5975 MSD shutting down unexpectedly

Following 1.5 years of shutdown and then a lab move, our 5975 is maintaining vacuum with the ion gauge reading 6e-6 torr. The GC will maintain either 1 bar or 30 mbar of He flowing at 10-200 ml/min, the conditions don't matter. With the instrument in standby (MS off) and seemingly at random, the MSD vents and cools down, but the GC still maintains its pressure and flow conditions.  The m/z ratios for 28, 32, and 18 relative to 69 are 8%, 1.4%, and 0.4%, and 28/69 increases when the MS is on because of contamination of the source housing (visually observable), however the venting issue happens with the MS off. There is no clear indication of an air leak.  What else might cause the MSD to vent besides air? Might this be a failing electrical component.

  • What is the column volumetric flow - like 1.2 ml/min ?    Does this system have a turbomolecular or a diffusion high vacuum pump?    After it sat for 1.5 years plus the move - was the rough pump oil (and diffusion pump fluid if it's a diffusion pump system)  changed before starting it up again?

    Turbo pumps don't like to sit without running once in a while, like very few to six months, max. If it's a turbo system and this is happening...well, I would suggest restarting it some number of time and see if just running it helps.  It's doubtful, but maybe possible.   Also - if it's a turbo pump, which one?  The older ones cannot be replaced any more as the upgrade power supply required for the new style turbo pump is no longer available.

  • We typically keep the column flow at 1 ml/min. It has a turbo pump that is 10 years old. I’ll have to check on which one but I know it is a Pfieffer. 

    thank you for your input. I’ll let in run and see what happens. Maybe it’s time for a rebuild of the. turbo

  • Shutting down intermittently is one symptom of an old turbo.  They're spinning 60,000 rpm or so and typically work great or don't work at all.  It is incredibly weird, like never seen one, to have one spinning slower than 100% except for a huge leak.  The other symptom is one that is running fine, system shutdown for maintenance, and then it will not spin up again.

    Let us know what happens.

  • I have seen cases where the rough pump shuts down because it's working too hard, which will cause the MSD to shut down also.  Typically the MSD will have an error message of "Vac Sys Fail" or something similar.

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