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  • Acetylene tank warning sticker

    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?

  • #2
    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.

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    • #3
      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.
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      • #4
        Would that problem be addressed sufficiently with check valves on the hoses?

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        • #5
          bugger that ..the stuff is way too expensive ..and the tank rental more ..

          I'd drop it like a hat ..

          all the best.markj

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          • #6
            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.
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            • #7
              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.
              Jim H.

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              • #8
                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.

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                • #9
                  If you are using an acetylene/air torch then no worries.
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                  • #10
                    Originally posted by JCHannum
                    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...

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                    • #11
                      Originally posted by Evan
                      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 ...

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                      • #12
                        I haven't seen reverse flow checkvalves either. I will have to ask around.
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                        • #13
                          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.
                          Last edited by MichaelP; 04-25-2011, 03:49 PM.
                          Mike
                          WI/IL border, USA

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                          • #14
                            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)
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                            • #15
                              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.
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