Hello Greg,

Another trick I have used is to use two washers at the top fitting instead of one.  If the angle of the top fitting is off, it might not seal well.  But, if you increase the effective level of the viton o-ring (angled o-ring), pushing it further up, it will deform better in the top fitting of your auto-sampler.  Just use an extra washer from another EA. So two large washers, then the viton o-ring on your ceramic reaction tube, then attach your auto-sampler. This approach worked for me.

All the best,
Bill Anderson
Earth Sci/SERC
FIU



> 
> From: Greg Cane <[log in to unmask]>
> Date: 2005/08/30 Tue PM 06:35:11 EDT
> To: [log in to unmask]
> Subject: TC/EA leaks
> 
> Dear TC/EAers,
> 
> At the risk of sounding frustrated, which I am, here's a simple 
> question for those screwing the fittings at the top and bottom of a 
> TC/EA column. I am having leak issues at the top fitting of our 
> column. This is a relatively new instrument purchased through 
> Finnigan along with a Delta Plus MS. I am monitoring mass 40 while 
> purging argon around the fitting and despite my triple checking the 
> order in which the metal washer and viton O-ring are placed (based on 
> Thermo's manual) and screwing the fitting as tight as I can get, I am 
> still having leak issues. I have performed leak checks both while the 
> column is at room temp. as suggested in the manual and at sample 
> operating temperatures. Despite having leaks at BOTH bottom and top 
> fittings at room temp., I figured the viton O-rings would be happier 
> making a seal with an increase in temperature. So, I've checked for 
> leaks again, at T=1350 C (for liquids) and sure enough, the leak at 
> the bottom fitting is no longer. However, the top is still giving me 
> problems as M40 rises steadily while applying argon. How tight is the 
> top fitting supposed to be? I can't get it any tighter by hand, and 
> I'm assuming this is not normal to be tightening it so much. My 
> background on M40 has been as low as 18mV (on previous column 
> installations), which I still find high. And I'm still not happy with 
> backgrounds on M30, which are around 200 mV. Thermo recommends limits 
> of less than 10mV on M40 (which is what I'm used to seeing with 
> IRMS), and less than 100 mV on M28, 29, and 30. My water signal is 
> fine. I was using viton O-rings from Thermo a couple of weeks ago 
> with much better M40 stability, yet still a very very slight 
> increase. I had to change the column this week, and I'm using O-rings 
> from Costech (part no. 061106). Any difference between the two?!? 
> Does it take a while for these O-rings to create a seal at high 
> temperature? Another question: At its tightest, the top fitting still 
> displays its threads and I'm wondering if this is normal? Other 
> potentially noteworthy info. I'm using a brand new glassy carbon tube 
> and alumina tube. The helium carrier is with the new setup of bottom 
> fed supply. I have also been able to tighten the fittings somewhat 
> with the oven at temperature, yet still a leak at the top persists. I 
> also have fans blowing on both the bottom and top fittings. 
> Unfortunately, I do not have an extensive amount of experience TC/EA 
> but this does not seem like rocket science at the same time. I know 
> where the leak is after all. Any recommendations will be extensively 
> appreciated.
> 
> Greg
> P.S. Mike, thanks for all your help so far, but I had to throw this 
> one out to a wider audience. Frustration is getting the better of me 
> right now.
> 
> 
> -- 
> Greg Cane
> Associate Specialist
> Department of Earth System Science
> University of California, Irvine
> 2224 Croul Hall
> Irvine, CA 92697-3100
> phone: (949) 824-6446
> fax: (949) 824-3874
> e-mail:[log in to unmask]
> ****************
>