The UP 9000s had two outside 27"x32" cylinders driving the third set of drive
wheels and a third 27"x31" cylinder in the center driving the second axle.
The 9000s had 67 inch drivers. They were constructed with "blind" driver
tires on the third and fourth axles, that is, without the usual flanges,
in an effort to promote easy passage through tight curves. The blind
drivers were found to be unnecessary as tests of the first 4-12-2 proved
the usefulness of the lateral motion devices fitted to the first and sixth
driving axles. There was an attempt to see if they could negotiate the
Oregon Short Line in the Mountains of Oregon. The test failed and they
were returned to the prairies of Nebraska for which they were designed in
the first place.
There is an extremely accurately detailed model of
the UP 4-12-2 available for general viewing at the Schenectady Museum, in
Schenectady, NY. The model is in a section of the museum called the
Schenectady Heritage Area. The model provides an excellent view of the
lateral motion devices fitted to the first and last driving axles, spring
rigging, main and side rod designs, cylinder configurations, valve gear
arrangements, etc. The model is covered by a clear plexiglass cover which
allows for viewing but no touching.
1st Axle Clearance Crank?
There has been some disagreement on whether or not the first drive axle
on this class of locomotives has a 'clearance crank'. The typical
configuration for a three-cylinder steam locomotives is to have a
cranked first axle so that clearance is provided to the connecting rod
that is connected to the second set of drive wheels. The
Guide to
North American Steam Locomotives by George Drury states that the
first axle is cranked. I have also received e-mail which stated that
the first axle has a crank. However, I have been in contact with
John E. Bush who was the co-author
of an excellent reference book on these locomotives (Volume 2 of
The
Union Pacific Type by Kratville and Bush). This book has several
photos which show quite clearly that it does not have a 'clearance crank'
on the first axle. Instead, it explains, the builders added 18 inches to
the distance between the first two axle centers, thus precluding the need
for a 'clearance crank' on the first driving axle. This has been verified
by Barry Koeb who is the R&LHS member responsible for the UP 9000 who
has been inside the frame of the 9000. I am now convinced that the first
axle on this class of locomotives did not have a crank. The last time
I was in LA, I tried to look under 9000 and photograph the first axle.
However, the front of this locomotive is so tightly packed that I could
not see the front axle let alone photograph it.
In summary, the 9000's designers wanted to avoid having to put a crank in
the axle of driver number 1. So they did the following things:
- They increased the distance between the #1 and #2 drivers by about 18" over the spacing between the other drivers.
- They increased the distance between driver #1 and the cylinder saddle.
- They raised the middle cylinder to about 9" above a line parallel to the two outside cylinders.
Driver "Quartering" and Valve Gear
I have been told that the designers had to keep the quartering at equal 120
degree angles partially for centrifugal mass balancing reasons. However,
if the inside cylinder is inclined at say 7°, it would normally be
necessary to set the cranks at 120°-127°-113° to preserve the
torque distribution. Apparently, this was not necessary for the 9000s.
The #2 driver has an enormous inside steel crank/counterbalance assembly
that has to spin in concert with, and balanced to, the outside main rods.
(One hundred and twenty degrees is the quartering angle listed in the book
"Union Pacific Type, Volume 1" and confirmed by one of the co-authors,
John Bush.) It is suspected that one of the reasons the Baldwin #60000
used a 90°-135°-135° configuration had to do with it being
a compound locomotive, with the center cylinder receiving high-pressure
boiler steam, and the outer cylinders receiving the low-pressure steam
from the center cylinder. And according to John Bush, the locomotive had
"a very interesting" outside valve gear design. The original valve gear
used a conjugated assembly that synthesized inner cylinder valve gear
motion from the outer valve gear on either side of the locomotive.
"Lopping" Exhaust
Many have pointed out the "lopping" exhaust rhythm one hears in recordings
of the 9000 class. The sound may be the result of a number of factors:
- The center cylinder being located just below the exhaust jet means that its exhausted steam had a shorter distance to travel before hitting the stack, as opposed to the longer path the outer cylinder's exhaust had to move. So, it was likely that its exhaust 'beat' hit sooner, and louder.
- The center cylinder stroke is one inch less than the outside cylinders, which could have resulted in slightly earlier exhaust sounds.
- A lack of maintenance on the center cylinder might have lead to uneven bearing wear resulting in an uneven exhaust sound.
When released from shops with running gear trammed "to dimension" and valves
set correctly, a 9000 had a very even 1-2-3, 1-2-3 beat. All of the main
dimensions were the same for the outside and inside cylinders (except that
the inside cylinder was one inch shorter) and valves and when everything
was right they were square like any engine, only with six exhausts per
revolution. Like other power, the unevenness developed as miles grew,
and in particular as maintenance forces allowed the inside main rod to
languish! If you've heard Howard Fogg's recordings of 9009 on his great
album "The Big Steam" and think thats what a 4-12-2 regularly sounded like
please consider it as virtually totally unrepresentative of their sound.
That engine was horribly out of time and in fact would scare one at speed.
When badly out of dimension, engines can begin working against themselves.
Three cylinder, 
