Railroad Switch ->>->>->> https://bytlly.com/2t7wvj
A railroad switch (AE), turnout, or [set of] points (BE) is a mechanical installation enabling railway trains to be guided from one track to another, such as at a railway junction or where a spur or siding branches off.
The most common type of switch consists of a pair of linked tapering rails, known as points (switch rails or point blades), lying between the diverging outer rails (the stock rails). These points can be moved laterally into one of two positions to direct a train coming from the point blades toward the straight path or the diverging path. A train moving from the narrow end toward the point blades (i.e. it will be directed to one of the two paths, depending on the position of the points) is said to be executing a facing-point movement.
For many types of switch, a train coming from either of the converging directions will pass through the switch regardless of the position of the points, as the vehicle's wheels will force the points to move. Passage through a switch in this direction is known as a trailing-point movement and switches that allow this type of movement are called trailable switches.
A switch generally has a straight "through" track (such as the main-line) and a diverging route. The handedness of the installation is described by the side that the diverging track leaves. Right-hand switches have a diverging path to the right of the straight track, when coming from the point blades, and a left-handed switch has the diverging track leaving to the opposite side. In many cases, such as rail yards, many switches can be found in a short section of track, sometimes with switches going both to the right and left (although it is better to keep these separated as much as feasible). Sometimes a switch merely divides one track into two; at others, it serves as a connection between two or more parallel tracks, allowing a train to switch between them. In many cases, where a switch is supplied to leave a track, a second is supplied to allow the train to reenter the track some distance down the line; this allows the track to serve as a siding, allowing a train to get off the track to allow traffic to pass (this siding can either be a dedicated short length of track, or formed from a section of a second, continuous, parallel line), and also allows trains coming from either direction to switch between lines; otherwise, the only way for a train coming from the opposite direction to use a switch would be to stop, and reverse through the switch onto the other line, and then continue forwards (or stop, if it is being used as a siding).
A straight track is not always present; for example, both tracks may curve, one to the left and one to the right (such as for a wye switch), or both tracks may curve, with differing radii, while still in the same direction.
Simple single-bladed switches were used on early wooden railways to move wagons between tracks. As iron-railed plateways became more common in the eighteenth century, cast iron components were made to build switches with check rails. In 1797, John Curr described the system that he developed which used a single iron blade, hinged on a vertical pin that was tapered to lie against the plateway. By 1808, Curr's basic design was in common use.
Prior to the widespread availability of electricity, switches at heavily travelled junctions were operated from a signal box constructed near the tracks through an elaborate system of rods and levers. The levers were also used to control railway signals to control the movement of trains over the points. Eventually, mechanical systems known as interlockings were introduced to make sure that a signal could only be set to allow a train to proceed over points when it was safe to do so. Purely mechanical interlockings were eventually developed into integrated systems with electric control. On some low-traffic branch lines, in self-contained marshalling yards, or on heritage railways, switches may still have the earlier type of interlocking.
A railroad car's wheels are primarily guided along the tracks by coning of the wheels, rather than relying on the flanges located on the insides of the wheels. When the wheels reach the switch, the wheels are guided along the route determined by which of the two points is connected to the track facing the switch. In the illustration, if the left point is connected, the left wheel will be guided along the rail of that point, and the train will diverge to the right. If the right point is connected, the right wheel's flange will be guided along the rail of that point, and the train will continue along the straight track. Only one of the points may be connected to the facing track at any time; the two points are mechanically locked together to ensure that this is always the case.
A mechanism is provided to move the points from one position to the other (change the points). Historically, this would require a lever to be moved by a human operator, and some switches are still controlled this way. However, most are now operated by a remotely controlled actuator called a point machine; this may employ an electric motor or a pneumatic or hydraulic actuator. This both allows for remote control and monitoring and for the use of stiffer, strong switches that would be too difficult to move by hand, yet allow for higher speeds.
In a trailing-point movement (running through the switch in the wrong direction while they are set to turn off the track), the flanges on the wheels will force the points to the proper position. This is sometimes known as running through the switch. Some switches are designed to be forced to the proper position without damage. Examples include variable switches, spring switches, and weighted switches.
If a switch becomes worn or the operating rods become damaged, it is possible for the flange to split the switch, and go through the switch in the direction other than what was expected. This happens when the flange strikes a small gap between the fixed rail and the set switch point (whichever is touching the main line); this forces the switch open, and the train is diverted down the incorrect track. This can either happen to the locomotive, in which case the whole train can be directed onto the wrong track, with potentially dangerous results, or it can occur at any point through the train, when a random truck is directed down a different track from the rest of the train; if this happens on the front truck of a car, the usual result is derailment, as the trailing truck of the preceding car attempts to go one way, while the leading truck of the following car tries to go another. If it happens to the trailing truck of a car, the front truck will follow one track, while the trailing truck follows a parallel line; this causes the whole car to "crab", or move sideways down the track (derailment often results eventually, due to the lateral forces applied when the train tries to brake or accelerate). This can have disastrous results if there is any obstacle between the lines, as the car will be propelled into it sideways, such as happened in the 1928 Times Square derailment. In some cases, the whole train behind the car will follow the errant car onto the other track; in others, only one or a few trucks are diverted, while the rest follow the correct track. In cases where it is a simple siding, rather than a continuous parallel track, the diverted truck(s) can travel the whole length of the siding until it turns back to the main track, where it performs a trailing point movement, forces the switch open, and ends up back on the same track again, with only damage to the switches. This is far less likely in cases of diversion to a parallel track, since switches on both lines will often be interconnected, so to set the switch on the main line to straight-through will set the other switch to straight-through as well (otherwise there is a risk of turning off the track only to find the joining switch is set the wrong way, and running the train through it). Because derailments are expensive and very dangerous to life and limb, maintenance of switch points and other trackwork is essential, especially with faster trains. Another derailment that occurred due to a split switch is the ProRail Hilversum derailment on 15 January 2014.
If the points are rigidly connected to the switch control mechanism, the control mechanism's linkages may be bent, requiring repair before the switch is again usable. For this reason, switches are normally set to the proper position before performing a trailing-point movement.
Generally, switches are designed to be safely traversed at low speed. However, it is possible to modify the simpler types of switch to allow trains to pass at high speed. More complicated switch systems, such as double slips, are restricted to low-speed operation. On European high-speed lines, it is not uncommon to find switches where a speed of 200 km/h (124 mph) or more is allowed on the diverging branch. Switches were passed over at a speed of 560 km/h (348 mph) (straight) during the French world speed run of April 2007.
Under cold weather conditions, snow and ice can prevent the proper movement of switch or frog point rails, essentially inhibiting the proper operation of railroad switches. Historically, railway companies have employees keep their railroad switches clear of snow and ice by sweeping the snow away using switch brooms (Basically wire brooms with a chisel attached onto the opposite end of the broom - quite similar to ice scrapers used today), or gas torches for melting ice and snow. Such operation are still used in some countries, especially for branch routes with only limited traffic (e.g. seasonal lines). Modern switches for heavily trafficked lines are typically equipped with switch heaters installed in the vicinity of their point rails so that the point rails will not be frozen onto the stock rail and can no longer move. These heaters may take the form of electric heating elements or gas burners mounted on the rail, a lineside burner blowing hot air through ducts, or other innovative methods (e.g. geothermal heat sink, etc.) to keep the point & stock rails above freezing temperatures. Where gas or electric heaters cannot be used due to logistic or economic constraints, anti-icing chemicals can sometimes be applied to create a barrier between the metal surfaces to prevent ice from forming between them (i.e. having frozen together by ice). Such approaches however, may not always be effective for extreme climates since these chemicals will be washed away over time, especially for heavily thrown switches that experience hundreds of throws daily. 2b1af7f3a8