THE SIGNAL BOX
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[ No closing switch | With a closing switch | Switching in | Time to go]
Bert thinks he has told you quite enough to give you a background to Absolute block, in fact he says you have tired him out and he wants to close the box and go home. Before he does so, he says he will show you the different ways it can be done.
Where a closing switch is not provided
Bert says this is easy. As soon as the last train has gone, he would send Closing of signal box (7-5-5) to all adjacent boxes, and run.
When re-opening, Bert would send Opening of signal box (5-5-5).
A closing, or block, switch allows a signal box to temporarily cease to exist - in our example, box B could close and allow Boxes A and C to communicate directly with each other. The block sections become between A and C, so Bert's signals no longer serve a purpose and can be left in the clear position. The disadvantages are, of course, that the capacity of the line is reduced by the longer block sections, and of course the points and branch cannot be used.
There are two ways to "switch out", dependent on whether Line Clear is required on the block instruments to clear the signals.
If the signals are not released by Line Clear, Bert will (provided no trains have been signalled) send 7-5-5 to Boxes A and C. When both have acknowledge the signal, he turns the closing switch and clears his signals.
After he has turned the switch, Arthur at Box A and Charlie at Box C will test the bells and block indicators by exchanging 16 beats and working the instruments through their normal sequence. As each indication is displayed, the signalman at the opposite end of the section confirms it with one beat on the bell. Bert will check that communication has been properly established before leaving.
If the signals are released by Line Clear on the block instruments, the method is a little more complicated because Bert will not be able to clear his signals after turning the closing switch. (Note:- some locations on the Western Region had the electric locks on the levers wired to release the signals after the switch had been turned).
To clear his signals, Bert will need to send Closing of signal box where section signal is locked by the block (5-5-7) to Arthur and Charlie, who will each place their indicators to Line Clear and reply with just one beat on the bell. Bert now clears his signals, and sends one beat back to Arthur and Charlie. They then respond by sending 5-5-7 back to Bert, upon receipt of which he turns the switch. Arthur and Charlie confirm they have established communication as above.
Before switching in, Bert must check the state of the sections between Arthur and Charlie by telephoning them. He will be permitted to switch in if the sections are clear, or if one or both of the indicators are at Train on Line. He must not switch in if either section's indicator is at Line Clear.
According to the state of the sections, Bert changes his commutators to match the existing through section. He then turns his switch and sends Opening of signal box (5-5-5).
Time to go
That was the theory, now Bert reckons its time to show you how its really done.
He jumps to his feet and rings 7-5-5 to Doris on the branch line. Before she has finished replying, he is rattling out 5-5-7 simultaneously to Arthur and Charlie. With a ting and a tong, they reply with one beat and the blocks turn to Line Clear. Bert bangs the levers of the main running signals over. He rings one beat back on both main line bells.
In a cacophony of noise, Arthur and Charlie ring 5-5-7 back to Bert. With a final flourish, he turns the block switch and all goes quiet. He steps across to the Train Register, where he scribbles entries in the book whilst his other hand puts the omnibus telephone to his ear.
After a moment, he asks into the telephone "Are you through?" and after a pause "See you Monday, then". Bert then throws the phone back on the hook, grabs his newspaper, pipe, bag, coat and cap and hurtles out of the door and down the stairs, shouting as he goes "Its all yours, chum!" He hops on his bicycle, and is last seen pedalling into the distance across the field, merrily whistling.