Railway block code
The railway block signalling bell code is a system of bell sounds used in Great Britain to communicate between manually operated Signal Boxes in implementing the railway block system. Each such signal box has a bell circuit to the boxes on either side of it along the line. The equipment consists of a plunger or tapper which when pressed, rings a single-stroke bell in a neighbouring box. That box similarly has a tapper for communicating back, so boxes have keys each of which rings the bell in a neighbouring box. The bells sound different tones, so that the signalman can tell them apart by ear.
Examples
Although codes varied from region to region, the following shows a few selected standard UK bell codes:| Code | Meaning |
| 1 bell | Call attention |
| 2 bells | Train entering section |
| 2 - 3 bells | Is line clear for light engine? |
| 2 - 2 - 1 | Is line clear for empty coaching stock train? |
| 3 | Is line clear for stopping freight train? |
| 3 - 1 | Is line clear for stopping passenger train? |
| 3 - 1 - 1 | Is line clear for express freight train? |
| 4 | Is line clear for express passenger train? |
| 4 - 1 | Is line clear for mineral or empty wagon train? |
| 2 - 1 | Train arrived |
| 3 - 3 | Blocking back outside home signal |
| 5 - 2 | Release token |
| 2 - 5 | Token replaced |
| 5 - 5 - 5 | Opening signal box |
| 7 - 5 - 5 | Closing signal box |
| 6 | Obstruction danger |
| 4 - 5 - 5 | Train running away on Right Line |
| 2 - 5 - 5 | Train running away on Wrong Line |
| 16 | Testing bells and instruments |
Typical use
These would be used as follows between two signal boxes A and B. Assume a train is to pass from the block controlled by A to the block controlled by B. This must be agreed and permitted by the signalman in box B. Here is the sequence of bell codes and associated actions:- Box A sends 1 bell to box B.
- Box B replies with 1 bell to box A.
- Box A sends 4 bells to box B.
- Box B sends 4 bells to box A.
- Box A sends 2 bells to box B as the train passes box A and enters the block controlled by B. This is acknowledged by box B.
- Box B sends 2 - 1 bells to box A after confirming that the train has arrived complete and no portion of it remains within the block section between A and B or the clearing point for that section. This could be done by the guard of the train notifying the signalman or by the signalman observing the tail-lamp. This is acknowledged by box A.