I appears to be the opposite? Valve closed. Would let air out if tank built pressure. That is to say it "opens" when you push in on it. Unless there is something I am missing. My thought is to drill a tine hole somewhere in the cap. Bu I know these original vented caps are rare. I would hate to modify one if it doing what it should and I just don't get it. Which wouldn't be that rare of an event.
