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Vertical
Pump Monitoring Application
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by
MachineryWatch.Com, Inc.
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| Situation: |
| Machine: |
Vertical
Pump Motor |
| Industry: |
Water
Treatment Plant |
| Location: |
Virginia |
| Equipment: |
Long
Drive Shaft, Centrifugal Pump, Wound Rotor Variable Speed
Motor, 6'4” above base: Motor Speed = 540 RPM |
| Instrumentation: |
MAARS
Model 5000, accelerometers |
| Condition: |
Looseness
induced Resonance at 1X RPM |
| Indication: |
Excessive
Vibration (Shaking) at 1X RPM, resonance verified with
transient capture, coast-down and impact tests |
| Corrective Action: |
Tightened
Motor Hold Down Bolts 1/16 to ¼ turn |
| Results: |
Vibration
reduced at 1X RPM by approximately 67%.
To further reduce levels the speed of the pump was
going to be
slightly reduced to provide further separation of the
natural frequency and the running speed. |
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Description:
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The
subject pump motor had been recently overhauled by a local
shop.
When the site personnel reinstalled the motor there
was excessive vibration felt and viewed.
The repair shop and facility requested an analysis be
performed to determine the source of the vibration.
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The vibration tests showed the vibration was highest at the top of the
motor and very directional.
These are characteristics of vertical pump
resonances. The
spectral data also showed a clear large amplitude peak at
3600 CPM (60 Hz) which is also typical for these motors.
Both impact tests and uncoupled coast down tests were
used to verify the natural frequency. The
table shows the data before and after tightening the base
bolts and also compares the levels to those found on an
adjacent identical pump.
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More bump tests were done after the bolts
were tightened and the results are shown in the spectra
above via the
higher response frequency (591 CPM vs 539 CPM).
Another proof of the shifted natural frequency is
shown below in the coast-down waveform captured before
tightening the bolts. The
highest amplitude spectra captured during this and the
coast-down captured after the bolts were tightened follow
the displayed waveform.
The spectra showing the higher frequency peak was
captured after the bolts were tightened.
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Measurement
Position |
EFF#2
As Found |
EFF#2
Tightened Bolts |
EFF#1
As Found |
| 1 |
1.63 |
0.313 |
0.279 |
| 2 |
0.870 |
0.069 |
0.080 |
| 3 |
0.200 |
0.023 |
0.100 |
| 4 |
0.650 |
0.064 |
0.063 |
| 5 |
0.130 |
0.036 |
0.078 |
| 6 |
0.190 |
0.087 |
0.072 |
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Vertical Pump
