After I bought a pressure gauge, I found that my first bellows did not maintain pressure as the demand for air increased. My first thought was that the pantagraphs weren't working properly so I removed them and placed enough weight on the top plate of the bellows to get the correct pressure. I knew that weights were sure to keep a constant force on the bellows. I measured the same drop in pressure as the demand increased. After some experimenting, I found that the force needed to increase by several pounds as the top plate dropped to keep the pressure constant. There is a certain amount of tuning you can do with the pantagraphs to make the force not constant but there was no way I could make the output force of the pantagraphs increase as much as it needed to. So then I decided to make new single fold bellows with an internal curtain valve. When I designed the first bellows, I was afraid of trying to make a bellows with folds with all the leathering of the corners. Now that I have a little experience working with hot hide glue, I decided to give it a try. There is some information on making bellows in the books but I got the most useful information from the following website. The leathering turned out to be a lot of fun. I really felt like an organ builder doing it. The results are a little sloppy looking but they work. The bellows crackle and pop a little as they go up and down but hopefully it won't be objectionable.

Here's the top frame being glued:

I first used doubled sided tape to hold the ribs in position while I glued the first strip of leather:

I didn't glue the ends because they will go on the top side of the gussets in the corners:

Then I folded the ribs over and glued a strip of leather on what will be the inside edge:

The next two photos show the strips on the outside edges of the ribs:

I made some braces to hold the plates in the correct position while I installed the ribs:

And finally here are the gussets. One thing I learned is don't get any glue on your fingers because then it's really hard to push the leather down.

Here's what the bellows will look like when assembled:

Click here (2.1MB) for a movie of the curtain valve in action.

Here's the pulley mechanism for the curtain valve: