High Vibration of Boiler Feed Pump

Aerated water. Any leaks? Valve malfunctions?

Solids in the water?

Other conditions?

No sir no such conditions have been observed. But some times whenever we keep ARC Bypass line drain open while starting the pump the pump starts. But it is rare. Actually the Pump trips before it actually starts that in one or two revolutions of the shaft as i said earlier.

Consider current pikes instead of vibration, monitor the starting current and if you find it to be causing the problem, install variable frequency drives to each pump, so you have a smooth soft start.

"Trips" what? Circuit breaker? Overload? Vibration monitor?

All the pumps are tripping due to high vibration. It is Observed that the vibration in the horizontal direction found high in all cases.
CLICK HERE for a really good PDF on vibration analysis. It has to do with a boiler feed pump.
If all your pumps are tripping, I would be looking at the bearings and alignment again especially if it is horizontal vibration.
Check all of the following again:

• How many pumps are tripping?
• How many pumps do you have?
• Bearings?
• Alignment?
• Check your alignment equipment and specs. I've seen motors vibrate heavily after they were aligned with the improper foot and soft foot calculations.
• Impeller - broken, cracked, plugged, loose, out of balance?
• Shaft couplers?
• How old are the pumps and motors?
• What is the HP and voltage of the motors?
• What is the pump output in GPM?
• When did they start tripping on high vibration

2 Nos of pumps are tripping.

3 nos of pumps are we are having, but the third pump is also having vibration in the higher side.

Alignment is proper.

Voltage and HP of the motor is proper.

Pump output is 112m3/hr

ANY vibration monitoring MUST be set off during motor starting. Many conditions during startup can cause a short lived vibration (air in the impeller housing, mechanical resonance etc), that is normal and should not be allowed to cause vibration tripping to any control system. S.M.

The vibration monitoring equipment must be bypassed during the starting time period of the pump otherwise it will perform as designed and trip the motor.

Once the motor/pump has reached full speed operation the vibration monitoring equipment is then armed.

You will also need to defeat the vibration trip circuit but not the monitoring & reporting on the BFP motor and pump whenever a normal stop is initiated but make sure the alarms & DATA reporting are still active.

This will allow the motor & pump to be monitored during stopping for important operating DATA gathering while preventing unnecessary trip lockouts.

They all trip after a few revolutions of the shaft??? Have you checked the balance of the rotors, sounds like there is a broken vane/impeller or some kind of debris in the casing. Also, did you follow the procedures for alignment properly, especially regarding the differential expansion limits, temperature gradients, and soak times?

Something is broken or jammed in those units, time to do a complete internal inspection, clearance check, and rebalancing.

If it is indeed tripping by vibration monitor, Here is a clue:"But some times whenever we keep ARC Bypass line drain open while starting the pump the pump starts."

Also:"vibration in the horizontal direction".

These may be indicators of temporary surging during startup and as others have suggested, ignored during start phase.

BFPs need head at the suction or they cavitate.

This ARC bypass line .......what is ARC an acronym for ?

Automatic recirculation control valve....ARC ....This could be the culprit...

http://valves.pentair.com/valves/Images/YAWMC-0489-US.pdf

Bingo!

Mechanical overload and earth faults are also among the possibilities -it depends on what operated to cause the trip, which you have withheld.

Sounds like you have the wrong pumps or the wrong voltage supply or they are not wired correctly, or you haven't used a good start mechanism strategy...I would check the amp draw and voltage characteristics against the stated requirements from the supplier....What is your starting strategy? Do you have a starter?

Have they ever ran properly? or is this a commissioning observation?

If they are "aligned and balanced" when rolled over by hand, then the problem relates to a dynamic issue. Most responses so far are focussed on what the pump is trying to do, but it might be a motor issue.

Loose windings, poor concentricity of rotor/stator (variable air gap) and such will create vibration due to the outcomes of the electromagnetic fields when powered up and during operation.

If they have recently been "re-wound" then I would suspect the windings.

If they've been in service for some time (with higher than rated voltage) or "tested" (using inappropriate technique with Megger) and had coil insulation broken down (shorted windings) there can also be vibration.

If the laminations are shorted, there can be other vibration issues.

Is it possible to disconnect the motor from the pump and see if there is significant motor vibration? At least this would focus the diagnosis.

Maybe I think this way because I'm and EE not an ME.

The pump was running properly earlier while commissioning. The pump was not running for 3 months. When the pump has been tried to start after 3 months the pump started giving issues. Pump alignment has been checked and found proper. The pump has been rotated by hand and it is free to rotate.

The pump trips due to high vibration in the Pump side not in the motor side.

to me if the pumps are tripping due to vibrations than it is vibration related,

could be from the vibration sensors it self or related equipments..

from the motor bearings

from the pump and bearings

from the couplers . what kind of couplers are used.

any pittings in the bearings.

does it trips on vib if you try to to disable vib sensors during startup and reintroduced after start up as mentioned earlier.

is it vfd or with soft starters.

has it got similar history earlier.

Dear Mr.Aminul,

From your posting - some more details are required, like

1. H.P of the Motor and Type of Starter, whether the Motor is of VFD Type.etc.

2. Is there any leakage in the Delivery Valve - which will increase the load and increase in the starting current of the motor.

3. Whether the leak of connection is proper and does not leak.

4. Whether the rotor of the motor is electrically intact or any loose windings are found. If loose connections are found it will create problem.

5. Faulty thermal relay or faulty starter may be the issue.

6. Whether required NPSH is available.? But for cold start this may not be a problem, once hot condensate is handled then NPSH is a must.

7. If the motor is of VFD type, then problem may be with VFD Drive, Insufficient Earthing, Drive gets quickly heated etc.

The tripping problem appears to be more on the Electrical aspect rather than mechanical aspect.

DHAYANANDHAN.S

1. The motor is of 800KW, The Motor is Equipped with VFD.

2. There was leakage from the discharge line but the same has been resolved and tried to start again, the same problem persists.

3. The leak of connection is proper.

4. The motor has not been checked for the rotor of the motor is electrically intact.

5. Faulty thermal relay or faulty starter issue is not there as per inspection.

6. NPSH in enough. The Pump has been drained and vented properly but the problem persists.

7. Insufficient Earthing will be checked.

The pump has been tripped due to high vibration in the pump Driving End. If the problem is from the motor end the pump should trip due to motor vibration as per my observation.

Thank You for the Response.

Are your pump vibration sensors of the axial type, meaning do they sense lateral movement, such as would occur during surge.

are the pumps direct coupled or belt driven?

The Pumps are direct coupled through a gear box using flexible couplings.

Check the check valve to see if it is not closing after feed, or not opening during feed. What is the pressure of the boiler & type? Do they start with couplers removed? Are all valves open ( gate valves or ball valves )?

Also, what is the temperature in the feed water tank? Sounds like you are starting against some kind of pressure, or feedback from the tank causing the vibrations.

It's a boiler feed pump. Starting against pressure is what they do.

After the pumps shut off they should equalize back to atmospheric pressure if the check valve is working. The feed water tank is not pressurized.

The pump feed is pressurised if the feed tank is higher than the BFP. 2 to 3m is what was recommended on my last install.

Does the problem occur regardless of boiler pressure?

For pumps of that size,we've experienced bearing failures that was traced to having been left in static condition while in storage. This showed as vibration.

You say these were "run up" OK and then static for 3 months. Could be bearing fault.

While sitting idle for 3 months, were the pumps drained and dried? If they only partially emptied, could it be corrosion on impeller or other internal component is causing the imballance?

"The pumps were running properly after commissioning. The pumps were not running for 3 months. When they were tried after 3 months the problems started" I think this explains everything.

Three months of idling is very grey period, anything could have happened internally. Were the pumps mothballed properly during this idled period?

If not properly handled, the deposits from the pipeline could have been forced in to internal vulnerable clearances, around labyrinths, especially into the clearance at the balance piston. Heavily clogged rust particles around balance position or enlarged clearance around balance piston will imbalance the axial thrust. There had been indications for that. If the freeness of the pump rotation by hand and the axial float were checked and found satisfactory, the only way to ensure is to dismantle the pump and check for functional clearances.

Is your pump not throttled at discharge or at feed? Do not choke it. What's the feed pressure?

It must be ARC bypass line then. If the bypass orifices are corroded or damaged then the pump must be drawing high current at starting as it is not being started at 0 flow. So the pump is tripping at the start. Repairing ARC should fix the problem i guess.

• Broken impeller vanes?
• Dead rat lodged in the impeller?
• Pumps running at the wrong point on their performance curves?
• Net Positive Suction Head wrong:
• blocked inlet pipe?
• inlet pipe too small?
• upstream valve closed or partially closed?
• something else?
• Have the bearings "Brinnelled" during the non-running period, i.e. have flats developed where the surfaces should be round?

It's rather difficult to see from here.

Has the pump manufacturer been called in to investigate and advise?

Please help the forum to provide the help requested.