Reference Material
Use of Leather in an Organ Mechanism
Heavy Leather for Reservoirs
November 23, 2000
Nearly all organs use two kinds of leather
Right: Heavy white leather on a wind pressure regulator (reservoir, bellows). Black spots are holes due to age.
Below: Thick white leather for valves; Heavy leather to make airtight flexible joints.
Lightweight Leather for Valves
Some organs also use thin tan lambskin for pneumatic motors, devices which when filled with wind cause something else to move like a bellows in reverse. Organs with these devices are said to have pneumatic action. If electricity is involved, it is called electro-pneumatic action.
At right: Brown box is an organ windchest in our shop to be releathered. Bill Bastable is holding two pipes in place as they would appear in an actual organ.
The chest is filled with wind (air under pressure) and contains valves, which admit wind to pipes when the organist presses a key.
Below: Bill removes a valve board from inside the chest. The valve board holds 12 valves corresponding to 12 pipes.
The valves are white leather disks glued on top of green felt disks that are glued to thin tan leather pouches.
The dark spot visible on some valves shows where the valve touches the underside of the top board of the chest, which is where the pipes sit.
At right: Bill presses down a valve to show how it moves when the organist presses the corresponding key.
When the valve moves down, it comes away from the hole in the top of the chest, allowing wind to blow upward into the pipe.
In operation, pressing a key in the console sends an electrical signal to a magnet in the chest, which operates a valve not shown in these photos. The valve controls the flow of wind to the pouch. When the air under the pouch is exhausted through the valve to atmosphere, wind inside the chest presses down on the leather pouch. As the pouch moves, it pulls the white leather valve open.
Below: Bill lifts up a valve to show a tear in the leather, a fault that prevents the note from playing.
Leather is flexible and long lasting. This particular chest is out of an organ that was built in 1951. Most of the leather is in good condition even though it is nearly 50 years old.
Not all chests are built precisely as the ones shown here. Sometimes a leather-covered rectangular pneumatic device replaces the round pouch, but the principle of operation is the same.
