Leak inside of Foreline Pump

[MSCHemist]

For those who have been following my Foreline pump nightmare I have a new issue.

The new E2M1.5 runs beautifully, achieves a good vacuum pressure but has a leak somewhere in the system. In profile mode I am at 200,000 counts N2 and 50000 O2. I've tried 3 different O rings on the centering seal between the foreline hose adaptor and Pump inlet KF16 flange. I clamped down on the hose clamp attaching the hose to the adapter and tried 2 different clamps. I also plugged the column to ensure it is coming from the MSD.

Where can the foreline pump be leaking? I know the inlet KF16 flange screws onto another o ring inside the pump. I am not to familiar with what the insides look like.

The counts seem pretty high but the ultimate vacuum was good. When I plugged the GC it went into the E-6 torr range but still had 200k N2

[MSCHemist]

It has subsided to ~50k counts running overnight that puts it at 6% N2. Still definately a leak. I sprayed duster at the KF flanges and the inlet flange and the ballast knob and didn't see anything on manual tune.
Is it possible it need a break in period or something?

[cleh]

You won't see the dust off or argon at those connections because it's below the analyzer. Try using a syringe and spraying the connections with methanol or isopropanol while watching your vacuum readout for fluctuations. Know this probably isn't the problem, but make sure the ballast is closed. If that all checks out, you said you plugged the column. If you mean you plugged the front of the column, try removing the column from the transfer line and plugging the transfer line with a nut and no-hole ferrule. You can then spray the dust off on the analyzer door, transfer line nut, vent nut, and cal gas assembly. If this all checks out and you have a diffusion pump, the oil may be cracked and need to be changed.

[MSCHemist]

The company I bought the pump had me do a simple test on the pump. plug it into the wall take off the foreline hose/adapter and centering seal and plug the inlet with a rubber stopper. Let it run for a little bit. Then stick a piece of tape over the exhaust port (you need to remove the oil mist filter as well). There should be no flow after the initial evacuation of air from the pump. It should also hold the seal on the inlet after you turn it off. Mine did indicating the inlet side and ballast aren't leaking.

The first one I recieved was blowing at ~20-40ml/min sealed off so It had a bad valve or something.

The weird thing is it was giving me a pretty good vacuum but the N2 was 20% which fell to 7 the next morning. They are sending another pump.

Just a run of bad luck I suppose or My instrument is having a mid life crisis.

[KM-USA]

I'm still not sure why a possible leak in a foreline pump which pulls good vacuum could result in high nitrogen level. Any such leak would be "after" the MSD chamber, so any air sucked in would get out the foreline pump exhaust and not back into the MSD chamber, correct?

Or do I have this wrong?

[MSCHemist]

My guess is the ventuuri effect. It's the same reason why air enters a connection during a leak even though pressure the line is at higher pressure and stuff is leaking out.

My Agilent manual says any of the connections in the vacuum system can cause a leak.

[Yama001]

Plugging the column with a septum does not seem to work all the time. If I plug the column with a septum and do not see a leak, I believe it. If I still see a leak, I would not assume the septum plug has prevented air from getting in to the column.

[MSCHemist]

Still at 6% N2. It must be the pump/hose/adapter connection. Are those KF flange connections typically delicate. The hose clamp bit into the foreline hose a fair bit and the flange/hose adapter is a bit scratched. I've already tried multiple o rings on the center seal and 2 clamps.

Can you cut the foreline hose a bit?

I've very sure my system isn't leaking. I went over all the gas lines, seals, connections with IPA/water and duster spray. Also they were fine before the foreline pump died.

[MSCHemist]

The more I think about it the more I am convinced it is coming from the joint where the end of the foreline hose is on the hose adapter. It seems like a real poorly designed connection. You have a big thick hose and a hose clamp that probably isn't able to put a lot of compression on where the hose and adator are touching due to how thick the hose is. Is there a good way to confirm and if so is there anything I can do other than replace the entire foreline hose?

I was reading some articles. One says spray acetone or MeOH on it and watch for vacuum changes (the total system vacuum?). Another says use SF6 and watch the MSD for a 127 ion. I don't have any is there a way I can obtain a small amount?

Is it possible to cut say 4" off of the foreline hose say using a strong diagnal cutter?

[MSCHemist]

I came in this morning and did the air and water check. I am running 3.65% N2 and 1.84 O2. I also sprayed MeOH at all the juntions and o-ring arround the MSD and saw no deflection on the HiVac.

What can cause higher than normal N2 and O2 but not at air ratios as my O2 is over 50% of my N2.

[Yama001]

I had a 5972 that ran that way for a year or two. We eventually just stopped looking at the air and water check. It stopped doing that at some point, because it looks fine now and no one else has touched it.

PS - I assume when you do the air and water check you allow it to 'adjust to standard settings' or have a fresh autotune (not BFB, DFTPP, Target, etc). 'Detuning' to meet method specific tuning criteria can occasionally result in conditions that amplify the gas' response.

[MSCHemist]

The values keep dropping each day so I probably had a stubborn pool of air somewhere in the system. Is that what everyone calls a "virtual leak"

[mckrause]

It's quite possibly the hose. I've had to replace several - almost always seems to be the connection at the high vac end. Comes and goes, then comes back. I get the same thing you're seeing - stubborn N2 and O2, with occasionally weird ratios. Change out the hose and Wham-O! You're back in business.