So you were right, when I blew into EV-281 a lot of air was coming out.
That said, all 3 of my EV-289's allow air to blow out as well, it doesn't seal fully but it doesn't flow as much as EV-281. On my EV-290 and EV-297, one of them barely had any flow out. 2 of them had some flow that I could only detect if I put my finger under the plunger and released repeating this, so I could hear a change in air pressure. But none of them were 100% fully sealing under my "lung boost".
The black valve (EV289) is suppose to slightly leak. It’s a “calibrated” leak. The engineer who has been helping me, worked with Ford in 2010. The Ford engineers wanted a valve that had little to no flow under vacuum and some backflow under boost. The reason why, I don’t know.
EV290/297/298 are designed to have no back flow at all. They are just like an ordinary PCV valve designed for a boosted application. Which was used on SHOs, Explorers, etc.
The crossed section is what’s know as an “Oil Drain Back”. Think of baffling in a valve cover. Aids in keeping oil from traveling thru the valve.
The hole or donut is known as a “Backfire Suppression ”. So in the case of a boosted application/backfire the plunger seats over the hole completely.
Flows remain the same. Only difference is the function of the end piece.