1. Case Study: Lovejoy Coupling Degradation/Shaft Misalignment
Plant Application: Centrifugal Charging Pump Aux Oil Pump
Machine Description: 5 hp, 3600rpm coupled to oil pump through Lovejoy 3-jaw coupling. Symptoms: High magnitude vibration all points including axial. Vibration at harmonics of running speed with highest peaks at 3x, 6x, 9x etc Findings/Conclusions: Shaft was misaligned and coupling insert was damaged. 3x/6x/9x pattern is associated with 3-jaw coupling.*
* “3x” is shorthand notation for 3 times running speed
11/29/2018

2. CCP 1B Aux Oil As-Found/As-Left Info
Alignment of the pump was found out of alignment from 0.012” to 0.015” angularity (face measurement) and 0.010” on vertical offset (rim).
The coupling rubber “spider” was found nearly destroyed.
Work performed:
The pump was aligned to the motor using the “straight edge and feeler gauge” method. NOTE: The configuration of this pump does not have enough room to utilize the standard Rotolign or dial indicator methods.
Some base holes were elongated to allow proper alignment (bolt-bound)
Spider was replaced..
Vibration Overalls
Position After Before % Change
POS 1A ips POS 1H ips POS 1V ips POS 2H ips POS 2V ips POS 3H ips POS 3V ips
11/29/2018

3. Axial Spectrum As-Found – At first glance looks similar to looseness
Axial Spectrum As-Found – At first glance looks similar to looseness. Closer inspection shows the predominance of 3x/6x/9x which points towards coupling or misalignment. (If pattern peaked at 3x w/o 6x, 9x, diagnosis might be looseness.) 3x 6x 2x 9x 5x 1x 7x 8x
10x 4x
12x
11x
11/29/2018

4. Axial Spectrum after repair/alignment (note change in scale)
Axial Spectrum after repair/alignment (note change in scale). Magnitudes are much lower and 3x/6x/9x no longer predominant 2x 3x 4x 8x 1x 6x 9x
12x 5x 7x
10x
11x
11/29/2018

5. CONCLUSIONS from Case Study: Lovejoy coupling
High 3x is a sign of possible misalignment or coupling problem on a Lovejoy 3-jaw coupling.
High 3x / 6x / 9x pattern (vs 3x only) greatly increases the confidence in the diagnosis, because it helps distinguish the coupling problem from a looseness pattern which may contain harmonics 1x 2x 3x 4x etc and may happen to peak at 3x.
11/29/2018