1" burner tube on forge

K

Ken H>

Joined
Dec 31, 2011
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Hello ya'. If you remember I built a new forced air forge a while back with Stacy's and JT's (and other fine folks) advice. I also got some advice on another board where the expert there insisted I needed a 1-1/2" burner pipe. Stacy 'n JT both suggested a 1" pipe (or possibly even as small as 3/4"), so I sorta split the difference and went to a 1-1/4" burner pipe. Yesterday I built a new burner using a 1" sch 40 pipe.
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While I could "make" the 1-1/4" pipe burner work, it really needed to be hot before it really started burning properly. I think the air velocity was a tad slow with my small (remember the Amazon?) blower. There would be a shadow on the interior wall where the flame hit until forge got hot, then it looked really good. No problem heating at all, had to turn gas 'n air both down to prevent getting too hot.

With the 1" burner pipe there is no shadow on wall from cold forge up thru heated forge. Gets plenty hot, as you can see in this image showing the blower closed off completely, needle valve is part closed, and regulator is sitting at 1.5psig, and it's holding the temp around the 2339F you can see on the display. I'm forging a railroad spike and when I remove spike temp will move up to 2350F range, put spike back in and falls to 2335F range. I had spike out longer than normal once and temp hit 2366F but started falling as soon as I put spike back in. You can see where the blower air is set, and the regulator (you can't see) is at 1.5 psig. Tith the forge temp adjusted down to around 2288F (I think), I put a long TC in from rear, between the two firebricks and the TC was showing 2405F. Just as I expected forge is hotter at rear where fully closed off.

I cut the 2" blower pipe to form a "Vee" with the elbow so the burner would fit the cart better. I think this Vee gave better air/propane mixing, perhaps some restriction in air flow but it seems there is plenty of air flow.

For the 1" pipe to joint the 1-1/4" elbow I took a 1-1/4" to 3/4" reducer, drilled out the 3/4" pipe threads so the 1" pipe would slip inside. Screwed the reducer into elbow, and backwelded threads, and then welded the 1" pipe to reducer. Anything to keep from spending money - I am NOT Diamond Jim {g}

I think I'm getting forge where I want it, and thanks to ya'll, I've learned LOTS about forges.
 
If you used a smaller orifice and higher PSI, you would have a better mix in a much shorter distance. I have always been told "you don't want an orifice in a blown burner." Think of it like a jet on a carburetor. A small, high pressure stream mixes very well, and you can precisely control the gas much better through 0-20 PSI than you can 0-1.5 PSI. Thanks to the calculator by Vincent, we learn that 100k BTU only needs around 20 CFM air. This 26 CFM blower works great, and the control from a 78¢ PWM is far more efficient than a gate valve on a large blower. Side benefit, you can easily power it with a battery if needed.
 

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I think you're right. I used a .062" orifice with the 1-1/4"' burner tube, injected in the 2" blower pipe right at the blower and it worked really good. Only problem I had was turning my blower down low enough for good burning to hold 2200F. With a short burner tube as you've got, I fully expect a small blower would do a good job.

I think using an orifice jet it allows better mixing so the burn is more efficient with lower air flow.
 
I don't think it would make any difference if I made the burner tube 36" long or 7" long, once it's mixed you can inject it into the chamber and get a good flame. Air flow per BTU is a constant ratio. Gate valves, however, are tricky compared to a smooth PWM control. The simple adjustment from a knob is just easier compared to a large valve and non-linear control.
 
Would you care to share info on your blower motor and PWM controller? You mention the PWM controller is only 78¢ - that's a good price. What voltage are you using - I expect it is 12 DC voltage?

I think I agree with you there is no need for a long burner tube using this method.

The sole purpose of the long burner tube and 90 degree elbow it seems is to provide an uneven tumbling flow to allow better mixing of propane and air. A longer blower pipe, elbow, and burner tube provides a good bit of restriction which requires a larger blower to get your 20 CFM of air for efficient burn. Perhaps that's why the smaller tube is required with no orifice, to make the air/propane mixture flow faster (also requiring larger blower) to help with mixing.

With an orifice putting a fine mist of propane under high 15 or so PSIG into the air flow it's getting a good mixture and doesn't require the higher velocity flow for good mixing and burn.

Does any of the above make sense as to why the small blower works just fine with an orifice?
 
I’m glad the new burner is working for you.
 
JT, I think you along with stacy who said a 1" (or even 3/4") burner pipe would be plenty large. I've sure learned LOTS about burners and forges since building this forge thanks you folks like ya'll who have helped me. I do think Atlas Forge has some good ideas on how to use a smaller blower and still get good heat with a small forge using an orifice.

Thank ya'll for all the help 'n guidance on building my forge.
 
I built a damascus forge pretty much exactly like the one Ed caffrey made. It works great but I didn’t use it much cause it was so big. But I recently made a new vertical forge out of a 40lb propane tank. I used the same burner set up from the big forge but went with a 1” tube going into the forge. It works just as good as the 1 1/4. It’s way more burner than needed but better more than not enough
 
Yep, if you remember there was a recommendation for using 1-1/2" burner pipe, then later he mentioned he's put concentric rings of pipe (or tubing?) inside the last 3" of the burner tube and it made it better. My thinking is the reducing rings simply reduced the flow rate and increased mixing at the end. Simple way would be to use smaller pipe for burner pipe.
 
It would be interesting to hear how a 1" burner pipe would do with restriction of the concentric rings inside. What size and how many rings do you plan?
 
The concentirc rings inside the 1.5" pipe create a mixing chamber of sorts. It would create faster fluid flow with large turbulence. Then, after the last ring it would drop the flow speed and allow full burning as it enters the chamber. It roughly does the same (but in reverse) as a increase in pipe size in the standard mixing chamber. It sounds like a lot more work than simple adding an expansion chamber. The one advantage I see is that it will allow a shorter burner sassembly (no expansion and mixing chamber).
 
Think about using a thin walled tube rather than the thicker walled pipe will help. As Stacy said the big thing that's happening is the disturbance at the end is simulating a mixing chamber by creating turbance and speeding up air flow. I think Atlas Forge as the same idea by using an orifice and spraying the propane into airstream under higher pressure to give really good mixing.
 
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