Where can backwater/backflow valves be used in a building?

[buckyswider]

HI guys, just came from an interesting fire call. Commercial building had water backing up through a second floor shower and loo; however, the first floor was unscathed. Anyhow, I had to gear up to run through the "waterfall" in the basement in order to access the panel to secure power to the building. When I did that, water mysteriously stopped backflowing though the fixtures...

We also noticed that at after I did that water started accumulating more in the basement- the sump pumps stopped clearing the water flowing down from above. The sump pumps were plumbed into a couple T's directly above the sewer lateral egress and theoretically out into the street into the sewer

Our working guess right now is that the sewer lateral clogged and the sump was trying to push the rainwater out (the building owner says they always have problems when it rains, and we got about 2" here in the Philly area today), but the plugged lateral was having none of that, with the end result being the sump pushing the water back into the building drains.

So come full circle and my remaining question is why did this issue not exhibit in the first floor bathroom? The best guess right now is that there was some sort of backwater/backflow prevention valve on the line from the first floor bathroom. BUT, I thought (without much "knowledge" there to skew my opinion!) that the only place a backflow preventer was allowed on a drain system is the actual lateral itself. So is it likely/legal that there is a backwater valve on the first floor line??

Also (now I'm really talking out my derriere!) from reading about primary/secondary hydronic heating theory (Dan Holahan FTW!) that there is some law of hydraulics that prevents water from flowing out of a junction when the inlet is within 1 1/2 pipe diameters of that outlet. I did notice a big mess of tie-ins where the sump pump tied in- is it possible that the line to that first floor bathroom was too close to where the sump was flowing and thusly no water could backflow that way?? Well, now that I typed it it sounds even crazier than it did in my head, but I guess I'll leave it there for some giggles...

thanks!

 

[Jmaclicious]

One of the many reasons why here in my province Manitoba, in Canada.. cannot plumb our sump pumps into the sewer drain lines but rather out onto our lawns, because it will back up if everyone is pumping tons of water into the sewer.. We are required to have Backwater Valves on the basement bathroom drain line to prevent sewage back up.. the floors above do not need one as chances of it getting all the way like that are pretty slim to none here.