Issues with carrier gas flow and pressure with Agilent 6890A

[tv88]

Hello,

I'm experiencing a few issues with an Agilent system, and I wondered if you be able to provide some guidance?

I'm trying to set up a GC-TCD but I'm having issues with the carrier gas flow rate. Pressure is maintained, but higher than the setpoint pressure, and flow rate remains zero. I've checked the line for blockages and replaced the carrier gas cylinder. I know it's not an issue with the inlet (split/splitless) as there is a steady flow of bubbles when the end of the column is dipped in a solvent.

I've had issues before with no pressure and no flow, but never had issues with pressure and no flow! I suspect it's an issue with the EPC, but I would like a second opinion if possible please?

Thank you!

Toby

[Don_Hilton]

Check to be sure that the septum is properly in place and that all fittings are tight - inclulding those along the split vent line, back through the instrument. A leak faster than the instrument can supply could give no measureable pressure and still leave gas flowing through the column. Also be sure that the column dimensions are correctly set in the EPC - because I suspect that if correctly set, the EPC should be shutting down on falure to maintain correct flow and pressure. But assuming a column with significant pressure drop and no leaks in the inlet, the EPC does become suspect.

[Peter Apps]

Flow through the column, with the inlet pressure too high, but no indicated flow is strong evidence that the EPC is sick. What column do you have ? - a short megabore will allow flow at very low pressures. If you have a split-splitless inlet set it in split mode and measure the flow out of the split vent. Are you setting the flow or the inlet pressure on the the software, and does it make any difference if you do the other one ?

Peter

[tv88]

This sort of confirms what I thought regarding the EPC.

The column is a 30m x 320um x 15um Carboxen PLOT. We can attempt to set both inlet pressure and flow through the software, but the instrument is unresponsive, and only pressure only changes when we adjust the regulator.

Are there any further tests we can do to confirm that it's the EPC?

Thanks for all your help,

Toby

[Peter Apps]

If the regulator that you are talking about is the regulator on the cylinder that supplies the gas, then remember that it has to provide a pressure to the GC that is substantially above the highest pressure that you need to run the column - check the instrument manual for details.

You can check the inlet pressure directly by connecting an ordinary dial pressure gauge to a syringe needle and then inserting the needle through the septum.

Have you checked the split flow ? What were the results ? What split ratio are you using ?

Peter

[tv88]

The regulator is connected to the cylinder, and is supplying the correct pressure to the instrument.

Split ratio is set at 10:1, and is working fine, but can only be adjusted through Chemstation, and not the instrument panel. We seem to be getting flow through the column, but the flow sensors aren't acknowledging it!

Other information suggests that it is a blockage in the EPC, which unfortunately seems to be quite a pricy fix as it's a replacement!

Thank you for your help Peter.

Toby

[Peter Apps]

Before you buy a new one, check whether there is a way to re-initialize or recalibrate it. I'm not familiar with the latest Agilents, but I would imagine that this might be possible.

Peter

[gcguy]

With some Agilent kit it is possible to recalibrate the gas flows using the GC instrument panel but you will need a digital flow meter to do so. Or spend a lot of time with a bubble one!
The EPC units are really expensive so I agree with Peter, check and try to adjust the old one first.

"Split ratio is set at 10:1, and is working fine, but can only be adjusted through Chemstation, and not the instrument panel. We seem to be getting flow through the column, but the flow sensors aren't acknowledging it!"

Can you input any values using the keypad?



GCguy

[Stef261]

Hi, I'm actually having the exact same problem on my 7890A GC. Right pressure but 0 mL/min flow reading and there is flow coming out of the column. Fortunately my machine is still under contract service and the Agilent tech came. We changed the EPC and it didn't help, we changed the logic board and it didn't help. We updated the Firmware, no change… The tech is a little stumped right now.

I was wondering if you ever got your problem fixed and how…

[GasMan]

Is there something else in your system that you have not told us about, such as running the TCD in series with a FID or a methanizer?

Gasman

[Stef261]

I'm going to assume you are talking to me since tv88 hasn't been on this thread for awhile!

I'm using a very basic system in the sense that's is a Purged Pack injector with a TCD (no autosampler) and 60x0.53x0.5 columns.

Software is ChemStation B.04.02 and firmwarw is A.01.15.