ODS & Modal Case Histories
Barry T. Cease
Cease Industrial Consulting
February 20th, 2009
1
ODS & MODAL CASE HISTORIES
BARRY T. CEASE, CEASE INDUSTRIAL CONSULTING
FEBRUARY 20TH, 2009
INTRODUCTION
What is ODS analysis and why do we need it?
What is Modal analysis and why do we need it?
When should either technique be used?
Example of how to collect ODS & Modal data (test unit)
CASE HISTORY#1 – ACCEPTANCE TESTING OF AHU FAN
Equipment & problem description
Route data, coastdown data & determination of “offending frequencies”
Modal analysis of fan, motor & base
Conclusions & recommendations
CASE HISTORY#2 – ACCEPTANCE TESTING OF WATER PUMP
Equipment & problem description
Route data results versus standards & determination of “offending frequencies”
ODS analysis of pump, step 1 (baseline)
ODS analysis of pump, step 2
ODS analysis of pump, step 3
Conclusions & recommendations
QUESTIONS & CREDITS
“Modal Testing”, Robert J. Sayer, PE, Vibration Institute 31st Annual Meeting, June 19th, 2007
“Applied Modal & ODS Analysis”, James E. Berry, PE, 2004
“Machinery Vibration Analysis 3, Volume 2”, Vibration Institute, 1995
“Mechanical Vibrations, 2nd Edition”, Singiresu S. Rao, 1990
2
What Is ODS?
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ODS stands for operating deflection shape.
ODS analysis generates a computer model of your machinery that depicts its motion
while running at operating speed & load. You literally “see” how your machine is
moving as it operates. This modeling can be extremely useful to illuminate an
otherwise elusive solution to machinery vibration problems.
First, a CAD model of the machine or mechanical system is created (structure file).
Second, detailed & meticulous vibration measurements are made on the machine
typically during normal operation. These measurements consist of both the amplitude
& phase of vibration at one or multiple frequencies of interest all referenced to a
common point.
Finally, these field measurements are imposed on the model to generate visible
animations of the model/machine at the distinct vibration frequencies of interest
(typically the “offending frequencies”).
3
What Is Modal Analysis?
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Modal analysis identifies the frequencies & shapes your machine “likes to vibrate at”
(natural frequencies) and compares these to the normal forces present on the machine
to see if a match exists that produces an undesirable resonant condition.
If a resonant condition is identified, common solutions involve the following: force
reduction (ie: reducing the vibration forces present in the machine), tuning of the
mechanical system (ie: adding or reducing mass or stiffness to the system at the right
spots), or force “movement” (ie: changing the machine speed as possible to avoid the
condition).
The actual process of modal analysis is similar to that of ODS analysis except
measurements are made while the machine is not running typically using a force
hammer and one or more sensors. The hammer provides the input (force) and the
sensor(s) measure the response (motion) at multiple points on the machine.
These modal measurements are then processed thru a technique known as curvefitting and then like ODS measurements, imposed on the model to produce animations
that are analyzed.
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Vibration Spectra .vs. Modal Data
PLOT 1: Vibration data measured during normal operation. Dominant vibration at 1,789 cpm or 1x RPM of
machine (“offending frequency”).
PLOT 2: Modal data measured while machine down. Note the strong response at 1,837 cpm which is near 1x RPM.
5
When Should ODS or Modal Analysis Be Used?
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When standard vibration analysis techniques have failed to determine the exact
problem.
When resonance is suspected.
An ODS or Modal job begins best with a determination of the “offending frequencies of
vibration” usually made using standard, route vibration spectra.
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Example: Collecting ODS Data From
CMS Test Rotor Kit
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Machine operating.
Determine reference point (typically use route data point with strong vibration at all
“offending frequencies”).
First roving point collected at reference point (ie: 1Y:1Y).
Continue collecting other points all along machine at predetermined points.
Both the total number of points collected as well as the point locations are key to how
accurate the model animation will represent reality (ie: spatial aliasing).
7
Example: Collecting Modal Data From
CMS Test Rotor Kit
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Machine not operating.
Determine reference (driving) point. Like ODS analysis above, we want to use a point
with strong vibration at all “offending frequencies”, but for modal analysis, we must be
even more “picky” by applying the impact & measuring the response at many points
until good representation of all offending frequencies is found (“driving point”).
First roving point collected at driving point (ie: 1Y:1Y).
Usually, we rove around with the sensor(s) and apply impact at the driving point, but
this isn’t necessary. We could also rove around with the hammer with similar results
although getting a good impact at all points is typically difficult.
Continue collecting other points all along machine at predetermined points.
Like ODS analysis, both the total number of points collected as well as the point
locations are key to how accurate the model animation will represent reality (ie: spatial
aliasing).
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Case History#1: Acceptance Testing Of AHU Fan
Equipment & Problem Description
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Newly installed AHU Fan operating at
medical facility.
Vibration acceptance testing required
for all rotating equipment at facility.
Fan OEM contacted for vibration
specifications - maximum acceptable
vibration at 0.35 ips-pk.
Isolated, center-hung, centrifugal fan
driven thru v-belts by a 4-pole
induction motor operating on a
variable speed drive.
Entire machine supported by 4-ea
spring isolators mounted on floor
arranged per diagram at right.
Two spring isolators are also mounted
between the fan frame and wall to
counter fan thrust.
4-ea Floor
Isolators
2-ea Wall
Isolators
Fan
Motor
9
INITIAL DATA & FINDINGS, PART 1
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Initial vibration data was collected on both
fan & motor at 100% speed and overall levels
were compared to OEM specifications.
Because this machine operated on a variable
speed drive with normal operation anywhere
between 50 and 100% full speed, coastdown
data was collected between this speed
range.
Unfortunately, this machine failed to stay
within OEM specs both at 100% speed and at
many points between 50 & 100% speed.
Maximum vibration levels occurred not at
100% speed, but at lower speeds suggesting
possible resonance problems.
“Offending speeds/frequencies” were
identified from coastdown data at
approximately 1,500, 1,800 & 1,900 cpm.
Field observations noted the entire machine
visibly “jumped” when the machine speed
was set to 90-95% and motion at the motor
outboard isolator seemed worst.
Vibration @
100% Speed
Maximum
Vibration
Level
Fan Speed @
Max Vibration
OEM
Vibration
Spec
Motor, Outboard,
Horizontal
1.289
n/a
n/a
0.35
Motor, Outboard Vertical
1.475
n/a
n/a
0.35
Motor, Inboard Horizontal
0.955
n/a
n/a
0.35
Motor, Inboard Vertical
1.027
n/a
n/a
0.35
Motor, Inboard - Axial
1.205
n/a
n/a
0.35
Fan, Inboard Horizontal
1.929
3.11
1,903
0.35
Fan, Inboard - Vertical
0.605
0.45
1,495
0.35
Fan, Inboard - Axial
0.257
n/a
n/a
0.35
Fan, Outboard Horizontal
0.797
2.60
1,492
0.35
Fan, Outboard - Vertical
0.672
0.65
1,805
0.35
Fan, Outboard - Axial
0.258
n/a
n/a
0.35
Measurement Point
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INITIAL DATA & FINDINGS, PART 2
AHU SF1.3 MOTOR & FAN, OVERALL VIBRATION AT FULL SPEED
2.5
OVERALL VIBRATION (IPS-PK)
2
1.5
1
0.5
0
MOH
MOV
MIH
MIV
MIA
FIH
FIV
FIA
FOH
FOV
FOA
MEASUREMENT POINT
Plot of overall vibration levels at all measurement points at full speed.
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SPECTRAL DATA AT FULL SPEED
Spectral data from points of high vibration at full speed (MOH, MOV, FIH & FOH). Dominant
vibration in all spectra occurs at top fan speed of 1,987 cpm or 33.1 Hz.
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FAN COASTDOWN DATA, BODE PLOTS
PLOT 14: Coastdown data at fan, inboard, horizontal
(FIH) position in Bode format shows suspected natural
frequency at approximately 1,900 cpm (31.667 Hz). The
highest vibration level on the fan was measured at this
point at 1,903 rpm at 3.11 ips-pk!!
PLOT 15: Coastdown data at fan, outboard, horizontal
(FOH) position in Bode format shows suspected natural
frequency at approximately 1,500 cpm (25 Hz). The
highest vibration level measured at this point occurred at
1,495 rpm at 2.60 ips-pk!!
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INTERFERENCE DATA (MOTOR & FAN SPEEDS)
% Full Speed
Fan RPM
1x Fan
2x Fan
1x Motor
2x Motor
fn1
fn2
fn3
25
500
500
999
446
892
1,500
1,800
1,900
30
599
599
1,199
535
1,070
1,500
1,800
1,900
35
699
699
1,399
624
1,249
1,500
1,800
1,900
40
799
799
1,598
714
1,427
1,500
1,800
1,900
45
899
899
1,798
803
1,606
1,500
1,800
1,900
50
999
999
1,998
892
1,784
1,500
1,800
1,900
55
1,099
1,099
2,198
981
1,962
1,500
1,800
1,900
60
1,199
1,199
2,398
1,070
2,141
1,500
1,800
1,900
65
1,299
1,299
2,597
1,160
2,319
1,500
1,800
1,900
70
1,399
1,399
2,797
1,249
2,498
1,500
1,800
1,900
75
1,499
1,499
2,997
1,338
2,676
1,500
1,800
1,900
80
1,598
1,598
3,197
1,427
2,854
1,500
1,800
1,900
85
1,698
1,698
3,397
1,516
3,033
1,500
1,800
1,900
90
1,798
1,798
3,596
1,606
3,211
1,500
1,800
1,900
95
1,898
1,898
3,796
1,695
3,390
1,500
1,800
1,900
100
1,998
1,998
3,996
1,784
3,568
1,500
1,800
1,900
Interference data table. Forcing frequencies .vs. suspected natural frequencies.
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INTERFERENCE DIAGRAM
INTERFERENCE DIAGRAM, AHU FAN
4,500
4,000
FORCING FREQUENCY (CPM)
3,500
3,000
1x Fan
2x Fan
2,500
1x Motor
2x Motor
fn1
2,000
fn2
fn3
1,500
1,000
500
0
500
600
700
800
900
1,000
1,100
1,200
1,300
1,400
1,500
1,600
1,700
1,800
1,900
2,000
FAN SPEED (RPM)
Interference diagram of fan & motor speeds .vs. suspected natural frequencies at 1,500, 1,800 & 1,900 cpm.
Potential interference occurs at approximately 750, 850, 900, 950, 1000, 1075, 1,500, 1675, 1,800, 1,900 & 2,000 rpm.
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MODAL ANALYSIS OF AHU FAN
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A Simple CAD model of the fan,
motor & base was created and
modal data collected.
This modal data was imposed on
the model appropriately to
identify the natural frequencies of
the mechanical system.
The known offending frequencies
were compared with natural
frequencies found to identify a
match that would result in
resonance condition.
Two natural frequencies (modes)
were identified which most likely
are being excited by the fan
speeds as: 26.1 & 31.1 Hz or 1,566
& 1,866 cpm.
Both these modes involve
distortion of the machine base
near the motor.
Simple CAD Model of AHU fan.
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MODAL ANALYSIS – 26.1 Hz Mode
Modal animation at 26.1 Hz of AHU fan & motor
inboard. Note distortion of machine frame near
motor.
Modal animation at 26.1 Hz of AHU fan & motor
outboard. Note distortion of machine frame near
motor.
17
MODAL ANALYSIS – 31.1 Hz Mode
Modal animation at 31.1 Hz of AHU fan & motor
inboard. Note distortion of machine frame near motor.
Modal animation at 31.1 Hz of AHU fan & motor
outboard. Note distortion of machine frame near motor.
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CONCLUSIONS & RECOMMENDATIONS, AHU FAN
1) This fan failed OEM vibration specifications due primarily to resonances identified in
the machine frame at 26.1 & 31.1 Hz.
2) Unbalance may exist in the fan, but it’s contribution is minor by comparison to the
resonances identified. If balancing is done to reduce forces, perform at 1,200 rpm fan
speed or lower to avoid resonances and associated balance difficulties.
3) The isolator near the motor outboard may be loose with the floor. Please inspect &
repair as needed.
4) Resolving the resonance issues will likely involve either adding an additional pair of
isolators between the fan & motor or stiffening the machine frame near the motor or
both.
5) Stiffening the machine frame might be accomplished by welding either “X” bracing
inside the base near the motor or welding plate onto the machine frame for the motor
base to rest on.
6) A slightly larger AHU fan of similar design with six isolators instead of four was also
tested as part of this job – this six isolator fan passed acceptance testing at all speeds.
7) These conclusions were presented to the customer along with documentation. Months
later I checked with plant personnel who informed me my customer had opted to
balance the fan with disappointing results.
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CASE HISTORY#2 - ACCEPTANCE TESTING OF HIGH
PRESSURE WATER PUMP
Equipment & Problem Description
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Newly installed critical high pressure
water pump at plant.
Plant vibration specs called for maximum
vibration levels of 0.10 ips-pk.
At first glance, many problems were
seen with the design & layout of the
pump & piping.
What follows are vibration spectral &
ods data at progressive stages of our
attempt to bring this pump into plant
specs.
Initial state of newly installed water pump. What
is wrong with this design & layout?
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BASELINE OVERALL LEVELS 9/16/08
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Plant vibration specs called for overall levels no greater than 0.10 ips-pk.
Both the motor & pump failed specs during baseline measurements taken on 9/16.
Highest levels were seen at pump with much higher than expected thrust levels.
Movement could be felt at the floor while collecting data.
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BASELINE SPECTRA 9/16/08
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Pump spectra from 9/16/08 shows dominant vibration at the vane-pass frequency (4x rpm) of the pump.
A higher than normal vibration level at this frequency generally indicates flow problems of some sort with
the pump. From the photo earlier, what did you see that could be causing flow problems at this pump?
Horizontal measurement shows high 1x & 2x rpm vibration as well as vane-pass.
Thus, our offending vibration frequencies are primarily 1x, 2x & 4x rpm for this machine on 9/16/08
(baseline).
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BASELINE ODS 9/18/08 – MOTION @ 1xRPM (3,590 cpm)
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Pump maximum vibration at this
frequency occurred at the pump,
inboard, horizontal measurement
(PIH) at 0.05 ips-pk.
Note 180 degree radial motion
across the coupling at this key
frequency. Shaft alignment & soft
foot are suspect.
Note movement of both machine
pedestal & surrounding floor
suggesting significant problems
with this machine foundation.
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BASELINE ODS 9/18/08 – MOTION @ 2xRPM (7,180 cpm)
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Pump maximum vibration at this
frequency occurred at the pump,
inboard, horizontal measurement
(PIH) at 0.08 ips-pk.
Note vertical movement of entire
pedestal & surrounding floor at
this frequency (120 Hz) again
suggesting significant problems
exist with this machine
foundation.
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BASELINE ODS 9/18/08 – MOTION @ 4xRPM (14,400 cpm)
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Pump maximum vibration at this
frequency occurred at the pump,
inboard, vertical measurement
(PIV) at 0.24 ips-pk.
Note thrusting of both pump
suction area and entire pump
rotor. I suspect this is due in part
to turbulence at the pump
suction from “elbow entry”.
Note continued pedestal &
foundation movement.
Note little movement at motor.
25
BASELINE ODS 9/18/08 – MOTION @ 8xRPM (28,800 cpm)
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Pump maximum vibration at this
frequency occurred at the pump,
inboard, axial measurement (PIA)
at 0.04 ips-pk.
Note continued thrusting of
pump & pump suction at this
frequency.
Note relatively little motion of the
motor or pedestal at this
frequency.
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CONCLUSIONS & RECOMMENDATIONS, 9/18/08
CONFIGURATION
1) The suction piping entering the pump requires modification to allow for a minimum of
5 pipe diameters of straight length before entering the pump (10 diameters length
preferred). The presence of the elbow at the pump suction is no doubt causing
excessive turbulence in the fluid flow as it enters the pump which in turn is exciting the
pump vanepass frequency.
2) The shaft alignment is questionable due to the 180 degree radial motion across the
coupling. Please recheck shaft alignment & soft foot and correct as necessary to plant
specs.
3) The machine pedestal & surrounding floor appear loose from the ground. Movement
of the pedestal & floor were clearly seen in ODS at both 1x & 4x rpm.
4) Both motor & pump were hot to touch and low air flow was noted at the motor.
Uncertainty exists as to the existing & proper lube for pump. Install larger fan at motor
endbell & change oil to OEM specs.
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PUMP & PIPING CONFIGURATION 10/2/08
1) The suction piping was modified per
9/18/08 suggestions.
2) The alignment was checked &
reportedly corrected to plant specs.
Soft feet were reportedly identified
and corrected.
3) A new pump rotor was installed with
an impeller reportedly balanced to
plant specs.
4) A recirculation line was added.
5) A larger motor fan was added.
6) The pump oil was changed to an ISO 68
weight per OEM specs.
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OVERALL LEVELS, 10/2/08
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Unfortunately, both motor & pump vibration levels actually increased with the 10/2/08
modifications.
Motor vertical measurements were the only ones that decreased.
Both motor & pump remained out of plant vibration specs.
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SPECTRAL DATA 10/2/08
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High vibration at 1x, 2x & 4x rpm (vane-pass) remained in all pump spectra.
New appearance of vibration at 3x rpm with 10/2/08 modifications not seen in baseline data.
Highest vibration levels remain at 4x rpm (vane-pass).
30
ODS 10/2/08 – MOTION @ 1xRPM (3,590 cpm)
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Pump maximum vibration at this
frequency occurred at the pump,
inboard, axial measurement (PIA)
at 0.12 ips-pk.
Note the excessive horizontal
movement of the newly modified
pump suction piping at this key
frequency.
Notice how much more the piping
is moving when compared to
motion at either the pump or
motor.
Could the solution to the bad
actor at your plant be found at the
piping or ducting?
31
ODS 10/2/08 – MOTION @ 2xRPM (7,180 cpm)
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Pump maximum vibration at this
frequency occurred at the pump,
inboard, axial measurement (PIA)
at 0.08 ips-pk.
As in the earlier ODS at 1x rpm,
note how piping motion is much
greater than that seen at either
the pump or motor.
Note the near perfect 2nd mode
motion (sinusoidal) of the
horizontal run of discharge
piping.
Note the excessive vibration of
both the vertical run of discharge
piping as well as the newly
installed recirculation line (1st
mode).
Note how total motion of the
discharge piping seems to “pull
the pump” in the axial or thrust
direction.
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ODS 10/2/08 – MOTION @ 3xRPM (10,800 cpm)
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Pump maximum vibration at this
frequency occurred at the pump,
inboard, horizontal measurement
(PIH) at 0.16 ips-pk.
Again, notice how the piping motion
dwarfs that seen at either pump or
motor.
Note how excessive motion of the
recirculation line (1st Mode) is
“pulling the pump”.
Note how excessive motion of the
suction line is also “pulling the
pump”.
Note the excessive motion in the
short section of discharge piping
between the recirculation line &
pump discharge.
33
ODS 10/2/08 – MOTION @ 4xRPM (14,400 cpm)
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Pump maximum vibration at this
frequency occurred at the pump,
inboard, horizontal measurement
(PIH) at 0.36 ips-pk.
Again, notice how much more the
piping is moving (vibrating) compared
to either the pump or motor.
Note how motion of the recirculation
line at this key frequency is by far the
most and resembles a possible 2nd
mode.
Note how motion at the suction piping
remains high as well.
34
ODS 10/2/08 – MOTION @ 8xRPM (28,800 cpm)
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Pump maximum vibration at this
frequency occurred at the pump,
inboard, axial measurement (PIA) at
0.05 ips-pk.
Again, notice how motion of the
piping dwarfs that seen at either
motor or pump.
Note the excessive motion of the
discharge piping here.
Note how motion at the recirculation
line is relatively small when
compared to earlier frequencies.
35
INSPECTION RESULTS 10/2/08
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A close inspection of the piping found
a broken discharge pipe hanger just
above the horizontal pipe run in the
ceiling.
It was unknown how long this hanger
had been broken, but it’s absence no
doubt added flexibility to the
discharge piping run.
36
CONCLUSIONS & RECOMMENDATIONS, 10/02/08
CONFIGURATION
1)
2)
3)
4)
5)
Remove the recirculation line if possible. The addition of the new recirculation line has had a
negative effect on machine vibration levels due to multiple suspected resonances occurring there.
Like the recirculation line above, motion of the discharge piping at multiple frequencies is having a
negative effect on machine vibration. Add additional support to the discharge piping at the points
where high motion is observed in the ODS animations. If possible, try adding support from at least
two additional points.
Repair or replace the broken discharge hanger found at the ceiling.
Provide additional support (if possible) under the suction piping as excessive motion continues
here.
No soft foot records were identified from the alignment job performed since 9/16/08 on this
machine. Please perform another soft foot and alignment check on this machine, make corrections
as necessary and document results.
37
PUMP & PIPING CONFIGURATION 10/16/08
1)
2)
3)
4)
5)
6)
A new, larger standpipe was added under
the suction piping for better support.
A new support was added to the discharge
piping at the nearby wall.
A new stiffening “connection” was added
between the discharge & suction piping
above the recirculation line.
The recirculation line was not removed.
The broken discharge hanger was not
repaired or replaced.
Pump soft foot corrections were made and
documented. Machine alignment is
documented to plant specs.
38
OVERALL LEVELS, 10/16/08
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Both motor & pump overall vibration levels dropped significantly with the 10/16/08
modifications.
Motor overall vibration levels are now below plant spec at every measurement point.
Pump overall vibration levels are much better, but remain out of plant specs with highest
levels being seen at the pump horizontal measurement.
39
SPECTRAL DATA 10/16/08
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Significantly reduced vibration levels at all offending frequencies is seen in all pump spectra.
Remaining vibration still occurring at 1x, 2x, 3x & 4x rpm (offending frequencies).
Vibration at 4x rpm (vane-pass), although reduced, remains the dominant vibration
frequency in most measurements.
Vibration at 3x rpm, although reduced, is the highest single source of vibration in all three
pump measurements.
40
ODS 10/16/08 – MOTION @ 1xRPM (3,590 cpm)
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•
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Pump maximum vibration at this
frequency occurred at the pump,
inboard, axial measurement (PIA) at
0.12 ips-pk.
Notice how motion of the piping is
much greater than that observed at
either the pump or motor.
Note how now both the discharge &
suction piping are flexing in the axial
(thrust) plane and are “pulling the
pump” with them.
Notice how the motor is virtually
“still” at this key frequency – any
alignment or coupling problems are
now unlikely here.
Both the addition of the new
“stiffening connection” between
suction & discharge as well as the
continued existence of the
recirculation line appear to have
negative effects on machine vibration
(transmission path).
41
ODS 10/16/08 – MOTION @ 2xRPM (7,180 cpm)
•
•
•
•
Pump maximum vibration at this
frequency occurred at the pump,
inboard, horizontal measurement
(PIH) at 0.05 ips-pk.
The newly installed discharge
piping support at the wall was
found both loose from the wall and
the piping.
This looseness is at least partly to
blame for the excessive motion of
the discharge piping seen at or near
the location of this new support.
Both the newly installed stiffening
connection between discharge &
suction piping as well as the
recirculation line must be
eliminated to reduce machine
vibration levels.
42
ODS 10/16/08 – MOTION @ 3xRPM (10,800 cpm)
•
•
•
•
Pump maximum vibration at this
frequency occurred at the pump,
inboard, horizontal measurement
(PIH) at 0.14 ips-pk.
Note the excessive horizontal motion
of the discharge piping at this
frequency with maximum deflection
occurring somewhere between the
recirculation line & discharge valve.
The recirculation line should be
removed.
Horizontal bracing of the discharge
line somewhere between the
recirculation line & discharge valve
may be necessary to eliminate this
vibration. Only consider this
modification after the glaring
problems mentioned earlier are
corrected and high vibration levels
persist.
43
ODS 10/16/08 – MOTION @ 4xRPM (14,400 cpm)
•
•
•
Pump maximum vibration at this
frequency occurred at the pump,
inboard, horizontal measurement
(PIH) at 0.12 ips-pk.
Both the recirculation line as well
as the newly installed “stiffening
connection” continue their
negative effects on machine
vibration levels.
Again, notice how little both the
motor & pump are moving when
compared to the piping.
44
ODS 10/16/08 – MOTION @ 8xRPM (28,800 cpm)
•
•
•
•
Pump maximum vibration at this
frequency occurred at the pump,
inboard, axial measurement (PIA) at
0.02 ips-pk.
From the earlier spectral plots,
vibration at this frequency is small
when compared to the others.
Machine vibration levels at this
frequency could be reduced by
removing the “stiffening
connection” between discharge &
suction lines.
The suction pipe stand is vibrating
excessively at this frequency in the
horizontal direction.
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CONCLUSIONS & RECOMMENDATIONS, 10/16/08
CONFIGURATION
1)
2)
3)
Remove the recirculation line & stiffening connection. Excessive motion (vibration) was seen at
both the recirculation line & newly installed “stiffening connection” at many frequencies. Remove
these two piping components to reduce machine vibration levels.
Tighten up the newly installed support between the discharge piping and wall.
Repair the broken discharge hanger located in the ceiling.
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QUESTIONS & CREDITS
1) “Modal Testing”, Robert J. Sayer, PE, Vibration Institute 31st Annual Meeting, June 19th,
2007
2) “Applied Modal & ODS Analysis”, James E. Berry, PE, 2004
3) “Machinery Vibration Analysis 3, Volume 2”, Vibration Institute, 1995
4) “Mechanical Vibrations, 2nd Edition”, Singiresu S. Rao, 1990
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