How do I safely shut down gas flow to one uECD detector?

I am currently running two 8890 GC systems with dual inlets, dual columns, and dual uECD detectors. Due to reasons I don't want to get into here, there are currently no columns installed and the detector inlets have blanks installed on both systems. The oven and detectors are currently set to initial checkout conditions. I've been seeing this odd 24 hour cycle in the detector signal (similar movement over multiple days so it's definitely a pattern). The Agilent technician has suggested shutting off the flow to one of the detectors to see if it can be narrowed down to what the source of the issue might be. What is the safest way to shut down the flow to one of the detectors on each GC without risking damage to the detector?


In case you're curious, below I have the signal trends for all 4 detectors. The top pair has been sitting at a much lower baseline overall and is seeing much less movement, but still displaying the same pattern of movement. The bottom pair has been at a higher baseline overall and has been seeing a much larger range of movement over the same time frame. The acquisition times don't match but I've lined up the graphs so they match based on actual time.

I have been away from the GCs for several days and they stopped recording signal while I was gone so I don't have current trends, but the bottom GC with the higher signals has settled down a lot in my absence and now has a lower overall baseline than the top one.


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