How Does It Work

There is no secondary air chamber that gets filled when you cock a pcp. The air used for the shot cycle comes from the large reservoir on the pcp and in regulated pcp rifles there is a pre chamber that fills with the regulated air but its still on the back side of the valve and part of the main reservoir. So you just de cock a pcp and thats it there is no need to fire it.
 
"Jim81"which action will be the best to reduce the pressure on "O" rings involved during storage. Thanks.
well having a rifle without any air is not good for your seals. You should keep air in the gun when keeping it put so the o rings have constant pressure sounds weird I know. That will keep the orings good longer than zero air. 
far de cocking the rifle, it didn't let any air out or anything is just releases the hammer spring. I usually just de cock the gun and put it up