PDA

View Full Version : Acetylene tank warning sticker



taydin
04-25-2011, 09:05 AM
There is a sticker on my acetylene tank that says "don't let the pressure drop below 5 bar". When the tank was full, the pressure was about 10 bars. Now, the pressure is very close to 5 bar, but the flame still goes strong. Should I call for a refill?

PixMan
04-25-2011, 09:16 AM
Sounds like a welding supply vendor's way of getting you to pay for a full tank @ refill when you still have a third of it left. ;)

I run it until nothing comes out. I am still here.

Evan
04-25-2011, 09:35 AM
The reason for not running the acetylene tank empty is to prevent any possibility of oxygen back feeding into the regulator of the acetylene tank. If it does it will explode without any source of ignition. The minimum pressure should be around twice the maximum oxygen pressure ever used.

bruto
04-25-2011, 10:10 AM
Would that problem be addressed sufficiently with check valves on the hoses?

aboard_epsilon
04-25-2011, 10:13 AM
bugger that ..the stuff is way too expensive ..and the tank rental more ..

I'd drop it like a hat ..

all the best.markj

Evan
04-25-2011, 10:14 AM
I doubt it. The check valve is designed to close when hit by a pressure wave from a backfire inside the torch. I don't think that a slow steady backflow from the torch mixing chamber would be enough to close it.

You don't need to leave 5 bar in the tank. 50 psi is the recommended amount.

JCHannum
04-25-2011, 10:36 AM
There are two distinct safety devices that should be fitted to an O/A setup, reverse flow check valves and flashback arrestors. They and their functions are often confused. Since they each operate in a different manner, the best practice is to install both on your system.

The reverse flow check valve is that, and will prevent normal backflow from the torch. The flashback arrestor is designed to close in the event of a flashback and prevent it from entering the tanks. Normal practice is to install check valves at the torch and flashback arrestors at the tanks.

PixMan
04-25-2011, 11:21 AM
Since I use the acetylene alone as just a glorified propane, I should be OK then? 30 years and no problems doesn't mean I could blow myself up next week.
:p

Evan
04-25-2011, 11:24 AM
If you are using an acetylene/air torch then no worries.

taydin
04-25-2011, 12:48 PM
There are two distinct safety devices that should be fitted to an O/A setup, reverse flow check valves and flashback arrestors. They and their functions are often confused. Since they each operate in a different manner, the best practice is to install both on your system.

The reverse flow check valve is that, and will prevent normal backflow from the torch. The flashback arrestor is designed to close in the event of a flashback and prevent it from entering the tanks. Normal practice is to install check valves at the torch and flashback arrestors at the tanks.

I have flashback arrestors on both the oxygen and the acetylene hose, both at the torch end and at the regulator end. But I haven't seen any reverse flow checkvalves being sold here. Even a well known OA equipment manufacturer, Gloor, doesn't have them in their product line. I guess this is another area where safety equipment and requirements differ among different countries...

taydin
04-25-2011, 12:52 PM
You don't need to leave 5 bar in the tank. 50 psi is the recommended amount.

Because there are two flashback arrestors on each line, I am using a higher than usual pressure for acetylene and oxygen (0.5 bar and 2.5 bar respectively). So that means I shouldn't go below 3 bar in the acetylene tank, which comes to about 50 psi as you have stated. Thanks for the detailed explanation ...

Evan
04-25-2011, 03:09 PM
I haven't seen reverse flow checkvalves either. I will have to ask around.

MichaelP
04-25-2011, 03:14 PM
The check valves are usually called "backflow preventers". Some torches have them built in.

As for the minimum suggested acetylene tank pressure, 25 psi is an often suggested figure. Presumably, if the pressure is below that, there's a chance of drawing acetone along with the gas. Some sources suggest 50 psi. There are people that run the tanks down to almost zero (until they cannot maintain 3-5 psi after the regulator any longer).

I think that as long as you have the backflow preventers, 25 psi is reasonable figure.

Black_Moons
04-25-2011, 03:21 PM
When I initialy tryed my O/A torch with the smaller torch I bought, it recommended 3psi actylene and 3psi oxygen.

Now I have a 200psi oxygen gauge, so you can't really tune to anything less then 'well it made the needle move and I heard a hiss of filling the line, so it must be at least 10psi.. maybe up to 20". Oxygen flowed fine

The actylene on the other hand has the proper gauge of course.. I allways used it at 5psi for my big torch, but decided 3psi would be a good start for the smaller torch (as thats what the manual says)

Turn it to 3psi, try and light it and... Nothing.
Try and light it again... Nothing. Try and use a lighter to see if theres ANY gas getting through at all. Nothing! Not even a wiff.

Cranked the actylene pressure up to 5psi, and away it goes!
Try draining and going back to 3psi, Nothing.

I highly suspect the 'tank style' flashback arresters I have use spring loaded check valves that actualy need at least 4psi to crack open. at least on the actylene side. Can't accurately use low enough oxygen to check the oxygen valve. (annoying as my torch is VERY touchy on tuning the oxygen valve just right, excessive oxygen pressure does not make that easyer)

Havent checked my torch style yet, Never used the big torch below 5psi, And its only my big torch that can fit the torch style (my mini torch has its own gas lines, Hence why I had to buy the regulator style, after buying the torch style)

On a related note, Anyone got a chart or rule of thumb for actylene pressure verus tank capacity remaining? Or another way to check?

I know some gases don't change pressure at all untill empty (LPG/butane for example, since it boils off, the pressure only changes with ambiant temp)

Evan
04-25-2011, 03:25 PM
There isn't much correlation between acytelene pressure and tank capacity. There also isn't a good way to tell either except when it is really running low.

JCHannum
04-25-2011, 03:28 PM
Reverse flow check valves;

http://www.westernenterprises.com/enterprises/PDFS/wi24.pdf

Flashback arrestors;

http://www.westernenterprises.com/enterprises/flashback_arrestors.php

There are also combination units.

MichaelP
04-25-2011, 03:53 PM
On a related note, Anyone got a chart or rule of thumb for actylene pressure verus tank capacity remaining? Or another way to check?

You can do it by weight. Your tank should have the tare weight stumped on. Subtract it from the actual weight to find out the weight of the remaining acetylene. In order to convert it into cu.ft, multiply the acetylene weight in pounds by 14.7 (specific volume of acetylene is 14.7 cu.ft/lb at 1 atm and 68F).

If you know your tip's consumption rate per given pressure, you can divide the result above by the consumption rate to roughly figure out how long you'll be able to weld if you run the tank down to zero (naturally, you should use the same units of measure).

taydin
04-25-2011, 04:14 PM
I just looked at the Gloor product catalog again. Here is that link:

http://www.gloor.ch/pdf/P0128E.pdf

It seems their flashback arrestors are actually three safety products in one package. They contain a reverse flow checkvalve, a flashback arrestor and a third device, which blocks gas flow if a certain temperature is sensed. So does this change the picture? Or should I still call for a refill once the bottle is at 3 bar?

MichaelP
04-25-2011, 04:24 PM
As I mentioned above, I'd run it down to about 25 psi (1.7 bar). You might go down even more, but why risk drawing acetone from the bottle?

loose nut
04-25-2011, 05:50 PM
There is a sticker on my acetylene tank that says "don't let the pressure drop below 5 bar". When the tank was full, the pressure was about 10 bars. Now, the pressure is very close to 5 bar, but the flame still goes strong. Should I call for a refill?

I don't see what the problem is. If I have 5 bars that means I'm getting really good reception.

boslab
04-25-2011, 07:49 PM
if you want to make a flamethrower then run the tank to the ground, eventually youll get acetone out I promise!
I know that i did it! my contents guage was knackered, and so was my bank balance for a refill, over here were talking $100 for a refill, i think i'll take some carbide home and make my own like my dad used to do
mark

BigMike782
04-25-2011, 08:09 PM
Acetylene pressure is also affected by temperature to the point that in sub zero weather the cylinder can have zero pressure.
I doubt this is Taydins issue just bringing it up as a point of info.

JoeLee
04-25-2011, 08:17 PM
I've never seen a warning sticker like that on an acetylene tank and I've had torches for about 30 years, ran em empty as well, especially when I would loan them out they would always come back empty and I'm still here!!
I have flashback check valves but I think they are just reed valves, as Evan said I don't think they would work on a slow feed back.

JL...............

MichaelP
04-26-2011, 01:35 PM
There is one more possible explanation for the sticker presence. There is a chance that refilling the tank will be more difficult (=more expensive for you) if the pressure drops below the mark. I'd call the gas supplier and ask.

pressurerelief
04-26-2011, 02:49 PM
Flash Arrestors are generally not valves and do not close. Most cylinder arrestors work by absorbing the heat from a fire that is in the line and extinguishing the fire by removing the heat. The unit is rated per flow and product so that the correct amount of heat dissipation is built in. If you look inside of a 5 gallon OSHA approved gas can the brass looking screen is the flash arrestor.

Check valves do prevent the backflow of gas via a seat and piston/ball arrangement. They are not designed or approved to stop the propagation of a flame back the hose to the gas source.

If you get no flow at 3 psi and good flow at 5 psi your check valve is either dirty or has the wrong cracking pressure for the application.

gary350
04-26-2011, 06:15 PM
There are lots of tricks to get you to spend money. Like the law that says precription drugs over 6 months old are illegal drugs. Your suppose to trash your unused drugs and go buy more so it will make the drug companies more money.

jep24601
04-28-2011, 04:49 PM
Do the acetylene tanks in the USA have the acetylene dissolved in acetone like in the UK?

Black_Moons
04-28-2011, 04:54 PM
Do the acetylene tanks in the USA have the acetylene dissolved in acetone like in the UK?

Nope, Physics operate diffrently in the USA and they just pump the tanks full of pure acetylene, Using a couple sprinkles of religion to keep it stable.

(You know what a stabilising influance religion has on volatile situations)

Jaakko Fagerlund
04-28-2011, 05:15 PM
Nope, Physics operate diffrently in the USA and they just pump the tanks full of pure acetylene, Using a couple sprinkles of religion to keep it stable.

(You know what a stabilising influance religion has on volatile situations)
LMAO :D "God wants to keep that acetylene in the tank" :p

Edit: I thought you guys use the premixed gas that has acetylene and oxygen both in the same bottle ready for use ;)

MichaelP
04-28-2011, 06:02 PM
I thought you guys use the premixed gas that has acetylene and oxygen both in the same bottle ready for use ;)
We ain't have no stinkin' bottles here. Our utility companies supply the mix through gas pipes, so we can fry our burgers (what else?) quicker. :p

Do your saunas use bottled oxyacetylene? :D

jep24601
04-28-2011, 06:09 PM
From Wikipedia (which meams it must be true):

"....acetylene can explode with extreme violence if the pressure of the gas exceeds about 200 kPa (29 psi) as a gas or when in liquid or solid form. It is therefore shipped and stored dissolved in acetone or dimethylformamide (DMF), contained in a metal cylinder with a porous filling (Agamassan), which renders it safe to transport and use, given proper handling."

Evan
04-28-2011, 07:58 PM
That's the simplified version of the truth. To keep certain compressed flammable gasses stable the distance to the nearest hard surface must always be less than the minimum explosion cell size. That varies with the particular gas and pressure which varies with temperature. It also depends on the metal since some metals react with the gas to form explosive compounds.

In the case of acetylene, copper reacts to form an explosive so the brass used must not have more than 65 percent copper or there will be unalloyed copper in the mix.

The minimum pressure cell size is a space smaller than the volume required for a shock wave to propagate faster than the time it takes for the molecules to decompose. If the space is smaller than that then molecular decomposition remains localized and no explosion occurs. As the pressure is raised the required cell size diminishes. The 15 psi limit for welding gas bottles includes a 100% safety margin. The 30 psi explosion limit is due to the design of the bottles and the size of the largest open volumes within the bottle and valves.

To visualize the way that the volume restricts the shock wave velocity imagine a shock wave travelling through a 2" pipe vs a hypodermic needle. Surface and boundary layer effects are far more prominent in the smaller tube and slow the velocity tremendously.

boslab
04-28-2011, 09:05 PM
An interesting development, i just found not one but 2 absolutely empty acetylene cylynders today, ie open the valve and not a hiss, nothing.
they were connected to a perkin elmer atomic absorbtion spectrometer which was located on the 1st floor lab where i work, the instrument has not been in use for a long time as other more modern instruments have been the preffered choice, it dosent pull a lot of gas really and when on standby either is leaking through to the slit burner or deliberately bleeding as some of the perky instruments do, particularly the older ones.
I was sure you would have got acetone out but obveously i am once again proved wrong, isnt life interesting!
if your Acetylene flow is low then it seems you can in deed flatten a cylynder contents, i think the fact that these cylynders were manifolded together and feeding upstairs significant.
One would suppose that if you wanted to get the gas out without draining the absorbant then run the hose vertically up several feet then back down to the bench to form a trap perhaps?
I have a nearly empty bottle in my shop so i think i may give that a try to see if i cant get some more milage out of it, apart from the fact that i cant get a refill till next Tuesday as we have a holiday Friday because of some wedding, and then a bank holiday as they call them [they never rest do they!] on Monday and some sheet brass to braze
Can you braze with oxy propane fed into a normal oxy acetylene welding torch?
Ive used a cutting torch to do a rough braze but i need a finer fillet for 2 mm brass sheet.
regards
mark

Jaakko Fagerlund
04-28-2011, 11:17 PM
Do your saunas use bottled oxyacetylene? :D
Yup, the usual procedure is one bottle gently shaken and installed in the corner, adjust for proper valve opening and light it up. Please do not look at the flash! :rolleyes:

MichaelP
04-28-2011, 11:28 PM
Can you braze with oxy propane fed into a normal oxy acetylene welding torch? You're supposed to use oxy-propane tips with your torch. I've heard of some people using OA tips with propane, but never tried it personally (and have no inclination to try). Also, you should have T-grade hose if using propane. It's suitable for all fuel gases, unlike R-grade which is acetylene only.


Yup, the usual procedure is one bottle gently shaken and installed in the corner, adjust for proper valve opening and light it up. Please do not look at the flash!
:D

jep24601
04-29-2011, 09:34 AM
....One would suppose that if you wanted to get the gas out without draining the absorbant then run the hose vertically up several feet then back down to the bench to form a trap perhaps?..

DA (dissolved acetylene) cylinders are REQUIRED to be used in a vertical position so that you do not get any of the acetone (which remains in a liquid form) out of them. DA cylinders which have been transported in the horizontal position must be allowed to stabilize in an upright position before use.

boslab
04-29-2011, 11:16 AM
DA (dissolved acetylene) cylinders are REQUIRED to be used in a vertical position so that you do not get any of the acetone (which remains in a liquid form) out of them. DA cylinders which have been transported in the horizontal position must be allowed to stabilize in an upright position before use.
You misunderstand, the bottle stands in the vertical plane, then the hose goes vertically above the bottle, then back down to the bench to provide a physical barrier should you be unfortunate enough to get any acetone out of the cylynder, one would suppose the exercise would be limited to low gas flows, heating with pepperpot or cutting would be out of the question, cylynders should be allowed to stabalise in the vertical for at least 1 hour before use if they have been transported horizontaly, if yoy have a new bottle delivered, even by a supplier assume the bottle has been transported horizontally [at least thats what it says on the wall of my gas compound, courtesy of air products] also a safe seperation between acetylene and propane is now required, or as the new legislation over here states that a safe seperation distance should be maintained between all fuel gasses.
regards
mark

Evan
04-29-2011, 11:33 AM
Originally Posted by boslab
Can you braze with oxy propane fed into a normal oxy acetylene welding torch?

It's hot enough for brazing and I have tried it. The main problem is that the mixture is far more critical with propane than it is with acetylene. Oxy/acetylene will light and burn with nearly any mixture from only a few percent acetylene to pure aceylene. Oxy/propane has a narrow range and that makes it hard to adjust and keep lit.

More important is if you use propane you will use up the oxygen three times faster than with acetylene.

Mark, if you try to prevent the acetone from flowing through the hose by elevating it it won't work. The ID of the hose is small enough that surface tension effects will not allow the liquid and gas to pass each other in the tube. You cannot make a larger volume trap because of the explosion hazard.

lazlo
04-29-2011, 12:11 PM
Do the acetylene tanks in the USA have the acetylene dissolved in acetone like in the UK?
Nope, Physics operate diffrently in the USA and they just pump the tanks full of pure acetylene, Using a couple sprinkles of religion to keep it stable.

But in all fairness, our sprinkles are Imperial, so they're quite a bit bigger than Metric sprinkles.

MichaelP
04-29-2011, 12:42 PM
I didn't know British switched for metric sprinkles already.

Their Imperior Gallon used to be larger than ours. I just don't remember how many sprinkles in one UK gallon vs. US one. :confused:

P.S. By the way, congratulations to our UK friends! I didn't watch the news yet, but I assume the Royal Wedding went smoothly, and you're ready for the return of the regular TV News (murders, rapes, wars and other fun stuff).

derekm
04-29-2011, 12:54 PM
But in all fairness, our sprinkles are Imperial, so they're quite a bit bigger than Metric sprinkles.
Really? I thought it was because a court in rural u.s. had ruled exploding acetylene unconstitutional

MichaelP
04-29-2011, 01:19 PM
Not yet. The court is waiting for Pastor Terry Jones' "Burn The Acetylene Day"

P.S. Was your using small letters in "US" intentional? Is it because your gallon is larger? So it's now UK vs. u.s.? OK, let's step outside! :D

derekm
04-29-2011, 01:30 PM
Not yet. The court is waiting for Pastor Terry Jones' "Burn The Acetylene Day"

P.S. Was your using small letters in "US" intentional? Is it because your gallon is larger? So it's now UK vs. u.s.? OK, let's step outside! :D

no its because when its in capitals US is an acronym for UnServiceable.

As in " I had a prang and now my kite is US" :) :)

boslab
04-29-2011, 04:43 PM
It's hot enough for brazing and I have tried it. The main problem is that the mixture is far more critical with propane than it is with acetylene. Oxy/acetylene will light and burn with nearly any mixture from only a few percent acetylene to pure aceylene. Oxy/propane has a narrow range and that makes it hard to adjust and keep lit.

More important is if you use propane you will use up the oxygen three times faster than with acetylene.

Mark, if you try to prevent the acetone from flowing through the hose by elevating it it won't work. The ID of the hose is small enough that surface tension effects will not allow the liquid and gas to pass each other in the tube. You cannot make a larger volume trap because of the explosion hazard.
Aye your right, i'll stick to sending 5 bar back like usual, never mind, i still havent given up on the acetylene generator yet! [ the steel industry uses vast amounts to desulphurise molten iron, theres usually loads on the floor at the desulph station, just gets swept up and chucked in any old ladle, the other thing lieing round on the floor is magnesium powder!, nice combintion]
regards
mark

greybeard
04-29-2011, 07:53 PM
I learned a few things about acetylene when I was a cast iron welder.

-a- Once filled, a cylinder is never quite empty again...the cylinder can only give up 1/7
of its contents per hour. It will get so low as to not be able to sustain a useable flame,
but shut the valve firmly anyway when disconnecting the regulators. The whiff of gas left
in the bottle is still potentially very dangerous.

-b- The tare weight stamped on the bottle was put on after the bottle was filled with the
acetone, but before being pumped with the acetylene gas.

-c- Some identical cylinders have numbers written on them that are different...this number
represents the amount of gas volume (in cubic feet) that it took to top the cylinder off.
It is legal to charge only for the volume it took to top the cylinder off.

-d- One employer I worked for, insisted on weighing the bottles before and after use, then
paying only for the calculated gas useage. I had to weigh the bottles in and out every week.
Allegedly saved 30-35% on acetylene, compared to just paying for what was written on the
bottles. We used about 12-15 large 309 to 375 cu. ft. (waist high) cylinders per week...6
welders.

-e- It only takes about 1/600th the energy of the spark from your finger on the doorknob, to
ignite acetylene.

-f- If you must move a bottle down some steps, DO NOT let it bump from step to step. The gas
deliveryman told me of a guy who was doing this when the cylinder exploded...they had trouble
finding the guy's remains.

-g- If you must pick a smaller bottle up by hand, dont grab the cap with both hands with your
fingers locked together and pull straight up...if the cap slips off the threads, it can take
your front teeth out suddenly and completely. This, according to the delivery man.

-h- If you change bottles on the manifold often enough, you will soon be able to roll the
bottles by kicking them and steering by the cap with one hand...about as fast or faster than
you can with a two wheeled dolly.

-i- We used a flashback unit (shop built) that was a tank about the size of a 5 gallon bucket
that was 3/4 full of antifreeze. It had a volume several times the volume of the manifold.
The inlet line came from the manifold regulator into the bottom of the vessel. This forced
the gas to gurgle upwards through the antifreeze and into the header. If there was a freak
backfire, it would push the antifreeze down the line toward the regulator and the anti-
flashback valve, closing the valve, and hopefully retarding and/or extinguishing the flame.

I wont tell about the horseplay I witnessed as a youngster. I've seen miracles and luck at its
finest.

I hope this can help someone.

Greybeard