Barker lever
The Barker lever is a pneumatic system which multiplies the force of a finger on the key of a tracker pipe organ. It employs the wind pressure of the organ to inflate small bellows called "pneumatics" to overcome the resistance of the pallets in the organ's wind-chest. This lever allowed for the development of larger, more powerful organs still responsive to the human hand. These larger organs first flourished in France, e.g., the organ produced by Cavaillé-Coll at St. Sulpice. The first Barker lever was built in the Cavaillé-Coll organ of the Basilica of Saint-Denis.
This mechanism was named after Charles Spackman Barker, engineer and organ-builder. A similar lever was developed by David Hamilton in 1835, and there has been debate whether Barker stole the design.
Operation
A Barker lever uses the organ's air pressure to reinforce the action of each key.Air pressure in Chamber A is maintained by the organ's wind system. When a keyboard key is pressed, Valve 1 opens and Valve 3 closes, inflating Bellows C and actuating the tracker and thus opening the valve of the wind chest linked to the key. Meanwhile, Valve 2 closes, thereby isolating the bellows from Chamber B. The bellows remains inflated until the organist releases the key and Valve 3 is reopened. Weight G forces the air in the bellows to be discharged quickly.