Apologies for the delay, PM sent.

 

Its not clear to me what these check valves do. Could someone explain how they generate any vacuum?

 

I've Had this for more than a year on my car so far, never noticed any difference before vs after.

 

Car I had a set in kept blowing the dipstick out. Took them out and it stopped blowing out... They were facing the right direction too.

These things don't flow enough volume to be used in a PCV system and the intake will NEVER suck enough air to put vacuum in the crank case on a four cylinder built with tolerances to make power anyway. Route your lines to a can be vent it to atmosphere is the best you can do.