Smokebox Length Ratio

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FKreider
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Location: Sturbridge, MA

Smokebox Length Ratio

Post by FKreider » Wed Jan 13, 2021 1:04 pm

I have noticed that some of the most modern steam locomotives built (such as the Reading T-1, FEF-3, Big Boy, etc.) all have long smokeboxes in relation to their boiler length, especially when you compare them to some Atlantics and earlier engines which seem to have very short smokeboxes.

Can anyone point me to any literature that discusses this? I did a few searches on the net however did not come up with anything great. I'm betting this info exists in a book out there somewhere and hasn't been migrated to the net due to being mostly obsolete information. :D
-Frank K.

Pontiacguy1
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Location: Tennessee, USA

Re: Smokebox Length Ratio

Post by Pontiacguy1 » Wed Jan 13, 2021 1:16 pm

Some of the more modern locomotives also had feedwater heaters installed in them, which necessitated a larger smoke box. Some had their smoke boxes extended. Not sure why unless they were adding a feedwater heater, or there was some problem with draft and efficiency they were trying to solve. .

jkimberln
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Location: Richmond, California

Re: Smokebox Length Ratio

Post by jkimberln » Wed Jan 13, 2021 1:28 pm

My guess would be they had to accommodate particulate screens to try to get the smoke particles from being blown out the stack. I can't think of any thing else that would be large enough to require more space besides that and the aforementioned feedwater heater.

Berkman
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Re: Smokebox Length Ratio

Post by Berkman » Wed Jan 13, 2021 1:29 pm

I think this was also largely due to the front end throttles and type e superheaters taking up more space as well.

Many modern locomotives had access panels on top of the smokebox above the throttle and superheater manifold.

shild
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Re: Smokebox Length Ratio

Post by shild » Wed Jan 13, 2021 2:33 pm

Probably makes it more difficult to clean the smoke box if you extend it, doesn't it?

Berkman
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Re: Smokebox Length Ratio

Post by Berkman » Wed Jan 13, 2021 3:32 pm

I don't think the lenght would make a huge difference cleaning.

For example any of the LE 4-8-4s, will have a much longer smokebox than a LE pacific. It's not a big issue.

KarlKobel
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Joined: Sun Mar 31, 2013 9:53 pm

Re: Smokebox Length Ratio

Post by KarlKobel » Wed Jan 13, 2021 6:00 pm

It has a lot to do with smokebox throttle vs steam dome throttle.

Karl

Asteamhead
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Joined: Tue Jul 31, 2012 1:59 pm
Location: Germany, Duesseldorf

Re: Smokebox Length Ratio

Post by Asteamhead » Wed Jan 13, 2021 7:33 pm

Hello steamers,
please take into consideration that some boilers got longer than necessary due to length of big locomotives as UP 4000s. Length of both tubes and combustion chamber couldn't be much longer as desired due to construction limits. Thus big (long) engines like the UP 4000 got a very large front end due to excess length of it's 4 wheel truck :( . Look at the compact N&W Y6b that sports a short smokebox despite feedwater heater, netting, front end throttle and such!
A lot of different boilers are shown in Locomotive Cyclopedia to compare different constructions.
The worst example of unwanted excess length was the German DR class 06. Designed as 4-8-4 with the longest tubes ever used :x . It failed due to leaky (spaghetti-)flues. It had better being constructed as 2-8-4 with shorter tubes, boiler and smokebox (and a combustion chamber)!

Just my thaughts
Asteamhead
Attachments
DR class 06 versus Norther Pacific.jpg
DR class 06 versus NP Northern
Extreme long (yet narrow) boiler with extended smoke box due to length of that locomotive.
Length of tubes was 24' 7" - more than even the UP 4000's!

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Fender
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Location: Chattanooga TN

Re: Smokebox Length Ratio

Post by Fender » Wed Jan 13, 2021 7:36 pm

In the case of the Reading 4-8-4s, these were rebuilt from 2-8-0s with shorter boilers, so the additional length was added to the smoke box. In the case of the others, I have read that with longer boilers, there were diminishing returns with lengthening the tubes and flues in terms of steam generation. Most modern engines had a combustion chamber in front of the firebox, but even then there was a practical limit on tube length. So, they made the smoke box longer.
Dan Watson

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Fender
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Re: Smokebox Length Ratio

Post by Fender » Wed Jan 13, 2021 8:01 pm

Quite a few early-1900 locomotives burning coal had a riveted smoke box extension added after they were built. I assume this was to provide more room for the accumulation of cinders.
Dan Watson

FKreider
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Location: Sturbridge, MA

Re: Smokebox Length Ratio

Post by FKreider » Wed Jan 13, 2021 8:23 pm

Interesting discussions, some of these things I had not thought of. I had assumed it was something to do with grate area vs. smokebox area in order for these engines to draft correctly.
-Frank K.

Berkman
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Re: Smokebox Length Ratio

Post by Berkman » Wed Jan 13, 2021 9:32 pm

I think it comes down to:

1. Superheater & thottle arrangement
2. Feed water heater
3. Flue & Tube max lenght. ( i think around 22ft?)

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