58-995: The Port Perry Branch is a rail line owned and operated by the Norfolk Southern Railway in the U.S. state of Pennsylvania . The line runs from the Pittsburgh Line in North Versailles Township southwest through the Port Perry Tunnel and across the Monongahela River on the PRR Port Perry Bridge to the Mon Line in Duquesne along a former Pennsylvania Railroad line. The Main Line of
116-496: A triple valve , also known as a control valve . Unlike the straight air system, the Westinghouse system uses a reduction in air pressure in the train line to indirectly apply the brakes. The triple valve is so named because it performs three functions: It allows air into an air tank ready to be used, it applies the brakes, and it releases them. In so doing, it supports certain other actions (i.e. it 'holds' or maintains
174-447: A "service rate reduction”, which means that the brake pipe pressure reduces at a controlled rate. It takes several seconds for the brake pipe pressure to reduce and consequently takes several seconds for the brakes to apply throughout the train. The speed of pressure changes during a service reduction is limited by the compressed air's ability to overcome the flow resistance of the relatively-small-diameter pipe and numerous elbows throughout
232-476: A blown hose), the train breaking in two and uncoupling air hoses, or the engineer moving the automatic brake valve to the emergency position, will cause an emergency brake application . On the other hand, a slow leak that gradually reduces brake pipe pressure to zero, something that might happen if the air compressor is inoperative and therefore not maintaining main reservoir pressure, will not cause an emergency brake application. Electro-pneumatic or EP brakes are
290-596: A broken air brake hose) causes the air brakes to engage unexpectedly. An example of this problem can be seen in the accident that caused the death of John Luther "Casey" Jones on 30 April 1900 on the Illinois Central Railroad main line at Vaughan, Mississippi . The modern air brake is not identical with the original airbrake as there have been slight changes in the design of the triple valve, which are not completely compatible between versions, and which must therefore be introduced in phases. However,
348-683: 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 (but not exclusively) in North America , and railway , generally used in English-speaking countries outside North America and by
406-502: A long time a three-wire version of the electro-pneumatic brake, which gives up to seven levels of braking force. In North America , the Westinghouse Air Brake Company supplied high-speed control brake equipment for several post- World War II streamlined passenger trains. This was an electrically controlled overlay on conventional D-22 passenger and 24-RL locomotive brake equipment. On the conventional side,
464-403: A matter of preference by the locomotive builder or the railroad. In some systems, the automatic and independent applications will be additive; in some systems the greater of the two will apply to the locomotive consist. The independent system also provides a bail off mechanism, which releases the brakes on the lead locomotives without affecting the brake application on the rest of the train. In
522-433: A number of safeguards that are usually taken to prevent this sort of accident from happening. Railroads have strict government-approved procedures for testing the air brake systems when making up trains in a yard or picking up cars en route. These generally involve connecting the air brake hoses, charging up the brake system, setting the brakes and manually inspecting the cars to ensure the brakes are applied, and then releasing
580-726: A slot that allows the casting to fit over the rail near the wheel of a derailed car. The locomotive then pushes or pulls the car so that the derailed wheel runs up the rerailer and back on to the track. Also see Extended Wagon Top Boiler . Also see Waist sheet . Also see Expansion knee . Also see Valve gear. Also see Grate Also see Train air signal apparatus. Also see Control system. Also Adhesion railway . Also Adhesion railway . Also see Hub. Also Adhesion railway . Also see Whistle stem. Also Coupler Yoke , Bell Yoke , Guide Yoke , Valve Yoke . Railway air brake A railway air brake
638-616: A tunnel and a bridge. Together, this would provide a bypass via which traffic from the Main Line (today's Pittsburgh Line ) bound for the Panhandle Route, and vice versa, could skip the heavy congestion in the city and avoid Grant's Hill Tunnel. In 1877, the branch was complete between Brinton's Station on the Main Line and Port Perry on the north bank of the Monongahela River. The river bridge between Port Perry and
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#1732798275019696-743: A type of air brake that allows for immediate application of brakes throughout the train instead of the sequential application. EP brakes have been in British practice since 1949 and also used in German high-speed trains (most notably the ICE ) since the late 1980s; they are fully described in Electro-pneumatic brake system on British railway trains . As of 2005 , electro-pneumatic brakes were in testing in North America and South Africa on captive service ore and coal trains. Passenger trains have had for
754-534: 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 Westinghouse system uses air pressure to charge air reservoirs (tanks) on each car. Full air pressure causes each car to release
812-410: Is a little simpler than the air brake. Instead of an air compressor, steam engines have an ejector with no moving parts, and diesel or electric locomotives have a mechanical or electrical "exhauster". Disconnection taps at the ends of cars are not required because the loose hoses are sucked onto a mounting block. However, the maximum pressure in a vacuum system is limited to atmospheric pressure, so all
870-403: Is an indication that the cars' triple valves are malfunctioning. Depending on the location of the air test, the repair facilities available, and regulations governing the number of inoperative brakes permitted in a train, the car may be set out for repair or taken to the next terminal where it can be repaired. A different kind of accident can occur if a malfunction in the air brake system (such as
928-472: Is based on and aligned with UIC Leaflet 540, a document ratified by many train-operating companies. UIC Leaflet 540 explicitly approves the following brake systems: Historically, and according to UIC 540, we distinguish systems technically approved since 1927-1932 such as: Westinghouse W , Knorr K , Kunze-Knorr , Drolshammer, Bozic, Hildebrand-Knorr. In the steam era, Britain's railways were divided–some using vacuum brakes and some using air brakes–but there
986-477: Is called the automatic brake and provides service and emergency braking control for the entire train. The locomotive(s) at the head of the train (the "lead consist") have a secondary system called the independent brake. The independent brake is a "straight air" system that makes brake applications on the head-of-train locomotive consist independently of the automatic brake, providing for more nuanced train control. The two braking systems may interact differently as
1044-461: Is divided into two portions: the service section, which contains the mechanism used during brake applications made during service reductions, and the emergency section, which senses the faster emergency reduction of train line pressure. In addition, each car's air brake reservoir is divided into two sections—the service portion and the emergency portion—and is known as the "dual-compartment reservoir”. Normal service applications transfer air pressure from
1102-414: Is thus fail-safe —any failure in the train line, including a separation ("break-in-two") of the train, will cause a loss of train line pressure, causing the brakes to be applied and bringing the train to a stop, thus preventing a runaway train. Modern air brake systems serve two functions: When the train brakes are applied during normal operation, the engine operator makes a "service application" or
1160-458: Is where the locomotive's air compressor output is stored and is ultimately the source of compressed air for all connected systems. Since the main reservoir pipe is kept constantly pressurized by the locomotive, the car reservoirs can be charged independently of the brake pipe, this being accomplished via a check valve to prevent backfeeding into the pipe. This arrangement helps to reduce the above-described pressure loss problems, and also reduces
1218-598: The 1953 Pennsylvania Railroad train wreck involving the Federal Express , a Pennsylvania Railroad passenger train which became a runaway while heading into Washington Union Station in Washington, D.C. , causing the train to crash into the passenger concourse and fall through the floor. Similarly, in the Gare de Lyon rail accident , a valve was accidentally closed by the crew, reducing braking power. There are
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#17327982750191276-741: The International Union of Railways . In English-speaking countries outside the United Kingdom, a mixture of US and UK terms may exist. Various terms, both global and specific to individual countries, are listed here. The abbreviation "UIC" refers to terminology adopted by the International Union of Railways in its official publications and thesaurus. Also Centering spring cylinder . Also Railway air brake . Also Main Reservoir and Reservoir . Also see Reverser handle . A metal casting incorporating
1334-735: The Pennsylvania Railroad (PRR) was originally constructed with the goal of providing a rail link from the Eastern Seaboard to the waters of the Ohio River at Pittsburgh . By the 1870s, however, Pittsburgh was not just an endpoint; it had become a gateway through which all the PRR's lines to the Midwest passed. With the tracks in the city becoming increasingly more crowded, the PRR sought to bypass some of its traffic around
1392-411: The rate of brake pipe pressure reduction. Therefore, as long as a sufficient volume of air can be rapidly vented from the brake pipe, each car's triple valve will cause an emergency brake application. However, if the brake pipe pressure is too low due to an excessive number of brake applications, an emergency application will not produce a large enough volume of air flow to trip the triple valves, leaving
1450-753: The PV&;C opened the following year, completing the alternate route around the congestion of the Main Line and the passenger station complex in Pittsburgh. For some time, there was also a link from the Port Perry Branch to the main line heading westwards. This consisted of a curved bridge over Turtle Creek at Brinton, and was known as the Brinton "U". The PRR leased the PV&C in 1879 as part of its Monongahela Division. The branch passed to Penn Central Transportation in 1968, Conrail in 1976, and
1508-410: The air from the train line and vent the coupling hoses for uncoupling cars. The air brake only operates if the angle cocks are open except the ones at the front of the locomotive and at the end of the train. The air brake can fail if one of the angle cocks is accidentally closed. In this case, the brakes on the wagons behind the closed cock will fail to respond to the driver's command. This happened in
1566-441: The application and it permits the exhaust of brake cylinder pressure and the recharging of the reservoir during the release). In his patent application, Westinghouse refers to his 'triple-valve device' because of the three component valvular parts comprising it: the diaphragm-operated poppet valve feeding reservoir air to the brake cylinder, the reservoir charging valve, and the brake cylinder release valve. Westinghouse soon improved
1624-466: The basic air brakes used on railways worldwide are remarkably compatible. European brake systems vary between countries, but the working principle is the same as for the Westinghouse air brake. European passenger cars used on national railway networks must comply with TSI LOC&PAS regulation, which specifies in section 4.2.4.3 that all brake systems must adhere to the EN 14198:2004 standard. This standard
1682-401: The brake pipe's pressure directly to atmosphere. This serves to more rapidly vent the brake pipe and hasten the propagation of the emergency reduction rate along the entire length of the train. Use of distributed power (i.e., remotely controlled locomotive units mid-train and/or at the rear end) somewhat mitigates the time-lag problem with long trains, because a telemetered radio signal from
1740-573: The brake pipe, the rate of reduction is highest near the front of the train (in the case of an engine operator-initiated emergency application) or near the break in the brake pipe (in the case of loss of brake pipe integrity). Farther away from the source of the emergency application, the rate of reduction can be reduced to the point where triple valves will not detect the application as an emergency reduction. To prevent this, each triple valve's emergency portion contains an auxiliary vent port, which, when activated by an emergency application, also locally vents
1798-411: The brakes and manually inspecting the cars to ensure the brakes are released. Particular attention is usually paid to the rearmost car of the train, either by manual inspection or via an automated end-of-train device , to ensure that brake pipe continuity exists throughout the entire train. When brake pipe continuity exists throughout the train, failure of the brakes to apply or release on one or more cars
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1856-508: The brakes must be applied before recharging has been completed, a larger brake pipe reduction will be required in order to achieve the desired amount of braking effort, as the system is starting out at a lower point of equilibrium (lower overall pressure). If many brake pipe reductions are made in short succession ("fanning the brake" in railroad slang), a point may be reached where car reservoir pressure will be severely depleted, resulting in substantially reduced brake cylinder piston force, causing
1914-425: The brakes to fail. On a descending grade , the result will be a runaway. In the event of a loss of braking due to reservoir depletion, the engine driver may be able to regain control with an emergency brake application, as the emergency portion of each car's dual-compartment reservoir should be fully charged—it is not affected by normal service reductions. The triple valves detect an emergency reduction based on
1972-408: The brakes. A subsequent reduction or loss of air pressure causes each car to apply its brakes, using the compressed air stored in its reservoirs. In the air brake's simplest form, called the straight air system , compressed air pushes on a piston in a cylinder. The piston is connected through mechanical linkage to brake shoes that can rub on the train wheels, using the resulting friction to slow
2030-641: The city. Moreover, all the traffic bound for the Panhandle Route needed to pass through the Grant's Hill Tunnel in downtown Pittsburgh, limiting and slowing traffic through the city. Therefore, in 1871, the PRR planned a connection – later to be known as the Port Perry Branch – between its Main Line and the main line of a subsidiary, the Pittsburgh, Virginia and Charleston Railway (PV&C, today's Mon Line ). This connection would contain new trackage,
2088-466: The control valve set a reference pressure in a volume, which set brake cylinder pressure via a relay valve. On the electric side, pressure from a second straight-air trainline controlled the relay valve via a two-way check valve. This "straight air" trainline was charged (from reservoirs on each car) and released by magnet valves on each car, controlled electrically by a three-wire trainline, in turn controlled by an electro-pneumatic master controller in
2146-423: The controlling locomotive. This controller compared the pressure in the straight air trainline with that supplied by a self-lapping portion of the engineers valve, signaling all of the "apply" or "release" magnets valves in the train to open simultaneously, changing the pressure in the straight-air trainline much more rapidly and evenly than possible by simply supplying air directly from the locomotive. The relay valve
2204-408: The device by removing the poppet valve action. These three components became the piston valve, the slide valve, and the graduating valve. When the engine operator applies the brake by operating the locomotive brake valve, the train line vents to atmosphere at a controlled rate, reducing the train line pressure and in turn triggering the triple valve on each car to feed air into its brake cylinder. When
2262-419: The engine driver with no means to stop the train. To prevent a runaway due to loss of brake pressure, dynamic (rheostatic) braking can be utilized so the locomotive(s) will assist in retarding the train. Often, blended braking , the simultaneous application of dynamic and train brakes, will be used to maintain a safe speed and keep the slack bunched on descending grades. Care would then be given when releasing
2320-416: The engine operator in the front locomotive commands the distant units to initiate brake pressure reductions that propagate quickly through nearby cars. Many modern air brake systems use distributors instead of triple valves. These serve the same function as triple valves, but have additional functionality such as the ability to partially release the brakes. The locomotive's air compressor typically charges
2378-404: The engine operator releases the brake, the locomotive brake valve portal to atmosphere is closed, allowing the train line to be recharged by the compressor of the locomotive. The subsequent increase of train line pressure causes the triple valves on each car to discharge the contents of the brake cylinder to the atmosphere, releasing the brakes and recharging the reservoirs. The Westinghouse system
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2436-416: The engineer moves the automatic brake handle to a "service" position, which causes a reduction in brake pipe pressure. During normal service, the pressure in the brake pipe is never reduced to zero and in fact, the smallest reduction that will cause a satisfactory brake response is used to conserve brake pipe pressure. A sudden and substantial pressure reduction caused by a loss of brake pipe integrity (e.g.,
2494-400: The equipment has to be much larger and heavier to compensate. That disadvantage is made worse at high altitude. The vacuum brake is also considerably slower to both apply and release the brake, which requires a greater level of skill and anticipation from the driver. Conversely, the vacuum brake originally had the advantage of allowing gradual release, whereas the Westinghouse automatic air brake
2552-494: The event the train needs to make an emergency stop, the engine operator can make an "emergency application," which will rapidly vent all of the brake pipe pressure to atmosphere, resulting in a faster application of the train's brakes. An emergency application also results when the integrity of the brake pipe is lost, as all air will also be immediately vented to atmosphere. An emergency brake application brings in an additional component of each car's air brake system. The triple valve
2610-403: The length of the train, and the relatively-small exhaust port on the head-end locomotive, which means the brakes of the rear-most cars will apply sometime after those of the forward-most cars apply, so some slack run-in can be expected. The gradual reduction in brake pipe pressure will mitigate this effect. Modern locomotives employ two air brake systems. The system which controls the brake pipe
2668-429: The loss of the force applying the brakes. This could easily cause a runaway train . Straight air brakes are still used on locomotives, although as a dual circuit system, usually with each bogie (truck) having its own circuit. In order to design a system without the shortcomings of the straight air system, Westinghouse invented a system wherein each piece of railroad rolling stock was equipped with an air reservoir and
2726-460: The main reservoir with air at 125–140 psi (8.6–9.7 bar; 860–970 kPa). The train brakes are released by admitting reduced and regulated main reservoir air pressure to the brake pipe through the engineer's automatic brake valve. In America, a fully charged brake pipe typically operates at 90 psi (6.2 bar; 620 kPa) for freight trains and 110 psi (7.6 bar; 760 kPa) for passenger trains. The brakes are applied when
2784-435: The reporting back of performance of each wagon's brakes. The Westinghouse air brake system is very reliable but not infallible. The car reservoirs recharge only when the brake pipe pressure is higher than the reservoir pressure. Fully recharging the reservoirs on a long train can require considerable time (8 to 10 minutes in some cases ), during which the brake pipe pressure will be lower than locomotive reservoir pressure. If
2842-447: The service and dynamic brakes to prevent draw-gear damage caused by a sudden run out of the train's slack. Another solution to loss of brake pressure is the two-pipe system, fitted on most locomotive-hauled passenger stock and many freight wagons. In addition to the traditional brake pipe, this enhancement adds the main reservoir pipe, which is continuously charged with air directly from the locomotive's main reservoir. The main reservoir
2900-413: The service section to the brake cylinder, while emergency applications cause the triple valve to direct all air in both the sections of the dual-compartment reservoir to the brake cylinder, resulting in a 20 to 30 percent stronger application. The emergency portion of each triple valve is activated by the higher rate of reduction of brake pipe pressure. Due to the length of trains and the small diameter of
2958-544: The system were not dependent on each other in any way, and any or all of these options could be supplied separately. Later systems replace the automatic air brake with an electrical wire which runs in a circle round the whole train and has to be kept energized to keep the brakes off. In the UK it is known as a train wire . It is routed through various "governors" (switches operated by air pressure) which monitor critical components such as compressors, brake pipes and air reservoirs. If
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#17327982750193016-413: The time required for the brakes to release, since the brake pipe only has to recharge itself. Main reservoir pipe pressure can also be used to supply air for auxiliary systems such as pneumatic door operators or air suspension. Nearly all passenger trains (all in the UK and USA), and many freights, now have the two-pipe system. At both ends of each car, there are angle cocks fitted. These valves cut off
3074-412: The train divides, the wire will be broken, ensuring that all motors are switched off and both portions of the train have an immediate emergency brake application . More recent innovations are electronically controlled pneumatic brakes where the brakes of all the wagons (cars) and locomotives are connected by a kind of local area network , which allows individual control of the brakes on each wagon, and
3132-463: The train. The mechanical linkage can become quite elaborate, as it evenly distributes force from one pressurized air cylinder to 8 or 12 wheels. The pressurized air comes from an air compressor in the locomotive and is sent from car to car by a train line made up of pipes beneath each car and hoses between cars. The principal problem with the straight air braking system is that any separation between hoses and pipes causes loss of air pressure and hence
3190-514: Was a gradual standardization on the vacuum brake. Some locomotives, e.g. on the London, Brighton and South Coast Railway , were dual-fitted so that they could work with either vacuum- or air-braked trains. In the diesel era, the process was reversed and British Railways switched from vacuum-braked to air-braked rolling stock in the 1960s. The main competitor to the air brake is the vacuum brake, which operates on negative pressure. The vacuum brake
3248-553: Was assigned to Norfolk Southern in 1999. In the 1990s, Conrail began to use the Port Perry Branch, together with the Mon Line to Pittsburgh (including the former PV&C main line, a small portion of the Panhandle Route, and the Ohio Connecting Railroad Bridge ) as a double-stack high clearance route. It continues to be used as such (as of 2019). Rail line Rail transport terms are
3306-563: Was equipped with four diaphragms, magnet valves, electric control equipment, and an axle-mounted speed sensor, so that at speeds over 60 mph (97 km/h) full braking force was applied, and reduced in steps at 60, 40 and 20 mph (97, 64 and 32 km/h), bringing the train to a gentle stop. Each axle was also equipped with anti-lock brake equipment. The combination minimized braking distances, allowing more full-speed running between stops. The straight-air (electro-pneumatic trainline) , anti-lock, and speed graduating portions of
3364-437: Was originally available in only the direct-release form still common in freight service. A primary fault of vacuum brakes is the inability to find leaks easily. In a positive air system, a leak is quickly found due to the escaping pressurized air. Discovering a vacuum leak is more difficult, although it is easier to repair, because a piece of rubber (for example) can just be tied around the leak and will be firmly held in place by
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