This is an old thread, I know, but I’ll make some comments anyway.
I didn’t think there would be any inflation of the corrugated tube at lung pressures. But I found that if I closed off the far end and blew really hard, my tube stretched a bit.
I’m trying to think if this stretch would be a problem. When one or more reeds are open, I don’t believe you will get any stretch (you’ll increase the air flow instead), so I don’t see how it could be a problem when you are playing.
If you continue to blow when all reeds are closed off, you’ll pack a bit more air into the tube. [Since air is incompressible, you’ll only pack more air if the tube can stretch. However, this is only if you’ve got a great seal. When I tried it, I found the seal is the weak point–it releases air before the tube can stretch.] As soon as you play a note, the pressure in the tube will drop immediately. I don’t think there is enough energy in the tiny volume of air in the tube to even sound a single note. You need to continue supplying pressure (by blowing) to produce any sounds.
So why worry about this or invest time and money into work-arounds? Is there a measurable effect you’ve observed? It seems to me that if you are blowing hard enough to be concerned about the tube stretching, you are applying a lot more pressure than the reeds might like.