Do Foreline Pumps have to be vented??

[akthmps]

We are operating an Agilent 6890 with 5973 MSD. We have an Edwards foreline pump attached (model number G1099-80023). How necessary is it for the pump to be vented into a hood? Can I simply cap it off? I was wondering what the potential drawback of simply capping the pump off is.

We also have a Varian 3800 GC - Saturn 2000 mass spectrometer system with Leroy Somer Ulvac foreline pump (model number GLD-040) that is capped off and not vented at all. Upon installation, the GenTech technician said it was not necessary to vent this pump into a hood. Any thoughts?

Thanks for the feedback, particularly on the Edwards foreline pump attached to the Agilent system.

-Aaron

[EnvironLab]

How would you be able to maintain any vacuum if you're sending carrier gas and sample through your system and the forepump exit port is capped? Maybe I misunderstood what was said.

[akthmps]

What I am referring to is the "vent" exit, to remove any of the headspace vapors that presumably collect over the pump oil. I believe many labs run a tube from the top of the foreline pump to a fume hood, to get rid of any toxic vapors that may accumulate over the oil. My question is, how many of you out there who have GC-MS systems actually have your roughing/foreline pumps venting out to a fume hood? One of the chemists in my company says you MUST do this, whereas some other chemists I've worked with say that maybe once a month they simply open the vent valve on the pump and allow the vapors to go into the ambient air for perhaps 5 minutes. Any thoughts?

[Peter Apps]

You are confusing two different things.

While the instrument is running the carrier gas and sample vapours pass into the vacuum pump (that is how it makes a vacuum) and the carrier gas plus most of the the more volatile part of the sample pass out of the pump. The heavier, less volatile sample components and some of the sample solvent tend to stay behind in the pump oil.

There has to be a flow THROUGH the pump for it to pull a vacuum, this implies a free flow of gas downstream of the pump, which means that you cannot cap off the pump outlet. You can put an oil mist filter on it, which will catch liquid droplets, and a charcoal trap that will catch any organic vapours.

The rationale behind venting the pump into a fume hood is that if toxic samples (e.g. pesticides) are going into the GC-MS they must be coming out of the pump, which is reasonably logical.

The process you refer to of opening the "vent valve" on the pump once a month is usually referred to as "ballasting" and it is used to increase the flow through the pump to vapourise any volatile contaminants out of the oil and flush them to atmosphere. In GC-MS these contaminants are usually sample solvent.

The ballast valve is not where the pump discharges what flows through it while it is pulling a vacuum. I suspect that on the Saturn it is the ballast that is "capped off" (they all have caps on them, to open you unscrew slightly) and that the technician was (I believe mistakenly) recommending that you do not need to flush the volatiles out of the oil by ballasting the pump once a month.

To answer your original question, the potential drawback of simply capping off the pump is that you will not get any vacuum and you will blow the seals in the pump. Before you do serious damage to your intruments you need to chack though the pump operators handbooks !

As an aside, if you are running toxic samples the pump oil should be disposed of as toxic waste.

Peter

[MIB_EO]

Essentially it depends on the load. Backing rotary oil based pumps assist the turbomolecular pumps in obtaining high vaccums necessary for the safe operation of the high voltages in MS.

In an ESI system the pumps are continually "fighting" against the ingress of air through the cone. This means the rotary pumps are working hard and oil mist vapour is accumulating. This should always be vented to a fume hood and in a seperate line than your MS exhaust (otherwise in rare vacuum fault conditons oil vapour coudl be sucked back inside your MS which is not good for it). Gas Ballasting as described by Peter empties the Oil mist filter if fitted and may not be be necessary if there is no filter.

in a MALDI system which is normally closed there is not the continually ingress of air and the pumps don't work so hard. Oil mist filters on these systems are usually sufficient to trap any vapours and you may manage without a vent to a hood.

All used Oil should be treated with caution and disposed of according to local regulations.

[ods-at-pacific]

The exhaust of the mechanical pump associated with any mass spectrometer is hazardous and MUST be vented to a fume hood or filleted. Scientific Instrument Services (http://www.sisweb.com) has a nice kit that includes a mist eliminator and a carbon filter for vacuum pumps see it on their Home Page). Even if the pump has an exhaust line that runs into a fume hood, it should also have a mist eliminator on it.

You must remember to change the carbon filter EVERY 30 DAYS. The paper filter in the mist eliminator should changed every time you change the pump oil. Check the pump oil often to see if it needs to be changed. If the instrument is in continuos use, you should change the pump oil on a minimum every 60 days.

If you are doing slit injections on a GC-MS, the split vent should exhaust to a fume hood or have a carbon filter. The gases coming out of the mechanical pump and the split vent are toxic and should not be breathed under any circumstances.

The pump oil is a hazardous waste and should be properly disposed of.