O/A: why shut off acetylene first?
RSS | Subscribe | Contact Us | Advertise | About Us
Page 1 of 2 12 LastLast
Results 1 to 25 of 45
  1. #1
    Join Date
    Apr 2008
    Location
    Western Canada
    Posts
    102

    O/A: why shut off acetylene first?

    It's typically recommended that when finishing with the use of an O/A torch, you shut off the acetylene first, then sut off the oxygen. I realize that this extinguishes the flame immediately, because the fuel gas is gone. But in my experience it also often causes a pop (a big pop with larger tips). But if you shut off the oxygen first, your'e simply left with the loose acetylene flame of the type you have when you spark-light the torch at the beginning of the session. Then you can quickly shut this off. No pop. As long as you're careful where you're holding/pointing the tip, it does not seem unsafe.

    If the session has gone nicely and you're in control of the torch and flame, why is shutting off in this order (oxygen first, then acetylene) a problem? - or why is this recommended against? Has anyone here actually experienced a problem (your own problem, or somebody else's in a shop you were working in)?

  2. #2
    Join Date
    Nov 2008
    Location
    south GA where its hot in summer and cold in winter
    Posts
    3,474

    Re: O/A: why shut off acetylene first?

    If the acetylene is allowed to continue to burn, it can burn back into the torch body melting orings and valves. The oxygen quickly uses up spare acetylene. The loud pop is a quick backfire.
    Welders:
    Esab Migmaster 250
    Penncraft 230 (oldy but goody)
    HF Plasma 30 (Italian)
    Lincoln Ranger 8
    Smith Oxy/Acetylene/Propane
    Lincoln SA200
    Everlast Power Tig 250 EX
    Everlast PowerUltra 205

  3. #3
    Join Date
    Jan 2008
    Location
    Loveland, CO.
    Posts
    170

    Re: O/A: why shut off acetylene first?

    Who recommends that?

    I thought it was the other way around.
    Lincoln PowerMig 180c
    Victor O/A
    Bandaids and aspirin

    I don't know what I don't know!?

  4. #4
    Join Date
    Nov 2008
    Location
    Texas Near Dallas
    Posts
    988

    Re: O/A: why shut off acetylene first?

    It is the other way around. Straight from the victor manual:

    Follow these procedures when you finish your cutting, heating, or welding operations
    1) FIRST, shut off the oxygen control valve, THEN shut off the fuel control valve. A "pop" may occur if you reverse this procedure. The "pop" throws carbon soot back into the torch. The soot may partially plug the gas passages.
    2) Close both cylinder valves

    and so on and so on to bleed off pressure, etc.

    Dynasty200DX w/coolmate1
    MM210
    MM Vintage
    Lincoln AC225
    Victor O/A, Smith AW1A
    Cutmaster 81
    IR 2475N7.5FP
    Rage3
    Jancy USA101
    9" SB
    AEAD-200LE

  5. #5
    Join Date
    Mar 2004
    Location
    B.C. Canada
    Posts
    2,279

    Re: O/A: why shut off acetylene first?

    There is a few things to keep in mind. I don't know the exact speed but believe the number for speed of flame front for acetylene approaches the speed of sound. It is fast!
    Acetylene will burn in mixtures ranging from around 2 percent to 98 percent so it is easily ignited.
    When you turn off the acetylene the remaining oxygen in the will supply the trace amounts of acetylene with oxidizer until all the fuel is used up. If you shut off the oxy the acetylene flame will travel along the supply route to the closed oxygen valve. Gee I hope it is closed and not leaking.........
    General rule is fuel on first and fuel off first.
    The only exception is if you have a burnback into the torch handle or mixing chamber. You will see no flame but hear a high pitched scream. The next thing that can happen is the torch will glow red in the critical area or you get a flashback all the way to the gauges.
    The solution to a burnback is to quickly turn off the oxy and hopefully the acetylene will run out of oxidizer and reappear at the torch tip and then you can close the fuel valve off.
    Anti-flashback valves are required in almost all jurisdictions now for good reason.
    A torch that has experienced a burnback really should be sent in for cleaning, inspection and safety check.... by someone who knows what he/she is doing.

  6. #6
    Join Date
    Feb 2007
    Posts
    557

    Re: O/A: why shut off acetylene first?

    Quote Originally Posted by AndyA View Post
    It is the other way around. Straight from the victor manual:

    Follow these procedures when you finish your cutting, heating, or welding operations
    1) FIRST, shut off the oxygen control valve, THEN shut off the fuel control valve. A "pop" may occur if you reverse this procedure. The "pop" throws carbon soot back into the torch. The soot may partially plug the gas passages.
    2) Close both cylinder valves

    and so on and so on to bleed off pressure, etc.
    I've been following this procedure for over 25 years and my father for 25+ before that with no issues.

  7. #7
    Join Date
    Jan 2008
    Posts
    913

    Re: O/A: why shut off acetylene first?

    Fuel on first, off first. Most texts from the 19teens on list this method to PREVENT carbon build up in the mixer etc. In fact even durring lighting the torch they would instruct users to always have a bit of oxygen to prevent a "sooty" acetylene flame as this also causes carbon build up. Present day instructions seem to have gone away from this, especially Victor. However from first hand testing, using the older method DOES reduce the carbon build up in the torch. Start thinking about it, and the older method makes a lot more sense from a safety standpoint as well.

  8. #8
    Join Date
    Jun 2008
    Location
    Central California
    Posts
    3,768

    Re: O/A: why shut off acetylene first?

    The burning rate of the O2/Acet. mix depends on the gas ratio and is faster for higher O2 percentage. If you shut of fuel first, the mix O2 level will change upward within the torch, allowing the flame to suddenly burn back into the torch, causing the small 'pop'. If you turn of O2 first, the burning rate quickly lowers 'till only fuel is exiting the tip, so you get only a smoky flame.

    The safe and correct method is to shut off the Oxygen first.

    They can be lowered in steps to reduce smoking, but still in this order, not going to an oxidizing flame at any time.
    .

  9. #9
    Join Date
    Dec 2007
    Location
    Guerneville Ca
    Posts
    1,721

    Re: O/A: why shut off acetylene first?

    Use of a torch and procedures to turn on and turn off the torch is one of the first things you learn in beginning welding class.

    Extremely important!!!

    Bleeding your hoses also at the end of the day.

    Misuse of the torch has caused many deaths and injuries.
    I personally know of three incidents in my area that caused death or injury.
    One incident in Louisiana caused 18 deaths,blew the windows out of houses for 3 mile, and blew up a LPG tanker ship. All caused by one person that did not take care of their torches.

    Not bleeding hoses cost a guy in my town a jaw injury and partial loss of vision in one eye.
    Please be responsible. TAKE A CLASS or READ A BOOK.
    AWS certified welding inspector
    AWS certified welder
    44 years experience.
    Miller 110V 140 MIG
    Miller Elite auto sensing helmet.

  10. #10
    Join Date
    Jan 2008
    Posts
    913

    Re: O/A: why shut off acetylene first?

    Quote Originally Posted by Donald Branscom View Post
    TAKE A CLASS or READ A BOOK.
    Exactly!
    But there in lies the problem. We have two different methods, both coming from either instructions, or text books. Bleeding down the system is almost universal. One could argue that a newer text, must be better. One could also argue that an older text from when O/A was the mainstay would be a better source. Its like reading up on adjusting ignition points, do you trust the 2008 book or the 1968 book? Maybe we are all fools to think we understand the reasons behind why different torch brands had different procedures. Maybe the reasons themselves are foolish. We all know there are no standards for regulator pressure vs. tip size......at least I hope we all know that. Anyone that thinks there are needs to go back to fluid dynamics 101. Maybe victor had a reason for their procedure, maybe something specific or a flaw witth their design. Study the history of technology, and you will find the "historical information" we have now, is much the same as the childhood game of telephone, rather than an accurate recording of things learned in the past.

  11. #11
    Join Date
    Apr 2008
    Location
    Western Canada
    Posts
    102

    Re: O/A: why shut off acetylene first?

    Quote Originally Posted by makoman1860 View Post
    Most texts from the 19teens on list this method to PREVENT carbon build up in the mixer etc. In fact even durring lighting the torch they would instruct users to always have a bit of oxygen to prevent a "sooty" acetylene flame as this also causes carbon build up. Present day instructions seem to have gone away from this, especially Victor. However from first hand testing, using the older method DOES reduce the carbon build up in the torch.
    That leads me to another question: Where can I get information about cleaning out any carbon that may have accumulated over time in my torch handle?

    Seems to me that the sooty flame we get when first lighting the torch may contribute quite a bit of soot over time.

  12. #12
    Join Date
    Mar 2004
    Location
    B.C. Canada
    Posts
    2,279

    Re: O/A: why shut off acetylene first?

    If you have soot up inside the torch handle and mixing chamber it is time for a certified gas tech to clean, inspect, and repair. You do not want the liability even in Canada where lawyers are not completely free range. Add that to Worksafe BC on your butt and it is not worth it.
    I am collecting info on fuel on fuel off first to be presented later.

  13. #13
    Join Date
    Aug 2006
    Posts
    27

    Re: O/A: why shut off acetylene first?

    from what ive seen victor recommends shutting down the oxygen first but smith recommends the opposite.
    Last edited by jwright; 04-02-2009 at 09:24 PM. Reason: typo

  14. #14
    Join Date
    Jun 2005
    Posts
    1,242

    Re: O/A: why shut off acetylene first?

    Quote Originally Posted by AndyA View Post
    It is the other way around. Straight from the victor manual:

    Follow these procedures when you finish your cutting, heating, or welding operations
    1) FIRST, shut off the oxygen control valve, THEN shut off the fuel control valve. A "pop" may occur if you reverse this procedure. The "pop" throws carbon soot back into the torch. The soot may partially plug the gas passages.
    2) Close both cylinder valves

    and so on and so on to bleed off pressure, etc.
    X2, welding class
    My Babies:

    HF Drill press
    HF Pipe Bender
    3 4.5" Black and Decker angle grinders
    Lincoln Electric PROMIG 175
    that´s it!

  15. #15
    Join Date
    Mar 2004
    Location
    B.C. Canada
    Posts
    2,279

    Re: O/A: why shut off acetylene first?

    Elvergon is correct. That is indeed what is in the Victor literature.

    My Linde torch and Canox torch manuals say fuel off first. Modern welding (1988) also says fuel off first.

    At this point I guess we just have to follow specific manufacturers instructions. Anyone know a victor tech rep we can ask?

  16. #16
    Join Date
    Nov 2008
    Location
    south GA where its hot in summer and cold in winter
    Posts
    3,474

    Re: O/A: why shut off acetylene first?

    Welding Principles and Applications 6th ed says turn off gas first to blow flame out and away from tip, unless loud pops are observed everytime, then turn off oxygen first. Then be sure flame is out before putting down torch.

    I guess it depends.
    Welders:
    Esab Migmaster 250
    Penncraft 230 (oldy but goody)
    HF Plasma 30 (Italian)
    Lincoln Ranger 8
    Smith Oxy/Acetylene/Propane
    Lincoln SA200
    Everlast Power Tig 250 EX
    Everlast PowerUltra 205

  17. #17
    Join Date
    Jun 2008
    Location
    Central California
    Posts
    3,768

    Re: O/A: why shut off acetylene first?

    If anyone contacts a representative of any company which recommends the 'fuel off first' procedure, please ask for, and then report here, the reasoning behind it. Can anyone offer a reason why the explanation I gave is wrong?
    Seems to me that:
    Welding Principles and Applications 6th ed says turn off gas first to blow flame out and away from tip, unless loud pops are observed everytime, then turn off oxygen first
    is saying 'do it wrong if you feel like, unless it causes problems, and then do it right'.

    If there is some rare occurrence with either method, I'd like to understand it. Anyone have good access to the technical people at Linde or ???

  18. #18
    Join Date
    Jan 2004
    Location
    Northern Cal., Shasta County
    Posts
    6,825

    Re: O/A: why shut off acetylene first?

    I'll add one to the fuel 1st list.

    (US gubmint, 1993)

    TC 9-237

    OPERATOR'S CIRCULAR
    WELDING THEORY AND APPLICATION

    n. Treat regulators with respect. Do not turn valve handle using force.
    o. Always use the following sequence and technique for lighting a torch:
    (1) Open acetylene cylinder valve.
    (2) Open acetylene torch valve 1/4 turn.
    (3) Screw in acetylene regulator adjusting valve handle to working pressure.
    (4) Turn off the acetylene torch valve (this will purge the acetylene line).
    (5) Slowly open oxygen cylinder valve all the way.
    (6) Open oxygen torch valve 1/4 turn.
    (7) Screw in oxygen regulator screw to working pressure.
    (8) Turn off oxygen torch valve (this will purge the oxygen line).
    (9) Open acetylene torch valve 1/4 turn and light with lighter.
    NOTE
    Use only friction type lighter or specially provided lighting device.
    (10) Open oxygen torch valve 1/4 turn.
    (11) Adjust to neutral flame.
    p. Always use the following sequence and technique for shutting off a torch:
    (1) Close acetylene torch valve first, then the oxygen valve.
    (2) Close acetylene cylinder valve, then oxygen cylinder valve.
    (3) Open torch acetylene and oxygen valves to release pressure in the regulator
    and hose.
    (4) Back off regulator adjusting valve handle until no spring tension is left.
    (5) Close torch valves.


    http://www.govmedia.com/

  19. #19
    Join Date
    Aug 2008
    Posts
    8,502

    Re: O/A: why shut off acetylene first?

    WEIRD!!!!!!!!!!

    Maybe it's the torch brand. I use Harris. Light the acetylene w/o 02, give it 02 and adjust to neutral.

    When you shut it off, turn the Acetylene off first, then the 02. Do it in reverse, like y'all are talkin' about..........it POPS.

    Been using the same torch for 12 years, and if there's carbon in it, I wouldn't know. Still works fine.

    They use a Victor at the LWS, and light it with both gasses on. Crazy thing puts out a drastic flame imediately. I don't like that. Could burn the daylights out of the hand holding the striker. I really never watch the guy turning it off, but it pops every time. I'm pretty sure he's turning the O2 off first.

    And BTW..... how can you get carbon in the mixer when the flame's burnin' outside the tip. It ain' t burnin' inside the torch handle. I'm no expert, but it seems that if it pops, there's combustion inside the torch body. So turn the 02 off last so it doesn't pop.

    I dunno, maybe I just gotta weird torch. Wouldn't surprise me
    "Any day above ground is a good day"

  20. #20
    Join Date
    Jan 2008
    Posts
    913

    Re: O/A: why shut off acetylene first?

    Quote Originally Posted by Oldiron2 View Post
    If anyone contacts a representative of any company which recommends the 'fuel off first' procedure, please ask for, and then report here, the reasoning behind it. Can anyone offer a reason why the explanation I gave is wrong?
    Seems to me that:
    is saying 'do it wrong if you feel like, unless it causes problems, and then do it right'.

    If there is some rare occurrence with either method, I'd like to understand it. Anyone have good access to the technical people at Linde or ???
    I doubt you will find anyone left at most of those companies that knows. Especially victor, good luck getting ANYONE at that place that knows a thing about torches. For the most part all we have to go on is texts, and the majority fall into the "fuel first" category. From my experience with smaller torches, its THE method to use to reduce carbon buildup. However it may not fare so well on scrapyard equipment. Those of you that work at companies that develop and make products, know dang well how one persons preference, backed by data or not, can seem to make it into a product or printed instructions if they are in the right position. For all we know some guy in charge of tech writing at victor had a hair up his butt and just put whatever procedure he wanted in the literature, and everyone after him at the company just copied it for all these years. Ive seen it happen over and over.

  21. #21
    Join Date
    Jan 2008
    Posts
    913

    Re: O/A: why shut off acetylene first?

    Quote Originally Posted by farmersamm View Post
    WEIRD!!!!!!!!!!

    Maybe it's the torch brand. I use Harris. Light the acetylene w/o 02, give it 02 and adjust to neutral.

    When you shut it off, turn the Acetylene off first, then the 02. Do it in reverse, like y'all are talkin' about..........it POPS.

    Been using the same torch for 12 years, and if there's carbon in it, I wouldn't know. Still works fine.

    They use a Victor at the LWS, and light it with both gasses on. Crazy thing puts out a drastic flame imediately. I don't like that. Could burn the daylights out of the hand holding the striker. I really never watch the guy turning it off, but it pops every time. I'm pretty sure he's turning the O2 off first.

    And BTW..... how can you get carbon in the mixer when the flame's burnin' outside the tip. It ain' t burnin' inside the torch handle. I'm no expert, but it seems that if it pops, there's combustion inside the torch body. So turn the 02 off last so it doesn't pop.

    I dunno, maybe I just gotta weird torch. Wouldn't surprise me

    Use one 8 hours a day and you can build it up pretty fast without popping. The trouble seems to happen more in equal pressure mixers that may contain a pocket of oxygen if you shut the fuel off last. My victors are all equal pressure, and my J series all have the "twisty mixer" spiral bent copper strip in them. Its a mute point really, with a high ratio oxygen atmosphere inside the tip when you shut the fuel off first, there will be an excess of oxygen to combine with, so there should be no left over carbons with that final "pop" at shutdown. Anyway, fun discussion, but probably without a solid outcome other than confusion.

  22. #22
    Join Date
    Aug 2008
    Posts
    8,502

    Re: O/A: why shut off acetylene first?

    I've got a really weird torch. It was marketed by Sears, but it's made by Harris.

    Never seen a torch like it. The 02 mix knob is under the lever between the lever and the body. The lever depresses a little ball in the middle of the knob to supply the cutting oxygen. I'll post a pic tomorrow. Too lazy to unlock the shop and get it out right now
    "Any day above ground is a good day"

  23. #23
    Join Date
    Sep 2008
    Location
    Central PA
    Posts
    1,963

    Re: O/A: why shut off acetylene first?

    Fuel gas ON first, OFF first.

    Been doing that for 45 years now. Was taught that, and I taught that. I have a Dockson torch that's over 40 years old. NEVER had problems with carbon internally. Did have to change an "O" ring on the cutting head about 20 years ago. Motorcycle battery filler cap O ring worked great.

  24. #24
    Join Date
    Apr 2008
    Location
    Western Canada
    Posts
    102

    Re: O/A: why shut off acetylene first?

    Okay. Well, if I go with the predominant recommendation (acetylene off first, then oxygen), I'll get lots of pops. I know this from experience with my torch.

    That leads me to another question. I've got flame arrestors between my hoses and my torch handle. I bought the torch with the arrestors on it, secondhand from a friend who has since moved away - but I know the torch had quite a few years of use. No problems ever with the torch handle, since I've owned it. But do flame arrestors ever need to be replaced, to make sure they will function correctly when actually needed - and, if so, how often should they be replaced?

  25. #25
    Join Date
    Jan 2006
    Posts
    1,618

    Re: O/A: why shut off acetylene first?

    I'm with the fuel first crowd, a Smith rep gave me the reasoning. Turning off the fuel first allows the oxygen to purge the torch of combustables. If you turn off the o2 first, you'll have a combustible mix of fuel/air in the torch which can cause a flash back the next time it is lit.

    Flame arrestors only need to be replaced if they plug up.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
RSS | Home | Penton Media | Contact Us | Subscribe | For Advertisers | Terms of Use | Privacy Statement