Milt F. (thats me) wrote…
"What I have just described is true for propane tanks, but
not oxygen and acetelyene tanks, which do not have relief valves
because O2 and acetelyene behave differently from propane. I
would never bring a 20lb propane tank into my house!"............
And then James Binnion responded …
"All pressurized gas cylinders have over pressure vent
valves including oxygen and acetylene otherwise they are bombs .
Look for the little hex shaped cap with the holes in it on the
opposite side from the threaded receptacle where your regulator
screws into the valve body that is the relief
This is a bit of a dry topic, but I feel that it is worthwhile
setting the record straight for those who can hang in there long
enough to read it.
Both of the above are correct. All pressurized gas tanks have some
sort of pressure relief built into them. That is the law in North
America and hopefully the rest of the world. Propane tanks have a
spring loaded relief valve that pops open at a certain high
pressure and then snaps shut when the pressure in the tank drops to
a safe level.
Oxygen and acetylene tanks DO NOT have spring loaded relief
valves. They do however have pressure relieving devices that do not
reclose once they are open. This means that once they open, the
entire contents of the tank is released.
Oxygen tanks have a device known as a rupture disk (also called
burst disk or frangible disk). When an oxygen tank exceeds a
certain safe pressure, the rupture disk ruptures and allows all of
the oxygen to escape. It does not reclose and has to be replaced by
a qualified person. An oxygen tank will generally only overpressure
if it is exposed to extreme heat, such as a large fire. Leaving it
out in the sun can not cause an overpressure as with propane.
Acetylene tanks are equipped with a different device called a
fusible plug. This is a plug that is set into a threaded hole in
the tank. The plug is designed to melt when exposed to high heat
from a fire. The plugs melt at somewhere between 205 to 240 F
depending on teh age and style of the tank. Once the plug melts it
does not reseal, therefore the entire contents of the tank are
You might wonder if its a good idea to empty an entire acetylene
tank into a fire. The bottom line is that it is better to feed the
fire than to have the tank explode and the pieces fly hundreds of
The reason that different tanks have different relief devices is a
function of the properties of the gasses that are stored in these
tanks. (by the way I am referring to B tanks, and other typical
welding/soldering sized tanks)
Propane is mostly liquid at its storage conditions, and vapourizes
as it is drawn from its storage tank
Oxygen is a gas at 2200 pounds pressure
Acetylene is unstable and likes to explode under pressure, so it
is actually dissolved in acetone and comes out of the acetone
solution as you use it.
Most of these devices are similar to oressure relief devices that
are found in a typical refinery or chemical plant (which I design
for a living when I am not in my basement crafting jewellery)
Hope that some of you got to the end of this and found it