Problem reaching rear injection port pressure

The rear column on my 7890B is not holding pressure. I have removed the column and plugged the inlet (where the column nut fits) with a plug nut (#21883), checked the nut that covers the septum for tightness, and the housing portion that enters the oven and encases the gold seal for tightness. Still no pressure increase. I moved the carrier gas weldment that normally feeds into the front port to the rear. It is not holding pressure. However, I don’t know at what point the GC actually measures the injection port pressure, so I’m unsure whether this means the weldment is cracked or the problem lies elsewhere. Can you please help me interpret this result? 

  • The pressure sensor is located in the EPC module. So if you moved the weldment from the front to the rear, means the leak is probably in the rear inlet and both EPC works fine. 
    So you set up a pressure value like 25 psi and the GC is not able to reach the setpoint? What is the maximum value the inlet can reach? 

  • Hello  ,

    Do you have enough pressure coming from the gas source (whether gas tanks or gas generators)? Check if the gas tank has enough gas in it AND that the pressure at the second regulator of the tank is high enough (usually 60-80 psi is good enough).

    If you have shutoff valves at the back of the GC make sure they are not in the off/closed position.

    Also, do you have any other accessories (Agilent or otherwise) on the inlet that are directly on the flow path, that might affect flow to the inlet?

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