Cleaning Foreline backstream and servicing diff pump

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Hi all I could use some advice. I've never serviced a diff pump system before.

This is a QC mass spec that I am not directly responsible for. Anyways I came by and it is a real mess. It is a 6890-5973. Anyways the foreline has been backstreaming oil all the way up to the outlet of the diff pump and foreline guage. Can I use MeCl2 to clean the tube and foreline guage?

Finally I noticed the vacuum was lousy. I opened the cover to find almost no diff pump oil. it was almost below the bottom of the window. I vented and took it apart and now that it is unhooked there looks to be a lot of fluid kind of 2 layers. a darker cream at the bottom up to the low mark and a whitish colloidal cream extending above the top of the hot mark. Am I seeing moisture or foreline oil contamination?

Anyways game plan is new foreline pump, rise everything with MeCl2, new Santovac for diff pump and put it back together. Does that sound good?
Sounds like a lot of water got in there, or possibly the backing pump fluid. The Santovac fluid is a glycol. I have cleaned it with MeCl2 before but it doesn't dissolve it that great, so you may want to try Methanol as well. The backing pump fluid will be soluble in MeCl2, but so will the PVC vacuum tubing to some extent. Not sure but you may want to use Hexane on that instead, it should dissolve the pump oil well.

Was the unit just turned off and never vented? Seems like the only way it could have sucked back that much oil from the backing pump.
The past is there to guide us into the future, not to dwell in.
No they have been having trouble with that foreline pump for a while (E2M1.5). It smokes and backstreams oil. There is a valve right below the inlet that is basically a platform on a spring that should prevent fore-line oil from backing into the hose. That is probably the issue but they want to get a whole new pump as long as they fix it.

I usually like cleaning gunk with toluene but because it has a higher boiling point and is a larger molecule I'm worried it will leave background for quite some time. All the materials I've read indicate use MeCl2 for Diff pump service (including the Agilent service manual). I'm just worried about getting it close to the foreline guage.
I forgot about the 5973 having the E2M1.5. I got rid of ours a long time ago and went to the E2M2 plugged directly into a power outlet. Have to turn it off manually but it is so much quieter and cooler, and I had several of them left over from the old 5995s, 5970 and 5971s we had. I have a few that have been in constant operation for over 25 years and never rebuilt. Those little pumps never lasted over 5 years for us.

I'm not sure if the vacuum gauge is a transducer type or filament type. If it doesn't have internal o-rings then it should be ok to clean with MeCL2.

If my E2M2s ever fail I will try to replace them with the pumps that ship with the 7000QQQ, more vacuum oh oh oh :)
The past is there to guide us into the future, not to dwell in.
Can anyone point me to a website or anything that shows how to disassemble and reassemble the diff pump stack or do you think that is unnecessary. Looking down into the pump the top most portion of the stack cone had some black char on it but the fluid visible now is not black. Can I just keep it assembled, pour in some MeCl2 and rinse it a few times and bake it at 60C at the end.
Edwards says the E2M2 is no longer made the next step up from the E2M1.5 is the RV3
The pump on the 7000 is the RV5 which is a little bigger than the E2M2.

From what I remember the diff stack is pretty simple, just pull out the flat spring retainer at the top and I believe there are three pieces that lift out. When I change oil I usually clean these, but it has been a couple years since I even changed the oil in the one we have. Running volatiles on it, I only vent once every 12-18 months when the filaments finally burn out.
The past is there to guide us into the future, not to dwell in.
I hope it is that simple but I keep reading be sure to align the stack correctly and troubleshooting guides saying misaligned stack so it seems like it is quite possible to not align it correctly.
I have not cleaned that pump in a while, but I recall it was much easier than the instructions made it out to be.
MSCHemist wrote:
I hope it is that simple but I keep reading be sure to align the stack correctly and troubleshooting guides saying misaligned stack so it seems like it is quite possible to not align it correctly.


I think the alignment that is necessary is to have the hole or tube that is at the bottom of the stack pointing towards the vacuum exit to the rough pump. Otherwise I think everything is symmetrical and doesn't matter which way they go in.
The past is there to guide us into the future, not to dwell in.
Yea I've found the 5972 manual. If the diff pumps are similar or identical there is simply a S shaped spring rod that holds the stack parts down and the hole in the stack needs to face the diff pump outlet.

Though if Santovac is a glycol why use MeCl2? At least ethylene and propylene glycol are totally insoluble in MeCl2. MeOH is a better bet but MeCl2 has a lower boiling point.
BTW is Santovac 5 sufficient or do you need the horribly expensive Santovac 5P
The bottle I have for the next change on our 5973 is Santovac 5P Ultra. I didn't think it was that expensive over at Scientific Instrument Service, but then it has been several years since we ordered that last bottle.
The past is there to guide us into the future, not to dwell in.
Yes SIS has it listed for $90 for 18.5ml so about $140 a fill
Be sure to warm the bottle in the GC oven before pouring it in, makes it a lot easier. I usually let it sit in there at 50C for a few minutes then just take it out and pour it in.
The past is there to guide us into the future, not to dwell in.
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