pulsing pressure on GC3800

[nickos012002]

I am running a Varian GC3800.

I recently changed the EFC and it has been working swimmingly for about 3 weeks. It has recently started to pulse. I.e. For a set column flow of 1ml/min, the achieved column flow is 1.1-1.4, with corresponding column pressure being 6.7-8.5. The pressure is constantly changing, meaning the system is unable to stabilise. I have autocalibrated the EFC and that passes. I have tried doing a purge valve calibration, but that is a bit difficult as the purge valve flow is also pulsing.

Its running a FID detector.

Any ideas anybody?

[Peter Apps]

A partially blocked split line by the looks of it. Did you change the inline filters when you changed the EFC ?

What is the split ratio (total flow) and does changing it make any difference ?

Peter

[Rndirk]

It might be a leak/bad connection in your gas supply/split lines. Do you have a leak detector?

[nickos012002]

I have a hydrogen detector.

I recently changed the pencil filters so that could well be it, i'll investigate and get back to you

Cheers

[Peter Apps]

I have a hydrogen detector.

I recently changed the pencil filters so that could well be it, i'll investigate and get back to you

Cheers

New filters are unlikely to be the cause of the problem, but old ones would have been.

Your total flow may be too low, especially if there is an leak in the inlet or the septum purge is higher than its setting. Changing the total flow (split ratio) is the diagnostic for that.

Peter

[nickos012002]

When the split ratio is set to "off", the pressure does not pulse. At a split ratio of 20, it pulses.

[Peter Apps]

Setting the split to "off" (i.e. splitless) does not affect the total flow, only the route that the gas takes through the plumbing.

Set the total flow to 100 ml/min, and check for pulsing in split mode and in splitless mode. Measure the flow coming out of the split vent under each condition, and with the total flow set to 20 ml/min in each condition.

Do not change the column flow or inlet pressure settings.

Peter