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Model C Oven Safety System

A Chambers Model C Oven Safety System


Why would you need a safety system? What does it save you from? How does it work?

PROBLEM: On the original Chambers oven without a safety system, if you were using the oven and the pilot light blew out, there is no way for the oven to know this. The oven continues to fill up with gas. Then when you later go to the kitchen to check on your dinner, you open the oven door and let out a whole bunch of unburned gas. This gas expands and can quickly find a source of ignition, be it the stove pilot light or a spark from someone turning on an appliance, the phone ringing, your kids playing with matches, your no-account brother-in-law smoking a fattie on the couch, etc., and BOOM. It’s a bomb going off. You are tossed across the room, have your eyebrows singed off, and maybe you are even killed. Probably not what you expected when you just wanted to check on the pizza.

SOLUTION: Chambers designed a safety pilot system in the 50’s to solve this problem. The safety system simply shuts off all gas to the oven if the oven pilot light ever goes out. Note that this system is only for the oven. The safety system described here does not have anything to do with the stove pilot or the thermowell pilot.

HOW IT WORKS: Added right next to the new oven pilot is a special temperature sensor called a thermocouple. Using an obscure principle of physics called the Thermoelectric Effect, this sensor generates a tiny electric current whenever it is immersed in flame. No battery or external AC power is required to generate this current, the effect is inherent in the design of the thermocouple itself. The other end of this thermocouple is wired to a safety valve located in the service cabinet. The safety valve has a small electromagnet in it that is energized by the current from the heated thermocouple. This magnet holds the valve open when energized. So as long as the thermocouple is bathed in flame, the safety valve allows gas to flow to the oven. Should the pilot go out, the thermocouple will stop producing its electric current, the electromagnet will no longer have power to hold the valve open. The valve closes, shutting off the gas within seconds of the fire going out.

What do you need? Where can you get it? How much does it cost?

SKILLS REQUIRED: You should not attempt to build this safety system yourself. Even if you know a nut from a bolt, you should never work on gas appliances yourself. Always hire a trained and licensed appliance technician to do everything for you. Depending on your local laws, it may actually be illegal to perform this work yourself unless you are a licensed gas technician.

PARTS NEEDED:You can order these parts for your technician from Patriot Supply at www.patriot-supply.com. Prices were what I paid in early 2006, they may vary for you.

1  $96.32 1720-007 1/2” NPT Valve Assembly with Magnet 
1  $35.28 1800-100 Universal 9B Pilot Kit
1   $4.37 1970-036 36” length thermocouple, 20-30millivolt

Standard gas fittings and tubes available at your local Ace Hardware, prices approximate:

6ft 41901 3/8" Aluminium Tubing  $6.54
5ft 41090 1/4" Aluminium Tubing $4.95
1   42048 1/8 pipe tee $3.00
2   41243 3/8 comp x 1/2 MPT $2.00
2   41236 1/4 comp x 1/8 MPT $2.00
1   40120 1/8 close nipple $0.89

The total cost is in the ballpark of $200. There are some miscellaneous items not listed here, like Permatex #2, sheet metal screws, angle brackets, machine scews, and cold beer for celebrating when you’re done. It is not necessary to tip your appliance technician, but they do appreciate a cold one. You should make sure however, that they do not open a brew until the job is done and the oven checks out. Voice of experience here, trust me.

What are we building? How is it built?

Fig. 1 – Crudely Drawn Schematic Diagram

THEORY OF OPERATION: As you can see from the crudely drawn schematic of Fig. 1, this oven safety is quite relatively simple. We’ll be adding a new pilot, a thermocouple, a safety valve, a tee, and some new aluminum tubing. Aluminum tubing has never been shown to cause Alzheimer’s disease, despite what you may have read in the National Enquirer.

Gas is taken from two places. First, pilot gas is taken from a Tee we’ll install on the manifold. I’ve shown it being taken here from near where the other pilot gas is drawn from the manifold. This runs to the pilot input of the safety valve. Second, gas is taken from the output of the oven thermostat and applied to the input of the safety valve.

Gas goes two places. First, pilot gas runs from the pilot output of the safety valve to the new oven pilot. Second, gas runs from the output of the safety valve to the oven burner.

The thermocouple is attached to the thermocouple input of the safety valve.

When the system is cold and no gas is turned on, the safety valve is closed. It stays closed until you press the red button on top of the valve. This manually opens the valve so that pilot gas can flow directly to the pilot, for lighting. You light the pilot with a match or butane lighter, and then you continue to hold the red valve for a minute to allow the pilot flame to heat up the thermocouple. The hot thermocouple generates a small current which energizes an electromagnet inside the valve, which means you can now take your finger off the red button. The electromagnet will hold the valve open until such time as the pilot goes out. With the pilot lit and burning, you can operate the oven gas valve and thermostat as per usual.

STEP 1: Shut off the gas to your oven. There is a cut-off valve usually behind your oven where the gas supply line attaches to the oven. Sometimes this cut-off valve is in the basement. If you do not have a cut-off valve you will have to call a plumber to install one before you can proceed.

STEP 2: Remove your old oven pilot. It unscrews from under the oven. I propped my oven up on bricks to be able to reach it. Unscrew the pilot from your oven thermostat using a small wrench. Take care not to kink the tube. Put it away with your spare parts. It’s a rare size that is useful if you ever need to service your other pilots.

STEP 3: Assemble the new pilot and thermocouple. There are several pieces that come with the pilot. Assemble them as shown, and follow the instruction sheet that comes with the thermocouple to mount it to the pilot. The little silver piece (maroon arrow, Fig. 2) is a gas orifice. Choose the one with the larger opening if you have natural gas. The smaller orifice is for propane. Choose the 1/4” size brass compression nut and ferrule and discard the others.

Fig. 2. Thermocouple Assembly

STEP 4: Drill holes for the new pilot assembly. The old pilot fit in a small hole (see maroon arrow in Fig 3.) just in front of the circular damper plate in the oven floor.

Fig. 3. Original Pilot Hole Location

The new pilot requires a bigger hole, and you’ll need another hole for the thermocouple lead (see maroon arrow, Fig. 4). I just used a drill to enlarge the existing pilot hole (shown at left), and drilled a new hole for the thermocouple lead. Don’t worry about the rockwool, it will be fine.

STEP 5: Fashion a mounting bracket out of an angle bracket you may find out in your garage. Failing that, Ace hardware will have what you need. Mount the bracket using a sheet metal screw.

Fig. 4. Pilot and Thermocouple Holes with Bracket

STEP 6: Mount the new pilot assembly using a machine screw and nut. Route the thermocouple cable through the hole, under the oven, and up into the service cabinet.

Fig. 5. Mounted Pilot and Thermocouple with Bracket

STEP 7: Attach the 1/4” aluminum tube to the thermocouple. Be sure to slide the nut on the tube first, then the 1/4” brass ferrule, then insert into the pilot and tighten down, as shown in Fig. 6:

Fig. 6. Pilot and Thermocouple Connections Under the Oven

Route the 1/4” tubing up through the access hole and into the service cabinet. This shot is also taken from underneath the oven:

Fig. 7. Showing how the Pilot and Thermocouple Lines Enter the Service Cabinet

STEP 8: Fashion a mounting bracket for the Safety Valve assembly, and mount it to the floor of the service cabinet just inside the door using sheet metal screws. There are other mounting possibilities, think of how you will want to use the safety. Will you want to leave your pilot burning all the time, then this is a good location. This is good if you use your oven quite frequently. If you’re like me and don’t use it but once a week, you may want to position the valve where you can reach it easier, say on the side of the oven box just inside the service cabinet, where you won’t have to remove the service panel floor pan to get to it.

Fig. 8 – Mounting the Safety Valve Bracket

STEP 9: Mount the safety valve to the bracket as shown, using machine screws:

Fig. 9 – Mounting the Safety Valve to the Bracket

STEP 10: Apply Permatex #2 to the 1/2” threads of the 3/8 comp x 1/2 MPT brass fittings and screw them into the ends of the safety valve as shown. The Permatex is important, do not skip it. Do not use anyhing else. Ace has Permatex #2. Get a tube.

Fig. 10 – Mounting the Brass fittings to the Safety Valve

STEP 11: Measure, then cut off and run a section of 3/8” aluminum tube from the OUT side of the safety valve to the oven burner jet. Use 3/8” brass ferrules and nuts for the compression fittings and tighten with a wrench.

STEP 12: Run the 1/4” line from the oven pilot assembly to the OUT side of the safety valve pilot connection. Use 1/4” brass ferrules and nuts for the compression fittings on the pilot line and tighten with a wrench.

STEP 13: Attach the thermocouple lead to the thermocouple fitting on the safety valve as shown, and tighten lightly using only a very small wrench. Do not overtighten this lead.

Fig. 11 – Routing the Gas Tubing and Thermocouple Lead to the Safety Valve

STEP 14: Measure, then cut off and run a section of 3/8” aluminum tube from the IN side of the safety valve to the output of the oven thermostat. (maroon arrow in Fig. 12 points to output of oven thermostat.) Use 3/8” brass ferrules and nuts for the compression fittings and tighten with a wrench.

STEP 15: Run the 1/4” line from near the pilot tee assembly on the manifold to the IN side of the safety valve pilot connection. Use 1/4” brass ferrules and nuts for the compression fittings on the pilot line and tighten with a wrench.

Fig. 12 – Routing Gas Tubing to the Oven Thermostat Output

Fig. 13 – Routing Gas Tubing to the Safety Valve Inputs

STEP 16: Time to insert a Tee connection for the pilot gas. You can tap in just about anywhere on the manifold. The flow of gas has to be uninterrupted, so you can’t take it off the oven thermostat, much though you might like to. I took mine from the existing tees that were already coming from the manifold to supply pilot gas for the stove and thermowell. Use Permatex #2 on the threads before final assembly of these parts.

Fig. 14 – Inserting a Tee for the Oven Pilot Gas

Fig. 15 –Location of Tee for Oven Pilot Gas

STEP 17: Complete the 1/4” line from the pilot tee assembly on the manifold to the IN side of the safety valve pilot connection. Use 1/4” brass ferrules and nuts for the compression fittings on the pilot line and tighten with a wrench. Depending on how much tubing you had for your stove pilot and thermowell pilot, you may need to extend these lines using the tube you salvaged from the original oven pilot.

Fig. 16 – Routing Pilot Gas Tubing to the Safety Valve Input

STEP 18: Plug the pilot hole on your thermostat. I have a rare Wilcolator model, yours will likely vary from this photo. You need to plug the hole where you detached the original pilot from your thermostat (see maroon arrow, Fig. 17). I went to Ace hardware to get a small threaded allen set-screw. Apply Permatex #2 to the threads before threading it in. You don’t have to use a wrench, hand tight is OK.

Fig. 17 –Plugging the Now-Unused Pilot Hole in the Thermostat

STEP 20: Now you’re ready to test it. Have your licensed gas appliance technician double-check the work. Have him check for gas leaks, have him check the pilot operation, make sure that when the pilot is snuffed out that the valve closes after a few seconds.

Fig 18 -Pilot Flame Alignment
It's important during the check-out phase that you ensure the pilot flame bathes the tip of the thermocouple in flame. The flames come out in an X pattern, and you have to ensure that one of the legs of the X touches the thermocouple tip. Otherwise, the thermocouple won't get hot enough to generate the required current to keep the safety valve electromagnet energized and open.

That’s it. Now you’re cooking safely!

In preparation of this information, every effort has been made to offer the most current, correct, and clearly expressed information possible. Nevertheless, inadvertent errors in information may occur. In particular but without limiting anything here, the author disclaims any responsibility for typographical errors and accuracy of the information that may be contained on this page. The information and data are subject to change without notice to you. The author makes no warranties or representations whatsoever regarding the quality, content, completeness, suitability, adequacy, sequence, accuracy, or timeliness of such information and data. Use of this data is entirely at your own risk. Always seek out the services of competent licensed professionals to perform work on gas appliances.


Copyright (c) 2006-2007 Mark Gessner. All Rights Reserved.

Created on 04/07/2007 09:50 AM by lowracer
Updated on 04/10/2007 08:03 PM by lowracer
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