Help w/ Sigma 300 (again)

Chromatography Forum: GC Archives: Help w/ Sigma 300 (again)
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Russell R on Thursday, January 6, 2000 - 01:20 pm:

Problem: Can't get the ECD makeup flow over 30 mL/min; it's supposed to be 40. The last time I made a run, it was fine. I have ck'd all the fittings from the carrier inlet tee, to the regulator and thru the panel, up to the detector. I can't ck the actual connection to the detector w/out removing the detector and I do not have a leak detector. But I did remove the makeup line that goes from the makeup regulator to the pass thru panel and connected that to my pressure guage via the flow dial. The carrier gas outlet at the panel was capped off and I observed the same pressure as set on the tank regulator. I shutoff the gas at the regulator and lost approx 10# of pressure in 15 min. Good/bad?

Pressure regulator for makeup is set at max. Any body have any experience w/ this veteran GC? I'm sort of at wit's end. Thanks in advance.

Russell Rondeau

Top of pagePrevious messageNext messageBottom of pageLink to this message  By Bill Jenko on Thursday, January 6, 2000 - 09:42 pm:

Do I understand you correctly? You pressure leak checked your make-up line, and lost 10 psig in 15 minutes! Not good.

When we pressure leak check a system of tubing, we pressure it up with 80-100 psig of Helium and like to see no more than 1 psig change per hour when left overnight. Ideally, you want to see no change at all, assuming the temperature of the system stays constant.

Back in the days when Freon came in spray cans (I think I just dated myself) we used to spray a bit of Freon at each connection in the plumbing. If there was a leak, the ECD would go off-scale. You might try that same trick with any other halocarbon (a drop of Methylene Chloride or a small blast of Methyl Chloride) at the point of a suspected leak.

Top of pagePrevious messageNext messageBottom of pageLink to this message  By Scott Fredrickson on Tuesday, January 11, 2000 - 02:35 pm:

We scrapped our Sigma II PE's years ago, but they had some very good ideas, particularly the flow systems. We loved their NPD.

Even with the flow at 30 instead of 40, it would probably still work. If it doesn't, that fact also points to a major leak.

I would disconnect the fitting closest to the detector that I could get to, cap it, pressurize it, and use Snoop to check all the other connections. When the system is tight, it should come close to the above-mentioned criteria.

To leak check, cap the line, turn the gas back on, and then turn the regulator off, not the tank. As Mr. Jenko says, the regulator pressure should stay put. Check each remade fitting with soap soln.

Because the detector vents at atmospheric pressure, it's unlikely that a 'leak' at the detector connection would matter, unless it is a nut that was never tight, a broken weld due to flexing, or??

Maybe you have a broken regulator, leaking through the diaphragm. Those can be difficult to isolate because they are unusual, but I've seen a few.

Some detectors can also be sealed at the outlet, allowing the entire system to be checked if the column inlet is capped.

Sounds like a leak, but if the flow is restrictor controlled, could it be plugged?

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