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. Scott Grossman’s article, “How Much Sensitivity is Needed in a Leak Detector?” demonstrates that the sensitivity of the Restek Leak Detector may negate the need for pressure decay. 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.

Follow these simple steps:

1. Set inlet pressure to 50 psig.*
2. Cut column 10 cm from injection port and seal with a septum, cat.# 23864 (figure 1).
3. Seal column to detector using a septum, cat.# 23864 (figure 1).
4. Seal split vent and septum purge vent using ¹⁄₈’’ brass plug, cat.# 23113 (figure 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.# 23261.
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.# 28500, to find the leak.

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. 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.

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