Study on Optimum Configuration of a Volute Pump of Very Low Specific Speed.

Pump efficiency drops rapidly with a decrease in specific speed ns in the very low ns range. In order to improve a pump efficiency and to establish the optimum design method of a volute pump of very low specific speed around ns=60∼70[m, m3/min, rpm], several combinations of centrifugal impeller and volute casing were tested. The results showed that the maximum efficiency is largely influenced by the volute design parameters, such as a volute tongue, a volute width and a gap between the impeller exit and the volute tongue, while the maximum efficiency differs little by the design of impeller. The BEP of a very low ns pump agrees well with the designed discharge of a volute and is far form that of an impeller. With a decrease in the space between an impeller and a volute-tongue, the pump efficiency increases, and the pressure fluctuation due to interference does not increase, which is quite different from usual ns pumps.