Helium Detector

Because helium permeates leaks very well and is easy to separate from abundant background ions in a cheap mass spectrometer.

-- Regards, Carl Ijames carl dott ijames aat verizon dott net (remove nospm or make the obvious changes before replying)

Helium is the only gas that is monatomic and therefore smaller than the diatomic, or molecular, form of all other gases such as H2, O2, N2, etc; and it will find leaks nothing else will. Art

If you've never used a helium leak detector, you don't NEED much of it. Some pros who go around large labs finding leaks use tanks just the next size up from a lecture bottle, and that lasts them months. A 5' tall tank (120 CF? 160 CF?) lasted us about 8-10 years in our lab. You let the helium trickle out of an un-sharpened hypodermic needle just fast enough to make bubbles in water.

Jon

Jon they are called "drawing up" needles. used to load a syringe with a dose of medication delivered through a very fine needle. they are made with a squared off tubular end. Stealth Pilot

Hydrogen also works, but is explosive and harder (more expensive) to detect.

Free men own guns - www(dot)geocities(dot)com/CapitolHill/5357/

Yes, but our stockroom doesn't have them, so we just grind down a standard sharp needle. It is pretty quick to do.

Jon

Argon is also monatomic, but way too big to use for leak detection.

I can't find the reference now, but as I remember the diffusion rate is 1/AT^.5( inversely proportional to the square root of the atomic weight.)

Dan

Everyone always says that, but ISTR some experiments which showed that the permeability wasn't all that different. OTOH the rarity of He other than from the leak site is a very good reason.

I think hydrogen will diffuse through insanely small holes very well, too, making it hard to keep it in sealed systems. But, it has this other property, related to hydrogen embrittlement, and adsorption on and in a number of metals, such as Ti, W, Mg, etc. Once you get H2 adsorbed onto metals, it can take years to go away if you don't cook the metal. So, allowing H2 to get into a vacuum chanber will result in a LONG time decay of the tracer gas. He has that inertness that means it won't stick to ANYTHING, and will just diffuse away as fast as it diffused in, thus making it a GREAT tracer gas.

Jon

I did a temp job at a place that made sealed opto-electro-mechanical instruments which were leak-tested with hydrogen. The H2 background level in the room was significant despite a rollup truck door that was opened several times a day.

Hydrogen doesn't use 2 atoms for a gas it uses 1. When forming the oxide of oxygen - H2O it uses two. Without the oxygen atom one would have two atoms of Hydrogen gas.

One would not want to put Hydrogen in steel pipe as stated embrittlement. So it would be He or Ne(on). are the best. Putting a tracer on one or the other would be best. Easier to trace the tracer (radio-active) than that of a atom or a bunch...

Mart> newshound wrote:

Well, no, hydrogen gas is composed of H2 molecules. Two atoms.

I do think that Artemus was incorrect in saying that helium is the only monatomic gas. There's neon, argon, krypton, xenon and radon.

Slater

Electrolysis of water does produce about twice the volume of hydrogen gas (H2) as the volume of oxygen gas (o2). Exactly twice the number of molecules. Maybe that's what you were thinking of?

Slater

On Wed, 14 Nov 2007 19:14:20 -0800 (PST), with neither quill nor qualm, SL8 snipped-for-privacy@yahoo.com quickly quoth:

True, but when encruptured by the Retro Encabulator, an additional atom of oxygen is introduced and di-hydrogen monoxide results. The toxic result has to be removed, at great cost, mind you, by the burly and spacesuited men from deep in the bowels of the EPA's Superfund.

-- Real freedom lies in wildness, not in civilization. -- Charles Lindbergh

I'll be darned.

You are right - hum - so much work in the old days with H. 1h1 2h1 3h1. But that was 40 some odd years ago.

Mart> Mart>

Hey - that isn't funny -

Just moved out of a 100 site super fund area. That map was freaky. Shown once and then hidden for all eyes but the EPA and those who did it.

Martin

Mart> On Wed, 14 Nov 2007 19:14:20 -0800 (PST), with neither quill nor

Not in the least. Both Hydrogen and Oxygen have two atoms per molecule.

Mark Rand RTFM

I'm not sure what you're disagreeing with.

Yes, gaseous hydrogen and oxygen each have two atoms per molecule, as I indicated by saying "H2" and "O2". Water, however, has two hydrogen atoms and one oxygen atom, so decomposition releases twice as many molecules of H2 as O2:

Two H2O -> two H2 + one O2

The volume of the hydrogen gas will be about twice that of the oxygen gas at STP.

Slater