jet size for 3/4" burner tube

[JamesBBrauer]

I've been using a 1-1/2" Tee -> 1-1/2" connector -> 1/1-2" to 1" reducer -> no flare with a tweco tip on a 1/8" brass tube as the burner in my well insulated tube shaped forge for quite some time. This sucker simply roars with a fierce blue flame, inside or outside the forge. It drinks propane, but I am quite happy with the performance. Many happy hours pounding on hot metal.

Now have built a couple of 1'x1'x2' rectangular ovens. They are packed with Kaowool and stabilized with kaolin, and have a volume of about 200 cu/in each. One is going to be a ramp-controlled electric oven for heat treating steel, annealing glass, and firing pottery. The other oven is going to be for casting glass/metal, heating pottery for raku, and maybe some blacksmithing if the work piece fits better. This is the oven where I am trying to get a propane heat source working.

My plan was to use two 3/4" burners to heat the oven, and I am pretty much locked into doing that at this point. The tube holders are welded to the oven frame, and mortared in, and I bought an expensive bag of parts to build (at least) two of this size burner. But my burner building work hasn't been producing the nice fire my previous burner makes. My latest effort is a 1" Tee -> 1" connector -> 1" to 3/4" reducer -> 3/4" pipe of varied lengths. The general problem is when I crank up the gas to what would make my other burner roar, it just blows the flame off the end. My gas comes out of a 1/8" brass pipe with a coupler and male cap. I tried a 0.05" hole drilled in the cap and I got a blue flame with lots of orange at the end, which I am guessing is caused by too much gas with not enough velocity. If I cranked up the gas, it blew the fire out. So I opened out my 0.05" hole and tapped it for a 0.035" mig tip. It nearly makes a flame, but in the oven it looks more like a puddle of blue flame than the raging torrent of fire I am looking for.

Is anybody else running 3/4" pipe like this? If so, how do you have it setup, and does it look like a blowtorch flame?

thanks
James B

[LouieIV]

Take this with a grain of salt because I'm very much a newbie.

It sounds like your problem is possibly the Tee. You need a Ward brand reducing Tee for best performance. These don't seem to be readily available at HD or Lowe$. Smaller hardware stores or local plumbing supply stores might carry them. The other choice is to order one.

Here's a link on the basic 3/4" side arm burner assembly. Scroll down a little and it is there.

You can order them from Larry Zoeller. Down towards the bottom he has just the tee for sale.

Hope this helps,
LouieIV

[LouieIV]

Take this with a grain of salt because I'm very much a newbie.

It sounds like your problem is possibly the Tee. You need a Ward brand reducing Tee for best performance. These don't seem to be readily available at HD or Lowe$. Smaller hardware stores or local plumbing supply stores might carry them. The other choice is to order one.

Here's a link on the basic 3/4" side arm burner assembly. Scroll down a little and it is there.

You can order them from Larry Zoeller. Down towards the bottom he has just the tee for sale.

Hope this helps,
LouieIV

Also lack of a flare might be affecting performance too.

[ThomasPowers]

I assume this is an aspirated burner and not a blown one?

[LouieIV]

I assume this is an aspirated burner and not a blown one?

I assumed that also. :D

[JamesBBrauer]

assumed no blower

Your assumptions are quite correct, no blower attached. Is it reasonable for me to expect something like a pointed blue flame from a 3/4" pipe? If it is I'll keep experimenting with gas hole size, and maybe turn another venturi coupler on the lathe to see if that does some good. My first venturi coupler fit so good I couldn't get it apart to adjust the little stainless tube I had blowing into it. I think my next step will be to hammer out a flare on the end. If it works, I can go stainless after.

[reefera4m]

A photo would help. In my experience, the placement of the nozzle in the venturi cup can be crucial. On my forges ($20 Forge), I'm able to adjust the nozzle position within the venturi cup which. Finding the right position makes a world of difference in my design.

Also check for any leaks at the nozzle - I once had a small leak right at the nozzle and it interfered with the venturi to the point that I got very poor performance at the burner end.

You're somewhat correct about the flame, lots of orange indicates a carburizing flame and rather than not enough velocity it is an indication of not enough air/too much gas. The solution is to reduce the gas or enable more air while maintaining enough velocity in the venturi.
Nozzle position in the venturi cone along with the gas pressure has a hugh impact on determining the gas/air mixture to the burner. Too far in or out can chage the gas/air mixture and produce the results you're seeing.
If you can't adjust the nozzle position or doing so doesn't help, using a larger venturi would probably help as would reducing the gas prssure. However, the use of the larger tip (.050) at a reduced gas flow (pressure) might prevent the gas from picking up enough ir in the venturi. A smaller tip at higher pressure would provide enough gas velocity to pick up the air in the venturi while reducing the relative amount of gas to air mixture.

Hope this helps.

[Steve Shimanek]

I am no expert but i have made 4 working venturi burners from plumbing parts using info from the Net such as Reil and Zoeller info plus other various folk's comments. I beleive you need to increase the size of your "T" to minimum 1 1/2 inches, and you need a flame holder that is adjustable on the end of your 3/4 burner tube. A 1" pipe that is sanded out to let it fit over the 3/4 pipe will work; a 1/12 taper is recommended but not required. Burner tube length also has an effect; 8 to 9 inches seems to work. Also, a smaller orifice in the mig tip may help according to some info i have seen; the theory being that this helps increase the injection velocity. Mine work acceptably well using an .035 tip but at some point i will experiment with a smaller orifice. Make sure that there is a good seal so gas does not leak past the tip orifice. See Reil's info on tuning the burners and troubleshooting. Hope this helps.

[welder19]

You may want to try a .023" or .030" mig tip, my 3/4" burner uses a .023".
Also a pic would be helpful to see if there are any other potential issue's.

welder19

[JamesBBrauer]

I wanted to post a follow-up on how all this worked out, and what I did to get things working. Based on all of your excellent advice, I did a couple of things, first to get it working at all, then to tune it:

First off it needed a flare on the end. I hacked one out of some thin sheet metal and was able to get a halfway decent flame running constantly. So after rough turning a 5-degree taper out of aluminum on the lathe, I first cold bent some 12-gauge stainless into a half-circle, then clamped the sheet against the taper jig, heated it, and hammered it around to close the circle. I got tired of trying to find my calculator, so I just laid out a 5-degree taper on paper with a protractor and measured off the width of the flare over the three inch length to get the dimensions for the taper. The stainless to stainless, and stainless to steel pipe are both welded with flux-core (not TIG), and it seem to hold up fine.

The other thing that helped get a better flame was reducing the size of the MIG tip from .035" to .030". Those were the only two sizes I had around. I suspected from the smell, the combustion was incomplete at .035", and with the .030" there is almost no orange at the end. The MIG tips are for a Lincoln, and are threaded at 1/4"-20, and I'm glad I went to the trouble of tapping this; it was an easy change to try. For adjusting the center of the jet, I tapped my pipe with a #10-32. This gives roughly four thread turns in the pipe, and was easier than welding 1/4" nuts on the side of the pipe like on my last burner.

This setup gets a good flame over a range of pressures, and heated the inside of my oven nicely. The interior of the oven is rectangular, and the burners are pointing diagonally at the floor from the upper rear corners of the box. With the door open, this arrangement circulates nicely, without blowing much flame out of the front. When closing the door it does take at least 10 square inches of exhaust to stay burning. I'm using a Harbor Freight MIG regulator, converted to fit propane. This will make up to about 25 psi, at some unknown volume, which seems to be more than what I need.

- James Brauer