The Most Typical Appliances

All locomotives are fitted with a variety of appliances. Some of these relate directly to the operation of the steam engine; while others are for signalling, train control, or other purposes. In the United States the Federal Railroad Administration mandated the use of certain appliances over the years in response to safety issues. The most typical appliances are as follows

Steam pumps and injectors

Water 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 use turbopumps. Standard practice evolved to use two independent systems for feeding water to the boiler. Vertical glass tubes, known as water gauges or water glasses, show the level of water in the boiler.

Boiler lagging

Large amounts of heat are wasted if a boiler is not insulated. Early locomotives used shaped wooden battens fitted lengthways along the boiler barrel and held in place by metal bands. Improved insulating methods included: applying a thick paste containing a porous mineral, such as kieselgur; fixing "mattresses" of stitched asbestos cloth stuffed with asbestos fibre around (but on separators so as not quite to touch) the boiler; attaching shaped blocks of insulating compound. The most common modern day material is glass wool, or wrappings of aluminium foil. The installation is covered by a close fitted sheet-metal casing. Effective lagging is particularly important for fireless locomotives.

Pressure gauge

The earliest locomotives did not show the pressure of steam in the boiler, but it was possible to estimate this by the state of the safety valve. However, the promoters of the Rainhill trials urged that each contender have a proper mechanism for reading the boiler pressure and Stephenson devised a nine-foot vertical glass tube of mercury, mounted alongside the chimney, for the Rocket. The Bourdon tube gauge, in which the pressure straightens an oval-section, coiled tube of brass or bronze connected to a pointer, was not introduced until the 1850s. This is the device used today. Some locomotives have an additional pressure gauge in the steam chest. This helps the driver avoid wheel-slip at startup, by warning if the regulator opening is too great.

Superheating

In the 1800s most engines used saturated steam. Post-1900 superheated steam appeared in the U.S.A. Prior to superheating locomotive development had almost reached its practical capacity with saturated steam. Swengel (1967:122) said that 'no single development ever equalled the superheater as a means of removing limitations from steam locomotive design'.

The normal method for superheating is to route the steam from the dome to a header in the smokebox. The steam is then directed through a set of small "U" shaped tubes in enlarged boiler tubes, and then into a second header and on through the cylinders. Superheating produces an increase in efficiency of 10-15% for an increase in temperature of 100 to 150 F° (55 to 85 C°). Although some locomotives have a greater degree of superheat applied, higher temperatures do not offer proportionally greater efficiencies. Superheated locomotives were sometimes fitted with pyrometers to indicate the steam temperature which, towards the end of the steam era, was typically around 600°F (315°C).

One pound of saturated steam at 200 p.s.i. occupies 2.134 cubic feet of space and when admitted to the cylinders the water (condensation) content is about 7%. At higher boiler pressure the water content in the cylinder increases. Prior to superheating, the boiler limit for any given locomotive was 200 p.s.i. as a locomotive could not as a rule, handle more than 7% water in its cylinders. Superheating, in short, dries out the steam, increases its volume and this gain increases the amount of work delivered from the same one pound of water. For this reason, it was common to find that the best improvements did not occur until locomotives were some way into their overhaul cycle and leaks had started to develop. The use of superheaters became standard in all high-powered locomotives of the 20th century.

Stokers

A factor that limits locomotive performance is the rate at which fuel is fed into the fire. In the early 20th century some locomotives became so large, that the fireman could not shovel coal fast enough. In the United States, various steam-powered mechanical stokers became standard equipment and were adopted and used elsewhere including Australia and South Africa.

Feedwater heaters

Introducing cold water into a boiler reduces power, and from the 1920s a variety of heaters extracted waste heat from the exhaust and raised the temperature of the feed water. An example of the pre-heater is found on the Franco-Crosti boiler.

The use of live steam and exhaust steam injectors also assists in the pre-heating of boiler feed water, though there is no efficiency advantage to live steam injectors. Such pre-heating also reduces the thermal shock that a boiler might experience when cold water is introduced directly.

Condensers and water re-supply

Steam locomotives consume vast quantities of water, and supplying this was a constant logistical problem. In some desert areas, condensing engines were devised. These engines had huge radiators in their tenders and instead of exhausting steam out of the funnel it was captured and passed back to the tender and condensed. The cylinder lubricating oil was removed from the exhausted steam to avoid a phenomenon known as priming, a condition caused by foaming in the boiler which would allow water to be carried into the cylinders causing damage because of its incompressibility. The most notable engines employing condensers (Class 25C) worked across the Karoo desert of South Africa, from the 1950 until the 1980s.

Some British and American locomotives were equipped with scoops which collected water from "water troughs" (US: "track pans") while in motion, thus avoiding stops for water. In the US, small communities that were established near sections of the railroad with track pans were often referred to as "jerkwater towns" (a term which today is considered derisive). In Australia and South Africa, locomotives in drier regions operated with large oversized tenders and some even had an additional water wagon, sometimes called a "canteen".

Steam locomotives working on underground railways (such as London's Metropolitan Railway) were fitted with condensing apparatus for a different, but obvious, reason. These were still being used between King's Cross and Moorgate into the 1950s.

Braking

Locomotives have their own braking system, independent from the rest of the train. Locomotive brakes employ large shoes which press against the driving wheel treads. With the advent of air brakes, a separate system also allowed the driver to control the brakes on all cars. These systems require steam-powered pumps, which are mounted on the side of the boiler or on the smokebox front. Such systems operated in the United States, Canada and Australia.

An alternative to the air brake is the vacuum brake. Where vacuum brakes are used, a steam-operated ejector is mounted on the engine instead of the air pump. A secondary ejector or crosshead vacuum pump is used to maintain the vacuum in the system. Vacuum systems existed on British, Indian and South African rail networks.

Steam locomotives are nearly always fitted with sandboxes from which sand can be delivered to the rails to improve traction and braking in wet weather. On American locomotives the sandboxes, or sand domes, are usually mounted on top of the boiler. In Britain, the limited loading gauge precludes this, so the sandboxes are mounted just above, or just below, the running plate.

Lubrication

The pistons and valves on the earliest locomotives were lubricated by the enginemen dropping a lump of tallow down the blast pipe.

As speeds and distances increased, mechanisms were developed that injected thick mineral oil into the steam supply. The first, a displacement lubricator, mounted in the cab, uses a controlled stream of steam condensing into a sealed container of oil. Water from the condensed steam displaces the oil into pipes. The apparatus is usually fitted with sight-glasses to confirm the rate of supply. A later method used a mechanical pump worked from one of the crossheads. In both cases, the supply of oil is proportional to the speed of the locomotive.

Lubricating the frame components (axle bearings, horn blocks and bogie pivots) depends on capillary action: trimmings of worsted yarn are trailed from oil reservoirs into pipes leading to the respective component. The rate of oil supplied is controlled by the size of the bundle of yarn and not the speed of the locomotive, so it is necessary to remove the trimmings (which are mounted on wire) when stationary. However, at regular stops (such as a terminating station platform) oil finding its way onto the track can still be a problem.

Crank pin and crosshead bearings carry small cup-shaped reservoirs for oil. These have feed pipes to the bearing surface that start above the normal fill level, or are kept closed by a loose-fitting pin, so that only when the locomotive is in motion does oil enter. In United Kingdom practice the cups are closed with simple corks, but these have a piece of porous cane pushed through them to admit air. It is customary for a small capsule of pungent oil (aniseed or garlic) to be incorporated in the bearing metal to warn if the lubrication fails and excess heating or wear occurs.

Buffers

In British practice, the locomotive usually had buffers at each end to absorb compressive loads ("buffets"). The tensional load of drawing the train (draft force) is carried by the coupling system. Together these control slack between the locomotive and train, absorb minor impacts, and provide a bearing point for pushing movements.

In American practice all of the forces between the locomotive and cars are handled through the coupler and its associated draft gear, which allows some limited slack movement. Small dimples called "poling pockets" at the front and rear corners of the locomotive allowed wagons to be pushed on an adjacent track using a pole braced between the locomotive and the cars.

Pilots

In the United States, South Africa and Australia, locomotives had a pilot at the front end. Plow-shaped, and called cow catchers, they were quite large and were designed to remove obstacles from the track such as cattle, bison, other animals or tree limbs. Though unable to "catch" stray cattle these distinctive items remained on locomotives in those countries until the end of steam. Switching engines usually replaced the pilot with small steps. In places like Victoria, Australia, the cow catchers became a trade mark of that state's engines (Dee:1998).

Headlights

When night operations began, railway companies in some countries equipped their locomotives with lights to allow the driver to see what lay ahead of the train or to enable others to see the locomotive. Originally headlights were oil or acetylene lamps, but when electric lights became available they quickly replaced the older types.

Britain used low intensity oil lamps and were not intended to allow the driver to see the way ahead (locomotive drivers were expected to have sufficient route knowledge) but were used to indicate the class of a train by their position on the front of the locomotive. Four lamp irons were provided: one below the chimney and three evenly spaced across the top of the buffer beam.

In some countries heritage steam operation continues on the national network. Some railway authorities have mandated powerful headlights on at all times, including during daylight. This was to further inform the public or track workers of any active trains.

Bells and whistles

Locomotives used bells and steam whistles from earliest days. In the United States and Canada bells warned of a train in motion. In Britain, where all lines are by law fenced throughout, bells were never a requirement; whistles are used to signal personnel and give warnings. In Australia, locomotives carried distinctive whistles heard at long distances.

Automatic Train Control

From early in the twentieth century operating companies in such countries as Germany and Britain began to fit locomotives with in-cab signalling which automatically applied the brakes when a signal was passed at "caution". In Britain these became mandatory in 1956.

Booster engines

In the United States and (sometimes) Australia the trailing truck was often equipped with an auxiliary steam engine which provided extra power for starting. This booster engine was set to cut out automatically at a certain speed.