My Crawford 40 Is Back From the Stove Hospital

i am trying to sort out the things I have heard about check dampers.

it seems that the use of the check damper provides / allows the desirable amount of sufficiently warm draft up and out the flue while at the same time dropping the amount of primary air and draft up through the coal bed to the lowest level that still supports burning.

is this the correct frame of reference ?

thanks,
steve

Well there are basically two types of check dampers; one goes on or near the exhaust collar of the stove and is external and the other is only found on base burners and some coal burning oaks with back pipes.
The external check damper is very common. It basically reduces draft in the exhaust by admitting outside air right into it just as it leaves the stove. These are used for draft control and in wood burning to reduce creosote buildup in the chimney.
The external check damper must be used with caution as it creates a direct connection between the exhaust and the room the stove is in. If there is a draft reversal, exhaust will back into the house. I would never use this type of check damper overnight while sleeping.

Now the internal check damper found on base burners is a totally different animal. It controls air within the stove body and therefore poses no risk of CO poisoning or smoke backing into the house. They are 100 percent safe.
They like you suppose controls how much PRIMARY air is available for the fire. It does this by connecting the ash pit directly to the back pipe. When it is open primary air passes straight into the chimney from the ash pit, thus; by passing the fire altogether. The area of the check damper is smaller than the area of the grate so there is some air going up through the fire.
The draft is also reduced in velocity through the fire also.
I can operate my Crawford 40 in base burner mode at 225-250 degrees constantly with the check damper open and the primaries open just a sliver. The other day I had a load of 15 pounds of coal simmer from Thursday at 6:00 PM until Saturday afternoon at 2:00.

wsherrick wrote:It basically reduces draft in the exhaust by admitting outside air right into it just as it leaves the stove.

Sounds like what a barometric damper does.

wsherrick wrote:When it is open primary air passes straight into the chimney from the ash pit, thus; by passing the fire altogether.

Do you believe the extra air mass that's not contributing to combustion, helps maintain draft in the chimney? I find this to be true with my set up. I add extra secondary air during warm weather burns to help chimney draft and has totally solved the draft failure issues I used to have.

wsherrick wrote:Well there are basically two types of check dampers; one goes on or near the exhaust collar of the stove and is external and the other is only found on base burners and some coal burning oaks with back pipes.
The external check damper is very common. It basically reduces draft in the exhaust by admitting outside air right into it just as it leaves the stove. These are used for draft control and in wood burning to reduce creosote buildup in the chimney.
The external check damper must be used with caution as it creates a direct connection between the exhaust and the room the stove is in. If there is a draft reversal, exhaust will back into the house. I would never use this type of check damper overnight while sleeping.

Now the internal check damper found on base burners is a totally different animal. It controls air within the stove body and therefore poses no risk of CO poisoning or smoke backing into the house. They are 100 percent safe.
They like you suppose controls how much PRIMARY air is available for the fire. It does this by connecting the ash pit directly to the back pipe. When it is open primary air passes straight into the chimney from the ash pit, thus; by passing the fire altogether. The area of the check damper is smaller than the area of the grate so there is some air going up through the fire.
The draft is also reduced in velocity through the fire also.
I can operate my Crawford 40 in base burner mode at 225-250 degrees constantly with the check damper open and the primaries open just a sliver. The other day I had a load of 15 pounds of coal simmer from Thursday at 6:00 PM until Saturday afternoon at 2:00.

interestingly, tonight I found that the lower exit damper, the one I keep shut to help get the stove lit and run in direct mode, does nothing to drop the mano. reading of draft in base mode.

BUT I can watch as I turn it further and further closed to reduce air coming up thru the coal bed by the flames reducing down in length, then extending again as I open it back up.

have I then accidentally created a check damper ?

Maybe this will help. You may already have seen it. If so ignore it. It represents the "Glenwood 6" style stoves.

I have viewed all your pictures but can't seem to correctly visualize your modifications to the stoves gas path. Could you draw a rough sketch and post it up please?

yes I saw that great diagram, it was part of my studies into the concept of how base burners work.

i can't scan right now but I might be able to show you the gas path with photos, i'll see what I can work up.

the biggest thing to remember about my design is that the gas travels down the sides of the stove into the base chamber, not out the back and into the base chamber.

i am putting up a photo essay in my own thread to show gas path.

Lightning wrote:

wsherrick wrote:It basically reduces draft in the exhaust by admitting outside air right into it just as it leaves the stove.

Sounds like what a barometric damper does.

wsherrick wrote:When it is open primary air passes straight into the chimney from the ash pit, thus; by passing the fire altogether.

Do you believe the extra air mass that's not contributing to combustion, helps maintain draft in the chimney? I find this to be true with my set up. I add extra secondary air during warm weather burns to help chimney draft and has totally solved the draft failure issues I used to have.

It's essentially the same but manual.
I don't know if you mess with cars at all but if you do, think of it as a vacuum leak below the carb plates or at the intake manifold/head interface. If air is sneakin' in there, it's not pulling it through the burn pot.

On my #8, the operation of the stove is night and day different with the check damper in various stages of open than it does with it closed.