search  current discussion  categories  kilns & firing - burners 

orifice over/under burner tip...does it make a difference?

updated wed 28 jan 04


Richard Aerni on mon 26 jan 04

OK, for those of you who have been following this small bit of kiln-
building info with bated breath, I can supply something of an update.

As you may recall, Fred Olsen states that the burner orifice should never
be located above the burner tip, without giving the reason(s) why. I
speculated, on my own, that it may have had something to do with the
relative weight of propane or natural gas as it pertains to the weight of
the normal atmosphere, but could sustain no rational argument why that
would be so. (In other words, if that were the case, then the orifice
should logically be located over the burner tip for propane, and under the
burner tip for natural gas, given their differences in weight relative to
normal atmospheric pressure.) It seemed to me that normal pressure from
the pipe through the orifice, combined with the inspirating nature of the
primary air feed and the kiln's draft, would counter the relatively small
effect of the weight of the fuel. The other reason I could come up with
was the possibility that metal scale from the black iron fuel lines could
possibly clog the orifice when the fuel feed came from above. But again,
it would seem given the pressure of the gas and the draft, that orifice
clogging from this source could very well be present whether the fuel feed
was from above or below. In addition, the installation of a collection
tube in the pipe in the joint where the fuel feed transitions from vertical
to horizontal would surely catch this scale, if that were the problem.

So, I was left with no logical reason why Olsen would make this statement.
Some of you on list have speculated that the reason was the difference in
weight of the gasses, leading to the possibility of backburning at low
pressure. Well, I've never had a problem with that in any of my kilns, and
I single fire, so I have low pressure through much of the firing. Others,
off list, including Marc Ward, Val Cushing, John Britt, Craig Martell and
others, have basically said that Olsen was just repeating something that is
an old potter's tale, with little or no basis in fact. And, in the absence
of supporting evidence from Mr. Olsen, I have to come to the same
conclusion. I am going to build my burners with the feed from above, and
if there is a problem, I'll be sure to report that to the list.

So there. I'm reassured. Thanks to all of you out there who took the time
to think over, and answer, my query.

Richard Aerni