Other Switch Components

A railroad switch is a mechanical installation enabling trains to be guided from one set of rail tracks (or tramway tracks) to another. In the UK and Commonwealth countries, railroad switches are known as (sets of) points. In technical usage a switch may be called a turnout. more...

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In the illustration on the right, rail track A divides into two tracks: B (the straight track) and C (the diverging track). Each switch contains a pair of linked tapering rails known as points (point blades). These can be moved laterally into one of two positions, determining whether a train coming from A will be led towards B or C. This is known as a facing-point movement.

A train coming from B or C will be led to A regardless of the position of the points, as the vehicle's wheel will force the points to the proper position. Passage in this direction through a switch is known as a trailing-point movement.

A switch can be described by the direction in which the diverging track leaves the straight track. A right-hand switch has track C to the right of a straight track formed by A and B. A left-hand switch has track C is to the left.

A switch can also be symmetrical, or have the two tracks curved at different radii in the same or different directions.

Operation

A railroad car's wheels are guided along the tracks by coning of the wheels. Only in extreme cases does it rely 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 in this way. However, most are now operated by a remotely controlled electric motor or pneumatic motor.

In a trailing-point movement, the wheels will force the points to the proper position. This is sometimes known as running through the switch. 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. .

An example of mechanism that would require repair after a run-through in the trailing direction is a clamp-lock. This mechanism is popular in the UK, but the damage caused is common to most types of switches. However, some switches are designed to be forced to the proper position without damage. Examples include variable switches, spring switches, and weighted switches.

Read more at Wikipedia.org