Fire box door size

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ianrichards
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Fire box door size

Post by ianrichards » Sun Oct 22, 2017 4:49 pm

I’m just about to commence completion of a part built Lune Valley boiler that I acquired and I need to determine the optimum door size opening. I was told that 6”x4” would be sufficient but that seems dreadfully small.
Your advice would be greatly appreciated.
I’m happy to build the door from scratch, but is it possible to purchase one in the UK?
Many thanks
Ian
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DetroiTug
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Re: Fire box door size

Post by DetroiTug » Sun Oct 22, 2017 5:24 pm

I've seen boilers with very small firehole doors and it makes it difficult to tend the fire, but for a water tube boiler it is better, when the door is opened its less cold air rushing in cooling it down.

-Ron
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Re: Fire box door size

Post by cyberbadger » Sun Oct 22, 2017 6:47 pm

What's your fuel going to be?

I use "standard"-ish 16" length logs available in the US. (I usually cut them into 3-4 chunks)

I'm very happy with my 8'x10" door.

-CB

P.S. I have more of a problem with length. But I have made my own personal rule, fuel can't come onboard and be longer then that ~16", because It won't fit lengthwise and it is a PITA to saw or break wood underway.
ianrichards
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Re: Fire box door size

Post by ianrichards » Sun Oct 22, 2017 7:02 pm

I plan to use wood, hence my concern about the 6x4 opening.
I was think that 8x6 would be better, that would be double the suggested size.
Do you think that 10x8 would be too big for a Lune Valley?

cyberbadger wrote:What's your fuel going to be?

I use "standard"-ish 16" length logs available in the US. (I usually cut them into 3-4 chunks)

I'm very happy with my 8'x10" door.

-CB

P.S. I have more of a problem with length. But I have made my own personal rule, fuel can't come onboard and be longer then that ~16", because It won't fit lengthwise and it is a PITA to saw or break wood underway.
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Re: Fire box door size

Post by cyberbadger » Sun Oct 22, 2017 7:24 pm

I think there is definitely something to what Ron is saying. You are more vulnerable with a water tube boiler to be chilling your tubes when you open a bigger door.

I think that enlarging it to 8"x6" sounds reasonable, 10"x8" would be your call of course.

I get asked by my fireman (even by my mechanical engineer steamer friend) if they can keep the door open at the dock after a good days steaming for ambiance and I tell them, "No! That heats for the boiler. Make a camp fire elsewhere."

-CB
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Re: Fire box door size

Post by ianrichards » Sun Oct 22, 2017 7:37 pm

8x6 sounds and “feels” right ... if you know what I mean ;-)
On the other hand ... maybe 7x5 .... decisions, decisions
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Re: Fire box door size

Post by Mike Cole » Mon Oct 23, 2017 5:43 pm

Hi Ian
I also have a lune valley boiler and mostly burn wood. Just because it was for sale at a SBA AGM I use a 7 inch by 3 inch firebox door. It is just a tad too small. I buy wood in the red nets bags and find I have to chop about a third of them up, the others chunks fit fine. 6x4 would be fine. IF I ever rebuild it I would go for 6 x5.

Mike
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ianrichards
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Re: Fire box door size

Post by ianrichards » Mon Oct 23, 2017 5:52 pm

Excellent, thank you so much for that.
6x5 it’s going to be.
Could I trouble you to email me some pictures of your boiler.
I’m trying to determine the best layout for ash tray access, boiler doors etc.
My email address is ian@ian-richards.com
Many thanks
Ian
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Re: Fire box door size

Post by barts » Mon Oct 23, 2017 6:29 pm

On Rainbow, her Scotch boiler has a central firebox 13" inside diameter (the boiler is 24" in diameter). Being able to easily place firewood (16" x 2-3" x ~2-3") in the firebox is critical as the firebox is ~34" long and I'm often using the fresh firewood to shove the already burning pieces into the rear of the firebox. The door is often open for a bit as I load several pieces into the boiler at once, but this boiler reacts very slowly as it holds many gallons of water.

Our Otter has a Lune Valley style boiler I built that is oil fired. It responds quite rapidly to firing changes; if yours is similar you'll be likely working with smaller quantities of wood to keep more even steam conditions. Making it easy to spread the fire out will be important as well. You might consider having a stack damper (like an carburetor choke) above the boiler so that you can reduce the amount of cold air that rushes in when you open the firebox door; this could also be done w/ a lever & spring setup so that the damper closed automatically most of the way when the door was opened.

- Bart
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Bart Smaalders http://smaalders.net/barts Lopez Island, WA
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Re: Fire box door size

Post by DetroiTug » Mon Oct 23, 2017 8:33 pm

ianrichards wrote:might consider having a stack damper (like an carburetor choke) above the boiler so that you can reduce the amount of cold air that rushes in when you open the firebox door
Thats a good idea. I plan Ofeldt'ing the tug in the future and I am concerned about charging the fire box and having this issue. I heard that a wood fired Ofeldt, when the fire door is opened under way, the engine slows down. That is the trouble with fast, it's fast both ways. On our little steam cars we have a leather curtain that hangs in front of the engine, while driving if that is lifted, the added air - thermal loss, slows the car slightly.

Sounds like your comparably sized scotch is like the big FT in the tug, raging fire, roaring popping and cracking and the gauge looks like it's stuck :). It's very relaxing though.

-Ron
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