The key relay system:
Each keyboard (manual) can play/operate a number of registers (sets of pipes).
It is impossible to place as many contact springs on blocks (BL) under the keys of the keyboard as there are registers.
If the organ is very small, having for example only four registers, that could be possible. A minimum of five contact springs would then be required, one for the positive contact which can then be switched through to the four registers. Therefore a system is required which will multiply the contact made by the key by the number of registers.
That system is the key relay.

The key operates a magnet which in turn operates a bellows (B) that supplies current to all the contact springs via the contact sheet (K).
In rest state, the wind pressure in the relay box can access the bellows via the open solenoid valve (MK). The spring (V) keeps the bellows open.
When a key is pressed, the respective key magnet is energised. This pulls the solenoid valve shut cutting off the wind supply to the bellows.
The wind in the relay box pushes the bellows downwards resulting in the contact sheet transmitting the positive electric current to the register relay.



Do you have any further questions or would you like to know more? There are a number of technical teams associated with theatre organs.
Everyone will be happy to speak to you.
Come along to a concert or an open console day.