Chromatography Forum

I am attempting to troubleshoot and repair an aux EPC for a PTV inlet on an Agilent 7890A GC. The inlet conditions are 190 kPa (constant pressure) with 3 mL/min septum purge and 100:1 split ratio.

The issue is that the pressure reading was about 130 kPa one morning and following leak checks and powering up again, the pressure reading was providing negative values. (~-4 kPa) Attempting to input other pressure settings did not change the reading.

I attempted to uninstall and reinstall the EPC on the keyboard but the problem persisted. Looking around for documentation on pressure calibration of this EPC turns up resources for the 6890 but not 7890 series.

Are there any steps I can take to try and recalibrate the EPC, or should I replace the pressure sensors and valves?

Do you measure any flow from the split vent or septum purge vent?

0.6 mL/min from the split vent, no flow from the septum purge vent.

It is correct that it should be giving very little flow is the pressure is so low.

Try taking an autosampler syringe and placing it into the inlet through the septa, if the pressure sensor is bad and it is reading too low then the pressure should be high in the inlet and it should push the plunger up, maybe even eject it completely from the syringe. If it doesn't then maybe no gas is making it to the inlet.

If you can't find a leak then it is probably a bad EPC board.

Oh and be sure to wear proper eye protection in case the plunger comes out quickly.

The issue was a leak in a split connector for an inlet backflush before the capillary column. The pressures are now reaching desired setpoints. Thank you for the advice, this has been an educational repair job.