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Posted by Peter Fairbrother on September 7, 2008, 7:23 pm
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Curt Welch wrote:
> This is all very good stuff and I feel I need to read it a few more times
> to really get it all. Thanks for posting it.
>
> You talked about a lot of things that explains why we need to keep the
> pressure low to keep it safe. But the more complex question is that in the
> tank valve and high pressure side of the regulator, there is higher
> pressure acetylene. What keeps that safe? Is it the volume issue? Do
> they have to take care to not use passage ways and pipes which are too
> large to keep it safe?
>
> What about the guy that started this thread who is using a splitter on the
> high pressure side of the flow to allow one tank to feed two regulators?
> Is there danger in that if it's not designed correctly for that
> application?
I've been trying to avoid answering these questions, because I don't the
which answer is correct - but here goes.
Yes, the volume, or rather shape, and the materials the mainfold/bottle
space is made from (bottle spaces are very small, the porous stuff
almost completely fills the bottle) are important, and if small enough
and the right shape, material etc this will prevent any detonation
spreading. See my next email for more details.
The other possible answer is the minimum energy issue - it takes a
minimum amount of energy to cause a detonation in acetylene, and it's
unlikely that that amount of energy will ever be available in a
manifold/bottle space.
The real answer is probably a mix of both, tending towards the first -
the second is not reliable all by itself.
>
> Some wording I found in an MDS sheet for acetylene on the internet seemed
> to imply that flow rates were connected with the danger which implied to me
> part of the issue was controlling the amount of turbulence in the flow.
Two points about flow - the first point is the rate of flow from the
bottle. The bottle is completely filled with porous stuff, with acetone
coming about half-way up, in which the acetylene is dissolved. When the
bottle is opened the acetylene fizzes out of the acetone, a bit like
opening a coke bottle but more so.
The acetone is removed from the fizz by the extra porous stuff.
However if the flow rate is high enough, more than 1/7 the capacity of
the bottle per hour, acetone can be forced into the regulator, hoses
etc, which has all sorts of nasty effects, some of which can be dangerous.
The second point about flow is flow in tubes. There are three main
possible effects, the first is particulate impact, where a particle of
dirt or dust gets accelerated by the flow then hits an obstacle - this
can release a lot of energy locally, maybe enough to cause a
deflagration or even a detonation, though the latter is unlikely.
The second effect is adiabatic heating, where some acetylene is at a
lower pressure and then gets quickly raised to a higher pressure - this
causes the gas to heat up. It's most common when opening valves, and is
why you should open valves slowly.
The third effect is about turbulence, as you guessed. This can cause
local areas to get hot, or higher pressure, or both, when opposing
subflows meet. It's complicated, as it involves mathematically
unpredictable ("chaotic") phenomena, but basically keep flows slow. This
in contradiction to the need to keep passageways small, but the
manufacturers have worked it out, usually by hard experience.
>
> I need to re-read what you posted and think some more.
>
> Obviously, the big point is that acetylene is just unstable stuff and wants
> to fall apart releasing lots energy in the process and the higher the
> pressure and the larger the volume, the more risk there is that it will do
> just that.
Indeed.
Though it can also release energy slowly, which is more likely to kill
or injure than a fast detonation nowadays, what with all the safety
stuff the acetylene equipment manufacturers do to prevent detonations.
But then you usually have time to do something about it (turn off the
valve if you know it's safe to do so, eg in a hose blowback, it usually
is, then get out and call the fire brigade: however if the bottle is
rocking and getting hot, just run!), unlike a detonation :)
-- Peter Fairbrother
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Posted by Peter Fairbrother on September 9, 2008, 9:13 pm
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Peter Fairbrother wrote:
> Acetylene can burn with air or oxygen,
> forming carbon dioxide and water:
>
> C2H2 + 3 O2 -> 2 CO2 + H2O (+ heat)
Duh !!!
2 C2H2 + 5 O2 -> 4 CO2 + 2 H2O (+ heat)
My apologies,
-- Peter Fairbrother
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Posted by Martin H. Eastburn on September 9, 2008, 10:34 pm
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4C, 4H, 10O -> 4C, 8O, 4H, 2O. Matches.
No fair using quarks and imaginary particles. :-)
Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/
Peter Fairbrother wrote:
> Peter Fairbrother wrote:
>
>> Acetylene can burn with air or oxygen, forming carbon dioxide and water:
>>
>> C2H2 + 3 O2 -> 2 CO2 + H2O (+ heat)
>
> Duh !!!
>
> 2 C2H2 + 5 O2 -> 4 CO2 + 2 H2O (+ heat)
>
>
> My apologies,
>
> -- Peter Fairbrother
----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
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Posted by Peter Fairbrother on September 9, 2008, 10:55 pm
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Martin H. Eastburn wrote:
> 4C, 4H, 10O -> 4C, 8O, 4H, 2O. Matches.
> No fair using quarks and imaginary particles. :-)
But if we are using quarks and imaginary particles, and presumably
quantum foam as well, then (very) small microdetonations are going on
all the time! Everywhere!
:-)
- Peter F
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Posted by Peter Fairbrother on September 9, 2008, 11:06 pm
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Peter Fairbrother wrote:
> Martin H. Eastburn wrote:
>> 4C, 4H, 10O -> 4C, 8O, 4H, 2O. Matches.
>> No fair using quarks and imaginary particles. :-)
>
> But if we are using quarks and imaginary particles, and presumably
> quantum foam as well, then (very) small microdetonations are going on
> all the time! Everywhere!
and how could it be unfair - it's how the universe behaves, and fairness
doesn't come into it.
(this has nothing whatsoever to do with acetylene safety, or welding -
maybe)
-- Peter not-fair-brother
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> to really get it all. Thanks for posting it.
>
> You talked about a lot of things that explains why we need to keep the
> pressure low to keep it safe. But the more complex question is that in the
> tank valve and high pressure side of the regulator, there is higher
> pressure acetylene. What keeps that safe? Is it the volume issue? Do
> they have to take care to not use passage ways and pipes which are too
> large to keep it safe?
>
> What about the guy that started this thread who is using a splitter on the
> high pressure side of the flow to allow one tank to feed two regulators?
> Is there danger in that if it's not designed correctly for that
> application?