Performing the leak tests

With the large amount of tubing and connections in a multiplexed system, leaks may develop over time. This is especially true as the system ages. Fortunately, it is relatively easy to check for any leaks using the System leak test and to further narrow down where the leak is with the Component leak test.

Figure 7‑9. A diagram showing the flow of air through the LI-8250 Multiplexer and the various loops.

System leak test (without 8250-01 Extension Manifolds)

The following steps will walk you through the leak test without an 8250-01 Extension Manifold. These steps can be used in situations where you either do not have an extension manifold or you will not be testing the port with an extension manifold.

During the System leak test, the LI-8250 Multiplexer pump draws a vacuum on the system for each port selected. Pressure is monitored to determine the total leak rate for that port. Before moving to the next port, the system is purged to prepare for the next port to be evacuated. The recommended leak rate for each port is ≤ 1 cm3 s-1 to minimize error in your measurements.

The System leak test requires you to seal the analyzer tubing and each tested port to form a closed loop. To do this, disconnect the chamber and analyzer tubing, then connect the male and female ends together.

Note: At least one port must be left open to allow the system to purge itself. The port left open will need to be checked for leaks after testing the others.

Performing the test

To perform the System leak test:

  1. Connect to the LI-8250 Multiplexer user interface.
  2. Expand the Tools drop-down and click Leak Test.
  4. Disconnect the analyzer tubing from your analyzer or analyzers.
  5. Connect the disconnected ends together.
  6. Leave the tubing connected to the multiplexer.

Note: For analyzers with Swagelok fittings, such as the LI-78xx Trace Gas Analyzers, use the Swagelok Union (part number 300-15249) found in the Spares Kit (part number 9982-072) to connect the ends.

  1. Disconnect the chamber tubing from each chamber.
  2. Connect the ends of the chamber tubing together for each port you would like to test.
  3. Leave the tubing connected to the multiplexer.

Note: At least one port must be left open to allow the system to purge itself.

  1. Select the ports you would like to have tested in the user interface.
  2. Verify the tubing lengths for the analyzer tubing and the chamber tubing are correct. These lengths can be found on your Configuration page under their respective blocks. If you are using cable assemblies provided by LI-COR, see Table 7‑1 for tubing lengths.
Table 7‑1. Tubing lengths for LI-COR cable assemblies.
Instrument Cable assembly part number Tubing length (cm)
LI-870 CO2/H2O Analyzer 9982-010 120
LI-78xx Trace Gas Analyzer 9982-011 200
8200-104/C Long-Term Chamber
or 8250-01 Extension Manifold		 9982-056 1500
T-split tubing 9982-073 30
  1. Click Start. You will then receive two warnings to verify you have plumbed your system correctly for the leak test. To begin the test click Start Test.

The multiplexer will then run through the System leak test port by port. After the leak test, you will receive a report on the leak rate of each port tested. If the report has no warnings, as in Figure 7‑10, no ports exceeded the 1 cm3 s-1 threshold. You are finished or you can move on to testing any additional ports that were not tested before.

Figure 7‑10. Leak test results with no warnings.

Any port that exceeds the 1 cm3 s-1 threshold for a leak will provide you with a high leak rate warning and advise you to run the Component leak test to troubleshoot where the leak may be occurring, see Figure 7‑11.

Figure 7‑11. Leak test results indicating a high leak rate on port 1.

Component leak test (without 8250-01 Extension Manifolds)

If the System leak test indicates that one of the ports has a high leak rate, you can use the Component leak test to narrow down the location of the leak on that port. You will need the leak test plug (part number 300-18823), see Figure 7‑12, for this test. The LI-8250 Multiplexer user interface will guide you through when to use the plug.

Figure 7‑12. The leak test plug.

The leak test plug is stored inside the multiplexer case. It is connected to post on the lower right side, see Figure 7‑13.

Figure 7‑13. The leak test plug is found connected to a post in the lower right side.

The Component leak test requires you to seal the analyzer tubing and the tubing of each tested port to form a closed loop and to leave at least one port open. This test will check six components for leaks:

  • Analyzer tubing
  • Multiplexer tubing
  • Tubing from IN to valve manifold
  • Tubing from OUT to valve manifold
  • Tubing from IN to chamber
  • Tubing from OUT to chamber

Each subsequent step of the test relies on the previous steps to estimate the leak of that component. If one component exceeds the 1 cm3 s-1 threshold, you will receive a warning message under Component Leak Rates. The test will stop and indicate the component with the high leak rate that needs to be addressed. Address the component with the high leak rate to continue the test.

Performing the test

To perform the Component leak test:

  1. Connect to the LI-8250 Multiplexer user interface.
  2. Expand the Tools drop-down and click Leak Test.
  4. Disconnect the analyzer tubing from your analyzer or analyzers and connect the disconnected ends together.
  5. Leave the tubing connected to the multiplexer.
  6. Disconnect the chamber tubing from each chamber you would like to test and connect the ends of the chamber tubing together.
  7. Leave the tubing connected to the multiplexer.

Note: At least one port must be left open to allow the system to purge itself.

  1. Click Component at the top of the Setup pane.
  2. Select the port you would like to have tested.
  3. Verify the tubing lengths for the analyzer tubing and the chamber tubing are correct.
  4. These lengths can be found on your Configuration page under their respective blocks. If you are using cable assemblies provided by LI-COR, see Table 7‑1 for tubing lengths.
  5. Click Start.
  6. You will then receive a warning to verify you have plumbed your system correctly for the leak test. To begin the test click Start Test.

After the analyzer tubing is tested, the user interface will ask you to connect the leak test plug into the port IN connection, the port OUT connection, and between the ends of the chamber tubing.

At the end of the Component leak test, you will receive a Total Leak Rate calculation. If the Total Leak Rate exceeds the 1 cm3 s-1 threshold, you will see a warning to address the areas with a high leak rate. It is possible to have no individual components exceed the threshold but to have a cumulative total that requires components to be addressed.

Figure 7‑14. A Total Leak Rate calculation is given at the end of the Component leak test.

Note: The Component leak test total leak rate may differ from the System leak test leak rate because the System leak test is more accurate.

System leak test (with 8250-01 Extension Manifolds)

The following steps will walk you through the leak test with an 8250-01 Extension Manifold.

During the System leak test, the LI-8250 Multiplexer pump draws a vacuum on the system for each port selected. Pressure is monitored to determine the total leak rate for that port. Before moving to the next port, the system is purged to prepare for the next port to be evacuated. The recommended leak rate for each port is ≤ 1 cm3 s-1 to minimize error in your measurements.

Figure 7‑15. The system leak test with an extension manifold on port 2.

The System leak test requires you to seal the analyzer tubing and each tested port to form a closed loop. To do this, disconnect the chamber and analyzer tubing, then connect the male and female ends together.

Note: At least one port must be left open to allow the system to purge itself. The port left open will need to be checked for leaks after testing the others.

Performing the test

To perform the System leak test:

  1. Connect to the LI-8250 Multiplexer user interface. Expand the Tools drop-down and click Leak Test
  3. Disconnect the analyzer tubing from your analyzer or analyzers. Connect the disconnected ends together. Leave the tubing connected to the multiplexer.

Note: For analyzers with Swagelok fittings, such as the LI-78xx Trace Gas Analyzers, use the Swagelok Union (part number 300-15249) found in the Spares Kit (part number 9982-072) to connect the ends.

  1. Disconnect the chamber tubing from each chamber connected to the multiplexer. Connect the ends of the chamber tubing together for each port you would like to test. Leave the tubing connected to the multiplexer.

Note: At least one port must be left open to allow the system to purge itself

  1. Disconnect the chamber tubing from each chamber connected to all extension manifolds. Connect the ends of the chamber tubing together for each port you would like to test. Leave the tubing connected to the extension manifold.
  2. Select the ports you would like to have tested in the user interface.
  3. Verify the tubing lengths for the analyzer tubing, extension manifold tubing, and the chamber tubing are correct. These lengths can be found on your Configuration page under their respective blocks. If you are using cable assemblies provided by LI-COR, see Table 7‑1 for tubing lengths.
  5. Click Start. You will then receive three warnings to verify you have plumbed your system correctly for the leak test. To begin the test click Start Test.

The multiplexer will then run through the System leak test port by port. After the leak test, you will receive a report on the leak rate of each port tested. If the report has no warnings, as in Figure 7‑16, no ports exceeded the 1 cm3 s-1 threshold. You are finished or you can move on to testing any additional ports that were not tested before.

Figure 7‑16. Leak test results with no warnings.

Any port that exceeds the 1 cm3 s-1 threshold for a leak will provide you with a high leak rate warning and advise you to run the Component leak test to troubleshoot where the leak may be occurring, Figure 7‑17.

Figure 7‑17. Leak test results indicating a high leak rate on port 1.

Component leak test (with 8250-01 Extension Manifolds)

If the System leak test indicates that one of the ports has a high leak rate, you can use the Component leak test to narrow down the location of the leak on that port. You will need the leak test plug (part number 300-18823), see Figure 7‑12, for this test. The LI-8250 Multiplexer user interface will guide you through when to use the plug.

The leak test plug is stored inside the multiplexer case. It is connected to post on the lower right side, see Figure 7‑13.

The Component leak test requires you to seal the analyzer tubing and the tubing of each tested port to form a closed loop and to leave at least one port open. This test will check 12 components for leaks:

Multiplexer Components

  • Analyzer tubing
  • Multiplexer tubing
  • Tubing from IN to valve manifold
  • Tubing from OUT to valve manifold
  • Tubing from IN to 8250-01 Extension Manifold
  • Tubing from OUT to 8250-01 Extension Manifold

Extension Manifold Components

  • Pump tubing
  • Extension manifold tubing
  • Tubing from IN to valve manifold
  • Tubing from OUT to valve manifold
  • Tubing from IN to chamber
  • Tubing from OUT to chamber

Each subsequent step of the test relies on the previous steps to estimate the leak of that component. If one component exceeds the 1 cm3 s-1 threshold, you will receive a warning message under Component Leak Rates. The test will stop and indicate the component with the high leak rate that needs to be addressed. Address the component with the high leak rate to continue the test.

Performing the test

To perform the Component leak test:

  1. Connect to the LI-8250 Multiplexer user interface. Expand the Tools drop-down and click Leak Test.
  3. Disconnect the analyzer tubing from your analyzer or analyzers. Connect the disconnected ends together. Leave the tubing connected to the multiplexer.
  4. Disconnect the chamber tubing from each chamber you would like to test. Connect the ends of the chamber tubing together. Leave the tubing connected to the multiplexer.

Note: At least one port must be left open to allow the system to purge itself

  1. Click Component at the top of the Setup pane.
  2. Select the port combination you would like to have tested.
  3. Verify the tubing lengths for the analyzer tubing and the chamber tubing are correct. These lengths can be found on your Configuration page under their respective blocks. If you are using cable assemblies provided by LI-COR, see Table 7‑1 for tubing lengths.
  4. Click Start. You will then receive a warning to verify you have plumbed your system correctly for the leak test. To begin the test click Start Test.

After the analyzer tubing is tested, the user interface will ask you to connect the leak test plug into the LI-8250 port IN connection, the LI-8250 port OUT connection, between the ends of the extension manifold tubing, the 8250-01 port IN connection, the 8250-01 port OUT connection, and between the ends of the chamber tubing.

At the end of the Component leak test., you will receive a Total Leak Rate calculation. If the Total Leak Rate exceeds the 1 cm3 s-1 threshold, you will see a warning to address the areas with a high leak rate. It is possible to have no individual components exceed the threshold but to have a cumulative total that requires components to be addressed.

Figure 7‑18. A Total Leak Rate calculation is given at the end of the Component leak test.

Note: The Component leak test total leak rate may differ from the System leak test leak rate because the System leak test is more accurate.