GC 7890B Leakage with graphite O-Ring (5180-4173)

Hello everyone,

As I want to run a higher S/SL injector temperature on my Agilent 7890B GC (approx. 320-360°C), I wanted to replace the previous Viton O-rings with the Graphite O-rings. Unfortunately, I can't get them to seal using the normal installation method.
In fact, the injector is so leaky that it can't even reach 10 psi inlet pressure. If I change back to the Viton O-rings, the S/SL injector is perfectly tight again.

Any tips/experience on this?

Many thanks in advance.

  • Maybe you used too much pressure to try to seal the injector. Graphite deforms easily and even breaks and you'll have a leak. Also check the metal surfaces touching the O-ring if there is debris from something or a scratch. And ...

    5180-4173 (splitless liner) has an ID of 6.52 mm
    5180-4168 (split liner) has an ID of 6.35 mm

    Maybe O-ring and liner are not compatible.



  • Norbert, thank you for your answer.

    I am very sure that it is not due to too much pressure. As the graphite O-ring still looks good afterwards and there are no deformations or cracks. I also only screwed it on very lightly on the 2nd attempt and then observed the inllet pressure and only then tightened it again and checked the inlet pressure further.

    The metal surfaces also look good and there is no damage to be found.

    Liner: Single Taper Splitless Inlet Liner, 4.0 mm x 6.5 x 78.5 (Restek 22406)
    O-Ring: Inlet liner O-ring, graphite, for splitless liner, 9.63 mm od, 6.52 mm id seals (Agilent 5180-4173)

    Should therefore also be compatible with each other.

  • All seems to fit, then it will be difficult to give advise from a distance. Maybe some of my instrument colleagues can give you some input

  • The graphite must deform to seal. It can only deform one time as there is no spring-back.  Install it with the inlet cold and the inlet pressure set to zero psi. I like to put the liner in, then place the seal around it using a gloved hand, then tighten the liner retainer weldment once.  Set the inlet pressure to 5psi, then heat the inlet to maybe 150°C and let it get stable and only then turn up the pressure. The expansion of the inlet weldment and llner retainer weldment will essentially tighten up the seal the tiniest amount.  Once the inlet is up to full temperature it must stay at that temperature until it is necessary to do inlet maintenance. Once the inlet has been cooled down again, that graphite seal may not work again and may even lose pressure as it is being cooled off.

    And also try an Agilent splitless liner. I would hope that Restek liners have tight o.d. tolerance specifications but I know that Agilent ones do.

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