keeping it pressed the second time, will turn the commutater to the right hand position. Now the needle in the lower panel at Valsad will turn to the position Line Clear. Similarly, the needle in the upper panel at Dungri will also turn to the position Line Clear. As soon as Dungri station gets the Line Clear, his Up Advance starter is unlocked and can now be taken Off. Dungri station takes Off the advance starter which also constitutes the Authority to Proceed for the driver of the train.
Now the train passes through the station section and as soon as it passes the advance starter, a buzzer sounds in the Dungri cabin and the advance starter reverts to danger which indicates that the train is entering the block section. Now the cabinman at Dungri presses the block plunger three times (to indicate Train Entering Section) slowly and distinctly. In turn Valsad acknowledges the signal by pressing the bell plunger three times and at the third beat the plunger is kept pressed and the commutator is turned to the Train On Line position on the left most side. This also puts the needles on both the block instruments to the Train On Line position from the Line Clear position.
Now an electromagnet in the block instrument keeps the commutator locked at the Train On Line position till the conditions for giving the Train Out Of Section (TOS) signal are satisfied. When the train arrives at Valsad, it occupies the block overlap beyond the Home Signal. After clearing the block overlap, the TOS signal can be sent to Dungri. When a train occupies and then releases the Block Overlap, the Block commutater is released and is free to be turned to the Line Closed position. But before giving the TOS signal to the station in rear that is Dungri, the station master at Valsad must also verify that the train has arrived complete in all respects. It is possible that the train may have parted in the block section and only a part of the train has arrived and the rear end is still in the block section obstructing the line. To make this verification easy, a tailboard is provided on the last vehicle by day and a flashing red taillight is provided at night and is hung by the guard of the train. The tailboard has the letters LV written on it and means Last Vehicle. If the train has arrived completely then the tailboard is visible to the station master and now he can send the TOS signal to Dungri. The TOS is given by pressing the bell plunger four times and at the fourth instant keeping the plunger pressed; the commutator is