MSD pumpdown problem

"We have a 5973 Network Mass Selective Detector.  Recently, the pressure in the mass spectrometer rose to 4x 10-4 Torr and the gas chromatograph’s inlet pressure automatically shut down. Most of the pump oil in the fore pump had drained into the pan. The drain plug was in place and closed - the oil appeared to have leaked out of a flanged fitting on the pump (maybe a leaking seal?).  We vented the MSD, refilled the pump oil, and restarted.  We were unable to reach a vacuum below 10-4 Torr.

When we came back later, some oil had again leaked out of the fore pump, but there was sufficient oil in the pump to run it.  As recommended in the manual, we installed a solid ferrule (one without a hole) into the gas chromatograph interface (transfer) line (shutting off all gas chromatograph carrier gas flow into the mass spectrometer).  When we restarted the mass spectrometer’s pumping system it was able to reach a pressure of 10-5

Torr - suggesting that the vacuum problem was being caused by the GC.   We checked all of the gas chromatographic fittings, and re-attached the gc column to the mass spectrometer transfer line. We restarted the gc ms and it initially pumped down to 10-5

Torr and appeared ready to run, but then, after ~10 minutes, the vacuum again fell to 10-4

Torr and the gc inlet shut down. We rechecked all the GC fittings and everything appears okay.  Could the fore pump be the only source of the problem - the ability of the system to reach operating pressure with the solid ferrule in place has us worried other factors are causing our problem.  We’re hoping for some suggesting that will help us understand why the system reached and maintained operating pressure with the solid ferrule in place.  Could the leaking fore pump be the only source of our problems - i.e., it has the ability to pump down with the solid ferrule in place, but can no longer handle the gas flow coming from the gc?

Parents Reply Children
  • Hi Jeremy,


    It seems like you have a couple of things going on here. I agree with that replacing the rough pump would be a good start but this does not explain the inlet shut down, therefore I think there could be more then one problem here.


    A broken column (or cracked column) could be the cause both issues. This happens when the column is over heated (especially without flow). Try using another (newer or new) column.


    Just a few more things to thing about:

    What was the last thing you did on the system before the problem started?

    What are your column dimensions?

    Is the system a turbo pump or a diffusion pump system?

    Do you have a helium leak detector (assuming you are using helium carrier gas)?

    What is your supply gas pressure?

    Is the gas type configured correctly?

    Is the column length and ID etc configured correctly?

    Do you have gas flow from the end of the column when just plumbed to the inlet (and MS vented or blanked of course)?


    Best regards,



  • Thanks so much Nick,


    I will try a new column and go through all the questions you mentioned.


    Thanks again,


Was this helpful?