Adding and modifying parts makes more sense

Steam Special
Understanding
steam details
Adding and modifying parts makes more sense when you know
the locomotives’ systems
By Andy Sperandeo
Photos by the author
S
team locomotives can appear to be
plumber’s nightmares, and no doubt
many of them were. That’s especially
true of bigger engines with many appliances
added to increase efficiency and performance. The best way to understand their
complexity is to examine their various systems one by one:
• Water supply
• Fuel supply
• Steam distribution
• Sand for traction
• Air brakes
• Electric lighting
There were many ways to arrange these
systems, and even on one railroad engines
built at different times or maintained and
rebuilt in different shops could vary quite a
bit. An old joke about steam engines is that
they were built to “N.T.A. Standards” – the
abbreviation means “no two alike.”
But if you can identify the major systems,
locate their components, and trace their
piping, it’s usually not too hard to understand
the appearance of almost any steam engine.
Steam’s diversity ceded an advantage to
Atchison, Topeka & Santa Fe 4-8-4 no. 3751 posed
at Los Angeles Union Passenger Terminal in July
2005 for inspection and photography by members
of the Santa Fe Ry. Historical & Modeling Society.
standardized internal-combustion power, yet
when understood it’s part of the enduring
appeal of steam locomotives.
I’ll explain these systems using the Atchison, Topeka & Santa Fe modernized 4-8-4 no.
3751 and its sisters of the 3751 class as
examples. That’s the same prototype modeled
by Gil Bennett on pages 58-61.
For more-detailed information on a wider
variety of locomotive equipment, see the
Model Railroader Cyclopedia – Vol. 1: Steam
Locomotives, and the Guide to North American Steam Locomotives, both published by
Kalmbach Books. MR
More on our Web site
For additional steam engine photos, including coal burners
and locomotives with different feedwater heaters, visit
www.modelrailroader.com
© 2012 Kalmbach Publishing Co. This material may not be reproduced in any form
without permission from the publisher. www.ModelRailroader.com
Water supply – injector
The tender usually carries three to four times more water
than fuel, reflecting the typical ratio of consumption of these
supplies. The Santa Fe 3751 has a large box tender built by
Baldwin in 1938 with a capacity of 20,000 gallons of water.
The water supply for the boiler passes to the locomotive
through two large non-collapsing hoses coming out of the
bottom front of the tender tank on each side. Gravity keeps
the supply steady as long as there’s sufficient water in the
tender, but on the locomotive the water must be forced into
the boiler against the pressure of the steam – 230 psi on the
3751 and 300 psi or more on other modern locomotives. This
is the job of the injector.
The 3751 has a Chicago non-lifting injector below its cab
on the right (engineer’s) side. “Non-lifting means that it’s
mounted below the water level of the tender. A lifting injector
can be installed on the boiler inside or just in front of the cab,
and it will draw water up to that height by suction.
In either type of injector, live steam from the boiler is
passed through a nozzle where the venturi effect creates
suction to draw in the water. The water mixes with the steam
and passes through additional nozzles that increase the
velocity of the water sufficiently to force it though the delivery
pipe and into the pressurized boiler.
Any injector typically has four main pipes, for live steam,
water intake, water delivery, and water overflow. Injectors
mounted outside the cab will have two or more operating rods
extending to control levers or valve wheels inside the cab.
At the boiler end of the delivery pipe, usually but not
always near the front end of the boiler, the water passes
through a one-way check valve which allows water to enter
but closes to keep in the steam when the injector isn’t
operating. The Santa Fe rebuilt 3751-class engines had dual
top check valves mounted on a tee pipe ahead of the sand
box. The top delivery location was used in many modern
locomotive designs; on older locomotives check valves are
typically halfway up the boiler on either side.
Under the right side of the cab, the 3751’s Chicago nonlifting injector uses live steam and the venturi effect to force
water into the boiler against the pressure of the steam.
Air brake distributing valve
Air brake equalizing reservoir
Injector
Live steam
Delivery
Overflow
Intake
Water supply – feedwater heater
Every steam locomotive had two water delivery systems,
because failure to get water into a hot boiler often caused an
explosion. Most older locomotives had injectors on each
side, but beginning in the 1920s many engines were built or
retrofitted with a feedwater heater system in place of one
injector. Feedwater heaters used exhaust steam to preheat
water for the boiler, increasing efficiency by requiring less
fuel to boil a given amount of water.
The 3751 class was built with Elesco tank-type feedwater
heaters, but in their final rebuilt form most of them had newer
Worthington type SA feedwater heaters. The Worthington coldwater pump is under the 3751’s cab on the left side, a typical
location, though usually not shared with an air compressor.
The cold-water pump is a turbine driven by live steam that
forces water from the tender forward through a pipe leading to
the heater on top of the smokebox. The pump has a steam
supply pipe passing through a control valve in the cab, a water
intake pipe, a water delivery pipe, and a steam exhaust pipe
vented along the center of the track behind the trailing truck.
The feedwater heater itself has a heating chamber filled
with exhaust steam. The incoming water sprays into the
steam, absorbing heat and condensing in the bottom of the
chamber. When the heated water rises to a predetermined
level, a float valve turns on the steam supply to the hot water
pump, usually located at a lower level on the locomotive so
the hot water can flow to it by gravity. This a horizontal
reciprocating pump that forces water into the boiler.
The cold-water pump is a steam turbine supplying water to
the Worthington feedwater heater system.
Water delivery
Westinghouse cross-compound air compressor
Live steam
Exhaust steam
Cold-water pump
Water suction
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Water supply – feedwater heater (continued)
The hot-water pump on the 3751 is mounted behind the
pilot beam, to the right of the second air compressor. This
location is common, but the hot-water pump was also often
mounted under the running board on the left side.
The feedwater heater piping is mostly buried under the
smokebox jacketing of the 3751, and the delivery pipe runs
from the pump back under the left running board to a point
where it can turn straight up to the left check valve.
The Worthington type SA feedwater heater is at the top of
the smokebox, ahead of the smokestack.
The Worthington system’s hot-water pump is on the left
side of the pilot deck, behind a compressor-type shield.
Bell with anti-rotation bar
Feedwater
heater
Hot-water suction pipe
Conduits to headlight and
classification lights
Hot-water
pump
Hot-water delivery pipe
Pump
lubricator
Hot-water pump
Hot-water suction pipe
Fuel supply
On oil-burners like the 3751, the fuel supply is relatively
unobtrusive. A flat-topped tank holding 7,000 gallons of fuel
oil sits above the water space in the tender. An internal steam
heater supplied from the locomotive keeps the thick fuel fluid
enough to flow by gravity to the oil burner, which is located in
the bottom front of the firebox, facing the rear under a brick
arch. Because the oil burner’s location is usually occupied by
the motor and drive train on models, this feature is rarely
represented. Rather than a grate and an ashpan, oil burners
typically have a brick-lined fire pan below the firebox.
Coal burners have open-top coal bunkers in their tenders
along with ash pans under the firebox and extending out past
the boiler’s water legs along both sides of the firebox. There
is also an ash hopper (or hoppers) beneath the ash pan.
Engines with automatic coal stokers typically have a large
screw-conveyor housing running from under the front of the
tender coal bunker to the rear of the firebox on the engine.
There may be a small one- or two-cylinder steam engine
under the left side of the cab to drive the stoker, but sometimes this stoker engine was installed in a compartment in
the front of the tender.
Oil burner at bottom front of firebox
Fire pan
The 3751’s fire pan is visible under the firebox, but the oil
burner at the front of the firebox can’t be seen.
o3/o7 • Model Railroader
65
Steam distribution
A “dry pipe” inside the boiler collects steam under the steam
dome at the highest point of the boiler. In older engines the
throttle valve was located there, but the more modern
practice was to use a “front-end” throttle with valves in the
superheater header at the rear of the smokebox.
The dry pipe brings steam to the header. From there it
circulates through long U-shaped tubes, the superheater
elements, inside large flues connecting the firebox with the
smokebox inside the water space of the boiler. This superheats the steam, and that increase in temperature boosts the
locomotive’s efficiency even more than the feedwater heater.
The front-end throttle then controls the flow of superheated
steam to the valve chambers in the cylinder chest.
Besides the small steam dome to the rear of the larger
sand box, there are typically two external signs of these
internal features, and they’re present on the 3751. They
include the front-end throttle linkage of rods and cranks
along the right side of the boiler and the front-end throttle
cover, the rectangular access plate secured by multiple dogs
on top of the smokebox behind the smokestack.
Steam dome
The most visible part of the steam-distribution system is
the valve gear. This arrangement of rods and linkage uses the
motion of the drive wheels to time the valve events controlling
the admission and exhaust of steam in the power cylinders.
The Santa Fe 3751 has Walschaerts valve gear, the most
widely used type. It uses the motion of an eccentric crank on
the main crankpin to drive spool-shaped piston valves in the
cylindrical valve chambers above the power cylinders. The
engineer controls forward or reverse movement and the setting of the valve cutoff by means of an air-operated power
reverse gear connected to the reverse shaft’s bell crank.
(Locomotive cylinders are double-acting, with a power stroke
and simultaneous exhaust stroke in each direction. Two exhausts
from each cylinder per revolution of the drivers cause the fourbeat exhaust sound of most steamers. To be realistic, steam
sound systems for models should reproduce this relationship.)
The steam dome, front-end throttle linkage, and front-end
throttle cover are the external signs of the internal steamdistribution equipment of the 3751.
Dual top-feed check valves
Whistle
Front-end throttle linkage
Front-end throttle cover
Wagner cylinder bypass valve
Reverse shaft crank
Power reverse
Valve chamber
Mechanical lubricator (driven by reverse link movement)
Cylinder
Walschaerts valve gear
Valve gear step
The Walschaerts valve gear controls both the admission and the exhaust of steam in the locomotive’s power cylinders.
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Sand for traction
Spreading sand on the rail to increase traction goes back to
the earliest days of steam locomotion (and is still used by
today’s diesel electric power). A sand box (often domeshaped) sits atop the boiler to hold the dry grit. Air-operated
valves allow it to run by gravity through sanding pipes to
nozzles ahead of the drivers and just above the railhead.
Originally, 3751-class engines had two sand boxes on the
forward half of their boilers, a common feature of Santa Fe
power built in the 1920s. The final modernization of these
engines gave them just one larger sand box. The three
forward sand pipes on each side of the 3751 sand ahead of
the first, second, and third drivers. The single reverse sand
pipe on each side sands behind the fourth driver.
On many modern steam locomotives the sanding valves
are enclosed in a casing alongside the sand box, and the
sand pipes are hidden inside the boiler jacket. The 3751’s
sanding equipment is all out in the open.
The 3751’s sand box carries dry sand to spread ahead of
the drivers for extra grip on the rail.
Sand box
Sanding valves
Sand pipes
Air brakes
Locomotives supply compressed air for the train’s automatic air brake system, for their own independent air brakes,
and for air-powered auxiliaries such as the power reverse,
sanding valves, and air-operated bell (if used). From around
World War I to the close of the steam era, most locomotives
carried one or two steam-powered Westinghouse crosscompound air compressors. Compound compressors used
steam twice to drive their two reciprocating pistons.
The 3751 originally had one cross-compound pump on its
left side above the fourth driver. When modernized in 1941 it
received two compressors as already described, one under the
cab and one behind the pilot beam, with individual intake filters.
Live steam from the turret ahead of the cab powered the
compressors, which pumped air into two main reservoirs. On
3751 these cylindrical tanks are under the running boards on
either side of the boiler. The piping between the compressors
and the reservoirs was often routed through cooling coils or,
Air compressor
on later engines, a radiator, so its temperature wouldn’t affect
the function of the brakes. The 3751 has only one short
cooling loop below the running board on the left side.
The brake stand with the engineer’s control valves is in the
cab on the right side, and the distributing valve and equalizing reservoir are below the cab on that side. The piping under
the right-hand running board includes the train pipe, the
conductor’s air signal pipe for passenger operation (the 3751
was primarily used in passenger service), and the pipe to the
driver brake cylinders behind the steam chest.
The 3751’s independent brakes apply only to its drivers
and tender trucks. Some other large steam engines also had
brakes on the engine- and trailing-truck wheels.
Santa Fe no. 3763, shown here some time after its 1941
modernization, has the same layout of air brake equipment
as its sister engine, the 3751. Santa Fe photo
Main air reservoir (1 of 2)
Cooling loop
Air compressor
o3/o7 • Model Railroader
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Electric lighting
A steam-powered turbogenerator (sometimes called a
“dynamo”) supplied electricity for the headlight and for the
classification lights, illuminated number boxes, cab and
gauge lights, and tender lights. The generator is usually on
top of the boiler or on its shoulder. The 3751 carries it on the
left shoulder of the boiler above the firebox. Sometimes a
handrail was used as an electrical conduit from the generator
location, but the 3751 has separate conduits just above the
handrail stanchions along its left side.
Locomotives with additional signal lights or other electrical equipment such as automatic train control systems or
(late in the steam era) radios required more than one generator. Also, some locomotives assigned to suburban service
carried an additional, usually larger, turbogenerator to supply
electricity for coaches that lacked their own axle-driven
lighting generators. As a result, a few locomotives carried
three or four generators, but in most cases one was enough.
Santa Fe no. 3759 has her headlight and class, number, and
cab lights burning as her crew prepares to double-head a
diesel on the first section of the California Limited out of
San Bernardino, Calif., and up Cajon Pass. Robert Hale photo
Classification lights (green)
Number box
Headlight
Cab lights
Cab
Turbogenerator
Steam separator
Conduits
Bell cord
The 3751’s turbogenerator is ahead of the cab on the left shoulder of the boiler, with conduits connecting to the locomotive’s lighting. The can-like appliance ahead of the generator is the steam separator for the foam-collapsing automatic
blowdown system, a feature that helped with the poor boiler water found in so much of the Santa Fe’s territory.
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