- Thread starter Jaeger_S2k
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Jaeger_S2k
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I suppose there is the extra weight on the torch, especially for light brazing setup (why I have asked).
2 makes all the sense in the world, too.
Torch end I'd say is the best for first line defence, so mine are staying there. Double protection from crappy hoses, then cylinder end, Hmm.
2 makes all the sense in the world, too.
Torch end I'd say is the best for first line defence, so mine are staying there. Double protection from crappy hoses, then cylinder end, Hmm.
An oxygen cylinder glowing red hot in 2 seconds doesn't make sense. There would have to be a "perfect storm" of a combination of factors, such as a nearly empty cylinder (internal pressure less than acetylene cylinder pressure), and a torch tip blockage, causing acetylene to flow back in into the oxygen cylinder, combined with operator error in failing to check for gas flow out of the nozzle.
Acetylene's ability to polymerise spontaneously, and potentially explosively, is well documented, and seems more likely.
brightspark
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the hoses are a good branded one and been on 25 years in nice condition. the gear gets used about 8 times a year but i wouldnt be without it . i hear these horror storys all the time from people who have never even used it
They are there to prevent a flashback getting to the cylinders so that is where they go. Waste of time having a set at the torch end.
brightspark
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yep just the one wa
YEP just the one way check valves on torch to stop the gas mixing in the hoses .the only time flashbacks are fitted on both ends is if the hoses are long
If you were doing a risk analysis, you would likely set the probably of failure quite low, but the consequences of failure at catastrophic. The weighted risk is then significant.the hoses are a good branded one and been on 25 years in nice condition. the gear gets used about 8 times a year but i wouldnt be without it . i hear these horror storys all the time from people who have never even used it
I too have been using O/A for over 50 years and in that time, I have not died even once. It does not follow though that O/A is intrinsically safe and that no one need take any precautions. I would like to think that I was aware of the risk and mitigated it as necessary.
It's a case of being aware, but not alarmed.
Jack
As I mentioned, they also protect the hoses. Here is an excerpt from a standard published 25 years ago.
AS 4839—2001
7.3.3 Flashback arrestors at both hose ends (optimum protection)
Optimum protection is provided when at the blowpipe end a flame arrestor and a non-return valve for each gas line is fitted, and at the regulator end a flame arrestor, a non-return valve and a temperature activated cut-off valve for each line is fitted. Pressure activated cut-off valves at the regulator end are optional. The options in Clauses 7.3.4 and 7.3.5 below provide lower levels of protection and should be used only when it is not otherwise possible to achieve the rated flows of the end heat output device through the lack of outlet pressure from the pressure regulator.
7.3.4 Flashback arrestors at the blowpipe hose ends only
A flame arrestor and a non-return valve shall be fitted to each blowpipe inlet connection.
7.3.5 Flashback arrestors at the regulator hose ends and check valves at the blowpipe ends
At the blowpipe end, non-return valves shall be fitted on each gas line. At the regulator end, a flame arrestor, non-return valve and a temperature activated cut-off valve shall be fitted to each gas line. A pressure activated cut-off valve may also be fitted at the regulator end of each gas line.
Note that there is not a clause that lists "protection" at the regulator only. Where flashback arrestors are only listed for fitment at the regulator, non-return valves are fitted at the torch.
Such standards legally apply to industry, not a backyarder, but that doesn't make them a "waste of time".
Jack
You are quoting an Australian standard.
I was trained using British standards. If you have only one set of flame arrestors they must be fitted at the regulator end. The main danger of a flashback is from the gas bottles.
If the hoses get cut and you have the arrestors fitted at the torch end the bottles no longer have any protection.
I've been using and testing oxy fuel equipment for many years and I've yet to see 2 sets of arrestors fitted.
The standard setup is arrestors at the tanks and non return valves at the torch end of the hoses.
Yes, I understand that is an Australian standard, I am just pointing out that placement and numbers are topics that were deemed important.
How many of your British standards are now identical to ISO standards? That rationalisation is happening is most places - even in the US.
British requirements are less stringent, but getting closer (as you stated).
The Acetylene Safety (England, Wales and Scotland) Regulations 2014 (ASR 2014) came into force on 1 October 2014.
2. Non-return Valves
Non-return valves (also referred to as hose check valves) manufactured to BS EN 730-2 should be fitted to the blowtorch prevent back-feeding. Nowadays, most oxyacetylene hose assemblies from reputable manufacturers are supplied with non-return valves pre-fitted.
3.Flashback Arrestors
In addition to non-return valves, flashback (flame) arrestors manufactured to BS EN 730-1 should be fitted onto the pressure regulators on both the acetylene and oxygen cylinders. For additional safety, flashback arrestors may also on occasions be fitted to the blowpipes, especially if access to the cylinders is confined or they are remote from the operator by virtue of an excessive length of hose, making the cylinders difficult to isolate.
My point is, there is a case for fitment at both ends, even if you decide not to implement it. I am also suggesting that people be aware of potential dangers and base their actions (even if there are none) on that awareness - not just ignore it.
Jack
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That's a brown trouser moment when that happens.... hoses whipping around wherever they want with a fireball on the ends.
Only did that once
Erie Fred
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If the hoses get cut, how will anything flow backwards ?
Dcal
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A leak at the regulator or hoses wrapped up and placed on the bottles.
Acetylene is dissolved and stored at really low pressure.
If it's full there is less chance of a problem but as the bottle empties and the pressure drops even further the chance of the flame popping into the bottle increases and then the **** really hits the fan.
Erie Fred
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A leak at the regulator would be to free air or "atmosphere" ?
Acetylene at "Really low pressure" of how many PSI ?
A leak of hoses wrapped around a bottle somehow get's forced under pressure into a acetylene bottle ?
Pete.
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Fun story:
I was once cutting out a load of sheet piling around an excavation. Some other contractors were doing burning nearby and had dragged their hoses across the site and up other side of the sheet piles. I was working away merrily when I heard a load of shouting. I looked up and this guy was hollering at me "Hey mate you've burned through your pipes". I held up my perfectly burning torch and he said "Oh Fook - they're my pipes" and off he ran
I was once cutting out a load of sheet piling around an excavation. Some other contractors were doing burning nearby and had dragged their hoses across the site and up other side of the sheet piles. I was working away merrily when I heard a load of shouting. I looked up and this guy was hollering at me "Hey mate you've burned through your pipes". I held up my perfectly burning torch and he said "Oh Fook - they're my pipes" and off he ran
Just as a matter of interest, if the hose is cut, arrestors at the regulator will not help, even if there were the possibility of a flashback.
Normally - they will cut off the gas if there is a flashback or over temperature, but not if the hose is cut.
Jack
If the hoses catch fire there is the possibility of a flashback.
How?
A flashback requires a mix of fuel and oxygen in the hose that generally requires a closed system under at least mild pressure. An acetylene hose fire is dangerous but will not feed a combustible mixture back up the hose.
If the hose burnt back to the regulator (arrestor), the thermal cutoff would (eventually) be useful.
It is hard, at least for me, to think of all possibilities but I can't think how a cut hose would cause a flashback. I'd also prefer to be safe than sorry - but I am curious.
Jack
premmington
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I done it once - years ago - severed a pair of hoses - torch went out - snaking hoses - no flame - no drama - walked to bottles and turned bottles off at valves. Flash back arresters did not trip (no back flow).
I would not use a set of bottles without flashback arresters. Most torches have - flame traps in the threaded ends - some have one way valves as well.
I don't use O/A now - only Oxy Propane - and I think the biggest risk is old tired hoses - I not long bought a new set for myself.
I would not use a set of bottles without flashback arresters. Most torches have - flame traps in the threaded ends - some have one way valves as well.
I don't use O/A now - only Oxy Propane - and I think the biggest risk is old tired hoses - I not long bought a new set for myself.
