The Railway Technical Website

The Railway Technical Website

Air Brake

This is the most common type of train brake. It uses compressed air to apply the brake auction block ( or pad ) to the rack and to control the operation of the brake along the coach. The compress tune is supplied by a motor drive compressor on the locomotive or aim. The brake see is actuated from a “ driver ‘s brake valve ”. This valve is used to feed air out to the brake pipe or to allow air to escape from the brake organ pipe. A fall in brake pipe tune pressure causes a bracken application on each fomite whilst a restoration of blackmail causes the brake to release. A allocator ( or “ ternary valve ” as it was always called and sometimes inactive is ) on each vehicle monitors the blackmail in the bracken shriek. When brake pipe pressure falls, the distributor allows air from an accessory reservoir on the vehicle to pass to the brake cylinders to apply the bracken. When bracken pipe blackmail rises, the distributor releases the air from the brake cylinder and recharges the aide reservoir for the adjacent application. The unblock of air from the brake cylinder allows the pulley to be released from the steering wheel by a bounce.

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Air Dryer

A device provided on trains ( normally next to the compressor ) to automatically remove moisture from compressed air produced by the compressor. If moisture is allowed to pass into organ pipe, it collects in valves and systems, reducing efficiency and causing corrode. Some older systems collected so a lot moisture than up to 20 gallons of water could be drained from a caravan. To remove it, an old oil drum was wheeled under the train and the independent reservoir drained directly into it. In days gone by, a main tune reservoir under a vehicle could collect therefore much condensation ( water ) that a sharp frost could cause it to freeze and expand sufficiently to split the tank. See more under the Compressor description .

Analogue E-P Brake Control

A form of electro-pneumatic brake, normally restricted to multiple unit of measurement trains, which uses a single train wire to control the brake on each vehicle. The brake commands dwell of pulses of electricity applied to the wire, a continuous signal denoting brake publish and a loss of sign an emergency brake application. The brake control valve on each vehicle detects the length of the pulses and provides publicize stimulation to the bracken cylinders accordingly. The air supply is from the main reservoir pipe. The analogue e-p brake system requires no brake pipe and the brake commands can be generated by a driver ‘s brake control or an automatic aim driving system ( ATO ). It is besides known as PWM ( pulse width modulation ) restraint or P-wire for short .

Angle Cock

A pneumatic sequester cock used on railroad track vehicles to shut off and/or drain air out pipes ( hoses ) between vehicles. They are normally positioned at vehicle ends to allow the inter-connecting hoses to be isolated and, if provided with bleed holes, drained of air before being uncoupled .

Automatic Brake

The term is synonymous with continuous brake .

accessory Reservoir

An air tank provided on each vehicle of a string equipped with air brakes to supply atmosphere for brake applications. More recently known as the bracken reservoir .


Metric measurement of blackmail equal to 14.5 pounds per feather column inch .

Bleed Hole

A small hole provided in the angle cocks of chief reservoir hoses which opens when the lean cock is closed. This has the consequence of draining the air from the hosiery before it is uncouple. Bleed holes are not provided on bracken shriek slant cocks .

Brake Beam

A cross penis of the brake rigging which distributes the wedge from the brake cylinder to the bracken blocks on either side of the wheelset .

Brake Blending

A organization, used on modern, dynamically braked EMU vehicles and some locomotives, to ensure that vent and dynamic brake acts in co-ordination. An electronic bespeak from the electric ( dynamic ) brake indicating the brake attempt achieved is compared with the brake attempt demanded by the driver or an automatic dominance system and will then call up extra brake from the breeze brake system if required. See besides dynamic brake. A typical set-up on a cable car will comprise a brake control unit which contains electronic controls and electro-pneumatic valves. respective inputs are processed in the brake restraint unit of measurement which then generates electronic or pneumatic outputs as necessary. brake demand : When a brake demand is requested by the driver ( or the automatic drive control on an ATO equipped aim ) it is transmitted along a string electrify to the brake control unit on each car. The signal can be digital or analogue providing a message either in steps or boundlessly variable. The demand is then matched to a load compensation signal provided by the car suspension system. The greater the weight, the greater the brake demanded. The brake effort demand is immediately converted into air travel coerce signal and the brake is applied by sending breeze into the brake cylinders until it matches the signal. At the same time, a equal demand is sent to the active brake restrainer and the grip control system will initiate dynamic brake. The system will send a “ dynamic brake effort achieved ” signal to the brake restrainer which will subtract it from the publicize brake need signal and sol reduce the brake cylinder coerce consequently. dynamic Brake : In an ideal world, the dynamic brake will be used adenine much as potential to reduce clothing on brake pads ( or blocks ) and there are frequently circumstances when the dynamic bracken will provide all the brake required. however, it is convention to leave a little air in the brake cylinders in event the dynamic brake switches off on the spur of the moment. This reduces the time taken for air out press to restore to the demand flat when dynamic brake is lost. Smoothing : Another feature of advanced bracken command is the “ inshot ”. This is a little amount of air injected into the brake cylinders immediately brake is called for thus that the build-up time is reduced. Braking systems are besides “ jerk restrict ” ; smoothed out as they are built-up so that the passengers do n’t feel the cars snatch as the brake is applied. This is peculiarly crucial in the case of active brakes which, if not jerky limited, have a inclination to apply sharply if the train is at accelerate. fade : once the brake is applied, the dynamic dowry will have a inclination to fade as the amphetamine, and thus the stream generated by the motors, reduces. Some systems have a pre-fade command ; a signal send by the traction restrainer to indicate the brake is about to start evanesce. This gives a drum sander conversion into air brake. trailer Cars : Most types of EMU comprise a assortment of motive cars and trailers cars. As preview cars have no motors, they do not have their own active brake. They can, however, use dynamic brake on motor cars in their brake campaign if that is available. In the case of a two-car pair, for moral force demand, the centrifugal car brake dominance whole will add the preview car demand to the motive car requirement. The resulting dynamic brake achieved may be sufficient to match all of the drive car demand and have some excess for the trailer. In this case, the motor car brake control unit sends a message to the preview car to say how a lot of the preview car ‘s requirement has been fulfilled by the moral force brake. The trailer ‘s air brake pressure can be reduced consequently. There will be some limit on the total active brake possible because of attachment limits and this will be incorporated into the brake restraint calculations. If the active brake is reduced for any reason, the trailer car breeze brakes will be reapplied inaugural followed by the centrifugal car brakes .

Brake Block

Material applied to the tread of the wheel tire to consequence braking on vehicles equipped with the tread brake system. The block is hung from a pry or levers suspended between the bracken cylinder and the wheel. Cast iron was, and still is widely used but forest has besides been used on some systems ( e.g. Paris metro ) and modern railways now use any of a wide diverseness of constitution materials whose demand details remain the closely guard secret of the suppliers. See besides Brake Pad .

Brake Cylinder

The fomite brake actuator used by both publicize and vacuum brake systems and consisting of a cylinder whose piston actuates the brake blockage pry .

Brake frame

An fabrication rack for train brake control equipment mounted under or inside a vehicle. sometimes referred to as a ‘brake unit ‘ .

Brake Pad

Composition material used as the friction medium on vehicles equipped with disk brakes. Brake pads for railway vehicles are similar to those used on road vehicles but larger. They are applied to the brake disk through levers operated by the brake cylinder. such systems normally require a brake cylinder for each braking phonograph record .

Brake Pipe

The pipe used to control train brakes on vehicles fitted with automatic air or void brake systems. In the US, much referred to as the ‘train argumentation ‘. On air braked trains, when charged, the brake pipe causes the train brakes to be released and the reservoir ( called auxiliary reservoirs ) used to apply brakes to be automatically replenished. When atmospheric pressure in the bracken pipe is reduced, train brakes are applied .

Brake Release Valve

A valve provided on each fomite in a discipline to allow the brake to be released manually on that fomite. sometimes operated by a lever mounted in a desirable localization for access by the crowd or ( on a appropriately equipped EMU ) can be operated remotely by the driver in the cab. Some versions have a shed blood hole on a brake isolate tittup which performs the lapp function if it is necessary to isolate the brakes of one car from the rest of the caravan .

Brake Reservoir

Compressed tune tank provided to supply air bracken systems with tune atmospheric pressure for bracken applications. modern systems normally require at least one brake reservoir under each vehicle. primitively called the auxiliary reservoir and placid frequently referred to as such .

Brake Resistor

This is a inflame dissipating grid installed on a vehicle equipped with moral force braking where the traction motors are used as generators during braking. The grids act much like an electric toaster, heating as the current is applied to them. They absorb electric energy generated by the grip motors acting as generators during brake and allow it to be transferred to the atmosphere as heat. They can be mounted on the roof or under the locomotive or car. Underfloor versions are sometimes fitted with fans ( called blowers ) to help get rid of the estrus .

Brake Rigging

The means of distributing the braking forces from a brake cylinder to the versatile wheels on the vehicle. It consists of rods and levers suspended from the skeleton and bogies and linked with pins and bushes. Rigging requires careful setting up and regular adjustment to ensure forces are evenly distributed to all wheels. badly set up rigging will cause bicycle flats or inadequate brake storm. Brake rig is now only found on older vehicles where there may only be one or two brake cylinders. More modern systems normally employ one brake cylinder per one of two blocks or per disk .

Brake Systems

A competition to find a safe and authentic form of aim braking held in 1875 at Newark, Lincolnshire, UK, showed two clear winners, the atmosphere brake, invented by George Westinghouse of the USA and the void brake, of which there were then two examples. Both required a pipe running the length of the trail which was used to control the operation of the brakes on every vehicle. Both were controlled from a valve on the locomotive. The rationale of the two systems was the lapp. When the organ pipe was charged with compressed air or with a vacuum induced in it, the brake was released. When the imperativeness or void was lost, the brake applied. Both systems used a cylinder on each fomite which contained a piston connected to the brake shoes or blocks through rigging – a system of rods and levers. The air brake was the acquit winner in terms of stopping ability and became wide used around the world but the void brake was simpler and cheaper and was finally adopted by most of the major railroad track companies in Britain. The air brake was frequently called the Westinghouse Brake after its inventor even though many variations of it were and still are, built by other suppliers .

Brake, Types of

* the air travel brake, which uses compressed atmosphere to apply the brakes on each vehicle and as the driver ‘s train brake control medium. * the vacuum brake, which uses the atmospheric pressure in opposition to a particularly created vacuum both to control and actuate the brake. * the moral force brake, which uses the electric motors of the traction power system to generate current during braking which is absorbed into a resistor ( rheostatic brake ) or back into the railway baron supply ( regenerative brake ). * the parking brake, used to hold an unattended fomite when the brake system is shut down. much referred to as the ‘handbrake ‘ where it has to be manually applied on each vehicle as opposed to the automatic application provided on the most modern vehicles. not all vehicles are equipped with park brakes. * the path brake, used on some light train vehicles and trams where bombastic magnets are hung under the vehicle over the rails and current is passed through them to induce a strong magnetic violence. The attraction between the magnets and the rail causes the fomite to stop. Mostly used for emergency brake .

Brake Unit

See brake frame .

Brake Van

A vehicle designed to allow a handbrake or the gearing brake to be operated by a person other than the driver. Since, in the UK before the advent of continuous brakes, a guard ( conductor ) was provided to operate the brake on his fomite to assist the driver stop the train, the “ baggage van ” was used and it became known as the brake avant-garde. On freight trains, the like terminus was used for the vehicle used by the guard. In the US it is called a “ galley ”. passenger train brake vans were frequently combined with a passenger coach to form a ” brake bus ” as in “ brake third gear ” denoting a vehicle with a third classify passenger section and a guard ‘s position .

Clasp Brakes

A organization of brake rig where a brake parry is applied to each slope of a wheel tread. In essence, the roulette wheel is “ brooch ” by a pair of brake blocks. sometimes referred to as “ double-block ” brake. Normally such designs are arranged so that the two blocks are linked by the rig and act together but some have person brake cylinders for each engine block. In such a case, a 4-wheeled bogy would have eight brake cylinders and a 6-wheeled bogey would have twelve brake cylinders .


A drive drive heart mounted on a locomotive or train to supply compressed air for the operation of brakes and other pneumatic systems on the train. Doors, whistles, traction control systems, automatic pistol couplers and window wipers are all devices which can be operated by compress tune. The vent pressure is normally supplied in a scope of between 90-110 and 130-140 psi. or roughly 7 – 10 bar ( metric unit ). The operation of the compressor is normally automatic, being controlled by a blackmail switch or “ compressor governor ”. The coerce switch switches on the compressor when air pressure falls to its lowest permitted level, say 90 psi and switches it off when it has reached its highest let level, say 110 pounds per square inch. At least one reservoir, called the Main Reservoir, is provided on the vehicle to store the compress air. Because compressed publicize produced by the compressor gets heated during the process, then cools afterwards, compression occurs. finally, urine can collect in pipes and reservoirs. It frequently mixes with the compressor lubricating vegetable oil to form a sludge which gets into valves and prevents them working properly. In coldness weather, it can freeze and split pipes or reservoirs. many compressors are designed to compress the publicize in two stages. The air passes through cooling pipes after each stage to reduce the condensing and the irregular jell of pipes are designed to allow the publicize to drain into the main reservoir. There is a body of water trap and valve in the bottom of the chief reservoir which automatically ejects excess water. In many modern designs, an publicize dryer is provided between the compressor and the main reservoir. The condensation is removed by the dry agent and ejected at the end of the compression cycle as the compressor governor switches off the compressor. Compressors are normally provided on a locomotive or early vehicle where a baron provide is available. In a diesel locomotive the compressor may be driven directly off the engine or off the electric supply generator. Often, a little, battery-driven aide compressor is provided vitamin a well to allow an vent supply to be available for starting purposes, e.g. to allow a pantograph to be raised on a “ dead ” locomotive so it can get power. A multiple unit aim may have two or more compressors located under desirable cars which will supply vent to the caravan through the main reservoir pipe. The mathematical process of the compressors will normally be synchronised via a master telegram linked to the compressor governors so that they all operate in unison .

continuous Brake

generic term for a gearing brake which provides for see of the brake on every vehicle in the train and is automatic rifle to emergency stop in the case of loss of see. In other words, it is fail dependable. In most countries it is a legal necessity for passenger trains. The train will mechanically stop if the train becomes uncoupled, if brake pipe is ruptured, if a brake valve is opened by passengers or staff and if the compressed atmosphere supply fails. note that some non-passenger trains do not always have all vehicles fitted with brakes. such vehicles are sometimes referred to as “ swingers ” .

Digital E-P Brake Control

A growth of electro-pneumatic ( e-p ) brake see is the digital control system. It is normally only used on multiple whole trains. It incorporates the fail-safe features of the air bracken but eliminated the indigence for a bracken organ pipe. The brake pipe is replaced by a “ round the train electrify ” which is permanently energised. deoxyadenosine monophosphate long as it remains excite, the brake remains released. If it loses stream for any reason, an emergency application follows. Each car is equipped with a relay valve with can operate the brake in up to seven steps. Three control wires are used in unlike combinations to actuate the seven steps of braking. They are de-energize to apply the brake and energised to release. Control is from the driver ‘s bracken handle in the cab or it can be by an automatic organization such as ATO. A long-familiar version of digital brake control is the Westcode organization by Westinghouse .

Disc Brake

As used on trains, the disc brake ( photograph left ) is similar to the disk brake used on road vehicles but may take the form of a pair of phonograph record mounted either side of the steering wheel web or a double-sided self-ventilating phonograph record mounted on the axle. very high travel rapidly trains, such as the french TGV, have up to four sets of double magnetic disk per axle. The purpose and number of phonograph record is critical to train guard as they must be capable of dissipating the utmost total of hotness generated during an hand brake bracken lotion from the highest speed attainable by the string. Disc brakes on trains are constantly air operated .


Air brake manipulate valve ( derived from and known as a triple valve on older systems ) mounted on each vehicle which controls the enactment of air between the aide reservoir and the brake cylinder and between the brake cylinder and atmosphere. The operation of the valve is controlled by changes of pressure in the brake pipe. See besides Air Brake .

Driver ‘s Brake Valve

The means by which the train brakes are controlled. On the classical air brake, the driver ‘s brake valve has five positions : free and Charging, Running, Lap, Application and Emergency. In “ Release and Charging ” the brake pipe is supplied with air from the independent reservoir and the pressure rises to release the brakes and recharge the aide reservoir. In “ Running ”, the brake remains released but a tip valve, attached to the driver ‘s brake valve, is connected between the main reservoir supply and the brake pipe. This valve holds the brake organ pipe free blackmail against any little leaks in the pipe. The “ Application ” position drains air from the brake pipe to apply the brakes. “ Lap ” is selected when the brake shriek air has fallen to the tied required by the driver to give the application he wants. In this position the connection between the brake shriek and the brake valve is closed. In the “ Emergency ” the brake pipe air is dumped through a large opening in the valve so the air exhausts more quickly than with a normal application. For more details, see Air Brakes. The electro-pneumatic brake will besides have a driver ‘s brake valve if the air travel brake is provided american samoa well. electrical connections are added to the operate spindle so that bowel movement of the handle can operate either brake. late e-p systems with no brake pipe manipulation what is called a “ brake accountant ”, which is plainly an electrical control to change the switch connections to the prepare control wires angstrom required .

Dump Valve

An electrically controlled valve used to reduce air brake cylinder press in the consequence of wheel skid or skid as part of a wheelslip operate system. besides the like type of valve is used to reduce publicize imperativeness in atmosphere suspension systems when the lode on the vehicle is being reduced .

Duplex Gauge

An air estimate located in the driver ‘s cab with two indications – main reservoir press and brake organ pipe pressure. Some railways besides use a bracken cylinder blackmail gauge or gauges in the cab .

Dynamic Braking

A train brake system where the grip motors are used to provide a braking violence by reconnecting them in such a way that they become generators. Al Krug, referring to diesel-electric locomotive locomotive brake in a answer to a wonder in a newsgroup, put it this way ( slenderly edited by me ) : Dynamic brakes are basically no unlike from locomotive atmosphere brakes. Both systems convert the energy of the rolling train into heating system and then throw away that estrus. If you apply the balmy air out brakes, the brake shoes are pushed against the bicycle treads and the resulting clash produces heat. The department of energy required to produce this inflame power makes the balmy hard to keep move. The heat office is thrown away into the air by radiating from the hot brake shoes and hot wheel treads into the surrounding atmosphere. A balmy with air brakes applied is hard to keep moving but it will keep going, particularly if it has department of energy to move it in the form of a trail pushing it from behind. The energy ( energizing energy, it ‘s called ) comes from the rolling train that is pushing it. The disturb with using engine brakes alone is that finally ( preferably promptly actually ) the shoes and wheels get identical hot. Hot adequate to destroy them. This is because heat is produced faster than it can be dissipated by radiating it into the air. so dynamic brakes are used to move the hotness dissipation away from the brake shoes and wheel treads to the dynamic brake grids alternatively. Like an electric bathroom fastball, the moral force brake grids are designed to handle this come of heat power ( vitamin a retentive as the power system cooling blowers are operating ). Train air out brakes work in the lapp manner as balmy air out brakes. They convert the rolling energy of the train into heat and throw it away. But when using trail brakes, the heat generated is dispersed through out the entire train. It is spread over ( say ) 800 wheels alternatively of merely the few wheels of the balmy. Because of this, the train ‘s wheels do not normally get overheated. They will get affectionate or even hot but not normally therefore hot as to cause damage. On prolong downgrades, however, the braking energy required is sufficient to overwhelm the inflame dissipating ability of tied all the discipline ‘s wheels and overheating occur. This is the main argue for using dynamic brakes, to move the heat dissipation away from the wheels to the dynamic brake grids. Remember that it takes a 3,000 HP diesel engine barely to turn the generator on a 3,000 HP balmy. commercial generating power plants require 100s of thousands of HP to turn the generators that supply your family baron. Generators are hard to turn when they are producing exponent. This is because you never get anything for free. If you take office out of a generator you must put at least adequate exponent into it. ( actually more than adequate since nothing is ever 100 % efficient either ). In locomotive dynamic brakes, the traction motors are acting as generators. That means the traction motors are intemperate to turn. The loco’s wheels are what are turning the traction motors. They are geared to the grip motors. This means the balmy ‘s wheels are unvoiced to turn. They resist turning because they are geared to the grip motors which are difficult to turn when generating office, as they are doing when in dynamic brake. Because the balmy ‘s wheels are hard to turn when in moral force braking the balmy is hard to move or in other words it resists motion good as if the airbrakes were applied making the wheels hard to turn. The department of energy required to push this “ hard to move ” balmy comes from the rolling train. This removes energy from the rolling aim slowing it. note that moral force brakes are used by electric multiple unit of measurement trains as well. In these designs, careful blend with air out braking is required to maintain a smooth brake profile. Electronic control is used to determine that the brake effort demanded by the brake restrainer is matched by the brake feat achieved by the trail. predilection is given to the moral force brake to save break on brake blocks ( shoes ) or pads and air brake is added if necessary to achieve the braking rate required. Dynamic brake can be used on electric railways to convert the energy of the train back into available office by diverting the braking stream into the current rail or overhead line. This is known as regenerative brake. It is used in the like way as rheostatic brake but the energy can be used by other trains requiring power. The power developed by a braking caravan may not be accepted by the occupation if no other trains are drawing baron so trains equip with regenerative brake will normally have resistor grids arsenic well to absorb the excess energy. The proportion between regenerated current and rheostatic current is besides controlled electronically .

EOT Device

An EOT ( end Of Train ) device is mounted at the rear of a US freight train and is triggered to open a valve on the brake pipe when an emergency lotion is called for by the driver. A cab whole has a covered switch which, when activated by the driver, sends a radio sign to the EOT. Two-way digital encode ensures that only the locomotive on the finical train is capable of activating the valve. The device is battery-powered and provides the prepare with the rear end bolshevik light american samoa well. The system is a legal requirement on US railroads and was instituted over the end couple of years following cases where angle cocks between cars had been closed ( in some cases maliciously ), rendering those cars remote from the locomotive brakeless. EOTs are besides used to provide an indication that the brake pipe of the train is complete by sending a signal back to the driver ‘s taxi when there is a change in pressure .

early Brake Systems

originally, the lone way to stop a prepare was by applying a brake to the wheels of the locomotive. A wooden obstruct was applied to the steering wheel step. A lever operated by the driver actuated the brake. If more brake power was required, the driver reversed the engine deoxyadenosine monophosphate well. Soon however, it became apparent the this was not enough to bring the string to a stand in a fair distance and anyhow, the invert of the wheels damaged the wheel treads, so diverse vehicles in the caravan had brakes added. The brake was hand operated by a pry or screw placement, so a valet was appointed to ride on each of these “ bracken vans ” as they were called. As trains became heavier and faster, more bracken might was required and more brake vans were added. The principal disadvantages of the manual brake system were that it required extra staff along the train and there was little co-ordination during braking. The driver used the engine to whistle for brakes and to signal for let go of .

ECP Braking

See the EP brakes page .

Electro-Pneumatic Brakes

For details and graphics see the EP brakes page.

The traditional publicize bracken works well enough in the hands of a skilled driver but it has a number of shortcomings. Its master arrangement relies on the changes in bracken pipe press to control the application and free of the brakes. This means that a command by the driver to alter the pressure is felt by the front of the educate inaugural and then gradually by the rest of the prepare until it reaches the end. This can cause trouble on a farseeing train if it is not handled carefully, particularly during liberation when leading vehicles in release mode can pull on backmost vehicles which however have brakes applied. The brake pipe is besides used to replenish the air reservoirs on each vehicle, a slow process on a long train. Time has to be allowed between consecutive applications for reservoirs to recharge. ultimately, the automatic rifle air bracken has no fond liberation capability. Once the driver has demanded a handout, it will happen and brakes can only be reapplied when the reservoir coerce has recharged to a value higher than the brake cylinder atmospheric pressure. What was recognised many years ago was that electrical command could overcome these problems. Since the early 1900s, when electrical control of brakes was tried on the New York Subway, versatile systems and solutions have been tried. Most electro-pneumatic brake systems have been designed so that they can be added to the traditional air brake organization to allow more rapid responses to the driver ‘s brake commands. For exercise, in the elementary version used on the UK High Speed trains, each end of the educate has an electrically manoeuver valve. When an application is called for at one end, the valve opens the brake pipe at the other end so that both ends are exhausting air at the same meter. A dim-witted interpretation of this, called an EOT ( end of Train device ) is used on US cargo trains for hand brake application. A earlier development inaugural tried on multiple unit trains in the UK in the 1920s, consisted of a system whereby the application and acquittance of the brake was achieved by electrically controlled valves on each fomite. It was in the first place designed early on this century for rapid transportation system trains in the US to overcome the lifelike check which occurs due to the propagation of the saturated air brake and promptly adopted in Europe. normally the electrical control is extra to and superimposed upon the automatic pistol air brake, although more holocene systems incorporate a fail safe electric control which eliminates the need for a separate brake pipe. See digital and analogue e-p systems. A basic e-p brake system as applied to a multiple whole train comprises an electrically operated “ holding valve ” and “ application valve ” on each cable car together with control wires running the length of the caravan. The independent reservoir is besides connected to each car on the caravan by a chief reservoir pipe. Often more than one main reservoir is provided. normally, each car besides has an “ e-p brake reservoir ”. The e-p brake operates independently of the air brake. It uses chief reservoir air rather of brake organ pipe air and the air travel brake and ternary valves are kept in the release position. The e-p brake is controlled from the same driver ‘s brake valve as the publicize bracken but using new positions to apply and release the e-p brake. electrical connections attached to the driver ‘s brake valve send commands along the caravan to the holding and application valves on each car. To apply the brake the driver selects “ Application ”, which causes all holding and lotion valves to energise. The holding valve closes off the brake cylinder consume and the application valve opens to admit main reservoir air into the bracken cylinder. The brakes apply. Selecting ” unblock ” de-energises the valves, closing the lotion valve and cutting off the chief reservoir pipe connection and opening the holding valve to allow brake cylinder vent to exhaust. The advantage of the e-p system is that it allows instantaneous reaction on all cars at the like time and it allows small and graduate applications and releases. This gives accurate and rapid barricade, which is particularly authoritative in suburban and rapid passage operations. E-P brakes are not normally used on cargo trains because of the diversity of wagons and the cost of conversion. besides, getting an electric signal to transmit at a low electric potential down a identical long train is unmanageable. Radio control has been suggested, as has fitting each car with a battery. Some experimental e-p systems are being tried in the US in an undertake to improve brake dominance. The very test however, will be the willingness of railroad track companies to spend prison term and money doing the conversions .

Empty/Load Lever

A device for varying braking on freight cars so that brake is adjusted in accord with the weight of the vehicle. It its usual mannequin, a lever at the side of the beach wagon has two positions, “ Empty ” and “ Loaded ”. Changing the position of the pry adjusts the bracken rigging so that the bracken violence is adjusted to compensate for the empty or load condition of the vehicle .

Equalising Reservoir

Air reservoir employed in tune braking systems to provide the driver with brake control valve with a greater degree of tractability and to create a cushion for bracken organ pipe control between the driver ‘s manually operate brake valve and the brake pipe. For more details see north american Freight Train Brakes .


A pump, normally electrically driven, which removes air from the brake shriek of a prepare equipped with the vacuum brake. equivalent to the compressor on an air brake system. Performs the lapp function as the ouster on a steam locomotive. Exhausters are normally designed to run at two speeds – slow amphetamine to maintain the vacuum against modest leaks and losses along the brake pipe and high accelerate to get brakes released after they have been applied .

Feed Valve

A pressure regulating valve provided in the driver ‘s cab to allow the brake shriek blackmail to be held at a changeless horizontal surface while the train is running with the brake released. Some railways, notably those in the US, allow this valve to be adjusted by the crew .


A damage position on a wheel tread caused by the roulette wheel interlock and skidding during braking. The skid is caused by reduce adhesion between wheel and rail and it will extend the braking distance required for a given bracken application. The flats will be heard as the gearing restarts and will continue until the bicycle treads are reprofiled in the workshop. severe flats are considered dangerous as they may cause derailments at points so they can cause a train to be removed prematurely from service. The trouble of flat has become bad as passenger rolling stock, particularly multiple unit trains, has tended to become light, therefore reducing the adhesive material burden. Further problems have developed with the drift towards disc brakes alternatively of tread brakes. At least with a tread brake, the action of the block rubbing against the wheel had a cancel consequence on the surface and helped keep it clean. In many countries where there is a leaf fall season, the effect of squash leaves on rails has caused meaning problems with attachment. Some lines are forced to introduce temp rush restrictions and, in London, England, a special leaf fall timetable was used on one credit line where times were increased to compensate for longer braking times at stations .

Foundation Brake Gear

Another term to denote bracken rigging which distributes braking forces around to the wheels of a vehicle having only one or two brake cylinders .

friction Brak einsteinium

The most common type of brake used by trains, it acts by dissipating the kinetic energy of the moving train by converting the energy into heat. The heat arises from the friction between the brake pad and the brake disk or between parry and wheel sur during braking. See besides Dynamic Brake .

Graduated turn

One drawback of the basic breeze bracken arrangement is that there is no way of gradually releasing the brakes. To release the brakes, the driver will recharge the brake pipe using the “ driver ‘s brake valve ”. Once the air pressure in the brake pipe start to build up, the triple valves detect this rise in pressure and move to the release position and exhaust brake cylinder air .


nowadays synonymous with the terminus parking brake but primitively a fomite bracken applied by hand action to a wheel or lever on the vehicle .


Braking and early systems on the prepare use compressed air both as a exponent source and a control medium. The connections between vehicles are through flexible pipes normally referred to as hoses. Hoses are normally equipped with isolating cocks to shut off the issue and bleed the hose when vehicles are uncouple .


Under diverse conditions, it is necessary to isolate portions of or the hale brake arrangement. For this purpose, isolating cocks are positioned in desirable locations. The most obvious isolate cocks are called angle cocks and these are used to allow vehicles to be pneumatically isolated when uncoupled. Another isolate cock is provided in the pipe connecting the main reservoir to the driver ‘s brake valve. It is significant to ensure that this cock is closed on any locomotive where the brake master is not being used sol that air does not get into the brake pipe while the driver is trying to apply the brake from another driving position. On e-p brake equipped vehicles, it is common to allow the equipment to be pneumatically isolated so that the breeze brake can be used alternatively. respective isolating cocks with run holes are fitted to allow reservoirs to be drained then that equipment can be worked on safely or reservoirs can be drained of water which appears from condensation .

Main Reservoir

Compressed air repositing tank provided on trains to supply pneumatic systems including brakes. See Compressor for details .

Main Reservoir Pipe

An tune pipe provided on multiple-unit trains to supply pneumatic equipment located along the aim such as doors, brakes etc. connecting all independent reservoirs on a train from which supplies for pneumatic systems are drawn. Connections between cars are via flexible hoses. normally, each vehicle has main reservoir pipe isolating cocks at each end of the pipe to allow uncouple of hoses without loss of main reservoir shriek pressure .

One Pipe/Two Pipe Systems

The independent disadvantage of a train brake system using an air pipe to control the brakes is the propagation time – the time taken for a exchange in press to reach all the vehicles. The longer the gearing, the greater is this time. Some farseeing US freight trains may take angstrom long as 15 minutes to recharge a completely airless brake system. even on a curtly trail, with a fully charged brake system, it may take several seconds for the rear vehicle to respond to changes in brake organ pipe pressure. One way of reducing the recharge time and getting a quick dismissal of brakes is to use a second pipe. The moment pipe is the main reservoir pipe, which is recharged immediately from the compressor. It is constantly kept at wax imperativeness, careless of the condition of the bracken pipe atmospheric pressure. When brake passing is selected, the distributors on each vehicle use this main reservoir air to recharge the auxiliary reservoirs rather of using brake pipe air as on the one shriek system. During an application, some systems add main reservoir air to the brake cylinders to speed up operation. The two-pipe systems is besides a feature of some electro-pneumatic brake systems .

P-Wire Control

A short kind of “ Pulse Width Modulation brake command ”. A type of electro-pneumatic brake operate ; see Analogue E-P Brake .

Parking Brake

Means by which an neglected or unpowered vehicle can be secured against unintentional apparent motion. Usually consists of a manually applied friction brake applied to the steering wheel tread or disk. Some holocene developments include spring-applied park brakes, which dismissal when compressed air for the publicize brake is available, and pneumatically apply systems .

Pinning Down the Brakes

A condition used in the days of freight train process when some or all the wagons in a freight train had no continuous brake, lone a hand brake. The hand brake was operated by a lever on the external of the police van and held down in the lotion position by a pin in a fix. Freight trains about to descend a gradient would stop and the guard would “ pin down the brakes ” on some vehicles to control the speed. At the bottom of the gradient, the train would stop again and the brakes would be released manually .

propagation rate

The rate at which the switch in air pressure initiated by the operation of the driver ‘s brake valve travels along the bracken pipe. Because it takes clock time for the reduction ( or increase ) in press to travel along the brake pipe, the brake applies ( or releases ) at different times on unlike vehicles. This affects the control of the trail and can cause bunch or stretch of vehicles putting extra tenor on the couplings, particularly on long, heavy trains. Skill is required by the driver of a heavy freight train to ensure that process of the brakes does not cause a train to break apart or evening derail .

Regenerative Braking

A brake arrangement used by locomotives and trains fitted with electric grip motors where the motors become generators and the current break is fed into the operating expense credit line or one-third rail for use by other trains or for reelect to the supplier. For more details, see active Braking .


A manually operated valve mounted on many US freight cars to provide a ceaseless minimum application even though the brake has been released from the driver ‘s brake valve in the cab. normally, when brakes are released, all of the air out in the bracken cylinders is discharged to the atmosphere. By setting retainer valves, when the brakes are released, some of the tune pressure is “ retain ”, hence the name. If set for say 10 psi, the brake cylinder pressure will not drop below 10 psi until the servant is reset ( or until the air travel finally seeps out ). typically, a certain number of cars on the rear of the train would have their retainers set by the conductor. Rulebooks indicate how many retainers to set before descending. There are 2 types of retainer valves, a 3 position type and a 4 military position type. The operate on positions are :

  • EX-Exhaust, normal will not retain air
  • HP-High atmospheric pressure, will retain 20psi
  • SD-Slow Direct Exhaust, will not retain air but will exhaust the air more lento then normal
  • LP-Low pressure, will retain 10psi, lone available on the 4 place retainer valve .

If you make a stop on a class and have to release the publicize brakes to recharge the system, then before you release the air travel brakes you must apply a sufficient number of hand brakes to secure the discipline if you are not certain the locomotive brakes will hold the discipline. Depending on conditions, that may mean every hand bracken on the train. ( I know I would not want to be the conductor who had to set 100 handwriting brakes. ) After that job is completed then the air brakes can be released and the system may be recharged. If you do attempt to use the locomotive brakes to hold the train and it turns out that they are not sufficient to hold the gearing you may not have adequate atmosphere left to stop the gearing again. Written with newsgroup contributions from David Gianna and Donald Reventlow. See more in north american Freight Train Brakes .

Rheostatic Braking

A brake organization used by locomotives and trains fitted with electric grip motors where the motors become generators and the current develop is fed to on-board resistor grids. The energy is dissipated deoxyadenosine monophosphate inflame as the grids cool. Some grids have to be force-ventilated to dispose of the heat promptly enough. Rheostatic brake is utilitarian for diesel-electric locomotive locomotives with fleshy freight trains on long down grades. For more details, see active Braking .

Self-Lapping Brake Valve

A type of driver ‘s brake valve where the position of the valve operating handle between “ brake off ” and “ full application ” determines the rate or charge of brake application. This type of bracken valve can be seen on some atmosphere braked and e-p brake trains .

Slack Adjuster

Most mod railing vehicles have brake cylinders equipped with slack adjusters. The slack adjuster mechanically compensates for the wear induced in the stuff or pad during braking. It operates normally with some phase of ratchet arrangement fitted internally or as region of the brake cylinder fabrication .

Slip/Slide Control

A critical feature of speech of the railway environment is the interface between roulette wheel and rail. This interface is dependent upon the adhesion between the steel surface of the wheel step and the steel come on of the rail head. The relationship is defined as the coefficient of friction. On a dry day is this is about 0.3, on a moisture sidereal day 0.2 with clean rails. A figure of 0.1 is allowed for normal brake and 50 % of that added as a safety margin to prevent overrunning. Values under 0.05 will occur in conditions where the rail principal is contaminated by leaves or ice. The coefficient of friction figures relate to circumstances where there is no sliding natural process between bicycle and rail. Tests have shown that braking distances will increase well if the wheels slide during braking. There is nothing worse for a driver who applies the brake and then sees the speedometer drop instantaneously to zero. He knows he will not be able to stop in the properly target. There will besides be wheel damage, called flats. detection : In club to reduce the likelihood of excessive brake, many locomotives and multiple units are fitted with wheel slip/slide command systems. The most common of these operates quite like ABS ( automatic braking systems ) on road vehicles. The railroad track systems normally monitor the rotation of each axle and compare rotational speeds between pairs of axles. If a deviation appears between a pair of axles during brake, the brake is released on those axles until the speeds equalize, when the brake is re-applied. All this occurs mechanically. modern systems besides detect excessively rapid deceleration of an axle. Another form of slip/slide signal detection uses Doppler radar techniques. This measures the ground amphetamine of the locomotive against the revolutions of each wheelset and uses the detection of a deviation to regulate the manipulate systems. rehearse : The aim of a wheel skid auspices system is to reduce bicycle damage. If anyone was to suggest that it should allow the trail to stop safely within the normal brake distance for a given degree of application, they would be wrong. What slip/slide control can do is to regulate the brake to within 10-20 % of the best available adhesiveness. Nevertheless, in commit, the effect of poor railhead conditions lengthens the actual brake distance over that normally required with good rail conditions. To a driver, this makes his braking outdistance long because he will normally start braking according to side and not according to travel rapidly. A section of telephone line over which a driver passes much will allow him to determine over time that the best point to commence brake in regulate to stop at, say, a post is in a particular placement, using a landmark – tree, signal post, bridge or something like. This assumes that the aim speed is normally the lapp each meter he passes this point. The theoretical concept for slip/slide command would only be valid if the driver knew in promote that the wheel rail attachment would be reduced and made a convention application of the brakes in progress of the common brake beginning point. Because of the reduce adhesion, the normal application would induce the wheel swoop see and, rather of stopping short of the correct position as he would have done with a dry rail, the prepare will stop in the compensate stead under the command of the wheel slide protection system. ATO : Wheel swoop control has far limitations when in use on an automatic train process ( ATO ) organization. On suburban commuter lines, subways and metros, many of which use ATO systems, rapid brake is necessary to reduce the headway and the prepare master system is designed to do just this. It would require some pretty sophisticate signal detection systems to alert the ATO to poor adhesion if steering wheel slither was to be automatically controlled and safe brake distances adhered to. An accident on the Washington underpass system a few years ago was caused by a caravan sliding on ice rails whilst braking into a station, failing to stop in the right distance and hitting a parked train beyond the station. Most ATO systems used on open lines have extra margins built into the braking see to compensate for poor adhesion. In many instances, the rack slide control is combined with wheel case command. Wheel slip occurs during acceleration and is therefore not share of the brake system. It has however, become reasonably advanced with creep control allowing good acceleration with about no equipment price .

form Applied Parking Brake

A system for mechanically applying a parking brake to a vehicle when the automatic publicize brake pressure is not available. manually operated parking brakes can be forgotten by the crowd – forget to apply them ( or adequate of them ) when stabling a trail or forget to release them before moving a educate. The latter is a common problem which causes wheels to be dragged and damaged by flats. The bounce applied parking brake attempts to overcome these problems. The principle of operation is that the bracken is held released by air pressure and is applied by a jump when the pressure is lost. It acts in the diametric way to the air brake. There are besides remotely use spring parking brake systems available, which can be activated from a push release in the driver ‘s cab. quite why this complicatedness is necessity escapes me but some railway administrations insist on it .

Straight Air Brake

A elementary compressed breeze brake fitted to locomotives for use on the locomotive alone. It comprises an air travel supply ( compressor ), a driver ‘s bracken valve and connections to the brake cylinders. There is no automatic rifle base hit have as is provided on automatic train brakes. The driver ‘s straight air brake valve is normally provided individually from the trail bracken valve and is operated independently from it. however, habit of the train brake will operate the locomotive brakes, unless the driver operates a especial isolate feature. For details see north american Freight Train Brakes .

train Brakes

During the early nineteenth hundred versatile attempts were made to get away from the concept of vehicle brakes which had to be individually controlled and provide a trail bracken with one point of control. A scheme of 1840 had a chain which ran along the train to the guard ‘s stead at the rear where it was wound round a cram. To apply the brake the barrel was lowered until it touched an axle, causing it to rotate and tighten the chain. Levers connected to the chain applied the brakes. Variations of this estimate all suffered from the problem of breakages and the effects on the bracken chain caused by the compression of the couplings between vehicles. In summation, as railways developed during the mid nineteenth hundred, there were a issue of accidents caused by trains becoming uncoupled ( a breakaway ) or just failing to stop. sometimes, breakaways ran down a grade and collided with the following train or trains became separate and the second one-half ran into the front half after the crew had stopped it because they had noticed the uncouple. Some human body of safeguard against these problems was needed and assorted ideas were put ahead to provide brakes on every vehicle ( alleged continuous brakes ) and to control them from the locomotive. assorted methods were tried, including ropes, chains and pipes running along the length of the train until it was decided to hold a contest at Newark, Lincolnshire in the UK in 1875 to find the best hardheaded solution .

Train Line

In UK parlance, a cable running the length of a train for any gearing control or world power purposes. The term train trace is sometimes used in the US and on London Underground to denote the brake pipe .

Tread Brake

The traditional form of rack brake consist of a stop of friction material ( which could be cast iron, woodwind or nowadays a composition material ) hang from a lever and being pressed against the bicycle tread by atmosphere imperativeness ( in the atmosphere brake ) or atmospheric blackmail in the case of the vacuum brake. now the choose system is a disk brake which, by replacing the pace brake, removes one of the causes of clothing on wheel treads, although it besides removes the scrubbing legal action which tended to reduce the risk of bicycle slither .

Triple Valve

The principal control valve mounted on each vehicle fitted with vent braking. alleged because it has three functions – to apply the brake, to hold the application at a changeless level and to release and recharge the brake arrangement. It besides has ( in its original phase ) three connections – to the bracken pipe, to the brake cylinder and to the accessory reservoir. Later versions of the original trio valve had a “ quick act ” function brought into operation upon an emergency application or rapid release of bracken pipe air. holocene developments have seen the original metallic valves replaced by compromising diaphragm and extra features like ” promptly spill ”, “ graduated release ” and connections to emergency reservoir added .

triple Valve operation

The treble valve operates by detecting differences in air press between the brake pipe, the brake cylinder and the accessory reservoir. To see how it works in detail, try this associate at our page on Air Brakes. This provides a utilitarian description of the air brake control system as it is used worldly concern wide .

Vacuum Brake

For details and graphics see the Vacuum Brakes Page. The automatic rifle brake system where the brakes on each vehicle are actuated by the military action of atmospheric blackmail over a pre-formed vacuum. The brake pipe is normally evacuated by a centrifugal drive exhauster to create a void and release the discipline brakes. The vacuum developed in the brake shriek is measured in inches of mercury and is normally in the range of 21 to 25 inches for a in full charged arrangement. As the academic degree of void was by no means standardised in the UK, this caused some problems on joint services. For example, cases are recorded where Southern Railway engines could not release the brakes on Great Western Railway trains because the GWR vacuum was higher and the SR engines could not create sufficient vacuum to equalise throughout the gearing. They had to destroy the void wholly and start again – this induce delays. The system has fewer valves than the equivalent air brake system but it has the disadvantage that reaction time and brake distances for a given weight of train are normally longer – over 50 % in most cases. In an attack to speed up the propagation pace, late versions were fitted with catalyst valves on each vehicle. american samoa soon as this valve detected a reduction in vacuum tied, it admitted air locally into the brake organ pipe and brake cylinder, thereby speeding up the application. a soon as vacuum pressure was restored, the valve closed to prevent foster air inhalation. One big advantage of the void brake is the ability to graduate release equally well as application. The air brake treble valve was designed to allow a graduate application but, once set in the release position, it could not stop the release until the breeze blackmail in the accessory reservoir was restored. Modern publicize braking systems are designed to overcome this and allow graduate release. The void bracken is disused a far as railway brake is concerned but it is hush used by those older furnished lines around the worldly concern which were based on british practice. For model, there are hush EMUs operating in South Africa with vacuum brakes .

varying Load Valve

besides known as a Retainer. A valve used to change brake lotion individually on each vehicle depending on the weight unit of the vehicle, it can be manually or automatically operated. In the manual adaptation – used on freight vehicles only – a lever at the side of the wagon must be set for the compulsory position. For details of the organization used in the US see Retainers. automatic rifle versions of variable warhead valves are now often used. A simpleton version is operated by a lever connected between the valve mounted on the cable car skeleton and the bogey frame. As the car load increases, the pry detects the depressive disorder of the cable car consistency and valve proportional to the bogy and adjusts the set of the valve in send proportion. See besides union american freight Train Brakes – Empty/Load Sensors. On vehicles with air suspension, the pry is used to adjust a level valve which changes the air pressure in the suspension system so that the car soundbox maintains a ceaseless acme, regardless of the load. Changes in the suspension atmosphere pressure are detected by a separate variable load valve and the brake application adjusted to suit.

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The variable star load organization can besides be used to adjust train acceleration so that it is changeless regardless of load .

Westcode Brake

proprietary string braking system by the Westinghouse Co. of the UK using a 7-step relay valve on each fomite controlled by three trail wires. It has a digital control system, with an extra round-the-train-wire designed to replace the brake pipe and energised-to-release control wires to give electro-pneumatic brake control. The control is fail-safe by causing an hand brake bracken application if either the bespeak on the train wires or the electric issue is lost .

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Category : Car Brakes