Field
Instrumentation and Diagnostics of Pump Vibration Problems
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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