Types of Railway Turnouts and Their Components

What is railway turnout?

Railway turnout is a mechanical device that used to guide the trains from one rail track to another. As an important part in rail construction, turnout helps to enable the trafficability of the rail.
Through leverage principle, the railroad switch rod switches the two movable rails to ensure the trains drive into the appointed route.

Railway Turnout Components

Among all kinds of turnouts, the most common one is single turnout.
Single turnout is consisting of three parts: railroad switch, connection part, frog and guard rail.

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By using the switch machine to change the position of switch rail, a train can change the running routes from A to B. Put point rail I close to stock rail I and separate point rail II from stock rail II, then the route B will be opened and route A will be closed.

1. Railroad Switch:

One set of railroad switch includes 2 stock rails, 2 switch rails and a switch machine. It is used to change the position of switch rails by switch machine to ensure the turnout open direction.
 

Stock Rail

Stock rail refers to the steel rail that made from standard rail profile, with one side straight and the other side curved. To avoid stock rail from moving, rail braces are installed on the outer side. The top of stock rails are always quenched to improve surface hardness and wear resistance.
 

Point Rail

Point rails, also named switch rail or point blades, which lie between the diverging stock rails, are movable and direct the trains coming from the rail points towards either the straight or the diverging track.

Switch Machine

Switch machine, also known as point machine, is the executive part of railway turnout control system. It is electric, hydraulic or pneumatic machinery that used to change turnouts, belock point blades and show the position of switch rails. The machine is usually controlled remotely by the dispatcher. There are some electrical contacts inside the machine to detect whether the switch is fully set and locked. In case of any emergencies, a manual operating device is quite necessary.
 

2. Connection Parts

Connection parts consist of 2 straight rails and 2 curve guide rails, which are help to connect the switch rail with frog and guard rail as a complete railway turnout.
 

3. Frog and Guard Rail

This part is made up of guard rail, wing rail and railway frog to ensure the safety trains passing through the junction of two routes.
 

Guard Rail

Guard rail, or called check rail, is a short rail fixed alongside the outer rail and opposite the frog to guide the trail wheels passing through the appropriate flange way and avoid derailing. Guard rails are placed in pairs, in other words, each frog require two check rails.

Frog

The frog is the crossing part of two tracks, which consist of frog, wing rail and connecting components. It can be assembled by several cut and bent rail pieces, or single casting steel.

Gap in the Frog

There is a gap between the throat of frog, where is the narrowest part between two wing rails, and the actual point of switch rail, it is called gap in the frog or open throat. The gap threatens the railway safety. When the wheels passing through, it may cause derail by running wrong flangeway. Check Rails are placed to guide the trains’ moving direction compulsively. However, the gap seriously limits the passing speed.



To solve this problem, it should use movable point frog to completely eliminate the gap, especially heavy or high-speed traffic lines.

Railway Turnout Types

According to different structures and usages, there are different kinds of railway turnout, such as single turnout, equilateral turnout, three-way turnout, multiple slip switch, diamond crossing and double crossover, etc.
Equilateral turnout is Y-shaped that the two jointed tracks are diverged to the two sides.



Three-way turnout is Ψ shaped and connect three rail tracks. It uses two switch machines to control two sets of point rail.



Multiple slip switch is X-shaped. It looks like the combination of four sets of single turnout and a diamond crossing.



Diamond crossing is composed of two acute frogs and two obtuse frogs. Without switch machine, it cannot change routes.



Connect the upper two points with the lower two points of multiple slip switch will form the double crossover. It opens more directions but needs less occupied area.

Disadvantages:

1. Complex structure
2. Short working life
3. Speed limited
4. Low driving safety
5. High maintenance cost

Railway Turnout Maintenance

With above disadvantages, turnout is among the weakest parts in railway. Therefore, in order to improve the traffic capacity and avoid accident, regular maintaining of turnouts is quite necessary. High quality of railway turnouts ensures the running safety of trains.