Reservoir bellows
Bellows in an organ or harmonium that store wind rather than generating it.
What it means
The reservoir bellows is a bellows in an organ or harmonium that does not itself generate wind but stores the wind supplied by one or more feeder bellows and passes it on to the pipes or reeds at as steady a pressure as possible.
Musical use
In mechanically operated organs, feeder bellows and reservoir bellows work together: the feeder bellows pump the air, and the downstream reservoir smooths out the pulsed supply, providing a calm, stable wind pressure that keeps pitch steady. In electrically blown organs, the reservoir still serves to absorb short-term pressure fluctuations. It should be distinguished from the feeder bellows, which actively draws in and pushes air, while the reservoir only stores and evens it out passively.