Vibration Signature of Misaligned Rotors of Centrifugal Pump

Abstract

The cost of breakdown of rotating machines such as centrifugal pumps encouraged the industrial sector to develop technics for early fault detection. Vibration analysis is a powerful tool to diagnose the problem. It’s used for fault diagnosis and distinguishing the fault types at an early stage, where each faulty element has its exciting frequencies. This paper focus on the shafts’ misalignment. This fault is one of the most common problems that can be found in pumping stations. Misalignment is the condition where the two shafts of the drive and driven machine are not on the same centerline. More vibration and excessive forces in the bearing area are generated due to the misaligned rotors. Two cases were measured on a centrifugal pump to predict the vibration signature due to shaft’s misalignment. The studied system consists of one stage centrifugal pump driven by a motor with rated power 55 kW @ 2980 rpm and flexible type coupling. FFT analyzer is used to analyze the frequency spectrum of the vibration. Vibration data of the inspected pump is collected in the normal and abnormal conditions. The vibration signature of both cases is compared with ISO10816.It has been found that the shaft misalignment causes high peaks at 1X, 2X, and 3X. The amplitude of the 2X vibration is higher than that of the 1X, when misalignment is parallel and lower than 1X, when misalignment is angular. The experimental results obtained from this study gave more understanding on the effective role of vibration analysis in predicting and diagnosing machine faults.