Diagnosis and Resolution of Vibration Issues in Vertical Centrifugal Pump

Abstract

Centrifugal pumps are more popular for industrial and domestic applications because of small in size, less in capital cost, easy to maintain, able to work at medium to low heads and low viscous fluids when compared to other pumps. Present problem is to diagnosis and resolution of vibration issues of the vertical centrifugal pump at Visakhapatnam steel plant by using experimental and numerical vibration analysis methods. The power, speed, discharge and pressure head of vertical centrifugal pump used in present analysis are 75 kW, 3572 rpm, 150 m3/h and 190 m, respectively. Experimental vibration analysis and modal analysis are carried with the help of fast Fourier transformation analyser, impact hammer and acceleration sensor. The dimensions of various parts of domestic vertical centrifugal pump are obtained using reverse engineering method. Vertical centrifugal pump parts like motor, pump shaft, motor shaft, coupling, coupling cover, pump, tie rods and base frame are modelled and assembled using CATIA. The solid model of vertical centrifugal pump is exported into ANSYS to carry out numerical modal and harmonic analysis to find natural frequencies and vibration levels, respectively. Numerical modal and harmonic analysis results of existing vertical centrifugal pump are compared with experimental results and found that there is good agreement between the results (the maximum error is 5.6%). From the experimental vibration analysis, peak vibration velocity of 12.3 mm/s is observed at coupling cover. From the experimental natural frequency test, the natural frequency of coupling cover of vertical centrifugal pump is observed at 59.3 Hz and it is close to operating speed. So, problem in vertical centrifugal pump is identified at coupling cover. Structural modifications are carried out on coupling cover of vertical centrifugal pump to increase the natural frequencies to reduce the vibration levels. Numerical modal and harmonic analysis are carried out on modified pump to find the natural frequency and vibration levels to quantify the reduction in vibration levels. From this analysis, it is observed that natural frequency is increased to 137.5 Hz and vibration levels are reduced to 0.7 mm/s.