Baxter oil adapter on a pentastar v6

I don't care what it is. It's not gonna stop the flow of oil being upside down.
ok, help me understand this...why not ?

i got valves in my tires that hold 75 PSI of air in, why wouldnt a similar valve work to keep 15 psi of oil in?
(figuring atmospheric pressure is 1 bar, is 14.5 psi)

im not trying to be obstinate, im just trying to understand it