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The primary supply of air to the fire is from below, via the ash-pan. Dampers are the flaps, operated from the cab, which regulate the flow of air through the ash-pan. They also provided access to rake out clinker and ash from the ash-pan.


A handle used to secure the smoke-box door of a steam locomotive.


A long straight fire iron.

Dead-Man's Handle

A control device on electric or diesel trains which the driver must keep depressed in order to prevent the brakes from being automatically applied.


A locomotive which according to the Whyte classification is of the 0-10-0 wheel arrangement. The term is sometimes used also for 2-10-0 locomotives.

Deflector Plate

An inward-protruding plate inside the firebox of a steam locomotive, secured just above the fire-hole door. The plate is used to deflect incoming cold air away from the tube plate. Also known as the flame scoop.


A small explosive charge set off by the wheel of a train passing over it. Detonators consist of a small metal cap attached to two soft metal strips which would be used to clip it on top of a rail. Used in emergencies to provide a clear audible warning to drivers. Carried on all trains for use by the guard in emergencies.

Diamond Crossing

The crossing of one train track with another on the same level.

Die Block

A component in the Walschaerts valve-gear which is able to slide within the radius link; or a similar sliding device in other forms of valve gear.

Diesel Electric

Diesel Electric locomotives are effectively electric locomotives which carry their own generating plant. The diesel engine and generator typically being directly coupled together, and the motors being mounted on the bogie frames.

Diesel Hydraulic

Diesel Hydraulics are largely mechanical in principle and rely on the properties of liquids, namely that they are practically incompressible, as such they can be used to transmit force that can be guided into well defined channels. A hydraulic torque converter is basically a pump and a hydraulic turbine in a common casing. Since there is no direct mechanical connection between input and output, an infinitely variable range of speeds is possible between fixed limits. Power is transmitted to the wheels via mechanical drive-shafts from the torque converter/gearbox.

Diesel Mechanical

Diesel locomotives with mechanical transmission rely upon gear boxes in a similar way to most cars and drivers therefore have to change gears regularly as the speed varies. Usually only used for low power shunting locomotives.

Direct Admission Valve

A valve fitted to a brake cylinder of a vacuum-braked train. The valve is designed so as to open and allow atmospheric air into the brake-operating system when only a small reduction of vacuum has occurred in the train pipe. This has the effect, in a long train, of bringing the brake fully on, quicker than would have been the case if the vacuum had simply leaked away through the brake-actuating valve.

Disc Signal

A semaphore signal where the indication is given by a rotatable disc.

Displacement Lubricator

A device often seen secured to the side of a steam-locomotive smoke-box. The device is used to bleed oil into a steam pipe for lubricating the cylinders. It usually has the appearance of a small vertical cylinder, with an adjusting screw on the top and a drain cock on the bottom.


The disposing of the remains of the fire at the end of a days working for a steam locomotive. This consists of three main tasks, removing the remnants of the fire from the grate, emptying the ash-pan and emptying the ash out of the smoke-box.

Distant Signal

A caution signal which when in the on position, indicates that the next stop signal is at danger, or at least one of the stop signals within the approaching station limits is at danger.


Common acronym for Diesel Multiple Unit.


A LNER long (62-64ft) open wagon with drop sides used for ballast, rail and sleepers. BR later adapted this design for their Sturgeon wagons.


A dome-shaped protrusion on the top of a steam-locomotive boiler. Typically this conceals the steam collection pipe for the regulator, which needs to be at the highest point of the boiler to minimise the chances of priming. Domes may also be used for other purposes.

Double Chimney

An elongated chimney of normal width, but about double normal length, into which two blast pipes exhaust steam.

Double Frames

A railway-vehicle frame which has side plates located both between the wheels and outside the wheels.

Double Header

A train which is hauled by two locomotives coupled together.

Double Slip

The combination of a diamond crossing of small crossing angle interlaced with four sets of points so as to provide a route between any two opposite tracks. When four of the point blades are located totally within the central diamond, it is called an "inside slip", and when all point blades are outside the diamond, it is called an "outside slip".

Double Track

A railway route in which one track is provided for each direction of travel.

Down Line

That line on a multi-track main line where the direction of travel is away from the major city.

Drag Box

A cast or fabricated member at the extreme rear end of a locomotive main-frame, and on which the draw-gear is mounted.

Drain Cock

Used to drain the contents of a cylinder or other container.

See also: Cylinder Drain-Cocks.

Draw-Ahead Signal

A subsidiary signal, usually mounted on the same post as a starting signal. When the draw ahead signal is off, the train may draw ahead cautiously against the starting-signal's indication, but only as far ahead as the line is clear, or as far as an advanced starting signal (see also calling-on signal, shunt ahead signal and warning signal).

Draw Gear (or Draw-bar)

A mechanism having spring-controlled movement, which is connected to the main frame of a railway vehicle, and on to which a coupling is attached.

Draw-Bar Pull

The force exerted by a locomotive on the leading coupling of the vehicles which it is hauling.

Driving Wheel

The wheels which actually drive the vehicle along. In the case of a steam engine these will be the large wheels in the middle of the locomotive connected together by coupling rods. They may sometimes have smaller wheels either in front of behind them - see wheel arrangements for more details.

Drop Coach

Another term for a slip coach.

Drop Head Buckeye Coupling

A buckeye coupling that can be lowered to reveal a standard hook for a screw or three link type coupling.


The opening window in a carriage door, or other similar window which opens by dropping down into the coach body.

Dropper Wire

Wires hanging from a catenary on to which the contact wire for railway electrification is attached.

Dual-Fitted Stock

Rolling stock which is fitted with both vacuum brake and air brake systems.

Dual Gauge

A mixed-gauge railway line designed for two different track-gauges.


Lookout for the guard which projects from the side of a brake coach or guards van.

Dumb Buffers

Long-ago-obsolete type buffers used on rolling stock.

Duplicate Signal Arm

The lower arm of a co-acting signal.

Dynamometer Car

A railway vehicle which incorporates apparatus for measuring draw-bar pull, speed, and work done by the locomotive to which the vehicle is coupled.