Hi all! I am experiencing high vibration problem with a condensor vacuum pump in a 500 MW coal fired plant.

The vane pass frequency is appearing in spectrum.

There are two vacuum pumps out of which only one is kept in service. The same problem is observed in both of the pumps.

What could be the problem?

Kindly give your suggestions.
Original Post

Very Less Info Dear. What are the amplitudes? I am pretty sure 500 MW is not the pump capacity .

What's construction type of vacuum pump?

 

Regards,

 

The pump is a liquid ring vacuum pump.

The motor rating is around 160 KW.

500 MW is the capacity of the entire power plant. It was just to give an overall idea.

The velocity is around 12 mm/sec (0-pk)

The dominant frequency is the vane pass frequency.

There are two pumps in parallel. Only one of them is kept in service.

The max vibration is sometimes occurring in Horizontal, sometimes in vertical and other times in axial. But always in the pump only. Motor vibration is normal.

Check what is the correct water flow rate.

Sometimes in case of small leakage, water flowrate is increased to get the vaccumm . This is not good for the pump and create vibration and quick wear for bearings and pump. 

Vibration image can be: in high freq: bearing wear, in low freq:unbalance and harmonic of 1/2 rot freq.

Recommendation: Check for leakage, check for the normal water flow.

The pump can be damaged (bearings and plate impeller to be changed), or change the pump.

 

Compare two pumps that are identical which you mention parallel. This will give you an idea about the equipment condition and characteristics.

 

 

To share,we have experienced this problem on liquid ring vacuum pump with dominant frequency at 2X peak, but we look closely on HP PeakVue and noticed 1X peak harmonics which we suspect internal wear causing looseness then we replaced and send the pump for repair. it improved from there. 

 

Current vibration we have now is at the range of 3-5 mm/sec.

Thank you so much for your suggestions.

 

We found that the pump was cavitating. After taking the ejector into service, vibration came down from 20 mm/sec to 5 mm/sec!

 

Luckily there was no damage to the pump impeller.

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