Contents: When a Downdraft Vent Does Not Remove All Fumes Basic Kiln Sitter Maintenance Reader Response: A Kiln Story with a Safety Tip
WHEN A DOWNDRAFT VENT DOES NOT REMOVE ALL FUMES
A downdraft vent comes in several brands. It is used on ceramic and glass kilns to prevent fumes from escaping the kiln into the firing room. (Small jewelry, dental, and enameling kilns normally use the overhead vent instead of the downdraft.)
The vent removes just enough air to create negative pressure inside the kiln. This prevents fumes from leaking out. On most kilns the vent is positioned between the kiln bottom and kiln stand. (The fan on the new Orton Vent Master mounts away from the kiln.)
If you can still detect odors during vent operation, check the following:
1) Make sure you can hear the fan spinning. This is basic but easy to overlook in a busy studio.
2) The holes that draw air out of the kiln must be free of obstructions. If the exit air holes are in the bottom of your kiln, the bottom shelf should be positioned 1” or more above the kiln floor. The shelf must not block the holes.
3) The intake and exit vent holes must be of the correct number, size, and location in your kiln. See the vent instruction manual to be sure, or call the manufacturer. (Orton downdraft vents: 614-895-2663.) The vent housing must cover the air exit holes. Otherwise hot particles can fall onto the floor from inside the kiln.
4) Insert all the peephole plugs and keep the lid/door fully closed throughout the firing.
5) Check the vent duct for leaks.
6) Make sure the duct is free of obstructions and that the vent flapper on the outside of the building can open freely. Go outside. You should feel warm air coming out of the vent.
7) If you fire ware that contains many impurities, you may need to fire smaller loads.
If you still smell fumes after checking the 7 points above, you may need to drill another air exit hole in the kiln.
BASIC KILN SITTER MAINTENANCE
In last week's Kiln Pointer, Dave Coggins mentioned the importance of regular Kiln Sitter maintenance. I have included Kiln Sitter tips below at the request of a reader:
1) Before loading a cone onto the cone supports (the metal tabs where the small pyrometric cone is placed), check that the actuating rod can lift up and down freely. If the rod movement feels sluggish, corrosion may have built up inside the tube. Sometimes you can clean out the tube using long cotton-tipped applicators. (They look like Q-Tips.) Do not fire the kiln until the actuating rod moves freely. If necessary, replace the tube.
2) The cone supports must be clean. Use emery cloth to remove traces of greenware, corrosion, or bits of melted cones. These foreign materials will catch on the cone, preventing it from slumping freely. Coat only a small amount of kiln wash on the lower side of the rod and on the upper edges of the cone supports. A build-up of kiln wash will alter the cone’s shut-off temperature.
3) If the Kiln Sitter does not shut off when the weight drops, the locking slide inside the Kiln Sitter may be corroded or dirty. About once a year, unplug the kiln and remove the switch box that houses the Kiln Sitter. Pull the box straight out to avoid damaging the Kiln Sitter tube. Leaving wires attached, clean the backside of the Kiln Sitter. Canned air is helpful. (But do not blow air into the Kiln Sitter tube.) When you reinstall the switch box, arrange the wires so they do not interfere with the locking slide that trips when the weight drops. (You can see how the locking slide works by lifting the weight, pressing the plunger, and then dropping the weight.) Also, arrange the wires inside the switch box so that wires do not touch element connectors or the kiln case.
4) Adjust the Kiln Sitter every dozen or so firings using the firing gauge. This is a small disk that ships with new kilns. (Many people throw away the firing gauge thinking that it is used only during shipping.)
THE KILN SITTER FIRING GAUGE
Place the gauge on the cone supports, sliding the actuating rod through the hole in the gauge. If the actuating rod is not centered in the porcelain tube, loosen the two screws on the guide plate and move the plate from side to side.
Lift the Kiln Sitter weight to the raised position. With the firing gauge in place, the trigger should just barely clear the release claw, coming as close as possible without touching. If the gap is wrong, loosen the set screw in the center of the weight, move the trigger, and retighten the set screw.
This adjustment is easier to understand when you see pictures. You can download the Kiln Sitter instruction manuals at Paragon’s website:
READER RESPONSE: A KILN STORY WITH A SAFETY TIP
Earl "E" wrote, "Always keep a fire extinguisher handy around your kiln no matter what. I was melting out the left-over wax from a lost-wax casting mold and behold, the Paragon was up in flames to the ceiling. With my good ole fire extinguisher, all was okay except for my Paragon. The wiring was cooked. Carbon all over."
Earl, thanks for sharing that story and for the safety pointer. We should all have a firing extinguisher not only in the kiln room but the kitchen too. One of my neighbors almost burned his house down because he didn't have a fire extinguisher when grease caught fire on his stove.
I hope you are enjoying the change of weather. On Monday for the first time this year, I wore a jacket to work.
With best wishes,
Arnold Howard Paragon Industries, L.P. - Better Designed Kilns 2011 South Town East Blvd. Mesquite, TX 75149-1122 Voice: 972-288-7557 & 800-876-4328 / Fax: 972-222-0646 firstname.lastname@example.org / www.paragonweb.com