NDE Bearing Burn in Boiler Feed Pump

[mmmumuw]

Hi....
i have problem in boiler feed pump, the NDE bearing is over heat and burn only in seconds, we replace with new bearing, and the problem still same. 10 stages pump with balancing device and balancing pipe, gland packing. type of bearing tapper roller bearing, balancing drum is new, clearance balancing drum 0.3mm. please help me to find the problem.
thank you.

 

[JJPellin]

I would be most curious if the bearing is seeing an excessive pre-load. This could be a result of incorrect installation, you could be purchasing the wrong bearing or the bearings you are receiving could be defective. Tapered roller bearings can be set up such that the stack up of parts will produce the proper internal clearance when installed. Or, the bearings can be set up such that the installation technique needs to provide for the proper clearance. The best example that occurs to me would be wheel bearings on old cars. They used to use pairs of tapered roller bearings set up so that the bearing lock nut determined the clearance or pre-load. I was taught to tighten the nut until I could feel the bearing start to drag and then back off till it just turned freely. If the nut was tightened to the point of drag and locked there, the bearings would burn up quickly once placed in service. But, all of this is speculation. If you want meaningful advice, you need to provide specifics about the bearing you are using, the way it is mounted and the procedure being used during installation.

Johnny Pellin

 

[rmw]

Is this a new problem with a new pump, or a new problem with an old pump or a old problem with an old pump. When did it start?

What type of coupling? Could the driver be imparting a thrust into the shaft?

Are you starting the pump under load or isolated? Is the pump primed when starting.

Have any modifications been made to any of the pump stage impellers?

Is it a double flow first stage, or single flow?

Give with some more information so we can help you.

 

[NGLENGR]

Is the pump de-staged? We had a pump with an 11 stage case but had two blank stages (effectively a 9 stage pump). The shop had installed the #6 stage (high pressure side to the balance bushing) instead of the #2 stage (low pressure side) and sized the balance bushing for the lower thrust condition. We burnt two sets of thrust bearings before sending it back to the shop.

The problem in most multi-stage pumps that are de-staged, is that when you change which stage is blanked (high pressure side or low pressure side) it changes the thrust balance. If you size that bushing wrong (too large, or too small) the thrust balance can lead to an overloaded or underloaded bearing.