column flow problem

[cmoral]

Hi all,

I am finding that I can't get any flow into the column through the injector. The GC is a 5890 Series II with two split/splitless injectors.

The second injector works fine. I can measure the total flow from the split/splitless injector port and can also measure the flow for the septum purge and the column head pressure gives me a reading that is adjustable, no problem.

But I am having problems with the second injector. I can't get any flow reading from the two ports mentioned above and no column head pressure no matter how much I open the valves. Can anybody give me some advice as to how I should go about actually checking where the problem might be? I am pretty handy with these type of GCs and not afraid to take anything apart...but not sure whether I should start with the first flow block that allows me to adjust the total flow. Certainly gas is getting to it, it's a straight line from the tank regulator but it seems that nothing is coming out to the other flow blocks but not sure how to test it. Or should I just assume that its failed and not fixable?

Any assistance would be appreciated. Thanks.

[MSCHemist]

Could be a major leak somewhere. Check the gold seal perhaps. the inlet tubing, linet liner o-ring etc.

[cmoral]

Thanks MSChemist. I don't think it is a leak but I'll check. Am now wondering if enough pressure is getting to the flow controller since I believe it needs a certain pressure to activate and I am supplying two injectors and two FIDs from the same tank. Will check that as well.

[Consumer Products Guy]

Not a fix, but you do know that you can use front inlet to back detector, and vice-versa?

[cmoral]

Thanks CPG. Yes, I am aware but I was hoping to use two inlets with two separate columns to two different detectors with two different gases. The alternative is to use a y-splitter with the one working inlet for the two columns going to two detectors but use a single gas. I have done that before with success. Not quite sure why I didn't think of that again....(musing here)...probably because I wanted to use H2 for the FID column and need to use He for the TCD. But, of course, I could use He for both.

However, it bugs me that I can't get the second inlet working. I did speak to an engineer friend who explained a bit about how flow controllers generally work and so either not enough pressure is getting to the controller to open up the internal valve or the thing is toast. So, I'll check the pressure first and see.

[Peter Apps]

My recollections of the plumbing in a 5890 are slightly hazey, but as a general principal you can disconnect lines from controllers to see up to what point you have pressure and flow, I recall right the 5890s had compression fittings rather than tubes welded into chunks of metal. You can either start downstream and work back until you find gas, or start at the input and work down. I prefer starting at the end because you can leave stuff disconnected.

Aren't there some little frit cartridges somewhere in the plumbing ? Good candidates for a blockage if there are.

Peter

[cmoral]

Thanks Peter for your reply. It does certainly seem that there could be a leak somewhere but for the life of me, I can't find any yet. I have managed to confirm that it is not a low delivery pressure problem and I think I confirmed that the "total flow" controller is working. The gas flow enters that controller first from a direct feed from the tank then exits to a small carbon (or moisture, not sure which) trap and into the injector head.

I thought maybe the moisture trap might be clogged but I used a digital flow meter attached to the exit end of the trap and think I got a flow although it was intermittent so I am not positive...was a bit difficult actually getting a matching hose from the trap exit to the flowmeter. Might try to test again later.

I spent two hours after that trying to trace the lines and testing the flows but my fingers felt like they had been playing with thorns after having to disconnnect and reconnect those small plastic fittings several times. No luck yet. Working inside that GC is like working inside a modern small car engine. I am sure it was designed to frustrate anybody but the good folks at HP so that we'd be obliged to send it to them for repair!

The column ends are tight into the injector and detectors...i.e. can't pull them out when the nuts are tightened and the column end cuts are nice and clean. So I figure any leaks are not there and I certainly don't hear any obvious hissing from anywhere.

So, I am giving up for a bit to let my fingertips rest.

[Yama001]

Removing the outlet line from the flow controller is difficult as the 7/16 nut from the incoming gas line gets in the way - sometimes it is easier to remove that line first. A small needle nose plier is useful here as well.

It might be useful to swap to outlet line from the working flow controller on the other inlet. If you do not have the same issues, then the flow controller is the problem. There is a restrictor behind the big colered screw - perhaps that has gotten clogged.

Those moisture traps can get clogged eventually as well - I recall bypassing them a lot.

[cmoral]

Thanks Yama001 for your input. You are right about having to remove the gas inlet line nut first to get at the 7/16 plastic nut. Those plastic nuts are a pain because they come apart easily...i.e. they're not a single piece. And everything is so tight in there. I even considered simply disconnecting the flow controller from the GC front panel but that's a pain too.

I wasn't sure how to bypass the trap. But now that I think about it, maybe there is enough play in the outlet from the trap to go directly into the outlet from the flow controller. Something to try. If you have done it several times, then obviously there is no really detriment. Did you then leave it bypassed or were you able to replace the trap?. With this being a 5890 GC, it's hard to get parts like that for it. I did think about doing what you suggested, hooking up the flow to the column from the working controller but can't remember if I actually tried it. I think I did but will have to revisit.

I am not familiar with the restrictor you are talking about but I'll check it out. I am not giving up yet so all other suggestions are most welcome.

[Yama001]

I have bypassed that trap and never looked back, so it is workable that way. Traps are useful and important, but many labs never replace them, so they can become a problem.

You may be able to get enough tubing to reach the flow controller by rerouting straight from the inlet, rather than the original setup that routes the gas line at the the top rear of the GC.

[cmoral]

Thanks Yama001. I will see what I can do next week and let this forum know if I was successful.

[AICMM]

cmoral,

I believe either a leak or you are plumbed wrong. Without a leak detector I would try the following. Plumb the split line and inlet weldment from the working inlet to the non-working inlet. If you get head pressure all of the sudden then you know your plumbing cabinet is culprit, if you don't get head pressure then you know your inlet has a problem. If you get pressure, then I would focus on how the lines run into the splitless/split valve since this is often problematic is someone has messed with it. Possibles are a missing 0-ring or improperly routed gas lines.

If it were me, I would also take all the covers off including the front panel since a dual inlet is a rats nest.

Best regards,

AICMM

[cmoral]

Thanks AICMM. I will do as you suggest and get back to the forum on my progress.