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Tongue Rail
A tongue is tapered in shape having toe at one end and heel at other end. It fixed at heel end and can move about this point.
The length of tongue rail depends upon the value of switch angle. Its length should be carefully selected because use of long tongue rail will increase the overall length of turnout whereas the short tongue rail will increase the angle of switch.
The tongue rails are kept as long as possible to reduce the switch angle and to maintain high-speed at turnout. In India straight tongue rails are used to suit RH turnout and LH turnout. The minimum length of tongue rail is calculated by
Heels Divergence
It is the distance between the gauge face of the stock rail and gauge face of the tongue rail at the heel. It also known as heel offset or heel clearance. It is kept as equal to flange clearance plus the width of head of tongue rail. The usual values of it are 13.65 to 13.34 cm, 12.06 to 11.75 cm, and 9.84 cm for broad gauge, meter gauge, Narrow gauge respectively.
Throw of switch
It is the distance through which the toe moves laterally from adjacent stock rail when fully opened. Minimum values are 9.52 cm, 8.89 cm, meter gauge and narrow gauge respectively. The general practice in India is 11.43 cm for broad gauge.
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