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Propane torch problem diagnosed with a laser.

Marco Polo

New member
Nov 2, 2012
I couldn't get a really good photo of this, but these are OK. I guess I need a good digital SLR but given my income and need to constantly scrimp on every bloody thing, good luck with that.

I've been having problems with this propane torch. The flame isn't very stable, it surges a lot and a couple times when I turned it up, there was a "blow-back" and massive gout of fire from the air inlets. Or, rather, I thought it was gas leaking from the inlets causing this.

I diverged out my laser and aimed it at the wall, and if you put the torch in the path of that, you can see the gas coming out. If you light it, you can see the flame in terms of how it bends light due to temperature differences throughout. What I didn't expect is that the valve was to blame. I could see large amounts of gas pouring out of the valve assembly and some of it was being pulled into the air inlets. That was the cause of the surging, apparently, and blow-back was due to the leaking gas contacting the flame.

Oddly enough, if I turn the gas up high, the valve seal will engage properly and stop leaking, at which point the torch will work normally. I can tell when it happens by the sound, and the "laser-gram" view confirmed no further leakage.

I just thought it was cool that I was finally able to diagnose the problem with this torch thanks to a laser. Otherwise, I doubt I would have found out what was going on. Looks like I should be able to replace the valve seal and be good to go, much better than having to replace the whole torch :)

The laser in these photos is the LaserBTB 520nm 50mW (one of the really early ones, from Offroadfreak's GB). It still works perfectly and measures 49mW on my LPM. I really need to get back into doing laser photos. It has been way too long.

Here you can see the flame. The valve is not leaking at this point.

Here you can see the gas leaking out of the valve, visible just to the left of the knob. I didn't get a very good picture here because it's a PITA to get a well-focused image, and I didn't want to release too much propane into my bedroom.

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Well-known member
LPF Site Supporter
Jul 10, 2015
Ahh you could see the gas distorting the light just like invisible exhaust gas distorts daylight, cool.


Super Moderator
Staff member
Dec 11, 2015
Seen this happen with compressed air too, really cool stuff! Invisible to the eye but very interesting with a laser.