Inlet Pressure Shutdown / Gas Cannot Achieve Setpoint

This Information Applies To: All Agilent GC systems, focusing on 8890 and 7890A/B, but also applies to 6850A/B, 6890A/N, 7820A, and 8860.

Issue:

If the inlet pressure / carrier gas flow fail to achieve the setpoint after a few minutes, the inlet pressure will shut down automatically. This article will help you to identify the possible causes of this issue.

Steps to follow: 

1. Leak at the inlet
   To detect big leaks in the inlet, perform one of the diagnostic tests for the inlet: Inlet Leak Check, or Leak and Restriction Test depending on the instrument model. If the results of the test show an important leak, check the following causes

   1. Septum hole is deformed or widened. Installing a new septum will resolve the issue.

   2. Inlet to column connection is not fully tight, wrong positioned or column is broken near the inlet. Recommended to check for breaks, trim the column if necessary, use new ferrules, and reinstall the column. See capillary column installation guide.

   3. Liner, O-ring, split filter, gold seal, or washer under gold seal are not positioned correctly or damaged. Exchange them if you find them fractured or broken.

   4. Make sure the fittings around the inlet and the weldment nut had been tightened properly. Check if tubes at weldment are intact.

      Tips: For further instructions see Troubleshooting a leak in a SSL, Inlet Diagnostics 6890/7890, 8890 Troubleshooting Manual, 8860 Troubleshooting Manual.

2. Source pressure not high enough

   1. The carrier gas regulator must be set at least 20 psi greater than the maximum inlet pressure required in the GC method. Check the Site Preparation Guide of your respective GC model to get more information on gas supply pressure requirements.

   2. Make sure the gas regulator on/off valve is fully opened.

   3. Is the gas cylinder full or going to finish? Agilent recommends exchanging the gas cylinder when its pressure is about 150 psi. For more information, watch the video about Gas Management Best Practice.
      
      

      Tips: 8890 and 8860 GCs have a Gas Supply Pressure Check diagnostic tool. This tool is not available if a mass selective detector is configured with the system.

   4. To run the Gas Supply Pressure Check in the 8890 or 8860 GC, on the touch display press Diagnostics > Diagnostic Tests > Front (or Back) Inlet > Gas Supply Pressure Check > Start Test (See Figure 1).
      The test checks for the maximum pressure the gas supply can deliver. It will pass if the gas supply can deliver at least 276 kPa (40 psi) to the instrument.
      

        
      Figure 1. Gas Supply Pressure Check for the Agilent 8890 GC
      
      

3. Configuration

   1. Check if a column is installed in the inlet.

   2. Compare installed and configured column type. Configured column length and diameter will affect the calculation of the inlet gas pressure to set the specified column flow.

   3. Check if the correct gas type is connected and configured.

If you still cannot determine where the leak is located after have been following the preceding steps, contact your local Agilent support representative.

Learn how to effectively troubleshoot your split/splitless inlet: Agilent 7890 Series GC: Split/Splitless Inlet Troubleshooting e-learning course available from Agilent education.