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Why different smokestack shapes?

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Why different smokestack shapes?
Posted by Ray Dunakin on Sunday, June 4, 2006 11:04 PM
What is the purpose of the various smokestack shapes used on steam locos? There seems to be quite a wide variety.

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Posted by markn on Sunday, June 4, 2006 11:49 PM
From what I have read-in the "earlier" days (mostly wood burning)a lot of the variation involved forms of spark arresting. I am not an engineer-all my thermodynamic training was in the Boy Scouts 40 years ago but it appears as the fuel, fire grate engineering, pressures etc all improved, the vertical size (and I assume need to create "draft" ) decreased to the point at steam's end the stack was no taller than a sand dome, ie Stephenson Rocket/John Bull-they were about 6-8 ft tall, 4-4-0s 3-4 ft, 1890-1900 1-2 ft etc, a "vent" in 1950 (see the Steam Glory 2 ad at the right of the page)
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Posted by Anonymous on Monday, June 5, 2006 9:42 AM
In Stephen Ambrose's book about the intercontinental railroad, two different types of stacks are mentioned. The ones that are straight up and down and the diamond shaped. Now I think I remember the difference; the diamond shape burned coal and the straight up and down burned wood (I'm sure I'll get corrected if I'm wrong). So at least between those two shapes it was a matter of function.
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Posted by CSSHEGEWISCH on Monday, June 5, 2006 10:05 AM
Smokestack and smokebox design have varied widely over the years, all with the goal of improving draft and performance. Oddly, there are no real empirical formulas involved and front-end design has been as much art as science.
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Posted by palallin on Monday, June 5, 2006 10:36 AM
A factor contributing the the reduced height of stacks is the increased height of the engines. Though the engines grew taller, the tunnels did not. Many engines even had to have odd-shaped domes and cabs to accomodate height restriction along the line.
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Posted by daveklepper on Monday, June 5, 2006 3:23 PM
The straight up and down was for coal, diamond stacks could be used for coal or wood, and previously, balloon stacks, looking something like funnels, were standard on woodburners.
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Posted by Anonymous on Monday, June 5, 2006 9:41 PM
A wood burning fire will produce more embers than a coal fire. These embers, if allowed to fall to the ground, can start fires. The balloon and diamond shaped stacks had a screen on top that captured large embers and let them fall and cool within the stack, some even having a pipe leading down to the ballast.

Guess it's better to burn up your ties and bridges than the countryside but, with any luck, the embers should have cooled off enough not to kindle ties.

Art
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Posted by Gunns on Friday, June 9, 2006 12:44 AM
Well,
our stack is over 20 feet above the roadbed.....
We need a special stack extender to keep the draft at all speeds.
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Posted by markn on Tuesday, June 13, 2006 10:35 PM
Check these stacks out: http://www.dself.dsl.pipex.com/MUSEUM/LOCOLOCO/chimney/chimney.htm
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Posted by Anonymous on Wednesday, June 14, 2006 9:11 AM
After the demise of woodburners on the Class I's, most of the odd stack shapes were found on backwoods shortlines only. THe diamond stack is seen a lot on the coal-fired geared locomotives of the east, with screens on top to sift cinders in order to cool them before discharge into the air.

THe Radley-Hunter stack was a patented design I believe, which actually trapped most all cinders using an ingenious series of baffle plates. The collected cool cinders would collect in a chamber at the base of the stack and later be discharged by the servicemen via a tube onto the ground. Examples of engines with these stacks were Cass Scenic RR Shay #7 (out of service), and Cass Heisler #6, both of which came from Meadow River Lumber Co, which used the Radley-Hunter stack exclusively on its geared engines. Both engines later had standard diamond stacks installed, probably due to maintenance considerations.

Woodburners on southern and northwestern logging roads often had balloon stacks, a rounded variation on the diamond design.
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Posted by Anonymous on Friday, June 16, 2006 8:40 PM
those funnel stacks on the old time woodburners were designed to control the burning embers created by the intense action of the fire in the firebox.

the exhaust steam was directed up through the center of the stack, and this creates a strong draft which sucks the fire through the boiler tubes which boils the water. this draft will carry any burning embers that will fit through the boiler tubes, and they are too big to dissipate their heat before landing on the ground (grass, trestle, forest, or snowshed) so they have to be broken up.

inside the funnel stack, at top center, facing down, is a cone that deflects this exhaust blast to the side walls where the embers are broken into smaller bits. they recycle through this system until small enough to go through the top screen where, in theory, they will cool before landing.

most of these embers cooled before landing, and some did not. that is why a lot of early right of ways were burned black, why wood bridges had waterbarrels and bridgetenders, and why the central pacific had a firetrain follow every consist through their forty miles of snowsheds.

coal burners did this cleaning up process in a forward extension of the smokebox, and used a straight stack to exhaust.

those doors on the front of boilers were used for cleaning up those smokeboxes when necessary
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Posted by Anonymous on Tuesday, June 20, 2006 7:45 AM
Most US locomotives seem to have used a straightforward arrangement of nozzle at the bottom of the smokebox, a petticoat to contain the exhaust and a cylindrical stack. Some of the larger locomotives doubled the number of nozzles and pipes, arranging them in tandem.

There was much more experimentation overseas. An example was the Giesl stack -- fan-shaped from the side with a narrow cross-section -- which supported a multi-ejector configuration that was thought to be much better than the standard nozzle and petticoat. See the Ultimate Steam Page essay http://www.trainweb.org/tusp/ex_dwgs.html
for a variety of stack shapes and their purposes.

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