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Hi Everyone,

May I inquire regarding high vibration of Feedwater Pump at a partial load range only. At partial load range, the vibration could reach up to 8 mm/s-rms, the alarm is set at 7.1 mm/s-rms. Vibration is normal at low load - when Automatic Recirculation Valve (ARV) is close and at full load - when ARV is fully open. We suspected that this was due to the actuation of the ARV (we assumed of a worn out valve internals). We replaced the valve with new, but did not solve the issue.

The ARV is on the discharge side (NDE) of the pump but the high vibration is on the suction side (DE).

I would like to hear if anyone has experience on this.

I can provide more information. Please let me know what information is needed that can lead to the cause of this.

Thanks,

Manolo1978

Tags: Automatic Recirculation Valve, FW, Load Range, ARV, Feedwater, High Vibration, Feedwater Pump

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Your statement, "Vibration is normal at low load - when Automatic Recirculation Valve (ARV) is close and at full load - when ARV is fully open", is confusing.   Let's change this discussion from "load" to "flow" and show us what this means on the pump's head curve which will be much more useful and informative.

It would also be helpful to the members here if you can provide background information (e.g. Has this issue always been a problem? <--suggesting a design issue    OR  something that recently changed <----suggesting a change in conditions (flow demand, NPSH issues, new piping lines, etc.) .

Finally, do you have spectral plot to provide?  showing the difference between normal flow/load vs partial flow/load

Regards

Jim P



Post-Edit : as I re-read this, my understanding now is that only at what you call "Partial Load"  seems to make more sense.   I would still request you provide operating conditions "flow/pressure" on the head curve.  Also, is it possible that some of the high vibration may be coming from the recirc line???   have you taken data from this valve/line during the instances of higher vibration?

RM
Last edited by Registered Member

To add more clarity (I hope ) and to be more specific:

1. No, I have not heard of a situation like this before. Typical problems with a recirc line occur when we deviate far from the BEP....which I am sure you are already aware.  Most of the problems I have seen are at one extreme or the other and not at partial recirc flow as you indicate. ASSUMING a good design up front; hence my asking about whether it was always like this or something new, perhaps changes to the flow path.   

2.  I did have an issue once with waste treatment pumps that were throttled "all over the place" depending on the whim of the operator and how quickly or slowly he wanted to lower the lagoon level. I took data and found severe cavitation noise (i.e. confirmed by a very identifiable spectral content - random noise) at levels on EITHER side of BEP.  This was later controlled by limiting the recirc line's flow limits.

3. So it would be nice to know where your BEP is and compare with the calculated points on the curve where "no flow - full close", "full open" and "partial flow" points are in relation to BEP and then correlate that with actual vibration data.

4. Having vibe data would be helpful to know if there is another issue (flow induced perhaps??) within the recirc line.  Overall levels as you provide do not help determine a possible cause.

Regards

JP

RM
Last edited by Registered Member

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