Turbine bearing Oil labyrinth sealing 1

[vali1]

Hi!

I have a small question.
I supposed it is quite simple, but....
It was impossible for me to find the priciple of Oil sealing labyrinth
I mean, I know the principle for steam labyrinth ( Increase the speed on decrasing pressure, and so on...).
I just can not find anything about oil labirinth, in steam turbine domain.
Please, if you have anything...

Thanks,
Vali

 

[byrdj]

I have not heard the phrase "labyrinth" used to describe steam turbine bearing oil seal deflectors.

an oil seal deflector is nothing more than several rows of teeth, very close to the rotating shaft. some of the design features I have seen to prevent oil from exiting the bearing standard around the deflector include:

1) there are at least two rows of teeth (usually more)
2) there is a cavity with a windage screen between the inner and outer teeth, the bottom of which has a drain hole back to the bearing side. the hole is placed too also have a loop seal, so drips that make it to cavity run back, but vapors can not enter cavity through drain hole
2) the deflector rotor area will have grooves
3) Just beyond the deflector rotor area will have a change in diameter.
4) the design of the bearing should have its own addtion oil seal that prevents its discharge from spraying the deflector
5) the lube oil tank is at slight vacumn so air is drawn into the bearing standard over the deflectors teeth.

and for some "problem" deflectors, I have
1)scratch a sprialling groove, to help "pump" oil droplets back into standard
2) provided a second cavity on the outboard side and applied very slight clean air pressure

Now, I don't understand what you mean by [the principle for steam labyrinth ( Increase the speed on decrasing pressure...0]

 

[dcasto]

labyrinth seal is any torcherous path arrangement where a fliud must take many bends, especially multiple 180 degree turns. Thats what btrdj is describing with the rows of teeth. This rows ovelap likea thread and bolt.

 

[vali1]

Hi!

Thank for your answer.
Yes, by that formula, I was trying to briefing. It was about the principle of the steam sealin, if I am wrigt:
velocity of the steam increases while steam pressure is decrasing because steam expansion.
The problem appears because it may be possible to have a problem with turbine oil deflector - first bearing. If will be like this I'll have to use some formula, and it is not possible to use the one from steam glands. Steam is compressible and oil is not.

 

[byrdj]

I understand.

I have been accused of appling formulars and equations to a lot of things to help me under stand a problem. I have never though about appling formular to a leaking oil deflector

The problem is usually adressed by corrective maintenance. for example, where i had a problem deflector was due to a lack of one or more of the features I mentioned (excessive teeth clearance or lack of drain tank vacumn causing air to be drawn accros deflector

The most common repairs I have made include not bolted together to close joints, excessive spray from bearing, no internal venting to allow tank vacumn accross the bearing

good luck

 

[Trublu97]

I might be able to help.
Steam seals are designed with a constant flow model. Oil is non linear, it is a splash. No equations.

the oil deflector, because it is deflecting oil, is usually specified at 10 mils/foot diamater of the rotor. You set the deflector with clearance 1/3 on the bottom and 2/3 on the top, center side to side. the rotor will lift on the oil film by 5mils at speed and move some distance over away from the rotation.

1. check the halves for ensure they are flat. no high spots. Might blue them to check contact. Might use a SMALL dab of permatext to ensure it seals
2. check clearances.
3. check the deflector with a feeler around the shaft to ensure a consistancy.
4. check the to see if the vacuume (if applicable) is correct. on tilt pad bearings, you need a vacuume to scavanging the oil out.
5. make sure the oil lines a ok and there is nothing spraying oil around (pin holes, cracks). visual.
6. check to make sure the orfice are put back into the correct oil line. you might be flowing too much oil to the bearing.
If it is on the HP end, you don't want any leaks. I would go as tight as I could with the clearance using the journal clearance as a guide.

Oh, make sure the bearing (if journal) outside clearance is within spec and not passing excessive oil. check obstructions flowing oil out of the bearing....

 

[turbineJunkie]

sometimes they are ressurized with air to prevent condensate to seep into the oil circuit