Loss of Precious Gas

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myID
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Loss of Precious Gas

Post by myID » Fri Jul 09, 2010 11:38 am

Hi-

I have a Linde Minican with the "Druckminderer mit Dosierventil".

http://www.linde-gase.de/produkte/gase_ ... nican.html

I am wondering if I loose more Gas if I connect the pressure reducer like once in a month and then deconnect it again after my short experiment (each time an expensive Pfffft...) or if Id better leave it connected?
Anybody any idea how much gas leaks out of the regulator when connected?
I am worried to leave it connected for a month or 2 without using it and then finding my bottle empty...

Thanks for saving me money
Greets

Tyler Christensen
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Re: Loss of Precious Gas

Post by Tyler Christensen » Fri Jul 09, 2010 4:18 pm

I would suggest leaving the pressure regulator on all the time, there is no good reason to take it off and it costs a lot of gas. Just make sure you always close the bottle's valve and there is no real concern there. Even while running my reactor, the bottle is closed, I'm just using what's left in the regulator body which can last for hours of experimentation. Then when I'm done, everything is closed up, regulator is turned off, and if I come back in a few weeks, the pressure reading on the high pressure side has not changed, no gas was lost. If this side goes down over time, then it indicates a leak somewhere that could be repaired. It is normal for the low pressure side of the regulator to slowly leak, but the high pressure side shouldn't.

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Doug Coulter
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Re: Loss of Precious Gas

Post by Doug Coulter » Fri Jul 09, 2010 4:32 pm

Yes, Tyler is correct in all regards. If I thought my regulator leaked, I'd get another right away for cheapness and uh, safety. I find with a pretty good (expensive too) one here that the low side pressure creeps up slightly over days, but that's not an issue (say, from 10 psi to 12 over 3-4 days), and yes, I just open the tank valve for a second and run all day on that unless I'm deliberately flushing the system to drive out other stuff.

To get there, the pump-out rate needs to be controlled well, and you should have that if you don't want to waste much gas during runs, either. I am running a variable speed turbo with a conductance valve on the input side, a solenoid valve between it and the forepump helps even more -- a short open pulse on that once in awhile controls the whole thing nicely.

I think Tyler is running a diffusion pump on a light dimmer -- same idea. Easy to pump so fast you need to flow "too much" gas through to keep the pressure in the desired range with a system that is otherwise "right sized" to get to good vacuum and purity in the first place, hence these tricks.
Why guess when you can know? Measure!

myID
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Re: Loss of Precious Gas

Post by myID » Fri Jul 09, 2010 5:19 pm

Thank you for the answers but the Minican does not have a "bottle valve". So I am afraid of leakage in the regulator. It just has a knob on the low pressure side of the regulator.
Still same suggestions?

Thanks
Roman

Tyler Christensen
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Re: Loss of Precious Gas

Post by Tyler Christensen » Fri Jul 09, 2010 5:29 pm

So is this bottle like a propane can where by engaging the fitting it opens the bottle? I would still avoid taking it off, just make sure you keep a close eye on the high pressure needle, especially over the first few days. If it starts to drop when you're not using it, definitely take it off, otherwise i would personally leave it on. Of course at any point it could become physically damaged or just wear out somehow and waste all the gas, I guess it comes down to a trade off between "insurance" versus a slight loss of gas every time you use the system. Your call to pick your preference.

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Re: Loss of Precious Gas

Post by Jerry Biehler » Fri Jul 09, 2010 5:29 pm

Either way you are dealing with rubber seals wether its the neck of the bottle or inside the regulator. You are probably just as likely to leak from the neck valve as the regulator is likely to spontaneously leak.

In other words leave it on.

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Doug Coulter
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Re: Loss of Precious Gas

Post by Doug Coulter » Fri Jul 09, 2010 5:57 pm

I'm kind of surprised no one has yet suggested an old standby here -- dunk the whole mess in a bucket of soapy water and wait and see if there are bubbles (shake off any bubbles stuck to it during immersion first). That will catch any fast leak. If you use a good diswashing detergent for the soap, the bubbles last awhile and you can just check back later...

I've had propane cylinders that leaked less with the regulator on than off....The dumb little schraeder valve leaked but the seal to the torch head stem didn't.
Why guess when you can know? Measure!

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Re: Loss of Precious Gas

Post by Wilfried Heil » Fri Jul 09, 2010 7:38 pm

Roman,

I have a couple of these bottles and regulators, but none with deuterium in it. The recommendation by Linde was to leave the regulator on the bottle. The neck seal isn't perfect either and you will slowly lose some gas in any case.

Make sure to close down the regulator's low pressure valve when it's not in use. If you are using Tygon tubing, which is quite leaky for hydrogen, you can quickly lose all of your gas by diffusion through the tubing if it is kept under pressure.

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Re: Loss of Precious Gas

Post by John Futter » Fri Jul 09, 2010 8:58 pm

Roman
We use these cans all the time @ work with gasses far more expensive than D2.
We try to leave the cans on the system for as long as possible N15, O18, He3, CO with the C being C13 are hideously expensive. All piping from the can is swagelock one eigth" SS and we leak check from the leak valve right up to the regulator valve.
If your piping is plastic replace it with SS

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