How does an oil catch tank work?

Answer 1

The oil catch tanks we used to build for Detroit brand Diesels was a oil air separator tank the the "Blower Box Drains" were piped into.

As the engine runs a twenty (ish) PSI blast of air comes out of these drains and into a chamber where the air speed drops so the oil is no longer blown around or supported and settles out, the air the escapes through another port open to the outside air.

This system separated virtually (95% + )all the oil keeping the vehicle legal.

If you have a different type of catch tank or application in mind please detail the application in another question.