if you INHALE thru your nose,and the mask stays on your face, the valve is working,(if there is one) if you exhale while HOLDING the mask to your face and you hear/lose pressure thru the valve of the mask, it is working JUST FINE.a nasal/clearance valve is used to expel excess water from the mask if so equipped, maskes that do NOT have this feature BUILT IN will have to be cleared by the AIR RISES method.- if this does not answer your question, then ask them for a
DIAGRAM !