Lighting a gas pipe

[Bod]

:-)

[Tim+]

Right, so you have to add excess air at a point upstream of the flame. How are you going to do this with your gas meter?

Tim

[Bod]

Of course, as an ex plumber and gas fitter, I wouldn't have a clue, would I, but then Harry knows everything. You've just accused me of *coming to conclusions*, whereas you've just done exactly that.

[Nightjar]

On 20/12/2013 08:15, harryagain wrote: ...

No comment.

Colin Bignell

[Uncle Peter]

What? And sets fire to the rubber hose? Never managed that when I was at school. Adjusting the air (I assume you mean the vent at the bottom of the Bunsen burner) only changes the flame to orange and burns cooler.

[meow2222]

Burning of gas & air produces considerable expansion, hardly a recipe for drawing more oxygen in

[Tim Watts]

On Friday 20 December 2013 09:17 [e-mail] wrote in uk.d-i-y:

CH4 + 2.O2 = CO2 + 2.H2O

So 3 volumes of source produces 3 volumes of product at constant temperature. (Avogadro's Law)

And as the product is a *lot* hotter than the source gases, burning methane causes rapid expansion - no way is that going to be able to suck air back down any normal pipe.

Acetylene is rather different and needs flashback arrestors - I would welcome an explanation as I've never known why :)

[Bod]

Ask Harry, he knows everything :-)

[Uncle Peter]

C2H2 + 2.5 O2 => 2 CO2 + H2O (I think) That's a reduction in moles from 3.5 to 3.

[Onetap]

If you turn the acetylene pressure down and oxygen pressure up and you can get oxygen going back up the acetylene hoses. You could then have an explosive mixture of fuel and oxygen.

I think that's what happens, it's a long time since I've done any gas welding.

[Uncle Peter]

Can't you get a regulator which mixes them correctly in the first place?

[John Williamson]

You also have blowback preventers (Effectively, non return valves) on the pipes.

You need two separate regulators due to the way most people use their gas kits.

[Tim Watts]

On Friday 20 December 2013 11:45 Uncle Peter wrote in uk.d-i-y:

Not relevant - please google Avogadro's Law...

[Tim Watts]

On Friday 20 December 2013 12:17 Onetap wrote in uk.d-i-y:

Ah - I see... Presumably partly because IIRC the acetylene gas is not liquified but rather dissolved in another liquid? So it could well be bottled at a pressure much lower than the O2 is compressed in its bottle.

[Uncle Peter]

What I read said the "number of molecules". This has been reduced by a seventh.

[Uncle Peter]

Even if not, if the pressure valves are a fair way back from the jet, you've got all that hose at lower pressure because you set it lower.

[Huge]

Decent kit has blowback preventers in the gas lines ...

[harryagain]

Your ignorance astounds me.

[Uncle Peter]

Why have you posted vague articles nothing to do with the above scenario?

[jrwalliker]

And the reason it is dissolved in a liquid soaked in inert powder is that acetylene spontaneously decomposes at high temperatures and pressures, releasing heat which makes it decompose faster ... etc.

So a detonation can propagate down a pipe filled with acetylene without any oxygen being present. This property is also what makes it so useful for welding - the flame deposits a lot of heat in the work.

John