Sump overflow pump shutdown in emergency: please make recommendations please.

I always plan for the worst case scenario


1) sump should be sized such that operating water level allow for draw-down during power off plus entire ATO reservoir. This is the worst case scenario, ATO pump sticks on right after you fill it, then the second it's empty, the power fails.


2) Never count on a check valve and never design a system that depends on it working to stop backsiphoning. IMO check valves are only useful in situations where you have a return pump that does not like to restart after a short outage in which the water is backsiphoning through the pump. Some Iwaki external pumps fall into this category, the pump won't restart, so a check valve is needed.


3) Place at least one return jet high enough in the water such that it will break the backsiphon. You can have other branches, as long as you have one near the top of the water. An anti-siphon hole in the return line will need to be cleaned out periodically, and will probably get clogged and fail at the most perfect moment.


4) Test your setup with a simulated power outage (without check valves installed)


When I build a system, I always make sure the top return jet is higher than the lowest point of the overflow, if possible. So the minimum power-fail water level in the tank is dictated by the overflow fence, and the backsiphon is guaranteed to stop before that point. Then you can calculate the draw-down volume by multiplying the LxW of the tank by the draw-down height, divide by 231, and this gives you gallons. You need at least this much additional capacity in your sump (plus ATO) to avoid overflow.


Following this technique, you will not have to worry about overflow.