In article mctzf.740907$xm3.31868@attbi_s21,
"Dave Lyon" wrote:

See my other post for more detail. In summary: Pure acetylene at 15-ish
pounds doesn't "burn", a process which does indeed require oxygen.
Instead, it "deflagrates", a process of chemical breakdown that has no
need whatsoever for oxygen to be present in order to happen. (presence
of oxygen may in fact inhibit deflagration in some cases) The only
commonality between the two processes is that they both generate a lot
of heat.


I read your other post. Thanks, very informative. But, I have a question.
If acetylene "defagrates" at around 15 psi, how do they get it into my tank
at 250 psi or more?

Dissolved under pressure into the acetone soaked into the cylinder
media. As I understand it, your standard acetylene cylinder only has a
couple teaspoons worth of "free" acetylene at high pressure in it at any
given moment - an amount insufficient to sustain a deflagration reaction
to the point where it could be dangerous. When you draw that amount,
however much it is, out of the tank, the pressure in the tank drops,
allowing more acetylene to "boil" out of the acetone, rebuilding the
pressure, lather, rinse, repeat until there's no more acetylene (or at
least not enough to be useful) left dissolved in the acetone. Even if
that small amount of "free" acetylene was enough to get a small
deflagration reaction going, the resulting pressure increase makes it
self-damping, since the rising pressure forces more more acetylene into
solution with the acetone soaked into the cylinder media, keeping it
from being able to participate in and help perpetuate the deflagration
reaction. The "boiling" process isn't the result of heat, but a drop
below the pressure needed to keep the acetylene dissolved in the acetone
- Kind of like taking water to very low pressure. At the right pressure
for the temperature, you can get a "full rolling boil" going in a
container of water at any temperature above freezing. You won't be able
to *COOK* anything with it, but it'll look exactly the same as the pan
of water boiling away merrily on the stove at 212 degrees F. Acetylene
"boiling" out of solution to replace what you've tapped out of the
cylinder is exactly the same mechanism in operation, just working on
different materials.

Additionally, acetylene cylinder are *NOT* hollow cylinders, the way
oxygen and other cylinders are - If you were to break one open somehow
(HIGHLY not recommended outside of properly equipped facilities - unless
you *WANT* to die) you'd find that it's almost entirely filled with a
highly porous block of something that looks much like concrete. This
"rock sponge" is what soaks up the acetone that the acetylene dissolves
in, preventing you from getting spits and spurts of raw liquid acetone
coming out the end of your torch. Gaps and voids in it are a certifiable
Very Bad Thing(TM), which is one of the (if not the main) reasons that
dropping an acetylene tank any distance is a Bad Thing(TM) and grounds
for having that tank pulled from service and stored someplace
"bomb-proof" until it's been inspected and tested to be sure the
"stuffing" is still intact and working as intended. If you ever get
handed a cylinder that "rattles when rocked" (something *INSIDE* the
cylinder rattling, not "stuff attached to the cylinder") immediately
hand it back - *GENTLY* - and demand another one. The "rattler" almost
certainly has damaged media in it, and is unsafe. It's unlikely, due to
the pre-fill inspection, that you'll ever get one, but "unlikely" and
"impossible" aren't equal.

Unlike oxygen or other tanked gasses, filling an acetylene cylinder is a
fairly time-intensive task - They don't just hook it up to a supply and
open both valves then wait for the pressure to equalize - They have to
let the fresh acetylene into the cylinder at a relatively slow rate so
that it gets a chance to dissolve into the acetone. Depending on the
size, filling one properly is a process that can take anywhere from a
couple hours, to several days, or even longer for really monster-sized
ones. Failure to fill properly can easily result in a bomb that's ready
to go off at any moment, in response to any (or no apparent)
provocation. Which is why, when you take an acetylene cylinder in to be
refilled, the most common practice is to simply hand you another one,
and put the one you brought in over with the rest of the "needs to be
refilled" ones, rather than filling your cylinder "while-u-wait". If you
want *THE SAME CYLINDER* back, you're going to have to wait for a while.
But since the places that fill them have to inspect, certify, etc. etc.
etc. every cylinder that goes through, "This other randomly selected
cylinder of the same capacity" is effectively identical to "The cylinder
I own and brought in to be filled", even if it isn't actually the same
cylinder. Which means, in effect, that when Joe Sixpack "buys an
acetylene cylinder", he's not really buying the cylinder itself - he's
buying the right to use any single member of a "pool" of
who-knows-how-many of that size cylinder, any of which is effectively
identical to the one he "bought".

--
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