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Introduction

Here is a collection of over 300 descriptions of the parts of the steam locomotive compiled to assist locomotive enthusiasts to further their knowledge of the most remarkable mechanical machine ever created by man.  Although it is based on UK practice and design, it has much of interest to world wide readers and it includes some historical notes about the development of the steam locomotive.

Further information is available at:
Modern Railway Terminology - The Brakes Glossary - The Electric Traction Glossary - US-UK Terminology - Acronyms and Abbreviations and the UK Railway Lexicon
Please allow time for the page to download (100k), then choose a letter to reach the section you want:

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A...
ADHESION

The grip of the driving wheels of a locomotive obtained on the rail, particularly important when starting.  The weight on the driving wheels is particularly helpful in this respect.

ADHESIVE FACTOR

The ratio of maximum tractive effort, expressed in pounds, to the adhesive weight, also in pounds, of a locomotive.  It will usually be about 25% of the adhesive weight for a locomotive with two or four cylinders. For a locomotive with three cylinders, the adhesive factor might be reduced to 3.5 to 1.

ADHESIVE WEIGHT

The adhesive weight is that part of the locomotive weight carried on the driving wheels which can therefore contribute towards adhesion.  See also Adhesive Factor.

ADMISSION, STEAM

In steam engine operation, the period during which the steam valve exposes the steam port to allow live steam to enter the cylinder.  The admission period is restricted to a percentage of the piston stroke.  See also Cut off and expansion.

ADRIATIC TYPE LOCOMOTIVE

A locomotive with a 2-6-4 wheel arrangement, first introduced in 1909 on the Austrian State Railway and said to have been named after its use on a route by the eastern shore of the Adriatic Sea.

AIR BRAKE

Standard train brake originating in the US using compressed air in which the control is actuated from a driver's brake valve.  A fall in brake pipe air pressure causes a brake application on each vehicle whilst a restoration of pressure causes the brake to release.  A triple valve on each vehicle monitors the pressure in the brake pipe.  When pressure falls, the distributor allows air from an auxiliary reservoir on the vehicle to pass to the brake cylinders to apply the brake.  When pressure rises, the triple valve releases the air from the brake cylinder and recharges the auxiliary reservoir for the next application, using air from the brake pipe as it recharges.  See more information in our Brakes Page.

Air brakes were not popular on most UK steam railways, who preferred the vacuum brake on account of its simplicity and cheapness.

AIR OPERATED REVERSER

Sometimes used on locomotives equipped with compressors for air brake operation.  William Stroudley of the London & Brighton & South Coast Railway used such a reverser in 1882.  It was widely used in the US where valve gear became too large to be operated manually.

ALLAN VALVE GEAR

A type of valve gear designed by Alexander Allan, one time locomotive superintendent of the LNWR, in 1855.  It was similar to the Stephenson valve gear but the reversing lever moved both the link and the block at the same time instead of only the link.  It enabled the link to be made straight and of less vertical height.  See also Link Valve Gear.

ANTI-VACUUM VALVE

Also known as a 'snifting valve'.  A valve provided on engines with piston valves to allow air into the steam passages while the locomotive is moving with the regulator closed. In this condition, the pistons act as pumps, trying to drag air into the cylinders and compress it.  A partial vacuum is created in the steam chest and this can drag ash into it from the smokebox.  Anti-vacuum valves provide some relief of this problem at low speed with a long cut off but will not help much at higher speeds.  For this reason, drivers normally open the regulator a little (crack it) when coasting to allow some steam to pass through the passages and exhaust in the normal way.  The anti-vacuum valves may be mounted on the steam chests or singly or in pairs on the smokebox when they are connected to the saturated side of the superheater header.

ARTICULATED LOCOMOTIVE

A locomotive where two engines (sets of cylinders, valve gear and wheels) were provided under the same frame but pivoted to allow transition through curves in spite of the long wheelbase. Garratt and Mallet were two types of articulated locomotives.  Much favoured in Africa, India and the US but not common in Europe and the UK.  Some locomotives built to Fairlie's patent also had two engines but not all were articulated.

ASHPAN

The light steel receptacle under the locomotive grate into which ash from the fire falls.  It is usually fitted with dampers to adjust the airflow through the fire.  Some ashpans were provided with water sprays to reduce dust when the fire was being cleaned.

ATLANTIC TYPE LOCOMOTIVE

Name given to the 4-4-2 type of locomotive, originally derived either from the locomotives of the Philadelphia Railroad which ran between Camden and Atlantic City NJ or from the group of this type built for the Atlantic Coast Railroad.    The type was first introduced in the US in 1888 for the Lehigh Valley RR and in UK on the GNR in 1898 to a design by H.A.  Ivatt.

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B...
BALTIC TYPE LOCOMOTIVE

A locomotive with a 4-6-4 wheel arrangement.  Referred to in the US as the Hudson type.

BAKER VALVE GEAR

A type of valve gear similar to Walschaerts but with less moving parts.  It was popular in the US but was rarely if ever tried in Europe.

BANJO

The UK locomotive driver's nickname for certain types of vacuum brake valve handle in the cab, from its shape.  Also used on some UK railways to denote a disc type ground signal.  The name was also used to describe the dome cover on certain LNER locomotives on account of its shape.

BANKER

Nothing to do with money.  See Banking Locomotive.

BANKING LOCOMOTIVE

A locomotive used to assist trains over a section of line incorporating a long or steep 'bank' or grade.  Many banks had permanent allocations of 'banking engines' or 'bankers', which were attached to the rear of heavy trains which stopped specially to pick them up.  At the end of the section where assistance was required, the banking engine would drop off without stopping the train and later return to the bottom of the bank to assist another train.  In US known as 'helpers'.

BAR FRAME

Type of locomotive frame almost universal in the US but rare in the UK.  It originated in the UK in 1830 when it appeared on an 0-4-0 locomotive named Liverpool built by Edward Bury which was sold to the Petersburg Railway in 1833.

Bar frames were constructed of steel bars of about 4 inches square section.  They were first used in US locomotive construction in the early 1840s.

BELL, LOCOMOTIVE

Locomotives in the US are required to carry a bell which is sounded as a warning when the train is moving within station limits.  On many locomotives, these are automatically operated. The bell was first required by a law passed in the State of Massachusetts in 1835.  Not used in the UK where, unlike many other countries, railways are fenced.

BELPAIRE BOILER

A design of boiler first developed by Alfred Belpaire, a Belgian locomotive engineer, in 1860, with an improved design in appearing in 1864.  This later design consisted of a firebox with a flat top which allowed the use of vertical and horizontal stays.  The type first appeared in the UK in 1891 and was standardised on the Great Western Railway from the early 1900s.  It was still in use for new locomotives during the 1950s.

BIG END

The crank pin end of the connecting rod, where it is larger than the crosshead end because the stresses are higher at that end.

BIGHOLE

US slang term for emergency brake application, arising from the use of the brake valve to create a 'big hole' in the brake pipe, thereby venting it to atmosphere and thus causing the emergency application.  Example:  "I bigholed her and we just barely stopped before the switch."   See more information in our Brakes Page.

BISSEL TRUCK

A two-wheeled truck designed to allow radial movement, where the pivot point was in rear of the axle.  Usually fitted at the leading end of a locomotive.  It first appeared in the US in 1858.

BLAST PIPE

The pipe which carries the exhaust steam from the cylinders to the centre of the smokebox. It is positioned below the chimney so as to allow the exhaust steam to escape directly and create the maximum vacuum possible.  In this way the draught drawn through the boiler tubes and fire is maximised.

The use of the exhaust steam to assist with draughting was an early feature of locomotive design and it was usual to pipe the two cylinder exhausts separately into the chimney.  The introduction of joining the exhausts into a central blast pipe below the chimney orifice came in 1827 and was gradually adopted from that time.

BLAST PIPE, VARIABLE

A variable blast pipe was introduced in 1839.  It consisted of a cone fitted inside the blast pipe which was operated from a lever in the cab.  Various manual systems were tried during the mid and late 19th century but they all fell out of fashion until the GWR introduced an automatically operated variable blast pipe system on its later locomotives.  This was known as a 'jumper'.

BLINKERS

UK railway slang for smoke deflectors.

BLOW-BACK

The forcing of flames and smoke from the fire through the fire hole into the cab of a locomotive due to the draught through the tubes being reversed.  It can occur when the regulator is closed while the locomotive is moving and is normally prevented by the use of the blower.  A blow-back can be very dangerous to the crew and there have been fatalities in the past as a result of blow-backs.

BLOW OFF COCK

A cock provided on a locomotive boiler, normally at the lowest point to allow it to be drained.

BLOWDOWN VALVE, CONTINUOUS

A valve provided to prevent priming in locomotive boilers.  It is normally fitted on the firebox backplate near the water level of the boiler and used to remove a small amount of water at that level to reduce the scum formed as a result of boiling water chemically treated or softened to reduce scale.  The continuous blowdown valve operates automatically when either exhaust steam is available or, in some locomotives, when steam is detected in either injector delivery pipe.  The process helped to reduce boiler washouts from weekly to monthly but it was disliked by the permanent way engineer because of the chemicals thrown onto the ballast.

BLOWDOWN VALVE, MANUAL

Some locomotives were fitted with a manually operated blowdown valve positioned in the centre of the firebox throat plate just above the foundation ring.  This valve was controlled from a lever in the cab and was used to discharge sludge which collects at the bottom of the boiler and foundation ring.

BLOWER

A means of providing a draught for the fire when no exhaust is available.  A pipe takes live steam to a 'blower ring' usually fitted to the top of the blast pipe or the base of the chimney.  The blower is used to maintain a draught on the fire.  It is controlled by the driver, who will open a valve in the cab to allow live steam from the boiler to escape into the chimney whenever there is no exhaust steam from the cylinders to provide the draught.

The draught from the blower keeps the gases from the fire flowing through the tubes to the smokebox and prevents the possibility of a reversal of the flow with the resultant blow back of fire into the cab.

BOGIE LOCOMOTIVE

A steam locomotive with a 4-wheeled truck (or bogie) provided as part of the wheel arrangement.

BOILER

The enclosure on a locomotive where steam is produced.  The boiler must be filled with water almost to the top.  When the water boils, the steam it generates forms in the space between the top of the water and the top of the boiler.  When enough steam collects, the pressure begins to build up until it reaches a useful working level.  It will continue to build up until the maximum pressure is reached.  This can be anything between 150 pounds per square inch (psi) and 300 psi, depending on the age and type of locomotive.  To get a locomotive boiler up to working pressure from cold takes several hours.

The water in the boiler is heated by fire.  The fire is placed in the firebox at the rear end of the boiler and the hot gases generated pass through hollow tubes (made of brass, steel or copper) running the length of the boiler.  "Tube plates", provided with a large number of holes to take the tubes, were fitted at the ends to seal off the boiler and to provide mounting plates for the tubes.  At the front end of the boiler the hot gases escaped from the tubes into the "smokebox" and then upward to atmosphere through a "chimney" or "stack" as the Americans call it.  At the rear, the tube plate formed the front of the inner firebox and is, in UK practice, made of copper, instead of the steel used for the front tube plate.

The traditional form of boiler was the same diameter throughout its length and was known as the parallel boiler.  A later type which became popular was the tapered boiler, which was narrower at the front than the rear.  This allowed more of the water to be at the rear where the greater heat from the firebox was available.

To reduce heat loss boilers are insulated and then covered with a thin steel sheathing.  For many years, the insulating material was wood and then asbestos.  In recent years various forms of natural or man-made insulating materials have been used.

BOILER BARREL

The main part of the locomotive boiler between the smokebox and the firebox.

BOILER CERTIFICATE

A formal notification verifying that a boiler is fit for use. Boilers are potentially dangerous and they are required by law to have regular inspections by qualified inspectors who must issue certificates to show that they are safe to operate.  In the UK, a boiler certificate is issued for seven years, after which time the boiler must be overhauled and re-certificated.  In practice, for use on preserved railways, ten years is possible with an insurance inspection after 5 years to confirm the extension to 10 years.  In South Africa it is nine years.  In the US it varies from state to state.

BOILER CLOTHING

See boiler insulation.

BOILER CONSTRUCTION

Locomotive boilers were originally made of wrought iron but a steel boiler was first used in the UK by George Tosh of the Maryport and Carlisle Railway in 1862.  A locomotive with a steel boiler had appeared in Canada two years before in 1860 and it gradually became general around the world from that time although wrought iron was still being used in the UK on some railways 30 years later.

The steel used in boiler construction has to be of good quality.  The stresses required of even a small boiler are considerable and the results of a weakness in design or construction could be fatal if a boiler explosion occurred. Leaks, although less serious, would cause poor steaming, with possible delays to trains and would cost money in repairs and lost availability.

It is essential that a boiler be manufactured to a precise circular form in section.  This ensures an even distribution of stresses.  The boiler plates are first bent by passing them through rollers and are then riveted together to form circular sections.  Barrels up to 12 feet long are usually made of two sections, longer ones being of three sections.

The rolled plate of each section is butt jointed to give the circular form required and special 'butt strips' added above and below the joint.  The whole seam is then riveted up so that each section or 'ring' has one longitudinal joint.  It is important that a true circle is formed by each boiler ring so that, when steamed, the boiler rivets are not put under excessive stress. Boiler rings were also secured to each other by riveting lap joints.

In the later years of locomotive development, some parts of and even complete boilers were welded.  An all-welded boiler was fitted in the US to a Delaware & Hudson 2-8-0 locomotive in 1934 but it had to undergo several years of regular use before it was accepted as safe by the Interstate Commerce Commission.  In Britain, the Southern Railway 4-6-2 locomotives designed by O.V. Bullied and introduced in 1941 had welded boiler seams and parts of the firebox were also welded.

Adding the firebox was a complicated operation.  The 'throat plate', which joined the lower part of the firebox to the boiler barrel was a particularly awkward shape requiring a hydraulic press for its manufacture.  The remaining parts of the firebox have also to be specially formed and then assembled to provide the inner and outer fireboxes.  The assembly involves screwing into position a large number of staybolts or stays, which hold the inner firebox in the correct position inside the outer firebox.  Later locomotive designs could have over a thousand stays in the firebox.

Before inserting the tubes, the riveted joints are caulked to ensure that the boiler is steam tight.  The tubes are expanded into position in the tube plates.

BOILER EXPANSION

The natural expansion of the boiler as it heats is allowed for in its design.  It is normally secured to the locomotive's frame at the smokebox end and only rests on the frame at the firebox end so that it may slide freely when it expands.

BOILER INSULATION

At first, locomotive boilers were usually insulated with wood battens secured by hoops and varnished.  Fireboxes were left bare at first but, from 1839 some were covered, either over the lower part or totally.  A layer of felt was sometimes added under the wood but this got wet in the rain and, from 1847 there was a gradual introduction of sheet iron covering in place of wood. From about 1900 asbestos was used and this remained until its use was rendered illegal in most countries and various forms of wool waste or felt were again adopted.

BOILER MOUNTINGS

Generic term for attachments to locomotive boilers e.g.  safety valves, dome, chimney, clacks, whistle etc.

BOILER PRESSURE

See Pressure, Working.

BOILER TUBES

See Tubes, Boiler.

BOILER TUBE CLEANING (on the move

A technique employed on oil-burning locomotives.  When running, sand is allowed to be sucked into the firebox by the draught  (via the fire hole, often called a "fire door" in the US), which will then be pulled into the flues by the draught, knocking the soot loose from the tubes.  This is necessary since the oil used for steam locomotives produces copious amounts of this deposit, and since the deposit from burning acts to insulate the tubes, it inhibits steaming.   A similar system was once tried on some coal burning LMS locomotives in the UK.

BOOSTER

A secondary steam engine provided on a locomotive's trailing axle or tender to assist with train starting.  As a result of the fact that a boiler's maximum capacity for steam generation is normally only tested when a train is running at top speed or working up a long steep gradient, extra steam is available at starting.  To assist with starting a heavy train, some locomotives were provided with boosters.

Tender boosters first appeared in the US in 1922 on the Delaware & Hudson RR and they became popular across the US.  Boosters were tried in the following year in the UK on the Great Northern Railway and appeared on a number of engines over the following few years. They were not considered successful.  See also Steam Tenders.

BOSS

The central, solid part of a railway wheel, which is pressed onto the axle.

BOXPOK 

Disc driving wheels common on US locomotives towards the end of the steam era.  In addition to being easier to manufacture and having a longer life than spoked drivers, they were much easier to balance, a necessity with the standard two-cylinder arrangement of the vast majority of US locos. 

BRAKE BLOCK

The friction material which is pressed against the tyre of the wheel during braking.  Early brake blocks were wooden and later became cast iron as train speeds and weights increased.  More recently, various types of composition materials have been introduced to reduce the weight and wear rates of the older types.

BRAKE RIGGING

The rods and levers which connect the brake cylinder to the brake blocks on each wheel.  See also our Brakes Page.

BRAKE SHOE

Synonymous with brake block.

BRAKES, TYPES OF

Steam locomotives originally had no brakes, they were braked from a hand operated tread brake on the tender.  In 1833, Stephenson fitted a steam-operated brake to his Patentee locomotive design, but this was not widely adopted.  Once continuous brakes were introduced from the mid-1870s, locomotives were also provided with brakes.

For detailed information on train brakes, see our Brakes Page.

BRASSES

UK railway slang for the bearings on locomotives such as the big ends etc.

BRICK ARCH

Said to have been first tried in 1841 by an engineer named Hall as a way of obtaining smokeless combustion of coal. Previously, engines had burned coke or (in the US) wood.  It is also said to have been used on the Scottish North Eastern Railway by Thomas Yarrow in about 1857.  It was patented in the US in 1857. It finally became universally accepted in Britain after its introduction on the Midland Railway, together with the firehole deflector plate in 1859.

The brick arch is located in the firebox over the grate and is attached to the forward firebox wall and the side walls.  Its purpose is to deflect the gases rising from the grate towards the back of the firebox so as to keep them over the heat source as long as possible before they pass up into the boiler tubes.  This ensures that more complete combustion takes place and that as little unburned smoke as possible escapes through the chimney.

BUNKER

The enclosure built at the rear of tank engines in place of a tender which carries coal and sometimes water.

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C...
CAB, ALL WEATHER

Popular component of colder-climate locomotive operations, where the locomotive cab was almost totally enclosed.  Canada and Russia had many examples.

CAB FORWARD LOCOMOTIVE

A rare type, where the traditional cab end and smokebox end was reversed, with the tender located at the smokebox end.  A type existed briefly in Italy (a 4-6-0 coal burner), but the more successful versions were the 4-8-8-2 oil-burning types used by the Southern Pacific Railroad in the US.  This type afforded excellent forward vision for the driver and fireman (so much so that the driver could see the whole road without the fireman's aid) and put the exhaust behind the crew, clearing both vision and breathing (especially when travelling through tunnels). 

CAMEL BACK LOCOMOTIVE

This unusual type was common on a lot of northeastern US railroads.  The driver's cab was wrapped around the mid-section of the boiler, affording him decent forward vision but cutting off communication with the fireman.  The Camelback approach (a.k.a.  "Mother Hubbard") was used in conjunction with the first Wooten firebox-equipped locomotives.  The fireman made do with a rudimentary shelter at the rear of the locomotive, sometimes needing two firemen to feed the large grate characteristic of a Wooten firebox.   

CAPROTTI VALVE GEAR

A cam operated valve control gear invented in 1921 by Arturo Caprotti, an Italian engineer.  It was first tried in the UK on an LNWR Claughton Class locomotive in 1926.  Various other railways have tried the system but it was never widely adopted, even though there were some examples which showed a reduction of coal consumption of 20%.

CHIMNEY

The opening in the top of the smokebox through which the exhaust steam escapes.  The design of the chimney and blast pipe (q.v.) is a crucial ingredient in ensuring a good draught through the tubes and fire.  Known as the 'stack' in the US.

CINDER STRIP

A strip of angle iron fitted to the roof of a locomotive cab to reduce the influx of ash from the chimney when passing under a bridge or entering a tunnel.

CLACK VALVE

A non-return valve provided to allow water to be fed into the boiler against the pressure of the water inside.  Sometimes the valve is mounted with the injector (q.v.), sometimes separately on the boiler side or top.

CLACKS

See 'Clack Valve'.

CLASP BRAKES

Brakes where the wheel is equipped with a block on each side of the wheel, as opposed to only one side.  See our Brakes Page for more details.

CLINKER

Solid matter produced by a coal burning fire, especially under poor combustion conditions or with poor quality fuel.  Clinker must be disposed of at regular intervals during its duty if a locomotive is to continue to produce sufficient steam to enable it to maintain a reasonable rate of work.  Sometimes this had to be done during a single trip where poor coal was used.  South Africa is a particular example of this problem.

COAL

Coal replaced coke as the principle locomotive fuel in the UK upon the introduction of the brick arch and firehole deflector plate about 1860.  It soon became obvious that some varieties of coal were better than others.  The so-called UK hard steam coals from Durham, Northumberland and South Wales were considered better, with the South Wales coal being the best.  These coals had a high carbon content and a volatile content below 14%.  When burnt, little clinker was formed and a good flame was produced. Yorkshire coal was also used by some railways but it was not such high quality as the South Wales type.

Poor coal produces clinker and does not allow good draught. Coal size is also important, in that larger pieces needed to be broken down to about the size of a man's fist to allow the spread of even flame over the whole grate.  Larger pieces would cause 'black spots' in the fire, a sure sign of lower temperatures and less effective combustion.

Coal burning locomotives were tried by Joseph Beattie in 1854 on the London & South Western Railway.  He designed a double firebox and combustion chamber to this end.  Various other devices were tried over the next few years in an attempt to improve combustion, including the use, by some engineers, of centrally divided fireboxes fitted with a mid feather to improve circulation.

COAL PUSHER

A steam powered device fitted to some larger UK locomotives on the LMSR which was mounted at the rear of the tender coal space and which assisted with the forward movement of coal towards the cab where it could be reached by the fireman.  It was controlled from the cab and acted by oscillating and thus vibrating the coal forward. Ordinarily, the fireman would have to go onto the tender to reach any coal which had not shaken forward as a result of the motion of the locomotive.

COAL RAILS

Slatted extensions to tender sides to allow coal to be stacked higher on the tender.

COAL STAGE

A special track raised above the surrounding track level so that coal wagons can be raised to allow them to be discharged into locomotive tenders.

COKE

Early steam locomotives in the UK used coke as fuel, instead of coal, because of an early legal requirement that locomotives should 'consume their own smoke'.  Coal produces smoke when burnt whereas coke burns almost smoke free.  Coke is created by heating soft coal in an airtight oven.  As it heats, the coal decomposes to give a hard, porous, greyish substance called coke, which contains almost 90% carbon.  When it burns, coke produces intense, smokeless heat.

A by-product of coke manufacture is coal gas, which was widely used for industrial and domestic heating in the UK before the advent of natural gas from the North Sea.  Coke was therefore a readily available fuel source for the railways.

It seems that coal replaced coke as the principal locomotive fuel after the introduction of the brick arch into locomotive fireboxes.  This occurred in 1847, but general adoption of the brick arch seems to have come after 1860.

COLLECTING PIPE

A pipe for the collection of the steam from the top of the boiler, used on boilers where the regulator valve was not housed in a dome.  Some boilers were designed without domes, principally because it was thought that cutting a hole in the top of the boiler would lead to weakening the structure.  In locomotives of this type, steam was collected in a pipe positioned at the top of the boiler barrel. The collecting pipe was perforated on the top side to allow the steam inside so that it could pass to the regulator valve.  In superheated locomotives, it was common to position the regulator valve in the superheater header instead of in a dome.

COLLOIDIAL FUEL

A semi liquid mixture of powdered coal and oil sprayed into the locomotive firebox with the assistance of steam pressure.  It was controlled by the fireman using valves in the cab.

COMPOUND ENGINE

A system applied to steam engines whereby the steam was used twice, once in 'high pressure cylinders' at the pressure developed in the boiler and afterwards in 'low pressure cylinders' using the steam exhausted from the high pressure cylinders.  The system was first tried on a locomotive of the UK Eastern Counties Railway in 1850 and later became popular for many locomotive designs world-wide.  The Midland Railway was the chief exponent in the UK.  It was sometimes referred to as 'continuous expansion'.

COMPOUNDING

The use of steam twice, once in a high-pressure cylinder and then in a low-pressure cylinder.  See Compound Engine.

CONED BOILER

See Tapered Boiler.

CONJUGATED VALVE GEAR

The system for operating the valves of a third cylinder by means of levers driven by the motion of the valve gear of the other two cylinders.  Its most famous version in the UK was that used by H. N.  Gresley on his 3-cylinder locomotives for the Great Northern and LNE Railways from 1922 and adopted by some other railways world wide.  Although it reduced the number of moving parts, its most serious disadvantage was the whip effect produced by the levers which caused excessive wear.

CONNECTING ROD

The steel arm which connects the piston rod with the crank on the driving wheel or driving axle.  It is used to convert the forward and aft motion of the piston into the rotating motion of the axle.  It is designed in a tapered form and has a 'little end', where it is connected to the crosshead on the piston rod, and a 'big end' where it is connected to the crank arm.  The tapering is to allow for the greater stresses experienced at the crank end.

CONSOLIDATION TYPE LOCOMOTIVE

A locomotive with a 2-8-0 wheel arrangement said to have been named after the merging of the Lehigh & Mahanoy RR and the Lehigh Valley RR in 1865.

CONTINUOUS BRAKE

Generic term for a train brake which provides for control of the brake on every vehicle and is automatic to emergency stop in the case of loss of control.  In most countries it is a legal requirement for passenger trains.  Some freight trains do not always have all vehicles fitted with brakes.  In the UK the two types of continuous brakes used were the vacuum brake and the air brake.  See also in our Brakes Page.

CORK

Used as a stopper for the filling points of lubricating reservoirs on locomotives.

CORRIDOR TENDER

A locomotive tender designed by Sir Nigel Gresley for the non-stop London - Edinburgh service in 1928 and fitted to some of his class A4 pacific locomotives.  It allowed the locomotive crew to be changed en route without stopping the train.  The changeover took place just north of York.  It allowed the longest regular non-stop steam locomotive trip anywhere in the world.

COUNTER BALANCE

A system for overcoming the forces induced by a steam engine in converting the sliding motion into rotating motion.  The most obvious counter balancing can be seen on the driving wheels where segments of steel, containing lead cores, are attached to the wheels to act as balance weights to reduce the hammer blow caused by the crank action.  Additional balance weight is provided on the motion to oppose the weights of cranks and levers.

COUPLING ROD

Steel rod which connects the crank on the locomotive's main driving wheel to cranks provided on the additional driving wheels.

CRANK

A crank is a fixed arm attached at 90 degrees to a rotating axis so that forward and aft motion can be converted to rotating motion and vice versa.  For the outside mounted cylinders of a steam locomotive so fitted, the means by which the horizontal motion of the piston is converted into rotary motion to drive the wheels.

CRANK AXLE

An axle on a locomotive where cylinders are mounted inside the frames and the drive of the pistons is transmitted to the wheels by means of cranks built into the axle to accommodate the motion of the connecting rods.  The first locomotive with a cranked axle was "Novelty", built in 1830 for the Rainhill locomotive trials by John Braithwaite.  Inside cylinders became a standard design for many locomotives in the UK and remained so until the 1920s.

CRANK, RETURN

See Return Crank.

CROSSHEAD

The steel block which carries the bearing joining the piston rod and the little end of the connecting rod. The crosshead is fitted between two slidebars so as to maintain the alignment of the piston rod with the centre line of the cylinder.

CROWN

The roof of the inner firebox shell.  It is secured to the outer firebox shell by crown stays.  See also Stays and Firebox.

CUT OFF

In steam engine operation, the point at which the valve closes the steam port to prevent more steam entering the cylinder, i.e.  the end of the admission cycle.  Beyond this point, the natural expansion of the steam continues the push of the piston started by the admission of steam.  The cut off point can be varied by the driver adjusting the position of the reverser in the cab.

Cut off is referred to as a percentage of the piston stroke. It will usually vary between about 15% and 75% of the stroke. When a locomotive is starting, maximum power is required so steam will be admitted into the cylinder for as long as possible, or about 75% of the piston stroke.  The engine is therefore working at 75% cut off.  Once the train is moving, the cut off is adjusted in steps (sometimes called notches) until it has reached the required speed on level track.  By this time, the amount of steam admitted into the cylinder for each stroke has been reduced and the reverser adjusted so that the engine may then be running at 15% cut off.

CYLINDER

The heart of the main power conversion system of the steam engine.  A locomotive has at least two cylinders, mounted at the leading end so as to be clear of the driving wheels.  Next to each cylinder is a valve which controls the flow of steam into and out of it.  Normally, a cylinder and its valve chest are cast in a single block which is carried on one of the side frames.

A locomotive may have two, three or four cylinders depending on the design and age, but there will always be at least two.  On some two-cylinder locomotives, the cylinders are hung between the frames ("inside cylinder locomotives") and drive the wheels through a cranked axle.  With this design the cylinders and valve gear are largely hidden from the outside and are difficult to see unless you know where to look.  Locomotives with three or four cylinders will have two outside and the others inside the frames.

Much importance is laid on the size of cylinders in relation to the boiler size and pressure and the amount of work the locomotive is required to do.  See also Cylinder Operation.

CYLINDER COCKS

The use of steam in locomotives causes much condensation which appears as water in pipes, valves and cylinders.  Water can reduce the efficiency of the steam and could damage cylinders where steam is admitted on top of water which has collected in them.  To eliminate the water, cylinders are fitted with small exhaust ports called cylinder cocks so that the water can be expelled under steam pressure.

The cylinder cocks should normally be left open when a locomotive is standing.  They should remain open as the locomotive is started so that, when steam is admitted into the cylinders the water is blown out.  Once the locomotive is moving and the cylinders are warmed up, the cocks can be closed and full pressure is available.  There are normally three cocks per cylinder linked together.  They are controlled from the cab and can be steam operated or mechanically operated by a lever.

CYLINDER OPERATION

When steam is released into a cylinder, it expands into the space available.  If a piston is placed inside the cylinder, the pressure of the steam and its expansion will push on the piston. When the piston reaches the end of its stroke, steam is admitted to the cylinder on the other side of the piston.  This pushes the piston back.  The steam used for the initial stroke is now pushed out of the cylinder as the piston returns and is exhausted into the smokebox, where it escapes through the chimney into atmosphere.  The puffs of exhaust steam escaping into the air make up the characteristic sound of the steam locomotive.

In detail, the cycle is as follows.  Before the piston starts to move, steam is admitted into the space between the cylinder end and the piston face to build up pressure.  This is known as 'lead'.  Once a certain amount of steam is admitted into the cylinder and the piston starts to move, the supply of steam is cut off.  Now, natural expansion of the steam takes place and the piston pushes as far as it can go.  For the last 25% or so of its stroke, the exhaust is opened and steam starts to escape.  By the time the piston starts its return stroke, the same process is being repeated at the other end of the cylinder.

Ahead of the piston during its return stroke, steam from the previous cycle is exhausted until it is 75% along its stroke, when the port is closed and the remaining steam is compressed up to perhaps 30% of the normal admission pressure.  At this point the lead position is reached again and the whole cycle is repeated.

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D...
DAMPERS

Adjustable doors fitted to the ashpan of a locomotive to enable the flow of air through the fire to be adjusted.  Dampers are controlled from the cab by a lever.

It was usual for most tender locomotives to have front dampers only but the GWR had rear dampers as well.  It was usual for drivers on that railway to run with the rear dampers only open and for them to open the front dampers only when required for harder working of the fire.

DART

The long, straight fire iron used by a fireman to clean the locomotive fire and remove clinker.

DE GLEHN

The name given to a French system of compounding used at the turn of the century, which involved the use of two high pressure cylinders driving the rear wheelset and two low pressure cylinders driving the front wheelset of a 4-coupled locomotive. Four sets of Walschaerts valve gear were used to give independent control of the two sets of cylinders.  Three locomotives of this type were tried on the Great Western railway from 1903 but they were not considered much better than the line's most modern engines and were not universally adopted.

DEAD LOCOMOTIVE

One which is cold and usually has its driving wheels disconnected from the cylinders.

DE-SANDER

A steam pipe positioned on some later designed steam locomotives to remove sand which has been applied to the rail head.  It was done because sand tends to cause poor train detection on lines where track circuits are used as part of the signalling system.

DETROIT SIGHT FEED LUBRICATOR

A type of locomotive lubricator - see Displacement Lubricator.

DIE BLOCK

In Stephenson's and Walschaerts and similar 'link' type valve gears, the block through which the radius rod (q.v.) moves and which itself slides up and down the expansion link according to the position of the reversing lever.

DISPLACEMENT LUBRICATOR

An oil lubricator for steam locomotives first introduced in the UK in 1857 by John Ramsbottom (of safety valve fame).  It operates by steam condensing to produce water which is fed into a chamber and which gradually displaces oil from the top of the chamber, allowing it to rise and overflow into delivery pipes. Often positioned in the cab where the feed glasses can be seen.

DOME

A boiler fitting (of dome shape) resting on top of the boiler and used to house (most commonly) regulator valves, safety valves, or sand.  The need for the dome first arose in the early days of locomotive design because the bubbling water near the top of the boiler often got carried over into the steam pipe leading to the cylinders -see also Priming. Cylinders were often damaged as a result.  To overcome the problem, a dome was placed on the boiler (or firebox) to collect steam and divert it to the regulator valve.

Some locomotive engineers preferred domeless boilers, believing that by requiring a large hole, they weakened the structure of the boiler itself.

DRAWBAR HORSEPOWER

See 'horsepower'.

DRIVING WHEELS

The large wheels connected to the steam engine pistons which therefore drive the locomotive.

DROP GRATE

First introduced by Edward Bury in 1852 to allow easier fire cleaning and removal, the drop grate comes in a number of varieties.  Usually designed as a part of the grate which can be opened on hinges and through which the clinker or the whole fire can be pushed if required.

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ECCENTRIC

In steam engine technology, part of the valve gear used by some designs to give motion to the valve.  It may best be described as an auxiliary crank.

It is essential to ensure that the valve events occur in the correct sequence in relation to the movement of the piston inside the cylinder.  The valve spindle is therefore driven off the motion of the piston by connecting it through links and levers to the connecting rod, crank or driving axle, depending on the design of the valve gear.

Where inside cylinders are used, it is usual to derive the valve motion off eccentrics fitted to the driving axle.  The eccentric consists of a circular disc, called a sheave, fitted to the axle so that its centre is offset from that of the axle.  An eccentric rod is attached to the sheave by means of a strap which allows the sheave to rotate within the strap.  When the axle rotates, the eccentric produces a fore and aft motion at the leading end of the eccentric rod.  This, in conjunction with the expansion link and the setting of the reverser, is used to give motion to the valve spindle.

EJECTOR

A steam operated device for creating a vacuum on trains equipped with the vacuum brake.  Normally there are two ejectors, a 'large ejector' and a 'small ejector'.  The latter is usually left on while the train is running in order to continuously evacuate the brake pipe at a low rate to overcome small leaks in the pipework.  The large ejector creates a rapid evacuation of the brake pipe to effect a brake release.  It is closed off once the brakes are released.

ENGINE, STEAM

The portion of a steam railway locomotive which consists of the cylinders, valves, valve gear and connecting rods.  Put another way, it is that portion of the locomotive which provides the drive.  The equivalent in a road vehicle would be the engine and gearbox.  The word 'engine' is often misused to mean the whole locomotive.

EXHAUST STEAM

The steam which escapes from the cylinders after the admission and expansion phases (see cylinder operation) have taken place, i.e.  after the steam has completed its work. Exhaust steam is used for a number of purposes after it has left the cylinders, e.g.  to operate injectors, ejectors etc.

EXHAUST STEAM INJECTORS

First introduced in the UK about 1876.  The use of exhaust steam to assist the work of injectors allowed some fuel savings over the pure live steam injector. BR class H, J, H/J and K types of exhaust steam injectors are all basically similar.  Two controls are provided in the cab, a water regulator and a steam valve.  The water regulator handle has a "sector" to denote the position of the valve.  The valve itself is part of the injector body mounted outside the cab - often under it.

The steam valve is mounted on the boiler backplate and its housing includes the water delivery pipe from the injector, which passes through the backplate, over the firebox crown and down the boiler to deposit the feed water towards the front.  Saturated steam is taken from the dome or the steam fountain to provide the live steam supply to the steam cone when the injector is turned on.

Exhaust steam for the injector is supplied from the cylinder exhaust.  Steam from this source is only at about 10 psi but it is combined with live steam to drive the water into the boiler against its pressure.  An additional supply of superheated steam from the downstream side of the regulator is passed from the smokebox to the injector to allow closing of the regulator to be detected.  The absence of superheated steam causes an automatic shuttle valve to close in the injector.  This prevents the saturated steam supply from reaching the exhaust valve control and this valve closes.  Since the closing of the regulator will mean no exhaust steam is available, the injector will work entirely on the saturated steam available.

EXPANSION

A given amount of steam will naturally attempt to expand into a space.  If that space is a cylinder occupied by a piston, the steam will push the piston until it can expand no further.  In a steam engine, the steam is admitted into the cylinder for a time until the supply is cut off.  The admission of steam pushes the piston until the admission is cut off, after which time the steam naturally expands and continues to push the piston.  The two phases are known as 'admission' and 'expansion'.  The point at which admission stops and expansion commences is known as cut off.

EXPANSION LINK

A curved, slotted lever provided in various designs of valve gear to allow adjustment of the valve events relative to the position of the reverser, hence its name referring to the period of steam expansion.  It carries the die block which is used to assist the setting of forward and reverse and the various cut off positions in between and provides a link between the eccentrics and the valve rod.

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FAIRLIE LOCOMOTIVE

An articulated type of locomotive designed by Robert F Fairlie in 1865.  The design was popular on narrow gauge lines.  The frame was mounted on to one or two engine units which could move independently.  The engine units could have leading and trailing trucks.  A double Fairlie had two engine units, a single Fairlie one, the other being replaced by a bogie.  The double Fairlie appeared to have two boilers but this was not the case.  They had a single boiler with a firebox and cab in the middle and a smokebox at each end.  The cab was in the middle, and the boiler barrel ran right through it, with the driver on one side and the fireman on the other.  The driver on a double Fairlie controlled the water supply to the boiler as well as driving, leaving the fireman to look after the fire.  This saved space on the fireman's side of the cab.  Over 500 Fairlies were built in the USA including, in 1871 the Mason-Fairlie locomotive.  They were also used in Russia, India, Australia, and New Zealand.  The Fell locomotives used in New Zealand were Fairlies.

FEED PUMP

The means of getting fresh water into the boiler from the tank before injectors became common from the 1860s.  Pumps could be worked off an extension of the piston rod, the engine crosshead or from an eccentric on an axle.  Some designers added a steam driven pump or donkey engine to allow water to be fed to the boiler when the locomotive was stationary.

FEED WATER HEATING

Various means of pre-heating the water supplied to the boiler were tried over the 125 years of steam locomotive development.  In 1854 Joseph Beattie of the London & South Western Railway introduced a steam heated water supply system on his new locomotives and in 1862, Stephenson & Co.  built a locomotive with a tank under the footplate which was used to heat the feed water using live steam.  Sometimes, tender water heating was used.

The introduction of injectors provided some pre-heating of feed water in themselves but they would not work if the water had already been heated to above 120 F in the tender or before reaching the injector.

In later years some locomotives used feed water heating and had to have steam driven feed pumps.  The French ACFI system was a well-known example.

FELL SYSTEM

A system which allows locomotives to climb gradients at or over the limit of adhesion by means of a central third rail.  The locomotives are equipped with a second set of cylinders driving wheels parallel to the ground and forced against the centre rail by spring or screw pressure.  The Fell system differs from other mountain railway systems in that it depends on friction alone; the centre rail is a plain section unlike the Abt and other systems where the rail is toothed to correspond with toothed wheels on the locomotive.

FIRE HOLE

The opening in the rear wall of the firebox through which access to the fire is gained from the driver's cab.  Its principal use is for shovelling coal onto the fire.  It is normally kept closed and only opened for firing or cleaning the fire.

FIRE HOLE DEFLECTOR PLATE

An angled plate fitted inside the firebox over the fire hole to assist the flow of air over the fire so that the best gas heating rate is obtained.  It works in conjunction with the brick arch.

FIREBOX

The compartment at the rear of the boiler which houses the fire.  The firebox is where the fuel, usually coal, but it can be wood or oil, is burnt to provide the heat to boil the water in the boiler.  The firebox consists of two copper or steel enclosures, the outer firebox and the inner firebox.  They are connected by 'stays', bolts which keep the inner box rigid within the outer box.  Normally, the stays are threaded at each end and are screwed into the steel plates of the firebox.  The ends are hammered down as a seal.

Copper fireboxes were the normal practice for UK railways but in the US, steel was the usual material.  The steel firebox was first tried by Alexander Allan on the Scottish Central Railway in 1860.

Boiler water surrounds the firebox sides front and top to allow maximum benefit from the fire for heating.  The two side areas are often referred to as "legs", as they take on this appearance in cross section.  The outer firebox is really an extension to the boiler.  When the boiler is filled, water will enter the outer firebox legs and cover the roof or "crown" of the inner firebox.  The boiler's tubes are connected to the front wall of the inner firebox so that the hot gases from the fire pass through them to the smokebox.

Inside the firebox a brick arch is positioned over the fire so that the heat from the fire is deflected towards the back of the firebox to ensure the hot gases are distributed towards the tubes more evenly.  In their inspection, the lighting- up crew will check that the firebricks are secure and undamaged.

The two shells of the firebox are joined at the base by what is known as the 'foundation ring' or 'mud ring'.  This name arises from the sludge with tends to collect there during the time between boiler washouts, as it is the lowest point of the boiler where water reaches.

Firebox shape has developed over the years.  To get the required grate area to heat a large boiler, older fireboxes tended to be long but narrow, as they had to rest between the locomotive's frames.  This led to difficulties with manual firing, as the coal had to be thrown towards the rear in spite of a slope being provided.  Later designs had the frames lowered at the firebox end to allow a wider firebox with a shorter grate.  See also the Belpaire boiler.

FIREMAN

Second crew member for a locomotive responsible for the production of steam.  This requires that he looks after fire upkeep and the maintenance of sufficient water in the boiler.  He will also assist the driver with observation of the road, care of the locomotive, coupling and uncoupling etc.

FLANGE

The fundamental element of the wheel-on-rail guidance system. The inner edge of each wheel is shaped to a larger diameter than the wheel tread resting on the rail to act as a guide for the wheelset.  The two flanges of the wheels on an axle guide the wheelset to follow the route of the track.  A characteristic squealing sound can often be heard on sharp curves as the outer wheels' flanges slice along the inner edges of the rails.

FLANGELESS WHEELS

Common on many early locomotives to ease travel around curves.  Also used on later designs such as 2-8-0 locomotives for the same purpose.

FOUNDATION RING

The base upon which the firebox is built.  Originally circular, the foundation ring (also known as the 'mud ring') joins the outer and inner firebox shells and seals the water space around the inner firebox.  The name mud ring arises from the sludge which forms at the base of the water space due to the collection there of impurities in the water.

FRAMES

Locomotive frames were generally of two types, plate or bar. In the UK plate frames became standard whilst in the US bar frames were standard.

In the UK during the 19th century, locomotives were built with inside frames, outside frames and double frames.  The arrangements were tried by various designers offering various reasons for their choice.  Double frames gave better stability and strength and it was the practice to provide two sets of bearings for the driving wheels and one set for coupled wheels.  Double frames made locomotives heavier but, given the science of metallurgy in those days, they were preferred against single frames because the latter showed a tendency to fracture more readily.  There were some who believed that with double frames, the risk of broken crank axles was reduced and, even if they did break, the risk of derailment was reduced. Eventually, improvements in the quality of the steel used and the need to reduce weight led to the universal introduction of inside frames by the end of the First World War.

During the construction of frames it was essential to ensure that they were square, as any deviation would result in the cylinders, valve motion or cranks being out of line and thereby causing damage during running.  Some locomotives used cast frame beds ,particularly in the USA and by Beyer-Peacock where the engine frame was a single piece steel casting, thus guaranteeing the thing stayed square and true.  The South African GM-AM locomotives also have cast beds.

FULL GEAR

The position of the reverser where the maximum cut off is selected to allow the maximum amount of steam into the cylinders.  Usually used for starting, after which the cut off is reduced or shortened to allow more expansive working of the steam.  A locomotive may be in 'full forward gear' or 'full reverse gear'.

FUSIBLE PLUG

In the UK it became common to provide a plug in the crown sheet of the firebox which had a lead core in order to protect the boiler against failure if the water level was allowed to become too low.  If water failed to cover the crown of the firebox, the lead core of the fusible plug melted and steam and water would escape into the firebox to extinguish the fire.  Embarrassing for the crew, who were responsible for ensuring the safety of the boiler, but not fatal, as a boiler explosion could often be.

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GARRATT LOCOMOTIVE

A type of articulated locomotive designed by Herbert W Garratt and built by Beyer Peacock of Manchester for various railways world-wide.  The first appeared in 1909.  The Garratt design consists of the engine superstructure, including water and fuel, which is on a rigid frame supported at the ends by two large bogies carrying the engines.  Both engine units are free to move and are not necessarily connected to each other.  The Garratt is simple expansion, both engines being supplied with high pressure steam.. Various wheel arrangements were employed e.g.  2-4-0 - 0-4-2, 2-8-0 - 0-8-2 and 4-8-2 - 2-8-4.  The advantage of the design was the large space available for the boiler and firebox and the high adhesive weight compared with axle load.  They were principally used for heavy freight service and were popular in Africa.

GAUGES

Locomotives are provided with various gauges: boiler water level (2), boiler steam pressure, steam chest pressure (recent locomotives only), carriage warming pressure, vacuum or air brake pressure.  Certain auxiliary equipment was also sometimes provided with gauges.

GRATE

The base of the firebox upon which the fire rests.  It comprises a grill of firebars with gaps between them to allow air in to assist with the combustion process.  See also Drop Grate and Rocking Grate.

GRATE AREA

The statistic used to determine the fire capacity of a locomotive.  Early locomotives had grate areas of about 6 sq.  ft. The most recent UK designs approached 50 sq.  ft and the largest US designs reached 150 sq.  ft.

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HADFIELD STEAM REVERSER

A popular and common type of steam assisted reverser seen occasionally in the UK but popular on the larger types of locomotives in Africa and India.

HAMMER BLOW

The force exerted by the thrust of the connecting rod on the crank and transmitted to the rail with each revolution of the driving wheel.  Rotating masses must be balanced but since this is only the wheels and the connecting rods, this is reasonably easily done by balance weights.

Reciprocating masses such as pistons, piston rods, etc are much more difficult to balance.  They are balanced at the wheel centres and on the crank axle itself.  In fact the design of the crank axle may be inherently self-balancing to some extent.  It is not desirable to balance 100% of reciprocating mass because this would result in the load on wheels dynamically changing during rotation (and this is exactly what hammer blow is).  It was common practice to balance 60% of reciprocating mass but this was found to cause hammer blow, so was reduced to 30% on two cylinder engines.  The balance is spread unequally over all coupled wheels. Four-cylinder engines, because of their cycle, are self-balancing, so balance weights are not used.  Once again, adding weights to them actually causes hammer blow.  Engines must not be operated under power without connecting rods as the unbalanced forces can actually destroy the track.  See Wheel Balancing.

HEATING, TRAIN

Locomotive produced steam heating of passenger coaches, which first appeared in the US in 1881 and in the UK in 1884.

HEATING VALVE

A valve provided in the locomotive cab to allow steam to be supplied to the train heating pipe through a reducing valve.  A pressure gauge was also provided.

HEATING SURFACE

The total of the area of the firebox walls and boiler tubes providing heating contact with boiler water and therefore the most important indication of steam production capability.

HORN BLOCKS

The brackets fitted to locomotive frames to act as guides for the axleboxes.

HORN PLATES

Plates fitted for strengthening purposes around the axle openings on locomotive frames.

HOPPER ASHPAN

A type of ashpan designed to collect ash which can be emptied directly from a drop grate.

HOT BOX

Excessive heating of a plain bearing axlebox due often to a loss of adequate lubrication and which required the locomotive to be stopped before severe damage and possible derailment occurred.

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INJECTORS

Locomotive boiler water feed apparatus.  Water in the boiler is consumed as steam is generated and it is essential that the water is replaced quickly to allow steam production to be maintained and to prevent too low a water level causing a collapse of the firebox crown.

Early locomotives were equipped with mechanical pumps operated by hand or driven off the valve gear or eccentrics.  Of course, these were only operational while the locomotive was moving and it became the practice to top up boilers of stationary locomotives by positioning the locomotive against a set of buffer stops, greasing the rails under the driving wheels and applying steam to drive the wheels.  This got the water pump working and allowed the boiler to be replenished without moving the locomotive.

In 1858 a French engineer named Henri Giffard invented the injector, a steam powered system for replenishing locomotive boilers.  In the US, Messrs William Sellers of Philadelphia started selling them in 1860, the first being applied to a Baldwin locomotive.

Early versions of injectors used live steam forced through a series of cones whilst mixed with water from the tender.  The pressure of the steam forced the water into the boiler.  The application of steam to the injector was controlled by a cock in the cab.  Later versions of injectors used exhaust steam piped from the cylinder exhaust while the engine was under power but used live steam at other times.  The changeover was automatic. This system saved steam (and therefore running costs) and eventually became common around the world.

The principle of the injector is based on the fact that steam escaping from a nozzle has a greater velocity than that of a jet of water issuing under the same pressure from a boiler.  If cold water is added to the jet of steam, it begins to condense and the velocity of the steam will increase sufficiently to overcome the pressure of water in the boiler.  By this means, water can be introduced into a boiler against its internal pressure

Some injectors used a combination of exhaust steam and live steam.  A connection at the base of the blast pipe was run to the exhaust part of the injector where it heated the feed water before it passes to an auxiliary injector.  The auxiliary injector used live steam to force the water to the boiler.  This type was patented by JJC and RD Metcalfe in 1908 and was claimed to save up to 15% on fuel and water.

There was a type of injector, with features patented by J Gresham in 1884 and 1887, which was a "vertical restarting injector".  Steam supply and feed water passed through the flange by which it was attached to the boiler.  There was also a Davies and Metcalfe type patented in 1899 and 1907 which was designed to operate with feed water too hot for an ordinary injector.

Injectors are tricky instruments and require a degree of skill to "prime" them and get them working.  This is normally the task of the fireman.  Once the steam is turn on, the right balance of water being applied has to be found.  This will only work if the steam and the water are at the correct pressure.  A balance also has to be found between too little and too much water being in the boiler.  Too little risks melting the fusible plug, too much risks boiler water rising to reach the regulator, known as "priming", and getting into the steam pipe leading to the cylinders.

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JIMMY

UK enginemens' slang for a steel bar unofficially fixed across the blast pipe in an effort to reduce the size of the orifice and therefore improve the steaming of a locomotive.

JOHNSON BAR

US term for the reversing lever in the locomotive cab.

JOURNAL

The housing in which the axle turns.  A source of much trouble if not kept lubricated properly.

JOY VALVE GEAR

A valve gear designed by David Joy in 1879 and quite widely used over the next 30 years.  It was simpler than other valve gears but required the provision of a hole for a link in the connecting rod which was found to be a source of weakness and eventually led to the demise of the type.

JUMPER

A form of automatic variable blast pipe designed by Churchward for use on his GWR locomotives.  Under high pressure exhaust steam a ring at the top of the blast pipe lifted to allow a wider exhaust opening and thus reduced the risk of the excessive exhaust pressure lifting the fire.

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KYLCHAP

Steam locomotive exhaust system designed jointly by Kyala and Andre Chapelon and named after them.

L...
LAGGING

See Boiler Insulation.

LAP (1)

The amount, expressed as a fraction of an inch, by which the valve in mid position overlaps the cylinder steam ports.  Valves provided with long lap required greater travel to operate effectively but this allowed a freer exhaust and more sharply defined stages in the cycle of valve events.  Long lap valves were introduced on the Great Western Railway in 1908 following importation of the idea from the US but it was not until the 1930s that their value was properly understood by other UK railways.

LAP (2)

Name given to the position on the driver's brake valve which closes all air ports between the brake pipe and the brake valve itself.  Used to hold the brake pipe pressure after a partial application has been made.  See Brakes Page.

LARGE TUBES

Tubes containing superheater elements.  See Tubes, Boiler.

LATERAL MOTION DRIVING AXLES

Employed on later locomotives in the US with eight or more coupled driving wheels.  Depending on the road, it usually negated the need for blind (flangless) drivers since the driving axles could turn with curves using this system, albeit within a limited curve radius. 

LEAD

The amount, expressed as a fraction of an inch, by which the steam port is open when the piston is static at the end of its forward or backward stroke.  The effect is to allow steam to enter the clearance space between the cylinder end and piston face before movement of the piston takes place so ensuring maximum steam pressure at the start of the stroke.

LIFTING THE FIRE

Railway slang for the occurrence of the draught being so strong that hot coals are sucked from the fire bed, drawn through the tubes and thrown out of the chimney.  Tended to occur when the locomotive is being worked hard or 'thrashed'.

LINK MOTION

See Link Valve Gear.

LINK VALVE GEAR

A form of valve motion designed by one William Howe at the Stephenson locomotive works in 1842 and thereafter fitted to all their locomotives and many others.  The design removed the need for clutch operated eccentric shifts and eliminated the vulnerable forks or 'gabs' of the older motion.  It subsequently became known as the Stephenson Valve Gear.  Later types of link motion included the Walschaerts valve gear.

LIVE STEAM

Steam supplied directly from the locomotive boiler and used for various devices such as the blower, ejectors, injectors, whistle, electric generators (where fitted), steam brakes etc.  In some cases, when available, exhaust steam is used for power as an additive or substitute for live steam, e.g.  as in the case of injectors.

LIVE STEAM INJECTORS

The live steam injector was a relatively simple device consisting of a steam inlet pipe, a water inlet pipe, a delivery pipe and an overflow pipe plus three internal cones.  Steam from the boiler was admitted into a narrowing steam cone which turned the pressure of the steam into velocity.  Next, the steam was allowed to combine with the water, piped from the tender tank, in the also narrowing combining cone.  The effect of combining the cold water and steam was to partially condense the steam and heat the water.  The hot water and remaining steam propelled itself at high speed out of the combining cone and into the neck of the delivery cone.  The delivery cone widened into the delivery pipe and allowed the conversion of the speed of the hot water into pressure sufficient to overcome the internal pressure in the boiler.

Live steam for the injector was supplied through a control valve in the cab.  There was also a water control handle. Normally, locomotives were equipped with two injectors.

LONG BOILER LOCOMOTIVE

A type of locomotive patented by Stephenson in 1842 which was provided with a boiler longer than the usual 9 feet of the day. The objective was to reduce the heat reaching the smokebox in an attempt to reduce the rapid destruction of smokeboxes and chimneys which had occurred up to that time.  By increasing the boiler length to 13 feet or more, the temperature was reduced by over 30% and the life of smokeboxes was considerably extended.

LUBRICATION

An essential part of steam locomotive operation, lubrication takes a variety of forms: Worsted pads fed from an oil bath below the bearing, siphoning from trimmings fed from oil baths, mechanical, hydrostatic, oil atomised by steam, and grease.

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M...
MALLET LOCOMOTIVE

Designed originally by Anatole Mallet in 1884, the design was a compound locomotive with two sets of engines on bogie frames. Later versions were simple expansion locomotives and were developed in the US to the largest locomotives ever built, the Union Pacific 4-8-8-4 'Big Boy' class.  A Mallet has the boiler rigidly fixed to the rear engine unit.  The front engine unit is articulated to the rear and the boiler unit is free to move over it.  This can result in the boiler unit projecting outside the front engine unit on curves (Reed has a photograph of this in 'Loco Profiles')

The Mallet is, strictly speaking, a compound with a high-pressure engine and a low pressure engine using the exhaust steam from the high pressure unit, although simple-expansion versions were built towards the end of steam in the USA.

MANIFOLD, STEAM

The steam pipe in the cab which supplied all the cab control valves such as the whistle, injectors, carriage heating, blower, sanding etc.  Sometimes referred to as the 'steam fountain'.  In the US it was known as the 'turret'.

MARS LIGHT

A special type of electric headlight mounted on some US locomotives which rotated and which could be changed from a white to a red light.  The change to red was automatic upon an emergency brake application.

MECHANICAL LUBRICATOR

Oil distribution system activated by pump action provided by mechanical connections to the valve gear of a steam locomotive.

MECHANICAL STOKER

A system for feeding coal into the firebox, removing the need for it to be done manually by the fireman.  It was generally accepted that a grate area over 50 sq.  ft.  required mechanical firing as it was too large to be manually supplied.  Mechanical stokers appeared in the US from 1905.

Most systems were steam powered and were controlled from the cab.  Some consisted of a chain belt and some operated with a steam jet.  The most successful was the archemedian screw type which appeared from about 1918.  In all cases, the coal had to be broken into small sizes to enable it to be used.  In the UK, mechanical firing was not tried until after World War II and then only a few locomotives were fitted.

MID FEATHER

A partition introduced into some firebox designs to try to improve both water heating and heat generation from the fire.  Various forms were tried during the mid- to late-19th century but the benefits were not considered sufficient compared with the expense of construction and maintenance.

MIKADO TYPE LOCOMOTIVE

A locomotive with a 2-8-2 wheel arrangement, the name being derived from a design built in the US and delivered to the Japanese railways in 1897.

MOGUL TYPE LOCOMOTIVE

A locomotive with a 2-6-0 wheel arrangement.  The first proper version of this locomotive was built in 1858 in the US by Baldwin.

MOTION

Generic term for the piston rods, connecting rods and valve gear of a locomotive.

MOTION PLATE

A large bracket attached to the locomotive frame which is used to support parts of the valve gear.

MOUNTAIN TYPE LOCOMOTIVE

A locomotive with a 4-8-2 wheel arrangement first introduced in the US in 1911 for the mountain section of the Chesapeake & Ohio RR.

MUD RING

See 'Foundation Ring'.

MULTI-TUBE BOILER

One of the principal design advances for the steam locomotive was the introduction of the multi-tubular boiler.  It was suggested to George Stephenson by Henry Booth and was fitted to his Rocket locomotive of 1829.  It also appeared in France at the same time on a locomotive built by Marc Séguin.  Before this, locomotives had single flue boilers or return flue boilers.

The multi-tube boiler contained a number of hollow tubes which allowed the hot gases from the fire to pass through the boiler to the chimney at the other end.  The distribution of the heating effect led to more efficient steam production and assisted with the forcing of a draught on the fire.  Note that this was different from certain other applications of multi-tube boiler, e.g.  marine, where the water passed through the tubes and the heat was applied to the outside of the tubes.

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NOTATION, WHEEL

See Wheel Arrangement.

NOTCHING UP

Slang term for moving the reverser to reduce the cut off of the engine as the need for power is reduced.  'Notching up' has also been adapted by diesel and electric locomotive drivers to mean increasing power. The term originated from the reversing lever quadrant which had notches cut into it to allow the lever to be latched in a particular position.

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PACIFIC TYPE LOCOMOTIVE

A locomotive with the 4-6-2 wheel arrangement.  The first 4-6-2s were built by the Baldwin Locomotive Works in the US for the NZ Railways, hence the name.

PANNIER TANK

A tank locomotive design where the water tanks were mounted on either side of the boiler as for a normal tank loco.  but were raised so as to be clear of the running plate.  The design was almost exclusively UK Great Western Railway.  It reduced the height of the centre of gravity as opposed to a saddle tank but allowed more access to the working parts than ordinary side tanks.  Some saddle tank locomotives were unstable at speed with full tanks.

PISTON ROD

The rod connecting the piston to the crosshead at the rear of the cylinder.  The piston rod is kept parallel to the cylinder by the slidebars guiding the crosshead as it moves forward and back.

PISTON STROKE

See Stroke, Piston.

PISTON VALVE

The type of steam engine valve, circular in shape, designed to overcome the design defects of the slide valve, specifically steam tightness and wear.

PLUG, FUSIBLE

See Fusible Plug.

POP SAFETY VALVES

A safety valve designed to reduce the 'dribbling' of steam from a boiler at full pressure and thus reduce wastage.  They were first used in the US about 1867 and in the UK about 1873.

POPPET VALVES

Steam chest valves opened and closed by cam action, in the same manner as in a road vehicle engine.  Better timing was possible with such systems but it was difficult to get the variations in cut off required to gain maximum efficiency.  Various poppet valve systems were tried over the years including the Caprotti, Franklin, Lentz (RC) and Reidinger.

PRAIRIE TYPE LOCOMOTIVE

A locomotive with a 2-6-2 wheel arrangement first introduced in 1885 and popular in the US mid-west.

PRESSURE, BOILER

Synonymous with working pressure.  See Pressure, Working.

PRESSURE, WORKING

The pressure of steam permitted in a steam locomotive boiler above which the safety valves will blow off the excess.  A good crew will attempt to work the locomotive without reaching this pressure as operation of the safety valves wastes steam.

Early boiler pressures were low.  Stephenson's 'Locomotion' of 1825 had a pressure of 25 pounds per square inch (psi), while his 'Rocket' of 1829 had a pressure of 50 psi.  Ten years later, boilers with 100 psi capability were being built.  By the turn of the century pressures had reached 200 psi on some larger locomotives and rose to 300 psi on some of the largest US locomotives.  280 psi was the highest pressure used in the UK.

PRIMING

The siphoning of water from the boiler into the steam pipe, caused by too high a water level or by certain chemicals used to treat hard water. If water gets into the steam pipe it will affect the performance of the superheater by reducing the ability of the steam to dry properly and, if it reaches the cylinders, it can damage them and the motion.  In extreme cases, cylinder ends have been blown out, valve gear bent and locomotives derailed by the carry over of water into the cylinders.

PUMPS, WATER

The means of supplying feed water to the boiler before the introduction of injectors. See Feed Pump and Feed Water Heating.

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R...
RADIAL AXLES

Axles designed to move laterally entering a curve in an effort to reduce the flange and rail wear incurred with rigid axles.  The design was normally confined to the leading or trailing carrying axles of a locomotive.  The idea was first tried successfully by W B Adams of the London & South Western Railway in 1863 and was subsequently taken up by FW Webb and others.  The axle could be guided by either curved axleboxes, as in the original Adams design, or by a curved transverse frame as in Webb's design.

RADIUS ROD

A part of Walschaerts valve gear connecting the piston rod motion to the valve gear motion.

REGULATOR

Once the boiler has generated sufficient steam, it can be used for useful work.  A valve fitted on top of the boiler and often housed in a dome, is used by the driver to admit steam to the cylinders.  The valve is called "the regulator" (known as the "throttle" in the US) and is opened and closed by means of a long shaft connected to a lever accessed from the driver's position in the locomotive cab.

The steam collected in the dome can be admitted, by use of the regulator, into a steam pipe which is connected to the cylinders.  Some locomotives have superheated steam and in such cases the regulator may be located in the smokebox.

The regulator is controlled from the cab by a lever.  UK practice is to mount the lever on the top centre of the firebox backplate so that it is moved clockwise or anticlockwise to open or close the regulator valve.  The shaft connecting the lever to the regulator valve passes through the boiler steam space.

An alternative form of regulator control has the operating rods mounted on the outside of the boiler (along the left or right side) and actuated by a forward and aft lever in the cab. This type was popular in the US but was used on many of the more modern locomotives in the UK.  It should be noted that just because the operating rods are visible on one side of the boiler, it will not necessarily follow that the driving position is on that side.  Some locomotives have the driving position on the other side with the regulator handle connected to the operating rods by a cross shaft.  In some cases, regulator handles were provided on both sides of the cab.

REGULATOR VALVE

The main steam control of a locomotive.  Various types of valve and various locations for it were to be seen during the history of the locomotive but it was normally at the top of the boiler where the steam was hottest and usually in a dome.  Some superheated locomotives had the regulator valve positioned in the superheater header in the smokebox.  For details, see Regulator.

RETURN CRANK

On outside mounted Walschaerts valve gear, the small crank which works off the main crank to take the place of the eccentric used with inside mounted valve gear.

RETURN FLUE BOILER

A type of boiler used for some locomotives in the 1820s and 1830s where the single flue was turned back to provide double the heating surface for the water in the boiler.  It required the chimney to be at the same end of the boiler as the fire.  Superseded by the multi-tube boiler.

REVERSER

The locomotive's forward and reverse control, which is also used to adjust cut off to vary the steam admission and expansion cycles in the cylinders.

The direction of movement for a locomotive is decided when starting by determining which direction each piston must move first.  This is done by adjusting the position of the valve gear of each cylinder with a reverser so that the first admission of steam will force the piston in the right direction to achieve the desired direction of wheel rotation.

A lever or handwheel is provided in the cab to control the reverser.  It has three principle positions, Full Forward Gear, Mid Gear and Full Reverse Gear.  Mid Gear is equivalent to 'neutral' on a road vehicle.  There are also intermediate positions to adjust the 'cut off' point for steam admission to the cylinders.  An indicator is provided to show the driver the 'cut off' position and the reverser lever is fitted with a locking ratchet to hold it in the required position.  Reverser levers are usually purely mechanical devices and require some effort to operate effectively while the locomotive is running since the valve gear is under considerable pressure from steam. Some locomotives are fitted with steam operated reversers.

REVERSER, AIR

A power assisted reverser which used air pressure supplied from the air brake compressor. The device first appeared in 1882 on the London Brighton & South Coast Railway.

REVERSER, STEAM

A method for operating reversing gear using steam power first introduced by James Stirling in 1874.  Two cylinders, one steam and one oil and connected by a rod, were mounted outside the boiler.  Often they were fitted inside the cab or housed in an extension of the driving wheel splasher but, if free standing outside the boiler, they looked similar to and could be mistaken for a Westinghouse air brake pump.

The reverser is controlled by two levers in the cab.  To move the reverser, steam is admitted to one side or the other of a piston in the steam cylinder.  The piston moves the rod and thus varies the reverser rod position.  A separate valve controls the flow of oil in the second cylinder between the two sides of the piston.  When the position of the reverser is set by the steam cylinder, it is locked by the oil cylinder.  A pointer in the cab provides an indication of the position of the reverser.  Single lever controls were later provided for some versions of this and other types of power reverser.

Steam reversers were generally difficult to maintain and were prone to "wandering" off position due to the escape of steam or the leakage of air into the oil cylinder.  They often required a degree of "persuasion" or repeated operation to get the reverser set in the correct position.

ROCKING GRATE

A system for allowing the firebars to be shaken by use of controls in the cab, usually hand operated in the UK or steam operated elsewhere.  The purpose was to assist with fire cleaning and the break up and disposal of clinker.  Rocking grates were common in the US and areas where coal was poor and caused clinker but were rare in the UK until after the Second World War when the quality of coal had deteriorated.

ROSS POP SAFETY VALVE

A type of safety valve designed to act in two stages to prevent 'dribbling' of steam from a boiler at full pressure.  Designed by RL Ross in 1902 and later to become widely used in the UK.

RUNNING PLATE

The narrow horizontal walkway seen at roughly boiler base level on most steam locomotives, along which it was possible to access parts of the boiler and its attachments.  Also sometimes used to provide access to the motion.

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SADDLE TANK

A tank locomotive which has the water tank mounted on top of the boiler so that they take the form of a saddle.

SAFETY VALVE TYPES

Lock-up, Spring balance, Salter, Pop, Ross Pop are all types of safety valves.

SAFETY VALVES

Pressure relief valves mounted on top of a boiler or firebox (sometimes both on early locomotives) designed to allow steam to escape if the boiler pressure exceeded the design limit

SAND

Gravity fed sanding of rails ahead of driving wheels to assist traction was first tried in the US in 1836 and in the UK in 1838. Steam assisted sanding was introduced in 1886 in an attempt to overcome the problem of side winds blowing the sand away before the wheel passed over it.

SANDBOXES

In the UK, it was the practice to fit the sandboxes near the running plate, sometimes attached to the wheel splashers.  US practice was to add a sand dome to the top of the boiler, in an attempt to use the boiler heat to keep the sand dry.

SATURATED STEAM

Steam which has not been superheated.  Also known as 'wet steam'.

SCOOP, WATER

See Water Scoop.

SELF-CLEANING SMOKEBOX

A system for removing ash accumulated in the smokebox using the gases from the fire, first introduced in the UK during the Second World War. A baffle plate placed in front of the tube plate directed the gases down and forward to lift the ash towards a mesh screen.  The screen has the effect of breaking up larger pieces of ash so the flow of gases will expel them through the screen and out of the chimney.

Some earlier systems of smokebox cleaning used a manually controlled blower to lift the ash into the exhaust blast.

SETTING BACK

The act of reversing the locomotive gently into its train in order to reposition the engines (i.e.  the pistons in the cylinders) into a more favourable position for starting.  Although it is not theoretically possible to leave a locomotive in a position where the engines are unable to start, it can happen that certain starting positions will provide insufficient power to move a train.  The driver will therefore 'set back' to get a more favourable starting position.

SIGHT FEED LUBRICATOR

A locomotive lubricator system where a reservoir of oil mounted in the cab was equipped with glass fronted tube to allow the crew to observe that oil was available.

SINGLE FLUE BOILER

A boiler with only one tube, or flue between the fire at one end and the chimney at the other.  This was the type of boiler common before the introduction of the multi-tube boiler in 1829.

SINGLE

The common term to denote a locomotive with only one driving wheelset.  In the older versions, the driving wheel was often very large in proportion to the rest of the locomotive.  The design was common in the UK during the 19th Century.

SLIDE VALVE

The traditional valve system used in the steam engine to control the flow of steam into and out of a cylinder.  As the name suggests, the valve slides horizontally over the steam ports leading to the cylinder, opening and closing the ports as required to supply steam or exhaust it from the cylinder. Eventually replaced by the piston valve.

SLIDEBARS

A fixed pair of bars fitted at the rear of the cylinders to guide the crosshead on which the connecting rod is connected to the piston rod.  The crosshead slides forward and back between the slidebars.

SMALL TUBES

See Tubes, Boiler.

SMOKE DEFLECTORS

Early locomotives had tall chimneys to carry the exhaust clear of the driver's line of sight but, as boilers increased in size, the height of chimneys was reduced to keep locomotives within loading gauge requirements.  Smoke deflectors were added on either side of the smoke box of large-boilered locomotives to force air upwards towards the chimney and thus deflect smoke upwards and clear of the cab windows.  They were originally a German invention and became common from the 1930s onwards.

SMOKEBOX

The leading end of the boiler through which exhaust steam from the cylinders passes and gases from the fire are drawn to exit via the chimney.

SMOKEBOX DOOR

An opening at the front of the smokebox to allow access for the removal of ash drawn through the boiler tubes from the fire.  The door must be kept air tight to ensure that the maximum draught is available to allow air to be drawn through the fire from the grate.

SNIFTING VALVE

The common name for an anti-vacuum valve.

SPECTACLE PLATE

The transverse member mounted between the locomotive frames to the rear of the cylinders on which parts of the valve gear are hung.  Sometimes wrongly used to describe the weather board (q.v.) at the front of the cab.

STAYS

The bolts which secure the inner firebox to the outer firebox. See firebox.

STEAM

Steam is the gas which is given off as a result of boiling water.  The normal boiling point of water is 100º C. Unconfined steam will expand to about 1325 times the size of the water from which it came.  If it is confined, it will build up pressure which can be harnessed to do work.

Incidentally, it is worth noting that pure steam is actually invisible.  The vapour associated with steam which we normally see is really small droplets of water which occur as a result of condensation.

The work which can be extracted from steam is achieved by allowing the natural expansion of the steam as it cools.  If the steam is carried away from the source of heat which produced it, it will cool and expand.  This expansion can be used to do work, like pushing a piston inside a cylinder.

Steam pressure can also be used to do work as well as expansion.  The steam collected by boiling water in a boiler can be contained in the space above the water level while its pressure is increased as more and more water is boiled. Eventually, the pressure reaches the safe working level of the boiler.  Spring-loaded safety valves are provided to allow steam to escape if the pressure rises above the normal working level.

If you see safety valves "blowing off" steam, you will notice that the steam is actually invisible for a short distance above the valve.  Only when it has cooled and expanded will the familiar white plume become clearly visible.  During blowing off, the nature of expansion can also be seen as the plume of steam widens the further away from the boiler it goes.

In a steam locomotive, both steam pressure and expansion are used inside cylinders to do the work of moving the machine.  Both can be varied by the driver to regulate the power used by the locomotive under the varying circumstances of train operation.

STEAM BRAKE

First used by Stephenson in 1833 on his Patentee locomotive and tried in the US in 1848 on the Boston and Providence RR. Later widely used both separately and in conjunction with automatic brakes, either vacuum or air.  The steam brake can be operated by either a separate brake valve in the cab or a combined automatic and loco.  brake valve.  For more information on train brakes, see our Brakes Page.

STEAM CHEST

The internal part of a locomotive's cylinder block where the valve chamber connects with the steam supply and exhaust pipes.

STEAM PIPE

The pipe which connects the regulator valve with the cylinder steam chest where the valves are located.  Steam passes down this pipe when the regulator valve is opened by the driver. In superheated locomotives, the steam is diverted into the superheater header before it reaches the steam chest.

STEAM REVERSER

See Reverser, Steam.

STEAM TENDER

A design of tender which had its own engines introduced in 1863 by Archibald Sturrock on the Great Northern Railway of the UK.  Two cylinders were mounted inside the tender frames and drove six coupled wheels.  The steam was supplied by the locomotive boiler and was exhausted into the tender tank to heat the water. About 50 were built but they were not considered economic and were later removed.  Not to be confused with 'boosters' (q.v.).

STEAM TURRET

See Turret, Steam.

STEPHENSON VALVE GEAR

See Link Valve Gear.

STROKE, PISTON

The length of the movement of the piston inside the cylinder and often quoted as an essential dimension of a locomotive's design.

SUPERHEATED STEAM

Steam which has been reheated or 'dried' after its production in the boiler.  Superheated steam has less water vapour and will therefore not condense as rapidly as 'wet' or saturated steam.  It can lead to a 25% saving in coal and 30% saving of water consumption.

SUPERHEATER

Equipment provided in a locomotive boiler for producing superheated steam.  Early superheaters were fitted in the smokebox and were little more than steam dryers.  Later superheaters used enlarged boiler tubes to dry the steam and raise the temperature to a higher level.  The first superheaters, designed by Wilhelm Schmidt in Germany, appeared in 1897.  The additional efficiency of the drier steam led to superheaters becoming standard equipment.

SUPERHEATER ELEMENTS

The coils of pipes provided inside the larger flue tubes of the boiler through which saturated steam from the boiler passes to enable its temperature to be raised.

SUPERHEATER HEADER

The connection box mounted in the smokebox next to the tube plate which contains the incoming saturated steam pipe and the tubes for superheating the steam.  Some designs of superheater header contained the regulator valve.

SUPERHEATER TUBES

See Superheater Elements.

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TAIL RODS

Extensions to the piston rods which protruded through the front of the cylinders so fitted.  Tried from time to time during the 1890s and early 1900s, fitting tail rods was said either to save wear on cylinders or to cause it, depending on who was speaking.  They were not taken up universally and many locos which had them when built were later modified to remove them.

TANK LOCOMOTIVE

A steam locomotive which has its coal and water storage on the same frames as the engine.  The design first appeared in 1835 in Ireland.  The water tanks are the most obvious feature as they are mounted on either side of the boiler partially obscuring it.  There are different types of tank engine, side tanks are the most common - see also Pannier Tank and Saddle Tank.  Well tank locomotives, where the tank is hung under the frames, were less common.

TAPERED BOILER

A boiler design where the diameter at the smokebox end is smaller than at the firebox end.  This was done so that the maximum area possible was available for heating around the firebox.  A tapered boiler was first introduced in the US in 1850, where it was referred to as the 'wagon top' boiler.

The design has the added advantage that the joints between the boiler rings do not require to be formed to provide a lap, but they will provide a natural lap.

TENDER

The vehicle attached to a locomotive carrying water and coal (or other fuel).  Some locomotives do not have tenders - see Tank Locomotive.  The name 'Tender Locomotive' is sometime used to distinguish it from a tank locomotive.

TENDER BRAKE

The only means by which early locomotives were stopped.  A hand wheel or lever on the tender was connected to brake blocks acting on the tender wheels.

TESTING PLANT, STATIC LOCOMOTIVE

There were six special steam locomotive static testing stations built in the world: Altoona, Pennsylvania, USA in 1904, Swindon, UK in 1905, Purdue University USA, Grunewald, Berlin, Germany 1931, Vitry, Paris in 1933 and Rugby, UK in 1948.

THERMIC SYPHON

A water passage built into a firebox in a Y shape so that the base of the Y is turned forward to connect with the water space at the front of the firebox and the two arms open into the crown space.  The purpose was to improve water circulation and its exposure to the hottest heating areas around and in the firebox.  First appeared in the 1930s but not used in the UK until 1940 when they were adopted for the Southern Railway 4-6-2 locomotive classes and the abortive "Leader" designed by O.V.  Bullied.  Popular in the US and France but very complicated to build and maintain in good condition.

THROAT PLATE

The portion of the firebox which joins the boiler barrel.  This is a difficult section to form as it is often of an unusual shape to accommodate the change from a circular barrel to a more rectangular and deeper firebox.

TOP FEED

A system of boiler replenishment, first tried in 1863 and occasionally from that time until Churchward of the GWR adopted it in 1906, where the feed water is passed through pipes to the top of the boiler where the non-return valves (clacks) are mounted and then into the steam space.  The water is deposited onto a tray (or series of trays) before it strikes the water surface.  The effect is to disperse the water before it mixes with the existing water in the boiler and it was said to reduce boiler maintenance although it was never conclusively proved.  It became standard in the UK on most new locomotives from the 1930s.

TRACK PAN

US term for water trough.

TRACTIVE EFFORT

The force exerted at the edge of the driving wheel of a locomotive expressed in pounds.

Calculated as: TE = (d² *n *s *(0.85 *p))/2*D,

where d = piston diameter (ins.), n = number of cylinders, p = boiler pressure (lb.), s = piston stroke (ins.), D = driving wheel diameter (ins) and P is 85% of boiler pressure (psi).

TUBE CLEANING

The removal of soot and ash from the inside of boiler tubes to ensure the effective generation of the draught for the fire.  Was often done with steam lances, latterly with compressed air and accompanied by brushing as required.

During the 1930s some UK locomotives were fitted with steam operated tube-cleaning guns, sometimes referred to as anti-carbonisers.  It was possible to direct sand, under steam pressure, to any part of the rear tube plate from a lever in the cab.

TUBE PLATES

The plates at the leading and rear ends of a boiler which were drilled with holes of the diameter required to hold the boiler tubes.  The leading tube plate separated the boiler from the smokebox, while the rear tube plate formed the front of the inner firebox.

TUBES, BOILER

The flues through which the gases from the fire pass to heat the water in the boiler.  The gas is drawn through the tubes by the draught created from the exhaust of the steam through the chimney.  Tube sizes are often quoted for locomotives because they are an indication of the heating surfaces available for the manufacture of steam.  More modern designs of boiler have two sizes of tubes, large tubes for the superheater elements and small tubes for normal water heating purposes.

TURNTABLE

Rotating section of track used to turn locomotives to face the direction of running required.  Originally hand operated, they could later be found to be steam, air or vacuum operated.

TURRET, STEAM

The US term for the steam manifold.

TYRE

The steel ring shrunk (or otherwise fixed) to a railway wheel to provide the bearing surface which will run on the rail.  The tyre is usually provided with a flange to give the guidance required to keep the wheels on the rail.  Some locomotive driving wheels did not have a flange because of the need to allow movement round severe curves without the risk of the flange riding up onto the top of the rail and derailing the locomotive.

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UNIFLOW LOCOMOTIVE

An experimental locomotive which worked on the South Eastern Railway between 1849 and 1852 using a large, externally piped exhaust system.  It did not find acceptance and was not used elsewhere.

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VACUUM BRAKE

The brake system which uses a vacuum formed in the brake pipe and cylinders to effect a brake release and the replacement of the vacuum by atmospheric pressure to cause an application.  The automatic vacuum brake was first used in the UK in 1878.  See more details in our Brake Pages.

VACUUM TURNTABLE

A turntable operated by vacuum power provided by the locomotive being turned.

VALANCE

The angled plate attached to the edge of a locomotive running plate to provide strength.

VALVE GEAR

The system of rods, levers, cranks and eccentrics which provide the links between the pistons, valves and wheels of a steam engine.  The two main parts consisted of the piston rod, connecting rod and crank which transmitted the drive from the piston to the wheel and the eccentrics, eccentric rods and valve rods which transmit motion from the axle to the valve.  For excellent live working programme see Valve Gear for the Computer.

VALVE SETTING

The action of fitting and adjusting the locomotive valve gear to ensure the most efficient operation of the valves.  This was a difficult job to do well and required skilled fitters with a thorough knowledge of the equipment in their care.  Many experimental valve gears introduced during the years of steam locomotive development failed to gain acceptance because the fitters working on them in sheds did not understand them properly.

VON BORRIES COMPOUND

A system of compounding where the low and high pressure cylinders drove the same axles requiring that the valve gear be adjusted to ensure that the same level of work was done in both cylinders at the same time.  It was used by TW Worsdell in 1884 on the Great Eastern Railway and later on the North Eastern Railway and by Beyer Peacock for some locomotives built by them in the 1890s.

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WALSCHAERTS VALVE GEAR

A form of link motion valve gear first patented in 1844 by Egged Walschaerts, a Belgian engineer.  It first appeared on a British railway in 1878 when an 0-4-4 tank locomotive fitted with it was purchased by the Swindon, Marlborough and Andover Railway.  It did not become popular in Britain until the twentieth century but it is now generally regarded as the best valve gear design, being easier to maintain and lighter than Stephenson valve gear.  It first appeared in the US in 1876 and was also widely adopted there and on the continent of Europe.

WASHOUT

The process of removing sludge and scale from the inside of a locomotive boiler.  The boiler was first emptied of steam and the hot water drained off.  Water was then hosed into the boiler through 'washout plugs' while long rods were inserted into the plug holes to remove scale from the interior surfaces.  After cleaning, the boiler was inspected for defects.  Washouts used to be needed on a weekly basis for many locomotives but varied according to the age of the locomotive, the design of the boiler, its usage and the type of water used.

WASHOUT PLUGS

In order to allow all the parts of the boiler interior to be reached during a washout, a number of plugs were provided in strategic positions.  They were screwed into the boiler shell and were often numbered to ensure that they are replaced in the correct positions.  Washout plugs were also useful for inspection purposes.  A modern locomotive may have had over 40 washout plugs located around the boiler and firebox.

WATER COLUMN

A hollow pole fitted with a leather hose and connected to a water supply for filling locomotive water tanks.

WATER CRANE

A type of water column with a movable arm which allows water to be supplied to locomotives on either of two adjacent tracks.

WATER GAUGE

Also referred to as "water glass" in the US.  The indication provided in every locomotive cab showing the level of water in the boiler.  Always provided in pairs, the water gauges were considered the most important part cab equipment.  Cocks were provided at the top and bottom of the gauges to test the connections above and below the boiler water level and thus ensure accuracy of indications.

WATER SOFTENING

The addition of chemicals to hard water to reduce the scale generated when boiled.  Widely used in the UK.

WATER SCOOP

A device, first used on locomotives of the LNWR in the UK in 1860 to allow water to be collected from a water trough laid along the track whilst the train was moving.  The scoop was mounted on the tender and was lowered by hand when required to collect water.

It was essential that the crew raised the scoop before the end of the trough or before the tender was filled to capacity and water spilled through the vent at the tender top.  If it did, the leading vehicle would be showered with the excess water and, if there were any open windows, so would the unsuspecting passengers inside.

WATER TROUGH

A channel laid between the running rails and filled with water, which can be collected by passing locomotives fitted with a water scoop.  Water troughs were first introduced in the UK in 1860 and in the US in 1870, where they are known as 'Track Pans'.

WATER TUBES

A system which tried to improve the circulation of water between the legs of the firebox by joining them with tubes running across the firebox.  The best-known UK example was applied by Drummond on some London & South Western Railway locomotives between 1897 and 1912.  The expense of maintaining them outweighed the benefits and they were not universally adopted.

WEATHER BOARD

A vertical sheet added to the rear of the firebox and fitted with two glass portholes to provide some protection for the locomotive crew.  They first began to appear in the 1850s.

WEDGE VALVE GEAR

A type of valve gear designed by Isaac Dodds, dating from 1839 and used occasionally until 1872, which had two eccentrics on a two-cylinder locomotive instead of four.  The single eccentric for each cylinder was changed from forward to reverse by drawing a wedge along a square section of the axle through the sheave to adjust its eccentricity.  The design failed because of the difficulty of keeping the wedges properly adjusted.

WESTINGHOUSE BRAKE

Air brake system first invented by George Westinghouse in 1869.  It comprised an air pump powered by steam, which provided the air pressure used in the brake cylinders.  An automatic version was patented in 1872.  This had a brake pipe running the length of the train which was filled with compressed air to release the brakes and to recharge air reservoirs on each vehicle.  To apply the brake, the air in the brake pipe was reduced and a 'triple valve' on each vehicle caused air in the reservoir to pass into the brake cylinder and apply the brakes. The system formed the basis of all future railway automatic air brake types.

Due partly to its cost, the Westinghouse brake was not favoured in the UK, only a few companies adopting it, but it, and its derivatives, became universal in the US.  See more details in our Brake Pages.

WET STEAM

The generic term for steam produced in a boiler and collected in the steam space above the water level.  It still contains an amount of water vapour which will quickly condense as the steam enters a cold cylinder.  Wet steam can be dried by 'superheating' (q.v.).

WHEEL BALANCING

The method of reducing the hammer blow caused by the action of the pistons driving the cranks as the crank approaches bottom dead centre.  Driving wheels had weights fitted into their rims to act as a counter balance.

WHISTLE

First fitted to a locomotive of the Leicester & Swannington Railway in 1833 following an accident at Thornton when a train hit a horse and cart.  Whistles soon became important for transmitting warnings to signalmen describing train routes at junctions and to guards to signal for brakes etc.  Most railways proscribed a series of codes for whistles.

WHITE FEATHER

Nickname for the steam seen escaping for the safety valves when there is full pressure in the boiler.

WHEEL ARRANGEMENT SYSTEMS

Different systems for denoting wheel arrangements have been developed in different countries.  In the US and UK is usual to refer to a steam locomotive wheel layout numerically by first the leading carrying wheels, then the coupled wheels (including the driving wheels) and finally the trailing carrying wheels, in that order, in a system invented by Frederic M Whyte in the US in 1900 e.g.

4-4-0 = ooOO

4-6-2 = ooOOOo

0-4-2 = OOo

0-6-0 = OOO

2-10-2 = oOOOOOo

A list of US wheel arrangements is available here on the Wes Barris US Steam locomotive site.

Some European railways used the Whyte system except that the number of axles was used instead of the number of wheels, 4-6-2 becoming 231.  This was developed by the French who used numbers for non driven axles and letters for driven axles, thus 2C1 and which was further modified by Bullied who reorganised it so that the non-driven axles were listed first in order, then the driven axles, thus 21C.

WHYTE WHEEL NOTATION

See 'Wheel Arrangement Systems'.   For a list of types and their nicknames, see the Steam Locomotive Wheel Arrangements page on this site.

WOOTEN FIREBOX

Developed to allow locomotives to burn anthracite.


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