This is a pic of my nearly complete slightly modified Arkmodel Song wtc:
The reversing pump simply pumps water in and out of the bag thru the solenoid valve. The bag is suspended in a tube within a tube. The manufacturer shows this inner tube well sealed up around all joints.
I like to be able to take things apart....is it important that the tube within the tube be airtight? The only advantage I can see that it would contain the change in internal pressure as the bag inflates...
Any bits of wisdom appreciated.
Model is getting closer to finished: