Rockwell Motor and Pump Inspections

Thomas Okamura

14 Jul 2025 — 6 min read

On June 5, 2025 conducted a ultrasound and vibration inspection on all the available motors and pumps. Looking at the data was very interesting, full of sound and vibration.

Both provide a TWF and FFT, but the point that these two data sets bifurcate is the fault frequency signature. Ultrasound shows harmonics of 50Hz in many of these measurements and the periodic bearing related frequencies. Vibration on the hand clearly indicates the motor running speed (which in this case, the same speed for the pump) and thus identifying multiples of running speed and bearing issues is easier.

I used the Mobius Institute Diagnostic Guide for drive and driven machine faults.

Approximately after a month I went back and took more measurements, this time focusing more on Chiller #4 equipment: Primary PU #4, Condenser PU #4. They both have what seems to be the worse and most distinct issues out of all the other machines (including the pumps).

I took measurements on the Motor NDE/DE (US-Vib), Coupling (US), Pump DE/ NDE (US-Vib) and Volute (US) (for Condenser PU4).

US-Ultrasound
Vib- Vibration

Since I don't have a triaxial vibration sensor, I had to take individual measurements of all three axis.

We'll look at Primary PU #4 first:

MOTOR

MOTOR NON-DRIVE END

NDE (US)

RMS (dBuV)	maxRMS (dBuV)	Peak (dBuV)	Crest Factor
40.85	40.94	54.12	4.61

ANALYSIS: Harmonics of 50Hz

MT NDE (Vib)

Harmonics: 1X, 2X, 3X, 4X, 6X, 7X
Bearings: 76.333, 217.333, 599.333

Harmonics: 1X, 2X, 7X
Bearings: 172.667, 212.667, 217.667

Harmonics: 1X, 2X, 3X, 4X, 6X, 7X
Bearings: 76.333, 172.667, 217.333, 517, 599.333

Axis	RMS (Acc) mm/s²	Peak (Acc) mm/s²	Crest Factor (Acc)	RMS Velocity mm/s
Vertical	853.18	2971.41	3.48	3.09
Horizontal	725.69	3040.06	4.19	1.92
Axial	1147.38	2853.74	2.49	6.22

_________________________________________________________

MOTOR DRIVE-END

DE (US)

Harmonics: Harmonics of 50Hz

RMS (dBuV)	maxRMS (dBuV)	Peak (dBuV)	Crest Factor
46.54	46.6	58.69	4.05

MT DE (Vib)

Harmonics: 1X, 2X, 3X, 4X, 6X,
Bearings: 76.333, 761.333, 872.333, 873, 904

Harmonics: 1X, 5X, 6X
Bearings: 145.333, 217.667, 761, 853
2X Line: 100, 120, 150

Harmonics: 1X, 2X, 3X, 4X, 6X, 7X,
Bearings: 76.333, 217.333, 599.333, 873

Axis	RMS (Acc) mm/s²	Peak (Acc) mm/s²	Crest Factor (Acc)	RMS Velocity mm/s
Vertical	578.59	2245.72	3.88	2.25
Horizontal	598.21	2412.44	4.03	1.46
Axial	1029.7	2892.96	2.81	5.54

_________________________________________________________

PUMP

PUMP DRIVE END

DE (US)

Must be noise.

RMS (dBuV)	maxRMS (dBuV)	Peak (dBuV)	Crest Factor
40.95	41.47	55.62	5.41

PU DE (Vib)

Harmonics:1X, 2X, 3X, 5X
Bearing: 76.333, 145.333, 172.667, 217.333, 493.667
2X Line: 120

Harmonics: 1X, 3X, 5X, 6X, 7X, 8X
Bearings:120.333, 145.333, 146, 518.333

--No Axial Measurement--

Axis	RMS (Acc) mm/s²	Peak (Acc) mm/s²	Crest Factor (Acc)	RMS Velocity mm/s
Vertical	1471	4599.32	3.13	8.06
Horizontal	1333.7	4677.77	3.51	2.15
Axial	NA	NA	NA	NA

PUMP NON-DRIVE END

PUMP NDE (US)

Mostly pump noise and cannot resolve what are the issues.

RMS (dBuV)	maxRMS (dBuV)	Peak (dBuV)	Crest Factor
40.55	40.91	55.84	5.82

PUMP NDE (Vib)

Harmonics: 1X, 2X, 3X, 5X, 7X, 14X, 20X, 21X
Bearings: 120.333, 172.667,
2X Line: 150

Harmonics: 1X, 2X, 3X, 5X, 6X, 7X
Bearings: 145.333, 518.333, 802,333
2X Line: 120Hz

Harmonics: 1X, 2X, 3X, 6X, 14X, 21X, 28X
Bearings: 76.333, 732.333, 737.333

Axis	RMS (Acc) mm/s²	Peak (Acc) mm/s²	Crest Factor (Acc)	RMS Velocity mm/s
Vertical	676.66	2559.54	3.78	2.19
Horizontal	608.01	2481.08	4.08	1.97
Axial	1529.84	5177.91	3.38	7.67

COUPLING/ FULL VIEW OF MOTOR & PUMP

DATA SUMMARY

Location	RMS (dBuV)	maxRMS (dBuV)	Peak (dBuV)	Crest Factor
Mt NDE	40.85	40.94	54.12	4.61
Mt DE	46.54	46.6	58.69	4.05
PU DE	40.95	41.47	55.62	5.41
PU NDE	40.55	40.91	55.84	5.82

Location	Axis	RMS (Acc) mm/s²	Peak (Acc) mm/s²	Crest Factor (Acc)	RMS Velocity mm/s
Mt NDE	Vertical	853.18	2971.41	3.48	3.09
Mt NDE	Horizontal	725.69	3040.06	4.19	1.92
Mt NDE	Axial	1147.38	2853.74	2.49	6.22
Mt DE	Vertical	578.59	2245.72	3.88	2.25
Mt DE	Horizontal	598.21	2412.44	4.03	1.46
Mt DE	Axial	1029.7	2892.96	2.81	5.54
PU DE	Vertical	1471	4599.32	3.13	8.06
PU DE	Horizontal	1333.7	4677.77	3.51	2.15
PU DE	Axial	NA	NA	NA	NA
PU NDE	Vertical	676.66	2559.54	3.78	2.19
PU NDE	Horizontal	608.01	2481.08	4.08	1.97
PU NDE	Axial	1529.84	5177.91	3.38	7.67

KEY FINDINGS

Misalignment – Highly Likely

Clear 1X, 2X, 3X harmonics present across multiple components.
High axial vibration on motor NDE and pump NDE → classic sign of angular misalignment.
Coupled with relatively high RMS and peak values, especially:
- PU NDE Axial: 1529.84 mm/s² (RMS)
- Mt NDE Axial: 1147.38 mm/s² (RMS)
- Suggests misalignment from motor to pump shaft.

2. Bearing Defects (Possibly Outer Race or Ball Pass Frequencies)

Strong high-frequency content in PU NDE and DE spectra.
Crest factors >3 in multiple cases support bearing wear/fatigue.
Peaks at calculated BPFO/BPFI lines (e.g., 732 Hz, 737 Hz, 518 Hz).

3. Looseness or Soft Foot

Multiple high harmonics (6X–28X).
High RMS + Peak in axial direction on motor & pump NDE could be amplified by structural distortion.
Mt NDE Axial = 1147.38 mm/s² RMS with low crest factor (2.49) → indicates energy but not impacting. Could be resonance or frame tension.

SUMMARY ANALYSIS

Elevated axial vibration on both motor and pump Non-Drive Ends (NDE), strongly suggesting shaft misalignment, likely angular in nature.
Multiple harmonic signatures (1X, 2X, 3X, 5X, etc.) across several planes, indicating possible soft foot or structural looseness, further amplifying vibration.
High-frequency peaks in spectra correlate with early signs of bearing wear, especially on the pump NDE side.

REFERENCE