A turntable (Fig. 27.6) is a device used for changing the direction of a locomotive. It is normally provided at terminal stations, locomotive yards, and marshalling yards.
A turntable basically consists of a track supported on two parallel fish-bellied girders which are braced together and supported on or suspended from a central pivot. Sets of flangeless wheels are attached to the ends of the girders, which roll over the rails along the circumference of the pit, called race rails. The turntable is installed in a circular masonry pit. The girders supporting the track move around the rail and can be fixed in the desired position with the help of locking bolts. The bottom of the masonry pit slopes towards the centre and a sump is provided for draining rainwater by means of a sump and drain arrangement. Two or more tracks radiate outwards from the circular edge of the pit and are so designed that they can be aligned and temporarily connected to the track of the turntable.
The diameter of the turntable should be such that it can accommodate the longest engine in service on the section. The turntables normally provided on Indian Railways are of the following sizes:
BG: 30.5 m (100'), 22.9 m (75'), and 19.8 m (65')
MG: 19.8 m (65') and 15.75 m (50')
A turntable helps in reversing the direction of an engine in the following manner.
1. When the direction of an engine is to be reversed, the turntable is made to revolve either manually or electrically on the pivot and is brought in line
with the track on which the engine is standing. This position is then locked with the help of locking bolts.
2. The engine is then brought on the track of the turntable and the locking bolts are removed.
3. The turntable is rotated again till the turntable track aligns with the track where the engine is required to go.
4. This position is locked with the help of locking bolts and the engine is shunted and brought on the required track.
It is essential that the turntable be properly maintained for it to work efficiently. The following aspects of turntable maintenance require special attention.
(a) The central pivot and other parts should be oiled and greased to ensure that they work smoothly.
(b) The level of the race rail should be perfect and its alignment should be correct.
(c) The various parts of the turntable should be painted periodically to avoid the corrosion and rusting of its steel parts.
As steam locomotives have been phased out on Indian Railways, all equipment connected with steam locomotives such as ashpits, ash pans, turntables, and water columns are now of historical importance only.