[TheForge] Problems with propane burner

[Marc Godbout]

Thanks, Jerry, for the input. My replies are below.

On Sat, 2003-09-06 at 12:33, Jerry Frost wrote:
> Morning Marc:
>
> First, you have a 90* bend in the burner tube, this will cause back
> pressure, requiring more psi to drive around.

It's not a tight bend, though. A 90* bend in rigid conduit has, I'm
guessing, a 5" radius to it. It's a very wide sweep. But your point on
back pressure is a good place to start. Anything other than straight is,
well, not straight.

> 
> Second, you're running a "sidearm" configuration jet ejector with only a 1
> 1/4" intake on a 1" tube. This is not a free breathing configuration and
> requires higher psi to draw sufficient air.

Ah, but I'm using a cross fitting (four joints). So I've got two 1 1/4"
intakes. The propane supply is through a 1/8 nipple through a hole
drilled in a 1 1/4" plug. I was able to plug one opening up completely
and saw no difference in performance at the low end. It did affect high
end, though.

> 
> Thirdly you're using a 0.035" orifice which requires more psi to deliver
> sufficient propane. How well aligned is your jet in relation to the burner
> tube? This is really critical.

This I don't know. Because of the bend, it's difficult to see how well
the jet is aimed. I did drill the hole through the plug while the plug
was installed on the cross to maybe compensate for any junky threads.
But I've got no more machining tools than a drill press and simple
woodworking squares. It is something to investigate, though.
> 
> You have several  options open:
> 
> First accept higher operating psi as normal for your burner, you're getting
> plenty of heat even though it doesn't idle like you want. Still, running a
> "smaller" orifice delivers less gas at a given psi so you may have the
> economy you're looking for already. In short it could already be singing the
> tune you want, just in a higher key. <grin>

Yeah, but I want it all and a place to put it :-) My existing forge
idles at a nice, little purr, so I've been spoiled. Besides the sound
difference, the heat output at idle on that forge is very much reduced.
I might be able to forge at that low temp, but I doubt it. On this new
burner, at its lowest setting, it's quite easy to forge at that heat. So
I'm pretty sure I'm spending more energy than the other.

> 
> Second look at changing the 90* to a longer sweep or even two 45*s . This
> will increase the radius of the direction change and reduce the back
> pressure a bit though probably not enough for a stable idle. You should also
> place any bends as far as practical from the throat (narrowest point between
> the intake and burner tube) of the burner. The longer the jet of propane can
> travel down the exact (as possible) center of the tube, the more efficiently
> it'll draw.

Way back, when I was experimenting, I tried to 45* elbows and straight
nipples. That was horrible. The flame started in the first elbow. But I
used threaded fittings and I think the first elbow provided the step
needed to hold the flame. A welded pipe setup would probably have worked
well. A friend of mine (and yours, too, by the way - Ralph) has such an
arrangement on his forges and they seem to work well. So that's an
option. But if such a tight bend works, why wouldn't my wide sweep? I
dunno.


> Fourth, filing the port in your forge liner to form a taper might be well
> worthwhile. On my next forge I plan on building my burner nozzles into the
> refractory liner myself, mostly to save on tube burnout but also to improve
> performance.

It is an easy enough thing to try, too. Probably not worth even talking
about.

> 
> Lastly, how completely are you closing your forge up? If you're not allowing
> enough opening for exhaust gasses to escape you're really building back
> pressure and inhibiting your burner performance.

I think this may well be the biggest issue. When you said backpressure,
I immediately thought of this. While it wasn't closed up tight, may have
had only 1" wide "crescent" on each end. I was curing the forge and had
the doors completely in front and back to cure them, too. 

I think the first thing to try would be to put the doors in their normal
resting place. That will leave a 4" X 8" opening in each end. Another
cheap thing would be to try a straight 10" length of 1" nipple instead
of my conduit bend.

Thanks for the feedback. 

-Marc


-- 
Marc Godbout
http://www.ironringforge.com

New England Blacksmiths Membership Director
http://www.newenglandblacksmiths.org