Extra air tank?

I'm wanting to plumb in an extra air tank to my compressor for more air storage. Question is if I put a t in the discharge hose(between the pump and the tank) do I need a check valve on the extra tank or will the original tanks valve be enough? Hope this makes since?

IMO redundancy is your friend. It's usually a cascade of component failures that runs the pressure up high enough to blow your lines. I doubled up on pressure relief valves on every system I've build.
If you use a check valve on the second tank, you will have to tap the air in two places. On the plus side, your refill times may be shorter during normal usage.

I have a OBA system that runs off my a/c compressor and i most definately did put a check valve in line.