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Flashback Arrestors


#1

I decided to start the new year off right and chuck the old
primitive torch and do it right with a Little Torch outfit. So
here it is, and the acetelyne regulator won’t fit on my tank, so
will have to send it back, call, and get one that will fit.
Darn, and I want to start playing with it right now! Also, I’m
unsure about which end of the hose the flashback arrestors should
go on. One manual says it can go on either end, and another
reference says to put it on the torch end. I don’t want to add
any more weight at that end if I don’t have to. I would be
grateful if someone would advise. Many thanks.

The NH Linda, where we finally have snow for x-country skiing,
so who’s gonna work, anyway?


#2
 I decided to start the new year off right and chuck the old
primitive torch and do it right with a Little Torch outfit. 
So here it is, and the acetelyne regulator won't fit on my
tank, so will have to send it back, call, and get one that will
fit. Darn, and I want to start playing with it right now! 
Also, I'm unsure about which end of the hose the flashback
arrestors should go on.  One manual says it can go on either
end, and another reference says to put it on the torch end.  I
don't want to add any more weight at that end if I don't have
to. 

You didn’t indicate what type of tank you had or what Little
Torch kit you got. Little Torch comes in 2 models, one with a set
of regulators for the disposable cylinders (propane/MAPP, Oxy,
etc) & one used with the larger regulators that are usually
equipped with gauges.

The regulators for the disposable cylinders won’t work with any
other cylinders. Usually these torch kits come with the hoses
attached to the regulators.

The other kit comes with a fitting on the end of the hose that
attaches to the regulator. The other end of the hose is
permanently attached to the torch body. If this is the type of
torch you have it can be used with any regulator rated for
welding service. The regulator output is a standard size & the
inputs are also standard sizes. The regulator fitting that
attaches to the Oxy supply is a female fitting with right handed
threads. The acetylene fitting is a male fitting with left handed
threads. These regulators will not work with the disposable
tanks.

Assuming you have the Little Torch kit for use with standard
regulators, from the description of the problem, I’d guess you
either have a ‘MC’ (about 16" from top of valve to bottom of
tank) or ‘B’ (about 23" from top of valve to bottom of tank).
These 2 tank use a different connector than the larger
acetylene/fuel gas cylinders. Any welding equipment/gas supplier
has adapters to adapt the connections on these tanks to the
standard regulator fitting.

The flash arrestors should be installed as close to the torch
body as practical. On a full sized welding torch, they’d be
attached at the torch body. On a Little Torch the closest they
can be attached to the torch body is at the end of the hose. The
other end of the hose is permanently attached to the torch body.
Assuming you are going to attach the hoses to the regulators &
not to any extension hoses or pipes, there’s no need to be
concerned how the arrestors are installed. They’ll only install
one way.

Dave


#3

Linda: I read with some interest your latest post. In answer to
your question, the arrestor valve should go on your regualtor.
Asyou might know, it’s purpose is to prevent the flame from your
torch from bacing up into your lines and causing an explosion
when it hits your tank(s). As long as it stops this fortunatly
infrequent problem from getting to your tanks, that’s all that is
necessary. As an aside, may I ask why you use acetylene/oxy
instead of the industry standard of natural gas or propane/oxy.?
You would find this to be a safer, much cleaner burning and less
offensive smelling setup. I keep a small tank of acetylene by my
bench and have a “Y” w/2 valves so that I can switch if
confronted with a big piece of silver or platinum. Then I simply
purge the line of acetylene and return to natural gas for almost
all my other work. Just thought I’d make the suggestion.

Reguards;

Steve Klepinger


#4

This isn’t an answer its another question…how important are
flashback arrestors anyway? I’ve had my Little Torch with
acetylene/oxy and my Hoke with propane/oxy and my Smith
acetylene/air for 6 years now and I don’t think there are
arrestors on any of the rigs but have never had anything weird
happen with them either. Just what IS flashback and how common
is it? Thanks to all…Dave

Kickass Websites for the Corporate World http://www.kickassdesign.com
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#5

Hi Dave,

Flashback can occur when the pressure of the fuel gas drops so
it is not sufficient to cause the gas to exit the tip of the
torch. The torch would have to been lighted & burning. Then the
fuel gas pressure drops & the flame follows the available gas
into the torch & down the hose to the tank.

I don’t know how often this happens. I’ve never heard of it
happening either, but the consequences of igniting an acetylene
cylinder aren’t something to look forward to.

Flashback arrestors can be likened to check valves, they won’t
allow anything to flow backward beyond the valve.

This is just supposition on my part, but if you had a incident
that could be attributed to flashback, you’d probably have a
devil of a time collecting anything from an insurance company.

Another Dave


#6

This isn’t an answer its another question…how important are
flashback arrestors anyway? Just what IS flashback and how common
is it?

I have never seen a flash back (just heard the stories) but my
welder father (who let us use his equipment as teens) taught me a
healthy respect for this equipment. And I think the small expense
(don’t remember what it was) is a small price to pay for safety,
like an insurance policy, really. I sure have them on all my
setups.

Lorri Ferguson


#7

I would say that flashback arrestors are a very important part
of your torch setup. most little torch sytems actually have a
plastic hose inside the heat shield that comes with the
torch.That heat shield will not stop the plastic from melting. If
, for any reason,your torch should backfire (loud popping
sound)… (this is actually a tiny fire/explosion inside your
torch),it is possible for a flame to go all the way back to your
regulator… If the flame/spark should get into your regulator,
YOU WILL HAVE A SERIOUS EXPLOSION at worst. The spark arrestor
helps to minimize/eliminate this potential problem.

Dan Grandi
http://www.racecarjewelry.com


#8

Dear Linda, Unless they have changed the design of The “Little
torch”, one can only ad the check-valve or flash arrestor at the
regulator. The “Little Torch’s” hoses do not have a standard
fitting that would allow one to attach any auxiliary devices.
If you using a torch that has standard fittings at the
torch-end, IMHO, that’s where one would attach the flash
arrestors. “Ya wouldn’t wanna flame to any farther than that
would’ja?”

As for the regulator not fitting with your existing tank, you
could visit a local welding supply (I’d call first) and buy an
adapter that might allow you to use both the regulator and the
tank together. There are three types of acetylene regulator
fittings commonly in use. The “Little Torch” regulators are
designed for the “MC” tank (its the smallest one you generally
see in the catalogues). The type of fitting generally
associated with air/acetylene, i.e., plumber’s torch
(Prest-o-Lite or Handi-Heat or Goss ,etc) is the “B” fitting.
This requires a “key” to turn on the gas. The third type is
called a "commercial fitting " or the P.O.L. fitting. This is
the type you’d find on a cutting torch in a garage or in some
industrial application.

My guess is that you purchased the “MC” regulator and you have a
"B" tank. I know of adapters for the P.O.L/“B” situation, I
assume there is one for the “MC”/“B” situation.

Hope this helps,
Eben


#9

Dave & all:

I’ve been using a Meco little torch for about 20 years and only
had one occasion when flashback was a concern. I had been using
the torch, turned off the oxy and let the natural gas flame burn
while I did other things. I’m sure most of us do the same.
While distracted, the gas flame backed up into the torch and it
became VERY hot. Of course, when I picked it up I burned myself
rather badly. I’m fortunate, however that I cought it before it
had crept back thru the hose further. It happened only once but
then, once is all it takes. You can believe that I installed the
arrestors soon after.

Hope this contributes to the thread;

Steve Klepinger


#10

I have seen the after math of being careless with torches. I
personally saw an oxygen tank shoot across a gravel parking
lot…Blotted out the sun it made such a dust cloud…scared the
heck out of us…I dove into corrugated steel pipe(lot of good it
would have done though). I saw a torch that had the tip and
nozzle blown off…looked like a mushroom with out the room. he
he. A friend that I used to weld with…Kind of my mentor said he
saw hoses and hands blown off. but he had been into welding about
50 yrs longer then I…he made me respect welding cutting and
general equipment…Thank God.

Yes they are very dangerous, Even the small units. Use flashback
arresters and checkvalves on your equipment…Think what could go
wrong and plan for it and thank God when it doesn’t.

Thanks
Kemp

http://www.valint.net/chp/treasure/index.htm


#11

G’day; flashback arrestors are simple devices, consisting of a
small bit of fine metal mesh, or metal ‘wool’ inserted in the gas
lines. How does that work? Well, on exactly the same principle
as the Davy Miner’s Lamp. invented by Sir Humphrey Davy, who got
worried about the large number of coal mine explosions and
fires, for the miner’s lights were oil lamps, and ignited the
ever present methane and other flammable gases in the mines. All
he did was to enclose the flame of the lamp inside a cage of
fine wire mesh. And those lamps soon caught on. Got access to
a Bunsen Burner? Well, light it and hold a piece of wire gauze
halfway down the flame. It won’t go past the wire mesh until the
mesh gets red-hot and itself ignites the gases above it. Let
the gauze cool, turn the Bunsen off, hold the gauze about an
inch above the burner , turn on the gas, and light the gas ABOVE
the gauze. The gas below it won’t catch fire! In the Davy lamp,
flammable gases outside the lamp’s gauze can’t catch fire. Hence
the gauze in the flashback arrestor. And there you have it! (As
another contributor would say) Here endeth the lesson.
Cheers,

     /\
    / /
   / /
  / /__|\      @John_Burgess2
 (_______)

At sunny Nelson NZ


#12

Hi, I have some background in industrial welding - what happens
without a flash back protector can be rather dramatic. Basically
your fuel lines split and becomes a self-fuelled wick for the
flame. Eventually the flame will reach the regulators and the
fuel source preventing any chance of shutting down the bottle. At
this point hopefully you will be about a block away on the phone
to the fire department. Don’t think it doesn’t happen - the most
common case is where a piece of hot metal in a flame cutting
operation falls on the fuel line. Given the fact that you are
releasing a small percentage of fuel when soldering you can image
what a wholesale emptying of a fuel cylinder can be like.

There is a reason that bottles are made of such heavy metal -
there is a couple hundred psi of compressed gas trying it’s best
to get out - with a melted regulator that is exactly what it will
do. My theromodynamics is bit rusty - but hmmm… that much gas +
atmospheric oxygen - the average shop size - should be just about
enough energy released to reach escape velocity.

I also developed a healthy respect for gas torches as a teenager

  • when my father came home with the better part of two fingers
    cooked. It was not even his fault - he is a very experienced
    welder and very cautious - the torch he was using was brand new
    and was defective from the factory. So even with correct safety
    equipment there is no guarantee - why increase the risk?

Take Care, money isn’t everything,
Cameron Speedie
Island Gem and Rock


#13

This isn’t an answer its another question…how important are
flashback arrestors anyway?

They are not important at all until something goes wrong, then

they can save your life.

Just what IS flashback and how common 

Flashback occurs when oxygen gets in the fuel gas hose or vice
versa and ignites. The ignition can be spontaneous due to the
mixing of oxygen and fuel under pressure or can be a flame
following the torch tip back down the tube. This can be bad news
as it can possibly follow the hose back and burn into the
regulator and cause an explosion or fire if it burns through the
hose and the flaming end of the hose thrashes about your studio.
If you ever turn off the fuel before the oxygen and get a "pop"
that is a small flashback that kind is not too dangerous with
small torches as the volume of gas is small but… on bigger
torches or if the conditions are right then you can have
problems. There are other sources of flashback like when you are
casting and the tip gets so hot the fuel ignites inside the torch
tip or mixer tube. This can be bad news as it can possibly
follow the hose back and burn the regulator and cause an
explosion or fire. There are two common causes for this either
the torch tip is too close to the melt and is actually bathed in
the flame or the pressure is too low for the tip size and there
is not enough cooling of the tip by the gas flowing through it.
Another cause of flash back is caused by hot metal , oxide or
flux getting inside the torch tip or mixer tube and igniting the
mix inside the torch. This is more common with oxygen acetylene
welding of steel as the molten steel “spits and pops” a lot and
the sparks that can end up in the torch tip causing a flashback.

 One other thing that can contribute to flash backs is uneven

pressures on the Fuel and Oxygen regulators. If the Oxygen is at
20 psi and the fuel is at 5 psi and you were to block the end of
the torch tip with the torch valves open then oxygen would try to
flow into the Fuel line and regulator causing an explosion if it
ignites. I know many of us do this but it is a very bad idea.
You should set your fuel and Oxygen regulators to the same output
pressure. There are times that this is not the case but mostly
they involve using a cutting torch where Oxygen is used to blow
/ burn the molten metal out off the kerf and a few other
specialized tasks.

Serious Flashbacks do not happen often but when they do they

can be deadly. A Flashback arrestor can be located either on the
torch or regulator end of the hoses and consists of a sintered
bronze filter and check valve. The check valve at only allows
gas flow in one direction (out of the regulator and into the hose
or out of the hose into the torch). The check valve can reduce
the danger from unequal regulator output gas pressures but you
should not rely on this as they are very simple check valves and
could allow some gas flow in the wrong direction. The sintered
bronze filter is a flame block it will not allow a flame to pass
through it, but if the flashback arrestor is on the regulator end
of the hose the gas in the hose could still ignite and cause a
serious fire when the hose ruptures and starts spraying flaming
fuel out of the end of the hose. This is why the really paranoid
use a flashback arestor on both ends of the hose. This can also
be a requirement of your insurance coverage if they know about
your use of oxygen / fuel torches.

Sorry for the rant.

Jim


@jbin
James Binnion Metal Arts
4701 San Leandro St #18
Oakland, CA 94601
510-436-3552


#14

Regarding the Meco torch and flashback. I have use this model
exclusively for 25 years with up to 16 of them going at once our
studio. We have found them to be a very reliable and versatile
for oxygen/natural gas or oxygen/propane. We have never had a
flashback.

Alan Revere
Revere Academy of Jewelry Arts
San Francisco


#15

Okay I haven’t been completely reading most of my flashback
arrestor mail so if this question has been asked a dozen times
already I apologize.

I use an aceytelene (spelt wrong) set up in my studio. The kind
of tank i have takes oxygen from the outside. I do not have an
oxygen tank. I get popping noises all the time when I shut off my
hose. Are these tanks prone to “flashback arrests” too?

DeDe


#16
  This is why the really paranoid use a flashback arestor on
both ends of the hose.  This can also be a requirement of your
insurance coverage if they know about your use of oxygen / fuel
torches. 

I just stepped up from the Blazer to a acetylene Prest-o-lite
torch. Air is let in through a valve. There is no compressed
oxygen or compressed air. Before I get a salesman to sell me
something I might not need… do I need flash protection too?
Having been badly burned at the age of six, I don’t want to take
any chances. What can you suggest? (I do get natural gas coming
into my home - what can anyone tell me about the
benefits/warnings of tapping into that?)

kathi parker
http://www.angelfire.com/biz/moonscapedesigns


#17

Hi Folks,

Just catching up after a prolonged period of email failure. I
have a question about which I hope someone has experience and a
possible solution. I acquired a set of flashback arrestors from
a well known and reputable jewelry supplier and installed them
on my Oxy/Acet. Little Torch. I get no gas flow at all! Of
course, the obvious answer is that they are installed backwards,
and the check valve is preventing flow. However, with the
male/female couplings, they will only go on one way. The
vendor’s tech support was unable to offer suggestions. I am
installing between the regulator and torch hose. I generally run
about 5lb. pressure on both gasses. Chances of both arrestors
(specifically for O2 and acetylene) being bad seem rather slim.

Thanks, in advance, for any ideas!

Happy New Year to y’all!

Dave

Dave Sebaste
Sebaste Studio
Charlotte, NC (USA)
dave@sebaste.com
http://www.sebaste.com


#18
I use an aceytelene (spelt wrong) set up in my studio. The kind
of tank i have takes oxygen from the outside. I do not have an
oxygen tank. I get popping noises all the time when I shut off my
hose.  Are these tanks prone to "flashback arrests" too?<<

The torch you’re using (generically called a 'Prestolite Torch)
will usually do that every time it’s shut off.

What’s happening is indeed ‘flashback’. The gas valve is usually
on the torch body before the tip is attached. Examination of a
tip removed from the torch body will reveal a number of holes
near the end of the tip that’s connected to the torch body. These
holes vary in size depending on the size of the tip. Larger tips
have larger holes. These holes allow the correct amount of air to
be drawn into the tip for the amount of gas being used.

When the gas valve is turned off, there’s no new gas entering
the tip to force the gas/air mixture already in the tip to the
business end of the tip. Since the mixture won’t go to the end of
the tip on it’s own, the flame comes back down the tip, consuming
the gas/air mixture as it goes. When it reaches the bottom of
the tip, the mixture is explosive & the path of least resistance
is out the air inlet holes at the base of the tip. Thus the
little ‘pop’ that’s heard when the torch is turn off.

Further examination of the base of the tip (look in the large
opening at the base) will reveal what looks like a brass colored
filter from a filtered cigarette. This is either a series a very
fine mesh screens or a porous sintered brass product (depends on
the mfgr.). It’s the ‘flashback’ arrestor for the tip. Thus
these types of torches come with a built in flash back arrestor.

Dave


#19
I get no gas flow at all!  However, with the male/female
couplings,  they will only go on one way. The 
vendor's tech support was unable to offer suggestions. I   
generally run about 5lb. pressure on both gasses. 

I once asked the welding shop about the release pressure for a
falshback arrestor, my application was for a checkvalve to a
hobby vacuum form box I wanted to construct. His reply was 15
psi (or some figure like that) which was too high for my
purpose.

It may be that your gas pressure at 5 psi may be too low to open
the falshback arrestor valve. The male/female coupling screw
threads are industry standard and not meant to be used any other
way so you couldn’t have put the arrestors on backward. Try
blowing into the valve (your breath is more than 5 psi) and if
you can’t blow through in either direction then that’s your
problem.

Kelvin Mok (klmok@shaw.wave.ca)

Home: (403) 463-4099 | Home FAX: (403) 430-7120


#20

Kathi, I too use a Blazer, and have been looking into a different
system. I have spoken to many. I recently had a Plumber friend
over and picked his brain.

I know I do not want acetylene/air, have read too many posts
about its being “dirty”. I too have natural gas and asked about
tapping into that. Basically it may not be legal into the home,
and may invalidate the insurance. I still feel there must be a
way to use natural gas, it is there, clean, and easy, but there
are pilot lights to be cautious of, the kitchen stove, and the
water heater, usually in the garage. I used to live in a
four-plex. The owners unit had a middle of the night fire due to
ignition in the kitchen of fumes. It scares me.

I have also considered propane, but again from online warnings,
it is best not to keep inside. So I still use the Blazer, and do
heavier soldering during my ongoing class at a local community
college.

My home is my workshop, I hope to eventually use the garage, but
for now, it is inside, and I am concerned. I too would welcome
suggestions. Teresa