Chromatography Forum

I have an issue with the rough pump oil backing up above the mist filter in my Edwards rough pump. See pictures below. I tried opening the ballast, but this did not solve the problem. Any idea what caused this and how to fix the problem (preferably, without venting the instrument)?

Thanks,
-Ryan

does your pump actually have a two-stage ballast valve with oil-return system, or is it just a normal ballast valve and a mist filter that needs emptying manually?

The mist filter automatically empties when the ballast is open. It's only a problem for this oil trapped in the vent line above it.

We had a similar problem as a 'one time only' kind of thing. I don't know how frequently or how severely this is affecting you, but I figured I'd throw in my two cents of what happened here.

Ours is a single quad Agilent 1946 MSD with a similar-looking rough pump as the one pictured. One night, the air supply to the nitrogen generator died, and with no nitrogen flowing into the source chamber, it basically started a chain reaction of vacuum which ultimately lead to pump oil being sucked up (via the same tube pictured) all the way into the spray chamber. The MSD didn't work, even after the nitrogen supply was reestablished. We wound up having to have someone in to completely disassemble, wash, and reassemble everything in the MS as there was trace evidence of oil all the way through the quad.

Moral of the story: Even your issue didn't come on this immediately, I would probably still recommend checking out the interior of the MS. Good luck!

How you got oil up there I don't know, but disconnecting the tube and cleaning it will not harm your MS (just don't do this when you are running any solvents).

As noted by lhm, you should have a small black tube from the mist filter that goes back to the pump.

We had the same problem some weeks ago. I cannot give you many details about its cause ( I'm no engineer) but I believe it's due to a leak of the oil indide the pump, probably through a faulty seal.
It should not be dangerous to your MS but be aware that you are expelling oil mist through that tube and there is the risk of running out of oil in the pump, which would cause a major damage.

The way in which you get oil into your MS is this.
There are two exhaust tubes in a typical Agilent 1946 installation. One is the exhaust from the "out" side of the rough pump. It should go off into a tube to a fume extraction system. The other is the exhaust from the spray chamber, taking away "used" drying gas and solvent. It should also go into a fume extraction system. If, as is commonly the case, the two fume extraction systems eventually join together, if you pump enough oil up the rough pump side of things, it will come back down the spray chamber side of things, and you can start looking for the budget to buy a new instrument.

If you pump enough oil into a mist filter that it overfills and starts to bubble up into the tube, it's not necessarily fatal. Clean out the tube and empty the mist filter, and remember to open the 2-stage ballast valve a little earlier next time! I've done it (once!), and our MSD survived.