Family Organ - The Bellows

The Bellows

After finishing up on the carcass, the next step was to take a look at the bellows assembly. I'm not able to find a lot of information on the name of the parts of a bellows just by searching, and Wikipedia was uncharacteristically of minor help, so my apologies in advance for errors in nomenclature. Clearly there is a large opportunity for someone to educate the world on bellows minutiae, but that someone won't be me except for what is included here.

As I said in a previous post, one of the pleasures of working on the family organ is learning how it all works. Unfortunately for you, dear person who is reading this, I feel the need to share that acquired knowledge with you. Might want to grab some coffee.

This post is a bit long, so my apologies. I tried to insert some internal links to let you jump around, but blogspot wasn't understanding what I was trying to do.

General Bellows Functioning

In general, a bellows has an air chamber that is accessed via baffles, or holes, that allow for air flow into and out of the bellows, and valves that cover the baffles to direct and limit the flow of air. In something like a fireplace or forge bellows, the bellows is filled by the user expanding it - the valves open to allow air from the outside to fill the interior. When the user compresses the bellows, the valves close and air is forced out through a nozzle. There is, of course, also a valve on the nozzle to prevent air from entering the air chamber via the nozzle while expanding the bellows. Still awake here? Air flows in one direction, from the outside through the nozzle.

The bellows on the family organ works a bit differently than a fireplace or forge bellows, but of course follows the same general principles.

Organ Bellows Functioning

The organ bellows assembly consists of two principal parts - the actual pair of bellows that are worked by the foot pedals, and an air chamber, or vacuum chamber, that sits above the bellows. These parts will be shown below.

The picture below shows the organ's two bellows. The strips of pigskin on top are the valves covering the lower baffles. There are another set of baffles and valves (the upper baffles) on the inside.

This is a picture of the vacuum chamber:

In the above picture you can see the top baffles. The top valves are under the baffles, on the inside of the bellows.

When the organist presses on a pedal, one of the bellows is forced to expand. The lower valve seals, restricting air from going into the bellows through the lower baffles. The upper valve relaxes, permitting the bellows to draw in air from the vacuum chamber, filling the bellows. When the organist relaxes the pressure on the pedal and allows it to return to position, a spring on the bellows forces the bellows to contract. During contraction, the lower valve relaxes and allows air from the inside of the bellows to pass to the outside, while the upper valve restricts air from returning up to the vacuum chamber. Thus, the direction of airflow is from the vacuum chamber to the outside, and a vacuum is created inside the vacuum chamber. This vacuum draws air in from the outside through the reed assembly, very conveniently, and, if organ keys are pressed and all goes well, the reeds vibrate and make a lovely racket.

Organ Bellows Restoration

Now having a pretty good idea of how everything is suppose to work, attention turns to our sad little artifact. I was very pleased (exceptionally pleased!) to discover that the bellows assembly was not in bad condition. It was filthy - evidently the bellows were prime nesting and/or shitting grounds for mice. Perhaps they enjoyed running in and out of the baffles. All of the pigskin valves were eaten away to a greater or lesser degree and needed replacing, and the springs that held the valves taut were corroded. 

However, the rubberized cloth that formed the walls of the bellows and the vacuum chamber appeared to be in fairly good condition and could be retained. The rubberized cloth would have been a colossal pain in my ass to replace, so, you know, whew! Even if it fails later (the rubberized cloth, not my ass), I'll probably just use a bicycle inner tube repair kit to patch it up.

Replacing the lower valves would be a small matter, as they are on the outside and easily accessible. Cleaning inside of the bellows and replacing the upper valves entailed a bit of bellows spelunking. The rubberized cloth forming the bellows was carefully separated from the chassis allow access to the interior:

One can also see the remains of one of the lower valves and lower baffles to the left in the above picture.

The bellows interior was cleaned with bleach to remove the blech, and the valves and valve springs were replaced:

I would be remiss if I neglect to honor the pig that provided the pigskin for the new valves and other coverings. The pig was clearly the most deeply invested participant in this project!

New valve springs were bent from steel spring rods:

Reassembly commenced (note the bellows springs have been reattached - the wooden square in the corner of the bellows attaches it):

And, presto! Mischief managed!

Following all of this, I positioned the bellows assembly in the carcass, attached the pedals, and gave it a little test: