Leak Checking Your GC: Leak Detector or Pressure Decay?

There are a variety of techniques for making sure your GC system is leak tight. Senior Technical Service Specialist Tom Bloom discusses different approaches for leak checking using leak detectors or a pressure decay test 1. Scott Grossman’s article, “How Much Sensitivity is Needed in a Leak Detector?” demonstrates the sensitivity of the Restek Leak Detector may negate the need for pressure decay 2. While both opinions are correct the approach we’ll take here incorporates both leak detector and pressure decay and is a bomb-proof method of leak checking.

Figure 1: Cap column at inlet side and column to detector side.

Figure 1: Cap column at inlet side and column to detector side.

Follow these simple steps:

  1. Set inlet pressure to 50 psig*
  2. Cut column 10cm from injection port and seal with a septum cat#27142 (fig 1)
  3. Seal column to detector using a septum cat#27142 (fig 1)
  4. Seal split vent and septum purge vent using 1/8’’ brass plug cat#21816 (fig 2)
  5. Shut gas off from back of instrument
    1. If connected directly to a tank shut the gas off at the dual stage regulator
    2. For other configurations make sure the gas can be turned off, for instance use a 2-way plug valve cat#21586
  6. Pressure shown on instrument display should not drop by more than 0.5 psig over 5 minutes.
  7. If the pressure drops use a leak detector cat#22655 to find the leak 3

Check out our 20 second video here.

Using a pressure decay at higher pressures (50 psig) exaggerates any small leak in the system and makes them easy to find; even difficult to access areas will produce a signal on the leak detector. Restek’s chemists and engineers have developed a way to prevent leaks using the Dual Vespel inlet seal at the bottom of the GC inlet. This patented technology provides a leak tight seal between the bottom of the inlet and inlet seal 4. This leak check procedure is a quick and easy way to guarantee a leak tight system and assure maximize column lifetime.

Figure 2: Plug both septum purge and split vent flow.

Figure 2: Plug both septum purge and split vent flow.

  1. http://blog.restek.com/?p=8942
  2. http://www.restek.com/Technical-Resources/Technical-Library/General-Interest/general_A019
  3. http://www.restek.com/catalog/view/8175
  4. http://www.restek.com/Technical-Resources/Technical-Library/General-Interest/general_A021

*For older instruments with 30 PSI maximum pressure set to 25 PSI.

2 Responses to “Leak Checking Your GC: Leak Detector or Pressure Decay?”

  1. Marc König says:

    Maybe it is good to mention, that heaters should be turned on to have an isothermal condition.
    Even if the inlet has cooled down to room temp, some like PTVs with very low thermal mass can be influenced
    by air condition or open window!

    And maybe plugging the inlet with an blind plug is much nicer, because after all you have to reinstall the column
    and doing again the “focus ferrule on column” step…
    greets marc

  2. Marc:
    Both excellent points! A colleague of mine Jason Herrington recently demonstrated the effect of flow / temperature on a 1 liter air canister (at atmospheric) where he attached a flow meter and simply wrapped his hands around the canister and was able to measure flow leaving the can. So your point about temperature is a very good one.
    Yes it would have made more sense to attach the injection port nut on the column end with a fitting. I have found that sometimes just putting a septa on the end of the column is the source of the leak.

    Thanks for reading our blog, I appreciate your comments and wish you the best of luck with your analysis!


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