Description of common terms used in fan shaped switch Assmbly

1. Tongue rail :

Tongue rail is a tapered movable rail, which is attached at or near its thicker end to a running rail.

2. Stock rail :

Stock rail is a running rail to which a tongue rail is attached.

3. Switch :

A pair of tongue rails, with necessary connection forms a switch (without stock rails).

4. Points :

A pair of tongue rails and stock rails with necessary connections forms points.

5. Lead rails :

Plain rails laid in a turnout between the switches and crossing assemblies are called lead rails.

6. Heel of switch :

It is an imaginary point on the gauge line mid way between the end of lead rail and the tongue rail in case of loose heel switches. It is a point on the gauge line of tongue rail opposite to the centre of the heel block in case of fixed heel switches. Heel block is the first block from the toe side fixing the tongue rail to the stock rail.

7. Toe of switch :

The thin tapering end of the tongue rail is called the toe.

8. Theoretical toe of switch :

It is the point of intersection of gauge lines of tongue rail at it’s toe when extended, and the stock rail.

9. Switch length :

It is the free length of tongue rail from the toe to the heel of a switch.

10. Loose heel :

When the lead rails form a joint with the tongue rail at the heel of a switch, it is called a loose heel switch.

11. Fixed heel :

When the tongue rail does not form a joint with the lead rail at the heel of a switch it is called a fixed heel switch.

12. Switch angle :

Switch angle is the angle between the gauge lines of the tongue rail at its toe and the stock rail, when the switch is in the closed position. In the case of curved switch, gauge line at the toe of the switch is the tangent to the tongue rail at its toe.

13. Throw of switch:

It is the distance through which a tongue rail moves at its toe from its closed to open position. The throw of any switch is fixed from the consideration of maximum flange way clearance obtained between the tongue and the stock rail at the point where tongue rail attains the full head width and is closest to the stock rail in the open position, i.e. point ‘p’ in fig. below.

Throw has been fixed at 115 mm for BG and 100 mm for MG.(for thickweb switches - it will be 160 mm) to get a minimum flange way clearance of 44mm and 41 mm respectively at point ‘P’

Fan shaped switch

14. Heel divergence :

Heel divergence is the shortest distance from gauge line of stock rail to gauge line of tongue rail, at the heel of switch i.e. it is the clear distance between the tongue rail and the stock rail at the heel plus rail head width. This is also fixed with the consideration of getting the minimum flange way clearance.

15. Left or right hand stock rails :

Tongue rails stock rails and other fittings are called left hand or right hand according to their position looking in the facing direction of points.

16. Stretcher bars :

Made of spring steel flats, they are rigidly fixed to the tongue rails by brackets and help to maintain the tongue rails at correct distance apart.

17. Gauge tie plates :

Gauge tie plates of 12mm thickness for BG and 10 mm thickness on MG made out of steel flats are provided over the wooden/prc sleepers directly under the toe of the switches, and over wooden sleepers under the nose of crossing to ensure exact gauge at these important locations.