×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Sidebands of pump rotation harmonics

Sidebands of pump rotation harmonics

Sidebands of pump rotation harmonics

(OP)
Measuring vibrations on a multistage pump (water pump) I find strong sidebands around rotation harmonics
Rotation is close to  3000 rpm (50 Hz) and side bands about +/- 2.5 Hz

Pressure fluctuations in the fluid are impossible

Any idea about the possible causes of such a phenomenon?

Thanks and regards

luimont

RE: Sidebands of pump rotation harmonics

(OP)
vanstoja
I find sidebands on the pump bearings
Motor shows normal spectra
Theoretically a transmission through the baseframe can occur but what I see is  not just an increase,it is a creation of sidebands
 
luimont

RE: Sidebands of pump rotation harmonics

It doesn't seem likely the motor pole pass frequencies would show up on pump bearings but in case they exist on both motor and pump (transmitted from motor), you can certainly check whether 2.5hz is your pole pass frequency if you know the exact speed (slightly below  3000 cpm).  2.5hz = 150cpm would be pole pass frequency if running speed were approx 2925rpm.

2nd guess as you have appeared to rule out is fluctuation related to the fluid system... valve or load changing at 2.5hz.

If you rule out the above you have definitely ruled out all the likely candidates.  The only other things I can even take a wild guess would be oscillation in the power system (possibly including vfd if present) that might cause torque oscillation at 150cpm.

And if I brainstorm what might possbily oscillate at 2.5hz to cause sidebanding I can guess resonance of very very flimsy structure (spring mounted machine or extremely flimsy cantilever support).  Actually I did have spring mounted machine that had the spring resonant frequency (200cpm) as sidebands to 1x.  It didn't fit any of the charts but I postulated possibly as the machine slowly  wobbled on it's base it was changing unbalance or misalignment response (even though both motor and fan were on same base).   Also possibly torsional resonance of flexible coupling... never seen it but seems possible.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Sidebands of pump rotation harmonics

I would suspect loose bearing to housing clearance or inner race spinning on shaft.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources