Chromatography Forum

I am having inlet pneumatics problems with a Agilent 6890A. It cannot stabilize the pressure. I have replaced the pneumatics board and have tried a new pneumatics module, but it did not help, so I put the old one back in. It will pass set point by a couple of psi then drop below a couple of psi, but does not ever stabilize. Does anyone have any ideas?
Thanks

I may have found the problem, but am not sure. Went into diagnostics/back inlet/pneumatics module and the temperature is incorrect (shows 80-84C and is not stable). All other instruments are ~35C and pretty stable. Must have gotten a bad pneumatics controller board.

I had that once with a Tekmar 7000 headspace sampler hooked up. If pumbed the way they suggest the inlet feed goes through an additional resistance frit for manual inlet control that caused issues. I replumbed it bypassing the frit and there were no more issues. It sounds like you may have a plug in the lines somewhere. One place to check is split vent tubing. That stuff fills with condensed tar (it is unheated) and can become blocked even.