front inlet flow and pressure shutdown 7820A/5977B

Hello Everyone,

I am using 7820A GC coupled with 5977B Mass Spec. After use I close the He tank and later on I get 2 messages - 'Front inlet flow shutdown' and 'Front inlet pressure shutdown'. I restarted the software but it fails to load any GC method and the flow shutdown problem also persists even after opening the He gas tank. The GC oven temperature become 25degC. Could you help me with this?


  • The GCMS should have helium flowing through the column the entire time the system is under vacuum so that it is ready to go.  It is not recommended to just turn off the helium and let the system sit with the GCMS pumping. If you turn off the helium tank, eventually there will not be enough pressure/flow to supply the inlet. The GC will start beeping to warn you and then do a shutdown so that nothing is harmed. The MS is still pumping, though, so the column then inlet will be evacuated and it will start sucking air back through the septum purge line which can cause problems with the hot ion source.

    In the 7820 Operating Manual, page 20 says:

    and page 29 says:

    If you think you need to shutdown the entire system, please read this:

    Shutdown Procedures of GC and GCMS Products (

    and this:

  • @paulsalverda

    Thank you so much for your detailed reply. For now, i have turned off both the GC and the MS as I cannot reach the machine at present. Next time, I switch it on, should the sequence of turning the system on be - computer --> carrier gas --> GC --> MS ? Also, do you recommend venting the system as well?

  • Please read the two linked documents as the start up procedure is detailed there, too. 

    The path depends on how long the system will be turned off. If it's only a short time, a few hours, you do things differently than if it will be for a few days or longer.  Agilent ships the MS under vacuum. For longer term shut downs, it's best to maintain vacuum as that helps maintain cleanliness and reduces any possibility of water.  So if it's going to be turned off longer than a few hours it is recommended to pull the column out of the inlet and plug it off by jamming it into the side of a septum. This can be done with the MS set to vent but not opened up so the residual vacuum does the job.  The other way would be to vent, remove the column from the MS, install a blank ferrule and the nut, then pump it down but don't start it up, set it to vent, and shut it down.

    After a system has been shut down it takes at least two to four hours of pumping to be back to some level of functionality.  It takes at least two hours for decent thermal stability inside the vacuum chamber.  It is always best to have a GCMS system pumping, hot, and ready to go if possible. 

    Now if Helium use is the issue then there are other choices.  You could plumb the system with a selection valve to switch to either Nitrogen or Hydrogen and use one of those gases for all the standby time.  There are resources here and on that explain that . Or ask here.

  • Thanks a lot ! Could you share the 2nd link again, it is not opening showing 'page not found'

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