Greetings,

What is the real purpose behind keeping the bearing housing at vacuum? and what would happen if the we lost the vacuum?

Thank you

 

Generally, bearings are under vacuum to help prevent lube oil from leaking out along the shaft, and to prevent the accumulation of high-temperature--and potentially explosive--oil vapours inside the bearing housing.

Usually, loss of vacuum in a bearing housing will result in oil leaks and, could, under the right circumstances, result in a fire or explosion.

But, you haven't provided any information about the bearing housing(s) in question. Are then turbine bearings, or generator bearings, or gear box bearings, or .?.?.? This may have some impact on the real answer.

 

Dear CSA,

I really wish you were my mentor in the plant. Is there anyway to get in touch with your more personally than the forum? sorry for this request.

I have understood your explanation.

Anyway, I was talking about Turbine & generator bearings, if there is any difference in the importance of vacuum in one of these two bearings over the other, please explain it.

 

Aptx4869,

Well, I'm glad you liked my reply; someone didn't, and it's frustrating when they don't take the time to ask for clarification or correct me....

Anyway, I choose to communicate with people via control.com--because I can answer one question and help a LOT of people (who read these threads). Whereas, if you send me questions, I can probably help you--but no one else. That's the beauty of these kinds of technical forums--many people can be helped by the questions and answers.

I hope you understand; it's much more efficient to write one answer and have many people read it (or sometimes it takes a couple of exchanges to clarify things), than to get the same--or nearly the same question--from many people and have to compose the same--or nearly the same--reply many times (not that we don't do that here... but not too often (thanks to the Moderators!).

You've chosen not to share any personal information here, so it's not like anyone at your plant is going to know your questions. This is anonymous, and it works just fine. The only negative here is we can't post graphic images or screen captures or photos or things like that (but the Moderators are working on that, and we do have work-arounds). So, remember--whatever questions you have, other people have the same questions, too. We're mostly good with GE-design heavy duty gas turbines here, and some limited steam turbine questions. And, if you like responses (or questions) you're free to give a "thumbs-up", but if you give a "thumbs-down" you really should state your reason. Healthy exchanges of ideas and impressions and comments are all good!

 

Hear, hear!

And as I look toward quitting this craziness and the technology chase. I feel compelled to share the knowledge as much as I can. People place such a low value on institutional memory and experience, They need to realize that those of us who have been around a while, have experiences and have seen and done things that those coming later will never be able to duplicate. In electronics especially, we used to do everything imaginable in this country and now its very much outsourced. I was deeply amused when of a fairly large collection of technicians gathered around a line stopping UV source failure, not one had any idea what a saturable reactor was or how to work around a failure of the controller board. And they were further baffled when I hooked up a DC power supply to this "transformer" turned it on and dialed up the lamp current needed. And it's not necessarily because they didn't learn, it's because they haven't _done_ things. And with things getting all point and click and dumbed down, who is gonna know what to do when the lights go out?

I highly appreciate your patience and sincere efforts to foster understanding rather than simply say do this and then that. And i have nothing to do with turbine generators.

Regards
cww

 

We are suffering from a phenomena called bearing coking in frame 7FA machine where lube oil consumption goes very high and brg vibration spikes also occur. what is the exact reason and operation point of view what are the causes which arises this issue?

Venkatesh

 

Hi Venkatesh,

We had the same issue once. The machine experienced vibration @ turbine bearing 2. there was coke formation on both the oil deflector and the air seal ring. One of the reasons that contributes to this issue is insufficient vacuum at the lube oil tank. maybe you have a checked mist eliminator filter or so.

Also, Inspect the inlet air filter clean area. if there is dust in it, then check if some of the air filters are loose by rotating them around their axis (using bare hands would be enough).

It is probably that the coke formation started long before you experienced the issue. but, once the coke formation gets into a certain level, the vibration will show up.

Also don't forget to clean the oil deflector and air seal ring or change them if required.

 

Dear friend

As a temporary solution we start second standby BN (Bearing#2) cooling fan in service. Is this a right decision on our part?

What is the vacuum need to be maintained?

Where is the exhaust of BRG#2 Fan connected. Is it either sucked by creating vacuum in lube oil tank or connected to GT exhaust?

CSA can also help me with his answer if possible.

Venkatesh