Scary problem w/ acetylene torch
D. scott snyder
someone in this newsgroup can help. The torch is an older Presto Lite
model equipped with a casting tip. When I first got it, it worked OK.
Lately it has been burning dirty, with much soot and no inner blue
flame. Occasionally,the flame even burns back into the air intake!
What is going wrong?
Dr. Scott
David Piccoli
gun barrels;
Or buy a new nozzle for $15
Soulman
================================
RRKDB
hose, and the torch handle for about 125.00. You are describing back flash,
this is very dangerous, as there is generally no mechanism in the torch body to
prevent this.Typically oxy/acetylene set ups will have a device built into the
body to prevent back flash.
ted.f...@virgin.net
Id like to add a little here about the problems of flashback. this is
due to the user having a too low an oxy/ acetylene pressure for the
torch tip. As I mentioned before acetylene has a very fast flame rate ie
you need the gas pressure to give you a faster gas flow than this flame
rate for the size of the tip. any competent torch maker will have
available the appropriate gas pressures for each tip size. Not to have
these available to the user is seriously negligent.
Like all technologies in our craft you have to do your research first on
the equipment your using. I have a torch here from the 1920's and inside
its wooden box is the label with the gas presures for each tip size
therin.
Ted Frater.
Peter W. Rowe
wrote:
>>Id like to add a little here about the problems of flashback. this is
>>due to the user having a too low an oxy/ acetylene pressure for the
>>torch tip. As I mentioned before acetylene has a very fast flame rate ie
>>you need the gas pressure to give you a faster gas flow than this flame
>>rate for the size of the tip. any competent torch maker will have
>>available the appropriate gas pressures for each tip size. Not to have
>>these available to the user is seriously negligent.
>>Like all technologies in our craft you have to do your research first on
>>the equipment your using. I have a torch here from the 1920's and inside
>>its wooden box is the label with the gas presures for each tip size
>>therin.
>>Ted Frater.
All very true, Ted.
But if you, and the prior poster will refer again to the orignal question,
You'll perhaps note that the torch in question is a prestolite air/acetyelene
torch. These torches do not use an oxygen, or compressed air supply. Air is
mixed with the acetyelen from the tank, only at the torch tip itself, being
introduced when the fuel gas is put through a small orifice feeding the tip.
The "downwind" side of the orifice has side vents to the atmosphere, so the gas
jet from the orifice into the remainder of the tip acts as a venturi, and this
is what mixes air into the tip. It's a fixed ratio, and the torches are
designed to be not exceptionally sensative to gas pressure, once you're past the
minumum required to light the things. At a very low gas flow, you can barely
light it and it will be a rather yellow flame, Anything past that, and the
flame characteristics stabilize, and then just get larger as the gas pressure is
increased. Because the prestolite torch does not have an air supply hose,
barring a leak at the regulator which somehow manages to introduce air into the
actylene mix, the possibility of a flashback with this type of torch is very
very small, since the flame cannot burn back into the torch body or hose unless
there is air there to burn it. These torches do not supply air that can then
get backwards into the torch body or hose.
A much more likely explanation of the problems being experiences is that for
some reason, air intake at the tips is being interfered with. The usual cause
I've seen is dirty or clogged orifices, which interfere with the symmetrical gas
jet needed for the venturi to work right. And it cuts down on gas volume, which
further impedes the proper flame mix. The result is a too soft, yellowy, very
sooty flame. If the problem with the orifice is just dirt, it can be cleaned.
Often it is corrosion, and when this is the case, I've seen it affect all the
various sized tips for such a torch, as all were stored together, and whatever
the external agent was which caused the corrosion, it affects all the tips.
That can make it confusing as it might seem unlikely that all the tips would go
bad simultaneously. In the case I'm familier with, the jeweler had been testing
gold content, and spilled a few drops (just a few drops) of acid. Apparently,
they ended up in the drawer where the torch tips and similar supplies were kept.
Everything in the drawer capable of corrosion from acid fumes was affected. The
problem described can also be caused by low gas pressure, perhaps due to a
faulty regulator, or leaking hoses (which you'd then smell as a gas leak,
usually) or a faulty torch handle valve. But I'd look first at the orifices on
the tip(s).
Peter Rowe
ted.f...@virgin.net
On the subject of torches.......
Over here in the UK the "torch industry" for the jewellery trade and
other trades needing hand held heating, didnt develop the torch that
uses acetylene on its own like you describe.
Looking a little at the history over here of heat for jewellery, its was
when the general availability of towns gas ( coal derived) that the use
of charcoal and blowpipe were replaced by this gas with the addition
compressed air.
this has in fact continued in use till today. When acetylene became
available it was not used in the jewellery trade as it was considerably
more expensive than coal gas.
It was only when the oil industry developed propane as a byproduct along
with butane that hand held torches burning propane and air like you
described for acetylene were developed here in the uk. Propane is still
very much cheaper here in the UK. For example I get deliverd from 40
miles away 4 by 47kg full propane cyls for $150.00 inclusive!!! with no
cyl rental.. Acetylene is 20 times as much for the same btu's.
Apologies for not knowing about your prestolite acetylene torches!!
Ted Frater.