6890 FID erratic makeup gas flow

One of our 6890 GC's shows a continually varying (in one minute the reading can vary up or down 20 ml/min) flow for the makeup gas. I shut down all the heated zones and turned the nitrogen flow off at the cylinder and the display on the GC still showed a flow present which of course was drifting up and down.  All the other gas flows look normal. Any ideas on what could be wrong.

  • This could be an EPC problem. As long as the gas supply is adequate with proper pressure, there is not much more to the makeup gas flow.



  • Thanks, James. I was worried it might be the EPC.  I replaced the EPC in October 2019 and that fixed a problem with hydrogen flow. Ran great until a couple weeks ago.  I will make sure all the electrical connections to it are secure before ordering another.

  • Hi,

    You can do one thing before replacing EPC.Remove Air, Hydrogen and Makeup lines from the back of GC and then see that flow is zeroing or not, in GC display.

    If flow is zeroing in GC display then after you can connect all lines to EPC again and use it.

    Second thing if flow is not zeroing then remove EPC from system and install back again.

    If still problem persist then you have to replace EPC. 

  • Thanks Ishtiyag, the problem was with the EPC.  I could not get the one that was in the instrument to work but I still had an old defective EPC that was pulled out of the GC a couple years ago.  I took it apart and replaced all the o-rings to the valves and sensors - which I do not recommend to anyone who is not very patient. Eventually I was able to get it reassembled and installed it on the system.  All the flows are normal and the chromatograms all look good!

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