I can't find any specifications on the valve in either the BMW manual or the Haynes manual, but was told by my dealer when my tank was replaced that the valve did not open until something like +2.0psi on the pressure side, and several inches of water on the vacuum side. In other words the valve, by design allows some "modest" pressure or vacuum to build up in tank... (this is on a 2009 model). I also can't find any specs on the (rumored) newer design that uses a sintered core ...
If anybody else has specifications please post!
Since this valve is a separate item from the "tip-over" valve, I'd really like to know if this valve has any function other than to reduce emissions (by reducing the amount of "breathing" that the tank does which would let more fuel vapors into the atmosphere when the bike is not running).