|The levers which have reversed
(pulled over in the frame) are numbers 4, 5, 6, 13 & 23. 4 ,5
& 6 having been pulled that the line has been cleared for a Down
train towards Camp Hill, and Signal 23 (Up Home from Camp Hill) is also
clear. Lever 13 is the Facing Point Lock (FPL on the diagram) for
the junction points No 14. This is a large bolt which holds the
point blades in position whilst a train is passing over them.
This lever would have be put Normal (back in the frame) before the
points could be changed to send a train to the GWR, and then
pulled again before the signal lever (No 2 or 3) could be pulled to
clear the signal itself.
Levers 11 and 12 are painted with distinctive black and white chevrons, indicating that they operate detonator placers. These are mechanisms which put a small metal can containing gunpowder on the top of the rail, this explodes under the train wheels to give a warning to the driver in case of emergency, such as a train having passed a signal at danger. The chevrons point up or down the lever according to the line to which they apply.
The instrument shelf above the frame (also known as the blockshelf) carries a number of vintage Block Instruments, which are used to control an indicate the state of the line between the signal boxes (the Block Section), ie, whether or not the section is occupied by a train, or if the signalman at the next box has given permission for a train to be sent to him.
Four of the instruments are of Midland Railway origin, whilst the right hand one is of the L&NWR pattern. Between the MR instruments are the separate bells for communication to the signalboxes either side, the tapper key is on the front is used to ring the bell in the next box. The L&NWR instrument has its bell built into the base under the main body of the instrument, the bell tapper key is in the bottom right corner of the instrument body.
Two of the MR instruments have commutator handles on the front, these are known as "Pegger" (or Pegging) instruments. The other two are "Non-Peggers" To communicate with each of the adjacent signalboxes requires a Pegger snd a Non-pegger. The Pegger instrument commutator operates its own needle (in the dial above the commutator), and the one on the associated Non-Pegger instrument at the adjacent signalbox. Similarly, the Pegger at the adjacent box operates the Non-Pegger instrument needle at this box.
The MR used separate instruments for each line, whilst the L&NWR used combined instruments, with two needles combined into one case, along with the Pegger handle (the wheel on the front). The lower needle is the Pegger. Both needles on the L&NWR instrument look like they are in the "Train On Line" postion, meaning that there are trains on both lines betwen Bordesley and the GWR.
Normally, and for obvious reasons, only one train is allowed in each section between signalboxes. However, the L&NWR instrument is of the "Permissive" type. These were used where it was necessary to permit more than one train to occupy the section between signalboxes, typically on busy Goods lines. Above the commutator handle on this istrument is a small circular window, which shows the number of trains in the section (in this case the number of trains coming from the GWR towards Bordesley).
To warn the driver that he is entering a section which is already occupied by one or more trains, a Subsidiary signal is provided. This has a smaller arm than a normal one, and is placed under the Main signal for the same line. You can see this on the diagram - Signal 2 is the Main arm for the GWR line, if this is cleared the driver knows that the section is clear of other trains, if the small Subsidiary arm (No. 3) is cleared instead, it indicates that the section is already occupied, so he needs to proceed with caution and to be prepared to stop on sight of any train ahead.
Signals reading into the section toward the adjacent box are controlled such that the signalman at Bordesley cannot clear them unless the adjacent signalman has given him permission to do so, by accepting the train on the relevant block instrument (giving a "Line Clear"). This is the meaning of the "Released By Block" note you can see against several signals on the diagram. The levers controlling such signals also have a white band painted on them to indicate that they cannot be pulled unless the block instrument shows "Line Clear".
The round instruments on the front of the block shelf are signal and track circuit repeaters. For signals, these are provided where the signal is out of sight of the box, and prove to the signalman that the arm has responded correctly to the movement of its lever.