Under pressure

[offcntr]

It started last winter. After discussing the issue for years, Club Mud finally decided to go ahead and install pressure gauges on all the burners on our gas kilns. I took on the project, tackling the big gas kiln first, using lots of odd plumbing bits and reels of yellow teflon tape. The installation was successful, and, after years of guesswork and "turn up the gas until you hear a fluttering noise," we could actually have objective measurements of just how high the flame was from firing to firing.

Then I turned to the small, outdoor kiln. And hit a snag.

The gauges went on just fine; in fact, the installation was even easier, as the gas lines took a right angle turn into the burners, so I could just replace each elbow join with a tee. The problem came when we turned the gas on.

Natural gas is a low-pressure medium; typically, mains pressure runs around 7 or 8 water-column inches (wci). When we lit a burner at what Annie assured me was typical firing levels, it pegged the needle. On a 15 wci gauge.

Something wasn't right.

Four somethings, in fact. It turns out that the orifice--the little hole that admits gas into the mixing chamber of a venturi burner--on all four burners was sized for propane, which is delivered at a higher pressure. They needed a much larger opening to run natural gas at any levels except flat out.

I installed the new orifices (orificii?) on Friday, lit a burner, and got a very nice flame at about 3 wci, as opposed to the 15+ we'd been doing. Should fire just lovely.

The problem is, habit. We're used to firing with the wrong orifices, all our experience and firing schedules rely on them. Someone would have to volunteer to do a test firing with the new set-up, figure out appropriate levels and timing--which we could now document objectively with our new pressure gauges.

Guess who raised their hand?

Yeah, on Monday I'll be firing the small gas kiln again, for the first time in over a decade. Wish me luck.

Comments

[danthered]

Tough day at the orifice, eh? (Thanks, I'm in town all week, try the chicken, etc).

How do you pronounce kiln? Specifically: do you pronounce or omit the final /n/? I've encountered many potters who pronounce it kill, which has fascinated me since the first time, when I was about five: I'd made a sculpture, of sorts, under the tutelage of a potter named Elaine Langerman who lived in Sundance, a neighbourhood in Southeast suburban Denver. She said "Great! Once it's dry we'll kiln it", and I said "Why do we have to kill it?" My mother, who was also there, laughed and explained there's a thing called a kiln, which is like a very hot oven for turning clay into a very hard material like glass, and that's what Elaine had said. Kiln. Only she hadn't; she'd said "kill", and she was only the first of many, many potters I've heard pronounce it that way.

What's up with that?

[offcntr]

I think it's a southern thing. Dennis Parks' wife Julie was from Alabama, and that's how she pronounced it. I got my training from Minnesota potters, so we pronounce the "n."

On the other hand, we spell the glaze "Tenmoku," but pronounce it "Temmoku."

Language is weird.