1. A vibration analysis of a positive displacement pump shows a predominant vibration reading at a frequency of 1x the rotational speed of the pump. There is a phase shift of 180º between axial readings taken in the same direction on the drive and non-drive ends of the pump. What would you suspect the cause of the vibration to be?
2. A vibration analysis on an electric motor shows significant radial vibrations at 1x, 2x, 3x, 4x the running speed of the motor. A particularly predominant peak shows near 12,000 cpm. If the motor has 4 rotor bars and runs at 2940rpm what would you suspect the problem to be and how would you confirm your suspicions?
3. You balanced a pump impeller by placing a 5 gram weight at a radius of 100 mm. The original vibration amplitude was 10 mm/s, and after adding the balancing weight, the vibration is 1 mm/s. The speed of the pump is 1500 rpm and the weight of the impeller is 3 kg.
a) Calculate the residual unbalance, the eccentricity and the balancing quality grade according to ISO balancing standard.
b) The stiffness of the pump’s shaft is 80 kN/m. Calculate the natural frequency for the pump impeller on the shaft (ignore the weight of the shaft).
c) What is going to happen if the pump speed is increased to 1560 rpm