Chromatography Forum

Hi everyone! I'm having the exact same problem as someone recently described but there seems to be no solution. The split/splitless inlet cannot reach pressure either while the GC (7890) is operating normally or during the Inlet Pressure Decay Test.

The carrier supply is fine and I am able to flow helium without a problem to the FID for the makeup flow. I have changed out the septum and checked extensively for leaks and found nothing. I swapped out the EPC (per Agilent's recommendation) and still have the exact same problem.

The weird thing is that the pressure is never able to get anywhere near the setpoint (it remains under 0.5psi) but sometimes when we set the flow it increases to the setpoint and holds for about a minute before going back down to a low flow.

Any recommendations would be greatly appreciated! I have never encountered as GC problem as mysterious as this one

Have you checked for leaks near the split vent trap?

Thanks for your reply! Yes we have checked for leaks around the split vent trap (we have checked pretty much every single part of the inlet flow paths)

The biggest problem area for me is the bottom seal. After changing it, before re installing the insulation, I hold my finger over the column connection to see if it holds pressure.

RESTEK sells an EPC Test Kit Cat# 24323 for $133 (similar to Agilent G1530-60960 EPC Test kit for 6890 GC). That will let you find out if the EPC is working properly. Beyond that, I would plug the inlet and use a leak detector to look for where it is leaking.

The biggest problem area for me is the bottom seal. After changing it, before re installing the insulation, I hold my finger over the column connection to see if it holds pressure.

I didn't change the bottom seal so I wouldn't expect it to randomly start leaking, but I used the helium leak detector extensively around that area just to make sure. Unfortunately there's no leak

RESTEK sells an EPC Test Kit Cat# 24323 for $133 (similar to Agilent G1530-60960 EPC Test kit for 6890 GC). That will let you find out if the EPC is working properly. Beyond that, I would plug the inlet and use a leak detector to look for where it is leaking.

Thanks. We have literally spent hours combing over every inch with a helium leak detector and found nothing. Is there any leak location you can think of that we wouldn't reach with a leak detector?

Is there enough helium fed to the instrument to begin with? Is there a possibility to connect the helium supply to another GC (as a test if the supply is OK), or perhaps this is already the case?

Is the target pressure that the instrument wants to reach a realistic value for the column that is installed? It might be possible that you (accidently or not) demand an unrealistically high flow from the system. The system converts the flow you want into a pressure, based on the dimensions of the column that you put in there. You could run into problems like you're having if the installed column is far from the theoretical column that the software is considering.

The biggest problem area for me is the bottom seal. After changing it, before re installing the insulation, I hold my finger over the column connection to see if it holds pressure.

I would set aside the leak detector and physically check for leaks as Bigbear describes. If you do not see a pressure increase doing as Bigbear describes then you know your problem is at the bottom seal or upstream. Next, I would check the inlet weldment by installing a new septum and holding a new septum on the bottom and see if that holds pressure. In this fashion I would systematically move from one potential leak area to the next until the leak was isolated.

Dave

Thanks everyone, we have fixed the problem.

Thanks everyone, we have fixed the problem.

Would you be willing to share the solution - for future reference if anyone else experiences a similar problem?

Thanks everyone, we have fixed the problem.

Would you be willing to share the solution - for future reference if anyone else experiences a similar problem?

I didn't share the solution because it turns out the problem was manufactured... another lab member was sabotaging the equipment

I didn't share the solution because it turns out the problem was manufactured... another lab member was sabotaging the equipment

Lovely...

Thanks everyone, we have fixed the problem.

Would you be willing to share the solution - for future reference if anyone else experiences a similar problem?

I didn't share the solution because it turns out the problem was manufactured... another lab member was sabotaging the equipment

Definitely the worst type of problem to troubleshoot.