CGA handbook, states that carry over begins at around 25PSIG. Gas
Pressure(acetylene in this case)will remain almost constant at a
given temperature. As you withdraw the acetylene from the solution
in the cylinder till very little remains. If you are taking the
gauge pressure down on the acetylene cylinder to below 25psig it can
cause acetone to be withdrawn with the gas.
Most books and courses, state is that is the suggested cut off of
use of the cylinder. 25 psig to 50 psig to minimize, acetone carry
over. Since the acetone in most tanks of an age over 5 years or more
isn’t what we think of acetone. They don’t change the acetone out in
the cylinder, just add fresh. So over time with the aging of the
fill material and changes dues to the loading and unloading of the
acetylene gas it gets thicker over time sort of approaching syrup.
At these lower pressures, the amount of solvent expelled is
dependent on the solvent vapor pressures, the condition of the
cylinder, and the conditions of withdrawal. The condition of the
cylinder is the inside and the number of charge discharge cycles, As
the solvent can be come thick with age,impurities and cycles etc.
Which has an effect on the impurities in the gas and then in the
liquid. There are two, acetone and Dimethylformamide DMF a polar
(hydrophilic) Aprotic solvent. Today, the gas is shipped and stored
in metal cylinders containing acetylene, dissolved in
dimethylformamide (DMF) or acetone.
A couple of other things that should be cleared up, are if you have
traveled with your B or MC cylinder laying down on its side. You
must place it in an upright position so the acetylene gas gas
reabsorb into the filler, and prevent carry over of the liquid into
the regulator,torch and flame. Which can cause contaminate the joint
you are working on. Not too mention the effect on the flame.
Something else that is often stated incorrectly is that the material
filling the inside of the cylinder is only part way that is
incorrect. As the material fills the cylinder, but it is extremely
porous. This along with the fill rate(dissolving rate into the
solvent 7 hours for a full charge, is were the 1/7 use rate comes
Agamassan (aga) is a porous substrate used to safely absorb
acetylene/solvent and thus allow the transport, storage and
commercial exploitation of an otherwise unstable gas. Asbestos was
only used by a limited number of cylinder makers for a few years,
and the Compressed gas association has very good records on them.
Since the rate of use is one seventh of the capacity per hour as the
acetylene comes out of solution. As it takes 7 hours to fill the
cylinder or put the acetylene in solution with the liquid in its
Acetylene cylinders are filled to 225 psig. That is a full cylinder.
The critical pressure is 15psig for acetylene in the atmosphere.
That is why it is pressurized and dissolved in acetone so the tanks
can hold a use able amount of acetylene. It becomes very unstable at
or above that pressure.
Ask for and carry in you vehicle, a MSDS at all times, in the glove
box. In case you are stopped, and they see it.
Just for fun did you know that a B cylinder refers to its old times
use as the size of cylinders used on buses, in the days before
electrical lighting on vehicles.
Am MC cylinder refers to Motorcycle as this size was used on the
cross member of the motorcycle hence the angled valve. To provide
lighting in the good old days.