The electro-pneumatic action is a control system for pipe organs, whereby air pressure, controlledby an electric current and operated by the keys of an organ console, opens and closes valves withinwind chests, allowing the pipes to speak. This system also allows the console to be physicallydetached from the organ itself. The only connection was via an electrical cable from the console tothe relay, with some early organ consoles utilizing a separate wind supply to operate combination
pistons.
The basic operation of the system is as follows: when the organist selects a stop and depresses akey, an electric circuit is completed, causing a low-voltage current to flow from depressed key,through the stop-tab switch, and on through the cable to the electro-pneumatic relay. The relayinterprets the command from the console and sends an electric current to the appropriate solenoid.The solenoid is energized, causing the pipe valve connected to it to open, which emits compressed
air into the pipe, allowing the pipe to speak.