Resolving a Leak Issue With the LI-6800

Resolving a Leak Issue With the LI-6800

Leaks will get your attention by causing a leak/flow test failure (Start Up->Warmup/System Tests), low ‘Flow’ reading (mass flow to chamber in the diagram), low ‘Flow_s’ or ’Flow_r’ reading (flow through the sample/reference gas analyzer). The following three warning messages may appear on the upper left corner of the display: ‘Console flow leak?’, ‘Flow_s low’, ‘Flow_r low’ (see Table 5-2 on the page 5-4 of the LI-6800 manual for more details).

  1. If you can achieve ‘Flow’ setpoint, but ‘Flow_s’ is near zero or much lower than the flow to chamber, you may want to check the following things:
  • Make sure that the chamber is installed tightly enough with two Phillips head screws (part# 144-15344) and is tightly closed.
  • Check the gaskets on the chamber. If the gaskets are flattened/torn, change them. When flattened, the black neoprene gasket can recover if left uncompressed overnight, but the white gasket material may not (part# fluorometer white: 6568-436, fluorometer black: 6568-413, 3×3 chamber white: 6568-429, 3×3 chamber black: 6568-384).
  • Make sure the thermocouple is installed and the O-ring (part# 192-14435) on the chamber bottom that seals the thermocouple is in place.
  • The lower chamber may have two flexible black ducts (depends on chamber type, part# 6368-345). They may wear out over time. Change if necessary. Damage to the ducts should rarely happen, but if they are kinked during removal or installation, they may develop leaks. Ensure that the bead of the duct seats in the groove.
  • Remove the chamber from the head and you will see the large chamber O-ring (part# 192-14438) and electronics gasket (part# 6568-327). Replace if damaged.


  1. If ‘Flow_s’ / ‘Flow_r’ is low and ‘Flow’ cannot reach setpoint, you may want to check:
  • The humidifier and desiccant columns (part# 9968-225) are present and securely attached to the console. Check for any cracks in the walls of the chemical columns. You may have forgotten to attach the humidifier column, since during transportation or storage, it is usually removed to ensure that water does not enter the console.
  • Check to see if any chemical debris or anything else has accumulated on the threads of the cap and the tube. This will prevent the cap from getting a good seal. This may especially be true with the humidification column, where hard-to-see ceramic particulates may accumulate. Wipe the threads, rim, and O-ring with a moist paper towel to remove any solid material. This will also help keep the column and cap from being damaged.


This example may be a bit exaggerated, but it happens. You may have hard-to-see particulates that cause leaks, too.

  • You may want to switch the soda lime column to the humidifier/desiccant position. If there is improvement after the swap, your humidifier/desiccant tube is causing a leak.
  • Make sure the O-ring (part# 192-14541) inside the bottom column cap is in place.
  • Each chemical column has two filters (part# 300-14319) held in place with rubber seals (part# 6368-225). Check if either of the two air filters is missing.
  • Make sure the air supply tube is securely connected to the console outlet and sensor head inlet.

If you have done all of the above, but flow problems persist, contact LI-COR.

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