The why, oh why, 38 stair, 290 gal build revised

[sphelps]

Originally Posted by reefwithareefer

I mean back-flow preventor, same thing as a check valve.
Yes, I would use the Apex to sense the pump failure, so it could turn on the back up pump.

I was thinking the check valves would be at the inlet , just because of the way the two pumps plumbed together.

I was thinking that I had to have the check valves at the inlet side, but the more I think about it, the outlet side makes more sense. I just worry about stagnant water in one of the pumps getting into the tank.

You wouldn't need any additional check valves or back flow preventers at the pump inlets, you only need a check valve on each pump outlet. In general check valves should only be installed on pump outputs, not inlets. With two pumps you'll always have stagnate water in the back up, not much you can do about it other than potentially program the back up to turn on for a minute or two each day. I see no reason why you can run both pumps together for brief amount of time provided it won't overload your overflow but most people design overflows for at least twice design.