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We have overhauled one boiler feed pump. The axile thrust was set to 0.012" as per the mfg. recomendations. However when we started the pump the axial thrust recorded at DCS was 0.51 mm. While assembly we have taken all car for all the problems related to thrust. All probable deffiencies are in order.

The pump is running , off the best effiency point & almost less than 50 % capacity of its designed all the time.

The thrust went on increasing & the pump was tripped at the tripped seating 0.62mm.

At suction piping there is a immediat elbow on the pump flange, the first stage impeller is double suction, the pump is ballance opposed configeration & is 5 stage. The design flow is 4000M3 per hour.

The pump have this problem since commessioning & almost for last Three years.

There are three more identical pumps side by side but all other three pumps do not have this problem. They are also running almost at 50 % capacity since commessioning & last 3 years.

Can some body put a light on it?

RE: Pump

Can you describe how the axial thrust is transferred to the bearings and how the bearing reactions to the ground/large mass; change in the thrust could be due to machining inaccuracies, as 4 pumps with similar duty seems to be working hydraulically and mechanically well. If you can refer to the manufacturer's site for the cross  sectional drawing it would help to comment.


C Ponnu

RE: Pump

Why are you running your pumps @ 50% capacity ?

If you look @ your curve you will find pressure increases as capacity decreases, this increases thrust.

Your pump is seeing more thrust than the balance drum was designed for.

Your curve should show a thrust constant, that you can calculate the differences in thrust along the curve line.


RE: Pump


These are very large BFP's, 4000m3/hr is over 19,000 gpm.  I'm assuming that for such a large pump, you have a hydraulic balance piston or balance drum to handle any axial thrust loads.  Radial bearings would be sleeve type.

Did you have the manufacturer assist in rebuilding the pump?  This would be essential unless you have a good deal of experience in refurbishing these pumps.

I also assume that you have some type of proximity probe (perhaps Bently Nevada?) installed which provides the axial distance measurement from the probe to the end of the pump shaft (or step in the shaft).  Is this the what you are measuring?

When you commissioned the refurbished pump did you gage the proximity probe, to ensure it is measuring properly?

On such a complicated pump, it will be unlikely that you will be able to identify your problems on this site.  So much depends on the design of the pump, how the pump was repaired and why, what was done during repairs and commissioning, what does the manufacurer say, on and on????

I would suggest that you hire a P.Eng. that has some large BFP experience.

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