how exactly the AOS works? is it vacuum or pressure activated?

Hi I was wondering if anyone knows how exactly the AOS works? is it vacuum or pressure activated?

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[Nick at Pelican Parts]

Pressure is built up in the crankcase from the increase in temperature and combustion blow by. As pressure builds the gases are drawn toward the AOS. There is slight negative pressure there from being connected to the intake system. As the oil moves through the valve liquid oil gets trapped in the baffles but the gases are allow to escape into the intake and get burned in the combustion process.

- Nick