A basic diagram of a tracker organ like St. Peter’s has is above. The organ’s sound is caused by vibrations created in a pipe, much taking an old coke bottle and blowing across it to make a pitch.
One set of pipes for each note on the keyboard makes just one kind of sound. The organ will have several sets of pipes; each of these sets of pipes is called a “rank”, which can make different sounds.
The pipes are made to sound when air under a low pressure is blown into the bottom or foot of the pipe. Each pipe sits on top of a hollow wind chest that is filled with compressed air provided by a bellows or blower and a set of valves which control the flow of air into the individual note channels. There is a separate channel for each note
Thus, the organ bellows are part of the mechnism that brings air to the pipes. The bellows have to maintain proper pressure for sound to be consistent. Brad equates the bellows to the "lungs" of the instrument.
Leather is an important ingredient in the bellows construction. Being a perishable material, its durability has always been a matter of concern. Pollution and inadequate protection can shorten its life. Here is how the leather comes into play:
The leather is like a gasket preventing air leaks and maintaining efficiency on the bellows. Air flow is impeded or interrupted if the leather meachnism is not working properly causing air leaks. Improper sealing by the leather would be similar to the effects of a human being with emphysema
Our bellows are shown below. The"white taping" you see is actually the leather. The leather on the bellows is what needs replacing. Typically it can last 25-50 years but ours has lasted longer than that. (Our leather may be the original from the 1850’s!).
Consider a gift to the organ fund this Easter to help replace this leather and keep our tracker organ in top shape.
Two views of the bellows
