Why sheridan valves don't leak

[yuyilibai]

After the hammer hits the cup seal, why doesn't a little air escape through the non-hat end of the cup seal into the chamber where the hammer resides? I'm looking at this animation for reference

http://www.zdspb.com/media/tech/animations/pgp.gif

[Jordan]

Probably does, tbh. The valve stem does have a fairly close fit through the valve, though, so I'd imagine it's negligible at best.

[Spider!]

Contrast that versus a blowback valve that has a port to blow back the hammer (which has a seal ring also). Not a lot of gas lost normally.

[XEMON]

Some does ... It is not a sealed end. But the flow will go with the path of least resistance, which will be up the transfer tube and push the ball out.