TABLE OF CONTENTS Every moving component of a rotating machine generates a vibration signal that is uniquely its own. For example, bearings cause a set of frequencies that are different from the frequencies caused by couplings, gears, impellers, or an out-of-balance component.
By gathering the total vibration signal of the machine in question at the appropriate locations, and breaking this information down into its frequency content, it is possible to learn the effects of each mechanical component. This chapter will begin by discussing the proper locations to gather data, some simple methods to diagnose certain kinds of problems, and a detailed section on using a single-channel FFT spectrum analyzer to do problem diagnostics.
It is important to remember that any rotating machine has many of the same vibration characteristics as any other rotating machine. This is true whether the machine is a 180-rpm water pump or a 10,000-rpm gas turbine. This is why vibration analysis has been as successful as it has been. If a new set of physical laws had to be written for each new machine, the technique would be next to useless. Throughout the following chapters, keep in mind that what is said concerning the behavior of a particular pump component, for instance, is just as true for the analogous component on the highspeed compressor that is presently shaking your entire plant.
For rotating machines, vibration readings are generally taken at each bearing housing in the system in the horizontal, vertical, and axial directions. This...
