Tank locomotive
Encyclopedia
A tank locomotive or tank engine is a steam locomotive
that carries its water in one or more on-board water tanks
, instead of pulling it behind it in a tender. It will most likely also have some kind of bunker (or oil tank) to hold the fuel. There are several different types of tank locomotive dependent upon the position and style of the water tanks and fuel bunkers. The most common type has tanks mounted either side of the boiler. This type originated about 1840 and quickly became popular for industrial tasks, and later for shunting and shorter distance main line
duties. Tank locomotives have advantages and disadvantages compared to traditional tender locomotive
s.
which ran at the Rainhill Trials in 1829, which was an example of a Well Tank. However, the more common form of Side tank date from the 1840s; one of the first of which was supplied by George England
and Co. of New Cross
to the contractors building the Newhaven, Sussex branch line for the London Brighton and South Coast Railway in 1848. In spite of the early belief that such locomotives were inherently unsafe, the idea quickly caught on, particularly for industrial use and five manufacturers exhibited designs at The Great Exhibition
in 1851. These were E. B. Wilson and Company
, William Fairbairn & Sons
, George England, Kitson Thompson and Hewitson
and William Bridges Adams
. By the mid 1850s tank locomotives were to be found performing a variety of main line
and industrial roles, particularly those involving shorter journeys or frequent changes in direction.
, and also common in Belgium, involved box-shaped tanks carried on the sides of the boiler. Unlike the side tank, they did not go all the way down and there was space between the tank and the running plate. The pannier arrangement lowered the centre of gravity compared to a saddle tank, whilst still allowing the easy access to the inside motion that the latter gave. The first GWR Great Western pannier tanks
were actually converted from saddle tank locomotives when these were being rebuilt in the early 1900s with the Belpaire firebox
. There were difficulties in accommodating the flat top of the latter within an encircling saddle tank which cut down capacity and increased the tendency to overheat the water in the tank. In Belgium, pannier tanks had been in use at least since 1866, once again in conjunction with Belpaire firebox locomotives built for the Belgian State and for la Société Générale d'Exploitatation (SGE), a private company grouping smaller secondary lines.
In this design, used in earlier and smaller locomotives, the water is stored in a 'well' on the underside of the locomotive, generally between the locomotive's frames. This does not restrict access to the boiler, but space is limited there, and the design is therefore not suitable for locomotives that need a good usable range before refilling. The arrangement does, however, have the advantage of creating a low centre of gravity, creating greater stability on poorly laid or narrow gauge
tracks. The original tank locomotive, Novelty
was a well tank.
In this design, the tank is placed behind the cab, usually over a supporting bogie. This removes the weight of the water from the driving wheels, giving the locomotive a constant tractive weight. The disadvantage is a reduction in water carrying capacity. A rear tank is an essential component of the American Forney
type of loco.
Excelsior which has been described, by various sources, as both a wing tank and an inverted saddle tank.
locomotive Wotton is believed to have had an inverted saddle tank. The inverted saddle tank seems to have been a speciality of W.G.Bagnall.
Large side tank engines might also have an additional rear tank (under the coal bunker), or a well tank (between the frames). This may have been to increase the water capacity, to equalise the weight distribution, or else improve the stability by lowering the centre of gravity.
A tank locomotive may also haul a tender behind it. This is usually found on narrow gauge
railways where the small size of the locomotive restricts the space available for fuel and water. Where a tender was used it usually carried only fuel with the locomotive's water tanks remaining in place. The tender offered greater fuel capacity than a bunker on the locomotive and often the water capacity could be increased by converting redundant bunker space into a water tank.
, the matching tank engine would be described as an 0-6-0T for a plain tank, an 0-6-0ST for a saddle tank, and so on ('PT' indicating a pannier tank, 'WT' a well tank, and 'CT' a crane tank).
Because tank locomotives are capable of running equally fast in both directions (see below) they usually have symmetrical wheel arrangements to ensure the same ride and stability characteristics regardless of the direction travelled, producing arrangements with only driving wheels (0-4-0T and 0-6-0T
) or equal numbers of leading and trailing wheels (2-4-2T
, 4-6-4T
etc.). However other requirements, such as the need to support a large bunker, would require a non-symmetrical layout such as 2-6-4T
.
Exceptionally, when many of the surplus New South Wales 30 class locomotive were converted from tank engines to tender engines, the tender engines were described as 30T class.
On a tank locomotive the fuel (most often coal) is carried in a bunker the location of which can vary. On a locomotive with a trailing carrying axle or a trailing bogie
the bunker is generally situated to the rear of the cab, but in cases where the firebox overhangs the rear driving axle, it has been common practice to situate the bunker on top of and to one side of the firebox; this concentrates the weight and stabilises the locomotive.
which carry their own fuel but which are usually categorised for different reasons.
A Garratt
type of locomotive is articulated
in three parts. The boiler
is mounted on the centre frame, and two steam engines are mounted on separate frames, one on each end of the boiler. Articulation is used so larger locomotives can go round curves which would otherwise restrict the size of rigid framed locomotives. One of the major advantages of the Garratt form of articulation is the maintenance of the locomotive's centre-of-gravity over or inside the track centre-line when rounding curves. Some other forms of articulation, notably the Mallet
, tend to move the centre-of-gravity outside the centre-line on tight curves, leading to problems with traction and stability.
A Crane tank (CT) is a steam tank locomotive with a crane fitted to it, thereby creating a small mobile crane for working in railway workshops or other industrial environments. The crane may be fitted at the front, centre or rear of the locomotive and gives it a rather "top heavy" appearance.
contractor
firms engaged in the building of railways. The locomotives would be used for hauling men, equipment and building materials over temporary railway networks built at the worksite that were frequently re-laid or taken up and moved elsewhere as building work progressed. Contractor's locomotives were usually saddle or well tank types (see above) but required several adaptations to make them suitable for their task. They were built to be as light as possible so they could run over the lightly built temporary rails and had deeply flanged wheels so they did not de-rail on the tracks which were often very uneven. At the same time they had to be very powerful with good traction as they would often have to haul trains of wagons up very steep gradients, such as the sides of railway embankment
s or spoil heaps. Many were designed so that large iron ballast blocks could be fitted to the frames when extra weight and traction was required, then removed when it was not. Most had sanding gear fitted to all wheels for maximum traction. Some method of keeping mud and dust from clogging the wheels and brake shoes was also required – this either took the form of scraper bars fitted to the leading edge of the wheels or wheel washer jets supplied from the water tank. To handle long trains of loose-coupled (and often un-sprung) wagons, contractor's locomotives usually had very effective steam-powered brakes. Most lacked a full cab, often only having a front 'spectacle plate'. If a cab was provided it was usually removable along with the chimney, and sometimes the dome, so that the locomotive could be loaded onto a flatbed wagon for transport to new locations by rail whilst remaining within the loading gauge
.
. The reservoir is filled from an external source of steam. Some types of fireless locomotives are "fuelled" by pressurized air, rather than steam.
The benefits of tank locomotives include:
There are corresponding disadvantages:
They were very common in the United Kingdom
, France
, and in particular Germany
where examples of large tank locomotives were built. In the United States
they tended to be restricted to push-pull
suburban service, always the tank engine's forte, and also for switching service
in terminals and locomotive shops. They were also popular in logging, mining and industrial service.
Tank locomotives are popular with heritage railway
s for a number of reasons. They are usually cheaper to purchase than a tender locomotive
due to their smaller size. This is also an advantage when working out the cost of transportation
to the heritage line, many of which are isolated from the national rail
network.
Most heritage railways only have short lines
and do not often have turntable
s at both ends of the line. A tank locomotive has good visibility for the driver in both directions. As the trains being hauled are usually light the tank locomotive is more fuel efficient
than a large tender locomotive.
Add to this the lower cost of maintaining the engine and the lower amount of wear and tear on the track. Another fact to consider is that many tank locomotives were bought from former industrial railways rather than the national network. Due to the higher availability it would be easier to secure a suitable locomotive for a reasonable price.
Steam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...
that carries its water in one or more on-board water tanks
Storage tank
A storage tank is a container, usually for holding liquids, sometimes for compressed gases . The term can be used for reservoirs , and for manufactured containers. The usage of the word tank for reservoirs is common or universal in Indian English, American English and moderately common in British...
, instead of pulling it behind it in a tender. It will most likely also have some kind of bunker (or oil tank) to hold the fuel. There are several different types of tank locomotive dependent upon the position and style of the water tanks and fuel bunkers. The most common type has tanks mounted either side of the boiler. This type originated about 1840 and quickly became popular for industrial tasks, and later for shunting and shorter distance main line
Main line (railway)
The Mainline or Main line of a railway is a track that is used for through trains or is the principal artery of the system from which branch lines, yards, sidings and spurs are connected....
duties. Tank locomotives have advantages and disadvantages compared to traditional tender locomotive
Tender locomotive
A tender or coal-car is a special rail vehicle hauled by a steam locomotive containing the locomotive's fuel and water. Steam locomotives consume large quantities of water compared to the quantity of fuel, so tenders are necessary to keep the locomotive running over long distances. A locomotive...
s.
Origins
The first tank locomotive was the NoveltyNovelty (locomotive)
Novelty was an early steam locomotive built by John Ericsson and John Braithwaite to take part in the Rainhill Trials in 1829.It was an 0-2-2WT locomotive and is now regarded as the very first tank engine. It had a unique design of boiler and a number of other novel design features...
which ran at the Rainhill Trials in 1829, which was an example of a Well Tank. However, the more common form of Side tank date from the 1840s; one of the first of which was supplied by George England
George England
George England and Co. was an early English manufacturer of steam locomotives founded by the engineer George England of Newcastle upon Tyne...
and Co. of New Cross
New Cross
New Cross is a district and ward of the London Borough of Lewisham, England. It is situated 4 miles south-east of Charing Cross. The ward covered by London post town and the SE 14 postcode district. New Cross is near St Johns, Telegraph Hill, Nunhead, Peckham, Brockley, Deptford and Greenwich...
to the contractors building the Newhaven, Sussex branch line for the London Brighton and South Coast Railway in 1848. In spite of the early belief that such locomotives were inherently unsafe, the idea quickly caught on, particularly for industrial use and five manufacturers exhibited designs at The Great Exhibition
The Great Exhibition
The Great Exhibition of the Works of Industry of all Nations or The Great Exhibition, sometimes referred to as the Crystal Palace Exhibition in reference to the temporary structure in which it was held, was an international exhibition that took place in Hyde Park, London, from 1 May to 15 October...
in 1851. These were E. B. Wilson and Company
E. B. Wilson and Company
E.B.Wilson and Company was a locomotive manufacturing company at the Railway Foundry in Hunslet, Leeds, West Yorkshire, England.-Origins:When Todd left Todd, Kitson & Laird in 1838, he joined Shepherd in setting up the Railway Foundry as Shepherd and Todd...
, William Fairbairn & Sons
William Fairbairn & Sons
William Fairbairn and Sons, was an engineering works in Manchester, England.-History:William Fairbairn opened an iron foundry in 1816 and was joined the following year by a Mr. Lillie, and the firm became known as Fairbairn and Lillie Engine Makers, producing iron steamboats.Their foundry and...
, George England, Kitson Thompson and Hewitson
Kitson & Co.
Kitson and Company was a locomotive manufacturer based in Hunslet, Leeds, West Yorkshire, England.-Early history:The company started as James Kitson at the Airedale Foundry, off Pearson Street, Hunslet in 1835 with Charles Todd as a partner...
and William Bridges Adams
William Bridges Adams
William Bridges Adams was an author, inventor and locomotive engineer.-Overview:He is best known for his patented Adams Axle — a successful radial axle design in use on railways in Britain until the end of steam traction in 1968 — and the railway fishplate...
. By the mid 1850s tank locomotives were to be found performing a variety of main line
Main line (railway)
The Mainline or Main line of a railway is a track that is used for through trains or is the principal artery of the system from which branch lines, yards, sidings and spurs are connected....
and industrial roles, particularly those involving shorter journeys or frequent changes in direction.
Types of locomotive
There are a number of types of locomotive, based on the location and style of the water tanks. These include the side tank, the saddle tank, the pannier tank, the well tank and others.Side tank
Saddle tank
Pannier tank
Pannier tanks, in Britain used almost exclusively by the Great Western RailwayGreat Western Railway
The Great Western Railway was a British railway company that linked London with the south-west and west of England and most of Wales. It was founded in 1833, received its enabling Act of Parliament in 1835 and ran its first trains in 1838...
, and also common in Belgium, involved box-shaped tanks carried on the sides of the boiler. Unlike the side tank, they did not go all the way down and there was space between the tank and the running plate. The pannier arrangement lowered the centre of gravity compared to a saddle tank, whilst still allowing the easy access to the inside motion that the latter gave. The first GWR Great Western pannier tanks
0-6-0PT
The GWR 0-6-0PT , is a type of steam locomotive built by the Great Western Railway with the water tanks carried on both sides of the boiler, in the manner of panniers. They were used for local, suburban and branch line passenger and goods traffic, for shunting duties, and as banker engines on...
were actually converted from saddle tank locomotives when these were being rebuilt in the early 1900s with the Belpaire firebox
Belpaire firebox
The Belpaire firebox is a type of firebox used on steam locomotives. It was invented by Alfred Belpaire of Belgium. It has a greater surface area at the top of the firebox, improving heat transfer and steam production...
. There were difficulties in accommodating the flat top of the latter within an encircling saddle tank which cut down capacity and increased the tendency to overheat the water in the tank. In Belgium, pannier tanks had been in use at least since 1866, once again in conjunction with Belpaire firebox locomotives built for the Belgian State and for la Société Générale d'Exploitatation (SGE), a private company grouping smaller secondary lines.
Well tank
Narrow gauge
A narrow gauge railway is a railway that has a track gauge narrower than the of standard gauge railways. Most existing narrow gauge railways have gauges of between and .- Overview :...
tracks. The original tank locomotive, Novelty
Novelty (locomotive)
Novelty was an early steam locomotive built by John Ericsson and John Braithwaite to take part in the Rainhill Trials in 1829.It was an 0-2-2WT locomotive and is now regarded as the very first tank engine. It had a unique design of boiler and a number of other novel design features...
was a well tank.
Rear tank (or Back tank)
Forney locomotive
The Forney is a type of tank locomotive patented by Matthias N. Forney between 1861 and 1864. Forney locomotives include the following characteristics:* An 0-4-4T wheel arrangement, that is four driving wheels followed by a truck with four wheels....
type of loco.
Wing tank
Wing tanks are side tanks that run the length of the smokebox, instead of the full length of the boiler. They were mainly used on narrow gauge industrial locomotives that could be frequently re-filled with water and where side or saddle tanks would restrict access to inside valve gear. See Kerry TramwayKerry Tramway
The Kerry Tramway was a gauge narrow gauge railway built in 1887 to serve the timber workings and slab quarry to the south of the village of Kerry, near Newtown in mid Wales....
Excelsior which has been described, by various sources, as both a wing tank and an inverted saddle tank.
Inverted saddle tank
The inverted saddle tank was a variation of the Wing Tank where the two tanks were joined underneath the smokebox and supported it. This rare design was used for the same reasons as the wing tank but provided slightly greater water capacity. The Brill TramwayBrill Tramway
The Brill Tramway, also known as the Quainton Tramway, Wotton Tramway, Oxford & Aylesbury Tramroad and Metropolitan Railway Brill Branch, was a six-mile rail line in the Aylesbury Vale, Buckinghamshire, England...
locomotive Wotton is believed to have had an inverted saddle tank. The inverted saddle tank seems to have been a speciality of W.G.Bagnall.
Combinations
A tank locomotive may also haul a tender behind it. This is usually found on narrow gauge
Narrow gauge
A narrow gauge railway is a railway that has a track gauge narrower than the of standard gauge railways. Most existing narrow gauge railways have gauges of between and .- Overview :...
railways where the small size of the locomotive restricts the space available for fuel and water. Where a tender was used it usually carried only fuel with the locomotive's water tanks remaining in place. The tender offered greater fuel capacity than a bunker on the locomotive and often the water capacity could be increased by converting redundant bunker space into a water tank.
Wheel arrangement
While a tender engine might be described as an 0-6-00-6-0
Under the Whyte notation for the classification of steam locomotives, 0-6-0 represents the wheel arrangement of no leading wheels, six powered and coupled driving wheels on three axles, and no trailing wheels...
, the matching tank engine would be described as an 0-6-0T for a plain tank, an 0-6-0ST for a saddle tank, and so on ('PT' indicating a pannier tank, 'WT' a well tank, and 'CT' a crane tank).
Because tank locomotives are capable of running equally fast in both directions (see below) they usually have symmetrical wheel arrangements to ensure the same ride and stability characteristics regardless of the direction travelled, producing arrangements with only driving wheels (0-4-0T and 0-6-0T
0-6-0
Under the Whyte notation for the classification of steam locomotives, 0-6-0 represents the wheel arrangement of no leading wheels, six powered and coupled driving wheels on three axles, and no trailing wheels...
) or equal numbers of leading and trailing wheels (2-4-2T
2-4-2
Under the Whyte notation for the classification of steam locomotives, 2-4-2 represents the wheel arrangement of two leading wheels on one axle, four powered and coupled driving wheels on two axles, and two trailing wheels on one axle...
, 4-6-4T
4-6-4
Under the Whyte notation for the classification of steam locomotives, 4-6-4 represents the wheel arrangement of four leading wheels on two axles , six powered and coupled driving wheels on three axles, and four trailing wheels on two axles .Other equivalent classifications are:UIC classification:...
etc.). However other requirements, such as the need to support a large bunker, would require a non-symmetrical layout such as 2-6-4T
2-6-4
Under the Whyte notation for the classification of steam locomotives, a 2-6-4 locomotive has two leading wheels, six coupled driving wheels and four trailing wheels...
.
Exceptionally, when many of the surplus New South Wales 30 class locomotive were converted from tank engines to tender engines, the tender engines were described as 30T class.
Fuel bunker
Bogie
A bogie is a wheeled wagon or trolley. In mechanics terms, a bogie is a chassis or framework carrying wheels, attached to a vehicle. It can be fixed in place, as on a cargo truck, mounted on a swivel, as on a railway carriage/car or locomotive, or sprung as in the suspension of a caterpillar...
the bunker is generally situated to the rear of the cab, but in cases where the firebox overhangs the rear driving axle, it has been common practice to situate the bunker on top of and to one side of the firebox; this concentrates the weight and stabilises the locomotive.
Other types of tank locomotive
There are several other specialised types of steam locomotiveSteam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...
which carry their own fuel but which are usually categorised for different reasons.
Garratt locomotive
- Main article GarrattGarrattA Garratt is a type of steam locomotive that is articulated in three parts. Its boiler is mounted on the centre frame, and two steam engines are mounted on separate frames, one on each end of the boiler. Articulation permits larger locomotives to negotiate curves and lighter rails that might...
A Garratt
Garratt
A Garratt is a type of steam locomotive that is articulated in three parts. Its boiler is mounted on the centre frame, and two steam engines are mounted on separate frames, one on each end of the boiler. Articulation permits larger locomotives to negotiate curves and lighter rails that might...
type of locomotive is articulated
Articulated locomotive
Articulated locomotive usually means a steam locomotive with one or more engine units which can move independent of the main frame. This is done to allow a longer locomotive to negotiate tighter curves...
in three parts. The boiler
Boiler
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...
is mounted on the centre frame, and two steam engines are mounted on separate frames, one on each end of the boiler. Articulation is used so larger locomotives can go round curves which would otherwise restrict the size of rigid framed locomotives. One of the major advantages of the Garratt form of articulation is the maintenance of the locomotive's centre-of-gravity over or inside the track centre-line when rounding curves. Some other forms of articulation, notably the Mallet
Mallet locomotive
The Mallet Locomotive is a type of articulated locomotive, invented by a Swiss engineer named Anatole Mallet ....
, tend to move the centre-of-gravity outside the centre-line on tight curves, leading to problems with traction and stability.
Crane tank
- Main article Crane tankCrane tankA crane tank is a steam locomotive with a crane fitted to it. The crane may be fitted at the front, centre or rear of the locomotive and gives it a rather "top heavy" appearance...
A Crane tank (CT) is a steam tank locomotive with a crane fitted to it, thereby creating a small mobile crane for working in railway workshops or other industrial environments. The crane may be fitted at the front, centre or rear of the locomotive and gives it a rather "top heavy" appearance.
Contractor's locomotive
The contractor's locomotive was a small tank locomotive specially adapted for use by civil engineeringCivil engineering
Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including works like roads, bridges, canals, dams, and buildings...
contractor
General contractor
A general contractor is responsible for the day-to-day oversight of a construction site, management of vendors and trades, and communication of information to involved parties throughout the course of a building project.-Description:...
firms engaged in the building of railways. The locomotives would be used for hauling men, equipment and building materials over temporary railway networks built at the worksite that were frequently re-laid or taken up and moved elsewhere as building work progressed. Contractor's locomotives were usually saddle or well tank types (see above) but required several adaptations to make them suitable for their task. They were built to be as light as possible so they could run over the lightly built temporary rails and had deeply flanged wheels so they did not de-rail on the tracks which were often very uneven. At the same time they had to be very powerful with good traction as they would often have to haul trains of wagons up very steep gradients, such as the sides of railway embankment
Embankment
Embankment may refer to:* A levee or dike, an artificial bank raised above the immediately surrounding land to redirect or prevent flooding by a river, lake or sea...
s or spoil heaps. Many were designed so that large iron ballast blocks could be fitted to the frames when extra weight and traction was required, then removed when it was not. Most had sanding gear fitted to all wheels for maximum traction. Some method of keeping mud and dust from clogging the wheels and brake shoes was also required – this either took the form of scraper bars fitted to the leading edge of the wheels or wheel washer jets supplied from the water tank. To handle long trains of loose-coupled (and often un-sprung) wagons, contractor's locomotives usually had very effective steam-powered brakes. Most lacked a full cab, often only having a front 'spectacle plate'. If a cab was provided it was usually removable along with the chimney, and sometimes the dome, so that the locomotive could be loaded onto a flatbed wagon for transport to new locations by rail whilst remaining within the loading gauge
Loading gauge
A loading gauge defines the maximum height and width for railway vehicles and their loads to ensure safe passage through bridges, tunnels and other structures...
.
Fireless locomotive
Fireless locomotives are tank locomotives insofar as they carry their "fuel" (steam) on board in a reservoir, known as a steam accumulatorSteam accumulator
A Steam accumulator is an insulated steel pressure tank containing hot water and steam under pressure. It is a type of energy storage device. It can be used to smooth out peaks and troughs in demand for steam. Steam accumulators may take on a significance for energy storage in solar thermal...
. The reservoir is filled from an external source of steam. Some types of fireless locomotives are "fuelled" by pressurized air, rather than steam.
Steam tram engines
Steam Tram engines, which were built, or modified, to work on a street, or roadside, tramway were almost universally also tank engines.Pros and cons
- Bi-directionality: most tank locomotives are capable of running at full speed in either direction. Most tender locomotives are unable to do this, because the heavy tender is not designed to be pushed and may become unstable at higher speeds. Tender locomotives generally require turning facilities, such as a turntableTurntable (railroad)A railway turntable is a device for turning railroad rolling stock. When steam locomotives were still in wide use, many railroads needed a way to turn the locomotives around for return trips as their controls were often not configured for extended periods of running in reverse and in many...
or wyeWye (railroad)A wye or triangular junction, in rail terminology, is a triangular shaped arrangement of rail tracks with a switch or set of points at each corner. In mainline railroads, this can be used at a rail junction, where three rail lines join, in order to allow trains to pass from any line to any other...
, at each end of the run. A tank locomotive, on the other hand, can simply run around the train and pull it back in the other direction. The crew of a tank engine generally have a better view in the reverse direction than for a tender engine and are protected from the weather.
- Fuel and water add to adhesive weight: the usable tractive weight of a locomotive is the product of the weight on its drivers multiplied by the factor of adhesionFactor of adhesionIn railroad engineering, the factor of adhesion of a locomotive is the weight on the driving wheels divided by the starting tractive effort.A common rule is that for a steam locomotive a good factor of adhesion equals or exceeds 4, but not by too much...
. Therefore, up to the limits of the maximum permissible axle loading, and other loading limits, the more weight on the driving wheels the better. In a tank locomotive the weight of its own fuel and water increase the available tractive weight.
- Compactness: A tank locomotive is shorter than the equivalent tender locomotive. This is important in environments limited space for locomotives, for example the headshuntHeadshuntA headshunt is a short length of track, provided to release locomotives at terminal platforms, or to allow shunting to take place clear of main lines.- Terminal Headshunts :...
of a run-round loop.
- Efficiency: Many train tanks are designed to be in contact with and be heated by, the boiler. Pre-heated water will reach boiling point faster than the colder water available from a tender. However, excessively hot water can interfere with steam injector operation and is to be avoided.
There are corresponding disadvantages:
- Limited fuel and water capacity: a tender can typically contain far more of both than is available on a tank locomotive. This restricts the range of tank locomotives between fueling and watering points.
- Varying adhesive weight: Use of the fuel and water for the purposes of adhesive weight means that the adhesive weight of the locomotive decreases as they are used up.
- Instability: Water surging inside large side tanks can cause the locomotive to become unstable and prone to derailmentDerailmentA derailment is an accident on a railway or tramway in which a rail vehicle, or part or all of a train, leaves the tracks on which it is travelling, with consequent damage and in many cases injury and/or death....
, as was the case with the LB&SCR L classLB&SCR L classThe LB&SCR L Class was a class of 4-6-4 steam tank locomotives designed by L. B. Billinton for the London, Brighton and South Coast Railway. They were known as the "Brighton Baltics", Baltic being the European name for the 4-6-4 wheel arrangement...
4-6-4T before they were modified.
- Axle loading limits a problem: For larger tank locomotives, it is hard to put much fuel and water aboard without requiring more axles than a rigid frame can handle.
- Limit of boiler diameter: The boiler and water tanks must fit within the loading gaugeLoading gaugeA loading gauge defines the maximum height and width for railway vehicles and their loads to ensure safe passage through bridges, tunnels and other structures...
of the railway being run on. Above a certain diameter of boiler there is little or no room for water tanks to be added and still fit within the loading gauge.
Popularity
Worldwide, tank engines varied in popularity. They were more common in areas where the length of run was short, a quick turn around time was needed or turning facilities were not available, mostly in Europe. With their limited fuel and water capacity, they were not favoured in areas where long runs between stops were the norm.They were very common in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, and in particular Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
where examples of large tank locomotives were built. In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
they tended to be restricted to push-pull
Push-pull train
Push–pull is a mode of operation for locomotive-hauled trains allowing them to be driven from either end.A push–pull train has a locomotive at one end of the train, connected via some form of remote control, such as multiple-unit train control, to a vehicle equipped with a control cab at the other...
suburban service, always the tank engine's forte, and also for switching service
Switcher
A switcher or shunter is a small railroad locomotive intended not for moving trains over long distances but rather for assembling trains ready for a road locomotive to take over, disassembling a train that has been...
in terminals and locomotive shops. They were also popular in logging, mining and industrial service.
Preservation
Heritage railway
thumb|right|the Historical [[Khyber train safari|Khyber Railway]] goes through the [[Khyber Pass]], [[Pakistan]]A heritage railway , preserved railway , tourist railway , or tourist railroad is a railway that is run as a tourist attraction, in some cases by volunteers, and...
s for a number of reasons. They are usually cheaper to purchase than a tender locomotive
Tender locomotive
A tender or coal-car is a special rail vehicle hauled by a steam locomotive containing the locomotive's fuel and water. Steam locomotives consume large quantities of water compared to the quantity of fuel, so tenders are necessary to keep the locomotive running over long distances. A locomotive...
due to their smaller size. This is also an advantage when working out the cost of transportation
Road transport
Road transport or road transportation is transport on roads of passengers or goods. A hybrid of road transport and ship transport is the historic horse-drawn boat.-History:...
to the heritage line, many of which are isolated from the national rail
British Rail
British Railways , which from 1965 traded as British Rail, was the operator of most of the rail transport in Great Britain between 1948 and 1997. It was formed from the nationalisation of the "Big Four" British railway companies and lasted until the gradual privatisation of British Rail, in stages...
network.
Most heritage railways only have short lines
Branch line
A branch line is a secondary railway line which branches off a more important through route, usually a main line. A very short branch line may be called a spur line...
and do not often have turntable
Turntable (railroad)
A railway turntable is a device for turning railroad rolling stock. When steam locomotives were still in wide use, many railroads needed a way to turn the locomotives around for return trips as their controls were often not configured for extended periods of running in reverse and in many...
s at both ends of the line. A tank locomotive has good visibility for the driver in both directions. As the trains being hauled are usually light the tank locomotive is more fuel efficient
Fuel efficiency
Fuel efficiency is a form of thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or work. Overall fuel efficiency may vary per device, which in turn may vary per application, and this spectrum of variance is...
than a large tender locomotive.
Add to this the lower cost of maintaining the engine and the lower amount of wear and tear on the track. Another fact to consider is that many tank locomotives were bought from former industrial railways rather than the national network. Due to the higher availability it would be easier to secure a suitable locomotive for a reasonable price.