Tender (rail)
A tender is a special rail vehicle hauled by a steam locomotive containing its fuel and water. Steam locomotives consume large quantities of water compared to the quantity of fuel, so their tenders are necessary to keep them running over long distances. A locomotive that pulls a tender is called a tender locomotive. Locomotives that do not have tenders and carry all their fuel and water on board are called tank locomotives or tank engines.
A corridor tender is a locomotive tender with a passageway to one side, allowing crew changes on the fly.
A brake tender is a tender that is heavy and used to provide greater braking efficiency.
General functions
The largest steam locomotives are semi-permanently coupled by a drawbar to a tender that carries the water and fuel. The fuel source used depends on what is economically available locally. In the UK and parts of Europe, a plentiful supply of coal made this the obvious choice from the earliest days of the steam engine. Until around 1850 in the United States, the vast majority of locomotives burned wood until most of the eastern forests were cleared. Subsequently, coal burning became more widespread, and wood burners were restricted to rural and logging districts.Water supply
By the mid-1800s, most steam locomotive tenders consisted of a fuel bunker surrounded by a U-shaped water jacket. The overall shape of the tender was usually rectangular. The bunker which held the coal was sloped downwards toward the locomotive providing easier access to the coal. The ratio of water to fuel capacities of tenders was normally based on two water-stops to each fuel stop because water was more readily available than fuel. One pound of coal could turn six pounds of water to steam. Therefore, tender capacity ratios were normally close to 7 tons of coal per 10,000 gallons of water.
The water supply in a tender was replenished at water stops and locomotive depots from a dedicated water tower connected to water cranes or gantries. Refilling the tender is the job of the fireman, who is responsible for maintaining the locomotive's fire, steam pressure, and supply of fuel and water.
Water carried in the tender must be forced into the boiler, to replace that which is consumed during operation. Early engines used pumps driven by the motion of the pistons. Later, steam injectors replaced the pump while some engines used turbopumps.
With track pans or water troughs
In the UK, the USA and France, water troughs were provided on some main lines to allow locomotives to replenish their water supply while moving. A "water scoop" was fitted under the tender or the rear water tank in the case of a large tank engine; the fireman remotely lowered the scoop into the trough, the speed of the engine forced the water up into the tank, and the scoop was raised once it was full.The fuel and water capacities of a tender are usually proportional to the rate at which they are consumed, although there were exceptions. The Pennsylvania Railroad and the New York Central Railroad used track pans on many of their routes, allowing locomotives to pick up water at speed. The result was that the water tanks on these tenders were proportionally much smaller.
In the UK water troughs were used by three of the Big Four railways. The exception was the Southern Railway – mainly because the majority of the Southern's operations were based around short-distance commuter, suburban and rural services with frequent station stops where water could be taken on from water columns. The Southern's decision to electrify its routes into London with a third rail system also made the installation of water troughs impractical. Only on the former London and South Western Railway routes west of Salisbury, where long-distance express trains operated, was the lack of troughs a problem. Rather than install troughs the L&SWR equipped its express locomotives with special high-capacity tenders with a water capacity of 4,000 gallons running on a pair of twin-axle bogies. These were known to railwaymen as "water cart" tenders.
Condensing tenders
s were designed to recycle exhaust steam by condensing it into feed water. The principal benefit is conservation of water, but the thermal efficiency of the engine is also increased, since much of the heat otherwise lost in the exhaust is used to preheat water injected into the boiler. In some cases condensing was employed simply to improve visibility by eliminating clouds of exhaust.A primitive approach to condensation simply injected the spent steam into the tender tank, relying on the mass of water for cooling. More sophisticated tenders, such as those used in the South African Railways Class 25 locomotives designed for service in the Karoo, replaced most of the water tank with a huge radiator, in which the steam was cooled and condensed. Exhaust steam, after passing through an oil-water separator, was conveyed to the tender, where it powered a low-pressure turbine used to drive the radiator fans. The steam then passed into the radiator. The condensate was injected into the boiler with another turbine-driven pump. This was a quite complex bit of machinery, also requiring another turbine in the smokebox to provide the exhaust draft normally obtained by blowing the exhaust steam up the stack. Eventually the SAR examples were converted to conventional locomotives by replacing the radiator with a long water tank.
Fuel supply
A factor that limits locomotive performance is the rate at which fuel is fed into the fire. Much of the fireman's time is spent throwing wood or shoveling coal into the firebox of the locomotive to maintain constant steam pressure. In the early 20th century some locomotives became so large that the fireman could not shovel coal fast enough. Consequently, in the United States, various steam-powered mechanical stokers became standard equipment and were adopted elsewhere, including Australia and South Africa.Tender design variants
In the early days of railroading, tenders were rectangular boxes, with a bunker for coal or wood surrounded by a U-shaped water jacket. This form was retained up to the end of steam on many coal-burning engines. Oil-burning engines substituted a fuel tank for the bunker. Variations on this plan were made for operational reasons, in attempts to economize on structure.Vanderbilt
In early 1901, Cornelius Vanderbilt III filed a patent application covering a new type of tender.Vanderbilt was the great-grandson of the founder of the New York Central Railroad; his tender featured a cylindrical body like a tank car with a fuel bunker set into the front end. This design was soon adopted by a number of American railroads with oil-burning and coal-burning locomotives.
Compared to rectangular tenders, cylindrical Vanderbilt tenders were stronger, lighter, and held more fuel in relation to surface area. Railroads who were noted for using Vanderbilt tenders include:
- Baltimore & Ohio
- Canadian National
- Grand Trunk Western
- Great Northern Railway
- Southern Pacific
- Union Pacific
- Hungarian State Railways
- New Zealand Railways Department.
- Nashville, Chattanooga and St. Louis Railway
- Seaboard Air Line Railroad
- South African Railways
Whaleback
Slopeback
In the United States, tenders with sloped backs were often used for locomotives in yard switching service, because they greatly improved the engineer's ability to see behind the locomotive when switching cars. The reduced water capacity was not a problem, as the tender's water tank could be frequently refilled in the rail yard. In the 1880s, numerous locomotive manufacturers were offering tenders with this design on small switcher locomotives.Corridor
For the introduction of the London and North Eastern Railway's non-stop Flying Scotsman service on 1 May 1928, ten special tenders were built with means to reach the locomotive from the train through a narrow passageway inside the tender tank plus a flexible bellows connection linking it with the leading coach. The passageway, which ran along the right-hand side of the tender, was high and wide. Further corridor tenders were built at intervals until 1938, and eventually there were 22; at various times, they were coupled to engines of classes A1, A3, A4 and W1, but by the end of 1948, all were running with class A4 locomotives. Use of the corridor tender for changing crews on the move in an A4 loco is shown in the 1953 British Transport film Elizabethan Express, the name of another London-Edinburgh non-stop train. The London Midland and Scottish Railway also possessed a solitary corridor tender from the late 1940s onwards, built purely for purposes of mobile locomotive testing using a dynamometer car etc. rather than to give any operating advantage in revenue earning service.Water cart
The water cart was a type of high-capacity tender used by the London and South Western Railway in England. Unlike the usual British six-wheel tender, it was a double-bogie design with inside bearings. This gave it a distinctive appearance because the wheels were very obvious.Canteen
An additional tender which holds only water is called a "canteen" or "auxiliary tender". During the steam era, these were not frequently used. Water tanks were placed at regular intervals along the track, making a canteen unnecessary in most cases. However, there were times that canteens proved economical. The Norfolk and Western Railway used canteens with its giant 2-8-8-2 Y Class and 2-6-6-4 A Class locomotives on coal trains, timed freights, fast freights, and merchandise freights. Use of the canteen allowed one of the water stops to be skipped, allowing the train to avoid climbing a hill from a dead stop. Currently, the Union Pacific Railroad uses two canteens with its steam locomotives 844 and 4014 on excursion trains. Virtually all the trackside tanks were removed when steam locomotives were retired. Nowadays, fire hydrant hookups are used, which fills the tanks much more slowly. The canteens allow for greater range between stops.Canteens were also used on the Trans-Australian Railway which crosses the waterless Nullarbor Plain. In New South Wales these vehicles were called "gins", and were used in the predominantly dry western region and on some branch lines. Now prominently use on heritage excursions due to the lack of places with accessible water points. During the catastrophic 2019-2020 bushfire season, as fires devastated towns near the Rail Transport Museum at Thirlmere, south of Sydney, a diesel locomotive from the museum hauled two gins to help replenish firefighting tanker trucks.
In the United Kingdom, a canteen was used on the preserved Flying Scotsman during enthusiast excursions in the late 1960s and early 1970s. The water troughs that had previously supplied long-distance expresses had been removed during dieselisation of the railway network. On 25 July 2009, Bittern made a 188-mile run from King's Cross to York non-stop using a second tender. As railways in Britain tend to be much shorter than those in the US, the canteen was not an economical proposition.