Re: Splitter on Acetylene tank

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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