Adding and modifying parts makes more sense when you know the locomotives’ systems

By Andy Sperandeo Photos by the author

More on our Web siteFor additional steam engine photos, including coal burners and locomotives with different feedwater heaters, visit www.modelrailroader.com

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.

Steam 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 perfor-mance. The best way to understand their complexity is to examine their various sys-tems one by one:

• Water supply• Fuel supply• Steam distribution• Sand for traction• Air brakes• Electric lightingThere 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

Understanding steam details

standardized internal-combustion power, yet when understood it’s part of the enduring appeal of steam locomotives.

I’ll explain these systems using the Atchi-son, 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 Ameri-can Steam Locomotives, both published by Kalmbach Books. MR

Steam Special

© 2012 Kalmbach Publishing Co. This material may not be reproduced in any form without permission from the publisher. www.ModelRailroader.com

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.

Injector

Air brake distributing valve

Water supply – injector

Air brake equalizing reservoir

Live steam

Under the right side of the cab, the 3751’s Chicago non-lifting injector uses live steam and the venturi effect to force water into the boiler against the pressure of the steam.

Delivery

Overflow

Intake

64 Model Railroader • modelrailroader.com

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 cold-water 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.

Water delivery

Live steam

Cold-water pump

Water suction

Exhaust steam

Westinghouse cross-compound air compressor

The cold-water pump is a steam turbine supplying water to the Worthington feedwater heater system.

o3/o7 • Model Railroader 65

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 some-times this stoker engine was installed in a compartment in the front of the tender.

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.

Bell with anti-rotation bar

Conduits to headlight and classification lights

Hot-water pump

Pump lubricator

Feedwater heater

Oil burner at bottom front of firebox

Water supply – feedwater heater (continued)

Exhaust steam

Hot-water pump

Hot-water suction pipe

Hot-water suction pipe

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.

The 3751’s fire pan is visible under the firebox, but the oil burner at the front of the firebox can’t be seen.

Hot-water delivery pipe

Fire pan

66 Model Railroader • modelrailroader.com

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 super-heats 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.

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 set-ting 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 four-beat exhaust sound of most steamers. to be realistic, steam sound systems for models should reproduce this relationship.)

Front-end throttle linkage

Steam domeWhistle

Dual top-feed check valves

Front-end throttle cover

Walschaerts valve gearValve gear step

Cylinder

Valve chamber

The steam dome, front-end throttle linkage, and front-end throttle cover are the external signs of the internal steam-distribution equipment of the 3751.

The Walschaerts valve gear controls both the admission and the exhaust of steam in the locomotive’s power cylinders.

Mechanical lubricator (driven by reverse link movement)

Power reverseReverse shaft crank

Wagner cylinder bypass valve

o3/o7 • Model Railroader 67

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 dome-shaped) 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.

Air brakes

Locomotives supply compressed air for the train’s auto-matic 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 cross-compound 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,

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 equaliz-ing 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.

Cylinder

Valve chamber

The 3751’s sand box carries dry sand to spread ahead of the drivers for extra grip on the rail.

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

Sand pipes

Sanding valves

Sand box

Cooling loop

Air compressor

Air compressorMain air reservoir (1 of 2)

68 Model Railroader • modelrailroader.com

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 electri-cal equipment such as automatic train control systems or

(late in the steam era) radios required more than one genera-tor. 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.

Cab

Conduits

Turbogenerator

Steam separator

Bell cord

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

The 3751’s turbogenerator is ahead of the cab on the left shoulder of the boiler, with conduits connecting to the locomo-tive’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.

Headlight

Cab lights

Classification lights (green)

Number box

Every issue of Model Railroader

includes intriguing articles that

take you on a tour of the world’s

finest layouts and introduce

you to the hobby’s experts.

You’ll discover:

• A wealth of prototype data

• Detailed how-to instructions

• Product reviews

• Tips & techniques

• And so much more!

Start building your dream layout!

Order online at

www.ModelRailroader.com/promoEnter promotional code: IK87M

CIR-ADH-09X1595RH

Plus, subscribers have

exclusive online access to

hundreds of track plans and

product reviews, videos,

bonus articles, and more!

Or call 1-800-533-6644Monday – Friday, 8:30 a.m. – 4:30 p.m. Central Time

Outside the U.S. and Canada, call 262-796-8776, ext. 661