Pump
Noise F. R. Szenasi/C. R. Sparks/J. C. Wachel, Sec.
8.5, Pump Handbook, 2nd Ed., McGraw-Hill, 1986
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The major concern regarding pump noise falls into two categories:
1. Noise levels which do not meet applicable environmental criteria.
Examples range fro personnel noise exposure criteria to overside
noise criteria for submarines.
2. Noise signatures which can be used to diagnose faulty pump operation
or incipient failure.
The proliferation
of industrial noise regulations in recent years has taken much
of the guess work out of allowable noise levels insofar as personnel
and community exposure is concerned, and various noise standards
have specified noise measurement techniques. Several organizations
have developed test procedures and codes for machinery-generated
noise levels.1,2 The Hydraulic Institute code was specifically
developed for the measurement of airborne sound generated by pumps
(Ref. 3, p297).
The most common
approach for controlling airborne noise levels from pumps is to
interrupt the paths by which noise reaches the listener. When
noise is an indicator of abnormal pump operation, modification
of pump internals or operating conditions is normally required.
The measurement
of noise for diagnostic purposes is not well prescribed, either
for instrumentation or for interpretation. Even a well-designed
and properly operated pump will of course produce noise. Variations
in noise amplitude and frequency which result from malfunction
or improper operating conditions will depend upon the type and
design of the pump and the type of problem causing the noise.
Measurement and analysis techniques for interpreting these signatures
will depend upon whether the noise is solid-, liquid-, or airborne
and upon the nature of coexisting noise from other sources.
Determining
the source and cause of noise is the first step in evaluating
whether noise is normal or an indicator of possible problems.
Noise in pumping systems can be generated both by the mechanical
motion of pump components and by the liquid motion in the pump
and piping systems. Liquid noise sources can result from vortex
formation in high-velocity (shear) flow, from pulsation flow,
and from cavitation and flashing.
Noise from
internal mechanical and liquid sources can be propagated to the
environment by several paths, including the pump and support structure,
attached piping, the liquid in the piping, and ultimately the
surrounding air itself.
This section
discusses various pump noise-generating mechanisms (sources) and
common noise conduction paths as a basis for both effective diagnostics
and treatment.
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