The Result of Gas Leaks #

A small leak in your GC or gas lines can result in:

1. the loss of sensitivity,
2. disrupting flow path, which causes the loss of sample,
3. the loss of valuable high-purity gas,
4. introducing oxygen into the system, resulting in damaging the column and instrumentation,
5. contaminating samples.

Gas Leak Problems? #

Transcript

Hello, chromatographers, and welcome to another Restek Tip. Let’s talk about the importance of leak checking our gas chromatographic system. It’s advice that you’re given all the time – to leak check, and leak check, and leak check again. But why? Why are we given this advice all the time? Well, the fact of the matter is with a high-pressure instrument and numerous seals and connections throughout, leaks can always crop up in a GC instrument. So, we want to be checking for them on a regular basis. But then the question is, well, so what? What’s the big deal if I do have a leak? And the truth of the matter is it is a big deal. And in a few different ways.

First, if we have a leak, we’re disrupting our flow path. That can result in loss of sample, poor chromatography, or other issues. So, we certainly want to eliminate those in order to get the best chromatography possible. But there’s another problem as well. Leaks can allow materials to get introduced into the system as well, especially compounds like oxygen. Why is oxygen a big deal? Well, oxygen is a pretty effective column killer and can damage many gas chromatographic columns. So, we certainly want to have a leak-tight system to get the most lifetime out of our GC columns.

What do we do about all of this? Well, we leak check regularly. And ideally, we use an electronic leak detector. We want to avoid liquid leak detectors. Those liquid materials can get actually sucked into the instrument through those leaks and can contribute to contamination. So, that’s a little bit of why leak checking is so important. And again, the idea of making sure that we use an electronic leak detector regularly to look for those leaks throughout our instrument. Thanks very much for joining us for this Restek Tip.

Diagnosing Leaks #

Transcript

Hi and welcome to this Restek Tip where we’ll talk about pressure decay tests for your gas chromatograph. So what is a pressure decay test anyway? It’s a test where you close off all of the means of egress out of an inlet in your GC and you pressurize it. And then you turn the pressure off. And what you’re looking for is, while you monitor the pressurized system, you don’t want to see that pressure drop because if it’s a truly leak-free system all of that pressure you created in there will have nowhere to go. And in some instruments you actually will see the pressure climb just a little bit. But if, on the other hand, you see the pressure begin to drop, well that means you’ve got a leak somewhere. So, the pressure decay test is a great way of not just trouble shooting a suspected leak, but also if you’ve done maintenance somewhere on your inlet or on the gas lines and you want to just reassure yourself that all of those points of connection are leak free then you can conduct a pressure decay test.

Like I said, the pressure decay test is a great way for determining whether or not you have a leak. But, it won’t find the leak for you. That’s where having an electronic leak detector will really come in handy. Isolating where that leak is if it’s present at all. Now, to do an actual pressure decay test for your particular instrument you will want to consult your instrument manufacturer’s literature. This is a little known but very useful technique for ensuring that you have a leak-free gas chromatograph.

Find and Eliminate Gas Leaks #

Transcript

Gas Leaks in Your GC System How to Find and Eliminate Them Featuring the Restek Electronic Leak Detector.

Even a small leak in your GC or gas lines can result in the loss of sensitivity, sample, and valuable high-purity gas. A leak can also damage your column and instrumentation as well as contaminate samples.

The Restek Electronic Leak Detector is an essential tool for troubleshooting and routine maintenance of your gas chromatograph. It should be used daily to ensure that your instrument and gas delivery systems are in top working condition. Full instructions are available at www.restek.com/leakdetector but here is a quick overview of some best practices for leak checking and maintenance.

Prior to leak checking a GC, we recommend that you increase system pressure while the GC is cool to accentuate any potential leaks and make them easier to detect. Then, after bringing the system up to operating temperature, be sure to recheck critical seals. You should leak check your gas delivery system and instrument, especially the critical seals, on a daily basis.

The septum is a common source of leaks. If the septum is leaking, simply replace it. By checking the septum regularly, you will be able to learn how long your septum generally lasts, and then avoid unplanned downtime by anticipating when to change it before it starts to leak. Incorrectly tightening the septum nut or injection port weldment after changing the septum and liner can lead to leaks. To fix a leak here, try loosening and correctly retightening the nut or weldment.

Frequently moving the injection port weldment can crack the welding around gas lines. A leak can indicate that cracks have developed and that the weldment should be replaced. Leaks around the bottom of the inlet— specifically the reducing nuts, column nuts, and detector nuts — are common, especially since temperature cycling can loosen nuts that are not properly tightened. In addition, ferrules, especially Vespel-graphite blend ferrules, tend to shrink slightly after initial heating cycles,which may also lead to a leak.

If you encounter a leak near the column nut, reducing nut, or other threaded connection, first attempt to fully tighten the nut. After the fitting has been tightened, recheck it to confirm that the leak has been eliminated. Column connectors are common sources for leaks, even if they are leak-free after initial installation. Check them regularly during use. Reinstallation may be necessary if you discover a leak.

Detector nuts from atmospheric pressure detectors such as F.I.D.s and T.C.D.s can also leak if improperly tightened or if a column breaks during installation. We do not recommend the use of a leak detector to check M.S.D. nuts because the vacuum draws in any leaking gases and prevents detection of a leak. Performing an air/water check using your mass spectrometer will indicate if there is a leak in your system.

As moving parts in valves age and wear, they can become another common location for leaks. Replacement may be necessary. After installing new gas lines, always remember to pressurize the system and check for leaks. Check for leaks any time you install new or replacement gas filters. If one of your gas filter compression fittings is leaking, check the fitting to make sure it’s in good condition. Then, tighten it appropriately. Afterwards, continue to routinely check around seals and fittings.

Leaks aren’t always immediately near your GC. After changing gas cylinders you should also check around the regulator. Be sure to check any manifolds as well.

10 Places to Check for GC Gas Leaks #

Transcript

Gas leaks are the bane of every gas chromatographer’s existence. Even the smallest leak can cause a loss in sensitivity, contaminate samples, damage columns and instruments, and lead to a lot of wasted time.

In this Restek Tip, we’re going to explore 10 places you must check for leaks to keep your GC in tip-top condition. Let’s get started!

Prior to leak checking a GC, we recommend you increase system pressure while the GC is cool to accentuate any potential leaks, making them easier to detect. You will also need a leak detector. Today we’ll be enlisting the help of Restek’s electronic leak detector. These tools are huge time savers and are very effective in helping you troubleshoot and maintain your gas chromatograph.

Now that we’re ready, let’s hunt down those leaks!

1. The Gas Supply
Sometimes the leak isn’t immediately near your GC. Always check your cylinders, generators, and manifolds. Each of these should be the first place you check when you suspect a leak. Pay special attention after installing new gas cylinders, particularly around the regulator.

2. The Gas Filter Connections
Check for leaks any time you install new or replacement gas filters. If one of your gas filter compression fittings are leaking, check the fitting to make sure it is in good condition. Then tighten it appropriately.

3. The Shutoff Valves
Moving parts can be more prone to leaking as they age and wear, so be sure to check the shutoff valves. A replacement may be necessary if you find a leak.

4. The EPC Connection
All gases enter the GC through the EPC so it’s a critical spot to check for leaks. If you find a leak, ensure all the connections into the GC are clean and secure.

5. The Split Vent Trap
Often overlooked during routine maintenance, the split vent trap could easily be the source of your leak. Be sure to check that the fittings are nice and snug. A replacement might be necessary if the leak is still present.

6. The Septum Nut
Another common source of leaks is the septum. If the septum is leaking, first attempt to tighten the septum nut, but only to finger tight. If the nut is not the source, try the septum; it may need to be replaced.

7. The Weldment and the Weldment Lines Check the weldment for leaks. If you detect a leak, it may be the result of an incorrectly tightened weldment, if so, retighten it. If a leak is still present, or detected around the weldment lines, it could indicate the presence of cracks. In this situation, the weldment should be replaced.

8. The Reducing Nuts Temperature cycling can loosen nuts if they are not properly tightened. If a leak is found, simply retighten the nut.

9. The Inlet and Detector Column Nuts Be sure to check the column nuts and fully tighten them if there is a leak. A damaged ferrule could also be the source of the leak and might need to be replaced.

10. The Column Connectors Don’t forget the column! Column connectors are common sources for leaks, even if they are leak-free after initial installation. Check them regularly during use, reinstallation may be necessary if you discover a leak.

Even if a leak is not detected at any of these spots, it is good practice to inspect and leak check your gas lines and instrument daily, paying close attention to critical seals.