstable discharge-head characteristics curves were transformed into stable ones. (3) Efficiency and cavitation characteristics were unchanged. (4) Specific speed was unchanged too. It becomes, accordingly, possible to run the pump over the whole range without overloading the motor. The main reasons of these improvements were (a) the reduction of power loss by circulating flow before the impeller blades, (b) the increase of discharge at which the backward flow begins on the suction side, and (c) the uniformalizing of the flow into the impeller blades.
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