Noticed a definite bump at the inboard bearing housing while taking normal route data on our fan pump. The data is showing impacting at turning speed of the pump and what I thought was posible looseness in the spectrum (or an excited freq caused by the impact?). Impact did not show up in the motor or the outboard bearing housing nor in any of my peakvue readings.
The next day the impact had dissappeared and has not returned. One of our mechanics said that he had noticed the bump 3 or 4 times in the past.
This pump has only been in service for six months, it is a Sulzer ZPP62-700, I do not have any info on the bearings at this time, the coupling is a falk 1045g20 gear coupling and is driven by a variable speed 700hp GE motor.

I would like your thoughts on what might be causing this impact. My first thought was a locknut backing off of the bearing alloying axial movement or can a coupling locking up show up like this?
This is a major job to rebuild this pump so I want to make sure that I am not missing something.
Any idea's that you have would be geatly appreciated.
Thanks and have a great New Year,
Scott

Bumping_on_Fan_Pump.ppt (94 Kb, 119 downloads) Fan pump data

Scott,

Let me make sure I understand everything here.

The motor is running at 505 rpm. The impacts are about 120 msec apart so they are most likely running speed. The sidebanded peak is at either 41 or 43 orders with spacing at running speed. This is a fan pump as in the basement of a papermill under the wet end. This only happens occasionally.

Does it only happen axially or is that just where you happened to be when it happened? The amplitude in the waveform is not that high, but if you don't know where or what direction the vibration is comming from, I wouldn't ignore it just because of that. How long does it last? How many vanes on the impeller? I really can't imagine how it could cause it, but do you have another coupling that you could count the teeth on. I think it may be more like 60 than 41 but a quick count wouldn't hurt.

How about the possibility of foreign matter getting that far along in the process? Does it ever occur at other speeds or have you only captured it once?

I think that if you have the CSI Transient program, you can hook up multiple channels and set a trigger point to capture data.

Good Luck,

Danny

Danny,
Yes,this is a fan pump for a paper machine. After first noticing the impact that morning I took two more sets of data though out the day, all showing the same thing. The axial and horizontal readings were about the same on the inboard bearing. The next day pump was running smooth.
I do not have the transient program so for now I do a walk by 3-4 times a day.
It is something that I could not ignore but did not want to get everyone to excited. After being told that others had noticed the vibration before I am really puzzled. Hopefully I will catch it if it reappears.
Thanks,
Scott

I had the experience that after installation of a new rotating assembly I picked up impacting at running speed at random intervals. In this case the the two flanges of the "tyre" coupling were so close that under certain flow conditions in the pump axial movement, although within spec, would allow the bolts holding the tyre in place to make contact.

The frequency you have marked is at 44 times turning speed. I would look closely at the coupling spacing and any odd wear pattern on gear teeth of coupling, loose coupling components. Do you have any process conditions like pressure flow temp to go along with this abnormal condition?

Scott,

it seems obvious, but what did the night shift guys say or do later that evening that may have caused a change in process or vibe readings. (repairs, adjustments, etc??

Regards
Brian

Dave, you were dead on with the coupling but with the vibration going away as often as it was the desicion was made to watch the equipment for a change.
Many of us have small windows of time to do maint. on our more critical equipment, we passed one and it cost us. Here are some pics of the coupling.
Scott

Fan_Pump_Coupling_show.pps (2,878 Kb, 63 downloads)

quote:

Originally posted by Dave Reynolds:
The frequency you have marked is at 44 times turning speed. I would look closely at the coupling spacing and any odd wear pattern on gear teeth of coupling, loose coupling components.

A side question ... Does anybody know why would a worn gear type coupling with 44 teeth produce clean 44x (clearly visible in the motor spectrum )? After all, physically torque transmission is not occurring like in a gear set where gear mesh occurs at 44x.