Oil breather blockage and oil leakage through the seal

[Hamza1988]

Hi, lately, we at our company are having quite a lot of oil leakages in centrifugal pumps with deflector seals. Someone suggested that the reason of oil leakage through a deflector type seal or a bearing isolator could be a blocked oil breather. Is this true and how would a blocked breather on a bearing housing cause oil to leak through the end seals? Thanks

 

[electricpete]

You are relying on oiler to regulate oil level by feeding only when level is low. Oiler relies on pressure in bearing compartment being close to atmosphere (the pressure seen in oiler vicinity if oiler tube above the oil, below the bulb.) With clogged breather, pressure in bearing compartmentmay deviate due to thermal changes etc, resulting in over feeding or under feeding. Over feeding can increase level and increase external oil leaks

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(2B)+(2B)' ?

 

[Hamza1988]

Thank you electricpete. Yes the system is a constant oil leveler based and every time we run the pump, the whole oiler empties out within 3 to 4 hours. What I understand is that the pressure above the oil level inside the pump bearing housing increases with time and increase in temperature as the vent of breather is blocked but how does it make the oiler overfeed??

 

[JJPellin]

Windage from a cooling fan can drop the pressure in the housing. If the oiler is on the side such the rotation of the shaft draws the oil away from the oiler, the oiler can malfunction and add oil excessively. What type of oil rings (slingers, flingers, other) does the pump use? Which side of the housing is the oiler located on relative to shaft rotation? What is the pump manufacturer and model? Some are prone to this problem.

Johnny Pellin

 

[electricpete]

Thank you electricpete. Yes the system is a constant oil leveler based and every time we run the pump, the whole oiler empties out within 3 to 4 hours. What I understand is that the pressure above the oil level inside the pump bearing housing increases with time and increase in temperature as the vent of breather is blocked but how does it make the oiler overfeed??

Look at the top figure attached which illustrates basic operation of a common oiler (there are a lot of variations).

On the right is the bearing compartment. On the left is the oiler. You'll notice the oiler has an upper chamber (bulb) and a lower chamber (cup). What is depicted is a slant-cut vertical tube coming from bulb down to cup. The bulb is sealed except for that tube. The cup is (generally) vented to atmosphere.

INTERACTION BETWEEN BULB AND CUP (COMPLICATED AND NOT SO RELEVANT)

Assuming the pressure above the oil in the cup is atmospheric, then the space above the oil in the bulb is at a vacuum equivalent to the vertical height difference between level in cup and bulb (for example dp is often given in inches water elevation, oil is close to that to the extent the density is the same).

If oil level in the lower chamber ever uncovers a portion of the slant tube, then air can bubble up from the cup into the bulb. Oil flows from bulb to cup. Cup/reservoir level increases until the slant tube is again covered. The vacuum above the oil is now slightly less equal to the new height difference.

That's a lot of words and maybe not too relevant so let me summarize that the bulb feeds into the cup whenever oil is below the top of that slant cut, and stops feeding when oil in the cup reaches the top of that slant cut. This setup roughly acts to keep oil in the cup at a constant level (the top of the slant cut in the tube).​

INTERACTION BETWEEN CUP AND BEARING HOUSING (SIMPLE AND RELEVANT)

ASSUMING pressure above the oil in the cup is same as pressure above the oil in the bearing compartment, the levels are the same (it's a u-tube with both ends vented). But if you put a vacuum above the oil in the bearing compartment, the bearing compartment oil level will be higher than the cup level and the bearing compartment level will be higher than the target level.

I wouldn't think positive pressure in the bearing compartment could cause overfeeding​

That's my take anyway based on you'd think they would act (not that they always act the way I think they should). Sorry if I stated the obvious.

Good comments by JJPellin as usual.

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(2B)+(2B)' ?

 

[Hamza1988]

Thank you electricpete and JJpellin. I am going to try and clean the breather on one of the pumps next week and see if this stops the leakage through the seal.

 

[LittleInch]

Also if the breathe ris blocked than as / if temperature rises the small increase in pressure forces oil out past the seal and also might blow air into the oiler compartment. Once oil is forced out, the pressure drops, more oil joins and the cycle repeats.

If you can't get positive or negative pressure through a reather then you won't have a problem, probably.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[electricpete]

Also if the breathe ris blocked than as / if temperature rises the small increase in pressure forces oil out past the seal and also might blow air into the oiler compartment. Once oil is forced out, the pressure drops, more oil joins and the cycle repeats.

If oiler is set up correctly and oiler is controlling level as designed (disregarding malfunction due to vacuum influence already discussed above), then, then the oil level should be below the seal and all that comes out is air/vapor, right? Or maybe I'm missing something…wouldn’t be the first time.


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(2B)+(2B)' ?