Harald,
now it is much clearer and my valves are mostly the same as yours. I was a little bit afraid to drill a hole in the cap, because I thought I will not get it airtight again.
Also thinking about installing a second valve without a flap, for deflation. This will make rolling up the packraft much easier. But for now I open the zipper a little bit. Works the same.
I glued another cap in the inflation bag. Works great and is simple.
