Calculation of cavitation parameters of centrifugal pumps

Summary

The efficient long-lasting operation of pumping units with centrifugal pumps is achieved to a large extent by avoiding cavitation during the operation. To ensure the operation of pumps avoiding cavitation at the design and operation stage is only possible on the basis of correctly performed calculations of the cavitation parameters. By comparing the cavitation parameters with the required ones developing the essential operation modes of the pumping units is possible. Particular attention should be paid to pumping units with variable speed drives, since the recalculation of the cavitation characteristics while changing the rotation frequency of the impeller according to the one available plant characteristic does not always provide for obtaining an adequately changed cavitation characteristic. Therefore, for large pumps and with a sufficiently small cavitation NPSH, a method for recalculating cavitation characteristics using two basic cavitation characteristics of the pump is proposed. While using a pump with a sheared impeller, the cavitation characteristic for the sheared impeller shall be applied that is often just over the characteristic for the rated impeller. Another factor that should be taken into account to avoid cavitation in pumps is gaseous cavitation while determining the available NPSH. A widely used in foreign practice method for recalculating the available permissible NPSH to the actual one with account of the presence of gas cavitation, is given.

Key words

centrifugal pump , NPSH required, vaporous cavitation , vaporous cavitation , gaseous cavitation , head and rate , cavitation characteristic , pump impeller , pump impeller shearing