The rotating speed has an influence on the pump performance. The operating point of centrifugal pump is affected by the characteristics of both pumps pipelines. By changing the rotating speed of pump in both open and closed pipelines, together with experimental data and calculated results for 50 - 160 type pumps, the effects of power are studied in detail. The effects of energy saving of variable speed pumps in the closed circuit are different from those in the open pipeline system. The reason is that there is a static head in the open system causing the pump efficiency varying. The energy sav...