Steam & Excursion > Abilene & Smoky Valley Railway 3415, 4-6-2

Santa Fe 3415, 4-6-2 oil burner, Abilene & Smoky Valley Railway at Abilene, Kansas, after sunset 14 September 2023.

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Santa Fe 3415, 4-6-2 oil burner, Abilene & Smoky Valley Railway at Abilene, Kansas, after sunset 14 September 2023.

Former Rock Island Depot now used by Abilene & Smoky Valley Railway.  14 September 2023.

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LOVE them newer driver centers and them big, fat tires!

RRs only did those things if the rest of the engine was rebuilt & in 
good shape.

You'd only find fat, new tires on locos that were deemed as 'keepers'.
They wouldn't go the expense of putting new tires on a "worn-out " engine.

That's the crucial factor in estimating rebuild expenses ... That, and 
soaked, soggy asbestos boiler insulation...if those two things are in a sorry state,
look for a better candidate!

​W.

 

Being a Pacific with tall drivers, its too bad it will never get to run on a mainline again, and really stretch her legs.

He Who Shall Not Be Named worked on the original restoration and said that being a park engine the firebox area around the door / peephole had a lot of damage from a certain readily available corrosive fluid.

I’ve spoken with more than one ASV engr who, after running the 3415 would remark something to the effect of: “I can tell she really wants to get up and RUN!” I’ll be very surprised if we ever see that happen…

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She hasn't been proven that she could survive out on the main.
Being the skunk at the picnic here, I hope when she gets the 1472, it is thorough and all problems addressed.  I also hope her livery gets corrected to look as she did when running on the Santa Fe.  A few changes would make a huge difference cosmetically.  If you're gonna do it, then dammit do it right.  Its no harder.

Hey, Wes!

I’ve read that a 4-8-4 runs smoother than a 2-8-4 because the 4-8-4 is linked to the cylinders on the #2 driver as opposed to the 2-8-4 being linked on the #3 driver. If this is true, did the pacifics have any advantages ride-wise utilizing the center of the 3 drivers?

Thanks for any reply,
Mark V.
The Fort in Indiana

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The explanation sorta refers to aircraft body design:  the key in
desigining an aircraft is making sure the weights and forces are 
applied evenly about the center of gravity of tte entire 'structure'.

So, whatever force affects the COG, affects the whole plane.

With steam locos, the 'center of mass' is a little above the longitudinal
frame rails, on the centerline of the locomtive, and about 3 feet in front 
of the 'throat sheet' of the firebox. 

With 0-8-0s, 2-8-0s, 2-8-2, and 2-8-4 locos, with the main rod 
connected to the 3rd axle, places all those unbalanced counterweights
 very close to the COG of the loco's mass.

On the smaller classes, their track speeds were low, and the thrashing 
was not severe in the cab.  When the 2-8-4 came into being, the originals 
had driver diameters similar to the then-popular 2-8-0s & 2-8-2s... 
relatively small..

With the larger grates, came extrodinary steaming capacities --- so, 
they didn't out-run the boilers' abilities to make copious amounts of 
superheated steam...  The greater speeds, made the whirling drivers'
massive counterweights shakes the frame, and is very close to the COG!
" Whatever shakes the COG , shakes the whole 'structure'...."

The COG for 2-8-4s is close to the distance between axles 3 & 4...
Larger drivers can somewhat mitigate the thrashing counterweights.
When you increase the driver diameter, you CAN reduce the mass of 
the counterweights. Going from 63" drivers of the earlier engines,
to about 70" inch drivers meant a serious reduction in the counterweight 
masses.

Again, the larger diameter drivers, meant bigger trains, going faster.
Going faster meant greater pounding ----
Part of the solution was to move the main rod connection further from
the center of mass of the loco --- moving the Main Driver to the 2nd axle..

Now, you've got an incredibly short Main Rod, very close to the pistons 
and cylinders ... What to do?

What you DO, is to move the driving cylinders well forward.
But, to move the massive cykinders you must carry that weight on
more axles ---- thus, they supported the moved mass on a 4-wheel
pilot truck.  Thus, the evolution to the 4-8-4!

The 4-8-4 also lengthens the locomotive --- which helps to lower 
the center of mass of the loco.  Moving the Main Driver to the number 2
position, made a smoother riding loco, at higher track speeds..

Bigger boilers, bigger grates, all made it easy to add larger drivers..
so drivers 79" & 80" diameters also meant smaller-mass counterweights..

Thus, the term "Dual Pupose" came to be applied to the 4-8-4 locomotives.

It's interesting to see how the Reading Company made some of its old,
slow 2-8-0 locos into 1940s wonderful 4-8-4 2100s... Good examples 
are 2102 & 2100...  they took a small 2-8-0 and made a successful 
class of 30 superlative engines.  Truly "dual purpose" locomotives.

At the root of the locos' development was their designers seeking the 
answer to the similar question that you posed.

​W.


Not proofed, yet!







 

Mark, 
To more directly answer your question,  the Pacfics'  had 
the advantage of larger diameter drivers, and thus, lighter counterweights.

The lighter counterweights are possible, because with larger diameter drivers,
you can get an effective increase in 'counterweight mass' by the fact that the centrifugal 
forces ( apparent masses) are greater at high driver RPMs.

So, the Pacfics tended to ride much smoother...the Pacifics were 
improved by the development of the 4-6-4,  the earliest 4-6-4s
were bought by the NKP.  But, NYCentral got to name the 
class: "Hudsons"..

Again, the biggest improvement was the application of larger
grates and bigger volume fireboxes.... better supported by the 4-wheel 
trailer-truck...

In later designed fireboxes it was found beneficial to have large firebox volume
( + 'combustion chambers' --- these are cylindrical firebox extensions into the
   tube space in the boiler cylinder).

Also, an added improvement was the use of 'finger grates', these were individual 
grate bars, with a bottom extension that interlocks with the lateral grate bars.
There are 16 -18 'fingers' on a bar, and typically 3 to 5-groups of bars, about 4 bars
to a group.  The fingers rock freely on the bars, and when thundering down the road,
they shake constantly --- sifting  the dead ashes into the ash pan.
( steady shaking also gets some of the lighter ash air-borne, and headed out the stack...).

The firebox drafting improvements led to lower wind velocities  through the firebed, lower
wind velocity through the firebox, & higher firebox temperatures..... which translates into
higher steam superheat temps.  I've seen Doyle running tye 4449, near top speed, with
a partially closed throttle!   Because, at high superheat, MORE steam leaves the units,
than enters them!   Actually, it's less weight of steam, and the pressure is maintained 
by the higher state of molecular-vibration ---- caused by greater amount of heat
absorbed ...  Steam at boiler pressure is the same temperature as the water that 
boiled it.---- at 300 psi bolier pressure that's about 400F, steam temperatures.
Superheating can add another 300F to further 'excite' the water molecules ---
and increase the distances between individual molecules --- so, MORE superheated 
steam exits the units, than had entered.  So, to hold track-speed in control, 
Doyle closes-down the throttle --- which increases the duration-time of steam --- in order
to INCREASE superheat temperatures.... However. it also translates into easier firing
for the fireman, and his oil-flow, control-valve ---- and there's an INTENSE draft, up the stack!

When pulling a long freight train, you'll have a high superheat steam temperatures,
and modest wind speed through the firebox and flues, as well as a valve cutoff-setting
which allows the greatest amount of steam expansion in the cylinders.

A "clean-to-slightly gray" stack tells you that the firebox temperatures are 
very near 3,000F !!  
The darker the exhaust smoke, the cooler the flame temps....
typically, a constantly-dark stack, with a stoker equipped engine, 
indicates there's a wind-hole in the coal firebed.   A novice fureman
will typically add more stoker-fed fuel.  That worsens the amount of 
cold fuel, cooling off the firebed, while making darker smoke.

The strongest wind velocity is at the rear firebox sheet ( 'door-sheet),
and all that air burns the coal much faster than across the rest of the grate-
--- thus, the back region burns-out, and burns away, very quickly ( Duh!)...

Keeping the back region deep in an 'active heel', (a big-bank of coal-)--
makes most of the flame area over 3/4 of the rest of the grate.

With a light train, you don't need a lot of grate area --- so, to keep the firebox 
hottest, you'll carry a much broader rear-bank, across the rear of the grates...
With a heavier train, maintain a smaller banked area.  In fan trip service,
you typically only need an "active grate area" of 75% of the full grate.

With a long hill-climb, your rear-area bank burns-down much more rapidly..
so you must add more green coal ( being wet, helps) more frequently to that region --
particularly, the far-right and left corners of the grate.

Scoop-de-jour, says that he likes to "keep a lot of money in the BANK"...
He's good at it.


​W.



Edited 4 time(s). Last edit at 09/17/23 15:11 by wcamp1472.

Its like a master's class in steam locomotive design. 

Thanks.

RickL

Thanks so much Wes!! I appreciate your well thought out and easy to understand explanation. Love reading your posts. Please keep ‘em comin!!

Mark V.
The Fort in Indiana

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