Hello everyone,
It comes up very often here, abnormal vibration levels 1x and 2x on the pump but negligible on the motor or driver, what accounts for this? Isn't it true that misalignment problems will be seen across the coupling on both driver and driven?

Hi

vibehigh attatch the data - spectra and time waveform

Bent Shaft can also be the problem...But povide machine details and vibration data.

Sorry guys, please find attached signatures and waveform of the unit in question

OM_PUMP.doc (94 Kb, 58 downloads)

vibehigh,
Is this a 4 vaned impeller? If so, looks like excessive head pressure (vane passing). With this much, it will also affect 1x.
Ron Brook

Generally speaking, keeping in mind that vibration is a function directly proportional to excitation force and inversely proportional to dynamic resistance ( just stiffness in a simple case ) at a given frequency, difference in vibration on different equipments even they are connected trough a coupling should be expected.

In regards to a different 1x across the coupling, imbalance in the motor may differ from that in the pump.

David

quote:

It comes up very often here, abnormal vibration levels 1x and 2x on the pump but negligible on the motor or driver, what accounts for this? Isn't it true that misalignment problems will be seen across the coupling on both driver and driven?

Vibration displays its highest amplitude in the path of least resistance, as does electricity travel the path of least resistance.

The farther the vibration is from the source the lower the amplitudes are "supposed" to get, unless resistance is very low along the path being traveled, and then the amplitude may even be amplified in some cases (resonance)

In your case, the high amplitude in the pump may or may not be from the pump, it is just that the pump is mounted with less resistance to the vibration than is the motor. If the vibration in the pump is from the pump, then most paths, including the coupling, are absorbing the amplitude before reaching the motor, including the motor.

If misalignment is the cause here, the same holds true, the pump may have the least resistance to the forces of the misalignment.

I have seen many times where vanepass is much higher in the motor outboard than it is in the pump being driven by the motor. Same reason, resistance or the lack of.

VibeHigh,

What is the type of coupling used in this train?

Also, pl. check for mechanical looseness. Tighten all fasteners. May be, some looseness in pump might be genrating higher vibration as compared to motor. Check phase across the coulping (180+-40) to confirm misalignment. If phase is erratically varying at 30 degree interval around the pump, it may be looseness.
Regards. Pl. keep informed about developments.

Hi VibeHigh--

I've seen this when the pump was softfooted. I had a high axial 1X on the pump only and phase analysis showed out-of-phase movement between both ends of the pump, but ok across the coupling to the motor. Hope this helps!

Tony

Pl. attach vibration history. Since vibration is there in all directions on each pump bearing, problem may be of foundation. With time foundation bolts corrode,loosen, grouts start becomiong loose and so and so forth. History my cast a reflection.
Regards.