Milky foam in rough pump oil.

[bcd_GCLCMSMS]

We have an LC-MS/MS with 2 rough pumps ganged together with a vacuum 'T'.
One of the pumps has a layer of milky/foam visible in the level checking sight window. The other pump is normal.

We have ballasted the pump, changed the oil, and changed the exhaust filter. After running the MS in standby with fresh oil, the problem has recurred the next day.

Any ideas what the problem may be?

[70 eV]

Could be the pump seals going bad. Is it getting foamy idling or after you smash some hot trash though it?

[bcd_GCLCMSMS]

Could be the pump seals going bad. Is it getting foamy idling or after you smash some hot trash though it?

Thanks! This LC-MS/MS has been powered on, but in standby (no solvent flow) since the oil was changed and the oil is still developing the milky appearance.

I was guessing bad seals or a bad ballast valve that isn't really shut (and constantly pulling in air), even though it appears to be.

The other pump off of the same "T" isn't like that, so I doubt it is contamination.

[Multidimensional]

Foaming or brown milky color is an indicator of system contamination, usually water or other solvents, directly into the vacuum pump. Seals would be the first thing to inspect and change.

[James_Ball]

Is the oil milky or have a layer when it is drained?

Contamination would be evident in the drained oil, while a simple foam of bubbles while running would indicate a lot of air flow through the pump which could be bad seals.

If it became badly contaminated with water then it could leave some in the new oil after the oil change, if so a second change could help to flush it out.

[bcd_GCLCMSMS]

Is the oil milky or have a layer when it is drained?

Contamination would be evident in the drained oil, while a simple foam of bubbles while running would indicate a lot of air flow through the pump which could be bad seals.

If it became badly contaminated with water then it could leave some in the new oil after the oil change, if so a second change could help to flush it out.

It is only foamy when running - I also suspect an air leak within the pump, even though the vacuum is within specification. We are planning to swap it out and have it rebuilt.