Bearing oil sightglass venting question 7

[electricpete]

This is an indoor 4kv vertical motor manufactured by Westinghouse with oil-lubricated upper and lower bearings (picture below)

http://home.houston.rr.com/electricpete/VertMotor1.jpg

The lower bearing housing has a pipe that extends outward to the bottom of a sightglass chamber. The sightglass chamber has a fill plug on top and a drain plug near the bottom (at the same elevation as the pipe to the bearing housing).

The motor is identified with a static fill level.

The sightglass chamber is not vented. After adding oil when we screw the fill plug back in, we have noticed that the indicated oil level decreases, as if the screwing of the plug creates a positive pressure in the sightglass chamber which pushes down on the oil in the sightglass chamber and displaces into the bearing.

Questions:
Would you consider this behavior normal?
Is it safe to assume that the bearing itself breathes to atmosphere (even though the sightglass design obviously doesn’t).
Would it be a problem to drill a hole in the vent plug to eliminate this phenomenon? If not, should we shoot to have the level at the static mark before or after screwing in the fill plug.

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[electricpete]

After motorman's post I took a close look and did see 2 of the other units have vent ports in the plug. Based on discussion with W we will ensure that all have vent ports drilled in the plug.

Now another question - there is another group of motors also Westinghouse Lifeline D verticals slightly smaller (frame 5000 series).

One has high directional vibration up to 0.6 ips at top of the motor which we have attributed to resonance at running speed (confirmed by bump test). The condition has existed for several years (the motor operates only standby/intermittent use). Recently we have seen some oil droplets spread around below the motor (coupling area). We don't see this on any of the other motors. What could be the cause of this?

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[MikeHalloran]

Conjecture:

- Clogged/blocked sightglass vent and clogged/blocked bearing chamber vent.

- Aging/ stiff/ seal lip no longer compensating for normal shaft runout.

- Aging/ worn seal lip no longer maintaining normal contact with shaft.

- Incipient seal failure associated with in-progress bearing failure. Droplets in combination with the vibration are somewhat suggestive of a bearing that's been chewing on its separator for a long time.

I'd tear it down and replace the bearings and seals just for fun.




Mike Halloran
Pembroke Pines, FL, USA

 

[motorman]

The Westinghouse 5000, 5800 and 6800 frame series vertical motors used non-contact, labyrinth shaft seals. So there is no seal lip to wear out and no chamber vent to get clogged.

If you only notice the drips after the machine has just been shut down from a run but not when the machine has been idle then I would concentrate only looking for sources that are above the static oil level. While running, the bearings whip up quite an oil mist in the oil pot [sump]. This then can cause nuisance dripping because the mist will seep around the o-ring where the shaft seal is bolted on or it can and does seep around the bolt heads that hold the seal on. Check the o-ring gasket and make sure that a sealant such as Duxseal has been used under the heads of the seal bolts.

If the drips occur independent of the machine running then concentrate on areas that are below the static oil level. Such as a hole in the rubber hose going to the sight glass; leaking around the fittings. The oil pot [or sump] on those machines are a casting. Hairline cracks could be developing especially where the standpipe is press-fit into the cast oil pot.

A neat way to trace oil leaks is to darken the area as much as practical and look around using a fluorescent trouble light except with a black light tube. The oil path will really show up. Or, if you prefer periodic checks, spray some developer [I think that’s what it is called] like the white colored stuff that is used for dye penetrate testing welds, all around the most likely joints and surfaces. The oil will turn this white into a blood red.

 

[MikeHalloran]

Thanks, motorman, for the education about the seals.

I'm still suspicious of the bearings.



Mike Halloran
Pembroke Pines, FL, USA