Steam generator (railroad)
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Steam generator is the term used to describe a type of boiler used to produce steam for climate control and potable water heating in railroad passenger cars. The output of a railroad steam generator is low pressure, saturated steam that is passed through a system of pipes and conduits throughout the length of the train.
Steam generators were developed when Diesel locomotives started to replace steam locomotives on passenger trains. In most cases, each passenger locomotive was fitted with a steam generator and a feedwater supply tank. The steam generator used some of the locomotive's fuel supply for combustion. In the event a steam generator-equipped locomotive was not available for a run, a so-called "heating car" fitted with one or two steam generators was inserted between the last locomotive in the consist and the rest of the train. In Ireland, Córas Iompair Éireann used "heating cars" as standard and CIE diesel locomotives were not fitted with steam generators.
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[edit] Background
During the early days of passenger railroading, cars were heated by a wood or coal fired stove—if any heat was provided at all. It was difficult to evenly heat the long, narrow and drafty cars of the time. Passengers who sat closest to the stove often found it uncomfortably hot, while those at a distance faced a cold, unpleasant ride. Aside from their poor heating qualities, the bulky, cast-iron stoves were one of the classic safety menaces of early railroading. Often cars were set ablaze by hot embers and cinders escaping from the stove, especially in the event of a wreck, during which the stove often became dislodged and would turn over, dumping burning coals into the car.
The idea of using steam from the locomotive to heat cars was first exploited in the late 19th century. Initial efforts involved the passage of high pressure steam from the locomotive boiler to the rest of the train via pipes and hoses. The obvious dangers of this arrangement quickly became evident in the numerous accidents that plagued the industry at the time. The solution came in 1903 when Egbert Gold, a Chicago businessman, introduced the "Vapor" car heating system, which used a low pressure, saturated steam system that was self-regulating. The Vapor system proved to be safe and efficient, and became nearly universal in railroad applications.
When steam locomotives began to be retired from passenger runs, Gold's company, now known as the Vapor Car Heating Company, developed a compact water-tube boiler that could be fitted into the rear of a Diesel locomotive's engine room. Known as the Vapor-Clarkson steam generator, it and its competitors (notably the unit built by Elesco) remained a standard railroad appliance until steam heat was phased out of railroad applications.
[edit] Steam generator types
[edit] Oil-fired
These burned Diesel fuel, which is a lightweight fuel oil. The term steam generator, as opposed to boiler, usually refers to a fairly automated unit whose heart consists of a long spiral tube that water is pumped into and is surrounded by flame and hot gases, steam issuing out the end. There is no pressure vessel in the ordinary sense of a boiler. Because there is no capacity for storage, the steam generator's output must vary directly in proportion to demand. To avoid having to station an operator at the steam generator while the train was underway, automatic regulatory systems were employed to raise or lower the rate that water was pumped into the coil, fuel was burned, and combustion air blown through the generator.
By pumping slightly more water in than can be evaporated, the output was actually a mixture of steam and a bit of water with concentrated dissolved solids. A steam separator removed the water before the steam passed along to the train. Also, an automatic blowdown valve would be periodically cycled to eject solids and sludge from the separator. The purpose of this process was to reduce limescale buildup caused by boiling hard water. Such scale buildup that did occur had to be removed via acid washout of the coils.
[edit] Electrically-heated
In British electric locomotives the steam generator was usually an electric steam boiler, heated by a large electric immersion heater running at the (then) line voltages of 600 volts from a third rail or 1,500 volts from an overhead wire.
[edit] Modern times
Steam heated or cooled rail cars have been replaced or converted to fully electric systems. Wisps of steam coming from under cars are now part of the past in the USA, Canada, and much of the rest of the world.
