The design of the mixers and tips is slightly different for each
fuel gas, and yes, it really does matter. Acetylene in a
natural-gas tip is actually quite dangerous.
With some, especially larger torches, this can be true, since
larger orifices such as sometimes found on natural gas torches can
let an acetyelene flame flash back into the torch body, or
conversely, the tips designed for acetylene, especially smaller ones,
can be difficult to light with natural gas, which prefers larger
orifices or multiple ones.
What exact type of torch do you have? You mention a "micro torch".
Do you mean a "little-torch"?
There are a number of different incarnations of that beast,
depending on which fuel gas they're intended to use.
Yes, sort of. The torch body, hoses, and tips are all the same. The
things that change are available hose connectors and regulators sold
for different fuel gasses. The Smith Little torch itself, or the
tips, are NOT made differently for different fuel gasses. The
instructions supplied with the torch actually tell you the various
fuels you can use, and it ranges from acetylene, or hydrogen, to
natural gas mapp, or propane, all with the same torch and tips.
However, not all the tips are equally usable. The three smallest
size tips are useful with hydrogen or acetylene, but are virtually
useless with natural gas or propane, since you simply cannot keep
them lit. (well, you can sort of light the #3, but it’s really not
good for much beyond perhaps polishing wax models. All of the larger
tips will work safely with any of the fuel gasses, though you may not
need them all the same. With acetylene or especially hydrogen, for
example, the largest tips may be simply too much for the usual jobs
that torch is asked to do, whereas with propane or natural gas, that
number six or the number seven if you special ordered it, may be the
most used tips.
But beyond the different usability, there is no design difference in
the Little torch tips for use with different gasses. (their long
"casting/melting" tip with it’s multi orifice tip may be an
exception. I don’t know, as I don’t have one) And most of the time,
in fact, the hose connectors are the same as well, since most
regulators, even for different gasses, use standard size connectors.
If not, adapters are easily available.
By the way, this situation is not unique to the Little torch, though
that was the one I believe she mentioned. The meco midget torch, for
example, is also fine with a variety of fuels. I use mine with
propane or natural gas for jewelry, but one time I needed to do some
welding, and didn’t have a proper welding torch. You could get
different tips at that time, and acetylene tips were available. The
only difference was just that the acetylene tips were a single
orifice. But you can also get natural gas tips that are the same, and
work just as well with acetylene. Only the multi orifice tips
designed for natural gas or propane don’t work so well with acetylene
(though I doubt there’s any safety issue with them. They just don’t
work as well). With oxy/acetylene, the meco midget is a bit short for
comfortable welding, as your hand is somewhat close to where you’re
welding. You can get a longer neck to fix that. But the tips and
torch body remain the same.
With different fuel gasses, you DO need some changes. Regulators,
for one thing, are not totally interchangeable, and working pressures
for the oxygen and fuel will be different with different fuels. And
for safety, you need to know the right settings to avoid flashbacks
and the like, as well as just getting good results. But in the case
of the Little torch (and I suspect it’s close imitators too), I
believe your worries simply aren’t justified. I’ve used my little
torches with all four of those mentioned fuels at various times,
pretty much interchangeably, and the instructions from Smith verify
that this is fine to do.
In your defense, you’re correct in some cases, especially with
larger torches, and those torches intended originally just for use
with natural gas, especially those wanting natural gas and compressed
air rather than oxygen. Switching those to use oxygen can be a real
problem. That’s as much or sometimes more a concern than switching
fuel gasses. The other common issue with switching fuel gasses is
that standard acetylene welding hoses are not compatible with
propane or natural gas, so you need to use hoses specified as Ok with
propane or natural gas if you use these fuels (those hoses, though,
are fine with acetylene too.) So your cautions are indeed sometimes
quite correct. Just not, I think, in this particular case with the