Ability to anticipate type of problems in centrifugal pump is essential to prevent surprises in day to day operations. If we know problems in advance, repair jobs can be planned accordingly. Manpower, parts & special tools can be properly provisioned. Production window can be adjusted to suit the repair. Experience shows planned work gives better result than unplanned activity. Reactive maintenance tends to be counter productive and should be kept to the minimum.
Vibration is external signals that can assist plant people in troubleshooting effort. Centrifugal pump will send out complex vibration signals that can be tuned into frequency. By determining the frequency at which the vibration occurs, mechanical or hydraulic problems can be predicted. Vibration diagnostic chart shows nature of faults and its associated frequency. For example, 1 x rpm is associated with rotating members unbalance and misalignment is usually 1 x rpm & often 2 x rpm. Misalignment can sometimes occur at 3 and 4 x rpm. By using data from vibration analysis together with plant experience, we should have a better chance of detecting pump problems.
A case in point, an impeller of an overhung centrifugal fan (not pump) has to be balanced frequently. There are times when the balancing has be carried out twice a week. The balancing technicians has to camp near this fan to attend to unusual balancing requirements. In this case, the predictive capability enable by online vibration monitoring has no use – the root cause of the frequent imbalance has to be understood and solved first. Vibration analysis certainly helps and condition monitoring is an essential program for plant reliability. However, the vibration monitoring is not an end in itself. Good practices in other areas such as design and operations are necessary to achieve desired plant reliability.