smith torch question/s

Hi,

I have managed to by a smith little torch, and am trying to run it on LPG
and Compressed air (one of the local jewellers reckons it can be done.)
He claims that with LPG at 2.8kPa, and compressed air at 20 PSI (or mouth
blown) I should be able to get a small tight cone on a #5 tip.

What I am seeing with my current set up is:
LPG at 2.8kPA the flame tends to not stay at the tip of the torch... the
moment I introduce any air, the flame leaps off the end of the tip, and
blows out... my air has been at between 1-11kPa. Varying the pressure of the
air seems to make no difference on the flame colour or shape, but adjusting
the air control on the otrch certainly take s the flame further away from
the tip.
The flame is a long (4") flame, medium blue in colour, with a upward curve
and a yellow brushy tip. As it moves away from the tip, the base of the cone
opens larger (visualise a cone with the apex at the torch tip.)... changing
the tip (3 -6) makes no apparent difference.

the manual for the smith doesn't mention plg and air at all, but in the lpg/
o2 sections it talks about pressures in the region of 2-8 PSIg. - quite a
bit more than I am running.
I would have expected the increase in pressure to make things worse, not
better... Can any one shed light in this?

I'm seriously considering taking the torch to the jeweller and asking him to
set it up in his workshop and get him to check the operation of the unit
(blockage in a pipe maybe??)
I did try the mouth blowing on the air line, and I witnessed the same
"blowing out" of the flame.

I saved up to get this, and I'm quite dissapionted it's not working as well
as I'd hoped.

Thanks,
Des bromilow

On Mon, 27 Sep 2004 18:53:17 -0700, in @õ "Des Bromilow"
wrote:

Hi,

I have managed to by a smith little torch, and am trying to run it on LPG
and Compressed air (one of the local jewellers reckons it can be done.)
He claims that with LPG at 2.8kPa, and compressed air at 20 PSI (or mouth
blown) I should be able to get a small tight cone on a #5 tip.

I think your friend is wrong. I've never seen a smith little torch run with
compressed air. Always, they're set up with oxygen. The design of the tips, a
straight single orifice, isn't well suited to compressed air, normally. might
work with a very fast burning fuel like hydrogen, or perhaps acetyelene, but
even then, I'd rather expect it to not work well, if it does work. The problem
is that combustion with compressed air is not aggressive enough, and the speed
with which burning progresses through a gas stream is slow enough that with any
decent gas flow through the tip, the gas stream (fuel plus air) is moving faster
than combustion can travel along the gas strem, so it blows off the tip. tips
for compressed air generally utilize a multiple orifice design that uses a wider
head, with more orifices or cross sectional area to the flame, which lets the
gas slow down before it exits the torch. Then the flame stays on the torch.

another consideration is that even the largest tip on the smith torch is quite
small. The tiny flame you get with it, needs to be quite hot to be at all useful
for soldering or working metal. You'll find that with compressed air, even if
you get the tip to stay lit, there's just not much heat there. An oxygen/fuel
flame is MUCH hotter, which is why those small tips are then useful.

Bite the bullet and get an oxygen tank. You'll find that the little torch, due
to it's very small tips sizes, uses only a slow rate of oxygen consumption, and
even a small little R sized tank will last you a good long time. I'd recommend a
larger tank, like a 40 cubic foot one, however, since the tank costs a bit more,
but not in proportion to the cubic feet, and the refil on the larger tank is not
much more than the refil cost of a small one. But a 40 cubic foot tank, running
just a single little torch, even if running it quite a lot every day, might
easily last you many months, or even a year. makes the cost for the refil rather
trivial in the end.


..... changing
the tip (3 -6) makes no apparent difference.


As I said, the basic problem is that the tips on the little torch are just not
designed for the slow speed combustion you get with just compressed air.

the manual for the smith doesn't mention plg and air at all

Because the torch is not designed for it.

, but in the lpg/
o2 sections it talks about pressures in the region of 2-8 PSIg. - quite a
bit more than I am running.

Are you sure? You might be right, but note that the torch manual is listing
pressures in PSI (pounds per square inch), not klPa, as you specified your gas
pressures used. Different units of measurement. I'm not sure of the
conversion, and am too lazy to go look. but for the record, in general, the
little torch is intended to use gas and oxygen pressures considerably lower than
is used by most larger torches. In fact the regulators (gas and oxygen) that
smith sells for use with that torch are specifically modified to give stable gas
flows at the low pressures and low flow rates used by that torch. You can use
cheap regulators, of course, but the flame is not always as stable in size.
that's more of an issue with more than one torch running on a setup, but appears
in single torch setups too.

I would have expected the increase in pressure to make things worse, not
better... Can any one shed light in this?

See above. Note, though, that with very low pressures, some cheaper regulators
are not good at delivering stable pressures, but sort of cycle on and off, a sort
of "chattering" effect. That can be annoying.


I'm seriously considering taking the torch to the jeweller and asking him to
set it up in his workshop and get him to check the operation of the unit
(blockage in a pipe maybe??)
I did try the mouth blowing on the air line, and I witnessed the same
"blowing out" of the flame.

I saved up to get this, and I'm quite dissapionted it's not working as well
as I'd hoped.

I'm surprised that you didn't fully check out the specs of the torch before you
bought it. Nowhere have I ever seen or heard this torch recommended for use with
compressed air. There are considerably cheaper torches out there designed for
such use. Normally, gas/air torches are larger, however, so if you intended a
tiny torch, that may have mislead you. In general, my recomendation if you wish
a fuel only torch, is to not bother with compressed air, but to go with the sort
of torch that just burns propane, mixing with atmospheric (non compressed) aire
at the torch head, such as the typical plumbers torch. Inexpensive and
reasonably useful. A step up are the air/acetyelene torches such as the Smith
Handi heat, or the prestolite types, which for general fabrication, especially in
silver, are actually wonderful torches.

If you wish the type of control over the flame often found in european workshops,
where torches are fed just fuel gas, and mouth blown, then you need the type of
mouth blown blowpipe torches designed for that type of fuel. Highly versatile
tools, they take a bit more practice to master. Few people in the U.S. use them,
but in Europe, they're what a lot of smiths learned with, and in the hands of
someone who's used to them, they're very good tools, and cheap to run. And they
generally cost less than a little torch setup. The same type of torch design,
but with an additional valve to control air flow, are what's used with compressed
air.

Peter


Thanks,
Des bromilow

Peter W.. Rowe, wrote:
On Mon, 27 Sep 2004 18:53:17 -0700, in @õ "Des Bromilow"
wrote:


Hi,

I have managed to by a smith little torch, and am trying to run it on LPG
and Compressed air (one of the local jewellers reckons it can be done.)
He claims that with LPG at 2.8kPa, and compressed air at 20 PSI (or mouth
blown) I should be able to get a small tight cone on a #5 tip.


I think your friend is wrong. I've never seen a smith little torch run with
compressed air. Always, they're set up with oxygen. The design of the tips, a
straight single orifice, isn't well suited to compressed air, normally. might
work with a very fast burning fuel like hydrogen, or perhaps acetyelene, but
even then, I'd rather expect it to not work well, if it does work. The problem
is that combustion with compressed air is not aggressive enough, and the speed
with which burning progresses through a gas stream is slow enough that with any
decent gas flow through the tip, the gas stream (fuel plus air) is moving faster
than combustion can travel along the gas strem, so it blows off the tip. tips
for compressed air generally utilize a multiple orifice design that uses a wider
head, with more orifices or cross sectional area to the flame, which lets the
gas slow down before it exits the torch. Then the flame stays on the torch.

another consideration is that even the largest tip on the smith torch is quite
small. The tiny flame you get with it, needs to be quite hot to be at all useful
for soldering or working metal. You'll find that with compressed air, even if
you get the tip to stay lit, there's just not much heat there. An oxygen/fuel
flame is MUCH hotter, which is why those small tips are then useful.

Bite the bullet and get an oxygen tank. You'll find that the little torch, due
to it's very small tips sizes, uses only a slow rate of oxygen consumption, and
even a small little R sized tank will last you a good long time. I'd recommend a
larger tank, like a 40 cubic foot one, however, since the tank costs a bit more,
but not in proportion to the cubic feet, and the refil on the larger tank is not
much more than the refil cost of a small one. But a 40 cubic foot tank, running
just a single little torch, even if running it quite a lot every day, might
easily last you many months, or even a year. makes the cost for the refil rather
trivial in the end.


..... changing
the tip (3 -6) makes no apparent difference.



As I said, the basic problem is that the tips on the little torch are just not
designed for the slow speed combustion you get with just compressed air.


the manual for the smith doesn't mention plg and air at all


Because the torch is not designed for it.


, but in the lpg/
o2 sections it talks about pressures in the region of 2-8 PSIg. - quite a
bit more than I am running.


Are you sure? You might be right, but note that the torch manual is listing
pressures in PSI (pounds per square inch), not klPa, as you specified your gas
pressures used. Different units of measurement. I'm not sure of the
conversion, and am too lazy to go look. but for the record, in general, the
little torch is intended to use gas and oxygen pressures considerably lower than
is used by most larger torches. In fact the regulators (gas and oxygen) that
smith sells for use with that torch are specifically modified to give stable gas
flows at the low pressures and low flow rates used by that torch. You can use
cheap regulators, of course, but the flame is not always as stable in size.
that's more of an issue with more than one torch running on a setup, but appears
in single torch setups too.


I would have expected the increase in pressure to make things worse, not
better... Can any one shed light in this?


See above. Note, though, that with very low pressures, some cheaper regulators
are not good at delivering stable pressures, but sort of cycle on and off, a sort
of "chattering" effect. That can be annoying.


I'm seriously considering taking the torch to the jeweller and asking him to
set it up in his workshop and get him to check the operation of the unit
(blockage in a pipe maybe??)
I did try the mouth blowing on the air line, and I witnessed the same
"blowing out" of the flame.

I saved up to get this, and I'm quite dissapionted it's not working as well
as I'd hoped.


I'm surprised that you didn't fully check out the specs of the torch before you
bought it. Nowhere have I ever seen or heard this torch recommended for use with
compressed air. There are considerably cheaper torches out there designed for
such use. Normally, gas/air torches are larger, however, so if you intended a
tiny torch, that may have mislead you. In general, my recomendation if you wish
a fuel only torch, is to not bother with compressed air, but to go with the sort
of torch that just burns propane, mixing with atmospheric (non compressed) aire
at the torch head, such as the typical plumbers torch. Inexpensive and
reasonably useful. A step up are the air/acetyelene torches such as the Smith
Handi heat, or the prestolite types, which for general fabrication, especially in
silver, are actually wonderful torches.

If you wish the type of control over the flame often found in european workshops,
where torches are fed just fuel gas, and mouth blown, then you need the type of
mouth blown blowpipe torches designed for that type of fuel. Highly versatile
tools, they take a bit more practice to master. Few people in the U.S. use them,
but in Europe, they're what a lot of smiths learned with, and in the hands of
someone who's used to them, they're very good tools, and cheap to run. And they
generally cost less than a little torch setup. The same type of torch design,
but with an additional valve to control air flow, are what's used with compressed
air.

Peter


Thanks,
Des bromilow
Peter hascovered all you need to know at this stasge

Peter has covered all you need to know at this stage.
your not giving your torch a chance to show what it can do.
Its by the sound of it a smaller version of what we have here in
Europe as a small version of a general engineers torch. these will run
well on oxygen and propane ,acetylene and hydrogen, tho propane is the
cheapest of fuel gases.
I suggest you beg borrow or steal an oxygen tank and reg and give your
torch a chance to show what it can do. youll be pleasntly surprised!!.
If youve the time to waste get your s/smith friend to show you how it
might work with compressed air. Wed all be interested to hear if he can
get it to work.and more importantly how.