Repeated Feed Pump Bearing Failures
Repeated Feed Pump Bearing Failures
(OP)
Hi all, longtime lurker, first time poster.
I have a situation which is made more difficult in that I am getting only word of mouth from two middle-men, but I will try to be as detailed (or concise) as possible.
We have a customer who has two feed pumps, both KSB HGC 3/10 (size 3 pump, 10 stages). Both pumps meet rate but one of the pumps (lets call it the south pump) continually wipes bearings and has had multiple occasions where the balance disk has failed. The other pump (call it north pump) runs without issues. My shop repaired both pumps so I'm inclined to believe that we can get to the bottom of this since one of the repairs was successful.
Both pumps are motor driven and coupled via Voith variable speed fluid coupling. The pump cases are center-line mounted and the fluid coupling is floor mounted, which I think is one issue. The techs are aligning the pump and motor under a cold condition. My gut tells me they should align it, run the pump to warm up both the case and coupling, and then re-align it. I don't know much about these fluid couplings so they may be more forgiving than that but it seems unlikely that a boiler feed pump could run hot when it is aligned cold. In addition, the techs are starting the pump with the fluid coupling 85% engaged, which means it spins right up and I wish they would just get rid of the dang thing (the fluid coupling not the tech).
Furthermore, the techs recently found that the north pump has dowels which encourages the case to grow away from the driver. These dowels are on the drive-end of the pump at the centerline. The south pump does not have these dowels, which I think is obviously an issue. By not doweling the south pump, I would think the case is allowed to grow axially in both directions instead of favoring one, which I think could work in concert with the fact that the train is cold aligned. I don't like either of those things and yet somehow that is procedure.
The last thing and the reason I posted this thread is that the bearing lube oil is discolored and eventually both bearings will get wiped (drive-end goes first). These pumps have a common bearing design that can be run in multiple configurations (pressure fed, oil rings, flooded housing), but these pumps both use oil rings. On both pumps, the bearing temperatures (drive-end and non drive-end) don't exceed 100F during operation. However, the south pump bearing oil is discolored and eventually the bearings rub. I believe the techs are over-filling the reservoirs which is causing too much drag for the oil rings to be effective, but I'm not sure that would discolor the oil or cause a bearing rub. They have done contamination checks and they were clear. They also found that the bearing housings we're not square with the case so they squared them up but it changed nothing. A vibe tech also went out and measured vibration, I'm not sure where but his results were that the dominating response was synchronous and there was a slight broadband response around 2X, but maybe not enough to be conclusive. I can share photos to provide a visual aid but it seems I'm limited to one per post.
Thoughts and suggestions are welcome and I apologize for the novel. If you have made it to this point kudos to you and thanks for your attention.
I have a situation which is made more difficult in that I am getting only word of mouth from two middle-men, but I will try to be as detailed (or concise) as possible.
We have a customer who has two feed pumps, both KSB HGC 3/10 (size 3 pump, 10 stages). Both pumps meet rate but one of the pumps (lets call it the south pump) continually wipes bearings and has had multiple occasions where the balance disk has failed. The other pump (call it north pump) runs without issues. My shop repaired both pumps so I'm inclined to believe that we can get to the bottom of this since one of the repairs was successful.
Both pumps are motor driven and coupled via Voith variable speed fluid coupling. The pump cases are center-line mounted and the fluid coupling is floor mounted, which I think is one issue. The techs are aligning the pump and motor under a cold condition. My gut tells me they should align it, run the pump to warm up both the case and coupling, and then re-align it. I don't know much about these fluid couplings so they may be more forgiving than that but it seems unlikely that a boiler feed pump could run hot when it is aligned cold. In addition, the techs are starting the pump with the fluid coupling 85% engaged, which means it spins right up and I wish they would just get rid of the dang thing (the fluid coupling not the tech).
Furthermore, the techs recently found that the north pump has dowels which encourages the case to grow away from the driver. These dowels are on the drive-end of the pump at the centerline. The south pump does not have these dowels, which I think is obviously an issue. By not doweling the south pump, I would think the case is allowed to grow axially in both directions instead of favoring one, which I think could work in concert with the fact that the train is cold aligned. I don't like either of those things and yet somehow that is procedure.
The last thing and the reason I posted this thread is that the bearing lube oil is discolored and eventually both bearings will get wiped (drive-end goes first). These pumps have a common bearing design that can be run in multiple configurations (pressure fed, oil rings, flooded housing), but these pumps both use oil rings. On both pumps, the bearing temperatures (drive-end and non drive-end) don't exceed 100F during operation. However, the south pump bearing oil is discolored and eventually the bearings rub. I believe the techs are over-filling the reservoirs which is causing too much drag for the oil rings to be effective, but I'm not sure that would discolor the oil or cause a bearing rub. They have done contamination checks and they were clear. They also found that the bearing housings we're not square with the case so they squared them up but it changed nothing. A vibe tech also went out and measured vibration, I'm not sure where but his results were that the dominating response was synchronous and there was a slight broadband response around 2X, but maybe not enough to be conclusive. I can share photos to provide a visual aid but it seems I'm limited to one per post.
Thoughts and suggestions are welcome and I apologize for the novel. If you have made it to this point kudos to you and thanks for your attention.





RE: Repeated Feed Pump Bearing Failures
RE: Repeated Feed Pump Bearing Failures
RE: Repeated Feed Pump Bearing Failures
RE: Repeated Feed Pump Bearing Failures
Further, have you had a failed bearing analysed by the bearing manufacturer?
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Repeated Feed Pump Bearing Failures
I am not familiar with this manufacturer or model. But I would expect a very specific arrangement to direct this thermal growth. The inboard feet should be fixed axially. There may be a pin block on the base under the inboard end. The inboard feet may be doweled. But, the arrangement of the outboard is more important. Those feet must be free to slide. There may be a key block on the base under the outboard end to direct the growth. There may be blocks along the sides of the outboard feet. The hold-down bolts on the outboard must be loose. They may be sleeved to leave a gap under the washers. They may be torqued to a low value to allow movement.
The alignment concern is real, but seems less serious. I would measure the support temperatures on the running pump and calculate the growth. I would use those results to cold-align the pump with offsets to accommodate the growth.
Johnny Pellin
RE: Repeated Feed Pump Bearing Failures
Fluid couplings are great, but they aern't really "couplings" per say. A power transmission coupling's primary responsibility is two fold; Transmit torque and Take up misalignment. The fluid coupling is more like a clutch it does great attenuating torque spikes and allowing for line starts, but it is terrible in taking up misalignment. In fact almost 90% of the time I see them installed, there is another coupling present to take up misalignment. For thermal growth applications such as yours, center line mounting a fluid coupling is paramount, however, depending on coupling model that may not be possible. The dowel pins are a nice way to push misalignment in the opposite direction, but that will not solve the misalignment perpendicular to the axis of rotation. Thermal growth causing misalignment perpendicular to the axis of rotation may not be of terrible concern since the pumps are centerline mounted, but that would be assuming uniform growth and no other connections functioning like the dowel pins.
Doing an alignment check in the hot condition of both pumps should give you insight in to how well each are holding alignment, then you can draw conclusions on to how much of an impact the differences in set-ups is effecting alignment in the running condition.
When it comes to couplings we are always here to help.
WWW.PSCCOUPLINGS.COM
RE: Repeated Feed Pump Bearing Failures
RE: Repeated Feed Pump Bearing Failures
Johnny Pellin
RE: Repeated Feed Pump Bearing Failures
The current climate surrounding this project is not great because its become a warranty issue but we hold that if the customer is performing their installation incorrectly, we can't be held liable. ANYWAY, I had the techs check the bearing constant levelers and they state that they are properly filled and that their vents are all sealing properly so they believe the discoloration is coming from oxidized oil and/or babbitt (as opposed to some foreign contaminant).
I got the Operation and Maintenance Manual from the customer this morning and on pg. 13 is the procedure for DOWELING THE INBOARD CASE FEET.
I am still going to chase down the hot alignment vs cold alignment (if they let me) to show that these pumps distort on their way to 330F (the techs think physics is hooplah).
I hope this licks the issue and will update when I hear back. Thanks again!
RE: Repeated Feed Pump Bearing Failures