How it works...

…the pipe organ is a big box of whistles. Each pipe sits on top of a hollow wind chest that is filled with compressed air provided by a bellows or blower. Each ‘stop’ at the organ console represents a set of pipes (a rank) of a particular tone color, with a different pipe for every note on the keyboard. Pulling the stop activates a slider under that specific set of pipes on the windchest, making them available as a sound-source. The wind chest also contains a series of valves (pallets) connected to the keyboard by a mechanical linkage. These pallets govern the flow of air to each pipe, and even though a stop may be on, no pipes will sound until a key is depressed and its respective pallet opens. This allows the compressed air to pass up through the pipe for that note, creating sound. 

 

Cross-section of a mechanical action windchest. Trackers attach to the wires hanging out on the left. The pallots are pressed against the windchest by wire springs and wind pressure. The register  slides (black) allow to select the set of pipes the organist want to use