Air Supply: this image shows the sandwich of bellows and reservoir. This sandwich disassembles so that the units can be serviced.

As I was building the air supply I found that I simply could not get myself to seal the bellows and reservoir together as one “glued together unit”.  Part of who I am is an ex IBM field engineer.  I am used to working on things that are designed to be repaired.  Gluing the bellows into one unit didn’t make sense…so I engineered a mounting plate onto which the bellows and reservoir would mount.  All in all this has been a very satisfactory solution for me.  I have had a need to access the bellows valves so that I could redo their fastenings…and was easily able to do so.