Troubleshooting a Leak in a Split/Splitless Inlet

Answer

This Information Applies To: Agilent GC Systems with Split/Splitless Inlet.

Issue

A leak may produce the following symptoms:

• Inlet pressure unable to reach setpoint (probably a large leak) - will lead to a flow shut-down.
• Failure of Any Diagnostic Tests from the associated tab on the front panel of the GC and/or the Browser Interface
  • Leak & Restriction Test
  • Pressure Decay Test
  • Septum Purge Test
  • Split Vent Restriction Test
• The cause of many chromatography issues can be leak in the inlet.

Steps to follow

1. Confirm that the GC is receiving enough carrier gas pressure. The carrier gas pressure should be 10 to 20 psi higher than required by the inlet pressure or set under 120 psi. It can be read directly from the regulator on the tank.
2. Navigate to the Maintenance tab and select Perform Maintenance to evaluate all consumables on the instrument are installed properly.

• Septum: make sure it is in good condition and seated properly, and that the septum retainer nut is not overtightened. You should just be able to fit a fingernail between the nut and the retaining clip (See Figure 1)

 
Figure 1: Proper spacing for the green nut and retaining clip

• Liner O-ring: make sure it is installed, and firmly seated against the inlet body. Check the liner for cracks or breakages.
• Gold seal: make sure that the washer is underneath the gold seal, and the gold seal is installed with correct way. The line going through the middle of the seal should be facing up, with the raised portion facing down. Also make sure it is tightened enough - finger tight then an extra 1/4 turn with a spanner.
• Column: make sure that there is a column installed. Make sure it is installed correctly (the appropriate length above the ferrule is 4–6 mm). Make sure it has been configured correctly (the column dimensions have been inputted to the GC).
• Column nut and ferrule: make sure that the column nut and correct sized ferrule are installed (and that the ferrule hasn't become too squished). Do up finger tight, then an addition 1/4 to 1/2 turn (the column should not be able to be pulled out). Check for column nut crossthreading.
• The split vent line: The split vent line is typically replaced during an annual maintenance or if there has been known carryover issues. Check that the large stainless steel nut that holds in the slit vent trap has been tightened enough. Check that the brass nut that connects the split line to the inlet has been tightened enough

If there is still a leak after the previous steps, then it means that there is a hardware leak. A good trick to half-split the system is known as the "septa sandwich." It isolates the septa assembly weldment and the electronic pressure controller (EPC) from the inlet body and split line, to help determine the location of the leak.

Septa sandwich Procedure for 7890, 8860, 8890

1. While the inlet is still cooled, Get a spare septum, and unscrew the green septum retaining nut and disconnect the top inlet weldment assembly (See Figure 2)
   
   
   Figure 2: Disconnected top inlet weldment assembly and parts require for test.
   
   
2. Utilize the spare septum, hold it underneath the weldment so there is a septum on either side. Squeeze these septa together to create a seal (See Figure 3)

   

   Figure 3: Squeeze these septa together to create a seal 
   
   

3. While holding the septa, pressurize the inlet from the GC front touch screen (Initially start with 5–10 psi).
   1. If the inlet takes a while to pressurize or can't reach pressure, this means that the leak is in the weldment itself or the EPC (or even in the gas lines leading to the instrument). In this case call Agilent for service on your instrument.
   2. If it does pressurize quickly and reaches the setpoint, it means that the leak must be in the inlet body or the split line

Septa sandwich Procedure for 6890 and 7820A Gas Chromatographs

The preceding procedure is slightly different for 6890 & 7820A GC models. 6890 and 7820 GCs will require a change to step one where the removal of the top weldment must be done with the provided wrench or utilizing the flip-top that is installed on some 6890 systems. (See Figure 4)

Figure 4: Top Weldment does not have a yellow flip top lever as above and must be removed with the provided wrench. 

Testing the split line

If the large stainless steel nut that holds in the split vent trap and the 1/8" brass nut that connects the copper split line to the inlet are done up tightly, then there is a small chance that the one of the valves in the split line has failed or stuck open. A quick test is to stick your finger against the split vent creating a seal (See Figure 5)

Figure 5: Test the inlet by covering the split line to determine if the valve has failed.

If the system pressurizes with your finger in the split vent, please call Agilent for service on your instrument.

If you still cannot determine where the leak is after following the preceding steps, contact Agilent Technologies.

Learn how to effectively maintain and troubleshoot your 8890/7890 Split/Splitless Inlet: GC-7890-2245s - Agilent 7890 Series GC: Split/Splitless Inlet Troubleshooting  GC-8890-2200s - Agilent 8890 GC Maintenance and Troubleshooting e-learning available from Agilent education.