I haven't had any issues with air trapping. In my conversation with Tkdcol I broke out a pretty thorough how to on them... Want me to clean it up into a single document and send it?Thanks for responding. I've made my own bladders for an xdeep ghost type and a razor sidemount type, both of which worked ok. I tried to make an oval one like you do but it wasn't great so maybe the swimring is the answer. Do they trap air because the shapes are different or am I imagining an issue that doesn't exist?
I have a dodgy shoulder and can't reach doubles valves so wont be needing to make a doubles wing any time soon!
Cheers