Smokebox Length Ratio

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Bill Shields
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Re: Smokebox Length Ratio

Post by Bill Shields »

4. Whatever looks good and will allow you to get your full size hands inside of a scale model smokebox to do assembly and maintenance work
Too many things going on to bother listing them.
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NP317
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Re: Smokebox Length Ratio

Post by NP317 »

Also involved in smokebox length is fuel used:
Coal required significant screens and baffles in the smokebox.
RussN
Santafescotty60
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Re: Smokebox Length Ratio

Post by Santafescotty60 »

Hello, These are all good answers, for those old time slide rule engineers somewhere in a book, I am sure there is a smokebox formula. As well I was under the impression that the early 1890 or 1900 locos with long smoke boxes were for burning wood as per Dan above with screens to catch ash and soot , they may have switched to coal later. The Screens in the smoke box helped the women on wash day too! Hanging hand scrubbed clothing on the wash line to dry, only a few had Maytag's back then... Happy Wife Happy Life
LOL Scotty
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Bill Shields
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Re: Smokebox Length Ratio

Post by Bill Shields »

If you stop and think about it.. what does the length of the smokebox have to do with anything except how much stuff you can cram in there?
Too many things going on to bother listing them.
Doug_Edwards
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Re: Smokebox Length Ratio

Post by Doug_Edwards »

For a little perspective, here are some examples of tube lengths:

SP class A6 4-4-2 16 feet
SP Harriman 4-6-2 (classes P1 through P7) 20 feet
SP Cab forward classes AC4 through 12 22 feet
Keep in mind that the AC4 - 12 had combustion chambers.
The Atlantics had a 75" smokebox, and the Pacific classes P1-P5 had a 96" smokebox.
I would guess that the shorter smokebox on the Atlantic would be to get more tube length, as the length in front of the stack is the same. However it looks like the max tube length is 22 to 24 feet.

Regards,

Doug
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Building a 80 ton Climax in 1.6"

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Loco112
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Re: Smokebox Length Ratio

Post by Loco112 »

Bigger is better. Contestant vacuum is better, abrupt changes/surges are bad (but unavoidable).

Thats what the builders decided, although its always a moving target. Space is always limited.

For a larger volume of smoke box, the vacuum (applied by the venturi, created by exhaust steam from the cylinders) is not as abrupt in its pressure changes as a smaller smoke box is.

So, a larger smoke box create a more stable vacuum on the fire, so it tears the fire less. A larger volume of smoke box vacuum can also pull a little longer as it pulls softer, all good for the fire.
FKreider
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Re: Smokebox Length Ratio

Post by FKreider »

Loco112 wrote: Mon Jan 25, 2021 4:24 am Bigger is better. Contestant vacuum is better, abrupt changes/surges are bad (but unavoidable).

Thats what the builders decided, although its always a moving target. Space is always limited.

For a larger volume of smoke box, the vacuum (applied by the venturi, created by exhaust steam from the cylinders) is not as abrupt in its pressure changes as a smaller smoke box is.

So, a larger smoke box create a more stable vacuum on the fire, so it tears the fire less. A larger volume of smoke box vacuum can also pull a little longer as it pulls softer, all good for the fire.
Interesting, thanks for the info!
-Frank K.
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NP317
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Re: Smokebox Length Ratio

Post by NP317 »

I just received a good photo (below) of the Northern Pacific #666 American.
This Baldwin locomotive was delivered in 1887 and scrapped in 1947.
This 1930s image shows modernization with a steel cab and turbo-electric lighting.
A coal burner, it had an extended smokebox for the cinder screens. A good example of a more unusual smokebox design.

My friend is planning on modeling this locomotive in 7.5" gauge live steam, basing it on the Allen American.
The Allen's long boiler is correct for #666. He already has the castings and the boiler. 'Just needs the time.
RussN
NP666__classB-1.jpg
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Fender
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Re: Smokebox Length Ratio

Post by Fender »

I came across this interesting drawing from the Baldwin Locomotive Works Engineering Department on standard practice for smokebox design. The drawing is dated 1947, so this is pretty much the final word from Baldwin on this subject. Although this is not to scale, notice how the cinders are directed to the front of the smokebox, where they would pile up there, and a longer smokebox would provide a place for them to accumulate.
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Bill Shields
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Re: Smokebox Length Ratio

Post by Bill Shields »

Easier to clean with a shop vac
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pat1027
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Re: Smokebox Length Ratio

Post by pat1027 »

Martin Evans and Greenly say little about the smokebox itself other than it be tight fitting. They talk mostly about the stack and blast nozzle.

Until the mid 1930's Purdue operated a locomotive test plant. A search of their library shows several articles on smokebox's and a dissertation from 1940 titled "Design of a Locomotive Smokebox Arrangement". You need a Purdue University account to view them online. Know any alumni or students? They can be viewed in person on a public computer at the library. The librarian said a inter-library loan might be available through your local library.

https://purdue-primo-prod.hosted.exlibr ... _entrys,lk
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