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This is Locomotive Wiki's {{#NewWindowLink: wiktionary:glossary#English| glossary.}} Please refer to this page for definitions of technical terms that appear in articles.

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Contents of "a"

AAR Classification

Main article: AAR Axle Classification

An axle notation system used by the USA in particular, and works as follows: A powered axle is shown by a capital letter, e.g. A = 1, B = 2 and so on; non-powered axles are represented by a number; trucks are separated by a hyphen "-"; and articulated chassis are denoted by a plus sign "+".


The amount of grip a locomotive has on the rails. In certain conditions, e.g. wet weather, this may be reduced.


Where the frame, or set(s) of driving wheels, pivot to help a large locomotive navigate sharp curves.


A spindle that joins a pair of wheels.


Allows an axle to rotate freely via bearings.


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A part, usually metal, made out of rolling or sliding pieces that is fitted between moving parts to reduce friction, thus slowing wear and tear.

blast pipe

A pipe through which exhaust steam travels from the cylinders of a steam locomotive to be exited through the chimney. Blast pipes are located inside the smokebox.


Alt: bodywork.

Non-structural panels attached to a frame in order to provide weather protection for equipment and crews. May also be added for aesthetics or streamlining.


Chiefly British form of truck.


A large drum in a steam locomotive that is filled with water and boiled to create steam. The steam then propels the locomotive.

brake lever

A lever that an engineer of a locomotive can use to slow and/or stop a train. These can be found in all popular types of locomotive or multiple unit.

brake shoe

Piece of material that is pressed against a rotating object to slow an axle.

brick arch

An arch of firebricks inside the firebox that funnels the hot gases evenly into the flue tubes.


Place for storing coal. Usually used in relation to tank locomotives.


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Contents of "c"


The place where the engineer can sit and operate a locomotive or multiple unit.


Part of a braking system. The caliper squeezes brake shoes onto a rotating brake disc (or the wheel itself) to slow and/or stop the train. This type of braking system is not favored as running brakes on modern equipment, instead dynamic braking (where traction motors exist) is used to avoid running costs and brake fade.


Main article: Catenary

Strictly, this describes the overhead cable that is strung between supports in a curve, holding up the contact wire that carries current for electric locomotives and EMUs. In common use, this term refers to all the wires, span cables, gantries etc. that completes an overhead power system.


See frame instead.


Main article: Smokestack

A vent to allow exhaust gases to escape a steam locomotive.


A specific two-stage design of steam locomotive, whereby the steam is first used in high pressure cylinders then in low-pressure cylinders. Therefore, the steam is used most efficiently.


Main article: Connecting Rod
Steam locomotive
Length of metal that connects the piston to the driving wheels and or coupling rod.
Diesel locomotive
Connects the piston head with the crank-shaft inside a diesel engine.

coupling rod

A metal bar usually used in pairs to link the driving wheels together on each side of a locomotive. Used solely for when only one axle is powered.


A wooden or metal cage-like structure on the front of a locomotive to move animals of the tracks.


Main article: Cylinder
Steam locomotive
Where the steam is injected to push a piston back and forth.
Diesel locomotive
Where diesel fuel is mixed with hot, compressed air to create an explosion that forces a piston to move away.

cylinder beat

The cylinders of a steam locomotive create a beat or pulse when they force exhaust steam through the blast pipe(s). This may have a negative flow-on effect to the firebox.


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diesel locomotive

Main article: Diesel locomotive

A locomotive that uses a diesel engine to either produce momentum, or via a generator create electricity to produce momentum.

disc brake

See disc rotor instead.

disc rotor

Braking system where friction is used to slow the vehicle. The rotor(s), connected to the axle of vehicle, are squeezed by a caliper to cause the friction which is actually the force of the vehicle's momentum converted into heat.


Where two locomotives pull a train from the front. Usually in reference to steam locomotives.

double chimney

Chimney with two openings. Used to increase volume, thus soften the cylinder beats of powerful steam locomotives. Some designs offer further technical advances too.


In British English, the person who drives the locomotive. See also, engineer.

driving wheel

Alt: drivers. (Not to be confused with driver.)

Main article: Driving Wheel

One of at least two wheels powered by a locomotive to achieve motion.

dynamic braking

Alt: rheostatic braking

System that switches traction motors from consuming power to generating power. Then, the motion of a locomotive is transformed into heat by rheostats and expelled into the atmosphere. Very efficient form of braking that reduces wear and tear on service brakes, and avoids brake fade. Ceases to work effectively below a certain speed, usually about walking pace, therefore locomotive still requires service brakes.


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A machine designed to create power, typically to achieve movement. Usually done by producing rotating force. May be used to describe an entire steam locomotive; rarely used in such way in relation diesel locomotives due to confusion with the diesel engine. See also, Diesel engine.


Person works on a locomotive to keep it running correctly; or person who builds locomotives; or person who builds railroads. In the USA, may refer to the person controlling the locomotive.


Gases left over after combustion or burning. Or steam left over after being through the cylinders.

exhaust system

Steam locomotive
Separate components that work in harmony to exhaust steam from the cylinders of a steam locomotive. Includes the early ports or later piston valves inside a steam chest facilitating the release of exhaust steam up the blast pipe and out of the chimney.
Diesel locomotive
Components designed to remove combustion gases from the engine in a diesel locomotive.


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Main article: Firebox

Place in a steam locomotive where fuel is burned creating heat to boil water in the adjacent boiler.


Chiefly British form, or archaic form, of engineer. Is still in use for stokers of steam locomotives in Britain.

flue tube

The escape route for exhaust gases from the firebox through the boiler. Multiple flue tubes are used to heat the boiler up evenly.


The place (floor) from where the driver and engineer operate a steam locomotive. Is sometimes used as a synonym for running-plate.


The metal plates or bars that form the basis of a locomotive or other rail vehicle, onto which the body is attached.


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Main article: Track Gauge

The distance between the rails a locomotive runs on.

Giesl ejector

Type of steam exhaust system, designed by Adolph Giesl-Gieslingen, which has multiple blast pipes fanned out to feed a long, flat chimney. The design improves fuel consumption and increases power.


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Using fluid pressure to operate something.


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Contents of "i"


Steam locomotive
Used to get new water from the tender into the boiler by fighting the pressure within.
Diesel locomotive
Sprays fuel into a cylinder.

inside cylinder

Describes a steam locomotive that has the cylinders placed underneath the firebox.


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Where two, or more, tracks are linked so that vehicles can transfer from one to another.


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Advanced blast pipe designed by André Chapelon to improve draft in the firebox. Used on fast, express steam locomotives, the design consists of two multi-port blast pipes feeding a double chimney to reduce the severity cylinder beats.


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A rail vehicle that propels itself.


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Abbreviation of "magnetic levitation"; the process of supporting a locomotive on magnetic fields.


Chiefly British form of engine, or a traction motor.

multiple unit

Alt: multiple-unit; MU.

Main article: Multiple Unit

A train made up of units that each have motors, or diesel locomotives coupled together. Either way the entire train is controlled from one cab, and by one engineer.


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Contents of "o"


Type of steam locomotive that has the frame on the outside of the wheels and running-gear.

outside cylinder

Describes a steam locomotive that has cylinders placed on the outside of the wheels.

outside-inside-outside cylinder

Describes a steam locomotive that has outside cylinders and inside cylinders.


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Contents of "p"


Main article: Pantograph

An arm that holds a wire against a live cable above the track. See also, catenary.


Main article: piston

A cylindrical plug that moves back and forth inside a cylinder.

piston valve

Double-ended piston that moves inside a steam chest administering steam into and releasing steam from the cylinders of a steam locomotive. See also, valve.


Process in a steam locomotive where water is carried into the cylinders, as a result of using low-acidic water.


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Used in parallel pairs to form a section of track, which the locomotive rolls on.


Component that slows down an electric circuit. It so works by converting the current into heat.


A rheostat is a resistor that is adjustable. Used in dynamic braking on modern locomotives and multiple units.


Steam locomotive
Foot-way that extends down the boiler sides and across the front of a locomotive.
Diesel locomotive
Foot-way that encircles a locomotive on most types.


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Contents of "s"

safety valve

Main article: Safety Valve

A valve that opens when pressure inside a boiler gets too great.

service brake

A locomotive's standard brakes which operate via air pressure (or even cables). Prone to fade at high speed.


Strip of wood or concrete that supports rails that are placed on top. Major part of a track.


Place, usually at the front, in a steam locomotive where exhaust is mixed with steam and sent out the chimney.

steam chest

Compartment within a steam locomotive which fills up with steam awaiting entrance to the nearby cylinder via piston valve or port.

steam locomotive

Main article: Steam locomotive

A locomotive that, via firebox(es), boiler(s) and cylinders, achieves movement due to the expansion properties of steam.


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Contents of "t"

tank locomotive

Main article: Tank Engine

A steam locomotive that does not use a tender, but instead uses integral bunker and water tank(s).

tank engine

See tank locomotive instead.


Main article: Tender

A wagon that carries fuel and water for a steam locomotive, usually placed behind the footplate.


Alt: tyre. (UK)

A protective ring that is fitted around a locomotive's wheel. The tire wears, and is eventually replaced, allowing the wheel to be longer lasting.


A pair of rails used to support and guide a locomotive.

traction motor

An electric motor on diesel-electric locomotives, electric locomotives and electric multiple units, that drives the axles to create motion. Traction motors are supplied with electricity to make them spin.


Alt: trainset.

The term used to describe a rail vehicle consisting of cars, pulled by a locomotive. Also used to describe multiple units.


Where three locomotives pull a train from the front. Usually in reference to steam locomotives.


A swiveling frame that carries axles on many steam, diesel and electric locomotives; the truck helps to guide the locomotive around corners. Elsewhere than North America these may be referred to as bogies.


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Contents of "u"


Either one locomotive, or one car in a multiple unit.


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Hole that opens and closes allowing the passage of fuel or steam.


Levers and rods that link the valves to the piston's movement on a steam locomotive.


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An upright, metal panel placed forward of the footplate on early, or cabless, steam locomotives in an attempt protect the driver and fireman.

wheel arrangement

The order of carrying and driving wheels on a locomotive; usually in a notation.

Whyte notation

Alt: Whyte's notation.

Main article: Whyte notation

A numerical method of classifying steam locomotives based on wheel arrangement. Numbers are separated by dashes. The first number defines the carrying wheels, the central number(s) defines the driving wheels and the last number defines the trailing wheels.


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