Westone earbud case thingy

[LowNloud1]

Bought a pair of WT earbuds. The come with a nice case. The case has a removable plastic screw that exposes brass threads and an o-ring. Anyone knows what it is for?

I sent an email to Westone a week ago but no answer from them.

 

[BBKINGBASS]

I'd they are like there Pelican case counter parts, it should be a pressure release valve.
What does the pressure release valve do, and how does it work?