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tenfingers
03-04-2005, 12:23 AM
I'm getting tooled up to try gas welding and I read that I need some sort of reverse flow valve or flashback arrestor. Which one would you recommend and would you install it on the torch or on the regulator?

I promise that I won't blame anyone if I follow their advise and become disfigured as a result.


Thanks for your opinions,
10F

precisionworks
03-04-2005, 12:52 AM
Check valves (reverse flow valve, backflow preventer) are usually installed between the hoses and torch & prevent back flow -- they close if a reverse flow starts. They contain a spring-loaded ball that allows flow only toward the torch. Check valves don't always stop a flashback from reaching the hoses, regulators, and cylinders.

Once a flashback starts, check valves can not stop it, but a flashback arrestor will. The arrestor usually connects between the hose and the regulator. It contains a sintered metal element that allows gas flow from tank to torch but absorbs flashback heat and prevents the flame from entering the tank. Most of them also contain a check valve.

Both check valves and flashback arrestors are needed for complete protection.

3 Phase Lightbulb
03-04-2005, 01:02 AM
Do you already have a torch? I just bought a O/A setup and I've found that most have built in arresters.. Most of the Victor's i looked at anyway.

-3Ph


[This message has been edited by 3 Phase Lightbulb (edited 03-04-2005).]

tenfingers
03-04-2005, 01:24 AM
3 phase,
Yes, I just bought a torch. It's a Meco Midget and doesn't seem to have any arrestor. At least nothing that I can see from the outside.

Precision,
Sounds like a combo check valve-arrestor would be safest. Id rather install it between the hose and regulator, but wouldn't you get a good pop if it flash- backed all the way up the hose?

10F

precisionworks
03-04-2005, 01:33 AM
10F,

Good pop is an understatement! I read somewhere that a balloon filled with O/A has the explosive force of 1/4 stick of dynamite. The article said that the volume in 25' of 3/8" hose is about the same as that balloon. You sure don't want someone calling you Sixfingers!

mattc
03-04-2005, 02:41 AM
tne torch I just got has them built into the handle but I cannot see them from the outside, if you read the manual for yours it may have them

Matt in AK

ricksplace
03-04-2005, 05:50 AM
10F -
I have combination flashback arrestors and checkvalves at the regulators and at the torch. If your torch is a small one, you can get slim profile torch arrestors. The arrestors at the torch stop a flashback from getting to the hose. If slag drops on the hose and ruptures it, the arrestors on the regulators prevent a flash from reaching the tank. Good insurance to have both.

rockrat
03-04-2005, 10:31 AM
Tenfingers, My flash arestors are before the torch handle and after the regulator. Also, I think that I have some extras sitting around here from an auction. You know, they were part of the little leftovers in the bottom of the box of the thing that you realy wanted. What size do you need? I'll send them to you (free) if they will work. I don't need them.

tenfingers
03-04-2005, 10:44 PM
Thanks to everyone for your help.

My torch instructions mention flashback arresters as an accessory, so mine must not have them. The hoses are only 9 ft long and 1/4 inch, so I might not lose 4 fingers as suggested by Precision. Still, I enjoy them all so I think I'll put arresters on both the regulator and the torch.

Special thanks to Rockrat for the offer. I've just e-mailed you the sizes I'm looking for.

Thanks again,
10F

smurph
03-07-2005, 09:05 PM
I had a shop instructor in high school demonstrate the exposiveness of O/A. He took a regular empty match box and put a hole 1/4" in the top, filled it with acetylene and lit it. The gas was not explosive at this point. All it did was produce a nice little flame from the hole in the match box. Then he proceeded to inject oxygen from the torch. BLAM! Heh, on hell of an explosion. http://bbs.homeshopmachinist.net//smile.gif All of the student's eyes were wide open with surprise. How can that little measure of gas do that? Well... it does.

The safety extent of the lesson was summarily lost to a bunch of high school boys though. My best friend and I went immediately to my house that afternoon and got out my step dad's O/A tourches and started blowing up every match box we could get our hands on! When we ran out of match boxes, we looked for some other suitable container to blow to shreds. Then we found one... An empty 12 gauge shot gun shell box. It wasn't that much bigger than the match box was it? We filled it up with acetylene and lit it. Then shot the oxygen to it and all I can say is it was the biggest explosion that I have ever been involved in! It propelled my friend and I into the air and back 10 feet. My friend just hit the ground, but I landed on the back bumper of our pickup truck. I remember coming to, dazed and confused, and looking at my friend. He was grinning ear to ear but his face was black as coal from the soot of the explosion. We were lucky. And we finally learned our lesson. http://bbs.homeshopmachinist.net//smile.gif

Now, I'm not sure just how much gas was in that shell box, but I would hate to see what would happen with amount of gas in a torch hose. I just know that the explosion of the gas in the shell box was orders of magnitude bigger than that of the match box.

Err... Take it from me, don't try this at home.


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That's my story and I'm sticking to it...