5890 inlet problem pressure fluctuations when purge valve on

[MSCHemist]

I am having more problems with my venerable 5890. I had it down for a few days to service the detector. Now when I tried starting it back up the pressure in the inlet fluctuates wildly. It cannot achieve any setpoint. When I close the purge valve it is perfectly stable and achieves stable inlet pressure and flow out the split vent. Any idea where the issue is?

[James_Ball]

Electronic flow control or manual pneumatics?

[MSCHemist]

EPC it is having a very tough time regulating the flow when the purge valve is open IE split but has no trouble when I close the purge valve.

I am wondering if that is something with the solenoid as the solenoid seals the splitline when the purge valve is off and routes the excess gas through the sept purge and from solenoid to the speta purge vent and PCV/split vent.

I just cleaned the split line to ensure there was no blockage there. Perhaps a blockage inside the solenoid valve where the split line comes in.

[MSCHemist]

I tried rinsing the solenoid with toluene followed by methanol and it did not have any effect but there is definitely no blockages in the split line or solenoid.. I am at a loss as to why the EPC cannot regulate the flow when it goes through the split line but has no problem when the excess helium goes through the septa purge line instead.


I am going to leave it going overnight. Perhaps there are just air pockets in the split line or something.

I swear that GC is going to drive me insane.

[MSCHemist]

OK the only thing I could come up with last night is the liner itself is heavily obstructing the split vent. I've ensured the path through the solenoid and split line are not obstructed and rinsed them with solvent into the inlet. If there was a problem downstream of the solenoid ie the PCV then it would be just as bad in splitless mode as the flow goes right back to the split path at the solenoid.

I'll switch liners but I've not had that happen before.

[MSCHemist]

I don't believe it it was the bleeping liner. I recently tried a few from a different manufacturer that does not have the little bump on the bottom. I just switched back to a Restek Blue with wool/bump on the bottom and it is fine again.

[MSCHemist]

I don't believe it it was the bleeping liner. I recently tried a few from a different manufacturer that does not have the little bump on the bottom. I just switched back to a Restek Blue with wool in the middle and bump on the bottom and it is fine again.

There where also a few pieces of loose graphite on the bottom of the liner near the aperture so that was probably also the issue.

[Peter Apps]

Another one for the unlikely problems list !

Those bits of graphite would have caused endless problems with peak tailing, so good riddance to them also.

Peter

[Consumer Products Guy]

I'd clean out the split vent plumbing from the "weldment" to the EPC, and change the split vent trap. We've seen deposits in that line.

[MSCHemist]

Did that though I started at the EPC and washed the line with toluene then methanol into the inlet then cleaned the inlet.

I don't have a trap on the split line. I looked into it and consulted with Agilent but because the 5890 EPC's PCV works by putting resistance on the splitline anything on the line that restricts the flow including a trap will mess it up. They recommend just have a long length of 1/8" split tubing.

[Bigbear]

Could it be the solenoid is not sealing. When I first contacted Agilent about gun brushing the inlet of my 6890, I was told not to get any solvents into the split vent line. BTW it's better just to cut a new length of cu tubing than to try and wash it.