Experimental Investigation of the Complete Characteristics of Rotodynamic Pumps

Abstract

Pump failure in a pipeline system can occur for several reasons and this undesirable event causes waterhammer phenomenon. While designing a pipeline system, minimum and maximum pressures caused by waterhammer and the variation of the pressure along the pipeline with respect to time must be determined. In order to calculate the time variation of the pressure, complete characteristics of a pump is used as one of the boundary conditions. In these unsteady conditions, the pump may turn in normal or reverse directions which define eight different working zones called pump, turbine, brake and booster. Specific speed is an essential parameter which affects characteristics of pumps. In the literature, for many years there have been only three complete pump characteristics obtained with the assistance of 1960’s measuring devices and techniques. Each one of those corresponds to pumps having centrifugal (nsq = 35), mixed flow (nsq = 147) or axial impeller (nsq = 261). Recently additional complete pump characteristics that belong to 14 different specific speeds have been published in the literature. By considering improvements in pump design during half a century and innovations in measurement techniques, the present study is performed to repeat experiments of complete characteristics of different specific speeds existing in the literature, and to obtain complete pump characteristics for different specific speeds. The complete characteristics of seven pumps with specific speeds of nsq = 20 – 23 – 33 – 55 – 105 – 209 and 261 are obtained experimentally. The results show that the complete characteristics of a pump is not only function of specific speed but also function of pump design. The number of the complete pump characteristics available in the literature is increased in this study. The obtained results revealed that, unlike the existing approach in the literature, the complete characteristics of pump that is used in the pipeline, must be used in the calculation of waterhammer pressures in the design of pipelines.