Experimental Investigations In Respect To The Relevance Of Suction Specific Speed For The Performance And Reliability Of Centrifugal Pumps

Abstract

Recently, several recommendations have been proclaimed concerning limitations of the maximums suction specific speeds (n85) of centrifugal pumps. These recommendations result from statistical evaluations of pump failures that seem to indicate a correlation between n85 and the failure probability. However, this correlation has not been proven by systematic tests applying scientific research methods. Therefore, a corresponding research project was initiated by the Association of German Pump Manufacturers and carried out at a university laboratory with the capability for research on centrifugal pumps. The aim of this project was to investigate the possible effects of high values of Nss on the operational behavior of centrifugal pumps, especially on those measurable dynamic quantities that can serve as indicators for the risk of failures. For the investigations, three standard pumps of different specific speed and size were selected that were designed and manufactured by three different German manufactures. All these pumps were alternatively equipped with two impellers. One of them was designed for high N85 –values, and one for n85 values below the recommended limit. Two of the pumps were run at 3480 rpm, and one pump was run at 3100 rpm.