Orifice Size for Propane Kiln?

[Polydeuces]

Hey y'all—I've been working with a propane kiln for the past year with mixed results. The orifice size I had drilled was (I thought) too large—it's a homemade burner out of black iron pipe. I had actually closely followed the High Bridge fellow in making it, since it seemed to work out pretty well for him.

Anyway, I recently acquired the means to drill a much smaller hole, like tiny—1/32". The previous orifice was (I think) 1/16".

So, when running it with a squirrel cage fan it *really* seemed to struggle to climb. It looked weird, sounded weird. I was just calcining some dry material as a test run, and wound up breaking the bisqueware that was containing it in the effort to push it up to △020. With the larger orifice, I felt like I could go easier on the pressure and it wouldn't struggle against the air as much.

I had the fan intake completely covered, and *also* tried putting a piece of cardboard partially between the fan's output & the burner's air-intake end.

So for now, I'm planning on drilling the hole a size larger (5/64") and seeing how that goes. But maybe I'm thinking I should just stick with the old orifice.

I thought that in the world of burner/torch things, you wanted the smallest orifice you could get—but I'm struggling to find the practical reasoning behind this, at least in my experience running it today. It felt like I had to shove the flame up into the kiln in order to get it to climb, and with a larger orifice I felt like it drifted or was "pulled" a little better, perhaps.

I hope I'm just doing it wrong. Would love y'all's input and to hear what you have to say about it. Thanks!

[Fred Sweet]

Polydeuces-

Take a look at this article regarding orifice sizes: http://www.wardburner.com/orificesmessing.html

 

You might be interested in the charts for propane or natural gas, available at Ward Burner: http://www.wardburner.com/otherproducts/orificechartsplugs.html

Or you could just call or email  Marc Ward, who can be reached at the contact link on the Ward Burner site.

Regards,

Fred

[Marcia Selsor]

I built on that sounds similar back in 1971. I put 5 holes very small into the black pipe which ran perpendicular to the burner body. Used the drill press at the local HS shop.  The design was by Don Bendel from Flagstaff.. Cant find the original mimeograph handout of it. the body was 2" pipe wit a bell reducer on the front end and squirrel cage blower behind and a tin coffee can lid screwed onto the air intake for air control.

Marc Ward makes great blowers and is very generous in answering questions. 

Marcia

[High Bridge Pottery]

I used a 1.5mm drill for my orifice which is near enough 1/16th of an inch.  Off the top of my head that works out at 60,000-70,000 BTU/h at 1 or 2 PSI but I would need to check the exact figures. Do you think the problem was too much air or not enough air? Maybe it is also not mixing great in the burner or do you have any kind of nozzle on the end?

When starting I struggle to keep the temps from shooting up. Never had an issue with getting the temperature to rise. The orifice size is more related to how many BTU/hour you want at the pressures you can get, not sure there will be too much difference in how it functions although you seem to have found a bigger one better. Maybe the lower pressure allows for better mixing of the gasses.

Do you have any photos of your burner? or a video would be great.

[neilestrick]

How big the orifice needs to be depends on how many BTUs you need, and the gas pressure.

You can't fire with the air intake on the blower completely covered. How did you fit a piece of cardboard between the burner intake and fan output? They should be joined together. 

What is the diameter of the burner pipe? How long is it? What is the CFM rating of the blower? How big is the kiln? What kind of bricks is it made from? Post a picture.

As you may see from my questions, it's not a simple thing.