This is an example of a very compact, full-security, extensible Cargo Bay system. It has all three levels of security (with Baggage Destroyer). It has a single incoming underground belt line from the Checkin Desks and a single outgoing belt line to the baggage carousels.
From Checkin Desks (incoming)
The green arrow is the incoming underground belt line. A Baggage Up Escalator carries the baggage to the Level 0 security device. From there, the baggage is scanned through five Level 2 specific scanners and finally the manual Level 3 scanner. A tilt tray directs the baggage towards the Cargo Bays or out to a satellite terminal Cargo Bay (orange arrow). At each Cargo Bay, a tilt tray directs baggage to the specific Cargo Bay entry (bottom).
To Baggage Carousels (outgoing):
Each Cargo Bay’s receiving (from aircraft) conveyor belt goes to a Baggage Down Escalator, which connects to an underground (Level -1) conveyor (small blue arrows). This conveyor belt then exits the cargo bay area at the red arrow and sends the baggage to the carousels.
To increase number of Cargo Bays, simply add additional ones below these.