Drain-line check valve?

Recently we had a terrible rain storm and I guess the main drains couldn't handle it. Two AC units on our second floor flooded. The drains are piped into a storm drain pipe from our roof (4 inch pvc) and the 2 AC units both 3/4 in drains. It rained so hard that the water came into the drain lines, filled the drip trays in the AC units and flooded the drop ceiling and made a mess. The 28 years that I've been working here I've never seen this happen. Now my boss wants me to come up with something so it won't happen again. So, I was thinking check valves on the 3/4 inch pvc. or re route the drains some where else. Any thoughts or ideas?

 

Not quite understand your setup, can you provide a photo ? is this an AC issue or building's drain issue ?

 

I would find it hard to believe a storm drain filled all the way up from ground level to the second floor.

These condensate lines should not be connected directly and you should have an air gap for this specific reason.

Also the storm drains often have an air gap and are usually never sealed completely that water cant escape somewhere.

Air gaps

 

A check valve is not going to work, and most likely would just cause another place for the drain to stop up.
I agree I'd be looking for a plugged up drain from the A/C unit to where it connects to your main drain.
Very common to have the drip loop plug up with slime and need to be blown out or snaked.