Stubborn air leak

[wenleonard]

I got an inlet pressure shutdown a few days ago, and since have been trying to return my system(Agilent HS 7697A, GC7890A, MS5975C) to airtightness. Yesterday I got the whole system connected and passing an air and water check. However once I returned the inlet, transfer line and headspace temperatures to normal (I had it cooled so I could do maintenance) my air and water check won't even finish the peaks are so noisy. I disconnected the transfer line to see if I can get just the GC/MS air tight again, but I am at a loss on where the leak is coming from. When I spray compressed air around common leak points I don't get any response, but it seems to be a large leak so I should get something. Also note that the original shutdown occurred right after the He gas cylinder was changed. Any help is greatly appreciated!

[Peter Apps]

You need to check for leaks with a leak seeker of some sort.

If you already have very high air levels then spraying compressed air around fittings is not going to produce a change. You could try with compressed freon or dichloromethane vapour instead of compressed air, but a leak seeker is by far the best for this kind of troubleshooting.

Peter

[wenleonard]

The compressed air I have is dichloromethane and you are correct it was difficult to see any change since the masses were fluctuating too frequently. A leak seeker would be nice but the price is out of the labs budget for now.

I think it may be an external leak. If I cut the system off at the MS and column or at the inlet I get a leak free system. The minute I attached the transfer line I get an issue. The inlet with the transfer line attached passes a leak check and I ran the headspace through the restriction and pressure decay test. Initially it would fail and say <<<<STOPPED>>>> Helium configured N2 detected. I switched the configuration to N2 gas just so it would run the pressure decay test. It passed that and the cross port leak check. I did a pressure drop test on the supply of Helium and got a drop of around 2psi in 5 minutes.

When the GCMS is connected to the headspace I get and air and water check like this before it fails:

https://drive.google.com/file/d/0B7ZnVv ... sp=sharing

Does this look like an external leak? And if anyone has had a similar experience advice is much appreciated.

[Peter Apps]

"The compressed air I have is dichloromethane" ??!!

From your testing so far it looks as if the leak in somewhere in the headspacer, or at the connection of the transfer line to the inlet. How are you making that connection ?

Peter

[James_Ball]

The compressed air I have is dichloromethane and you are correct it was difficult to see any change since the masses were fluctuating too frequently. A leak seeker would be nice but the price is out of the labs budget for now.

I think it may be an external leak. If I cut the system off at the MS and column or at the inlet I get a leak free system. The minute I attached the transfer line I get an issue. The inlet with the transfer line attached passes a leak check and I ran the headspace through the restriction and pressure decay test. Initially it would fail and say <<<<STOPPED>>>> Helium configured N2 detected. I switched the configuration to N2 gas just so it would run the pressure decay test. It passed that and the cross port leak check. I did a pressure drop test on the supply of Helium and got a drop of around 2psi in 5 minutes.

When the GCMS is connected to the headspace I get and air and water check like this before it fails:

https://drive.google.com/file/d/0B7ZnVv ... sp=sharing

Does this look like an external leak? And if anyone has had a similar experience advice is much appreciated.

Is it possible you got a Nitrogen tank instead of a Helium tank attached to the system. They both use the same fitting so it is possible (and I have done it before myself).

[wenleonard]

I switched the tank out to rule out a contaminated tank and both tanks are helium tanks. Where I am from bottled compressed air is actually compressed difluoroethane, but we still call it compressed air.

[Peter Apps]

Since the leak appeared when the headspacer, transfer line and inlet were heated you might get some indication where the leak is by cooling them all down again and heating them one by one.

Peter