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Saddle Tank

A steam locomotive which carries its water in tanks draped over the boiler barrel like a saddle.

Safety Valve

Fitted to boilers to prevent the working pressure being exceeded.


A long bolster wagon (62 foot) first introduced by the LMS in 1929. They are (or were) commonly used to transport pre-assembled panels of track, 60ft in length. BR continued to use them and built many more of the same type.


Portion of a carriage where the seating is arranged in an open layout, without partitions.

Saloon Coach

Description of a carriage usually for special traffic purposes, such as by the railway's directors, or private party or family hire. Sometimes also used as an alternative phrase to "open coach".

Salter Safety-Valve

A boiler safety-valve where the steam outlet caps are loaded down through long sprung levers.

Sand Drag

A short length of railway track buried in sand, and running from a set of catch points. It is designed to bring runaway vehicles to a halt rather than derailing them.

Sand Pipe

The delivery pipe of sanding equipment.


Slang term for sanding equipment on locomotives. To improve grip on slippery rails, sand is applied to the rail top just ahead of the leading driving wheel. Sanders are operated by the driver as required and are usually gravity fed on steam locomotives.

Sandwich Frame

A plate frame where the side plates consist of a sandwich of two outer metal plates, with a wooden plate in between.


The debate as to what is scale and what is not will go on and on. We have generated a list of different scales.more...

Scissors Crossing

A facing crossover and a trailing crossover that intersect each other.

Scissors Crossover

A facing crossover and a trailing crossover that intersect each other.

Scotch Block

A block of material which is placed on a rail near the wheel of a stationary vehicle to prevent the vehicle from accidentally moving.

Scotch Block

A wedge of metal, which can be located by mechanical linkages, on top of a running rail at the exit to a goods yard or similar location. The device serves the same purpose as catch points.

Screw Brakes

A hand-brake system used on heavy goods-vehicles, brake vans and passenger brake-coaches, where the brake is activated by a wheel and gears rather than a lever. On goods vehicles, the activating wheel is located on the outside of the vehicle.

Screw Coupling

See: Couplings.

Screw Reverser

As the name implies, this screw was used to reverse the direction of travel of the locomotive. Smaller adjustments could be used control the usage of steam in the cylinders.

See: Cut-Off.

Searchlight Signals

Colour-light signals, which by the use of a parabolic reflector, produce a very strong narrow light beam capable of being seen in direct sunlight.

Section Clear but Station or Junction Blocked

A signalling term which is normally only permitted to be used where goods trains are involved. The term is used when a signalman allows a train to enter a block section with caution, knowing that the section is clear only up to the next home signal, the line being blocked between the home signal and the clearing point.

Semaphore Signal

A signal where the indication is given by a movable arm or board.


A long bolster wagon (60 foot) used by the LNER to transport rail and pre-assembled panels of track, 60ft in length. They were later called Borail EA.

Setting Down Post

A line-side post upon which, without needing to stop, a member of a train crew places a single-line staff.

Shed Pilot

A locomotive used within the bounds of a locomotive depot for moving disabled locomotives, or locomotives out of steam.

Shell Vent

A type of ventilator seen on the roof of railway vehicles. The ventilator has the shape of a number of nested sea shells (see also torpedo vent).


The Japanese Bullet train first introduced in 1964. The latest Series 300 Shinkansen travels at up to 300 kilometres per hour.

See also: TGV


Another term for a skate.

Shoe Beam

A beam projecting from the sides of an electric locomotive or EMU, and suspended from which are one or more current-collecting skates.

Short Section

A block section which is so short that distant signals, which would normally be located inside the block section, are mounted on the same posts as the starting signals of the block posts in rear.


The raised edge of the ballast.


To move or rearrange rolling stock within the bounds of a station or goods yard.

Shunt-Ahead Signal

A Shunt-ahead signal authorises a move past a Section Signal for the purpose of then setting back (e.g. into a siding).


A locomotive used for shunting.


A person who organises shunting movements from the track-side.

Shunter's Pole

A pole with a hook on it, used by a shunter (person), for unhooking loose couplings.

Shunter's Truck

A small wagon designed for use permanently coupled to a shunting locomotive. The wagon is used for storing tools and for the shunter (person) to ride on.

Shunting Neck

The length of track joining a reception road in a marshalling yard to the sorting sidings.


The fixed side-windows of a railway carriage. Usually applied to the large lights used where there is no doorway between the seats.

Side Chains

Another term for emergency chains.

Side Rod

Another term for a coupling rod.

Side Tank

A steam locomotive which carries its water supply in tanks mounted on the running plates on either side of the boiler.


A length of railway track used for storing rolling stock between journeys.

Siding Signal

An auxiliary signal which controls the exit from a siding on to a running line. When of the semaphore type, these signals often have a large circle fixed to the arm (see also calling on signal, draw ahead signal, shunt ahead signal, shunt ahead signal and warning signal).

Sight-Feed Lubricator

A displacement-type lubricator situated in a locomotive cab, and consisting of glass tubes in which the rate of flow of oil can be observed.

Sighting Shield

A white board securely positioned behind a semaphore signal arm so as to make the signal easier to see from a distance.


A device used to indicate to a train driver whether he must stop; whether he may proceed normally; or whether he must proceed with caution.

Signal Check

An unscheduled stopping or slowing of a train due to adverse signals.

Signal Gantry

A framework suspended across several train tracks, and upon which many signals may be mounted.

Signal Section

The length of running line between any two consecutive stop signals.


A building where signal and points operating-levers are centralised.


A person employed in operating a signal-box.


A steam engine in which the steam is expanded only once before being exhausted (see also compound).

Single Locomotive

A locomotive with just one driving axle.

Single Acting

An engine in which power is developed in one direction only of the piston stroke only.

Single Line

Another term for single track.

Single Slip

The combination of a diamond crossing of small crossing angle, interlaced with two sets of points. The points are arranged in such a way that for two of the approaching tracks, there is a route to either of the two opposite tracks, but for the other two approaching tracks there is merely the straight across option. When two of the point blades are located totally within the central diamond, it is called an inside slip; but when all of the point blades are outside the central diamond, it is called an outside slip.

Single track

A railway route where only one track is provided for both directions of travel.

Sir Nigel Gresley

Sir Nigel GresleySome photos of the A4 Class locomotive Sir Nigel Gresley. This locomotive is the same as the Mallard which still holds the record as the fastest steam locomotive in the world.


An electrical pick-up device which rubs directly on studs or on a rail (see also pick-up).

Slaking pipe

A water hose which is used for damping down the coal dust on a steam- locomotive.


A beam spanning the track which is used to support the rails. Originally wooden but concrete sleepers are generally used now. Steel sleepers have also been used occasionally.

Sleeping Car

A railway coach in which beds are provided for passengers to sleep in.

Slide Bars

Guide bars for the cross-head at the back of the cylinders.

Slide Valve

A type of steam distribution valve in which an oscillating flat slide covers and uncovers openings on a flat plate.


The sliding portions of a side-light which open to provide ventilation.


A diamond crossing interlaced with two or four sets of points (see single slip and double slip).

Slip Coach

A railway coach which can be uncoupled from the back of a moving train, and then coast under the control of a guard to stop at the next station.

Slotted Signal

Semaphore signals which are interlocked by means of slots in such a way that conflicting indications cannot be given. The system is most commonly used at the entrance to a short section, where the distant arm may not be pulled off unless the corresponding starting signal, on the same post, is first pulled off.


The main structural member of a carriage or wagon under-frame running length-wise along the outer edge of the under-frame.

Small End

Another term for a little end.

Smoke Deflectors

Large boilers have short chimneys, smoke therefore tends to blow back along the side of the boiler obscuring the drivers vision. Large plates fixed alongside the smoke-box act to deflect the smoke upwards clear of the cab windows.


A cylindrical drum on the front of a steam-locomotive boiler, into which the hot gases from the boiler tubes pass. By routing the exhaust steam from the cylinders through a blast pipe within the smoke-box and directing the resulting jet out the chimney a partial vacuum is created in the smoke-box, and by making it as large as possible a more even draught is created over the area of the tubes. This vacuum draws the hot gasses from the fire through the boiler tubes thus heating the boiler water more rapidly and producing more steam to replace that used.

Snifting Valve

When a steam locomotive is coasting with the regulator shut, the pistons will create a partial vacuum in the cylinders and steam chest. This creates drag and may also draw ash into the cylinders from the smoke-box. To prevent this happening, one way valves are fitted to the steam chest to allow air to be drawn in when a vacuum begins to form. This is not very effective at high speeds. Experienced drivers would usually leave the regulator open a little to allow some steam to pass through the cylinders thus preventing this problem occurring.


Beams running down the full length of each side of a railway-vehicle chassis, and onto which the body sides of the vehicle are mounted.

Spark Arrester

A device made from wire mesh which is fitted inside the smoke-box or specially-enlarged chimney of a steam locomotive for the purpose of trapping hot cinders before they can be ejected.


The metal frame in which coloured glass is mounted, and through which a light may shine to give a signal's aspect.

Spectacle Plate

That part of the back or front of a locomotive cab where the window frames are attached.

Speed Restriction Board

A line-side board on which is indicated the speed to which traffic is restricted on that part of the line, or that a speed restriction has commenced.


A protrusion on the top of a locomotive running-plate which covers the tops of one or more coupled wheels.

Splitting of Points

The act of one set of wheels taking one route, and another set of wheels on the same vehicle taking the other route, when a vehicle passes through a set of points.

Splitting Signals

Two or more signals on the same post all concerned with the same approaching line, but each indicating a different route to which the line ahead may be set. As a rule, with semaphore signals, the signal for the deviating route is bracketed off the main post in the direction of the deviating route, and the height of the signal arms is arranged in respective order of the highest speed restriction of the routes concerned.

Spring Buckle

A "U" shaped bolt or clip which holds together the plates of a leaf spring.

Spring hanger

Vertical links which transfer the weight of a vehicle onto the ends of leaf springs.


A short railway line which branches off from a main line to give access to an industry or some minor concern.


An object which is the token of authority to drive a train over one section of a single line. The staff is carried in the driver's cab and therefore reduces the chance of two trains being dispatched in opposite directions along the same line.

Staff and Ticket

A system of operation on single lines when two or more trains are following each other over a single-line section without balancing workings in the other direction. The driver of one train is shown the staff and then given a ticket of authority to proceed without the staff. The last train in the procession then carries the staff.

Standard Gauge

The UK standard gauge is 4 foot 8 inches. Anything wider is referred to as broad gauge, and anything narrower as narrow gauge.

Starting Signal

In the normal direction of travel on any one line, the last signal encountered within a block post, is a starting signal.

Station Building

StationA structure located on or near a station platform and which incorporates services such as a ticket office, waiting room, stores and often the station-masters living quarters.

Station Limits

From a signalling point of view, the station limits of any block post or station area, is the length of line bounded by the most outer home-signal and the most advanced starting-signal.

Station Pilot

A locomotive which is standing-by at a station, and which may be used for any odd shunting job or emergency.

Station Throat

When approaching a station incorporating many diverging tracks, the location of the first diverging track is said to be the "station throat".


Stays are used to tie the inner and outer plates of a firebox together to prevent them buckling and collapsing. Typically stays would be simple studs screwed into the plates, although `girder stays' were also used on some boilers.


Steam is an invisible gas. The white cloud given off from a steam engine, or a kettle, is not steam but tiny droplets of water condensed from the real steam.

Steam Brake

A brake which operates by direct steam pressure on a steam locomotive. It can only be used on the locomotive to which it is fitted.

Steam Chest

A component of a steam engine inside which the steam distribution valves are located. The steam chest is usually an integral part of the cylinder casting.

Steam Dome

A dome-shaped protrusion on top of a steam-locomotive boiler, inside which the steam-collection pipe is located.

Steam Drier

A low-degree super-heater in which the temperature of the steam is raised to only about 200 C or about 400 F. The elements of a steam drier are usually located in the smoke-box.

Steam Heating Apparatus

A system for piping steam, for heating purposes, through a passenger train, or a train including banana vans. Where a train fitted with this apparatus is diesel or electric hauled, a special boiler is incorporated in the locomotive.

Steam Indicator Diagrams

The pressure in the cylinder is plotted versus the cylinder volume. This was developed by James Watt and John Southern to improve the efficiency of the steam engine. The work done is the area within the red curve. more...

Steam Pipe

A pipe in a steam locomotive which runs from the steam collection point in the boiler, to the steam chests. It is often partly visible in outside-cylindered locomotives where it comes out from the side of the smoke-box.


An alternative term, now little used, for standard-gauge. This gauge was originally specified as 4 feet 8 inches, and later changed to 4 feet 8 inches.

Stephenson Valve-Gear

A steam-engine valve-gear which is usually located between the main frames of a locomotive. Motion is taken from two eccentrics secured to one of the driving axles. From these, two rods (the eccentric rods) are connected to either end of a link (the expansion link), which is thus oscillated. Movement of the valve spindle is taken from a die block which is free to slide within the expansion link. Reversal is carried out by moving the expansion link bodily, so that the die block takes up a new position at the other end of its slide.

Stephenson Link-Motion

A steam-engine valve-gear which is usually located between the main frames of a locomotive. Motion is taken from two eccentrics secured to one of the driving axles. From these, two rods (the eccentric rods) are connected to either end of a link (the expansion link), which is thus oscillated. Movement of the valve spindle is taken from a die block which is free to slide within the expansion link. Reversal is carried out by moving the expansion link bodily, so that the die block takes up a new position at the other end of its slide.

Stock Rails

The two outside running rails in a set of points.

Stop Blocks

Another term for buffer stops.

Stop Signal

A running signal which, when in the on position, indicates that a train must stop short of the signal

Stores Van

A goods van or old passenger coach, specially adapted to carry items for the maintenance of the permanent way, signal-boxes, or other railway property.

Stove-Pipe Chimney

A straight-sided chimney on which there are no decorative embellishments.

Straight-Link Valve Gear

Another term for Allan straight-link motion.


Metal strips which are used to connect together the planks of wooden- bodied wagons and vans.


Short for frame stretcher.

Stroke (of a piston)

The distance traveled by a piston when sliding from one end of a cylinder to the other in its normal course of operation.

Stub Axle

An axle on which only one wheel is attached.

Stub Points

Points which have their blades hinged at their leading ends, and in which the stock rails end where the trailing end of the points blades are met. In stub points, the blades have no shaping and they end in a stub (hence the name).

Stuffing Box

Another term for a gland.


A long (62-64ft) low sided open wagon with removable sides and ends, typically used for transporting ballast, rail and sleepers. They were a BR adaptation of an earlier LNER design.

Subsidiary Signal

A signal which refers to movements within station limits only, or running signals which under special circumstances override the indication of the main running signals.


The transverse tilting or banking of a track on a curve.



Steam taken directly from a boiler retains the same temperature and pressure as when it was produced and is said to be "saturated". By taking such steam and heating it further, a much greater volume of gas can be produced for a small amount of extra heat. Tests have shown that superheating can result in a 25% economy in coal and 30% in water. Introduced in the 1900's and used mainly on the larger main-line engines. Superheated steam will always be dry.

Super-Heater Element

The steam tubes of a super-heater. Steam taken from the boiler is passed through these to heat it further, thus producing a much greater volume of steam.

Super-Heater Flues

Fire tubes within a boiler in which super-heater elements are located.


Collectively, those parts of a railway vehicle which are not part of the chassis.

Supplementary Steam Valve

Controls the supply of live steam to the exhaust steam injector.

Swing-Link Truck

A truck in which hinged links control the truck's lateral movement.

Swing-Nose Crossing

A set of points incorporating a moving blade in the Common Crossing that is moved according to the lie of the points. This eliminates the `gap' in the running rails and makes for a smoother ride and reduces wear.


One of a pair of linked tapering rails that can be moved laterally to allow a train to pass from one line to the other. The whole set of rails making up such a junction being commonly referred to as points. (Americans commonly call the whole thing a switch).

Switch Back

The Switchback was the second railroad in the US, completed in 1827.

The first was the Granite Railway of Massachusetts, built to haul granite from quarries near Quincy three miles to the construction site for the Bunker Hill monument. Service was inaugurated on October 7, 1826.

When operation began, in May 1827, on the railroad that came to be known as the Switch Back, there were only two other railroads in the United States -- an abandoned short wooden track at Leiper's stone quarry near Philadelphia and the three-mile track at Quincy. Both the Quincy and the Mauch Chunk were gravity-powered in one direction and beast-powered in the other.

Visit the Switch Back Gravity Railroad at:

Switch Diamond

A diamond crossing incorporating moving rails in the Obtuse Crossings that are moved (like two sets of points end to end) according to the direction of move to be made. This eliminates the `gaps' in the running rails and makes for a smoother ride and reduces wear. May also be referred to as `Moveable Angles'.