ABSTRACT
Appreciating how a centrifugal pump’s head and power characteristics vary with specific speed is important. A major factor in determining the necessary practices is the concept of suction specific speed, the second concept used to categorize centrifugal pump hydraulic designs. Stable operation requires that there is one, well-defined intersection between the pump and system head characteristic. The most common means of trying to insure this is to specify a constantly rising (with decreasing flow) head characteristic, the so-called “stable” characteristic. Pumps in parallel have a common suction and discharge, thus operate at the same total head. Total flow is therefore determined by adding flows at equal heads. A centrifugal pump is capable of a range of performance, not just the single head capacity characteristic. Performance is adjusted (permanently) by reducing the impeller outside diameter in radial, Francis, and mixed flow impellers, and by changing the vane angle in axial flow impellers.
