Losing Hydrogen pressure when running two GCs from Generator

[dlntx9]

We are using a domnick H generator model 4 H and am having issues running two gs simultaneously using it. As soon as the valve is opened the Generator loses pressure and can not ever rebuild pressure. The fluctuations in flow cause baseline irregularities in the baseline on the GC closest to the generator. The 2nd GC is not affected. Both instruments are 5890's the one closest to the generator does not have the electronic pressure control control, GC #2 does have electronic pressure control. Right now both instruments run on Hydrogen as a fuel gas and carrier gas. No make up gas is being used. Either instrument runs fine individually, it's only when valves are running to both instruments that we have issues. I purchased regulators to place on the lines between the valves and the instruments for both the fuel and carrier on each instrument , but the regulators despite being pricey had major leak issues. I'm looking for suggestions on good inline regulators or any tips on improving the setup so that both instruments can run simultaneously on the generator. In the pictures I have labelled the lines, and where I originally had the regulators.

[Peter Apps]

Before you do anything else you need to leak check the whole system, including the internal plumbing of the GCs - the tightness of the swagelok nuts in the pictures is inconsistent for a start.

What is the rated output of the generator, and how much are the GCs expected to use ?

What is the rationale for putting regulators in the lines ? they will not increase the hydrogen supply from the generator.

Peter

[dblux_]

In my opinion the installation should work properly without additional regulators. Set the pressure in the generator for sufficient value for both instruments and the regulators are built in GC's.
Doe's your hydrogen generator have sufficient flow rate capabilities to feed two GCs ?

[KM-USA]

Look for big leak. If you don't have an electronic leak detector, you shouldn't be using hydrogen at all !!!

If no leak detector, show boss photos of the Hindenburg, that usually helps.

[dblux_]

... The fluctuations in flow cause baseline irregularities in the baseline on the GC closest to the generator...

Try to increase pressure to ca. 5 bar (provided there are no leaks).

[aidnai]

The valves pictured appear to be plug valves rather than single piece instrumentation ball valves. Is this the case? I personally would not trust plug valves in hydrogen service.
I would also try to reduce the number of fittings as much as possible, and particularly focus on getting rid of fittings between the scrubbers and the GCs.
Peter mentioned inconsistent female nut tightening. A tool that is helpful for that problem is a no-go gap gauge from Swagelok.
One more idea to check for -- depending on how the lines are cut and the ends prepared, the ID can become constricted. It should be easy to push a few SLM of H2 through those 1/8" lines, but if the ends are pinched shut...
Also, as mentioned already, leak check leak check leak check.

Good luck!

[thohry]

Hi dlntx9
You should do the leak check, every nut and joint.
Usually, the FID consumes about 40ml/min of H2, that will be no problem with 2 GC unless you use H2 for carrier gas as well.

[dlntx9]

Thank you for all the information. I have an electronic leak tester, and am not getting any leaks at any connections, however I am getting leaks on the around the controls on the front of the GC's. How common is it for these to leak, and does anyone know of any resources on rebuilding/replacing them?

[aidnai]

If your split vent and septum purge vent are piped to the front controls (normal), you may be simply detecting that hydrogen. To get a better leak test, temporarily pipe the vents farther away.
If you still have issues with leaks there, see if you can pinpoint the leak to one of the o-ring sealed fittings. The plastic male nuts as well as the O-rings are replaceable.
Otherwise, start looking for injection zone replacements (for 5890 parts I have bought from Alpha Omega technologies as well as American Lab Trading in the past, recommend either).

Aidan

[dlntx9]

Thanks Aidan, I was able to divert the the the hydrogen from the vents on the front panel, and am still detecting a leak. I'll try to switch out the o rings next and see if that takes care of the problem.

[Peter Apps]

Before you start replacing things you need to locate exactly where the leak is. Since it is probably a few hundreds of ml/min it is probably filling the whole compartment with hydrogen, so reduce the pressure form the generator to reduce the leak and make it easier to localize.

Peter