Some steam locomotives had (exhaust) stack extenders. Why were these necessary?
RJ Emery near Santa Fe, NM
ATSF was a big user of stack extenders. I don't know the principles involved but I believe that the taller stack improved the draft and consequently was a relatively cheap way of improving performance.
I've always hered that the taller stack created a better draft going through the fire. Plus another advantage was hey had spark arrestors in ther to help prevent grass fires.
Not 100% sure on all of that but it's just what I've heard.
-Justin
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Are we talking about the movable extenders that could be lowered where there were clearance problems?
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Paul,
I suppose the extenders could be raised or lowered as needed, but my guess is that they were set once at a height that would have cleared all overpasses and coal docks in the division in which the locomotive operated, if not the entire road's mainline. These extenders only raised the stack a foot or two at most, so clearances should not have been a problem.
The stack extensions used by the Santa Fe could be raised and lowered, this improved the drafting of the boiler and was simpler than things like the KylChap or Giesl exhaust nozzles, though also less effective.
First! I am with Kootenay Central, I AM NOT any kind of steam locomotive expert and have not slept in any Holiday Inns, Recently!
But here in Wichita at the Great Plains Transportation Museum, there resides a ATSF 4-8-4 #3768 and it has an air operated stack extender on it.
This following link has information on the 3768 as well as photos in which the installation of the stack extender is pictured.
http://atsf.railfan.net/atsfpres/atsf3768.html
and another link: http://atsfrr.net/resources/Sandifer/Stacks/Tele.htm
The longer stack would give more of a chance for the exhaust steam to impart momentum to the flue gases, thus improving draft. My recollection of fluid mechanics was that the flow in a pipe took about 10 pipe diameters to fully develop. It wouldn't surprise me if the extended stack resulted in less smoke in the cab and trailing cars.
- Erik
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