5 Successful Predictive Vibrations - March - 2012
5 Successful Predictive Vibrations - March - 2012
5 Successful Predictive Vibrations - March - 2012
Rotordynamics of Pumps
Part I: Single-Stage
Overhung Pumps
BY MALCOLM LEADER, P.E.
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3/20/12 11:20 AM
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Thank you
In the 25 years that Judy Eshleman has served as the Editor of Vibrations, it has evolved from a
newsletter into the flagship publication for the Vibration Institute and the community it serves.
Under Judys direction and guidance, and the work of Ron Eshleman as Technical Editor, Vibrations
has become the standard for Vibration Analysts throughout the world. Judy and Ron were well
suited for this endeavor Judy had been senior editor for Encyclopaedia Britannica and The Shock
and Vibration Digest and Ron was a science advisor for IIT before he became Director of the
Vibration Institute
We would like to acknowledge and thank both Judy and Ron for all of their work over the years to
make Vibrations the publication it is today.
The Officers, Board of Directors and Staff of the Vibration Institute
3/20/12 11:20 AM
Vibrations
March 2012
Volume 29, Number 1
ISSN 1066-8268
Vibrations
Vibrations is published quarterly in March,
June, September and December by the
Vibration Institute.
Statements of fact
and opinion are the responsibility of the
authors alone and do not imply an opinion
on the part of the officers or members of
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advertising does not imply an endorsement
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Copyright 2012 by the Vibration Institute.
All rights reserved. Materials may not be
reproduced or translated without the express
written permission of the Vibration Institute.
editor
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kbresson@vi-institute.org
technical editor
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rsayer@vi-institute.org
advertising Manager
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list of advertisers
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4 | Vibrations
david a. corelli
Vibration Institute President
Successful Predictive
Maintenance Programs
Require a Skilled Analyst
When I started in the vibration analysis business in 1974, most people were still
using swept sine analyzers for obtaining frequency data. This was also about the
time that the first digital Fast Fourier Transform (FFT) analyzers, like the HP 5450
and 5451, were beginning to penetrate the market. The HP 5451A Fourier Analyzer
that I used at the Air Force Avionics Laboratory at Wright Patterson Air Force Base
had optional, external anti-aliasing filters and consisted of a full rack of equipment,
certainly not portable. Analysis of remote data meant collecting data using a tape
recorder, identifying data for playback using either a sound track or a time-code
signal such as IRIG, and then sitting at the system playing back data segments one
at a time for analysis. Thus, widespread data collection and analysis of industrial
machinery were not practical, if even possible.
In the early to mid-1980s, with the advent of the personal computer (PC) and verylarge-scale integration (VLSI) technology, the birth of portable data collectors and
predictive maintenance (PM) as we know them today emerged. VLSI technology
provided both the processing speed and downsizing of electronics required to
manufacture truly portable data collection devices that made it practical for largescale monitoring of industrial machinery. Additionally, PCs provided the power to
set up machine databases, store large amounts of data, and analyze the data at our
desks. Thus, wide-scale condition monitoring as we know it today was born.
It the 1980s and 90s, several companies manufactured powerful, portable data
collectors for collecting route-based data on industrial machinery. Most of these
units had off-route or analysis capabilities so that additional readings could be taken
and analyzed in the field or stored and downloaded to the PC for further analysis.
The interest from Industry in these new systems was high and competition for
sales was fierce. I know this from personal experience: I sold these systems during
that time. Sales took off because of the potential to reduce unexpected failures,
downtime and lost revenue. But, while some companies had success with the new
technology, many programs floundered or never got off the ground. Why was such
great technology failing in many cases? A key ingredient was missing.
Over the years, technology and industry have done an incredible job of giving us
powerful tools to collect and analyze vibration data. Unfortunately, what production
MARCH 2012
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contents
4
MARCH 2012
14
case histories
22
Bearing Clearance
Issue in Blower
By Greg Henson
23
certification corner
Vibration Institute
Vibration Analyst
Certification Renewal
Requirements Explained
By Brian Biby
and Nancy Denton, P.E.
16
Coupling Related
Vibration in MG Set
By Scott Tilley
20
Resonance: Cutting It
Down to Size
By Ashok Bhogle
Vibrations | 5
3/20/12 11:20 AM
feature article
Rotordynamics of
Pumps
Part I: Single-Stage
Overhung Pumps
By Malcolm Leader, P.E.
IntROductIOn
6 | Vibrations
MARCH 2012
3/20/12 11:20 AM
pump rotor.
Impeller
Eye Wear
Ring
MARCH 2012
Where:
Ball Diameter (inches)
Radial Force (pounds)
Number of Balls
Contact Angle (degrees)
For the bearings assumed for this example, the coupling end
bearing stiffness is 480,000 lb/in and the coupling end bearing
has a calculated stiffness of 630,000 lb/in. The damping in
rolling element bearings is not zero, but it is very small, on the
same order as structural damping, which is generally assumed
to be 1-2 percent of critical damping.
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8 | Vibrations
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When the seal and pedestal effects are included, the model
changes to look like Figure 9. Here the numbered black boxes
represent the pedestal mass, stiffness and damping. One
percent of critical damping (CC) was used where CC = 2(KM)
KR = 0.2(PDL/C)
In practice, the stiffness and damping generated by a liquid
annular seal are a function of the geometry (length, diameter),
fluid viscosity and density, and pressure drop. The inlet-swirl
ratio is usually assumed to be 0.5 unless swirl brakes are
used. Reducing the inlet swirl through the seal will reduce
the cross-coupling generated and increase stability, although
pump instabilities are relatively rare compared to machines
handling compressible fluids like compressors.
figure 7. typical Seal direct Stiffness
This model will show that the critical speed is eliminated,
as shown in Figure 10. However, this is for synchronous
unbalance as the forcing function. This curve is really valid
only up to the operating speed of the pump (3,580 rpm).
figure 10. Predicted unbalance Response of SSOh
Pump with Seal and Pedestal effects
MARCH 2012
Vibrations | 9
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RefeRenceS lISt
10 | Vibrations
certification Surveillance
In order to protect the Institute members who have
justly earned certification as a Vibration Analyst, the
Vibration Institute wants to pursue individuals who
falsify Institute certification in any manner.
If you are aware of any instance in which you believe an
individual is falsifying their certification status, please
call or contact the Vibration Institute immediately.
If you are aware of any individual whom you believe
is violating basic ethics, please contact the Institute
as soon as possible. Failure to do so degrades the
reputation of your certification and the Vibration
Institute.
(630) 654-2254
information@vi-institute.org
MARCH 2012
3/20/12 11:20 AM
VFD-Induced Bearing
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3/20/12 11:20 AM
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146273 Vibrations r7.indd 13
MKT10214
3/20/12 11:20 AM
caSe Study
Bearing Clearance
Issue in Blower
by greg henson
Elanco/Eli Lilly
14 | Vibrations
off on several of the units. The probes were placed in the same
location as the previous probes. So why were the readings
so much higher than before? Were the signature patterns
different? What was causing the change?
MARCH 2012
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mils (peak-peak)
Frequency (cpm)
mils (peak-peak)
Frequency (cpm)
MARCH 2012
Vibrations | 15
3/20/12 11:20 AM
caSe Study
Coupling Related
Vibration in MG Set
by Scott M. tilley
Burford Electric Service
Table1 lists the overall vibrations levels acquired from the unit
while it was operating. These data clearly indicated that the MG
set not only had high vibration when it was coasting down but
also had high vibration while it was running. Overall vibration
levels exceeded 1.2 ips peak velocity at the outboard horizontal
measurement point on the AC motor. Over 90 percent of the
vibratory energy was occurring at 1x turning speed, which was
recorded at 892 rpm using a strobe light.
16 | Vibrations
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MARCH 2012
Vibrations | 17
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PK Velocity in In/Sec
1.6
Route Spectrum
07-Oct-11 09:03:15
OVERALL= 1.28 V-DG
PK = 1.27
LOAD = 100.0
RPM = 892. (14.87 Hz)
1.2
0.8
0.4
0
Acceleration in G-s
20000
40000
Frequency in CPM
60000
0.6
80000
Route Waveform
07-Oct-11 09:03:15
RMS = .2355
PK(+/-) = .4796/.4239
CRESTF= 2.04
0.4
0.2
0.0
-0.2
-0.4
-0.6
0
0.3
0.6
0.9
Time in Seconds
1.2
Freq: 892.24
Ordr: 1.000
Spec: 1.259
1.5
PK Velocity in In/Sec
0.10
SMT - MG SET
-MOH MOTOR OUTBOARD BRG HORZ
Route Spectrum
28-Oct-11 11:01:35
OVERALL= .0865 V-DG
PK = .0862
LOAD = 100.0
RPM = 899. (14.99 Hz)
0.08
0.06
0.04
0.02
0
Acceleration in G-s
20000
40000
Frequency in CPM
60000
0.18
80000
Route Waveform
28-Oct-11 11:01:35
RMS = .0399
PK(+/-) = .1223/.1102
CRESTF= 3.06
0.12
0.06
0.00
-0.06
-0.12
-0.18
0
0.3
Recertification Requirements
SMT - MG SET
-MOH MOTOR OUTBOARD BRG HORZ
0.6
0.9
Time in Seconds
1.2
1.5
Freq: 898.43
Ordr: .999
Spec: .06559
18 | Vibrations
MARCH 2012
3/20/12 11:20 AM
ARMD
TM
THE MOST
COMPLETE WAY TO
EVALUATE ROTATING
MACHINERY DYNAMICS
RBTS, Inc.
caSe Study
Resonance: Cutting
It Down to Size
by ashok bhogle
Predictive Maintenance Engineer
20 | Vibrations
MARCH 2012
3/20/12 11:20 AM
Motor Lowered by
175 mm, belts
changed from
SPC3150 to SPC 2800
MARCH 2012
Vibrations | 21
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22 | Vibrations
MARCH 2012
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Certification Corner
bacKgROund
MARCH 2012
Vibrations | 23
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24 | Vibrations
MARCH 2012
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Form Layout
Vibration-Related Experience
MARCH 2012
Vibrations | 25
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RefeRenceS
26 | Vibrations
MARCH 2012
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Vibrations
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