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

Question

Hello everyone, 
 As I want to run a higher S/SL injector temperature on my Agilent 7890B GC (approx. 320-360&deg;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.

paulsalverda · Accepted Answer

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&deg;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.

Dr. Know · Answer

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. 
 Regards, 
 Norbert

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

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