Duty Cycle of Propane Torch?


I was using one of these propane torches yesterday to torture some weeds and grass that had sprung up between some paving stones.
http://www.bernzomatic.com/products/product-detail.aspx?xmidi48
I have used this same torch for sweating copper and never had any problems, but it was never on for as long as it was yesterday.
What I found was that after a few minutes (4 - 5?) of torturing weeds, the flame would get sloppier and sloppier - I'd lose the blue core, the cone shape would deteriorate and eventually the flame would just be a messy cloud of flame with no defined shape.
The other thing that would happen is that when I would turn the torch off, the gas seemed to take forever to shut down and a small (1"?) flame would hang around the tip for a while.
If I let the torch sit for 10 minutes or so, I could get another 4 - 5 minutes of burn time before the flame went all screwy again.
At first I thought it was the canister, but I tried another one and it did the same thing.
Do these things have a duty-cycle that I wasn't aware of? It was almost like the valve itself was screwing up since the torch seemed to stay on even after I shut it off.
Could it have been freezing up?
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On Mon, 17 May 2010 10:32:54 -0700 (PDT), DerbyDad03

<http://www.bernzomatic.com/PRODUCTS/TORCHES/STANDARDTORCHES/tabid/250/ctl/Detail/mid/1259/xmid/6953/xmfid/3/Default.aspx
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On May 17, 1:45 pm, snipped-for-privacy@dog.com wrote:

While I appreciate the link to an "option" for my weed-torturing sessions, I'm still curious as to why my current torch exhibits the symptoms it does.
Who knows...I might someday have a situation where I need extended run time from my small torch and I'd like to know why it's not up to the task.
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DerbyDad03 wrote:

My guess is that if you have a standard non-pressure regulated torch you are inverting the torch to aim it at the weeds and liquid propane is passing through the valve and into the neck of the torch where only gas is intended to go.
Then, when you shut the valve off that liquid propane takes quite a bit of time to turn to gas, creating the "afterburn" you're experiencing.
The same liquid propane where it isn't supposed to be can cause the flaring out effect you describe.
Jeff
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jeff_wisnia wrote:

My theory also. Try burning it for as long rightside up. Does it work OK?
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wrote:

..>- Hide quoted text -

Could be...
I didn't quite "invert it" but for the most part it was horizontal, so the liquid could certainly have passed into the neck.
Neither of the canisters were full, so that might explain why it took so long to "flame out". I'll bet a full canister would have caused the problem sooner.
I'll play around a bit with the torch upright and see what happens.
Thanks!
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0...>- Hide quoted text -

I just ran the torch upright for over 12 minutes with no change in the flame.
I guess we'll go with the "liquid in the neck" theory.
Thanks guys!
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Sounds reasonable, to me.
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In the first couple minutes, the orifice and torch body will still be warm. So, you'll get complete vaporization. After a while, the liquid propane turning to vapor will chill the torch head. Which leads to the changes in flame.
A similar operating time upright, would likely not give such problems. Maybe the OP can do an upright torch test, and see if that behaves differently. I'm curious if it does.
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On Mon, 17 May 2010 11:14:35 -0700 (PDT), DerbyDad03

Because your torch probably prefers that the fuel cyclinder be in the "upright" position during extended use. A problem overcome in the unit I pointed out.
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snipped-for-privacy@dog.com wrote:

http://www.bernzomatic.com/PRODUCTS/TORCHES/STANDARDTORCHES/tabid/250/ctl/Detail/mid/1259/xmid/6953/xmfid/3/Default.aspx I picked up one of those at a yard sale a couple years ago. They work great, but quickly use up propane with their bigger flame.
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Maybe I could use the burner from the Turkey Fryer I picked up for $4 at an Estate Sale a few years ago. Now that would eat some weeds...and use some gas!
Really...I paid $4 for a complete 32 qt Turkey Fryer set.
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wrote:

I find it perfect for the cracks between flagstone. A gas cyclinder lasts for a surprisingly long time, and gas cylinders are cheap. You can also refill them from your gas grill tank for VERY cheap.
For larger areas, I use this:
http://www.harborfreight.com/propane-torch-with-push-button-igniter-91037.html
It connects to a standard 20 pound propane tank from a gas grill.
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<http://www.bernzomatic.com/PRODUCTS/TORCHES/STANDARDTORCHES/tabid/250/ctl/Detail/mid/1259/xmid/6953/xmfid/3/Default.aspx
Sounds like a partially clogged orifice causing the sloppy flame. When you shut the valve, there is still backpressure in the line, and the flame continues until the backpressure is released.
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??? I'm not having any problem.
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On 5/17/2010 12:32 PM, DerbyDad03 wrote:

it had to do with being upside down for so long.
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DerbyDad03 wrote:

Wrong tool for the job. You need one of these instead:
http://www.harborfreight.com/propane-torch-91033.html
Jon
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On Tue, 18 May 2010 09:52:14 -0700, "Jon Danniken"

This one, for a few dollars more, has a built in igniter which is a lot more of an advantage than you might suspect:
http://www.harborfreight.com/propane-torch-with-push-button-igniter-91037.html
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And, wait a couple days and it will go on sale. I'd go another five bucks for the self starter torch. I've got a couple self lighting torches that take smaller tanks. Very convenient.
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