Pneumatic Plumbing for H2 FID on 4-unit Agilent 6/7890 array

[HippyLabRat]

Anyone have any practical suggestions for plumbing FIDs for four chromatographs? How should we feed them all? We have them run in a simple closed-end series and it causes problems when we have 4 FIDs lit at once. I've used the series electrical circuit example to try to explain why it might not be working in the current configuration.

We have a 500mL/min and a 600mL/min generators that both run max pressure of 100psi theoretical. They run in tandem, so running 4 FIDs at 100mL/min (arbitrary number that's way higher than the 40-50 we use in practice) should have way more than enough delivery flow to fuel them all without a problem. Any 3 of the chromatographs run just fine, so its not a system leak.

Help?

[la_donz27]

You running Hydrogen as a carrier too? Cylinders or a generator?

[HippyLabRat]

N2 carrier exclusively

We have a 500mL/min and a 600mL/min generators that both run max pressure of 100psi theoretical. They run in tandem...

[la_donz27]

N2 carrier exclusively

We have a 500mL/min and a 600mL/min generators that both run max pressure of 100psi theoretical. They run in tandem...

Sorry somehow missed that!

What are you measuring as the output directly off the generator? I'm guessing you have a flowmeter inline before the manifold.

Just wondering whether you're really getting the litre per minute theoretical output. If it's not leaking but generating more than you're using, something doesn't add up.

Our generator supplies both hydrogen carrier and dual detector gases for 18 GCs and is plumbed in series with multiple shut-off valves (at each GC station). Simple but it works fine. Only difference between ours and yours sounds like scale and one generator vs two.

Another idea - did you try running two GCs off of one generator, and the other two off the second? See what happens...

[Peter Apps]

What diameter pipes do you run from generators to GCs ?, and what valves, regulators etc do you have on the lines ?

And how do you know the flow / pressure is too low ?

Added: why do you think that there is no leak ? - have you checked with a leak seeker ? or is it just that 3 out of 4 of the GCs run OK ?

Peter

[KM-USA]

I don't understand: each FID should only require like 40 ml/min hydrogen, so not very much.

We use three benchtop hydrogen generators (500 to 850 ml/min capapcity per unit) plumbed together into a single manifold (using some kind of controllers) which supplies hydrogen to about 5 GC systems using FID. One system uses hydrogen also as the carrier gas, which uses more hydrogen when actively in the injection mode when the "gas saver" function hasn't kicked in. And our system develops plenty of hydrogen, and we add water like once a week.

[HippyLabRat]

I take that part about the leak back... (Agilent 7890N) I think that's the problem. It only seems to be a problem once the FID turns on. I can have the hydrogen on, and still no problem. Its literally only an issue after the FID ignites. Faulty fuel metering valve?

[AICMM]

I would not suggest in tandem unless you have the software to do that. Otherwise they will be working against each other. Why not run 2 on one and two on the other until you get stability? Divide and conquer. If half the system is jacked up, while the other half is fine, put one GC on the jacked up side and see if it works fine (again, divide and conquer.) If that works fine, then pull the fine one and install the other one and see if that is fine.

I have a customer running about 8 or 9 GC's on 1 high capacity generator (manifold - serial) without issues so, depending on your generator, it is entirely possible to run this way.

Best regards,

AICMM