Breather for upper-bearing oil bath 2

[electricpete]

We have 4000HP 1200RPM vertical motors with oil bath housing the thrust bearing and upper radial bearing (segmented pad). The oil bath is cooled by cooling coils supplied by plant cooling water system. Oil temperature is around 100F.d (slightly warm to touch on external surface).

There is a breather on top of the oil bath compartment whose apparent purpose is to prevent ingress of dirt. However, a film of oil appears to be coming from the breather and coating the top of the motor and flowing down the sides (sometimes getting into air intake). As a first attempt to solve the problem we put a pipe nipple between motor oil bath and breather which moved the breather up approx 1' above top of the motor (should prevent any oil splashing). This was unsuccessful.

I'm thinking maybe warm oil vapors enter the breather and then condense on the filter as they hit the cooler atmosphere. Does anyone have any thoughts on this? Any suggestions for type of breather that may eliminate the problem?
Thanks

 

[electricpete]

By the way, I forgot to mention that oil bath level is monitored by a sight-glass. We maintain level within vendor's recommended band, which is approx 8" below top of the motor (and 20" below breather).

 

[THooper]

From what I understand about these breathers Pete is they are design to continuously vent excessive pressure or vacuum. They equalize pressure by allowing air to flow into the bearing reservoir and housing through a micron filter which also helps prevent contamination.

Suggestion:

1. Replace filter (maybe dirty or plug)

2. Verify oil level, It seems a little high to me.
If possible, remove top cap, oil bath at stand
still or rest should come to the center of the
bearing.

Also most site glass levels are at the center
level of the glass at stand still or rest.

Kind regards,
motorhead

 

[motorman]

The breather is there to equalize the pressure between the air space on top of the oil level and the ventilating air that is moving past the shaft seal inside the motor. On most vertical motor designs this size that I have seen, all the ventilating air enters the motor at the top area of the frame, just under the upper bearing housing. The rapidly moving air inside the motor causes negative pressure at the top of the stand pipe and will suck (perhaps a better word would be push because the pressure above the oil level is higher than atmospheric) oil over the standpipe and into the motor... This condition can be worsen if the gap between the rotating thrust runner and the stationary standpipe causes a pumping action.

But what is causing the seepage from the breather ? I have seen this as the result of the oil foaming up into the breather (and even over the standpipe then into the motor). The foaming being because of contaminates in the oil. Do you see any foam in the sight glass when the motor as been operating for a while? Is this a new occurrence?