Effect of Impeller Trimming on Centrifugal Pump

Abstract

Pumps, especially centrifugal pumps, play an important role in engineering application, such as petroleum and petro-chemical industries, agricultural industries, portland cement industries etc. To obtain the best performance of the pumps, one has to operate the pumps at their design conditions. In some circumstances, however, the pumps must operate lower than their design conditions and result in the decrease in their performances. In such cases, it is possible to replace the pump impeller with the smaller impeller diameter or to cut its original impeller to smaller size as necessary. The cut of the impeller, or it is frequently referred to as impeller trimming, in some extence is preferable than replacing with new impeller or even by replacing with new pump with smaller head and capacity. In this study, we examine the effect of the pump impeller trimming to the pump performaces. The study was performed in the Fluid Mechanics Laboratory, Mechanical Engineering Department of ITS, Surabaya. The pump impellers were cut up to approximately 19 percent of its original pump impeller diameter, where the original pump impeller diameter is 129 mm. The pump has the maximum capacity of 100 liters/min and the total head of 31.5 m. The pump is powered by a 300 Watt electrical motor. Parameters to be studied in this research include pump capacity, pump head, pump power, and pump efficiency. The results of this study show that all data are in good agreement with the pump affinity laws. Pump capacity, pump head, and pump power decresase as the pump impeller diameter decreases. The pump efficiency is, however, in some extent, increases as the pump impeller diameter decreases. The maximum increase in pump efficiency is obtained when the ratio between the trimmed impeller to its original pump impeller diameter is approximately 89 percent (i.e. D₂/D₁ = 0.89), with the increase in pump efficiency of approximately 20 percent.