Boiler Feed Pump Rotor Shifting

Sounds like a Axial Thrust bearing problem.With a stacked rotor/diffuser pump design all the thrust is compounded and additional by each stage. If the bearing was not properly sized, installed or incapable of generated thrust you will have a problem. Also loss of cooling to oil could reduce viscosity below necessary for proper lubrication. If some sort of wiping ring to move oil to top of bearing is utilized then high temperature or improper installation will also create problems.

Don't know the operating conditions but depending on horsepower and thrust they may go with roller or tapered cone thrust bearings rather than a Kingsbury design which I prefer for this multistage stacked diffuser design.

Lastly, there may be some sort of equalizing drum with a balance line to cancel some of the axial thrust. If blocked, another possibility.

Check the direction of rotation of the pump.

Is this pump newly installed and just run for 1/2hour? or is it an old pump that has been running for some time?

If the thrust bearings and spacers etc are properly installed, there cant be any such displacement. Something has worn out or circlips/retainers have moved out of place ...

just a though, is the pump correctly sized for the application?

The shift of the rotor in such a short period is mainly due to following reasons. The main rotating parts in the rotor are impeller, Bearing & shaft.

1. Clearance fit between shaft & impeller in place of interference fit or excessive machining tolerances.

2. Unbalance of rotor.

3. Recirculation at discharge side.

Now, looking at your rotor displacement it seems that reason 2 & 3 stated above are dominant here. The problem may occur at the shut down also.

In my opinion you should check the rotor assembly & it's balance grade.

Also ask for the lateral speed analysis of the rotor so that check for the unbalance will be eliminated.

Also check for the MOC of the rotor & check whether your shaft is flexible enough or not (looking from rigid & flexible rotor point of view).

Primarily, you should check for the recirculation on the discharge side, because at the start up your pump will run at the low flow & your operating point will shift towards the shut off.

Check your enquiry; whether you have specified pump suitability at start up condition. Many times high pressure pumps are specified with balancing drum or balancing disc for taking care of the axial thrust. But these devices are designed for the normal operating point till EOC (at that region pump thrust will be maximum).

For start-up condition you have to have one recirculation line from pump discharge to feed water tank.

Recirculation in the pump will be dominant in high pressure pump at the time of start up & shut down. The clearance between diffuser casing & impeller back & front shroud plays major role in deciding the recirculation.

As you are saying that your rotor has shifted to discharge side it gives the indication that there may be recirculation on the discharge side of the impeller. Please look at the impeller front shroud area & diffuser casing for the cavitation/recirculation mark. Also check the clearance between impeller front shroud area & diffuser casing.

For recirculation phenomenon refer pump handbook.

Rest is the mechanical checking of the assembly & clearance between the rotating parts.

Also ask Sulzer whether "Permanent Magnetic lift-off Device Permavor" has been provided for the pump. This device is required to keep the clearances constant at start up & shut down condition (low flow condition).

The bearing oil film failure is ruled out because Sulzer MC 50/14 model incorporates Two Angular contact taper roller bearing (thrust) & one ball bearing (radial load). Still you can check for the proper installation of the bearing & concentric installation of the rotor & rotor parts.

Check sizing of the orifice located in the recirculation line for thrust balance.

Hello AYP,

Do you suggest that during the start up or shut down of the pump the axial force acting toward discharge side is bigger than axial force acting toward suction end created by pressure difference?

I am not so experienced in feed pumps just why I would like to be clear on this.

In hp pumps we have balance drum which prevents the axial thrust to be overloaded. But if the radial clearances are too big (worn) the balance drum is not going to take the axial load to designed extent what can lead to damages of thrust bearing working pads. That is why often OME;s provide the water leak off pressure measurement to monitor indirectly this clearance and do the pump overhaul in right time.

I know that in pump installation the recirculation line with valve is in place but thought that the main reason is to ensure minimum pump flow all the time.

Please be so nice and throw some light on this phenomena

Did you solve your problem or does it still exist?