KILN ASSISTANCE

GAS FIRING KILNS

UL LISTING FOR GAS COMPONENTS:

The following information provides UL listing for Olympic Gas Kilns’ components. There is not an AGA approving statue so we have been forced to rely on component recognition for local approval.

  • The electronic control when used is manufactured by Bartlett Instrument Company and bears UL’s Universal File Number E37370 and is so marked on each board.
  • Transformer: Texas Transformer Corp., P604800 – UL Recognized
  • Relay: Potterbrumfield, T92P7022-12 – UL Listed
  • Plug: Eagle 4867 – UL Listed
  • Cord: American Insulated Wire 12-3 SJ – UL Listed
  • Single Receptacle: 15A – 120V – UL Listed
  • Magnetic Valve: Johnson Controls, H15DA – 10 – AGA, CSA, ANSZ 21.20
  • Gas Thermocouple: Johnson Controls, Penn Baso Thermocouple Model K24BT – AGA, ANS Approved
  • Electric Valve: Johnson Controls, Series H91 Basotrol – AGA, ANA, CSA Approved
  • Thermocouple: JMS Southeast Inc., 1K1CMG6ZZX – 12ZPHA Type K

This combination has worked successfully for many years and has been approved on its merits throughout the world.

LOCATING YOUR KILN:

Three things should be considered when locating your Olympic Kiln:

  • Adequate space

  • Proper ventilation

  • Convenience of electric outlets (for kiln sitter-relay systems and electronic controller wall units) and gas sources

For the area that has been chosen, allow 12 inches of space between the kiln and the walls. All flammable materials such as curtains, plastics, etc. in the area of the kiln should be removed.

If the kiln is located in a confined area, it is essential that an exhaust hood be placed above the kiln and vented to the outside. During the firing, gases from combustion, including carbon monoxide will exhaust from the top port of the kiln.

If the kiln is to be placed outside, ensure that moisture is not permitted. Use a roof over the kiln or some type water resistant tarp when the kiln is not being fired. Temperatures above the kiln will not be excessive and you should be able to hold your hand two (2) feet above the kiln without discomfort; however, heat can accumulate in restricted areas above the kiln if a hood is not used. Because all kilns generate heat, the stand should be placed on a cement floor. Tiles or linoleum could be damaged without this precaution.

It is important that the kiln be fired only on the metal stand provided with the burner system. The eight- (8) inch height of the stand is necessary for proper burner positioning and adequate cooling beneath the kiln. Remember to use sheet metal or non-flammable material to shim the legs when leveling the kiln.

GAS USAGE FOR OLYMPIC GAS FIRING KILNS:

ITEMS TO PURCHASE FROM GAS COMPANY

  • LOW PRESSURE REGULATOR

  • PROPANE – 11" WATER COLUMN (GAS PRESSURE)

  • NATURAL GAS – 7" WATER COLUMN

  • ¾" PIPE LINE for TOP LOADING KILNS

  • 1" PIPE LINE for FRONT LOADING DOWNDRAFT KILNS

 
 

Olympic gas kilns burners are factory set for use on either propane, or natural gas from a street main. If propane is used, your tank must have a low-pressure regulator like those on a camper or trailer. If an adjustable regulator is used approximately ¾ to 1 ½ pounds of pressure is necessary. The larger the tank the better; however, a five (5) gallon tank is the minimum size for the 1827G and a 15 gallon tank is the minimum size for the 2327G and 2827G kilns.

For DownDraft Kilns use the following chart for propane usage:

DOWNDRAFT MODEL

PROPANE (GALLONS)

DD9

10

DD12

15

DD14

18

DD17

21

DD20

24

DD24

29

DD30

40

DD40

48

Due to gas flow, the tank may have a tendency to freeze solid. If ice is observed forming on the outside of the tank, water can be run over it to help keep it melted. The tank can also be lowered into a large bucket of warm water.

  • NATURAL GAS

A larger burner orifice in necessary when used on household gas pressure of six (6) to eight (8) inches of water column. If your kiln was ordered for use on household natural gas, it is equipped this way.

  • VENTING YOUR GAS KILN

Proper ventilation is required when firing your gas kiln. Vents for Olympic Torchbearer kilns, if fired inside, may be purchased from Clay-King.com at www.clay-king.com/ventpage.htm. Olympic Raku kilns are usually fired in a garage or outside due to the raku process and therefore do not require a vent.

For Olympic DownDraft kilns, you may create your own vent by purchasing sheet metal from a local heating and cooling manufacturer. Shape the sheet metal into a cone shape 36" wide in diameter. The vent should be placed 18" above the kiln top – center on the stack (damper opening) with an exhaust pipe 10" in diameter that is determined by ceiling construction, double walled if combustible

ASSEMBLY OF RINGS FOR TORCHBEARER KILNS:

When handling your new kiln rings, always be sure to grasp the rings by the outer surface only. Do not grasp the bricks as they are made of a porous material and may chip in your hand.

After making certain the stand is level, adjust the burner manifold so the pipe section on top of each air mixer is approximately ½ inch below the bottom of the kiln. The kiln bottom must be positioned on the stand so each burner is directly beneath one of the holes. It is recommended that the burners be positioned with the gas valve on the right side when you are facing the kiln, however, if it is more convenient to place the manifold in another position be sure to align the burners with a hole in the kiln bottom.

The kiln rings may now be stacked with the hose clamps in back and the observation holes aligned in front. If the kiln has the optional automatic shut-off system the ring with this device should be placed in the middle of the kiln to insure accurate results. Once the kiln is assembled, be sure the inside is clean and free of dust. It may be necessary to vacuum the inside of the kiln at regular intervals.

OPERATING YOUR KILN:

Once the kiln is hooked to a gas source, each burner may be ignited and the primary air adjusted for each of the air mixers or burners. Loosen the locking screw before attempting to adjust the burners. The locking screw needs not be retighten unless the kiln is being moved.

Air adjustment is very important and should be accomplished with care. The air adjusting plate is locked between the burner orifice and the burner. The burner must be loosened slightly from the brass orifice, which threads into the center of the burner, to move the air adjusting plate. After loosening the locking screw and the burner from the orifice, rotate each plate to insure it will move freely. Next position each air adjusting plate so the air inlets are 50% open. The kiln may now be ignited and the fine air adjustments can be made.

A properly adjusted kiln will have all flames uniform in appearance with the transition from candle flame to intense flame occurring at the same time for each burner as the gas valve is opened. The kiln operates most efficiently when the intense flame has a maximum of blue color. If the flame tends to blow out when the gas valve is opened the air inlet should be closed slightly.

The air adjustment of the burners need not be changed once the optimum settings are obtained; however, reduction firing in the kiln may be accomplished by closing the air inlets. The easiest and most reproducible reduction is done by dampering the vent hole in the lid and will be explain more thoroughly within this document.

IGNITION RING & THERMOCOUPLE SAFETY SHUT-OFF:

The ignition ring is used to:

  • Light the multiple burner system from one point

  • Maintain the flame on each burner

  • Re-ignite any burner that may extinguish

The thermocouple safety shut-off is used to:

  • Stop the gas flow if the flame is lost entirely by the kiln preventing an over firing.

To operate the ignition ring, depress the red button on the top of the magnetic valve and light the ignition ring. The small gas valve on the ring should be adjusted to allow sufficient gas flow to propagate a flame entirely around the ring when it is ignited at any point. Once the ring ignited the thermocouple on the ignition ring is hot and the valve will stay open by itself (approximately 60 seconds is required).

The burners may be lighted by turning the hand valve on the burner manifold.

Lighting instructions:

  • Depress button and hold

  • Light ring

  • After 60 seconds release button

  • For DownDraft kilns light the left side of the pilot bar first and then the right side bar.

LOADING THE KILN:

Olympic gas kilns are noted for their multiple burners, which are spaced around the perimeter of the kiln. All shelves and ware should be loaded inside the burners and spread one (1) inch apart to insure even heating. A shelf should be placed three (3) inches above the kiln bottom. Each additional shelf should be supported by posts that are placed directly over the ones below. All shelves should be turned over every other firing to prevent excessive sag and the larger shelves should have a support in the middle. This is especially helpful for the bottom shelf.

FIRING SCHEDULES:

The following firing schedules are recommendations and should be considered a starting point for the method eventually adopted by the user of the kiln. Each kiln has its own individual characteristics that may be influenced by location, gas pressure, gas flow, weather, and the potter’s own individuality. The user of a gas kiln needs to be willing to experiment with different firing techniques in an effort to express his/her own theories and develop methods which prove most satisfactory for the user’s own unique situation.

All firing schedules need to be adjusted to conform to the thickness and mass of the ware being fired and the load density of the kiln. The more pieces the kiln contains the slower it should be fired. Finally, the clay body must be considered, remembering its strength, reaction to thermal shock, dryness, etc.

BISQUE FIRING:

Dry the newly formed ware at room temperature until it is no longer cold to your sense of touch. Smaller pieces need seven to ten days drying time and larger pieces 10 to 15 days. Bisque of pre-firing is necessary to pre-condition the ware for glaze application and glaze firing. Bisque firing is a slow firing in which the physical and chemical water is driven off and the body becomes hard and solid. The ware is most susceptible to cracking during the early stages of bisque firing and several temperature zones should be crossed with extreme care.

The physical water leaves the clay at 212° Fahrenheit and the chemical water is driven off from 350° to 500° F. At 1073°F the quartz inversion occurs causing a size change in the body of approximately 2%.

To Bisque:

  • Ignite the burners and adjust the gas valve to allow the flame to burn with a candle flame for 30 minutes. The pre-heating period should be extended if thick walled pieces are being fired or the kiln is densely loaded. Some soot may be observed during the candle flame period; however, it will burn out when the kiln reaches higher temperatures.

  • Open the gas valve enough to increase the length of the candle flame and cover the top port about 80%. Leave the kiln in this condition approximately one (1) hour.

  • Turn up the gas to allow the flame to burn with more force and with little yellow color. Open the top port about half way. After several hours at this rate open the gas valve half way. Leave the kiln at this rate for two hours or until the inside coloration is a dull red.

  • After the ware has padded through its critical point, which indicated, by the dull red coloration, the burners can be turned up all the way and the top port can be completely opened.

  • When the cone has bent and the kiln has shut-off, cover the top port and plug the observation holes.

GLAZE FIRING:

The kiln should be warmed up with a slow flame for about one (1) hour. The flame can then be gradually increased at will until it is fully on. When kiln is fully on, the top port should be completely open. After the desired temperature has been reached, leave the kiln on for at least an hour at that temperature to properly soak the ware. Shut the kiln off as before, plug the observation holes and cover the top port. For best results do not reopen the kiln for 24 hours.

CONE 10 REDUCTION:

The easiest way to obtain reduction effects is to wait until the kiln is near cone 9 and then cover the top port about one (1) inch. Wait for 30 seconds and watch for a slight flame coming from the top port and observation holes. If no flame is seen, cover another ½ inch and wait for the flame. Keep doing this in small increments until a slight flame is seen. Leave the kiln in this condition for about one hour then take the top port cover off completely and bring to final temperature. It is important to remember that over reduction will drop the inside temperature considerably and waste both gas and time.

When firing with propane the flame is always evident at the top port. Turn the gas down a little if less flame is desired.

Body reduction may be accomplished by heating the kiln to cone 05 with top port open. At cone 06 cover the top port with the brick provided until the flame is evident from the top port and observation holes. The reducing atmosphere should be maintained for 30 minutes then the brick covering the top port should be pulled back until only an occasional flick of flame is seen from the observation holes. The kiln can then be heated to cone 9 and an additional reduction can be done as described above. A slightly reducing atmosphere from cone 06 to 9 will insure that the effects of the body reduction are not lost with additional heating.

RAKU FIRING:

Planning –

  • Adequate fuel supply

  • Reduction containers that are the correct size (arrange for easy access and clear movement around the kiln)

  • Combustibles should be at a safe distance form the kiln, yet easy to reach during post firing process

  • Helpers that know their job

  • Arrange water sources for cooling and emergency situations

  • Provide safe, clear avenues for unencumbered movement

Lighting the kiln-

  • Turn on the gas

  • Slowly open and light each burner or if kiln has ignition system push (red) button while lighting pilot bar (bar that runs underneath the kiln) until the flame holds. After ignition system is lit, burners will light automatically.

  • Slowly open gas valve (blue or red valve controls gas to burners). When the gas valve is perpendicular to the bar, gas is allowed to flow to the burners.

A pyrometer will greatly enhance your efforts during the raku process. As the kiln reaches approximately 1800º Fahrenheit begin loading your ware. Slowing lower the raku drum in 10-15 minute intervals to allow pottery to get use to the thermal shock until drum is completely closed. Around 1900-1950º F the raku process will begin to take place. You can tell the ware is ready to remove by its shiny, wet appearance. Raise drum, remove pieces and place in reduction containers as quickly as possible. Once ware is inside the container add more reduction material and cover within 15 seconds to ensure efficient smoking. (It is not how much reduction material you use, but how fast you can get pottery into the container and covered that provides exceptional raku pieces.) Keep container covered for 15 minutes - 1 hour.

Olympic Raku kilns are designed to maintain their temperature (even when drum is lifted) so that you can continue the raku process without interruption. Once ware is removed from the kiln to be placed in reduction containers, new items may be loaded in the kiln. You may also want to place items on top of the raku drum (on the outside) that you will raku next so that they are warmed up before placing in the kiln.

GAS KILN ACCESSORIES:

PYROMETER

An analog pyrometer used with kiln firings is similar to the speedometer in your car. The pyrometer shows how fast temperature is raising or lowering in the kiln.

Installing Pyrometer –

  • Kiln will have a hole punched out of the skin of kiln.
  • Drill a 5/16-inch hole through the kiln wall and insert the thermocouple from the pyrometer into the hole.
  • Pyrometer will show how fast temperature is rising or lowering in the kiln

KILN SITTER

The automatic shut-off system is used for accurate and worry free bisque firing and as a safety device when doing reduction firing. The system consists of a Dawson Automatic Kiln Sitter and an electric solenoid valve. When the kiln is assembled the solenoid valve will be on the right side as you face it. The cord from the solenoid valve on the burner system is plugged into the receptacle on the electrical box housing the kiln sitter. The electrical box on the kiln must be plugged into a 120-volt wall outlet. Before using the kiln sitter read the instruction manual for the kiln sitter that accompanies kilns purchased with kiln sitters.

To Initiate the Gas Flow:

Place a cone in the shut-off as outlined in the kiln sitter instructions and depress the button on the kiln sitter locking the cone in. Press the small black button below the kiln sitter to activate the relay system and open the solenoid valve allowing gas to flow to the burners.

If electricity is lost during the firing the kiln will automatically shut-off. To re-ignite the kiln when electrical power is resumed, press the black relay button and light the burners. Anytime the kiln is ignited the gas hand valve should be opened only enough to light a candle flame. The coil of the solenoid valve may emit an audible buzz. This is a normal occurrence and is simply a 60-cycle hum.

To bisque fire with the automatic shut-off system use the desired cone in the shut-off device, fire to maturity, and the kiln will shut-off on its own.

The kiln sitter is a safety device when doing reduction firing. A cone one or two numbers higher than the cone used for reduction end point should be placed in the shut-off. If the kiln is not manually turned off at the conclusion of reduction firing, it will shut-off on its own before damage from over-firing occurs.

ELECTRONIC WALL UNIT

Olympic’s electronic wall unit features programming by cone number or segment method allowing you to create your own programs. Each program has eight segments with ramp/hold profiles and controlled cooling rate. The controller also features a delay start for firing, numerous means for diagnosing problems and convenient program review before or during a firing. Olympic’s electronic controller on its gas kilns requires that the operator manually manipulate the gas valve while the controller runs the kiln. Because the electronic controller runs on an on/off mode, the gas kiln operator will need to adjust the gas flow accordingly.

  • Attach wall mount control vertically to wall.

  • Plug electric valve from the gas kiln ignition system into the wall unit.

  • Plug wall unit into power source.

  • Drill a 5/16" hole through the kiln wall and insert thermocouple from wall unit into the kiln.

  • Read electronic control instructions thoroughly and following programming instructions that best suit your firing requirements.

Once you are ready to fire the kiln follow the instructions for operating the ignition system.

  • Depress button and hold

  • Light ignition system (for DownDraft kilns light the left side pilot bar first and the the right side bar.

  • After 60 seconds release button

Turn wall unit on and hit Start. Slowly begin opening gas valve. As temperature increases within the kiln, continue to open gas valve as needed.

WHAT TO LOOK FOR WHEN YOU HAVE PROBLEMS FIRING YOUR KILN:

Bottom is Hotter Than the Top of Kiln

  • Excessive backpressure. Top port cover is closed too much.

  • Gas burning inside the horizontal air mixer tube*.

  • Primary air plate is not opened enough.

  • Top shelf is too close to the top port.

Kiln Does Not Get Hot Fast Enough

  • Primary air plate is not opened enough.

  • Insufficient gas pressure.

  • Gas pressure is not adequate which other gas appliances being used at the same time could cause.

  • Gas burning inside the horizontal air mixer tube*.

  • Over-reduction – excessive reduction drops temperature considerably.

  • Orifice size is too small for the gas pressure being used.

*Note – A good test to see if the gas is burning in the horizontal air mixer tube is to insert a broom straw about half way into the tube from the primary air opening. If the straw comes out burned the gas mixture is burning inside the air mixer. This condition is not dangerous, but will make it nearly impossible for the kiln to reach high temperatures. Turn the gas off and slightly increase the amount of primary air in the opening, then re-ignite to correct the problem.

CONVERSION FROM PROPANE TO NATURAL GAS:

If a conversion from propane to natural gas is made, the following table shows orifice sizes for each Olympic kiln.

Gas Kiln Size

Propane

Natural Gas

18 Inch

3/32

1/8

23 Inch

#40

9/64

28 Inch

#40

9/64

The burner system on a 27-inch deep kiln has sufficient power to allow the addition of extra rings to the kiln without burner modification. The actual gas connection may be made with flexible ½ inch gas line used in the installation of gas dryers or the kiln may be piped directly into the gas line with a ¾ inch black pipe.  If a conversion from natural gas to propane is desired, a new set of burner orifices may be ordered from Clay-King.com at 1-888-838-3625.