I recently invested in a new Portaflame MAPP/Oxygen gas welder. Results to date have been encouraging, and I am slowly improving my technique. The only problem I have is that on shutting down, by closing the torch controls for the MAPP and the oxygen a little at a time in turn, I always end up with a loud and unsettling high-pitched POP as the flame extinguishes. Can anyone give guidance on why this is happening, and whether it is likely to cause damage/injury? TIA.
CRB
It's normal with aceteline welding--probably the same with mapp.
Turn off the oxy first, then the fuel.
hi i recommend turning the fuel gas off first, that way the oxygen 'blows out' the remnents of the flame. if the oxygen is turned of first the fuel gas will 'flare up' this could be a hazard. bob
high-pitched
No!
Fuel gas on first AND off first to avoid the explosions. I was taught that the only time you should turn the oxygen off first is if you've had a blow back and the flame is burning in the torch - or horror of horrors in the pipe.
AWEM
taught
I'll second that, and always leave the cylinder valve key in the oxygen valve - oxygen being the far more volatile and dangerous gas.
Also, unlike someone I know (who should have known better...), install any flash-back arrestors at the gauge end of the hoses and not the torch end... :~(
So was I - I disagreed with it then and I do now (so do many others too as this argument has been around for years!)
The only side effect of turning off the oxy first is you temporarily get a large sooty flame. Where the explosion comes from I'll be buggered, when you light the torch, fuel on first then oxy - no bang. All you are doing when switching off is removing the oxidiser and going back to raw fuel again. If you light a torch, get the fuel on, then before the oxy is on you change your mind then turning off the fuel makes the flame go out - end of story.
Turn the fuel off first and you might just end up leaving the oxy on - a far more dangerous situation.
The oxygen and fuel mix inside the burner head, but they burn outside. What's actually happening is that the flame-front is continually trying to move back into the burner head, but the outward flow of the gas/oxygen mixture prevents it from doing that.
In operation, it settles into a stable situation where the flame is "attached" to the rim of the burner. The rate of burning exactly balances the rate of feed, and you have a stable flame.
When you turn the gas and oxygen right down, this balance no longer holds. The flame front strikes back into the burner head, and the whole volume inside the head burns all at once - pop.
If it just pops and blows itself out, then it really is mostly harmless. You're turning the torch off anyway so it's self-limiting. The situation to avoid is where the gas continues to burn inside the burner... so don't do that.
No, this is wrong and potentially dangerous.
Turn the fuel off _first_.
If you do it the wrong way round, then there's a risk of combustion in the mixer and sot buildup. If you allow this to buildup (and cleaning it's an awkward task) then you increase the risk of blowbacks and all those real safety problems you don't want to go anywhere near.
There's also the risk (mainly with big oxy-propane burners) that you can switch from a small but powerful mixed-gas flame to a pure fuel flame that's a couple of feet long (as you wound the thing up in stages when first lighting up). This can cost you eyebrows.
You may be shutting things off a bit too abruptly. There should be a pop, but it shouldn't be "loud" with a welding nozzle.
I'm not familiar with MAPP, but with some of my bigger oxy-propane kit I wear ear defenders. If one of those pops, it's loud enough to hurt!
================= BOC used to supply a welding guide (Publication TC 1430) with their 'PortaPak' welding equipment.
The lighting up procedure specified in the guide is, acetylene on first adjusted 'until the flame just ceases to smoke'. Then slowly feed in oxygen 'until the white cone of the flame is sharply defined with the merest trace of acetylene haze.'
Shutting down is the reverse - shut off the acetylene completely and then shut off the oxygen.
These were the instructions supplied about 30 years ago and as far as I know they're still the same today.
Just in case nobody else has told you - don't use any oil on the gauges / threads etc. It can be verydangerous.
Cic.
seconded :-)
Same as we do with O2/H2 welding kit.
How can any *gas* be volatile, let alone oxygen?
MBQ
Oxygen boils off very easily - I'd say that was volatile.
the
He said it was a volatile *gas*. How does a *gas* boil off?
I'm not disputing that liquid oxygen is volatile.
MBQ
When its liquified ;-)
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.