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A railway brake is a type of brake used on the cars of railway trains to enable deceleration, control acceleration (downhill) or to keep them immobile when parked. While the basic principle is similar to that on road vehicle usage, operational features are more complex because of the need to control multiple linked carriages and to be effective on vehicles left without a prime mover. Clasp brakes are one type of brakes historically used on trains.
In the earliest days of railways, braking technology was primitive. The first trains had brakes operative on the locomotive tender and on vehicles in the train, where "porters" or, in the United States brakemen, travelling for the purpose on those vehicles operated the brakes. Some railways fitted a special deep-noted brake whistle to locomotives to indicate to the porters the necessity to apply the brakes. All the brakes at this stage of development were applied by operation of a screw and linkage to brake blocks applied to wheel treads, and these brakes could be used when vehicles were parked. In the earliest times, the porters travelled in crude shelters outside the vehicles, but "assistant guards" who travelled inside passenger vehicles, and who had access to a brake wheel at their posts, supplanted them. The braking effort achievable was limited and it was also unreliable, as the application of brakes by guards depended upon their hearing and responding quickly to a whistle for brakes. [1]
An early development was the application of a steam brake to locomotives, where boiler pressure could be applied to brake blocks on the locomotive wheels. As train speeds increased, it became essential to provide some more powerful braking system capable of instant application and release by the train operator, described as a continuous brake because it would be effective continuously along the length of the train.
In the United Kingdom, the Abbots Ripton rail accident in January 1876 was aggravated by the long stopping distances of express trains without continuous brakes, which – it became clear – in adverse conditions could considerably exceed those assumed when positioning signals. [2] This had become apparent from the trials on railway brakes carried out at Newark in the previous year, to assist a Royal Commission then considering railway accidents. In the words of a contemporary railway official, these
showed that under normal conditions it required a distance of 800 to 1200 yards to bring a train to rest when travelling at 45½ to 48½ mph, this being much below the ordinary travelling speed of the fastest express trains. Railway officials were not prepared for this result and the necessity for a great deal more brake power was at once admitted [3]
Trials conducted after Abbots Ripton reported the following for an express train roughly matching conditions involved (such as a 1 in 200 downward run, but not braking under favorable conditions): [2]
Braking system | Train speed | Distance | Stopping time (s) | ||
---|---|---|---|---|---|
mph | km/h | yd | m | ||
Continuous (vacuum) | 45 | 72 | 410 | 370 | 26 |
Continuous (vacuum) | 45 | 72 | 451 | 412 | 30 |
3 brake vans | 40.9 | 65.8 | 800 | 730 | 59 |
2 brake vans | 40.9 | 65.8 | 631 | 577 | 44 |
2 brake vans | 45 | 72 | 795 | 727 | 55 |
1 brake van | 45 | 72 | 1,125 | 1,029 | 70 |
However, there was no clear technical solution to the problem, because of the necessity of achieving a reasonably uniform rate of braking effort throughout a train, and because of the necessity to add and remove vehicles from the train at frequent points on the journey. (At these dates, unit trains were a rarity).
The chief types of solution were:
Note: there are a number of variants and developments of all these systems.
The Newark trials showed the braking performance of the Westinghouse air-brakes to be distinctly superior: [14] but for other reasons [15] it was the vacuum system that was generally adopted on UK railways.
Braking system | Train weight with engine | Train speed | Stopping distance | Time to stop (s) | Deceleration | Rails | ||||
---|---|---|---|---|---|---|---|---|---|---|
long tons | tonnes | mph | km/h | yd | m | g | m/s2 | |||
Westinghouse automatic | 203 ton 4 cwt | 206.5 | 52 | 84 | 304 | 278 | 19 | 0.099 | 0.97 | dry |
Clark hydraulic | 198 ton 3 cwt | 201.3 | 52 | 84 | 404 | 369 | 22.75 | 0.075 | 0.74 | dry |
Smith vacuum [13] | 262 ton 7 cwt | 266.6 | 49.5 | 79.7 | 483 | 442 | 29 | 0.057 | 0.56 | dry |
Clark and Webb chain | 241 ton 10 cwt | 245.4 | 47.5 | 76.4 | 479 | 438 | 29 | 0.056 | 0.55 | dry |
Barker's hydraulic | 210 ton 2 cwt | 213.5 | 50.75 | 81.67 | 516 | 472 | 32 | 0.056 | 0.55 | dry |
Westinghouse vacuum | 204 ton 3 cwt | 207.4 | 52 | 84 | 576 | 527 | 34.5 | 0.052 | 0.51 | wet |
Fay mechanical | 186 ton 3 cwt | 189.1 | 44.5 | 71.6 | 388 | 355 | 27.5 | 0.057 | 0.56 | wet |
Steel & McInnes air | 197 ton 7 cwt | 200.5 | 49.5 | 79.7 | 534 | 488 | 34.5 | 0.051 | 0.50 | wet |
In British practice, only passenger trains were fitted with continuous brakes until about 1930; goods and mineral trains ran at slower speed and relied on the brake force from the locomotive and tender and the brake van —a heavy vehicle provided at the rear of the train and occupied by a guard.
Goods and mineral vehicles had hand brakes which were applied by a hand lever operated by staff on the ground. These hand brakes were used where necessary when vehicles were parked but also when trains were descending a steep gradient. The train stopped at the top of the gradient, and the guard walked forward to "pin down" the handles of the brakes, so the brakes were partially applied during the descent. Early goods vehicles had brake handles on one side only but, from about 1930, brake handles were required on both sides of good vehicles. Trains containing hand-braked vehicles were described as "unfitted": they were in use in Britain until about 1985. From about 1930, semi-fitted trains were introduced, in which goods vehicles fitted with continuous brakes were marshalled next to the locomotive, giving sufficient braking power to run at higher speeds than unfitted trains. A trial in January 1952 saw a 52-wagon, 850 ton, coal train run 127 miles (204 km) at an average of 38 miles per hour (61 km/h), compared to the usual maximum speed on the Midland main line of 25 miles per hour (40 km/h) for unfitted freight trains. [16] In 1952, 14% of open wagons, 55% of covered wagons and 80% of cattle trucks had vacuum brakes. [17]
In the early days of diesel locomotives, a purpose-built brake tender was attached to the locomotive to increase braking effort when hauling unfitted trains. The brake tender was low, so that the driver could still see the line and signals ahead if the brake tender was propelled (pushed) ahead of the locomotive, which was often the case.
By 1878 there were over 105 patents in various countries for braking systems, most of which were not widely adopted. [18]
As train loads, gradients and speeds increased, braking became a more significant problem. In the late 19th century, significantly better continuous brakes started to appear. The earliest type of continuous brake was the chain brake [19] which used a chain, running the length of the train, to operate brakes on all vehicles simultaneously.
The chain brake was soon superseded by air-operated or vacuum operated brakes. These brakes used hoses connecting all the wagons of a train, so the operator could apply or release the brakes with a single valve in the locomotive.
These continuous brakes can be simple or automatic, the essential difference being what happens should the train break in two. With simple brakes, pressure is needed to apply the brakes, and all braking power is lost if the continuous hose is broken for any reason. Simple non-automatic brakes are thus useless when things really go wrong, as is shown with the Armagh rail disaster.
Automatic brakes on the other hand use the air or vacuum pressure to hold the brakes off against a reservoir carried on each vehicle, which applies the brakes if pressure/vacuum is lost in the train pipe. Automatic brakes are thus largely "fail safe", though faulty closure of hose taps can lead to accidents such as the Gare de Lyon accident.
The standard Westinghouse Air Brake has the additional enhancement of a triple valve and a local reservoir on each wagon, enabling the brakes to be applied fully with only a slight reduction in air pressure, reducing the time that it takes to release the brakes as not all pressure is voided to the atmosphere.
Non-automatic brakes still have a role on engines and first few wagons, as they can be used to control the whole train without having to apply the automatic brakes.
This is not a complete list of all railway brakes, but lists most of the common examples.
Most tractive units, passenger coaches and some freight wagons are equipped with a hand-operated parking brake (handbrake). This acts directly (mechanically) on the vehicle's brake linkage. The activation of such a brake prevents wheel rotation independently of the pneumatic brake and is therefore suitable for securing parked wagons and coaches from unintentional movement. Only mechanical brakes can be used for this purpose, since the holding power of air brakes can decrease due to unavoidable leaks.
There are two types. The handbrake that can be operated on board the vehicle is used firstly to prevent it from rolling away and secondly to regulate the speed for certain shunting operations and to stop trains if the automatic brake fails. It is usually designed as a screw brake and is operated from a brakeman's platform or, in the case of passenger coaches, from inside the coach, usually from an entrance area. On UIC freight wagons, this braking weight is framed in white (white like the rest of the brake inscription, alternatively black on a white or light-coloured background). Hand brakes on tenders and tank locomotives are often designed as counterweight brakes.
A manually operating parking brake is only suitable for securing static railway vehicles from rolling away. It can be designed as a hand wheel or as a spring-loaded brake.
A direction-dependent pawl brake is often installed in vehicles on rack railways. It only brakes when going downhill. When driving uphill, the applied ratchet brake is released by a ratchet mechanism and prevents the train from rolling backwards.
In the early part of the 20th century, many British railways employed vacuum brakes rather than the railway air brakes used in much of the rest of the world. The main advantage of vacuum was that the vacuum can be created by a steam ejector with no moving parts (and which could be powered by the steam of a steam locomotive), whereas an air brake system requires a noisy and complicated compressor.
However, air brakes can be made much more effective than vacuum brakes for a given size of brake cylinder. An air brake compressor is usually capable of generating a pressure of 90 psi (620 kPa ; 6.2 bar ) vs only 15 psi (100 kPa; 1.0 bar) for vacuum. With a vacuum system, the maximum pressure differential is atmospheric pressure (14.7 psi or 101 kPa or 1.01 bar at sea level, less at altitude). Therefore, an air brake system can use a much smaller brake cylinder than a vacuum system to generate the same braking force. This advantage of air brakes increases at high altitude, e.g. Peru and Switzerland where today vacuum brakes are used by secondary railways. The much higher effectiveness of air brakes and the demise of the steam locomotive have seen the air brake become ubiquitous; however, vacuum braking is still in use in India, Argentina and South Africa, but this will be declining in near future.[ citation needed ] See Jane's World Railways .
Visual differences between the two systems are shown by air brakes working off high pressure, with the air hoses at the ends of rolling stock having a small diameter; vacuum brakes work off low pressure, and the hoses at the ends of rolling stock are of a larger diameter. Air brakes at the outermost vehicles of a train are turned off using a tap. Vacuum brakes at the outermost vehicles of a train are sealed by fixed plugs ("dummies") onto which the open end of the vacuum pipe is placed. It is sealed against a rubber washer by the vacuum, with a pin to hold the pipe in place when the vacuum drops during braking. [20] [21]
One enhancement of the automatic air brake is to have a second air hose (the main reservoir or main line) along the train to recharge the air reservoirs on each wagon. This air pressure can also be used to operate loading and unloading doors on wheat wagons and coal and ballast wagons. On passenger coaches, the main reservoir pipe is also used to supply air to operate doors and air suspension.
The counter-pressure brake is a type of steam locomotive brake that brakes the locomotive using the driving cylinders. The brake works by using the cylinders as air compressors and converting kinetic energy into heat.
A common feature on electric and diesel-electric locomotives is the dynamic brake; this operates by using the electric motors that normally turn the wheels as an electric generator, thus slowing the train.
An eddy current brake slows or stops a train by generating eddy currents and thus dissipating its kinetic energy as heat.
The higher performing EP brake uses a "main reservoir pipe" feeding air to all the brake reservoirs on the train, with the brake valves controlled electrically with a three-wire control circuit. If the wire is disconnected, the brakes automatically apply, so the fail-safe nature of other brake systems is retained. This provides between four and seven braking levels, depending on the class of train. It also allows for faster brake application, as the electrical control signal is propagated effectively instantly to all vehicles in the train, whereas the change in air pressure which activates the brakes in a conventional system can take several seconds or tens of seconds to propagate fully to the rear of the train. This system is not however used on freight trains due to cost. [ citation needed ]
Electronically controlled pneumatic brakes (ECP) are an American development of the late 20th Century to deal with very long and heavy freight trains, and are a development of the EP brake with even higher level of control. In addition, information about the operation of the brakes on each wagon is returned to the driver's control panel.
With ECP, a power and control line is installed from wagon to wagon from the front of the train to the rear. Electrical control signals are propagated effectively instantaneously, as opposed to changes in air pressure which propagate at a rather slow speed limited in practice by the resistance to air flow of the pipework, so that the brakes on all wagons can be applied simultaneously, or even from rear to front rather than from front to rear. This prevents wagons at the rear "shoving" wagons at the front, and results in reduced stopping distance and less equipment wear.
There are two brands of ECP brakes available in North America, one by New York Air Brake and the other by Wabtec. These two types are interchangeable.
A Heberlein brake is a continuous railway brake used in Germany that is applied by means of a mechanical cable. Train braking is therefore initiated centrally from the locomotive using a winder. This causes the brake clips to be applied on individual wagons, assisted by a servo system which makes use of the rotation of the axle. The brakes operate automatically if the cable snaps.
A steam brake is a type of brake for steam locomotives and their tenders, whereby a steam cylinder works directly on the brake linkages.
Brake connections between wagons may be simplified if wagons always point the same way. An exception would be made for locomotives which are often turned on turntables or triangles.
On the new Fortescue railway opened in 2008, wagons are operated in sets, although their direction changes at the balloon loop at the port. The ECP connections are on one side only and are unidirectional.
This section needs additional citations for verification .(July 2013) |
Defective or improperly-applied brakes may lead to a runaway train; in some instances this has caused train wrecks:
A railway air brake is a railway brake power braking system with compressed air as the operating medium. Modern trains rely upon a fail-safe air brake system that is based upon a design patented by George Westinghouse on April 13, 1869. The Westinghouse Air Brake Company was subsequently organized to manufacture and sell Westinghouse's invention. In various forms, it has been nearly universally adopted.
The Armagh rail disaster happened on 12 June 1889 near Armagh, County Armagh, in Ireland, when a crowded Sunday school excursion train had to negotiate a steep incline; the steam locomotive was unable to complete the climb and the train stalled. The train crew decided to divide the train and take forward the front portion, leaving the rear portion on the running line. The rear portion was inadequately braked and ran back down the gradient, colliding with a following train.
The vacuum brake is a braking system employed on trains and introduced in the mid-1860s. A variant, the automatic vacuum brake system, became almost universal in British train equipment and in countries influenced by British practice. Vacuum brakes also enjoyed a brief period of adoption in the United States, primarily on narrow-gauge railroads. Their limitations caused them to be progressively superseded by compressed air systems starting in the United Kingdom from the 1970s onward. The vacuum brake system is now obsolete; it is not in large-scale usage anywhere in the world, other than in South Africa, largely supplanted by air brakes.
Rail transport terms are a form of technical terminology applied to railways. Although many terms are uniform across different nations and companies, they are by no means universal, with differences often originating from parallel development of rail transport systems in different parts of the world, and in the national origins of the engineers and managers who built the inaugural rail infrastructure. An example is the term railroad, used in North America, and railway, generally used in English-speaking countries outside North America and by the International Union of Railways. In English-speaking countries outside the United Kingdom, a mixture of US and UK terms may exist.
On trains, the expression emergency brake has several meanings:
A vacuum ejector, or simply ejector is a type of vacuum pump, which produces vacuum by means of the Venturi effect.
The end of train device (ETD), sometimes referred to as an EOT, flashing rear-end device (FRED) or sense and braking unit (SBU) is an electronic device mounted on the end of freight trains in replacement of a caboose. They are divided into three categories: "dumb" units, which only provide a visible indication of the rear of the train with a flashing red taillight; "average intelligence" units with a brake pipe pressure gauge; and "smart" units, which send back data to the crew in the locomotive via radio-based telemetry. They originated in North America, and are also used elsewhere in the world, where they may include complete End of Train Air System (ETAS) or Sense and Brake Unit (SBU) devices.
An atmospheric railway uses differential air pressure to provide power for propulsion of a railway vehicle. A static power source can transmit motive power to the vehicle in this way, avoiding the necessity of carrying mobile power generating equipment. The air pressure, or partial vacuum can be conveyed to the vehicle in a continuous pipe, where the vehicle carries a piston running in the tube. Some form of re-sealable slot is required to enable the piston to be attached to the vehicle. Alternatively the entire vehicle may act as the piston in a large tube or be coupled electromagnetically to the piston.
A hose is a flexible hollow tube designed to carry fluids from one location to another. Hoses are also sometimes called pipes, or more generally tubing. The shape of a hose is usually cylindrical.
Main components found on a typical steam locomotive include:
Automatic Warning System (AWS) is a railway safety system invented and predominantly used in the United Kingdom. It provides a train driver with an audible indication of whether the next signal they are approaching is clear or at caution. Depending on the upcoming signal state, the AWS will either produce a 'horn' sound, or a 'bell' sound. If the train driver fails to acknowledge a warning indication, an emergency brake application is initiated by the AWS. However if the driver correctly acknowledges the warning indication by pressing an acknowledgement button, then a visual 'sunflower' is displayed to the driver, as a reminder of the warning.
An automatic lubricator is a device fitted to a steam engine to supply lubricating oil to the cylinders and, sometimes, the bearings and axle box mountings as well. There are various types of automatic lubricator, which include various designs of displacement, hydrostatic and mechanical lubricators.
The London and North Eastern Railway Gresley Classes A1 and A3 locomotives represented two distinct stages in the history of the British 4-6-2 "Pacific" steam locomotives designed by Nigel Gresley. They were designed for main line passenger services and later express passenger services, initially on the Great Northern Railway (GNR), a constituent company of the London and North Eastern Railway after the amalgamation of 1923, for which they became a standard design. The change in class designation to A3 reflected the fitting to the same chassis of a higher pressure boiler with a greater superheating surface and a small reduction in cylinder diameter, leading to an increase in locomotive weight. Eventually all of the A1 locomotives were rebuilt, most to A3 specifications, but no. 4470 was completely rebuilt as Class A1/1.
The Westinghouse Air Brake Technologies Corporation (WABCO) was an American company founded on September 28, 1869 by George Westinghouse in Pittsburgh, Pennsylvania. Earlier in the year he had invented the railway air brake in New York state.
An air brake or, more formally, a compressed-air-brake system, is a type of friction brake for vehicles in which compressed air pressing on a piston is used to both release the parking/emergency brakes in order to move the vehicle, and also to apply pressure to the brake pads or brake shoes to slow and stop the vehicle. Air brakes are used in large heavy vehicles, particularly those having multiple trailers which must be linked into the brake system, such as trucks, buses, trailers, and semi-trailers, in addition to their use in railroad trains. George Westinghouse first developed air brakes for use in railway service. He patented a safer air brake on March 5, 1872. Westinghouse made numerous alterations to improve his air pressured brake invention, which led to various forms of the automatic brake. In the early 20th century, after its advantages were proven in railway use, it was adopted by manufacturers of trucks and heavy road vehicles.
The electro-pneumatic brake system on British mainline railway trains was introduced in 1950 and remains the primary braking system for multiple units in service today, although London Transport underground trains had been fitted with EP brakes since the 1920s. The Southern Region of British Railways operated a self-contained fleet of electric multiple units for suburban and middle-distance passenger trains. From 1950, an expansion of the fleet was undertaken and the new build adopted a braking system that was novel in the UK, the electro-pneumatic brake in which compressed air brake operation was controlled electrically by the driver. This was a considerable and successful technical advance, enabling a quicker and more sensitive response to the driver's operation of brake controls.
Electronically controlled pneumatic brakes are a type of railway braking systems.
A Heberlein brake is a continuous railway brake used in Germany that is applied by means of a mechanical cable. Train braking is therefore initiated centrally from the locomotive using a winder. This causes the brake clips to be applied on individual wagons, assisted by a servo system which makes use of the rotation of the axle. The brakes operate automatically if the cable snaps. A typical feature of Heberlein brakes is the clearly visible cable run on top of the wagons, but cables can also be led underneath the wagons, as on the Spreewaldbahn railway line. Heberlein brakes were eventually largely replaced by compressed-air brakes or, sometimes, by vacuum brakes on narrow gauge railway vehicles.
The London Underground opened in 1863 with gas-lit wooden carriages hauled by steam locomotives. The Metropolitan and District railways both used carriages exclusively until they electrified in the early 20th century. The District railway replaced all its carriages for electric multiple units, whereas the Metropolitan still used carriages on the outer suburban routes where an electric locomotive at the Baker Street end was exchanged for a steam locomotive en route.
British Railways inherited a variety of brake vans from each of the Big Four: GWR, LNER, Southern Railway and LMS due to the nationalisation of the railways in 1948.
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