Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

498 Centrifugal Pumps: Design and Application
Figure 19*1. Basic conditions of misalignment.
book could be omitted. Experience has shown though, rather painfully at
times, that excessive misalignment can have undesirable consequences.
These include internal rubs, excessive vibration, increased static and cyclical
stress. These factors can lead to premature failure of bearings,
seals, couplings, and other parts. Service interruptions, fire, and personnel
injury can result. Figure 19-2 shows a catastrophic pump failure
caused by misalignment. Costs of such a failure will seldom be less than
several thousand dollars and can easily run into the millions if the failure
consequences go beyond the original pump,
Causes of Misalignment
Internal misalignment is generally caused by defective parts, poor machining,
and/or improper fits and assembly. One other occasional cause
is an improper field practice—varying the bolt torque or the gap at the
pump head joint on a vertically split pump to make external alignment
adjustments.
External (shaft/coupling) misalignment can be caused by a host of factors.
These factors are described in the following pages.