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Pump Vibration Increase At Low Flow


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#1 aanita

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Posted 22 May 2018 - 01:59 PM

When running at low flow( but more than minimum flow) motor driven side pump vibration increase. Several times try to reduce flow but not succeed as vibration increase, while at higher flow vibration become normal. What might be the root cause?



#2 Bobby Strain

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Posted 22 May 2018 - 03:25 PM

The pump probably needs repair. Better tend to it sooner than later.

 

Bobby



#3 aanita

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Posted 23 May 2018 - 01:11 AM

There are two pumps, one in service while another is on stand-by. Both are the same behaviour at low flow vibration increase. Pump has recently been maintenance done, but I don't know what the maintenance have been done.



#4 breizh

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Posted 23 May 2018 - 05:41 AM

Hi ,

Did you call the supplier to ask for support ?

Is the flow rate within the specification?

Is it new or was the case before ?

 

Good luck.

Breizh



#5 Amit J

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Posted 25 May 2018 - 03:53 AM

Aanita,

 

Check if density / viscosity / vapour pressure got reduced as compared to designed condition for process fluid. This may lead to cavitation at low flow and thereby may increase vibration.

 

Trust this helps.



#6 thorium90

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Posted 26 May 2018 - 12:37 PM

When you say reduce flow, what are you doing to reduce the flow? Are you throttling the pump discharge valve? Or is there a variable speed drive and that your are reducing the pump speed?

If you are using the discharge valve to reduce the flow, its probably just the recirculation effects causing more vibration.

If you are reducing the pump rpm, you are probably at a critical frequency.

Either that, or maybe there's really something loose.


Edited by thorium90, 26 May 2018 - 12:37 PM.


#7 NathanMac

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Posted 27 May 2018 - 03:18 PM

Is the suction pressure per design (not too low)? Where are you at on the pump curve?



#8 aanita

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Posted 31 May 2018 - 01:10 AM

thorium90:


 

Yes pump discharge is throttled as per operation requirements.  The pump having normal/rated flow of 1,000/1,100 m3/hr and at 800 m3/hr flow it is having high vibration.

 

The pump driver is a motor with fixed rpm.

 

Now the Vendor has told to chnage the vibration measurement from mm/s peak to mm/s RMS and doing so as per them vibration reading will come down.



#9 aanita

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Posted 31 May 2018 - 01:13 AM

Amit J:


 

Yes fluid properties will affects the pump performance but they are within the range. Pump suction pressure is also per design.



#10 thorium90

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Posted 31 May 2018 - 06:21 AM

Might I suggest using motion amplification technology to identify the cause of the vibration?

Some videos showing motion amplification for vibration analysis.

 

https://www.youtube....h?v=ijcJXcy_Ab4

 

https://www.youtube....h?v=wM4HmeSE9WM

 

https://www.youtube....h?v=23WnFWqKawQ



#11 thorium90

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Posted 31 May 2018 - 06:26 AM

aanita:

 

 

But is the vibration is higher than before?  Changing the vibration readings from peak to rms is akin to changing the flow readings from m3/day to m3/s. The number becomes smaller but the vibration is still the same isn't it. 

 

The vendor should have addressed the root of the question. Is the current vibration levels a cause for concern?






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