lenco feedback using 2 input shuttle valve on airpod.

Can anybody give me any feedback about using a 2 input shuttle valve on the air pod cant get my head around how the shuttle valve vents its air from the pod as I can only imagine it does when changing input signals.
Does it stop being a check valve on pressure dropping from one input and dump air or from the other input source being pressurised?
as the second one wouldnt allow it to de pressurise properly
Just trying to learn how the valve works as have a idea for it on another pneumatic application....
Thanks..

 

Think i found my answer..
The shuttle valve seems to be a opposing inlet check valve so when you drop pressurise it will drain the pod....
can delete this post now ...
Thanks