Tender (railroad car)

Steam locomotives often haul a tender, which is a special railway truck (railroad car in American usage) designed to hold the locomotive's fuel (wood, coal, or oil) and water. In America, tenders are sometimes called coal-cars. Steam locomotives consume large quantities of both fuel and water, so tenders are necessary to keep the locomotive 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 the locomotive itself are called tank engines.

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 to the railway. 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. Up to around 1850 in the United States, the vast majority of locomotives burned wood until most of the eastern forests were cleared; from that time on coal burning became more widespread, and wood burners were restricted to rural and logging districts.

Water supply

According to "Steamlocomotive.com", cite web|url=http://www.steamlocomotive.com/tenders/ |title=Steam Locomotive Tenders |accessdate=2008-08-20 |work=Steamlocomotive.com ]

By the mid-1800s most steam locomotive tenders consisted of a fuel bunker (that held coal or wood) surrounded by a "U" shaped (when viewed from the top) 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 (0.7 gallons) to steam. Therefore, tender capacity ratios were normally close to 14 tons of coal per 10,000 gallons of water.

The water supply in a tender was replenished at stopping places 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 exhausted after delivering a working stroke to the pistons. 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 (US track pans) were provided on some main lines to allow locomotives to replenish their water supply without stopping. This was achieved by using a 'water scoop' 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 again once it was full.

The fuel and water capacities of a tender are usually proportional to the rate at which they are consumed, though 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 track pans were called water troughs and were used by three of the Big Four railways. The exception was the Southern Railway and some Southern Railway locomotives were equipped with eight-wheel "Water Cart" tenders.

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, in order to maintain a constant steam pressure. However, in the early 20th century some locomotives became so large that the fireman could not shovel coal fast enough.cite book
last=Bell |first=A Morton
date=1950
title=Locomotives
edition=seventh edition
publisher=Virtue & Co Ltd,
location=London] Consequently, in the United States, various steam-powered mechanical stokers (typically using a screw-feed device between the fuel bunker and the firebox) became standard equipment and were adopted elsewhere, including Australia and South Africa.

Types of tender

Vanderbilt tender

In the early days of railroading, tenders were rectangular boxes, with a bunker for coal or wood surrounded by a U-shaped water jacket. However, in the late 19th century, this design was found to be impractical for locomotives using oil as fuel. In 1901, Cornelius Vanderbilt III, whose great-grandfather founded the New York Central Railroad, invented a cylindrical tender which was soon adopted by a number of American railroads with oil-burning locomotives. cite web|url=http://www.steamlocomotive.com/tenders/ |title=Steam Locomotive Tenders |accessdate=2008-08-20 |work=Steamlocomotive.com ]

Compared to rectangular tenders, cylindrical Vanderbilt tenders were stronger, lighter, and held more fuel in relation to surface area. Railroads in the U.S. and Canada who were noted for using Vanderbilt tenders include: cite web|url=http://www.steamlocomotive.com/tenders/ |title=Steam Locomotive Tenders |accessdate=2008-08-20 |work=Steamlocomotive.com ]

*Baltimore & Ohio
*Canadian National
*Grand Trunk Western
*Great Northern
*Southern Pacific
*Union Pacific

lopeback tender

In the United States, tenders with a sloped back were often used for locomotives in yard switching service, because the sloped back 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 from the water tower or water crane in a rail yard. cite web|url=http://www.steamlocomotive.com/tenders/ |title=Steam Locomotive Tenders |accessdate=2008-08-20 |work=Steamlocomotive.com ]

Canteen

An additional tender which holds only water is called a "canteen." 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 & Western used canteens with its giant 2-8-8-2 locomotives on coal trains. Use of the canteen allowed one of the water stops to be skipped, meaning that the train did not have to climb a hill from a dead stop. Currently, Union Pacific uses canteens with its steam locomotives 844 and 3985 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 far 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.

The only example of a canteen in the United Kingdom was on "Flying Scotsman" during the late 1960s and early 1970s. As railways in Britain tend to be far shorter than those in the USA, the canteen was never seen as an economical proposition.

Fuel tender

Sometimes a tender will be used for a diesel locomotive. This is typically a tank car with a fuel line that connects to the locomotive and MU connections to allow locomotives behind the tender to be controlled remotely. The Burlington Northern used fuel tenders in remote territory where fuel was expensive. Diesel fuel could be bought cheaply and loaded into the tender. A common consist was two EMD SD40-2s with a tender between them. Some of the tenders survived the Burlington Northern Santa Fe merger but retain the black and green BN colors. The Southern Pacific also briefly experimented with fuel tenders for diesels. Some slugs have fuel tanks and serve as fuel tenders for the attached locomotives.

Union Pacific used fuel tenders on its turbines. These tenders were originally used with steam locomotives, then reworked to hold heavy "Bunker C" fuel oil. Fuel capacity was about 23,000 gallons (87,000 liters). When the turbines were retired, some of the tenders were kept and reworked to hold water and used as canteens for steam locomotives.

Tenders have also been developed to carry liquified natural gas for diesel locomotives converted to run on that fuel. cite web|url=http://www.energyconversions.com/tender.htm |title=Fuel Storage - LNG Locomotive Tender Car |accessdate=2008-08-20 |publisher=Energy Conversions, Inc. ]

Brake tender

On British railways, brake tenders were used with early main line diesel locomotives. These were coupled in front of the locomotive to provide extra braking power.

Powered tender

Certain early British steam locomotives were fitted with powered tenders. As well as holding coal and water, these had wheels powered from the locomotive to provide greater strength and adhesion. However, these were abandoned for economic reasons - railwaymen working on locomotives so equipped demanded extra pay as they were effectively working on two locomotives. However, the concept was tried again on the Ravenglass and Eskdale Railway's "River Mite", and the Garratt locomotive may be seen as an extension of this principle. Powered tenders were also seen on the 2-8-8-8-2 and 2-8-8-8-4 locomotives in the United States, but these experiments were not considered successful.

German practice

In Germany, special attention was given to ensuring that tender locomotives were capable of moderately high speeds in reverse, pushing their tenders. The numerous BR 50 (2-10-0) locomotives, for example, were capable of 80 km/h (50 mph) in either direction, and were commonly used on branch lines with no turning facilities.

A source of possible confusion with regards to German locomotives is that in German, "Tenderlokomotive" means a tank locomotive. A locomotive with a separate, hauled tender is a "Schlepptenderlokomotive".

References

External links

* [http://www.steamlocomotive.com/tenders/ United States locomotive tenders]