Forever equilibrating of Varian 3800 ???

[zhi ju]

Hello, anyone has clue?

My GC Varian 3800 could never complete "Equilibrating" to get green "Ready" condition. I saw Front Oven temperature (Set 100 degree C) frequently appeared Stabilizing. Please help on how to fix the problem. I have many samples waiting for run. Thank you a lot!

[Peter Apps]

What about inlet and detector temperatures and gas flows and pressures. are they all at their set points ?

Peter

[zhi ju]

Thanks, Peter

Here are:

Front FID 275 C
Mid 1079 265 C
Column oven 100 C
Column gas flow 2.0 ml/min
Column pressure 0.5 psi

They all got the set values, but column oven 100 C frequently appearing and disappearing "Stabilizing".

[tdgcuser]

Wow, that's a low pressure. Are you using a 15m x 0.32 id column? That's the only one that gets close to that pressure and a 2.0 mL/min flow. I've never tried a pressure that low, maybe that's causing the stabilization delay? Is the septum purge flow setup correctly? We had a 3800 with an improperly set regulator that had trouble stabilizing. There is a procedure in the injector manual on how to fix this.

When the flapper motor is sticking on the Agilent 6890, the best thing to do is power cycle the GC and hope for the best. Maybe that will work for the Varian?

[zhi ju]

Hello tdgcuser,

I used column Omegawax 320 30mX0.32mmX0.25 um column.

We used the method to activity for last five years, it works with the low pressure and flow rate; only it did not work since last week. I had manfully injection, our 8200 autosampler was broken.

I also think flapper motor or fan motor broken, now nowhere to buy a new one. I wonder how "to do power cycle the GC", would you please explain this for me and I will try. Thanks!

[Peter Apps]

That pressure is absurdly low - what is the carrier gas flow rate and what are you trying to analyse ?

Did the stabilization problem appear at the same time that the autosampler broke ?

Try setting the oven to 101 C

Peter

[zhi ju]

Thanks, Peter,

We always do fatty acid analysis.
Gas flow rate is 2.0 ml/min. We have used the same method for last five years. Varian could not complete "Equilibrating" since last week.
Autosampler did not work months ago. We can use manually injection.
Please help to find possible reasons.

[Peter Apps]

You cannot get 2 ml/min through a 30m 0.32 mm column with an inlet pressure of 0.5 psi. So either the pressure is wrong, or the flow is wrong, which would point to a problem with the gas controls and that might be why the GC will not get ready.

How did you measure the flow ?

Did you try putting the initial oven temperature to 101C ?

Peter

[zhi ju]

Yes, I set oven temperature to 101C, and set column flow rate 10 ml/min and then column pressure showed 2.6 psi in GC screen. the GC still is on Equilibrating after 1.5 hours running.

I saw "Stabilizing" frequently appearing on Oven Temperature. Maybe Oven Temperature could not be stabilized?

I did not measure flow rate, I read the number from GC screen. WE used Star Workstation 6.30 software controlling GC.

Thanks, Peter.

[Peter Apps]

When troubleshooting it is very important to change only one thing at a time - you changed both gas flow and temperature.

There is definitely something wrong with your flow controller and/or readouts, you cannot get those flows with that pressure through that column.

Check the column dimensions that I assume you have entered somewhere on the GC or the control software.

Can you monitor the signal from the GC in any way, even though it is stuck at stabilise ? If you can you need to inject some methane or some gas from a cigarette lighter and measure how long it takes to reach the detector. This gives you the linear flow velocity through the column. At 2 ml min it should take about 1 min for the gas peak to appear.

Do you have a spare pressure gauge of any kind that can measure pressures in the range that is supposed to be in the inlet ?

You need to measure the volume fow rate from the split and septum purge outlets and check that they are the same as their settings.

Measure the oven temperature with a thermometer or thermocouple probe. Is it at 100C ?

Peter

[Jihad]

If your sample is dirty and the split line from the injector is blocked you will find the gc 3800 keeps showing equilibrating.

Thanks

Jihad