simple vs. compound

[NW Mailing List]

 1. Class A front cylinders steam pipe question (NW Mailing List)


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Message: 1
Date: Wed, 27 Sep 2023 14:48:20 -0400
From: NW Mailing List <nw-mailing-list at nwhs.org>
To: NW Mailing List <nw-mailing-list at nwhs.org>
Subject: Class A front cylinders steam pipe question
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What is the device at the end of the steam pipe and on top of the front
cylinder called, and what is its purpose?
Does it somehow "buffer" incoming steam "beating"?

Did the A and the Y's differ in steam delivery? Am I correct in thinking
the A's deliver steam using individual side pipes on the side/underneath of
the boiler, and the Y's deliver steam through a single central pipe under
the boiler?  What makes each option best fo the individual use case?  I'm
guessing it has something to do with compound vs simple?

Are there other locos on other roads where this device was present? I've
never noticed it, but then again, I've never looked?

Bonus question: How does it relate to beets?

Mike Rector

Mike and others:

I am far from the most knowledgeable person on this query of yours but the
first difference is the A's were 4-cylinder simple engines whereas the Y's
used the steam twice; first to rear cylinder under high pressure which was
then directed to those big bulging front cylinders that reused that exhaust
steam before blowing out the stack.
That's the Cliff notes version. If you want to know more there are books
that describe the methodology of what and why things were when it came to
simple vs. compound. And then there were those real dandies, the 3-cylinder
compounds that have never read the N&W ever tried. Some American RR's did
but most didn't like them because they were apparently maintenance
headaches. That said European RR companies loved them and they were quite
prevalent over there.

In the few videos that actually have genuine original sound for a
3-cylinder, it sounds mighty strange for that 3rd sounds like it's out of
synchronization. Fascinating.

By the 1930s or so, the compounds were getting out of favor for most RR's
except the N&W and that's due in large part because they designed theirs
for the job they were to do, something other RR's did not, hence the
failures. Also, those big front cylinders were heavy and those babies
tended to beat the rails and joints to death, literally.

Big Boy was simple 4-cylinder as was the N&W A that first came around a few
years before Big Boy. So were SP Cab Forwards, another designed innovation
JUST for the job required. There others as well, B&O EM-1's and perhaps the
greatest of them all, the C&O H-8, the Allegheny. I wish I had seen one of
them in service but alas poor yorick, did not.

Bob Cohen
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