Butane torch repair

I bought a cheap butane torch on Ebay to keep at the space (yeah, in violation of the “no pressurized gasses” rule, but stashed away in my box).  Worked fine, rarely used.

When I wanted to bend some laser cut acrylic to make  cases for 485 net nodes, it worked fine – until it didn’t.  It just wouldn’t stay lit.  I brought it home, refilled it and brought it back to the space the next week, but it still wouldn’t light and wouldn’t even stay lit if lit from another flame (butane lighter in electronics lab).

Failing to try the obvious small screws, and thinking it was all but junk, I tried to unscrew the obvious metal tip housing.  It turned, but didn’t feel like it was unscrewing.  No more acrylic bending for you.  Grumbling, I brought it back home.

I finally removed the little screws, (seen here in my nice Bondo-filled plastic cap parts tray).

Kudos to the manufacturer for making all 5 screws the same size. 🙂  When I popped it open, I was met with this interesting view:

It wasn’t too embarrassingly long until I realized this was the result of trying to unscrew the tip.  Not much gas gonna come out like that.  Fortunately, nothing was damaged, and it was an easy fix.

Side question:  The insulated wire is clearly (ha!) for the ignition spark.  But where’s the return path?  Is the black tube conductive?

But it still didn’t light or stay lit.  Butane torches and lighters are pretty similar, so after lots of YouTubes and nut-case lighter people forums, I learned:

• Many say you should vent it (hold with fill valve up, depress valve with small tool, let some gas out.)  Recommendations vary from “bleed it empty every time before you refill” to “every several months”, to “when needed”.
• There are religious arguments about fuel, with comments running 20-1 in favor of triple- or quintuple distilled brands.  Disbelievers point out the 5X stuff is really only distilled 3 times, with just filtration steps in between, so not really 5X.  <rolls eyes>  Ronson (what I have) is pretty universally put at the bottom of the list.  And then the 5% guy pipes up with “I use nothing but Ronson, and haven’t had a problem in 10 years.”  Hmm.
• LOTS of people complain about short lifespans of even name brand (Bernzomatic et al) torches.  The ignition systems are the biggest complaint.  My igniter still works fine – the torch just doesn’t work.
• One seller of torches (and 5X fuel!) started a video with half a dozen assorted torches customers had returned as not working.  He claimed “There’s nothing wrong with any of these.  They just used bad fuel!”  Hmm.

Because mine would ‘pop’ frequently, but just never stay lit, as I thought about it, it started to feel like a fuel problem.  If there were really some air in the tank, the mixture wouldn’t be right, and that might result in the behavior I was seeing.  (OK, if the flame didn’t back up into the air-sullied tank and explode first.  Which it hasn’t done, reflecting poorly on this hypothesis.  Fortunately.)  But the ‘purge’ idea resonated anyway.

Tried a couple of purge cycles – no change.  At least that’s consistent with not exploding.

The nozzle is a venturi/reverse carburetor (airburetor?) sucking the air in.  Might those passages be blocked?  Using another suggestion from the forums, I blasted it with compressed air.  No change.

I’d seen demos of torches with mixture adjustments go to a soft yellow flame with the air turned off.  Mine doesn’t have that, but what if I blocked the air inlets?  With blue painter’s tape putting it on ‘full choke’, I got this surprising but unsurprising (!?) result:

Slowly peeling the tape away gave a normal looking flame.  More air, and it blew out.  Hmm.

Playing with the red gas volume adjustment, it would close all the way off, and seemed closest to working with it on full.  Is there some further hidden adjustment?  Thinking back on what I’d seen when it was open – was that red adjustment on a splined fitting?  <opens it up again>  Sure enough!

I set it to about mid way, lifted it off and set it back so the red lever was close to its lowest setting.

Moving it back up to full throttle, it lit!

I moved it again to give myself a little more top end, put it back together, and it works again.  That’s great.  But why did it fail?

My best guess is there’s some crud (See?  I told you that Ronson stuff was crap!) in the gas path and the valve needs to be open more than when new to get enough gas out.  It could (well?) be that that’s what lots of short-lifespan people are seeing, but they don’t have a way to turn the gas up more.  I’m not going to do a clean room teardown to check that out.  It works again, so I’m done!

Maybe a takeaway is that a torch with more full-scale gas control (like a real needle valve) is more robust against a little crud in the line.  (And might as well ask for air/mixture control, too.)

A couple weeks later

I came across a closeout display of obviously identical design torches for $2.69 each (regular $4.99).  Only 2 left.  Their cool feature was a bottle opener in the screw-on base (which I had no interest in).  The clear blue one had the bottle opener (and visible fuel), but no gas came out.  The clear orange one didn’t have an opener (and thus a slightly less stable bottom), but lit.

I expect 60% I could have fixed the blue one, but didn’t have a #0 Phillips with me (and was standing in the aisle at Menards).  I took the orange one.

And a couple more weeks later…

11/30/19:  The orange torch was an impulse purchase – I had no particular use in mind for it.  (But it was such a deal!)  It lived on the electronics bench near the good Portasol torch (with soldering attachment) which is the reason I didn’t need another.

While finally working on cleaning off the bench the other day (yay!), I came across some bulky PCBs I’d apparently saved to salvage some parts from.  I almost just pitched them (in the electronics recycle), but saw the orange torch, thought it might work well, and gave it a try.

After I hit my stride, it worked about perfectly for the task, and I soon had a stack of clearly salvaged parts that might come in handy some day.  I don’t do that very often, but I’ll try to remember that a small torch works well for it.

Spark return path

10/29/23  I’ve long suspected that the black gas tube was the electrical return path for the ignition piezo, and have finally proved it.

I found an old torch, opened it up, and pried the black tube off at the tank end.  Measuring the resistance of the tube from end to end showed 600Ω.  This isn’t just any rubber tube!  That very unusually high conductivity is completely consistent with having it function as the spark return path.

With the hose so disconnected and held out of the way, I operated the spark generator several times, while looking carefully for a spark.  There was no spark.

Then I connected the loose end of the hose – still held out of the way – to the metal end of the piezo generator that originally touched the tank end of the hose.  And it gave sparks!

I take this as definitive evidence that the conductive black tube is indeed the return path in the spark circuit.

As for where to get conductive hose like that, a quick Google for ‘conductive rubber hose’ showed that conductive rubber really is a thing.  Who knew?