Defiant Secondary Air Shutter

[mdbartel]

I have a 1945 Defiant Cat stove that have been burning for about the last eight years. I have two questions:

1. I have noticed that the secondary air shutter for the cat will close as the stove heats up. As the cat get hotter, the bi-metallic coil continues to expand and goes around the 6 o'clock position and starts to re-open the shutter. I have taken care to ensure the probe is setup correctly, about the 4 o'clock position when cold. Is this expected operation for this stove?

2. How have you installed a cat temperature probe in your Defiant/Encore/Intrepid? I was thinking about doing this, but am hesitant to start drilling and would like some install advice. My original sales/installer was of no help.

 

[BrowningBAR]

2. How have you installed a cat temperature probe in your Defiant/Encore/Intrepid? I was thinking about doing this, but am hesitant to start drilling and would like some install advice. My original sales/installer was of no help.

On the back of the stove you will see a removable plug between the metal specs plate and the "secondary air shutter" cover. Remove plug and Insert probe.

 

[mdbartel]

Purchased the Condar digital catalytic probe thermometer. I was surprised when the catalyst temperatures were rising and the stove was back-puffing. Closing the primary air shutter only made the problem worse. Opening the primary air shutter stopped the puffing and caused the catalyst temps to return to normal.

My theory is lack of sufficient primary air generates excessive unburned wood gas. This gas gets burned in the catalyst. There is more gas than the catalyst was designed to handle. As the catalyst gets hotter and hotter, the secondary air shutter moves past its full shut position and starts coming more and more open, exacerbating the problem. These things cause the catalyst to get excessively hot. Therefore, there is a minimum amount of air that must be provided to the burn chamber.

I think my problem goes back to when I took the primary air shutter apart. I found the primary air rod bent, which prevented the shutter from going full closed. I assumed it was sloppy factory work, and maybe it was. I replaced the rod and cable, but I used the guidance in the Encore rebuild manual to set the shutter. It must be set a little too far towards the full closed position.

 

[Gark]

Thank you for that post, mdbartel- it alerted me to what is the problem with the replacement secondary probe/bimetal that we installed last December. After the new assembly, there were alot more instances overfiring and orange glow of death with the upper fireback and hood. Until your post, I never thought to remove the cover plate to view the coil during a burn, but indeed ours (set at 4:00 o'clock cold) now swings past 6: oclock all the way to 9: oclock when real hot. This pulls the secondary shutter way back open just when it should be closed. For now, until this gets solved, I set the cold position to 1:30 and hang a little weight on it. No more runaway burns - I think I got a defective probe assembly as it is " too reactive".

 

[Gark]

Also, regards the backpuffing- once the damper is closed, it' s a good idea to close down the primary lever VERY SLOWLY. IE, over a 10 minute interval. This lets the burning splits very slowly decrease their outgassing so the cat won't be overwhelmed.