wrote:
On Wednesday, April 16, 2014 8:23:05 PM UTC-5, Clare wrote:
On Wed, 16 Apr 2014 06:45:26 -0700 (PDT),

wrote:



On Tuesday, April 15, 2014 6:05:44 PM UTC-5, Cydrome Leader wrote:

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



Maybe try cleaning the mating surfaces with some fine steel wool. Check for daylight between the mating surfaces or mark the mating surfaces with a colored marker to see how they seal.

Water based only. NOTHING containing any oil or flamible materials

near oxygen.

No seals in danger of burning here. Any fuel content of markings from magic marker would probably be negligible, but I agree to keeping the mating surfaces clean.

well, I went ahead and cleaned the surfaces. I ran the the back of the tip
on fine sandpaper to romove the high spots and brushed the brass part of
the torch clean. The sharpie test shows what seems to be a good enough
seal now.

Setting the oxygen to just over 20psi did really help. I was able to slice
up some steel plate about 3/4" thick. Teh torch did backfire (if that's
what t the loud pop followed by the flame going out is) a few times, but
only when shutting off the oxygen before turning the torch off. Does this
indicate a problem may still be present?