Pump Vibration

Paper No. 19

J. C. Wachel/J. D. Tison/K. E. Atkins, Short Course, Rotating Machinery and Controls, Vibration Problems in Pumps, University of Virginia, 1983.

There have been tremendous improvements in the instrumentation and diagnostic procedures used to analyze pump vibration problems in the last few years. The use of FFT analyzers, multi-channel FM tape recorders and diagnostic software packages in conjunction with microcomputers has vastly improved the engineer’s ability to understand the types and causes of vibration problems. There are numerous instruments that can generate waterfall displays, order tracking, Nyquist diagrams, etc. Most vibration engineers find that these tools become a mandatory part of the diagnostic system once they have been exposed to them. The authors have found that these tools are so valuable that they need to be available at the job-site during the testing. This presents a problem since many of the systems would have a difficult time surviving the severe treatment that is usually encountered in shipping electronic equipment to the field.

Another important consideration regarding field diagnostics systems is the cost of the instrumentation. Most consulting firms charge a daily fee for the use of the equipment in the field. The costs per day typically run from 0.5 percent to 2.0 percent of the replacement cost. If all the testing went according to schedule, this would not normally be a problem; however, Murphy’s law says that anything that can go wrong, will, so the typical study ends up with many delays.

Faced with these constraints, many engineers tape record the data and ship the tape back to the diagnostic laboratory systems for the detailed analysis. This can sometimes result in several days of delay in obtaining the detailed analyses and eliminates the ability of the test engineer to interactively modify the test plan.

To solve the problems of durability and costs, our company has developed software to perform vibration diagnostics using a low cost Apple microcomputer. This allows the engineer to perform detailed diagnostic analyses at the job site a minimum cost to the client since the equipment costs for the microcomputer are less than $5000. In addition, the engineer can make on-the-spot analyses and determine what tests need to be made to more quickly develop a solution.

This paper describes some of the capabilities of the data acquisition system and shows how it has been used in the field to analyze some pump vibration problems. Other field problems, previously studied, are included to show, in general, the diagnostic procedures that have been used to define the causes of pump vibration.

 

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