TenderAttached rail vehicle that holds both water for the boiler and fuel such as wood, coal, or oil.
Cab Footplate Compartment where the engineer (US+) / driver (UK+) and fireman control the locomotive and tend the steam supply and firebox. • a
throttle lever or
regulator, which controls the amount of steam entering the cylinders
Brake shoe / brake blockCast iron or composite material that rubs on all the driving wheel treads for braking. Sand pipeDeposits sand directly in front of the driving wheels to aid traction on steep gradients, when starting or when the rail surface is not dry and clean.
Coupling rods / side rodsConnect the driving wheels (43) together.
Valve gear Motion System of rods and linkages synchronising the valves with the pistons and controls the running direction and power of the locomotive.
Connecting rod / main rodSteel arm that converts the reciprocating motion of the piston into a rotary motion of the
driving wheels. The connection between piston and main rod is a
crosshead, which slides on a horizontal bar behind the cylinder.
Piston rodConnects the piston to the cross-head.
PistonProduces the motion for the locomotive from expansion of the steam. Driven backward and forward within the cylinder by steam delivered alternately, in front and behind, by the valve.
CylinderChamber that receives steam from the steam pipe.
ValveControls the supply of steam to the cylinders. The valve gear, actuated by connection to the driving wheels, ensures that steam is delivered to the piston with precision. Types are
slide valves,
piston valves or
poppet valves.
Valve chest / steam chestValve chamber next to the cylinder (24) containing passageways to distribute steam to the cylinders.
FireboxFurnace chamber built into the boiler, which produces steam in surrounding water. Various combustible materials can be used as fuel; the most common are coal and oil but in earlier times
coke and/or wood were used.
Boiler tubes and
fluesCarry hot gases from the front of the firebox to the front of the boiler, producing steam from the surrounding water. Flues are larger in diameter than tubes because they contain superheater units.
BoilerHorizontal tubular vessel, strong enough to contain high-pressure steam in a harsh working environment; closed at either end by the firebox and tube plate. Usually well filled with water but with space for
steam – produced by heat from the firebox and boiler tubes – to be above the water surface.
Superheater tubesPass steam back through the boiler to dry and superheat it for greater efficiency. See
Superheater (32).
Throttle valve Regulator valve Controlled by the throttle lever / regulator (8), regulates the amount of steam delivered to the cylinders, which is one of two ways to vary power of the engine (throttle governing). For the other method, see
Throttle lever (8).
SuperheaterProvides additional heat – as much as hotter – to steam that has been generated in the boiler by sending it back through superheat tubes located in the boiler tubes (28), thus increasing engine efficiency and power. See also
Superheater tubes (30).
Smokestack Chimney,
funnel Vertical pipe on top of and inside the smokebox that ejects the exhaust (smoke and steam) above the locomotive.
HeadlightLight on the front of the smoke box to illuminate track ahead and warn of the approach of the locomotive.
Brake hoseHose for conveying force to train brakes by a differential in air pressure. Contains either high-pressure compressed air or air at lower than atmospheric pressure (vacuum), depending on whether the locomotive has an
air brake or
vacuum brake system.
Water compartmentTank for water to be used by the boiler to produce steam.
Coal bunkerCompartment for storage of fuel before being directed to the firebox. When the fuel is coal (and in the distant past, coke or wood), the fireman shovels it manually through the firebox door or, in larger locomotives, by operating a mechanical stoker. When the fuel is oil, it is sprayed into the firebox from a sealed tank.
GrateSupports the burning fuel while allowing the products of combustion – ash and small
clinker – to drop through.
Ashpan hopperCollects the ash from the fire.
Journal box Axle box Housing for the
bearing on the
axle of a
wheel (43).
Equalising beams / equalising levers / equalising barsPart of the locomotive suspension system. Its function is to prevent inequalities in the track or roadbed putting an excessive load on an axle, which is especially necessary on uneven or poorly laid tracks. The beam is connected at each end to a spring on an axle or to the end of another equalising beam (usually via a vertical spring hanger) to distribute the locomotive's weight between two or more axles. The frontmost and rearmost components are secured to the locomotive frame. An equalising system links not only the driving-wheel axles but also the trailing and/or leading truck axle(s).
Leaf springsMain suspension springs for the locomotive. Each driving wheel supports its share of the locomotive's weight via leaf springs that connect the axle's
journal box / axle box (40) to the frame.
Driving wheelsDrivers Coupled wheels Wheels coupled to the main/side rods, through which the power developed in the cylinders (24) is transformed into tractive power at the rails. The weight of bearings and coupling rods on the driving wheels is counterbalanced with cast-in weights to reduce "hammering" on the track when the locomotive is under way.
Pedestal / saddleConnects a leaf spring to a journal box / axle box (40) on a wheel.
Blast pipeExhaust pipe Directs exhaust steam up the smokestack/chimney (33), creating a draught that draws hot gases through the firebox (27) and along the boiler tubes (28).
Pilot truck,
pony truck Leading bogie / lead truck / bissel truck Wheels at the front of the locomotive to guide the front driving wheels around curves, and minimise
yawing at higher speeds with the attendant risk of derailment. The truck has some side motion and is equalised to the driving wheels (41). The names
Pony truck (US+) and
Bissel (or
Bissell) truck (UK+) apply when there are two wheels; the others when there are four.
Pilot / cowcatcher A shield made from bars, cast steel or sheet steel to prevent an object on the track from going under the locomotive and possibly derailing the train.
Coupler Coupling Device at the front and rear of the locomotive for connecting locomotives and
rolling stock. == See also ==