I have been searching for a bellows design that I would like to build. I have search all that I can find on this site as well as others. I found a design that was posted on this forum some time ago that has caught my eye and wonder if anyone has built it or knows about it. I have a small charcoal forge I built that is somewhat portable. I want to go with a none electric use air supply without going to the hand crank style. My work area is small and this pic of this bellows would be perfect if it is efficient and ease of use. If this all makes any sense. Here's the pic.Any thoughts or advise?

I'm going to add to this post. I read that one should make the top lung bigger than the bottom to have more volume going to the forge and if I am correct in thinking the bottom lung is just for pumping up the top one and maintain pressure. Is this correct? The sizing of the nozzle in comparison to the incoming vents is also a factor as to stay ahead of what's going out ? I read that one member had planned on upgrading to a 2" nozzle from the 1 1/2" and was glad he hadn't cause it would have let to much out and pumping would have been a chore.

What not make a traditional double lunged bellows based on designs that have been in use several centuries?  They generally have engineered out a lot of issues.  I built one based on a commercial version that was in a local (at that time) museum.  I used heavily treated canvas---tarpaulin---used for wind wings on oil drilling platforms and it worked great for 20 years! (I gave it on when I moved 1500 miles and ran out of truck space/money).

Making the upper chamber larger does give you more "buffer space"; on the other hand I liked to overblow my bellows at times---completely inflate the upper chamber and continue to pump more air it to clean out the ashes from the fire by the Mount Vesuvius method.  Harder to do with a larger top chamber.