Chromatography Forum

Hi, I have an Agilent 6890 that I am having pressure issues with. I'd like to preface this to say that this instrument doesn't see regular use, although it is left on and at temp. I have started having an issue getting stable pressures. When the EPC calls for a change, the actual is often several PSI behind where it should be. Actual pressure will also always overshoot the pressure before settling. I did several leak tests on the system, inlet leak check, inlet decay and split restriction. Of these, my system failed the inlet press decay test....pretty badly at that. As soon as I turn off the pressure module, I rapidly lose pressure. So, I am thinking the inlet body might be bad. Would it be safe to assume this and to purchase one? Or is there other testing I should do before throwing parts at it? Any help is appreciated!
Sean

The EPC costs ~$2000 with a core exchange. You can get one refurbished for less if you bargin or if you know it won't be an expensive rebuild. If you are handy, and have isolated it down to a valve, they are not too hard to replace. You can buy this EPC test kit from RESTEK if you need to isolate the EPC from the rest of the inlet system for testing. But first get a leak detector and make sure there are no leaks or blockages in the purge vent filter assembly or connections as well as the sample and carrier gas transfer lines. Also, check your inlet seals top and bottom. You can use an inlet plug to seal the bottom of the inlet and run up the pressure to help you find leaks.

We actually had a used EPC installed about 9 months ago. Initial testing showed we were good after that but I am not sure they loaded up the method in question (which starts at low psi). The problem has persisted through two EPC units so I don't think the controller is the issue. In the pressure decay test, you have to uninstall the column and install a blank ferrule. I also capped the septum purge so I believe I was only testing the inlet at that point. I will try to get my hands on a leak tester tho. Thanks!

http://wntechnical.com/6890epcrepair.html

If you feel comfortable taking out the EPC yourself.

It's unlikely that the inlet body is bad. I would check that everything connected to the body is tight, liner O ring, split vent and filter connections, bottom seal, and don't forget the septa.

I admit that it is unlikely that the inlet body is bad but I have had someone crack an inlet body by cranking too hard on the reducing nut because 'they really wanted to make sure the gold seal was sealed'.

To confirm though, you did check to make sure that your split vent was operating correctly, right? I've had those valves go out in the past.

Yup, split vent seems to be working correctly or at least it passed the test. I got ~7 psi on that one. According to Agilent literature, my target was 3-10 so I think I am good there. I honestly wouldn't be too surprised if the inlet is bad. The oven is starting to show cracking on the casing and this instrument has been used and abused over it's lifetime. It doesn't help that I am only partially trained in GC and aside from generalized electronics, not trained at all in GC repair. We need to purchase a leak detector so I can narrow down my leaks. I will go back through and check each fitting in the meantime. Thanks for the help so far!!