Chromatography Forum

in an Agilent 6890N, and I can't find a leak anywhere. Whatever I set the pressure to, the instrument will hit about 90% of the setting, start beeping, and shut down. I have checked all of the obvious leak points, and some not so obvious, and I am now looking at the Electronic Pressure Control module...has anybody had one of those exhibit similar faults?

thanks

Most of the time when I'm convinced I don't have a leak, I still do!

If you genuinely don't have a leak in your GC, there are a couple of ways you can still not get pressure (I'm sure there are others too, these are just the ones that I've had)

- You can actually setup an inlet so that the total flow is insufficient to pressurize the inlet before it shuts down.
- You can be losing enough gas out of the other inlet (in a dual inlet system) to not be pressurising the one you're trying to use.
- You could have a blockage, leak, or incorrect supply pressure in your gas system so that you don't have enough gas to supply your needs.

Check to make sure that you're not sending gas to the wrong inlet (as well as the right one). Try to pressurise the inlet with a moderate pressure and a 10:1 split and see how it goes. Note how fast the pressure actually rises from whenn you turn the pressure on.


I have a dual inlet 6890 system. I use the back inlet now, but 4-5 years ago was using the front. If I load an old method (usually by accident) even if I turn the gas flows to the front off, and to the back on, I still cant pressurise the back inlet. It strikes me as some kind of bug, but it's jsut as likely to be something I'm not understanding....

I seem to bring this up all of the time, but I've been burned by this so many times. Make sure your gas cylinder is completley open. If it is only partially open, the diaphram can shut down and come back on intermittantly. I actually had one customer who thought someone was messing with his carrier during the night.

What are the dimensions of the column you have installed in the front inlet?
What flow rate/pressure setting do you have set?
What is the pressure at the regulator at the bottle to the back of the instrument and do you have other devices sharing the gas line?
Is gass saver on or off? and if on, to what flow?
If off, are you running split or splitless, and if split what split ratio?

And are the column dimensions entered correctly into the instrument for the proper inlet and the settings for the other column are not shown as connected to that inlet?