wrote:
On Monday, April 14, 2014 3:02:24 PM UTC-5, Cydrome Leader wrote:
I finally dug out the $2 garage sale Craftsman (really Harris)

oxy-acetylene cutting torch. It came with a cutting head of unknown size

which I just cleaned out and #7 torch tip.



It passes the soapy leak test when pressurized, and the o-rings appear ok.



I've not used one of these before but have run into a problem.



I set the acetylene until the flame is not a smoky mess. Then I add oxygen

at the cutting attachment valve (It's wide open on the torch handle) then

I push the cutting lever and the flame gets really vicious. When let go of

the cutting lever, the thing goes BANG and the flame goes out.



What might be going on here? I've got a new set of torch side flashback

preventers to attach before I play with this more.



The welding forums go on about how this is backfire vs. backflash and that

the torch is leaking air or the O2 pressure is too low or something is

broken. It's all vague.



I had the O2 as about 10PSI at the regulator and the acetylene around 5.

Not sure if these are correct-ish.



Suggestions?

You probably have 6920 cutting tips (most common) on your torch. Make sure that the tip is clean (use a cutting tip cleaner). Regulator pressure depends upon the tip number that you're using (stamped on tip barrel). See:
http://www.harrisproductsgroup.com/~...onCUTTING.ashx

That looks about right. The cutting tip I have is apparently stamped "1",
so the chart indicates 35-40 PSI for the oxygen.

I did finally unscrew it from the torch head and there are half shiny
metal/half dark looking surfaces where the tip mates with the head. I'm
going to assume this is no good and it needs to be cleaned or corrected
somehow. Links to the photos are below:

the torch itself

http://www.panix.com/~presence/torch.JPG

the mating surfaces of the tip

http://www.panix.com/~presence/tip-seat.JPG