Check rails are positioned opposite all common crossings to constrain the wheel flange passing between the check rail and its running rail in such a way that the flange of the opposite wheels passing through the crossing is steered clear of the nose.
The clearances at check rails are so fixed that the nose of the crossing is protected under all service conditions.
For this purpose maximum and minimum check rail clearances for broad gauge (BG) have been fixed at 48 mm and 44 mm respectively. For metre gauge (MG) the figures are 44 mm and 41 mm respectively.
To ensure safety, it is very important that track gauge at the crossing particularly opposite the nose is maintained exact. The provisions of gauge tie plate on the sleeper at the nose helps to achieve this objective.
Check rails are so designed as to give the minimum clearance when used with ‘flare’ at the ends, but should any appreciable wear take place, the check rail can be moved towards the running rails by removing one or both of the 3 mm packing provided with the distance blocks between the check rail and the running rail.
The intersection of diamond crossings are not as effective as those in common process. To increase their effectiveness, check rail on all 1 in 8½ diamond crossing both on BG and MG are raised by 20mm, by welding a MS flat over their top table. For diamond crossing flatter then 1 in 8½ switch diamond are required to be used.