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Old 03-30-2019, 03:52 AM
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Default Shutting Off the oxygen first- why ?

Harris, the manufacturer of a range of Oxy and Acetylene welding and cutting equipment stipulates in its instructions that the shutdown procedure is Oxygen closed down first.

In Australia a long time manufacturer BOC says the shutdown procedure should be acetylene first.
I have always followed this as the explosive range of acetylene is between 2.5% minimum to 100% maximum.

Are any of you fellas aware of the reason why Harris say this?

I am not trying to generate any argument but simply wish to understand the the reasoning behind this statement.

Can any one shed some light on the pros and cons of this procedure.
Thanks
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Old 03-30-2019, 06:14 AM
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I was taught the Harris method and have always done it that way.

I believe the idea is that the oxygen is used at higher pressure and has the ability to push backwards from the mixing chamber if the fuel gas isn't flowing, causing a backfire or flash. I run oxy-propane which isn't as volatile but when I shut my oxygen off first I never get the loud pop that I notice a lot of guys get when they shut the acetylene down quickly
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Old 03-30-2019, 09:53 AM
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To Prevent flashbacks. from flashing back through the hoses from getting to the regulators and then tanks'. Using flash arrestors in line nowadays it is not so much a worry. It's when not using them, That the possibility of flashing back is more of a concern.

I have installed flash arresters on both ends, A set at the gauges. And set at the torch.
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Old 03-30-2019, 09:57 AM
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I was never taught otherwise, so I always have shut off fuel first. Never had flashback issues, and I always promise myself I will get FB arrestors, but somehow never get'er done.
I'm a propane user.
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Old 03-30-2019, 08:27 PM
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I've always shut off the O2 at the handle, then starve the flame out by shutting off the Acetylene. Then the tank valves, then bleed Acet., then O2 at the handle, then loosen the regulator "T" handles, coil hoses, done.
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Old 03-30-2019, 09:33 PM
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I always shut off fuel first then oxygen.

If I shut off the o2 then the fuel the flame will slowly taper down and the “POP” out
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Old 03-31-2019, 12:03 AM
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I always shut off the fuel gas, usually acetylene, first ...I don't like the little sooty paratroopers floating around if you shut off oxy first...
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Old 03-31-2019, 02:38 AM
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Quote:
Originally Posted by TEK View Post
I always shut off the fuel gas, usually acetylene, first ...I don't like the little sooty paratroopers floating around if you shut off oxy first...
Right and by the time I shut off the torch, there's usually, a little booger hanging off the tip. The pop blows it off. I do have the arrestors on the torch.


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Old 03-31-2019, 12:05 PM
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Fuel off first....
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Old 03-31-2019, 12:49 PM
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the order for lighting the torch is Fuel on light set flow for about correct add oxygen then fine tune.

To shut them off simply reverse the steps .
Remove oxygen by closing valve then close fuel. Takes about a second no pop or possible burn back.
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