Questions on refilling Hydrogen tank

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Corby Dawson
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Questions on refilling Hydrogen tank

Post by Corby Dawson » Tue Sep 11, 2018 11:31 pm

Hi,

First some background. I have an instrument that has a small Hydrogen tank inside. It runs 24/7 and a tank usually last 3 or 4 years. At that point I pull the tank (which still has some pressure), attach it to a manifold with a bleed port and a source tank. And after bleeding Hydrogen through to clear the manifold I close the bleed port and refill the small tank. The source tank is filled with ultrapure scientific grade Hydrogen gas.

I am getting stuff ready to replace the instruments tank and regulator assemblies and have a couple questions. I don't know how the supplier of the source tank did it (does anyone know?) but I need to make sure that there are no residual gases in the new tank to contaminate the Hydrogen. If I hook my turbo pump system to the manifold and pump down the tank before refilling would that be good enough?

Thanks!

Corby

John Futter
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Re: Questions on refilling Hydrogen tank

Post by John Futter » Thu Sep 13, 2018 3:30 am

I would leave a bit of hydrogen in the tank --just positive pressure so as to 2nd guess the idiot at the depot who will crack the valve to make sure it is nearly empty. This save air being sucked back in

John Myers
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Re: Questions on refilling Hydrogen tank

Post by John Myers » Thu Sep 13, 2018 4:37 am

At work, for our GC instrument we only pump down the internal CYL before filling if the pressure is too low. Otherwise we just purge the fill manifold and instruments regulator/plumbing before filling.

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Dennis P Brown
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Re: Questions on refilling Hydrogen tank

Post by Dennis P Brown » Thu Sep 13, 2018 10:02 am

Depends on how pure you want the gas in the tank and what contaminates are more or less acceptable (assuming worse case and the new empty tank has some air.) While a a turbo will easily get you to bottom out 10^-6 torr or better (likely) the issue is water being on the walls from the possible air exposure. Short of a bake out, this isn't going away any time soon. If trace water well below 1 ppm is acceptable, certainly the turbo will do the job. If that is an issue, than a mild bake out should be considered during pump out with the turbo.

Corby Dawson
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Re: Questions on refilling Hydrogen tank

Post by Corby Dawson » Thu Sep 13, 2018 11:54 pm

Thanks for the inputs!
On the existing tank I never let it get empty before topping off and bleed the manifold before admitting new gas.
This is a spanking new tank so does have air in It!. :-(
I've never come across any caveats about H20 levels but I'll take your advice and do a mild bake out prior to the filling.
Then I'll be good for 4 or more years!
I had been refilling the original every 3 or 4 years whenever the high pressure gauge got low.
However the last time I filled it the high pressure gauge read zero even though the manifold gauge read 1200PSI.
Looking over the source bottle readings when I refilled it the last 3 times I realized that the gauge has been failing all along and the bottle actually had way more pressure than I thought!
I probably will get by refilling every 8-10 years!
BTW the instrument (an active Hydrogen Maser) is currently 36 years old!

Cheers!

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