SI-Tech exhaust valve disassembly final steps?

[Subcooled]

I have managed to open the exhaust valve: the cover is off and the push button with spring etc has been removed. This took about sixty seconds and required a tiny screwdriver only: there is a tiny hole on the side of the valve. You just pry the valve open...

Unfortunately, the big rotating part is still attached to the base.

I can see a sealing edge between these two parts, but I cannot access it as I can't figure out how to separate the parts. Any ideas?

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The local diveshop said that they won't service these valves because they are way too complicated (the valves)

 

[runsongas]

iirc there is a retaining ring that prevents the bottom portion from unscrewing out usually. there may be a gap in the plastic where you can shimmy your screwdriver in to pop it out, else you need to dig along the inside wall to pop it out.