Burner tube length?

B

Boogaloo

Joined
Jun 20, 2013
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114
Getting close to done with my forge. Had a quick question about burner tube length. Any rule of thumb about how long it needs to be?
A little background:
I'm using the high temp tools blown burner kit and the burner tube is about 8-10". This puts the assembly pretty far out from the receiver tube in the forge body. I'd like to reduce that moment arm since I haven't fabbed up any additional support.
Any reason I can't just chop the tube in half so my reducer is sitting flush against the receiver?

Thanks to all those before me who have helped out with build logistics/optimization.
 
I kept mine short for the same reason. The only downside I see is a little more heat transfer up the burner tube but it seems to work fine. The air flow seems to keep it cool enough.

I suspect the tube length may be more critical with a Venturi burner.

If it's just a nipple, you could easily replace it if you figure it needs to be longer after you experiment.

 
Yes Brian talking about the 1" pipe nipple (think the Venturi burners are 3/4")

Thanks bare, think I'll go ahead and trim it down. Are you insulating between the nipple and receiver?
 
The shortest length is quite difficult to quantify without experimenting on the particular burner in question.

It is basically the minimum distance over which you can get adequate mixing of the fuel and air. Tiny changes to the installation can have a very significant effect on the amount of turbulence and therefore on the length needed.

On Bareknuckles setup, it looks like he's feeding the gas in at the elbow, which will generate plenty of turbulence.

On Naturally Aspirated burners, the tube length tends to be more critical than on blown burners.

If you don't get full mixing in the burner tube before the fuel/air reaches the forge, it will mix in the forge chamber and will still burn. However the temperature may be more uneven and there may be areas where there is enough free Oxygen to cause scale and decarb issues.
 
Hi Boogaloo,
No, I don't have any insulation between the tube and the receiver. The receiver produces an inch into the 2" insulation and is profiled to the shape of the forge, and then I coated the rest of the port with satanite, so the burner tube goes almost to the inner edge of the port, and there's only just enough space around it to get it in or out. I cut the nipple so the elbow would sit flush against the end of the receiver.
Seems to work fine.
 
BareKnuckles said:
Hi Boogaloo,
No, I don't have any insulation between the tube and the receiver. The receiver produces an inch into the 2" insulation and is profiled to the shape of the forge, and then I coated the rest of the port with satanite, so the burner tube goes almost to the inner edge of the port, and there's only just enough space around it to get it in or out. I cut the nipple so the elbow would sit flush against the end of the receiver.
Seems to work fine.
Click to expand...

Cool, I haven't done anything fancy there either, just tried to keep a pretty snug fit between burner and the satanite coat.

Fired it up as is for the first time. Took me a while to figure out I had to set needle valve to almost shit and choke the air way back to get a nice burn. At first was just getting major flames then a bunch of sputtering blue ones.

Looking forward to getting a proper anvil. I was squatting over a 3x6x8 block of steel I grabbed at the scrapyard....

Had fun hammering out a knife shaped object.
 
I would leave at least 6-8". The tube provides the mixing chamber for the gasses.
 
Stacy E. Apelt - Bladesmith said:
I would leave at least 6-8". The tube provides the mixing chamber for the gasses.
Click to expand...

Thanks for the input Stacy. There's about a 6" vertical space between the needle valve and the top of reducer elbow, a couple horizontal inches for the reducer itself then whatever length of pipe nipple I leave on the burner tube itself:



The machine design profs would scoff at me for this. If all that length is necessary I'll add some extra support but I'd rather cut down on the overall width too. Already a bit clunky wheeling/lifting in and out of my shed :P.
 
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That looks about right to me. Maybe a tad shorter would be OK. Weld a brace either way.
 
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