PTV on 7890 GC-ECD giving low response and not maintaining pressure ramp with set point

The PTV on my 7890 GC-ECD is giving me low response and will not maintain pressure ramp with the setpoint when I do a run. I have tired changing the syringe liner, ferrule, and glass wool. I also clipped the column at the inlet and the detector. Can someone please help?

  • Hello  , thank you for your message.

    Do you still need assistance with this? If you do, please take into consideration the notes below. However, if the issue was resolved, could you please share what the resolution was?

    For the PTV portion, is the starting pressure maintained, and as the ramp progresses you are getting pressure shutdowns? This could be caused by insufficient gas supply pressure. At any point during a run the pressure coming from the gas supply needs to be 15-20 psi higher than the maximum pressure the PTV needs during a run. However, the gas supply pressure cannot be higher than the highest rated pressure of the PTV EPC.

    Just using fictitious numbers, if the gas supply is at 30 psi, and the starting pressure of the PTV is at 3 psi, the pressure will be maintained no issue. If the ramp starts and eventually the inlet pressure requires 35 psi, your gas supply is nowhere close to being able to provide that pressure. In this case, the minimum gas supply pressure would need to be 50-55 psi minimum.

    In terms of the ECD, is this an established method that worked in the past, was giving a certain response and now the response is lower? If so, have you changed anything prior to this happening (gas tanks, inlet consumables, columns, or anything at all that might coincide to when the issues started)?

    Are either the GC or the Software giving you any errors at all?

  • Good morning CM,
    In answer to your questions, the supply pressure for the carrier gas(helium) coming in is ~55-60 psi.
    The PTV inlet pressure holds at 6 psi prior to the start of a run, but as soon as the temperature starts ramping, the pressure drops to about 5.1 psi and at that point will no longer maintain the pressure with the ramp. Is it possible that there could be a leak in the inlet?(I will check for a leak this morning and let you know.
    As for the low response from the ECD, I made the following changes, however none of these changes seemed to resolve the issue:

    <![if !supportLists]>-          <![endif]>Changed inlet liner and glass wool

    <![if !supportLists]>-          <![endif]>Changed inlet ferrule

    <![if !supportLists]>-          <![endif]>Clipped column at inlet and detector

    The idle output signal from the ECD is ~100, indicating that the ECD is “healthy”.
    I have not tried baking out the ECD and I am planning on trying that today.
    I will let you know how everything goes.
    Brian B. Barnes, Ph.D.
  • Good morning  

    Thank you for the details.

    You can definitely do a leak check, I will leave below a link that describes the procedure. Is your method split or splitless?

    Using the 7890 Service Mode Leak Check (

    Let me know what your findings are.

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