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 chamber obviously doesn’t).

Would it be a problem to drill a hole in the vent plug to eliminate this phenomenon? It seems like this would be necessary to ensure that the sightglass provides an accurate indication of bearing level during conditions which create a pressure or vacuum in the trapped air space above the oil in the sightglass.

If not, should we shoot to have the level at the static mark before or after screwing in the fill plug.

Pete

I guess you could call this normal but I don't like it. With as clean as your environment looks you could probably get away with drilling a small vent hole in the fill plug. You might also consider a different plug that has maybe a dessicant filter built into it.

I just ran into a problem with an unvented sight glass last week. It was on a circulator 1500 horse vertical motor. The upper bearing sight glass was gaining oil. We suspected that we had a cooler leak because the level was rising. When we pulled a sample from the drain on the bottom of the glass to check for water the level dropped to way below the recommended running level. Apparently the unvented sight glass was holding an artificial level. I still haven't figured out how the level was rising in the unvented glass. We didn't have any water in the oil so we topped it off and put the machine back in service. With our motor outside in the elements we really can't drill a vent and I haven't found a filtered vent cap that will fit the glass yet.

I think Mike brings up a good point about contamination here. Maybe the way the service fitter is to check this box for a true oil level in the future is to remove the plug and let settle as you previously mentioned. One thinng I will say is I have seen twice now with some sight glasses that they can get stained by the mineral oil and this can be very dangerous. In one plant I was involved with had two boxes with severe bearing deterioration at the input shaft. When the oil was drained to inspect the boxes about 5 litres remained in the box that should of held 20litres. The sight glass still showed plenty of oil remaining. The sight glasses were removed from the box and dip sticks were installed.

Hope this helps.

Hooch

Pete,

I would not suggest drilling a hole--this is an access point for contamination. Also, it can get easily clogged or painted over. There are numerous instances from my nuclear power days where a well-meaning person painted a vent plug, and subsequently bearing damage ensued from having the oil level improperly indicated.

I would suggest taking off the fill plug, and inserting a fitting and a filter-vent. If moisture is a problem in the area, you can consider a dessicated filter-vent as well.

You may be right that the sightglass is not externally vented, but it must at least communicate with the reservoir at the bottom, and with the headspace of the reservoir at the top, in order to properly indicate level.

Suppliers of these filter vents include Hydac and Des-Case

Hope this helps.

Rich Wurzbach
rwurzbach@mrgcorp.com

Maintenance Reliability Group

Dear Pete,

Constant Level Oilers usually have a mechanical plunger that separates the fill cavity from the system when the fill cap is removed (Pat. 1933). By using this type of mechanical separation between fill point and closed loop lubrication, the fluid level remains "constant". Your system may be similar, yet I cannot confirm by the photo. Simply investigate if your fill plug contacts a rod which may be spring loaded. This rod is usually spring loaded to force the fill area closed during "top off". When you replace the cap, the system becomes "live" again and will equalize. If the system requires the additional fluid added during the top off process, the level on the indicator will drop to show actual level during operation.
Otherwise; your system has a pressure equilibrium issue that would not be fixed by venting your cap. Equilibrium issues are solved by running a closed breather tube from the area above the fluid level in the refill portion to the area above the liquid level in the lubricated cavity.
If you present new findings, we may collective solve your issue.

If you have an extra plug try drilling a vent hole in it. See if that works , if it does then you know you have venting problem. You can then try and find a filtered vent to install permanently.

Hi Pete,
We have a couple of these Westinghouse Lifeline motors, but ours have a different style lower bearing sight glass. The sight glass itself is not vented, but we have a seperate fill tube connected to the sight glass that is vented. You can see it here: Westinghouse motor sight glass configuration
My guess is that the plug in your sight glass should have a "T" vent hole drilled in it. All of our sight glasses are either vented or have a tube going back to the reservoir from the top (closed loop venting). If the gauge is not vented, how can it read correctly? Any change in oil level would cause a negative or positive pressure in the sight glass affecting the indicated level. I did a quick look around and could not find a single sight glass on one of our motors or pumps that was not either vented to atmosphere or back into the bearing housing. The attached picture is typical of one that has a vent hole to the atmosphere.

This message has been edited. Last edited by: Ed Hudson,

levelgauge_002.jpg (65 Kb, 14 downloads) Sight Gauge